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UPTEC F10031
Master Thesis Project, 30 ECTS May 2010
Communal Polyethylene Biogas Systems
Experiences from on-farm research in rural West Java
Isak Stoddard
Teknisk- naturvetenskaplig fakultet UTH-enheten
Besöksadress: Ångströmlaboratoriet Lägerhyddsvägen 1 Hus 4, Plan 0
Postadress: Box 536 751 21 Uppsala
Telefon:018 – 471 30 03
Telefax: 018 – 471 30 00
Hemsida:http://www.teknat.uu.se/student
Abstract
Communal Polyethylene Biogas Systems - Experiencesfrom on-farm research in rural West Java
Isak Stoddard
In Lembang, a farming community on western Java, family-sized, plug-�ow, polyethylene biogas systems fed with cow dung, are being used as an integrated solution to issues related to energy, agriculture and waste management. Through simple, on-farm research and observation, a number of key problems have been addressed and improvements made to the design.
Due to the large supply of cow dung in the area, and the potential to spread the bene�ts of the technology beyond the homes of dairy farmers, the feasibility of developing a communal, polyethylene biogas system for several households, has been investigated. Experiments on small model-digesters were combined with observations of full-scale biogas systems in use. Measurement equipment and techniques were constructed and developed, in order to measure biogas production and other relevant process parameters. Results indicate that a communal system can be an appropriate choice, but only under a certain set of circumstances.
Keywords: polyethylene biodigesters, appropriate technology, on-farm research, communal biogas systems.
Supervisor: Sven Smårs, Department of Energy and Technology, Swedish University of Agricultural SciencesReviewer: Kjell Aleklett, Global Energy Systems Research Group, Uppsala UniversityExaminer: Tomas Nyberg, Department of Engineering Sciences, Uppsala UniversitySponsor: SLU Omvärld, SIDAISSN: 1401-5757, UPTEC F10031
Summary
Humanity faces a large number of global, interconnected and converging crises – in both
natural and human-constructed systems. There is an urgent need for research that aims to
understand their dynamics and find possible solutions to them. Local and contextual
research is especially important in areas where the people will suffer the worst
consequences of the above mentioned crises. In the rural areas around the city of
Lembang, on Western Java, people are experiencing an increased uncertainty in terms of
access to energy for cooking as well as other bare necessities. In the light of this situation,
a local biogas initiative was initiated in 2007. Two years later, field work for this Master
Thesis, contributed to the research activity of the initiative and helped to document the
findings of the past years.
Given the potential advantages and promises of communal solutions to problems of
regional resource scarcity, the main purpose of the study was to investigate the possibility
of developing a small-scale communal biogas system. Considering the economic situation
of the local people, the systems were designed to be affordable and constructed out of
materials that are locally available (mainly polyethylene plastic and PVC-pipes). The
biogas systems were analyzed both from a technical perspective, where different set-ups
were used to conduct relevant experiments, and from a user perspective, where biogas
systems in use were observed for a longer period of time.
Results indicate that it is fully possible to develop communal biogas systems but that they
only should be constructed and installed given a certain set of circumstances. Regulation
of gas flow, and a fair distribution of gas between connected households, turned out to be
the largest technical and operational challenge. The loading of the digester was also
identified as a major operational issue. In many cases a single-family system is a more
reliable and wise choice.
There is a large potential for continued development and diffusion of biogas systems in
the area around Lembang. 10 % of the total energy demand for cooking could be covered
by small-scale biogas production, if all of the substrate from the many cows in the area
was used. Unfortunately, out of the 14 biogas systems that have been installed so far, a
majority of them are no longer working as a result of either faulty design or
mismanagement. This clearly highlights the need for further research as well as
technician training, if biogas is to become a reliable and important source of energy for
cooking in Lembang.
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Table of Contents
1. Author‟s Note ........................................................................................................................ 4
2. Background ............................................................................................................................ 7
2.1 Setting the Context - Issues in Lembang ....................................................................... 7
2.2 The Biogas Initiative ..................................................................................................... 10
2.3 Purpose and Aim: Developing a Communal Biogas System ....................................... 12
2.4 Key Technical and Operational Issues ......................................................................... 14
3. Theory .................................................................................................................................. 19
3.1 The Process of Biogas Formation ................................................................................. 19
3.2 Biogas Production ......................................................................................................... 20
3.3 System Design ................................................................................................................ 28
4. Materials and Methods ........................................................................................................ 33
4.1 Experimental Set-ups .................................................................................................... 33
4.2 Measured Variables and Measuring Techniques ......................................................... 40
4.3 Biogas Systems in Use (Used for Observation and Evaluation) .................................. 48
5. Construction and Design: A Technical Perspective .......................................................... 51
5.1 Digester Dimension ....................................................................................................... 51
5.2 Slurry Flow .................................................................................................................... 53
5.3 Regulation of Gas Flow ................................................................................................. 57
5.4 Technically Feasible Biogas Production ...................................................................... 65
6. Installation, Operation and Maintenance: In the Eyes of The User ................................. 72
6.1 Available Space and Alternative Uses of The Land ..................................................... 72
6.2 Slurry Management ....................................................................................................... 76
6.3 Gas Flow Management .................................................................................................. 81
6.4 Balancing Biogas Production and Demand .................................................................. 85
7: Key Findings and Suggestions ............................................................................................ 95
7.1 Improving Single-Family Systems - Key Findings ...................................................... 95
7.2 Developing a Communal System .................................................................................. 97
7.3 When to Build a Communal System ............................................................................ 98
8. Biogas in Lembang ............................................................................................................ 105
8.1 Potential for Diffusion of Biogas in Lembang ........................................................... 105
8.2 Recent Development and a Look Ahead .................................................................... 110
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9. Conclusions ........................................................................................................................ 113
Acknowledgements ............................................................................................................... 117
Glossary .................................................................................................................................. 119
References .............................................................................................................................. 125
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1. Author’s Note
We live in a time of converging crisis - in both natural and human-constructed systems.
Economic and social crisis are likely to increase in severity and frequency as we
experience the effects of the interlinked crises in ecological, climatic and energy systems.
Most likely, we have already reached a peak in global oil production (Aleklett et al., 2010)
and are quickly running out of other fossil fuels (Heinberg, 2007). Considering the
complete dependence on fossil fuels in most agricultural and industrial processes, as well
as in the daily life and wellbeing of the majority of human beings, this is one of the most
critical challenges of our time (and for our species throughout history).
Corresponding and parallel to the energy crisis, we are approaching a number of
interlinked limits to growth: in human population, industrial output, food production,
pollution and resource depletion (Meadows et al., 2004; Meadows et al., 1972). Building
on this insight and the strong role of economic growth in driving us toward these limits, it
has been suggested that we are also approaching a limit to economic growth (Jackson,
2009; Daly, 2010). Approaching limits (or tipping points), in a self-regulating system such
as the earth, has consequences. Climate change is just one (albeit very large) consequence
which we are becoming more and more aware of but in many ways are completely failing
to address (Hansen, 2009). Another way to approach climate change is to relate it to the
concept of interlinked planetary boundaries. Loss of biodiversity, ocean acidification and
disruption to the nitrogen cycle are other consequences of transgressing these boundaries,
and which threaten the resilience of the biosphere and the stability of environmental
conditions that are conducive to human life. (Rockström et al., 2009)
The transition from a high-gain energy society (such as the one most humans live in
today) to a low-gain energy society1 (such as the one we will most likely need to transition
into) will require a paradigm shift of monumental proportion. Renewable energy such as
biogas, wind, geothermal, solar, wave and micro-hydro will obviously play a key role in
this transition. However, the fundamental differences of these energy sources (as
compared to fossil fuels) in terms of energy content, variability, energy return on
investment, required infrastructure, distribution and effects on ecosystems, must be
considered. Otherwise, the “renewable solution” could end up creating new and larger
problems than it was trying to resolve (Tainter et al., 2003). Therefore, research into
renewable energy technologies, and how they affect and are affected by both natural and
human-constructed systems, is of utmost importance in this day and age. As time is
running short, a major push for renewable energy, such as is outlined in the recent UN
report A Global Green New Deal for climate, energy and development (UNDESA, 2009),
is also of great importance. At the same time, local, traditional, indigenous knowledge as
1 For definitions of high- and low gain societies, see Tainter, J. A., Allen, T. F. H., Little, A. & Hoekstra, T.
W., 2003. Resource transitions and energy gain: contexts of organization. Conservation Ecology 7(3): 4.
5
well as local capabilities2 must also be nurtured, and the advantages of bottom-up
development not be forgotten.
According to a national socio-economic survey in March 2007, there were more than 37
million people in Indonesia (around 17 % of the Indonesian population) living below the
poverty line (less than 2 USD of income per day) (BPS, 2007). Due to the serious problems
in food security, health and sanitation that may arise from insufficient access to energy for
cooking, the Indonesian government has subsidized the price of kerosene since the 1970‟s.
However, in the last few years, increased global oil-prices have stressed government
expenditure and led to heavily reduced subsidies on the price of kerosene. This has
created large problems, mainly for the poor people of Indonesia, who have become utterly
dependent on subsidized fuel for their cooking needs (Sulistyowati & Sutasurya 2008).
The poor people‟s dependence on, and vulnerability to, an unstable global economy, could
be decreased by promoting small-scale, locally constructed, renewable energy technology.
In order to be affordable to the intended users, and to be independent of external funding
(from international or national funders, who in most cases also are more or less directly
dependent on the global economy) the introduced technology must also be of low cost.
Biogas systems are one of several promising renewable energy technologies which can fit
these criteria. Through rural development programs, mostly in the rural areas of central
Java, a few hundred biogas systems of various design and size have been built since the
early 1980‟s (Kossman & Pönitz 1999c). However, many of these systems have a
construction and installation cost that is too high for poor people to afford. Biogas systems
made of cheap and readily available polyethylene plastic provide a possible solution to this
issue. However, there are a number of problems with these systems that are important to
address (see section 3.3.3) - some of which have already been addressed by the biogas
team in Lembang (see section 3.3.4), the research documented in this paper (see section
2.4) and some which require further attention (see section 8.2.2).
In the Background chapter of this paper, we will see that the situation of poor people in
the Indonesian rural setting is complex. The energy-situation is highly coupled with issues
of agriculture, sanitation, economic development, social stratification and environmental
degradation. If implemented correctly, small-scale, polyethylene biogas systems could be a
catalyst to the transition to a more resilient, localized and prosperous society. A key idea
behind the biogas initiative which this paper is a part of (see section 2.2) is that
cooperation and the strengthening of communal capital is a central part of such a
development. In the light of this, an investigation into the potential of developing a
communal polyethylene biogas system is at the core of this Master‟s thesis project. The
management of common pool resources (such as the sea, the air, the land and other
ecosystems which we are directly dependent on) has within environmental discourse
often been seen as a case of the tragedy of the commons (Hardin, 1968). However, Elinor
2 For a definition see, Sen, A., 1993. Capability and Well-Being. In A. Sen & M. Nussbaum, eds. The Quality of Life. New York: Oxford University Press, pp. 30-54.
6
Olstrom, political scientist and recent winner of the “Nobel prize in economics”,
exemplifies and argues that this does not always have to be the case. Certain forms of
cooperation can lead to a successful management of local resources and resilient local
ecosystems (Olstrom, 1990). It is also in this spirit that this Master‟s thesis was carried out.
We will now take a closer look at the local context in which this project took place: the
rural community of Lembang, on Western Java.
Isak Stoddard Uppsala, Maj 2010
7
2. Background
The area of Lembang, and the many interconnected environmental, social and economical
issues that exist there, are introduced in section 2.1 below. A biogas initiative, that was
started in response to these issues, and the involved organisations are then presented in
section 2.2. The Chapter then moves on to describe the purpose and aim of this paper in
section 2.3. Lastly, key technical and operational issues for the development of
polyethylene biogas systems in Lembang, are introduced in section 2.4. The structure and
content of the main part of the paper (chapters 5, 6, and 7) is also laid out in the end of
chapter 2.4.
2.1 Setting the Context - Issues in Lembang
What makes biogas an attractive option is the fact that this technology can provide solutions to a variety of problems simultaneously. That is, if this variety of problems exists. (Kossman & Pönitz 1999)
Bandung is one of the most densely populated areas in South Eastern Asia and also one of
the world‟s quickest growing urban areas. The larger metropolitan area of Bandung is
home to 7.4 million people. It is situated at approximately 800 meters above sea level, in a
basin created when the ancient volcano known as Mount Sunda, erupted around 55,000
years ago. The crater rim is still lined with active volcanoes rising to a height of up to
2,400 meters. Due to its‟ geographic location and relative high altitude, Bandung and its
surrounding areas experience a rather temperate and cool climate, compared to the coastal
cities of Jakarta and Surabaya. The rainy season extends from December to April and
brings cooler temperatures than the rest of the year (Lonely planet, 2007).
The area north of Bandung is a very important water catchment area. Besides providing
water for the city of Bandung, water falling in this area eventually meets up with the
Citarum river, which flows all the way to Jakarta, providing water for drinking and
agriculture (such as irrigation of rice fields) along the way. In this area north of Bandung,
in the hills below the volcano of Tangkupan Perahu, lies the town of Lembang (see Figure
2.1). Lembang is a bustling little market town with a large vegetable market and an
increasing amount of tourism. About 180,000 people inhabit the urban area of Lembang.
Smaller rural communities are spread across the countryside around Lembang. The area
has experienced large economic growth in recent times, mainly driven by increased
tourism, vegetable farming and dairy farming. Vegetables and milk from Lembang are sold
in Bandung as well as cities as far away as Jakarta and Bogor (Sulistyowati & Sutasurya
2008).
8
Figure 2.1: Map of West Java and a typical view over the Lembang area.
The large volcanic activity in the area around Lembang has resulted in very fertile soils.
More than 83 % of the population in the rural areas around Lembang, are vegetable
farmers (22,000 people) and grow crops such as tomatoes, cabbage, chilis, cauliflower,
corn, beans and many more. The agricultural practices are highly dependent on chemical
fertilizers and pesticides as well as manual labour (no tractors or animals are used). A man
working in the fields earns around Rp. 15,000 per day (1.5 USD)3 while a woman will earn
around Rp. 10,000 (1 USD) (Sulistyowati & Sutasurya 2008). With this income they are
considered to be below the poverty line (along with 37 million other Indonesians, or 17 %
of the population) (BPS, 2007).
Dairy farming is the other major agricultural occupation in the area. According to KPSBU
(a cooperative for dairy farmers in Lembang), there were more than 5,000 dairy farmers in
the area in 2006, together owning more than 12,000 cows and 3,000 calves (Cahyono,
2009). A dairy farmer usually has between three and four cows. A few more prosperous
dairy farmers may have more than ten. A dairy cow produces between 14 and 20 litres of
milk per day and the price for a litre of milk is around Rp. 3,500 (0.35 USD). A calf costs
Rp. 3,000,000 (300 USD) and a full grown dairy cow Rp. 10,000,000 (1,000 USD)
(Wahyudi, 2009). Average daily earnings for a dairy farmer are around Rp. 40,000 (4
USD) (Sulistyowati & Sutasurya 2008), which is between three and four times more than a
vegetable farmer.
Due to very limited land availability and practical reasons, cows are stabled year round.
The dung from the dairy cows is hardly ever used as a fertilizer. Dairy farmers seldom
grow vegetables and hence lack a direct incentive to use cow manure on the fields. The
quality of cow dung as a fertilizer is also perceived as low (as compared to chemical
fertilizers) and there are difficulties in handling and transport. Instead, the cow dung is
placed either in a pile next to the stables, until the rain flushes it away, or thrown directly
into the river (see figure 2.2). The sanitary issues associated with this lack of waste
3 All exchange rates retrieved from www.xe.com on 2009-12-20.
9
management are quite significant, and affects all the people relying on water from the
Lembang catchment area.
Figure 2.2: Stabled cattle and a pile of cow dung next to a stable. Note the small water channel to the right.
Cooking, lighting and running electrical appliances (such as a TV) constitute most of the
household energy consumption in Lembang. For cooking, kerosene is the most widely
used fuel. For more than 30 years, the Indonesian government has managed to provide
even the poorest people with kerosene at a reasonable price with the help of subsidies.
However, with the drastically increased global oil price in the last decade, the subsidies
have heavily burdened state expenditure and subsidized kerosene is becoming
increasingly difficult to find. The state has been forced to lift all subsidies for industries
but managed to maintain at least some subsidized kerosene for poorer families. This price
gap has promoted smuggling, creating a kerosene scarcity for people and an extra burden
on the security sector. Unsubsidized kerosene today costs eight times more than
subsidized kerosene cost just eight years ago (Rp. 8,000 /l compared to Rp. 1,000 /l)
(Sulistyowati & Sutasurya 2008). Liquid Petroleum Gas (LPG) and fuel-wood are also used
for cooking in some households in Lembang. However, due to heavy deforestation in the
area, fuel-wood is quite scarce, and the cost of LPG is as high as that of kerosene
(Wahyudi, 2009).
Considering the vast amounts of cow dung that is produced each day in the Lembang area
(around 300,000 kg) and the increasing scarcity of affordable cooking fuels, there is an
obvious potential and incentive to develop and spread biogas systems for household use.
The cow dung could potentially be used to provide cooking fuel for more than 6,000
families. The sanitary gains of digesting the cow dung and the potential of producing a
high quality organic fertilizer are other very obvious advantages of the diffusion of this
technology. Biogas technology can be seen as an integral solution to interlinked issues of
waste management, energy scarcity and agriculture. However, the real advantages of
introducing the technology, and whom it will benefit in the long run, greatly depends on
10
the way that the technology is designed and diffused. If biogas systems are built and used
only by dairy farmers, their economic situation will improve whereas the vegetable
farmers situation will stay the same or even worsen (being dependant on fossil fuels for
both cooking and inputs into their agricultural production).
With increased prices of cooking fuels and fossil-fuel based inputs in agriculture,
vegetable farmers are experiencing an increasing economic stress. Less applied chemical
fertilizer, leads to lower yields which in turn leads to lower incomes. Besides being poorer
and more vulnerable to global oil prices, vegetable farmers also lack the organisational
infrastructure that the dairy farmers have (through the cooperative KPSBU).
2.2 The Biogas Initiative
In the light of the situation described above, an initiative to diffuse small-scale biogas
systems in Lembang, was started in early 2007. The initiators knew that there was a
chance that a large-scale biogas plant would be constructed in the area. They felt that such
a solution may end up being more detrimental than helpful to the farmers in the long run,
by locking them into yet another dependence on a system of which they had little control
over. Also, having witnessed and experienced the failure of a number of government
funded and NGO-run projects trying to diffuse “green technology”, the initiators felt there
was a need to investigate and better understand the dynamics of successful diffusion.
Systems thinking and Innovation Diffusion Theory as developed by Rogers (2003) was
used to create a project plan and strategy that would be evaluated as the project
progressed. The project is a collaboration consisting of four different organisations: YPBB,
PESAT, KAIL and Change Agent Inc.
Yayasan Pengembangan Biosains & Bioteknologi (YPBB) is non-governmental
organisation based in Bandung which focuses on environmental education and promotion
of a more sustainable lifestyle. One of their main activities is to develop “green
technology” and find self-sustaining diffusion strategies for them. YPBB is the main
organizer of the project. In the implementation of the biogas project they are in charge of
the technical and environmental aspects. They are also in charge of developing and
improving the technology and the diffusion strategy through research and observation.
Foundation for the Development of Community Self Support (PESAT) is also a Bandung-
based non-governmental organisation. PESAT involves rural communities in programs for
clean-water provision and sanitation. Their approach is highly participatory and aims to
improve the communities‟ overall wellbeing and self-reliance. In the implementation of
the biogas project, PESAT is in charge of the social and economic aspects of the
technology. Prior to the introduction of the technology in a village (done by YPBB), they
hold several community meetings to listen and learn from the villagers about their
problems, and present biogas systems as a potential solution to some of them.
11
Change Agent Inc. is a Japanese consultancy specializing in change and systems thinking
for sustainability. They have provided a large amount of the financial resources needed for
the initial stages of the biogas project. They also have provided assistance on how to use
systems thinking and innovation diffusion theory for project planning.
Kuncup Padang Ilalang (KaiL) is a non-profit organisation specializing in increasing
personal and organizational capacity for social transformation processes. In the biogas
project, KaiL acts as a supervisory organisation overseeing the project, assisting the project
team in training, and coordinating with Change Agent Inc. of Japan. Lessons learned from
the biogas project will be passed on to other projects and organisations that KaiL is
working with.
Besides these four organisations, a number of people from the village of Cicalung, where
the first biogas system was installed, have been a crucial part in the development,
construction and installation of the biogas systems.
Between January and April of 2009, the project was really set into motion, and 15 biogas
systems where constructed and installed in three different villages in the Lembang area.
The villages were selected by using a number of criteria: there had to be a significant
amount of cow farmers, they needed to be willing and interested in biogas, and finally, a
number of potential future biogas technicians needed to exist and be identified. The
villages were also chosen because of their quite different social and economic dynamic,
ranging from semi-urban (more competitively oriented) to rural (more cooperatively
oriented). This would hopefully lead to a better understanding of how diffusion and
adoption of biogas technology works in different contexts, and the future strategies could
be designed thereafter. For more information about these villages, and details about the
biogas systems installed, see section 4.3.
Prior to these installations, five biogas systems had been installed in the villages of
Wangunharja and Cibodas in the years 2007 and 2008, a period of trying out various
construction methods and materials in order to improve the design. These improvements
can be read about in section 3.3.4.
These improvements were to a large extent a result of local research and observations.
This research was continued and intensified in late 2008 in order to answer key questions
in regards to the construction and design of the biogas systems, before the biogas systems
have been widely diffused. This included research on: different ways to increase the
process temperature, changing the dimension of the digester, increasing the stove
efficiency, the durability of the polyethylene plastic used for the bio-digester and
construction of biogas lamps. This type of contextual research, which is performed in
close consultation with the users, has been called for in several studies evaluating the
diffusion and impact of polyethylene biogas systems (An, 2002; An et al., 1997).
12
The increasing economic stress on especially vegetable farmers in Lembang, described in
section 2.1, lead the biogas project team to think about ways that the benefits of biogas
technology could be extended to include more than just dairy farmers. One promising
solution, which also was hoped would lead to other advantages such as increased social
and economic equity, was to develop a communal biogas system that could be used by
both dairy farmers and vegetable farmers. The main objective of this thesis was to
investigate the feasibility of developing such a system.
2.3 Purpose and Aim: Developing a Communal Biogas System
A great number of articles and papers have been written over the years saying that community plants should be used in villages. They are more economic than individual plants and could be of help for those people with too few livestock or too little space for their own plant. The fact is that very few community plants have been built outside China and, of those which have, only some are still working. Although there are some minor technical difficulties, this is mainly due to sociological and managerial problems. (United
Nations, 1984)
Considering the large amount of unused cow dung in Lembang area and the sanitary
issues associated with it, there is a need to find ways to increase the amount of dung being
processed and utilized. Most dairy farmers own more cows than are needed to produce
input for a biogas system of their own. The excess dung could be used to produce more
biogas and thereby spread the benefits of the technology beyond dairy farmers. This could
either be done by building additional single-family systems or developing a communal
system that can be used by several families at once. A communal system can be more
efficient in regards to the cost and space required for construction. Since there is a large
income difference between dairy farmers and vegetable farmers (a factor of four), building
communal systems will ensure that this gap will at least not grow any larger. The
increased cooperation between the vegetable farmers and dairy farmers resulting from a
communal system, may also lead to a localisation of resource flows and economic
transactions (e.g. fertilizer and milk is traded for vegetables). A common investment like
this may also help to increase the social capital between the families, if it is managed well.
However, a communal system may also lead to problems and issues of operational,
technical, economic and social nature.
Whether a biogas system is designed for one or several families, it should be efficient and
adapted to the needs of the users as well as local conditions. In cooperation with the YPBB
biogas project team, a number of key operational and technical issues have been identified
(see section 2.4) in order to ensure that the efficiency and appropriateness of the systems
are maximized. Therefore an underlying inquiry throughout this paper is to investigate:
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How can the construction and design of all polyethylene biogas systems (including single-
family systems) be improved in terms of their appropriateness and functionality in the
Indonesian rural setting? (Research question 1)
Communal systems are here defined as a system that provides more than one household
with biogas for cooking. They can be divided into two general types:
A system that is comprised of several connected (by gas- and/or slurry flow)
digesters
A system that is comprised of one larger digester with gas pipes leading to the
different households.
Although communal systems have been designed and installed before, there has to date
not been any systems of the polyethylene-plastic digester type. This paper therefore aims
to answer the question:
Is it possible to develop a well functioning communal system with polyethylene plastic
digesters, with due consideration to key operational and technical issues of a biogas
system? (Research Question 2)
In order to answer research question 2, the difficulties of developing a communal system
must be identified and potential solutions investigated. Therefore a corollary research
question is:
What are the difficulties of developing a communal biogas system and how could they be
overcome? (Research Question 2*)
Furthermore, if a functioning design of a communal system is found, the circumstances
when one should be constructed in favour of a single-family system, should be
investigated. Therefore a third research questions is postulated:
Under which circumstances should a communal system be built instead of a single-family
system? (Research Question 3)
In order to answer research question 3, two corollary research questions were formulated:
What are the criteria and requirements when installing, operating and maintaining a
single family system, and what are they for a communal system? (Research Question 3*)
What are the potential advantages of installing communal systems and what are problems
that could arise? (Research Question 3**)
14
2.4 Key Technical and Operational Issues
In cooperation with the biogas project team, and in line with important considerations
mentioned in literature (United Nations, 1984), four key technical and operational issues
have been identified. These issues are all important to consider when developing a
communal biogas systems. Most of them are also crucial to the improvement of single-
family systems.
Available Space and Alternative Uses of the Land
An appropriate design of a biogas system is dependent on the amount of land that is
required for construction and installation. In many villages in the Lembang area there is a
shortage of available land, and many competing uses of the land exist. The shape of the
available land and it‟s location in relation to the users and cow pen, also varies greatly.
Designs of biogas systems that may require less space per produced litre of biogas, or, be
more suitable to the space available, include communal systems and digesters of different
dimensions and orientation.
Slurry Management
By far the hardest and most time consuming task, in the operation of a biogas system, is
the transportation and handling of the slurry - both influent and effluent. How, and by
whom, this task is performed can have great implications for the functioning of the
system. The location of the input and output in relation to the cow pen and households is
also important. For a communal system with several digesters, connecting them is of
interest since it simplifies the work of transporting slurry to and from the digesters.
Gas Flow Management
A well managed distribution of gas flow is crucial for the functioning of a communal
system. Each household connected to the system must be able to obtain a sufficient
amount of biogas to fulfil their cooking needs throughout the day. A number of options
for regulating the gas flow exists and need to be investigated. The relative location of
households connected to a communal system, also has implications for gas flow
management and design. A difference in gas pipe lengths may lead to an uneven
distribution of gas flow due to different pressure drops in the pipes. The location of
pressure valves will also affect gas flow.
Balancing Biogas Production and Demand
To design biogas systems that are adapted to the needs of the users, biogas production
rates and the anticipated biogas demand need to be determined. An appropriate sizing of
the digester is crucial in balancing production with consumption. The amount of cow
dung and water available, the efficiency of the biogas production process and ways to
increase this efficiency should be taken into consideration. The consumption patterns of
families also need to be studied. The quantification of these parameters helps to determine
how many cows, and what size of biogas system is needed to supply one or more families
with sufficient amounts of biogas for cooking.
15
An understanding of the social, economical and cultural aspects is highly important (not
least for communal systems) to get the systems to be operational and maintained correctly.
These aspects are also much intertwined with the above technical and operational issues.
Due to this papers limited scope, we will not delve deeply into these issues. However,
chapter 6 is based on observations from the villages of Pasir Angling and Cireyod, and
highlights some of the issues that can arise in the interface of the user and the technology,
when the systems are being used. Chapter 8 also brings some clarity to the economic
situation of the farmers.
The technical and operational issues mentioned above are all tied to three important
stages of the biogas system development process: (1) construction and design, (2)
Installation and (3) Operation and Maintenance. Chapter 5 deals with the technical issues
that affect the construction and design of the biogas system. The methodology for this
chapter is mainly experiments and the data is quantitative. Chapter 6 deals with
operational issues and is based mostly on observation of systems in use and discussions
with users. The data for this chapter is mostly of qualitative nature. Chapter 7 ties the two
preceding chapters together by summarizing how it is possible to improve single family
systems, suggestions on how to develop communal systems and under which
circumstances such a system should be built. Figure 2.3 provides an overview and outline
of chapters 5, 6, 7. Chapter 8 takes a look ahead at the potential to diffuse biogas systems
in Lembang and future needed research.
Figure 2.3: An overview and outline of chapters 5, 6 and 7.
16
Each technical and operational issue includes a number of questions that are of
importance to either single-family systems, communal systems or both. The following
figures provide an overview of each issue, the questions belonging to each one and where
in chapters 5 and 6 they are presented.
Figure 2.4: Overview of the key technical and operational issue Available Space and Alternative Uses of the
Land.
Figure 2.5: Overview of the key technical and operational issue Slurry Management.
17
Figure 2.6: Overview of the key technical and operational issue Gas Flow Management.
Figure 2.7: Overview of the key technical and operational issue Balancing Biogas Production and Demand.
A high interdependence exists between several of the issues. Some overlap is therefore
impossible to avoid. For example, the distance between the houses that are to be
connected to a communal system has implications for all four issues. Furthermore, the
relationship between the issues is not immediately apparent. Therefore, a decision making
diagram for developing communal biogas systems was constructed and can be seen in
Figure 2.8. The diagram also serves as a conceptual framework for this thesis. The issue
“Balancing biogas production and demand” can be seen as one of the main goals when
developing a functional biogas system and is therefore placed at the bottom of the figure.
However, many of the other boxes (e.g. Demand and Supply) are also directly connected
to this issue.
18
Figure 2.8: Decision making diagram and conceptual framework for the development of a communal biogas
system. The four key issues can be identified more or less clearly. The boldest arrows symbolize the main
causal connections in developing a functional communal system. The medium bold arrows are necessary
feedback mechanisms and the narrowest arrows are important factors affecting the final outcome.
The issue “Available space and alternative uses of the land” can be found in several places
in Figure 2.8. Slurry management and gas flow management come in as important factors
affecting the final goal (which is to balance the biogas production from all digesters with
the biogas demand of all households). That iterative character of the process is symbolized
by the many feedbacks (the medium bold arrows in Figure 2.8).
19
3. Theory
The very long history of biogas formation and the three main stages that it involves are
described in section 3.1. Biogas formation here refers to the natural microbiological
process. Biogas production, on the contrary, refers the controlled digestion of organic
material to fulfil human needs (such as producing biogas for fuel and treating organic
waste). The history of biogas production and key physical and environmental process
parameters are introduced in section 3.2. In section 3.3, the design of biogas systems are
explained and discussed. The focus is on the system design used in the Lembang area, its
shortcomings, and the improvements that the biogas project team has made to this design
in the last few years.
3.1 The Process of Biogas Formation
3.1.1 History
Methane producing bacteria, also known as methanogens, are some of the oldest life forms
on earth. Several billion years ago, long before cyanobacteria evolved and created an
oxygen rich atmosphere by inventing photosynthesis, methanogens dominated life on
earth. Today methanogens are found in the anaerobic environments that still remain –
from deposits deep in the earth‟s crust (where they convert plant-material to oil and
natural gas) to the bowels of herbivores (where they are an essential component in the
digestion process). (Nörretranders, 1994)
3.1.2 The Three Stages of Biogas Formation
Biogas is a product of a microbiological process, known as anaerobic digestion, in which
organic material is decomposed in an anaerobic environment (Ek, 2007). Methanogens are
just one of the micro-organisms involved in this process. Fermentative and acetogenic
bacteria also play a key role in the process, by splitting organic material and providing a
favourable environment for the methanogens. There are essentially three stages to biogas
formation: hydrolysis, acidification and methanogenesis (see Figure 3.1).
20
Figure 3.1: The three stages of biogas formation: hydrolosis (Stage I), acidification (Stage II) and
methanogenesis (Stage III) (Kossman & Pönitz 1999a).
In the first stage (hydrolysis), fermentative bacteria decompose the long, complex chains
of carbohydrates, protein and fats into shorter chains. E.g. proteins are split into peptides
and amino acids, polysaccharides are converted to monosaccharides. In the following
stage (acidification), acetogenic bacteria converts the intermediates of fermentative
bacteria into acetic acid, hydrogen and carbon dioxide. They require carbon and oxygen
for this process, effectively removing oxygen from the process and creating the anaerobic
environment that is essential for methanogens. In the third stage (methanogenesis),
methanogens use the newly produced compounds of low molecular weight, such as acetic
acid, hydrogen and carbon dioxide, to form biogas. (Kossman & Pönitz 1999a) Biogas is a
mixture of essentially methane and carbon dioxide. However, traces of hydrogen sulphide,
ammonia and oxygen in the biogas may also be found at times (Gustavsson, 2000).
3.2 Biogas Production
The biogas formation process can under controlled circumstances provide humans with a
valuable source of energy. In contrast to aerobic digestion processes (such as composting),
anaerobic digestion is characterised by small heat emissions (Gustavsson, 2000). Much of
the energy stored in the biomass is transferred to the methane and released when
combusted. Consequently, anaerobic digestion is very suitable for the extraction of
energy.
3.2.1 History of Biogas Production
The burning behaviour of biogas was first investigated in the 1770‟s by the Italian
physicist Allesandro Volta. More than a century later, the French chemist and
microbiologist Louis Pasteur conducted research on biogas from animal residues and
proposed that horse dung should be used to produce biogas for street lighting (Kossman &
Pönitz 1999a). Today, biogas is used extensively throughout the world as a source of
21
renewable energy. In more industrialized countries, large scale biogas facilities are used to
process organic waste as well as produce transport fuel and electricity, in both rural and
urban areas. In less industrialized parts of the world, biogas is used mainly for cooking and
lighting, and especially in rural areas. Two countries stand out in this regard: China and
India. By vigorous promotion and extensive support from the government, several
million family-sized biogas systems have been installed in these countries in the last few
decades (Kossman & pönitz 1999a). However, many of these systems have ceased to
function shortly after installation, due to limited knowledge of operation and
maintenance routines (An, 2002).
3.2.2 Key Physical and Environmental Process Parameters
The process of anaerobic digestion can be monitored and evaluated by looking at a
number of physical and environmental process parameters. They can be divided into
parameters that affect the magnitude of the biogas production (see section 3.2.2.1), and
ones that do not but still are important (see section 3.2.2.2).
3.2.2.1 Parameters Affecting Biogas Production
The physical and environmental parameters that affect biogas production are (Nyns, 1985;
Kossman & Pönitz 1999a):
1. Anaerobiosis
2. Substrate temperature
3. Substrate solid content and agitation
4. Retention time
5. pH level
6. Nitrogen inhibition and C/N ratio
7. Available nutrients
8. Inhibitory factors.
The different type of bacteria involved in the three stages of biogas production are all
affected differently by parameters 1-8. Since interactive effects between the determining
factors exists, no quantitative data on the effect they have on biogas production exists. The
following discussion is therefore limited to qualitative effects on biogas production.
(Kossman & Pönitz 1999a) At times, it may be practical and useful to see the biogas
process as a “black box” – i.e. just observing and recording the inputs and outputs (such as
the amount of dung loaded and the amount of biogas produced). Other times, and when
possible, observing and recording parameters such as pH-level, temperature and C/N ratio
may be helpful in understanding what is going on inside the “black box”.
A brief description of the eight parameters and the introduction of notation of key
variables (that will be used in the following chapters) follows:
22
1. Anaerobiosis
Methanogenesis is a strictly anaerobic process. Methanogens do not survive in the
presence of oxygen and hence biogas production requires the absence of air. However, in
practice, small amounts of oxygen will always enter into a digester (mostly through the
oxygen present in the influent slurry). As long as the rate of air diffusion into the digester
remains lower than the oxygen uptake rate of the fermentative- and acetogenic bacteria,
the process will not be inhibited (Nyns, 1985).
2. Substrate Temperature
In general, increased temperatures lead to quicker biological and chemical reactions. This
is also true for biogas production but only within the temperature ranges that the
participating bacteria can survive in (Ek, 2007). Anaerobic digestion is in principle
possible between 3°C and 70°C (Kossman & Pönitz 1999a). It occurs, more or less, in an
optimum way at two temperatures of the substrate: 35°C and 55°C. The biological
communities responsible for the digestion process at these two temperatures are quite
different. In fact, the process and the bacteria involved at different temperatures, is
different enough, that three general temperature ranges for anaerobic digestion, have
been identified (Nyns, 1985):
Psychrophilic (below 20°C)
Mesophilic (between 20°C and 40°C)
Thermophilic (above 40°C)
The yield, production rate and methane content of the biogas differ significantly between
the temperature ranges. Thermophilic digestion results in the highest production rates
and methane content of the biogas (Wellinger, 1999). However thermophilic digestion is
also said to be more vulnerable to changes in temperature (Kossman & Pönitz 1999a), will
most often require heating of the substrate and does not produce higher yields as
compared to mesophilic digestion (Wellinger, 1999). In the mesophilic temperature range,
biogas yield increases over-proportionally in the range 20-28°C (Kossman & Pönitz
1999a). The biogas production rate will also increase with increasing temperature, in the
mesophilic range. A substrate temperature around 40°C is to be avoided, since it is neither
suitable for mesophilic- nor thermophilic bacteria. Psychrophilic digestion results in rates
and yields that seldom will be cost-effective. If the temperature of the substrate is below
15°C, gas production will be so low that the biogas system will not be economically
feasible (Kossman & Pönitz 1999a). The temperature ranges distinguished above are not
absolute. In all anaerobic digestion there will be at least two of the three biological
communities, actively involved in the process at all times (Ek, 2007).
The process of anaerobic digestion is very sensitive to changes in temperature (Kossman &
Pönitz 1999a). However, if the change in temperature is slow, it will not have inhibitory
23
effects on the process (Wellinger, 1999). The degree of sensitivity, is in turn dependant on
the temperature range of the substrate. Brief fluctuations not exceeding the following
limits are seen as harmless to the process (Kossman & Pönitz 1999a):
Psychrophilic: (±2°C/hour)
Mesophilic: (±1°C/hour)
Thermophilic: ((±0,5°C/hour)
In polyethylene small-scale digesters without heating that are situated in tropical regions,
mesophilic digestion is pre-dominant.
3. Substrate solid content and agitation
The higher the solid content is the more matter which can be digested is found in the
substrate or slurry (in percent). However, the mobility of the methanogens gradually
decreases with an increased solid content, and the biogas yield may suffer as a
consequence (Kossman & Pönitz 1999a). The solid content of a substrate is defined as the
mass which remains when the water content is removed (by heating) and is denoted Total
Solids (TS) content (Örtenblad, 2000):
TS (in %) = (mass of dry matter / mass of substrate) *100 [Eq. 3.1]
The TS-content varies greatly between, as well as within, different substrates. For cow
dung the TS-content is usually between 10 and 24 % (Örtenblad, 2000; Thy, 2003).
The TS-content of the influent is an important parameter which is easily measured in
experiments with biogas production. It is a useful parameter since wet masses are too
relative to compare due to their variable water content. The TS-content is measured after
the chosen amount of water has been added to the substrate and the influent is ready to be
loaded into the digester (For details on measuring techniques for research in the field, see
section 4.2)
The dry matter in the substrate is a mixture of inorganic matter (such as metals and
minerals) and organic matter (the biodegradable part). The organic matter content is
defined as the mass which is removed when the dry matter is heated (from 105°C to
550°C) and is denoted Volatile Solids (VS) content (Örtenblad, 2000):
VS (in %) = (mass of organic matter / mass of dry matter)*100 [Eq. 3.2]
The VS-content varies depending on the substrate. For cow dung it is generally in the
range of 75 to 85 % (Örtenblad, 2000).
Agitation of the slurry may have a positive effect on biogas production and at times even
be crucial to the functioning of a biogas system. Agitation can help to mix fresh substrate
24
and bacterial populations, hinder the formation of scum and ensure a uniform bacterial
population density in the digester. However, too frequent agitation can also lead to
disruption of the symbiotic relationships between the various strains of bacteria and be
detrimental to the process. (Kossman & Pönitz 1999a) Some biogas systems can function
well without any form of agitation.
In a study from Vietnam by An et al. (1997), looking at the effects of agitation in tubular
polyethylene-digesters using pig dung as substrate, concluded that there were no
advantages gained by mixing the contents of the digesters. However, since the results of
agitation are highly dependent on the substrate in use, the frequency and amount of
mixing as well as the method of mixing, biogas systems can only be designed on the basis
of empirical data (Kossman & Pönitz 1999a).
4. Retention time - loading rate, process efficiency and system efficiency
The longer a substrate remains in the anaerobic environment of a digester, the more
biogas it will have produced. The amount of biogas produced daily from the substrate will
increase for a number of days (the amount of days, and how fast, will depend on the type
of substrate, it‟s temperature and all other parameters mentioned in this section so far)
until it reaches a maximum and begins to slowly decrease. In a continuously fed digester,
the Retention Time (RT) is defined as the average amount of days that a unit of substrate
will remain in the digester. This is often a valid approximation. However, if the digester
dimensions are greatly altered, the approximation may become invalid.
RT (in days) = Vl / Vi [Eq. 3.3]
Where Vl is the liquid volume of the digester and Vi is the volume of the slurry loaded per
day. The Vl of the digester is the volume of the slurry, as compared to Total Volume (VT),
which is the volume of the whole digester.
Finding an optimum RT is often a very complex task, involving a careful balancing of the
parameters discussed so far. When using cow dung substrate in continuous fed biogas
systems, an RT of 20-30 days is often used (Kossman & Pönitz 1999a).
Directly related to the RT, and the Vl of the digester, is the Loading rate (LR). LR is
defined as the amount of substrate loaded daily (measured in kg TS/day) per liquid
digester volume (measured in m3).
LR [kg TS /day/m3] = (mass of daily influent slurry * TS of influent) / Vl [Eq. 3.4]
LR is an important parameter that can be used when comparing the results of various
studies since it takes the size of the digester and the TS-content into consideration.
25
Biogas production itself can be quantified and compared in different ways. If we first look
at the biogas production rate (BPR) and define it as the amount of biogas (measured in
litres) produced every hour:
BPR [l/h] = Litres of biogas produced per hour [Eq 3.5]
The amount of biogas produced per day is then:
BPd[l] = BPR [l/h]*24[h] [Eq 3.6]
The system efficiency (SE) can then be defined as the ratio of the amount of biogas
produced daily and the digester's liquid volume Vl:
SE (in %) = BPd [l] / Vl [l] [Eq 3.7]
A good system efficiency is reached by experimenting with the RT and the TS-content of
the influent and finding values that optimize BPd. A high TS-content may at first seem
like a good way to achieve this. However, as is mentioned above, BPd is dependent on a
high mobility of the substrate in the digester and therefore a not too high value of the TS-
content. With unlimited supplies of influent substrate, optimizing system efficiency
would be the only method needed to optimize biogas production (since the amount of
dung used would be of no matter in this case).
If the amount of dung is a limited resource, a good complimentary parameter to measure
biogas production is the process efficiency (PE). The PE is defined as the amount of biogas
(measured in litres) produced per unit influent (measured in kg TS):
PE (in l / kg TS) = BPd / (mi * TS) [Eq 3.8]
Where mi is the mass of the influent that is loaded every day and TS is the solid content
(as a ratio) of the influent. For practical reasons mi is often substituted with vi (since it is
easier to measure volume).
PE (in l / kg TS) = BPd / (mi * TS) = BPd / (vi * TS) [Eq 3.9]
The relation between PE and SE basically lies in the chosen RT (and hence the LR and Vl)
and the TS-content of the influent. If a comparison of biogas production is conducted
between two digesters, with the same RT and TS-content of the influent, the choice
between using PE and SE as an indicator is of no importance – the comparative values will
be the same.
One does not necessarily have to use SE or PE as the only two criteria for optimizing a
biogas system. The amount of dung, water and labour that is available as well as an
appropriate sizing of the digester (e.g. in relation to available space), can also be important
26
criteria to be taken into consideration. In the end it boils down to making sure that biogas
production of the system is able to meet the biogas demand, a question that will be dealt
with in depth in chapters 5, 6 and 7.
For details on measuring techniques of biogas production for research in the field see
section 4.2.
5. pH level
Methanogens live best in neutral to slightly alkaline conditions (Kossman & Pönitz
1999a). Cow dung, as well as other animal dung, is a non-acidifying biomass substrate, and
will very seldom lead to acid conditions (Nyns, 1985). Once the process of digestion has
stabilized, the pH will normally take on a value between 7 and 8.5 (Kossman & Pönitz
1999a).
6. Nitrogen inhibition and C/N ratio
All substrates contain nitrogen. Under alkaline conditions, even a relatively low nitrogen
concentration may inhibit the process for a time. However, methanogens are quite
resilient and can over time adapt to higher levels of nitrogen concentration. Most
important is that the ammonia (NH3) level does not exceed 200-300 mg NH3 per litre
substrate (Kossman & Pönitz 1999a).
Microorganisms require both nitrogen and carbon for their cell growth. Experiments have
shown that the metabolic activity of methanogens can be optimized at a C/N ratio
between 8 and 20, depending on the substrate. For cow dung the optimum C/N ratio is
said to be around 18. (Kossman & Pönitz 1999a) However, the actual effect of the C/N
ratio on the metabolism of microorganisms is very hard to quantify. This parameter is
therefore of comparative low interest in relation to the other parameters discussed so far.
(Smårs, 2009)
7. Available nutrients
In order to grow, bacteria need more than just a supply of organic substances. In addition
to carbon, oxygen and hydrogen, the generation of biogas requires a supply of mineral
nutrients, such as, nitrogen, sulphur, phosphorus, and potassium, as well as, a number of
trace elements, such as, iron, zinc, and nickel. Most substrates, including cow dung,
include these substances. If the concentration of any individual substance is too high it
may have an inhibitory effect on the process. (Kossman & Pönitz 1999a)
27
8. Other inhibitory substances
Besides the inhibitory effect of high concentrations of mineral nutrients and heavy metals
(as mentioned above), antibiotics and detergents used in livestock husbandry can have
inhibitory effects on the process of biogas production.
3.2.2.2 Other Important Process Parameters
The following parameters do not affect the magnitude of the biogas production but are
still highly important process parameters:
1. Methane content of gas (the quality of gas)
As has been mentioned, biogas is essentially composed of Methane (CH4) and Carbon di-
oxide (CO2). When biogas is combusted, transformation of CH4 to CO2 releases energy in
the form of heat. The CH4 content of biogas is therefore a good indicator of the quality of
the gas in terms of combustion. The CH4 content of biogas varies significantly depending
on the substrate digested, the substrate temperature and more. Cow dung digested under
mesophilic conditions, produces a biogas with a CH4 content of around 65 % (55 to 75 %)
(Kossman & Pönitz 1999b; Örtenblad, 2000; Thy, 2003). For details on measuring
techniques for research in the field, see section 4.2.
2. Ammonia-content of influent and effluent
The process of anaerobic digestion changes the chemical, biological and physical
properties of the slurry. The viscosity generally increases due to the transformation of the
carbon in the dung into CH4 and CO2, the odour decreases and the amount of pathogens
decreases. The fertilizer value of digested slurry is generally higher than undigested
biomass substrates and can lead to higher yields. (Kossman & Pönitz 1999b; Örtenblad,
2000)
Among the many reactions resulting from anaerobic digestion, the metabolisation of
organic nitrogen into mineralized nitrogen (aka Ammonia or NH3), is one of the most
important in terms of the fertilizer value. NH3 is directly available to plants and is
therefore also known as plant-available nitrogen. The organic nitrogen remaining in the
digested slurry must be mineralized by soil bacteria before it is available to plants
(Örtenblad, 2000). Measuring the NH3-content of the influent and effluent, and observing
the difference, is a good and fairly simple way to quantify the improvement in terms of
fertilizer value, resulting from anaerobic digestion (Thy & Preston et al., 2003).
Besides being a good organic fertilizer, digested slurry also has soil improving qualities.
Substances such as protein, cellulose and lignin contribute to increasing a soil‟s
permeability and hygroscopicity while preventing erosion and improving agricultural
conditions in general (Kossman & Pönitz 1999a).
28
The NH3-content of fresh cow dung will of course vary depending on a cow‟s diet. An
average of 2,6 kg/ton can be found in literature. Digested slurry has an average NH3-
content of 3,3 kg/ton. (Örtenblad, 2000) For details on measuring techniques for research
in the field see section 4.2.
If the digested slurry is not used directly after it leaves the digester (e.g. left to dry), there
will be a loss of its fertilizing properties, mainly due to the evaporation of NH3. The
digested dung should therefore preferably be used rather quickly (or covered) if it is to be
used as a fertilizer. (Örtenblad, 2000)
3.3 System Design
In China, the majority of the installed biogas systems are of the fixed-dome design and in
India, the most common design is a floating dome. Both of these system designs are made
of cement and both the construction and installation require extensive knowledge and
experience. (Kossman & Pönitz; An et al., 1997) The price of these systems is also seen as
one of the major constraints to their diffusion (An, 2002), especially in countries where
little government support can be expected (Gustavsson, 2000).
3.3.1 Appropriate Biogas Technology
In response to this, the tubular plastic digester was developed in the early 1980‟ by
Preston and Botero (Botero & Preston 1987), based on the “Taiwan model” as described by
Pound et al. (1981). The cost of construction and installation was more than 5 times less
than the systems previously used (34- 60 USD compared to 180-340 USD) and hence
appropriate for use by farmers in poor rural areas, in countries without large support
programs. The technology specifically spread quickly in Vietnam. Within 10 years more
than 20,000 tubular plastic digesters were up and running. Animal dung (from cows and
pigs) is the most common substrate used in these systems. These systems are easier to
construct, install and maintain than the floating dome and fixed dome designs. (An, 2002)
However, there have also been a number of problems identified (see section 3.3.3 below).
3.3.2 Polyethylene Plastic Biogas Systems
The design and the materials used for polyethylene plastic biogas systems vary slightly but
in general you need: Polyethylene plastic, PVC pipes, flexible plastic pipes, a bucket,
manual ball-valves, plastic bottles, rubber, tape, thin rolled metal, and hardware – all
readily available in most local hardware and agricultural supplies stores around the world.
A design overview of a tubular plastic biogas system can be seen in Figure 3.2.
29
Figure 3.2: A design overview of a tubular plastic biogas system.
Here follows a brief description of the components of the biogas system and their
function.
Inlet bucket (with stirrer)
The substrate needs to be mixed with an appropriate amount of water before it is loaded
into the digester. An inlet bucket out of metal, with a plug in the bottom is often used for
this purpose. The stirrer is manually operated and can be as simple as a bamboo pole.
Digester
The digester is at the heart of the biogas system. This is where the slurry (mix of substrate
and water) spends a number of days, produces biogas, and then is let out the other end.
The digester is constructed out of transparent plastic film, preferably UV-coated
polyethylene plastic.
Inlet and outlet pipes
The inlet and outlet pipes are usually constructed out of PVC pipes and inserted into each
end of the digester and sealed off using rubber and tape. The inlet pipes and outlet pipes
must be below the slurry level at all times to avoid leakage. The outlet pipe‟s height is
adjusted at installation to obtain an appropriate slurry level in the digester. A plug may be
attached to both the inlet and outlet pipes to be able to regulate when the slurry is to flow
(this digester design is known as plug-flow, as opposed to continuous flow).
30
Gas pipes
The gas pipes transport the gas from the digester to the gas holder and on to the stove. The
pipes need to be well attached to the digester, gas holder and stove in order to minimize
leaks. The gas pipes can be constructed from different materials. PVC pipes and flexible
plastic pipes (hoses) are both common. Depending on the material, diameter and length of
the pipes, friction will generate a pressure drop in the gas when it moves from the digester
to the stove.
Safety Valve
A safety valve ensures that the pressure in the biogas system does not reach levels that
will risk making the digester or gas holder break. If the gas in the gas holder is not used
for a while, and the pressure reaches the determined upper pressure limit, gas will leak
out to the atmosphere through the safety valve. The upper pressure limit is set by
adjusting the water level in the valve. The Safety valve also functions as a water trap,
preventing water from condensation to block the gas flow in the gas pipes. Therefore,
safety valves should be placed at the lowest point of the gas pipes leading from the
digester to the gas holder (Ref 7, Ref 11). Safety valves can be constructed in different
ways, using different materials but a common way is to use a used plastic bottle and PVC
pipes.
Biogas Holder
The gas holder is, just as the digester, often constructed out of UV-coated polyethylene
plastic and is used as a reservoir for the gas before it is burnt in the stove. The gas holder
will increase the biogas flow to the stove since the volume of biogas in the system will be
larger than without having a gas holder (Kossman & Pönitz 1999a). Most gas holders
previously used in tubular plastic biogas systems, have been positioned horizontally and
weights have been put on top of it to increase the pressure of the gas.
Stove
The biogas stove is the last component of the biogas system and can be either a
commercial burner or of a simpler home-made design. An air-intake or mixing chamber is
not necessary but may increase the efficiency (but also the cost). The simplest stove
designs simply have a manual valve to regulate the flame and a manifold to create a well
shaped flame. They are constructed of sheet metal of various kinds.
3.3.3 Identified problems, critique and failure of polyethylene digesters
A number of problems with tubular plastic biogas systems, have been identified, and
written about in literature. One of the main problems is the durability and life-time of the
materials (the polyethylene used for digesters and gas holders and the plastic used for the
gas pipes) and their sensitivity to UV-rays and material damage from falling objects,
people and animals (An, 2002; Van Chinh, 2002; Kossman & Pönitz 1999a; Kossman &
Pönitz 1999b; United Nations, 1984). The polyethylene digester is also difficult to repair if
damaged (Kossman & Pönitz 1999b). Another problem is the low pressure, gas flow and
31
production rate often experienced (Cortsen et al., 1997; United Nations, 1984). The land
area required for installation is also larger than for other designs (Van Chinh, 2002). Leaks
from the seals between gas pipes and digester have also been known to occur.
3.3.4 Improved Polyethylene Plastic Digesters in Lembang
Since the biogas initiative started in 2007, a number of these problems have been
addressed, and solutions have been found by the biogas team in the Lembang area.
The plastic film used for constructing both the digesters and the gas holder is UV coated,
meaning that it is not as sensitive to UV-rays as regular polyethylene plastic. The plastic
film used is also thick enough that one layer is enough (reducing costs). To further protect
the plastic from sunlight, both the digester and the gas holders are covered with an
additional thin plastic film, known locally as “Mulsa”. Mulsa is used in agriculture to
retain heat and moisture in the soil around crops. Because of its insulative qualities, the
Mulsa also helps increase the process temperature of the digester.
By using a plastic sealer, the shape of both the digester and gas holder can be made more
like a cylinder (see Figure 3.3). For the digester, this ensures a tighter fit to the inlet and
outlet pipes, and for the gas holder it ensures that it can be completely emptied if needed.
The gas holders in Lembang are also positioned vertically (an idea pioneered in Vietnam)
instead of horizontally, so that weights can hang from the bottom of it, to increase the gas
pressure as it is emptied.
Pressure valves are another improvement introduced by the team in Lembang. In earlier
plastic tubular biogas system designs, pressure valves are not included. However, they can
be very useful, as they allow the user to adjust the pressure of the gas in the digester (by
changing the water level in the pressure valve). They also ensure that when the gas holder
is emptied (i.e. the stove is being used), the pressure of the gas can be regulated to a higher
degree and the gas pressure in the digester will never go below the level indicated by the
pressure valve (since the gas will only flow in one direction through the pressure valve).
The pressure valve is constructed with the same material as the safety valve and should be
placed close to the gas holder (for easy access). The safety valve and pressure valve have
also successfully been integrated into the same device, by using two pipes of different
diameter and length and inserting them into each other (see Figure 3.3).
„
32
Figure 3.3: A digester constructed using a plastic sealer ensures a cylindrical shape and a tight fit of the
outlet and inlet pipes. An integrated safety and pressure valve with the flow of gas indicated by the black
arrows. The white box highlights the end of the safety valve, which surrounds the white pipe which acts as
a pressure valve.
Leaks from the attachment point of the gas pipe to the digester are minimized by a seal
made of rubber from old bicycle tires, PVC plates, a metal valve, nuts and bolts. The gas
pipes used are also made of a flexible “hose-like” material, making the connection to the
digester easier (less weight on the connection). The flexible gas pipe is also less sensitive to
UV-rays and mechanical damage, as compared to PVC pipes.
The stoves used for the systems in the Lembang area are made of stainless steel and
constructed locally in a metal shop. The cost of the stove is around Rp. 100,000 (10 USD),
which is relatively low compared to commercial alternatives.
33
4. Materials and Methods
A wide range of methods and materials were used to close in on the research questions
presented in section 2.3. The technical aspects of constructing and designing communal-
and single-family biogas systems were investigated with the help of a number of
experimental set-ups presented in section 4.1. The measured variables and measuring
techniques are then presented in section 4.2. In section 4.3, two villages with biogas
systems that are in use and which were used to evaluate the functionality of real systems,
are briefly described.
4.1 Experimental Set-ups
In order to investigate the technical aspects of developing communal biogas systems, as
well as improving single-family systems, a number of experimental set-ups were
constructed and installed in the village of Cicalung. The set-ups ranged significantly in
size (from small all the way up to full-scale). The experiments run on these set-ups are
documented mostly in chapter 5, but a small part of Chapter 6 is also based on
observations of some of these set-ups.
4.1.1 Small-Scale Experimental Digesters in “Saung Richie” (A)
Small-scale experimental digesters where constructed in order to run a number of
experiments that would be very difficult and time consuming to conduct on full-scale.
These experiments are documented in Chapter 5.
Construction and Installation
Eight small scale digesters where built in a field made available by a local farmer in
Cicalung. They were protected from weather and wind by a “Saung” (a bamboo structure
covered with transparent polyethylene plastic). Each digester was connected to a gas
holder via a pressure valve and a safety valve. The gas holders where dimensioned large
enough so that gas production measurements would not need to be conducted more than
two times per day. The materials used to construct the experimental digesters did not
differ much from the materials used in real systems. Figure 4.1 shows the constructed
Saung and four of the digesters, pressure valves and safety valves.
34
Figure 4.1: The “Saung Richie” with digesters A1-A6. Digester A3a, A3b, A3c and A4.
For ease of reference each of the experimental digesters were given a name:
Digester A1: A standard dimensioned digester covered with soil
Digester A2: An uncovered standard dimensioned digester
Digester A3a: A standard dimensioned digester, 1st of the connected digesters
Digester A3b: A cement digester, 2nd of the connected digesters, in between A3a and A3c
Digester A3c: A standard dimensioned digester, last of the connected digesters
Digester A4: A standard dimensioned digester, covered with rice husks
Digester A5: A shorter and wider digester
Digester A6: A vertical digester with the same dimensions as A5.
Inoculation and Operation
Each digester was inoculated with a mix of fresh dung and water (1:1 Ratio ) and already
processed slurry (known as starter), taken from the output of Digester C (see below). They
were filled with an amount of slurry that was thought to result in a liquid volume of 80%.
Later, measurements of the total volume of the digesters resulted in liquid volumes that
differed from this. The digesters where then left to stabilize for two weeks before daily
loading commenced. Each digester was then loaded every morning with an equal mix of
fresh dung and water that resulted in a RT of 30 days. The calculated LR (in
kg/TS/m3/day) was based on measurements of average TS-contents of the dung using a
hydrometer (see section 4.2). An overview of the experimental digesters‟ design and
operation specifics can be found in Table 4.1.
35
Table 4.1: Design and operational specifics of small-scale experimental digesters A1 to A6. The difference in
liquid volume (in % of total volume) of the digesters at the start of the experiments is a result of incorrect
approximations of the total volume which were corrected later. The loading amount is calculated to result in
a RT of 30 days in all digesters. As for the LR, 1 liter of influent slurry is assumed to equal 1 kg since a
majority of the slurry is water (over 90 %). Digesters A3a, A3b and A3c differ a bit from the rest, since they
are connected to each other. Only A3a is loaded daily, and with an amount of slurry that will result in a
combined RT of 30 days (10+10+10) for the connected digesters.
4.1.2 Communal Prototype Digester (B)
A communal biogas system supplying biogas to two households from one digester was
installed in the village of Pasir Angling in January of 2009. For further information on the
village of Pasir Angling and details of the biogas systems there, see section 4.3. Due to the
difficulties of experimenting on this system while it is in use and to measure gas
production from a full scale system, a communal prototype digester (digester B) was
constructed and installed in the village of Cicalung. Digester B was meant to answer
questions related mainly to distribution of gas flow which is documented in section 5.3
and discussed in section 6.3.
Construction and Installation
Digester B was based on the communal system that had just been installed in the village
Pasir Angling which consisted of one long tubular digester and two gas holders, supplying
biogas to two different households. It was installed next to the “Saung” with digesters A1-
Digester
A1 Digester
A2 Digester
A3a Digester
A3b Digester
A3c Digester
A4 Digester
A5 Digester
A6 Length [m] 1 1 1 0.91 1 1 0.59 0.59 Diameter or width*height [m] 0.3 0.3 0.3 0.21*0.35 0.3 0.3 0.42 0.42 Total Volume [l] 70.7 70.7 70.7 66.9 70.7 70.7 81.7 81.7 Liquid Volume at start [l] 55.8 55.8 55.8 55.8 55.8 55.8 69.3 69.3 Liquid Volume at start [%] 78.9 78.9 78.9 83.4 78.9 78.9 84.8 84.8 Loading Frequency Daily Daily Daily - - Daily Daily Daily Loading amount [l/day]
1.86
1.86
5.58
-
-
1.86
2.31
2.31
Water:Dung ratio 1:1 1:1 1:1 - - 1:1 1:1 1:1 Loading rate [kg TS/m3/day]
2.72
2.72
8.17
-
-
2.72
2.72
2.72
Retention time [days]
30
30
10
10
10
30
30
30
36
A6 (see Figure 4.2). Two gas holders were also constructed and connected to the digester
via pressure valves. The pressure valves where especially designed so that the water
column could be adjusted to a high order of accuracy (<1 mm). Safety valves were also
installed. The gas holders were kept, hanging from the roof, under the “Saung”
constructed for digesters A1-A6.
Figure 4.2: Pasir Angling communal system, digester B inoculation, digester B ready for experiments.
Digester B was designed to be as similar to the full scale system in Pasir Angling as
possible. Unfortunately it was difficult to make it an exact model of the Pasir Angling
system. One of the major differences, that most likely had implications for the results of
the experiments, was the gas pipes used. Between the two systems, they differed quite
significantly in both size and material.
Inoculation and Operation
After construction and installation of digester B, it was inoculated with a mixture of fresh
dung and water (1:1 ratio) and starter taken from digester C (see below) until the desired
liquid volume and liquid height was reached (86.4 % of total volume or 70 % of the total
height). After inoculation, which took two days, the digester was loaded daily with an
amount of slurry resulting in a RT of 30 days. A small leak was discovered and fixed, and a
rather large one (created by the foot of a visitor) was also fixed before the digester B was
ready for experiments on the 6th day after inoculation.
A comparison of the design and operational specifics between the two systems can be
found in Table 4.2.
37
Digester
Pasir Angling communal digester
(PA1)
Digester B (communal prototype
digester)
Length [m] 7 3.5
Circumferance [m] 4 2
Diameter [m] 1,27 0.64
Total Volume [l] 8913 1114
Liquid height [%] 70 70
Liquid Volume [l] 7702 963
Liquid Volume [%] 86.4 86.4
Length/Diameter ratio 5.5 5.5
Wanted RT [days] 30 30 Required Loading amount [l/day] 256.7 32.1
Water:dung ratio 1:1 1:1 Loading rate [kg TS/m3/day] 2.72 2.72
Loading frequency ? Daily Gas Holders
Length [m] 1.5 0.75
Circumferance [m] 3 1.5
Diameter [m] 0.95 0.48
length/diameter ratio 1.57 1.57
Width [m] 0.75 0.38
Volume [l] 1074 134
Total volume [l] 2148 268 Gas Pipes Type flexible plastic tube flexible transparent plastic tube
Material ? ?
Diameter [cm] 1.91 0.7
Pressure and Safety Valves
Integration yes no
Measurement scale no in [mm]
Table 4.2: Comparison of design and operational specifics between digester B (communal prototype digester)
and the communal system installed in the village of Pasir Angling (PA1). Integration of pressure valves and
safety valves means they are built into the same device (see section 3.4 for a picture and explanation).
4.1.3 Wawa’s Full-Scale Digester (C)
Small scale models of biogas systems, such as the digesters A and B above, are useful when
running experiments that are difficult to conduct on full scale systems or systems in use.
However, certain experiments, such as measuring production rates, really require that a
full scale system is used. Fortunately, a biogas system in Cicalung that has been in use for
over two years, was made available for experimentation. The experiments and
measurements conducted on digester C are documented in section 5.4 and 6.4.
38
Construction and Installation
The system was constructed and installed over two years ago as one of the first
polyethylene tubular biogas systems in the Lembang area. The system was installed in the
backyard of Wawa Wahyudi‟s family‟s house. Originally it was designed and dimensioned
to provide two households with biogas, but is today only used by Wawa‟s family (a
household with 3 people) and for conducting experiments. The different parts of the
biogas system can be seen in Figure 4.3.
Figure 4.3: Digester C with influent bucket full. A full gas holder and hiding behind it - an emptied gas
holder with weights to increase the pressure of the gas, and the pressure valve to the right. Adjusting the
flame on the biogas stove in Wawa‟s household.
Operation
Since there is limited access to water on the plateau where the village of Cicalung is
situated, there are not many cow farmers in the area. The closest cow farmer to Wawa‟s
families household is Mr. Akang who lives in a nearby village, a 10 minute walk away.
Mr. Akang has two biogas systems installed but does not manage to use all of the dung
that his cows produce, in his systems. For the last two years, digester C has not been
loaded on a daily basis and at times quite sporadically. In general, the digester was loaded
with as much as 300 l of dung at a time (making 600 l of slurry) but only every two weeks.
This would equal a loading amount of approximately 43 l per day and results in a RT of
around 118 days. Before measurements commenced, the LR was changed in order to have
a RT of around 30 days. 80 l of dung was picked up every morning at Mr. Akang‟s and
loaded into the digester with a dung:water ratio of 1:1, resulting in 160 litres of slurry
going into the digester every day. This loading routine was started more than 30 days
before measurements began and maintained throughout the experimental period. Figure
4.4 shows the process of loading the digester.
39
Figure 4.4: Early morning dung pick-up. Carrying water to the digester. Mixing water and dung in the
influent bucket.
The design specifics of digester C and the operational specifics during the experimental
period, can be found in Table 4.3.
Table 4.3: Design specifics of digester C and operational specifics before and during the experimental period.
Digester C
Length [m] 10
Circumferance [m] 3
Diameter [m] 0,955
Total volume [l] 7162
Liquid Volume [l] 5053
Liquid Volume [% of total volume] 70,6
Loading frequency Daily
Loading amount [l/day] 160
Loading rate [kg TS/m3/day] 2,587
Retention time [days] 31,58
Gas Holder
Circumferance [m] 3
Height [m] 1,5
Volume of full holder (cylinder) [l] 1074
40
4.2 Measured Variables and Measuring Techniques
Considering the applied nature of the experiments and the limited resources available, the
amount of variables that can be measured and the accuracy of the measurements are
limited. Simple measuring techniques for research in the field were studied and the
required measuring equipment was either purchased in Sweden and then brought to
Indonesia, or purchased or constructed on the spot in Bandung. Most variables mentioned
below were measured in every experiment conducted. However, in many experiments,
several variables did not contribute much to the understanding of the studied phenomena,
and were therefore excluded from the experimental description in Chapter 5. Below,
follows a review of the measured variables as well as a description of the measuring
techniques and equipment.
4.2.1 Biogas Production Rate
Biogas production rate (BPR) is the volume of biogas that is produced per unit time.
Biogas BPR was the most crucial variable measured and the results ended up being used in
almost all of the experimental descriptions.
Measuring technique and measuring equipment
BPR can be measured in a number of ways. Flow-meters have been used in earlier
experiments and were an option considered (United nations, 1984). A flow-meter was
brought from Sweden but ended up not being used. Instead a technique known as Water
Displacement was used. This is a simple technique to measure BPR that has been used in a
number of earlier experiments on tubular plastic biogas digesters (Thy et al., 2003; Thy et
al., 2005; Kounnavonga, 2008). The basic principle is to let biogas fill a light-weight
bucket of known volume, turned up-side-down and floating in a larger, water-filled
bucket. As more biogas enters the light-weight bucket, it rises, and the volume of the
produced biogas per unit time can be calculated (since the volume of the light-weight
bucket is known). Two water displacement units were constructed for the experimental
set-ups. A smaller unit was constructed to measure the volume of the biogas produced
during the experimental periods of digesters A1-A6 and digester B. Later, a much larger
unit was constructed in order to measure the volume of the biogas produced from the full-
scale system (digester C).
Construction and installation of the smaller water displacement unit (WD unit AB)
To be able to measure biogas production from digesters A1-A6 and digester B, there was a
choice in either constructing one Water Displacement unit (WD unit) per digester
(meaning 9 in total) or, creating a single WD unit that could measure the volume of biogas
produced from all digesters (one at a time). The latter was chosen, as it seemed to be the
easiest and cheapest alternative. The design of WD unit AB and the materials required are
most easily understood by studying Figure 4.5 below.
41
Figure 4.5: The small water displacement unit (WD unit AB) used to measure the biogas produced from
digesters A1-A6 and digester B. The biogas was pumped from each gas holder into the unit by using the
pump seen on the left in the picture.
The larger bucket was built from a hard, albeit flexible, plastic sheet that was rolled into a
cylinder and a poly-ethylene “sock” that was inserted into it. Through the bottom of the
“sock” a pipe was installed that would reach above the water level in the bucket. The top
of the WD unit was created using a light-weight, transparent, plastic sheet that was
flexible enough to allow it to be bent and folded into a cylinder open only on one end
(using glue and tape). The top was dimensioned to be able to hold at least 25 litres of
biogas (the approximate size of the gas holder of digesters A1-A6). By knowing the
circumference of the light-weight plastic top, a scale (in litres) was constructed and taped
to its side (see Figure 4.6). WD unit AB was installed in the “Saung” next to digesters A1-
A6. A hole was dug and necessary piping and manual valves where connected to the unit.
Operation of WD unit AB
Before the gas holders belonging to digesters A1-A6 and digester B where emptied, they
were detached from the system (manual valves ensured that no gas leaked from the gas
holder or the digester at this time) and connected to the WD unit AB, via a manual pump.
Before the measurement started, it was made sure that the light-weight plastic top of WD
unit AB was at its starting position. Using the manual pump, the biogas was then sucked
out of the gas holder and into the light-weight plastic top. When the gas holder was
completely emptied (or the plastic top had reached its highest possible position, as was
often the case when measuring the volume of the biogas from digester B), the value on the
measuring scale was noted (see Figure 4.6). The biogas was then emptied and burnt, by
opening a manual valve that can be seen in Figure 4.5, before the next measurement could
commence. The manual pump was disassembled and rebuilt at one time during the
experimental period, when it seemed to be leaking, but we had no further troubles with
it.
42
Figure 4.6: The measuring scale on the light-weight plastic top of WD unit AB. The manual pump
disassembled for repair.
Construction and installation of the larger water displacement unit (WD unit C)
To measure the volume of the biogas produced in the full-scale digester C, there were a
few different options. Using a flow-meter would have been possible but there was no way
of calibrating the device, and it was uncertain whether the gas-flow would be large
enough for the device to measure it. Another alternative was to approximate the volume
of a gas holder and then note the time it took for it to become full (two extra gas holders
were produced for this purpose at first). This alternative was also repudiated, as it was
decided that the accuracy of the measurements would be too low and the measuring
procedure too time consuming. Instead, a large water displacement unit was designed and
constructed. The design requirements of WD unit C were that it would be directly
connected to digester C and that it would need to be emptied no more than two times per
day. The locally available materials also put constraints on the design and the construction
of the unit. A list of materials used in the construction can be found in Table 4.4.
43
Material Quantity Price/unit (Rp.) Price (Rp.)
Blue tarp, 1m*1.5m 4 9,500 38,000
Metal wire (diam 3 mm), 1 kg 4 13,000 52,000
Metal wire (diam 1 mm and 2 mm) 1 20,000 20,000
Wire mesh (1/2" squares), 1m*1m 6.5 13,000 84,500
PVC pipe (1/2"), 4m 4 9,500 38,000
Plastic manual valve (1/2") 3 9,500 28,500
Black tape, wide 3 10,000 30,000
Electric tape 1 4,500 4,500
UV (Polyethylene) for water bag 2.5 18,000 45,000 Plastic “Mika kardus” (for top), 1m*1,4m 6 17,000 102,000
Green plastic hose (3/4"), 1m 15 6,000 90,000
Blue rope (1 mm) for stabilizing top 1 15,000 15,000
Sum total Rp 547,500
Table 4.4: Materials needed for the construction of WD unit C and their cost. Rp. 547,500 is about 54.8
USD.
The wire mesh was tied together and formed into a cylinder using the lighter of the two
metal wires. The heavier metal wire was then used to give stability to the cylinder. A liner
for the cylinder was created using the blue tarp material. Using the same polyethylene
plastic used for the digesters and gas holders, a “sock” that would be inserted inside the
liner, was constructed. The plastic known locally as “mika kardus” (same material as was
used for the top of the smaller WD unit AB), was then used to create the top of WD unit
C. The top was closed at one end using the same technique as for WD unit AB. Different
stages in the construction can be seen in Figure 4.7.
Figure 4.7: Close up of the wire mesh work, Finished metal cylinder and blue tarp liner, construction of the
light-weight plastic top.
44
The top was enforced by attaching loops, made from the thicker of the two metal wires, to
the inside of the top. A measurement scale (in cm) was then painted on the side of the top.
WD unit C was installed indoors in a space made available by Wawa‟s family. A
supportive structure made out of wood made sure the unit would stand straight and would
not break. The gas pipe was connected directly from digester C to the WD unit C. After an
unsuccessful attempt to fill the bucket (due to a leak in the polyethylene “sock”), we
managed to complete the installation. It turned out that the light weight top needed to be
stabilized (so that it would move freely in a vertical motion) which was accomplished
using 4 strings running from the bucket up to the ceiling. The installation process can be
seen in Figure 4.8.
Figure 4.8: Preparing the spot where WD unit C was to be installed. WD unit C installed and ready to go.
Close up of biogas measurement scale and stabilisation system for the light-weight top.
Operation of WD unit C
Since WD unit C was connected directly to digester C, the only manual labour needed to
conduct the measurements was to record the height of the light-weight top before it
reached its maximum (two times a day was enough) and to return the top to the starting
position by emptying the biogas. When emptying WD unit C, the gas was led to a gas
holder where it then could be used for cooking by Wawa‟s family.
4.2.2 Temperature
As was explained in section 3.2.2.1, the process temperature (temperature of the slurry in
the digester) is of great importance to the process of biogas formation. Knowing the air
temperature is also of interest, since it can reveal how the process temperature is affected
by variations in the surrounding temperature (e.g. from weather changes and night/day
variations).
45
Five glass, stick-thermometers with a range of -10 to 100°C, were purchased. The air
temperature and process temperature were measured during all experiments conducted on
digesters A1-A6. The air temperature was measured simultaneously at two points – both
in and outside of the “Saung” covering digesters A1-A6, to see if there was any significant
difference. The process temperatures of digester A1-A6 was then measured using one
thermometer that was inserted into the influent pipe of the digesters, one at a time. The
thermometer was left for 2 minutes in each digester before measurements were taken in
order to ensure that the reading would be accurate. The temperature just on the side of
the digester, was also measured for digester A1 and digester A4 using separate
thermometers (for an experiment on insulation by earth and rice husks, see section 5.4).
The temperature measurements where conducted in a fairly sporadic manner. In general,
they were recorded at least twice a day.
4.2.3 Total Solids Content
The Total Solids content (TS-content) of the substrate was an important variable to
measure. The measured TS-content was used in calculating the process efficiency (l / kg
TS), which is a value of the biogas production rate that can be compared to other results
(from literature and between the experiments in this paper).
A hydrometer designed to measure the TS-content of slurry, was purchased in Sweden. It
was used to measure the TS-content of both the influent and effluent slurry (see Figure
4.9).
Figure 4.9: Measuring the Total Solids content of the influent slurry using a hydrometer.
The influent slurry of all digesters was a mixture of fresh dung and water (1:1 ratio). After
thoroughly mixing the slurry in a bucket and removing any larger objects (such as
undigested grass), the hydrometer was carefully placed in the middle of the bucket. The
value showing after one minute was recorded and multiplied by a factor two (since the
water/dung ratio was 1 to 1), to get the TS-content of the dung.
The TS-content of the effluent slurry was much more time consuming to measure, since a
measurement was needed for each digester, and was hence done only a handful of times.
46
The effluent was at times too viscous and had to be diluted with water in order to be
measurable. Furthermore, the effluent measurements did not reveal much useful
information and are therefore generally omitted from the experimental descriptions in
Chapter 5.
4.2.4 CH4-Content
CH4 (Methane) content is a direct indicator of the quality of the biogas, since when burnt,
it is the CH4 that is converted into energy in the form of heat. The higher the CH4-content
of the biogas, the more energy is available for heat-creation. The CH4-content of the
biogas produced during the experimental periods of digesters A1-A6 was measured.
The CO2-content of biogas was determined by using a device known as an Einhorn
fermentation-saccharometer, which was borrowed from the Institute of Microbiology at
the Swedish University of Agricultural Sciences (SLU). The device is based on the
principle that CO2 quickly is dissolved in lye (NaOH), whereas CH4 remains in gaseous
form. The device is first filled with 7 M NaOH. 5 ml of biogas is then collected into a
syringe from the relevant source. A longer curved needle is then mounted on the end of
the syringe and the gas inserted and made to pass through the lye in the device. The CO2
in the biogas is hence absorbed in the lye. Since biogas consist of almost solely CO2 and
CH4, the percentage of the initial gas remaining at the top of the device, indicates the
CH4-content of the biogas. Figure 4.10 illustrates the measuring procedure.
Figure 4.10: Measuring the CH4 content of biogas using an Einhorn fermentation-saccharometer.
4.2.5 NH3-Concentration
The NH3 (Ammonium) concentration is one of many indicators for the fertilizer-value of
the slurry. Ammonium is also known as plant-available nitrogen as it is the form of
nitrogen that plants are able to absorb. The process of anaerobic digestion has been said to
increase the Ammonium concentration (Thy et al., 2003), and hence also the fertilizer
value. The effect of anaerobic digestion on the ammonium concentration of the slurry was
studied by running measurements on both the influent and effluent. Measuring
47
ammonium concentration is the easiest analysis that can be conducted in terms of the
fertilizer value of the slurry, and is hence appropriate for field studies. Phosphorus
content can also be determined fairly easy (with the help of a hydrometer), while other
indicators of fertilizer value, such as Total Kjeldahl Nitrogen (TKN) and Chemical Oxygen
Demand (COD), require access to a laboratory.
Measuring equipment
A nitrogen meter built by the manufacturer Agros, was borrowed from the Swedish
Institute for agricultural and environmental engineering (JTI) in Uppsala, Sweden. pH-
adjuster (NaOH), reagent (Ca(ClO)2) and a measuring scoop was purchased from Agros
and brought to Indonesia along with the nitrogen meter. The reagent creates a reaction
where most of the ammonium in the slurry is released and the amount is measured with a
manometer. The nitrogen meter can be seen in Figure 4.11.
Figure 4.11: Agros Nitrogen meter. Measuring dung to be put into nitrogen meter. Nitrogen meter ready to
be closed and the reagent mixed into the slurry.
Measuring technique
For analysis of fresh dung (the influent), 80 ml of dung was mixed with 160 ml water in
the Nitrogen meter. The pH-adjuster was added to the mixture and a scoop of reagent was
put into the compartment provided. The lid was thereafter closed tight and the reagent
mixed into the slurry by turning a handle on the side of the device. The mixture in the
device was then mixed, using the handle, until the needle on the manometer stopped
moving or when 8 minutes had past. The value showing on the manometer was in kg
NH3/m3.
For analysis of the effluent, 160 ml of the slurry was mixed with 80 ml of water (since the
effluent already is at an approximate water:dung ratio of 1:1) in the nitrogen meter.
Thereafter the same procedure as for the influent was performed. The process of
measuring NH3-concentration can be seen in Figure 4.11.
48
4.2.6 Pressure
The pressure of the gas is not the same in all parts of the biogas system. The friction in the
gas pipes leads to drops in pressure. So the gas pressure indicated by looking at the
pressure valves only gives an approximation of the gas pressure in the digester. However,
the pressure drop is quite small compared to the nominal value of the pressure, so the
pressure valve can be used to approximate the pressure in the system “before” the valve.
The pressure after the valve is determined by the amount of gas in the gas holder. Gas
pressure is an important variable since a certain pressure (higher than the atmospheric
pressure) is required for the gas to be transported from the digester to the gas holder, but
it must also remain under a certain value due to material limitations of the polyethylene
plastic of the digester and gas holder. Earlier experiments performed by the biogas team in
Lembang, show that the plastic can withstand a pressure up to 20 cm Water Column
(WC), at least for a shorter period of time.
4.3 Biogas Systems in Use (Used for Observation and Evaluation)
Biogas systems (both communal and single-family) have been installed and are operating
in five areas in and around Lembang. The areas range from semi-urban neighbourhoods
such as Cireyod and Dago Pakar, to more remote and rural villages such as Pasir Angling.
Observation and evaluation of the biogas systems, which provides the base for the
discussion in Chapter 6 (Installation, Operation and Maintenance: in the eyes of the user),
was conducted mainly in Pasir Angling and Cireyod. Here follows a brief description of
these two areas and the specifics of the biogas systems installed there.
4.3.1 Biogas Systems in the Village of Pasir Angling
Around 240 households make up the small, remote village of Pasir Angling. It clings to the
hills lining the Lembang area, and lies in the border between forest and cultivated
agricultural land. Pasir Angling is a 15 minute walk from the main road along a steep and
often muddy road, climbing up through a steep, terraced landscape. Possibly attributed to
its remoteness, the sense of community is highly tangible in Pasir Angling – making it a
suitable candidate for a communal biogas system.
Three biogas systems had been constructed and installed at the time of this study‟s
completion. Two more installations were in progress. The specifics of the installed systems
can be found in Table 4.5.
49
Biogas system PA1
Biogas system PA2
Biogas system PA3
Type Communal Single-family Single-family
Amount of households 2 1 1
Amount of people 5+2 4 3
Number of cows owned 4+0 1 0
Orientation of digester horizontal vertical horizontal Dimension of digester (length*diameter) [m] 7*1.27 2.2*1.7 3*1.5
Table 4.5: Specifics of biogas systems installed in Pasir Angling. The number of cows owned does not reflect
the amount of cows available. Biogas system PA3 is given cow dung from a neighbour and Biogas system
PA2 uses cow dung from the owners of biogas system PA1 and another neighbour.
Biogas system PA2 was later incorporated into biogas system PA1 making it a communal
system providing cooking fuel for 11 people in 3 households. The three biogas systems can
be seen in Figure 4.12.
Figure 4.12: The vertical biogas system PA2 ready to be installed and lying next to the communal biogas
system PA1. Biogas system PA3 being installed.
4.3.2 Biogas Systems in the Village of Cireyod
Cireyod is a semi-urban village close to the town of Lembang and home to around 450
people. Houses upon houses, with little space between them, line the narrow streets.
Around 30 % of the inhabitants work in dairy farming. There are 4 larger cow pens
containing between 13 and 30 cows each. Very large piles of cow dung surround them,
creating an unpleasant smell and contamination of the local water supply. The economic
and social structure seems to be more hierarchical and competitive than in Pasir Angling.
Installing a communal system may be problematic if not managed with care and
precaution.
Three biogas systems had been constructed and installed at the time of this study‟s
completion. Two more installations were in progress. The specifics of the installed systems
can be found in Table 4.6.
50
Biogas system Ci1
Biogas system Ci2
Biogas system Ci3
Type Communal Single-family Single-family
Amount of households 2 1 1
Amount of people 4+3 6 3
Number of cows owned 0 5 0
Orientation of digester horizontal horizontal horizontal Dimension of digester (length*diameter) [m] 6*1.5 4*1.27 4*1.27
Table 4.6: Specifics of biogas systems installed in Cireyod. The number of cows owned does not reflect the
amount of cows available. Biogas system Ci1 is given cow dung from a neighbour and biogas system Ci3 uses
cow dung from the owners of biogas system Ci2.
The communal system Ci1 was shared by just one family, but living in two different
households. The biogas systems Ci2 and Ci3 were installed very close to each other. The
location of Ci1 and the cow pen providing the cow dung for Ci2 and Ci3 can be seen in
Figure 4.13.
Figure 4.13: The location where the communal biogas system Ci1 was installed later on. The cow pen
providing the cow dung for biogas systems Ci2 and Ci3 is located 200 meters away.
51
5. Construction and Design: A Technical Perspective
This chapter presents the purpose, background, theory, materials and methods, results,
analysis and conclusion of the experiments that were conducted in order to answer
technical questions related to the four key technical and operational issues, introduced in
Chapter 2.4. Each sub-chapter deals with a question that provides input to one of the
issues, and is in turn divided into two sections: one that deals with single-family systems
and one that goes into specific implications for the development of communal systems.
The sections on single-family systems are general, in the sense that they pertain to all
biogas systems, including communal systems. The methodological approach used for the
collection of empirical data for this chapter, was experiments with quantitative outcomes.
5.1 Digester Dimension
The question of digester dimension is in this section realized through a comparative
experiment on the performance of three digesters of different dimension and orientation.
The section will provide data for the discussion in Chapter 6.1 on the key technical and
operational issue: Available space and alternative uses of the land. Key findings and
suggestions from this section are also summarized and synthesized in Chapter 7.
5.1.1 Improved Single-Family Systems
Due to the limited and often oddly shaped space available for installing a biogas system, it
is of interest to investigate the effect, that using digesters of different dimension and
orientation, has on the performance of the biogas system. More specifically, the question
of how digester dimension and orientation affects biogas production rate (BPR) is
investigated.
Background and Theory
The effect of dimension on biogas production has been studied in Vietnam by Thu Hang
(2003) as well as in a larger study including 4 south East Asian countries (Thy et al., 2005).
Biogas production from cow dung from three digesters of different length:diameter ratio
was studied (5:O.65; 3:0.65 and 2:0.65) and it was concluded that the longest digester had
the highest production rate on average (91.2 l / kg TS compared to 65.8 and 55.0 l /kg TS
for the other two digester dimensions).
Material and Methods
The effect of digester dimension on BPR was studied using an experimental set up with
three differently dimensioned digesters (A2, A5 and A6). One digester was a “standard”
tubular digester with length:diameter ratio of 1:0,30 m (A2). The second digester (A5) was
shorter with a length:diameter ratio of 0.59:0.42. The third digester (A6) had the same
dimensions as the second digester but was oriented vertically. Even though the volume of
52
the two digesters mentioned last were slightly larger, the loading amount was adapted in
order to keep the LR and RT the same for all three digesters. Water displacement was used
to measure biogas production and a hydrometer was used to determine the TS-content of
the dung. CO2 absorption in lye was used to analyze methane content of the biogas. See
section 4.2.1, 4.2.3 and 4.2.4 for specifics.
Results and Analysis
Figure 5.1 shows the daily measured BPR for the three digesters during the experimental
period. As can be noted the Standard long horizontal digester (A2) shows the best
performance once the production has stabilized after a week of measurements. The low
value of the short horizontal digester (A5) around the 4-5 march is due to a mistake that
left the manual valve to the gas holder closed for a period of 10 hours.
Figure 5.1: The effect of different dimensions on the BPR (here represented by the process efficiency - PE)
over the experimental period between the 13th of February and the 13th of March, 2009.
The average BPR of the three digesters are summarized in Table 5.1. The short horizontal
digester (A5) has a PE that is around 87.4 % of the standard digester‟s (A2) PE. The
vertical cylindrical digester (A6) has a PE that is around 92.8 % of the standard digester‟s
PE. The same relation exists between the digesters‟ system efficiency since the LR and RT
are the same for the three digesters.
53
Digester Standard (A2) Short (A5) Vertical (A6)
Length/diameter ratio[m] 1/0.3=3.33 0.59/0.42=1.40 0.59/0.42=1.40
Process Efficiency (l/kg TS) 124.7 109 115.7
Systems Efficiency (% of liquid volume)
33.9 29.7 31.5
Table 5.1: The average process efficiency and system efficiency of the three digesters A2, A5 and A6.
One of the factors contributing to the difference in the digesters BPR could be the process
temperature. The methane content of the biogas from the three digesters did not differ
significantly.
Conclusion
Shorter digesters and vertical digesters are not as efficient at producing biogas as the
standard longer digester. The PE of a shorter digester with a length/diameter ratio of 1.4
has a PE and SE that is approximately 12.6 % lower than that of a standard digester with
length/diameter ratio of 3.33. The PE of a vertical digester with length/diameter ratio of
1.4 has a PE and SE that is approximately 7.2 % lower than that of a standard digester.
5.1.2 Developing a Communal System
When constructing a communal system it can be advantageous to be able to use digesters
of different dimension. The available space for biogas production does not always allow
the standard size of the digester, especially when several digesters (or one large digester) is
to be built (as is the case when installing a communal system).
One potential advantage of a communal system over a single-family system is the less
amount of land/person needed when a larger system is built (at least when it comes to
having a communal system with one large digester). However, a communal system can
require a larger area that is situated fairly close to all connected households – something
that is not always found in reality. See section 6.1.2 for a further discussion.
5.2 Slurry Flow
The question of slurry flow is in this section limited to an investigation into the possibility
of connecting several digesters to each other in series, and the effect that this would have
on the performance of the biogas system. The section will provide data for the discussion
(in Chapter 6.2) on the key technical and operational issue: Slurry flow management. Key
findings and suggestions from this section are also summarized and synthesized in Chapter
7.
54
5.2.1 Improved Single-Family Fystems
Connecting digester is not applicable on single family systems since they consist of only
one digester. However, slurry management (digester loading, use of effluent etc.) is of
course of much importance. See chapter 6.2.1. for a further discussion on slurry
management of single family systems.
5.2.2 Developing a Communal System
Connecting the slurry flow of digesters in a communal system may simplify the handling
of the slurry as well as minimize the area needed to build the system (only one input and
one output spot). It is therefore of interest to investigate how connecting the slurry flow
of three digesters in series affects their individual performance (PE and gas quality).
Background and Theory
Connecting digesters of the polyethylene tubular type has only (to my knowledge) been
attempted once and is described by Cortsen et al. (1997). The output of a vertical digester
was connected to the input of a horizontal digester and the system was said to function
well.
Methods and Materials
Three digesters (A3a, A3b and A3c) were constructed and connected using PVC piping.
The inlet of each digester was made sure to be higher than the outlet and a small “tilting”
of the digesters was incorporated in order to make the slurry flow easier. See Figure 5.2
for an overview of the systems design. The middle digester (digester A3b) was constructed
out of cement (to try a new design at the same time) and the other two digesters were of
the standard polyethylene tubular model.
Figure 5.2: Systems design of three connected digester - A3a, A3b and A3c. A3b is constructed out of
cement.
55
Each digester had its own gas holder, safety valve and pressure valve set up so individual
production rates could be calculated for the digesters. The gas quality (methane content)
was also recorded in order to see the differences between the digesters (since the slurry
was of different “age” in the three digesters). The LR was calculated so that the total RT
would be 30 days (and the results could be compared to the standard stand alone digester
(A2) that also had an RT of 30 days). Water displacement was used to measure biogas
production and a hydrometer was used to determine the TS-content of the dung. CO2
absorption in lye was used to analyze methane content of the biogas (see section 4.2.1,
4.2.3 and 4.2.4 for specifics).
Results and Analysis
Unfortunately the slurry flow through the digesters was inhibited quite quickly, and after
17 days (out of 30) we had to stop filling the system. Both digester A3a and A3b were
completely full with dung and a hardened layer of scum seemed to have formed in both
these digesters. Digester A3c was however not very full and almost no slurry was coming
out of its output. The small diameter of the connecting pipes is one contributing factor to
the limited flow. It may be a good idea to also increase the incline/decline of each digester
to make it easier for the slurry to flow. The PE for each digester for the 17 first days is
shown in Figure 5.3 together with an average PE for all three digesters and the PE for the
standard single digester during the same time period.
Figure 5.3: Process Efficiency of the three connected digesters A3a, A3b and A3c as compared to the
standard digester A2. As can be seen, the average of the three connected digesters is significantly lower than
for the standard digester during most of the experimental period.
As can be seen, there is a very large difference between the production rate of the middle
digester (digester A3b, in cement) and the other two digesters in the connected system.
The cement digester had a smaller total volume than the two polyethylene digesters (66.9
56
l compared to 70.7 l) which makes this difference even more significant. A major reason
might be the collection of a lot of the slurry in digester A3b when the slurry is at the top
of its production. An apparent obstruction between digester A3b and A3c may have
contributed to this collection further. The average PE/digester is lower than the standard
and seems to have stabilized around a value of 70-80 l/kg TS (compared to 124.7 l/kg TS
for the standard single digester A2).
When connecting digesters and decreasing the RT in each digester (10 days instead of 30
days) it can be of interest to look beyond the quantity of gas produced and take a look at
the quality. A comparison of the methane content of the biogas from the three connected
digesters, the standard biogas digester and values from literature is summarized in Table
5.2.
Reference/Digester Average CH4 content [%]
Standard Single digester (A2) 66.9
Digester A3a 71.8
Digester A3b (cement) 66.7
Digester A3c 68.1
Örtenblad (2000), Thy (2003) 55-75
Kossman & Pönitz (1999b) 65
United Nations (1984) 50-60
Table 5.2: Methane content of connected digesters (A3a, A3b and A3c) as compared to a single standard
digester (A2) and values from literature.
The methane content values obtained in the experiments do not vary much between the
different digesters and systems. The slightly higher methane content of digester A3a in
the connected system stands out, but we must also remember that the performance of this
digester was not good otherwise (the PE of this digester was very low and the digester was
overfull after only a few weeks). The values in our experiment are within, but on the
higher side, of the intervals for methane content of cow dung found in the literature.
The flow of slurry between the digesters and avoidance of clogging needs to be ensured
for this design to be applicable. The respective RT in each digester must also be long
enough for biogas to be produced, but not too long (so that e.g. the last digester does not
produce any biogas).
Sources of Errors
The small scale of the experiment may have contributed to the difficulties of the slurry to
flow between the digesters. If the same design was tried on full scale a steady flow may be
easier to obtain. However, one must still consider the fact that as the slurry travels from
the first to the last digester, it becomes older and hence gives different production rates in
the different digesters. If each family is only using biogas from one digester, it is important
to make sure that all digesters produce a sufficient amount of biogas. The size of the
digesters could be designed with this in mind. However, the design must really be tried by
conducting an experiment on a larger scale, where gas production rates from each digester
57
are monitored, to determine if it even can be functional. A longer RT may be useful in
order to increase the PE (of course not too much so that the SE becomes too small).
Conclusion
Connecting the slurry flow between digesters may be a good way to improve the
appropriateness of a communal system, if implemented correctly. Further experiments on
a larger scale must be undertaken to find appropriate values on design parameters such as
the size and length of the connecting pipes and the incline of the digesters.
5.3 Regulation of Gas Flow
If the distribution of gas flow, in a biogas system, is unsatisfactory, it can be regulated in a
number of ways. The section will provide data for the discussion (in section 6.3) on the
key technical and operational issue: Gas flow management. Key findings and suggestions
from this section are also summarized and synthesized in Chapter 7.
5.3.1 Improved Single-Family Systems
The distribution of gas in single-family systems is not an issue since all gas goes directly
from the digester to one gas holder before it is used for cooking with the biogas stove. In
terms of gas flow management however, there are implications for all types of biogas
systems. These can be read about in about in Chapter 6.3.1.
5.3.2 Developing a Communal System
The regulation of gas flow is of central importance to the development of a communal
system. All families connected to a communal system must be able to expect a fair and
controllable distribution of gas. The challenge lies in finding an accurate but simple way
of regulating the gas flow. Two potentially suitable solutions for regulation were therefore
tried and evaluated (see sections 5.3.2.1 and 5.3.2.2 as well as Figure 5.4). The magnitude
of the pressure drop in gas pipes was also investigated, since this will have implications for
the regulation of gas flow (see section 5.3.2.3).
58
Figure 5.4: Pressure valves and manual valves - two potentially suitable solutions for regulation of gas flow.
5.3.2.1 Regulation Using Pressure Valves
Background and Theory
Pressure valves are already an integral part of the single-family biogas systems developed
in Cicalung. By including a pressure valve on every gas pipe leading to a household in a
communal system, the gas flow should be able to be regulated by adjusting the water
column height in the valves. The appropriate water column height in each valve will
depend on the respective pressure (or gas flow) in the pipe at the point of entry into to the
valve. See section 5.3.2.3 below for a further investigation into the effect of pressure drop
in pipes and the implications for gas flow distribution. The sensitivity of gas distribution
to changes in the pressure valves‟ water column needed to be investigated in order to
determine if it is a good and sensible way to regulate.
Methods and Materials
A prototype for a communal system (digester B) was constructed that was a down-scaled
version of the system that was installed in the village of Pasir Angling a few weeks earlier.
Two gas holders were connected to the digester by flexible gas pipes and pressure valves
on each branch (see Figure 5.5). A mm-scale was included on each straw in the pressure
valves in order to be able to adjust the water column with high precision. The length from
the digester to both pressure valves was the same. For further details on the construction
and operation of digester B, see section 4.1.2.
59
Figure 5.5: Overview of the communal biogas system prototype.
Once the digester had reached a sufficient daily production (five days after inoculation),
the experiment started. The water column in each pressure valve was first set equal to
each other and the amount of biogas in each gas holder measured after 24 hours. The
experiment was then repeated, decreasing one of the water columns by 1 mm every time,
and noting the corresponding changes in gas distribution.
Results and Analysis
The distribution of gas as a function of the difference between water column heights in
the pressure valves, can be seen in Figure 5.6. As can be seen the distribution when the
water columns are set to be equal (0 mm difference) is fairly equal. However, as soon as
the difference is 1 mm or more, the difference in distribution is big enough to create
troubles for implementation on communal systems.
60
Figure 5.6: The sensitivity of the distribution of gas flow, to changes in the water column heights of the
pressure valves, is too high for the purpose of regulation.
The distribution‟s high sensitivity to changes in the pressure valve‟s water column height
suggests that using pressure valves to regulate the gas flow is not a good solution. A 2 or 3
mm difference mustn‟t make too big of a difference in the distribution of gas if the
pressure valves are to be used to regulate the gas flows. It is too difficult for people to
manage such a sensitive regulatory mechanism. See section 6.3.2 for a further discussion
on the issues of gas flow management in communal biogas systems.
Sources of Errors
The prototype differed from the real system in Pasir Angling in several important ways.
The gas flow was significantly lower, the diameter and material of the gas pipe different
and the length between the digester and gas holders was much shorter. See section 5.3.2.3
for a further discussion on the relation between gas flow, pipe diameter and length, and
pressure drop. The pressure valves were also constructed differently (e.g. the diameter of
the straw was significantly smaller) which may have an effect on the sensitivity of gas
distribution to changes in the water column.
Conclusion
Regulating gas flow with pressure valves does not seem like an appropriate solution. The
sensitivity of the distribution of gas flow to changes in the water column height in the
pressure valves is too large.
61
5.3.2.2 Regulation Using Manual Valves
Background and Theory
Another option for regulating the gas flow is to use manual valves (see Figure 5.4).
Regulation can either be done by manually closing and opening the valves to the different
digesters, at appropriate times, or by adjusting the size of the openings on the manual
valves until a wanted distribution is reached. The experiment which follows, investigates
the distribution of flow as a function of the ratio between the “openness” of two manual
valves.
Methods and Materials
The prototype (digester B) used in the previous experiment was modified by adding a
manual valve to each of the gas pipes leading to the gas holders. The manual valve leading
to one of the gas holders was then closed slightly until the opening in the valve was
approximately 75 % of the other manual valve. The amount of biogaes in each gas holder
was then measured after 24 hours and the experiment repeated, this time with 50 %
“openness” followed by 25 % and finally 12.5 %.
Results and Analysis
As can be seen in Figure 5.7, the sensitivity of the gas distribution to changes in the
“openness” ratio of the valves is much smaller than with the pressure valves. Fortunately
the sensitivity is still large enough, and sufficiently linear, for it to be useful for regulation
purposes.
Figure 5.7: The response of the distribution of gas flow to changes in the ratio of the “openness” of the
manual valves, is sufficient for the purpose of regulation.
62
The fact that it is possible to regulate the gas flow, using manual valves set to different
degrees of “openness”, means that the valves do not necessarily need to be opened and
closed manually every time the flow needs to be directed. By trying different ratios
between the “openness” of the manual valves in a communal system, a satisfactory
distribution of gas flow should be possible to reach. The ratio chosen should depend on
the relation between the gas pressures at the manual valves. The gas pressure difference is
in turn dependent on the difference in length that the gas has travelled from the digester
to the manual valves (see section 5.3.2.3 below for more specifics).
Sources of Errors
The sources of errors of the results, mainly arising due to the differences of the prototype
and the real system in Pasir Angling, are similar to the ones mentioned in the experiment
with pressure valves (section 5.3.2.1). The results should be verified by implantation on a
real system.
Conclusion
Using manual valves set to certain degree of “openness”, gas flow in a communal system
can be regulated to an acceptable degree of accuracy.
5.3.2.3 Pressure Drop in Gas Pipes
Because of pressure drop in gas pipes due to friction, and since a communal system will
exist of gas pipes of different length (to the different households), the pressure at the
respective pressure valves will differ. The question to be answered is how large this
pressure difference will be, and if it will affect how the gas should be regulated.
Background and Theory
The pressure drop in a gas pipe due to friction depends on a number of parameters
including gas flow, pipe diameter, pipe length and pipe material. In theory, pressure drop
in a pipe is given by (Sasse, 1988):
∆p = (Q2* s*L)/(c2*d5) [Eq. 5.1]
Where Q is gas flow in m3/h, s the density of gas relative to air, L the length of the pipe, c
a friction constant of the pipe‟s material and d is the diameter of the pipe.
This leads to the following theoretical values of the expected pressure drop in the gas pipe
of digester B and PA1 (the communal system in Pasir Angling), which can be seen in
Table 5.3.
63
PA1
Digester B (Prototype)
Q, Gas flow [m3/h] 0.075 0.0125
c, friction constant 2.8 2.8
s [density of gas relative to air] 0.94 0.94
L, pipe length [m] 20 10.4
D, pipe diameter [cm] 1.252 0.7
∆P (pressure Drop) [cm WC] 0.0106 0.00028
Table 5.3: Theoretical values for the pressure drop in the Pasir Angling system and the prototype (digester
B). The friction constant (c) of both system‟s pipes is assumed to be 2,8, which is the value mentioned in
literature for smooth plastic pipes (Sasse, 1988). The pipe length for digester B is the difference between the
two pipes in the first experiment explained below (see methods and materials).
A pressure drop in the magnitude of 10-4 cm (prototype) or 10-2 (PA1) should not be large
enough to affect the distribution of gas flow between two gas holders. Even if it did, we
have no way of regulating down to an accuracy of 0.1 mm.
Methods and Materials
The theoretical results have been tested by designing and conducting an experiment on
digester B. The length of the gas pipe leading to one of the gas holders was kept constant
at 2.10 m, while the length of the gas pipe leading to the other gas holder, was varied (6, 4,
2 times longer and finally of equal length). The distribution of gas flow as a function of
difference in pipe length between the two gas holders was then determined.
Results and Analysis
The experiments produced some surprising and interesting results. As can be seen in
Figure 5.8, the distribution of the gas flow between the two gas holders is very large
except when the relation between the gas pipe lengths is 1:1.
64
Figure 5.8: The distribution of gas flow is very sensitive to differences in the lengths of the pipes leading to
the two digesters. Be aware that the result for the 2:1 ratio are unreliable and not valid due to mistakes in
the measurements.
The pressure drop in the pipes seems to be much larger than expected. Alternatively, the
pressure valves are very sensitive to differences in pressure. This second hypothesis could
be partly true but is not able to completely explain the large difference in distribution (see
section 5.3.2.1, especially Figure 5.6). The result for the 2:1 pipe length experiment was
unfortunately not recorded correctly and is hence not valid.
Sources of Errors
The longer of the two gas pipes, in the experiments above, was by necessity not as straight
as the shorter one. Since bends increase friction in pipes (Sasse, 1988) this could be a
factor contributing to exaggerate the difference in the results. Another factor affecting the
results was that, compared to real systems (such as PA1), the diameter of the gas pipes in
digester B, was relatively small in relation to the gas flow. This could lead to a larger
pressure drop, per unit length of gas pipe, and hence results that are not applicable to full-
scale systems. The material of the gas pipes, connected to digester B, is also different than
in the real systems. It is difficult to say which of the materials has a larger friction
constant and hence leads to a larger pressure drop. However, the uncertainty of the results
is definitely increased by this fact, and the usefulness decreased. When it comes to the
theoretical calculations, the unknown friction constant is a source of uncertainty. Most
likely, the friction constant is slightly higher than the value used, and the calculated
pressure drop therefore a bit underestimated (see Equation 5.1 and Table 5.3)
Conclusion
Theory and Experiments do not seem to match. With the low flow rates and large pipe
diameters of the systems, theory predicts a very small pressure drop per meter.
65
Experiments however indicate that the pressure drop per meter is much larger. The
results may also indicate that the sensitivity of the pressure valves to differences in
pressure may be very large. However, this cannot completely explain the phenomena, as
the experiment on using pressure valves to regulate (section 5.3.2.1), indicates. A
distribution experiment should be done on a full-scale system in use (or at least on a
system that has gas flows, gas pipe material, gas pipe diameters and gas pipe lengths that
are closer to a full-scale system in use) to determine if the pressure drop per meter, really
is as large as it seems from the results of the experiment.
5.4 Technically Feasible Biogas Production
The technically feasible biogas production from a system under certain conditions is
investigated in this section, along with a discussion and experiment on how this could be
improved further. This section provides data, and contributes to the discussion (in section
6.4) on the key technical and operational issue: Balancing biogas production and cooking
demand. Key findings and suggestions from this section are also summarized and
synthesized in Chapter 7.
5.4.1 Improved Single-Family Systems
5.4.1.1 Technically Feasible Biogas Production
The technically feasible amount of biogas that can be produced per day, from a full-scale
digester, is one of the most important pieces of data needed to be able to appropriately size
a biogas system. The amount of biogas that 1 kg of dung (and the dung from one cow) can
produce is also investigated in order to determine the potential for biogas production that
a certain number of cows and dung has.
Background and Theory
Even though a large number of studies have been performed to determine BPR from
polyethylene biogas systems operating on cow dung (See e.g. Thy et al., 2005; Thu Hang,
2003) the results vary significantly and are highly contextual. Factors such as process
temperature, RT and agitation of the substrate have a direct impact on production, which
in turn are decided by such factors as the insulation used, time of year, LR, digester size
and digester design. Still, a general description of the production rates dependency on RT
and process temperature has been attempted in literature (Sasse, 1988; Werner et al.,
1989) and is used in the results and discussion section below to compare the experiment‟s
results with theory. In terms of the amount of biogas produced from 1 kg of dung and
from one cow this will also depend on the TS-content of the dung and how much dung
one cow produces per day.
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Methods and Materials
The gas production from digester C was measured two times daily using water
displacement technique. See section 4.1.3 for more specifics on the digester and section
4.2.1 for measurement equipment (WD unit C). The digester was loaded every morning
for 40 days with a fixed amount of slurry (i.e. the LR was constant). Measurements
commenced after 30 days of loading, and were recorded for a period of 10 days.
Results and Analysis
The average daily production of biogas was 1789 l which, given a LR of 2.59 kg
TS/m3/day, results in a PE of 136.8 l/kg TS. A comparison with theory (Sasse, 1988;
Werner et al., 1989) and earlier studies on gas production from cow dung (Thu Hang,
2003) can be seen in Table 5.4.
Digester C Thu Hang (2003) Sasse (1988)
Werner et al. (1989)
Type of digester polyethylene polyethylene All All
RT [days] 31.6 20 30 30
LR [kg DM/m3/day] 2.59 4
TS [%] 16.34 15.3 16 16
Process temperature [degrees C] 21.1 – 21.9 26.5 – 34.5 22 22
Average PE [l/kg TS] 136.8 55 – 91.2 106.25 121
Average SE [% of digester] 35.7 16.7 – 27.8
Table 5.4: Summary of results from measurements on digester C and values obtained from literature. Note
that the process temperature and the TS-content for digester C are averages based on recorded values
throughout the experimental period on another experimental set-up, digesters A1-A6.
As can be seen in Table 5.4, earlier studies with polyethylene digesters with cow dung
(Thu Hang, 2003) indicate significantly lower BPR (both PE and SE) than in the current
experiment. That the RT in that study is only 20 days contributes to a lower value while
the higher process temperature should increase the BPR. The values from Sasse (1988) and
Werner et al. (1989) were extracted from graphs showing the relationship between biogas
production from cow dung, RT and substrate temperature. The graphs were based on
averages from a large amount of studies. What can be noted is that the BPR from the
current experiment is significantly higher than those found in the literature.
In order to further analyse the results, a closer look at the extremes was taken. A high case
and low case for the current experiment was calculated by using the lowest and highest
measured TS-content (10 % and 23.6 % respectively). The high and low cases of the PE in
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the literature were calculated using the maximum and minimum gas yield from cow dung
(Werner et al., 1989) at the same RT and process temperature found in the experiment. In
terms of the SE, the highest and lowest measured values for daily gas production on
digester C were used, and in the literature taken from Thu Hang (2003). A summary can
be found in Table 5.5.
Source
PE [l/kg TS]
SE [% of digester liquid volume]
Average Experiment 136.8 35.4 Average Literature (Werner et al., 1989) 121 High case Experiment 223.6 38.4 High case Literature (Werner et al., 1989; Thu Hang, 2003) 170.6 55
Low case Experiment 94.7 32.3 Low case Literature (Werner et al., 1989; Thu Hang, 2003) 73.1 16.7
Table 5.5: Average, low and high case of BPR for digester C in the current experiment and values found in
literature.
As can be seen in Table 5.5, the current experiment exceeds the literature in both the high
and low cases in terms of the PE. In terms of the SE, the high case in the literature exceeds
the current experiment significantly. This can partly be attributed to the short RT (20
days) of the experiment in Thu Hang (2003), but possibly also to the fact that the specific
digester dimension showing this high SE in Thu Hang (2003) (in this case a length-
diameter ratio of 5:0.65 m), may be more optimum than the dimension of digester C
(length-diameter ratio of 10:0.95 m)
In terms of how much biogas can be produced from 1 cow we questioned the cow farmer
providing the dung to our digester, Mr. Akang, how many kg of dung one cow produced
in a day. He gave us an average of 20 kg per day. With a daily production of 1789 l and a
loading rate of 80 kg of fresh dung, this results in a production rate of 1789/4 = 447.25 l
biogas /cow/day.
The amount of biogas that can be produced from a 10 m long and 0.95 m wide tubular
polyethylene digester that is filled with 160 kg slurry every morning (RT of 30 days) is
1789 l per day when the average day air temperature is around 22°C. A cow producing 20
kg of dung per day hence supplies a system with 1789/4 = 447.25 l biogas per day (if the
water:dung ratio is 1:1). With an average TS-content of 16.34 % this leads to an average
PE of 136.8 l/kg TS.
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5.4.1.2 Ways to Improve Biogas Production
Even though the above results, in terms of production rate, are high compared to values
obtained in literature, there is still reason to look for ways to further increase the
efficiency of the biogas system.
Background and Theory
As was seen in section 3.2.2, there are a number of factors contributing to biogas
production. A number of these are difficult to affect with the limited resources available
in Lembang and the simple nature of the technology. There are however a number of
simple ways to increase the efficiency. Increasing the process temperature and
temperature stability (e.g. between night and day), by insulating the digester, is a simple
way to increase both PE and SE.
Methods and Materials
The effect of insulation on biogas production was studied using an experimental set up
with three equally dimensioned digesters (Digesters A1, A2 and A4). One digester (A2)
was covered only with the black plastic film used in agriculture, known locally as “Mulsa”.
A second one (A1) was buried in the ground and a third one (A4) was covered with rice
husks.
Results and Analysis
Average daily production rates from the three digesters during the experimental period
are summarized in Table 5.6. The digester which was covered with Rice Husks (A4) has a
somewhat higher production rate than the other two digesters, around 10 % higher.
BPR A1 (covered with soil) A2 (uncovered) A4 (covered with
Rice Husks)
PE [l/kg TS] 124 124.7 136.8
SE [% of liquid volume]
33.8 33.9 37.2
Table 5.6: Average PE and SE of three differently insulated digesters.
The time series underlying the calculated averages in Table 5.6, are presented in Figure
5.9. As can be seen, digester A4 shows a higher PE during more or less the whole
experimental period, except at a few points. The two low points on the yellow curve are
due to measurement errors. Note that these are 24 hour averages and do not take
day/night variations into account.
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Figure 5.9: The daily average process efficiency of digesters with different insulation.
As for Day/Night variations in BPR, a closer look was taken at the three digesters average
night and day BPR. It was only at the end of the experimental period that measurements
were taken both morning and evening. The analysis of these variations was therefore only
based on these later measurements, which explains the higher average production rates in
Table 5.7 (compared to Table 5.6).
Digester A1
(covered with Ground)
Digester A2 (Uncovered
Digester)
Digester A4 (covered with
rice Husks)
Day Average BPR [l/h] 0.9325 0.9992 1.0925
Evening Average BPR [l/h] 0.9274 0.872 1.047
Day Average PE [l/kg TS] 147.31 157.84 172.58
Evening Average PE [l/kg TS] 146.49 137.75 165.39
Difference (Day-Night) [l/kg TS] +0.81 +20.09 +7.19
Table 5.7: Differences in day/night performance of digesters with different insulation.
As expected, the largest variation can be seen for the uncovered digester (20.09 l/kg TS
higher during day). Sunlight and the black “Mulsa” plastic increase the process
temperature in the uncovered digester during the days, whereas the temperature drops
considerably during the night. The digester covered with ground has a very stable
production rate although it is considerably lower than the slightly more varied production
rate of the digester covered with rice husks.
Conclusion
Rice husks seem to be a very good (and cheap) way to increase the BPR. In this
experiment the BPR of the digester covered with rice husks was around 10 % higher than
for the uncovered and ground covered digesters. In reality the increase might be higher
since two of the production rate measurements for the digester covered with rice husks
70
were incorrect (too low). Covering the digester with ground decreases the variability in
the production rate but does not increase the BPR compared to leaving the digester
uncovered (i.e. with black mulsa only). Using only mulsa to insulate the digester is a good
choice when rice husks are not available or when there is much sunlight (increasing the
temperature of the mulsa covered digester during day time considerably). However one
must watch out so that the variability in the substrate temperature is not too large. As was
noted in section 3.2.2.1 , temperature change exceeding a degree C in a 1 hour period, can
inhibit a mesophilic process. However, no measurements in this experiment indicated
such a radical temperature change.
5.4.2 Developing a Communal System
5.4.2.1 Technically Feasible Biogas Production
Considering that a communal system can be comprised of a number of digesters of various
sizes, it is of specific interest to see how applicable the BPR, determined in 5.4.1.1, is to
digesters of different sizes.
Methods and Materials
Digester A2, Digester B and Digester C were used to compare the BPR of digesters with
different sizes. Relevant specifics of the digesters and experiments are included in Table
5.8 below.
Results and Analysis
Table 5.8 summarizes the results of the comparison between digesters of different size.
The TS-content of the substrate slurry is assumed to be the same for all three digesters and
equal to the average measured value (16.34 %).
Digester name A2 B C
Dimension: length; diameter [m] 1.00; 0.30 3.50; 0.637 10.0;0.955
Total Volume [l] 70.7 962.8 7161.9
Liquid volume [% of total volume] 78.9 86.4 70.55
RT [days] 30 30 31.58
LR [kg TS/m3/day] 2.72 2.72 2.587
Stabilisation period [days] 20 5 30
Measurement period [days] 30 5 10
Average PE [l /kg TS] 124.65 108.73 136.8
Maximum PE [l/kg TS] 176.69 123.43 148.45
Average SE [% of liquid volume] 33.75 29.48 35.4
Table 5.8: Relevant specifics of the digesters and experiments and the average BPR (PE and SE) of the three
different digesters.
As can be seen Digester C has both a PE and SE indicating that it might be slightly more
efficient to build larger digesters than smaller ones. However before we draw this
conclusion, let us have a look at the potential sources of errors in the comparison.
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Source of Errors
Unfortunately, the timing and length of the measurements on the three digesters were not
the same. However, the air temperature and weather patterns were more or less the same
during all experiments. A small source of error lies in the slightly smaller LR in digester C
which could mean that the PE is slightly exaggerated and the SE is slightly
underestimated in the comparison with the other digesters. A larger source of error of the
comparison may lie in the difference in the stabilisation period. It may take a number of
weeks after installation before maximum production is reached even though the digester
is inoculated with slurry from another digester. The short stabilisation period of digester B
is most likely the main reason the production rate is so much lower than the other two
digesters. The fairly similar results of the smallest and largest digester in the experiment is
enough to suggest that the BPR does not vary much with the size of the digester if the LR
(and hence RT) is kept constant. The fact that the maximum PE of the smallest digester is
the highest, and significantly higher than the average PE, may be a consequence of the
higher variability of results of small scale experiments.
Conclusion
The BPR determined for Digester C is applicable to digesters of different sizes and hence
applicable to designing communal systems with digesters of varying size. However, the
dimension and shape of a digester may still have an influence on the production rate of
biogas (as was seen in section 5.1).
5.4.2.2 Ways to Improve Biogas Production
The same improvements in the production rate by using rice husks can be assumed to
work on communal systems and increase the BPR with a similar amount (around 10 %).
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6. Installation, Operation and Maintenance: In the Eyes of The User
Despite the good impact of the technology, there were many questions from the users concerning digester feeding, appropriate maintenance and incorporation in farming systems. Future research should be focused on studies under farm conditions. (An, 2002).
This chapter takes a deeper look at the installation, operation and maintenance of both
single-family and communal biogas systems. Each sub-chapter deals with one of the key
operational and technical issues, introduced in section 2.4, and is in turn divided into two
sections: one that deals with single family systems and one that goes into specific
implications for the development of communal systems. The sections on single-family
systems are general, in the sense that they pertain to all biogas systems, also including
communal systems. Observation of - and measurements on - digester C (a full scale
digester) and biogas systems in the villages of Pasir Angling (PA1, PA 2, PA3) and Cireyod
(Ci1, Ci2, Ci3) provided the data and the basis of discussion for this chapter. The
methodological approach used for this chapter was a mixed bag of measurements,
observation of user behaviour and discussion with local technicians, farmers and users.
6.1 Available Space and Alternative Uses of The Land
Before a biogas system is to be installed, the key issue “Available Space and alternative
uses of the land” is important to consider. Questions such as the space-, cost- and process
efficiency of different designs, in relation to the size and location of the available spaces as
well as competing uses of the land, are expanded upon and discussed in this section. In
regards to the development of a communal biogas system, the issues of land ownership,
contribution to the preparatory work of installing a system, and the difference in space-
and cost efficiency, are also touched upon. Key findings and suggestions from this section
are also summarized and synthesized in Chapter 7.
6.1.1 Improved Single-Family Systems
The available space and the alternative uses of this land is something that should be taken
into consideration when a biogas system is to be installed. Other uses for the land include
pens for cows, goats, chickens and other animals, agriculture, dumpsite for dung and
septic tanks. In the Lembang area, especially in the slightly more urban villages, available
land is scarce and hence valuable. Since an unused space is not always available, the value
of the current use of the land must be weighed against having a biogas system (see Figure
6.1). E.g. in one case of installing a biogas system in the village of Cireyod, a septic tank
was discovered as the hole for the digester was being dug, and the hole (and biogas
system) had to be made smaller than planned.
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Figure 6.1: Many competing uses of the land exist. Future sites for two biogas systems in Cireyod.
In the light of this, it makes sense to look at the amount of biogas that is produced from
digesters of different dimensions in relation to the amount of space they require. Hence,
the concept of “space efficiency” is introduced:
Space efficiency = Daily average biogas production / area required by digester [l /m2/day]
For digesters A2, A5 and A6 used for the experiment in section 5.1, the space efficiency is
(Daily average biogas production taken from a detailed experimental result table – not
included in this paper. Area required by digester, taken from Table 4.1 in section 4.1.1):
Digester A2 (standard long horizontal): 18.94 / (1*0.3) = 63.1 l/m2/day
Digester A5 (short horizontal): 20.57/ (0.59*0.42) = 20.57/ 0.2478 = 83.0 l/m2/day
Digester A6 (vertical cylinder): 21.82 / (pi*0.212) = 21.82 / 0.138474 = 157.6 l/m2/day
As can be seen, the space efficiency of the vertical digester (A6) is significantly higher
than the other two. This should be taken into consideration when determining which
type of digester to install.
Another important consideration is of course the cost of the digesters. Three digesters
(PA1, PA2 and PA3), corresponding to the three different shapes that we just calculated
the space efficiency for, were installed in Pasir Angling in February of 2009. The total cost
of all materials (including digesters, gas holder, gas pipes, stove etc.) for the three digesters
were:
PA1 (Long horizontal; 7m*1.2m): Rp. 1,273,000 = 127.3 USD
PA3 (Short horizontal; 3m*1.5m): Rp. 865,000 = 86.5 USD
PA2 (Vertical cylinder; 2.2m*1.7m): Rp. 914,500 = 91.5 USD
The systems were designed to provide biogas to a different amount of people. Therefore it
is of interest to see the per person cost of the digesters:
PA1 (Long horizontal): Rp. 1,273,000 / 7 = Rp. 181,857 = 18.2 USD
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PA2 (Short horizontal): Rp. 865,000 / 4 = Rp. 216,210 = 21.6 USD
PA3 (Vertical cylinder): Rp. 914,500 / 4 = Rp. 228,625 = 22.9 USD
To ensure the functionality of the short horizontal and the vertical cylinder digester,
stirrers were constructed and installed. This added another Rp. 84,000 and Rp. 157,500 to
these digester‟s costs, respectively.
The labour and time for constructing and installing the digesters has not been included in
the above costs. Usually a biogas system can be constructed and installed in one day (if the
hole has been dug and the starter slurry has been prepared in advance). However, just the
installation of the short horizontal and the vertical cylinder biogas systems in Pasir
Angling, took three days. Heavy rain, the inclusion of stirrers in the design and the fact
that this was the first time digesters of these dimensions and shapes had been constructed,
complicated the installation process.
A few weeks after the installation, the vertical cylinder digester (PA2) was producing
biogas over our expectations. The methane content was also very high (82 %). The short
horizontal digester (PA3) however, experienced some issues and was not producing so
well a few weeks after installation (see slurry flow management, section 6.3 for further
discussion). Both of these digesters would experience serious problems in the months to
come. See section 8.2.1 for a more detailed discussion.
It should also be noted, that although a biogas system is built and installed, many of the
old uses of the land will persist. Chickens, cats and people will continue to use the space
and there is a large risk that the digester is punctured if it is not protected in some way.
Insulating the digester with either rice husks or soil is a good way to protect the digester.
However, there should be some sort of further protection, such as a bamboo mesh, so that
animals do not dig down too deep and damage the digester or people do not accidently
step on it. Covering the digester with soil is especially deceptive in this regard. Care
should also be taken when covering the digester with soil so that the pressure on the
digester does not become too large. If the digester is not insulated and covered with a
bamboo mesh, a thicker mat or old fertilizer bags can be used to protect it. Figure 6.2
shows some ways of protecting the digester from damage.
75
Figure 6.2: Protecting the digester from damage. From left to right: Using bamboo mesh, using thick mats
and damage caused to an unprotected digester by the foot of a person.
For further discussion on fixing leaks and breaks in the digester and other parts of the
system, see section 6.2.
6.1.2 Developing a Communal System
When looking for a space to install a communal biogas system, having found an available
area does not mean that it will be appropriate. Ownership of the land can complicate
things. In the village of Cireyod, a piece of available land was identified that would have
been suitable for a communal system with up to three large digesters. However, the
owner of the land did not want to give up more of this space than was needed to build a
system that would supply biogas to his house and his son‟s house - even thought the space
was not being used for any alternative uses at the moment. The owner of the land did not
own any cows himself and would hence need to rely on dung from a nearby cow pen. The
owner of the cows lived too far away from the available space to be connected to a
potential communal system. Otherwise a communal solution may have been possible to
negotiate. In semi-urban villages such as Cireyod, communal systems involving only
households with people of the same family, seem to be a more suitable solution. In the
much more rural village of Pasir Angling this does not seem to be as important.
Prior to the installation of a communal system, the question of who does the preparatory
work is of importance. Preferably all future users of the biogas system participate. The
hole for a communal sized digester with the dimensions 7m x 1,2m x 1,2m, takes four to
five days for 1 person to make. If three to four people work on making the hole, they
should not need more than a day.
In general, communal biogas systems will be more efficient in terms of both cost/person
and space than single-family systems (see section 7.3 for calculations and a more detailed
comparison between single-family and communal biogas systems). A communal system
with fewer, but larger digesters will also be more cost and space efficient than a
76
communal system with several, smaller digesters. However, often the size and shape of
the available space will put constraints on the design of the communal system.
6.2 Slurry Management
The key issue of slurry management is mainly connected to the installation and operation
of a biogas system. In this section a closer look is taken at questions such as the location
and ownership of dung, potential problems arising at the installation of a biogas system
and the effect that the frequency of digester loading has on biogas production and other
important process parameters. Specific considerations in terms of the management of
slurry in a communal biogas system, during installation and operation of the biogas
system, are also expanded upon in this chapter. Key findings and suggestions from this
section are also summarized and synthesized in Chapter 7.
6.2.1 Improved Single-Family Systems
6.2.1.1 Location and Ownership of Dung (Installation)
The location of the cow pen, where the dung is fetched, and the ownership of the cows
should be taken into account when installing a biogas system. If the cow pen is not
located close by, a system for transporting the dung must be developed. Using 20 l plastic
buckets and constructing a wheel-barrow to carry them in, has been a proven solution
when the cow pen is located far away from the digester. Obviously, having a cow pen
close by is a great advantage since it will greatly decrease the time needed for loading the
digester. If the future user of the biogas system being installed is not the owner of the
cows supplying the dung, an agreement must be set up. Usually dairy farmers will be
happy to have someone take care of the dung. At the moment most dairy farmers will not
see it as losing a resource and will not charge money for it. However, if biogas becomes
widely spread and successful, the perception of dung may change from being a waste
product to being a resource.
6.2.1.2 Dimension of Digesters, Slurry Flow and Biogas Production (Installation)
At the installation of a biogas system it is usually inoculated with a mixture of effluent
slurry from another digester, fresh dung and water. A rule of thumb is to keep the
water/dung ratio at approximately a value of 1 to achieve a good flow through the
digester. However, when installing digesters of different dimension than the standard long
tubular design, as was done in Pasir Angling, this procedure may need to be modified. The
production rate of the shorter horizontal digester installed in Pasir Angling (PA3) was low
for a long time after the installation. The output smelled bad and was bubbling (still
producing biogas). The slurry was obviously moving to quickly from the input to the
output and the RT was hence shortened. The quickness of the flow may be the result of
the short distance from input to output in this design but it may also indicate that the
initial water/dung ratio was too high (too much water in relation to dung). The output
77
was mostly water for the first few weeks. A potential solution to this problem is to install
a T-pipe at the end of the input pipe so that newly loaded slurry moves to the sides of the
digester instead of directly toward the output pipe. Use of the installed stirrer may help to
homogenise the slurry in the digester. However, care should be taken, so the mixing
doesn‟t move fresh influent too close to the output pipe, and that it leaves the digester
without having produced much biogas.
6.2.1.3 Frequency of Digester Loading (Operation)
The management of slurry is the most time consuming task in the operation of a biogas
system. Handling the influent and effluent slurry for a single-family system, where cow
dung is available fairly close by, will require around 30 minutes per day. This includes
fetching the dung, fetching water and mixing it with the dung, removing undigested
straws and grass from the dung, loading the digester with the influent slurry and
emptying an equivalent amount of effluent slurry. A regular management of the slurry is
required for the proper functioning of a biogas system. However, the required frequency
of the management needs to be investigated in order to see how flexible the functioning of
the biogas system is to user‟s potential infrequent management. Therefore an experiment,
on the effect that changing the loading frequency has on biogas production, was
conducted on the full-scale digester C.
Purpose
To investigate the effect that loading frequency has on the performance of a digester.
Background and Theory
No actual data was found that suggested which type of loading frequency was to be
preferred in a polyethylene plug-flow digester. However, in most literature, a daily
loading is suggested. It should be noted that the amount of influent slurry that was loaded
into the digester was not varied in this experiment - only the frequency of the loading.
Hence the RT was the same for the two experimental runs. Changing the amount of slurry
being loaded would affect the BPR further.
Material and Methods
Digester C was loaded daily for 40 days and measurements were taken for the 10 last days.
Thereafter, the loading frequency was switched to weekly loading and after a period of 50
days, measurements commenced again.
Results and Analysis
The results of the two runs with different loading frequencies can be seen in Figure 6.3
and Figure 6.4.
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Figure 6.3: Daily biogas production from digester C with daily loading of influent slurry.
Figure 6.4: Daily biogas production from digester C with weekly loading of influent slurry. Note the clear
increases in biogas production every 7 days. This corresponds to the filling of the digester.
The average production values from the two runs were 1788.55 l per day (or 136.82 l / kg
TS) for daily loading and 1786.2 l per day (or 136.65 l /kg TS) for weekly loading. Hence,
we see that in terms of quantity of biogas produced there is not a large difference between
the two loading frequencies. It should be noted however that the measurements during
weekly loading were taken two months later, and that the average temperatures are
higher at this time. Hence, the production rate for this type of loading frequency as
compared to daily loading, may be a bit overestimated.
79
Even though the quantity of biogas produced is very similar, the variation of daily biogas
production is significantly different between the two runs. When the digester is loaded on
a daily basis, the production stays relatively even at around 1,700 to 1,800 l per day.
When the digester instead only is loaded weekly, the biogas production just before
loading is down to less than 1,500 l per day and after loading it leaps up to over 2,000 l per
day. A large variation of biogas production can be an issue for the household using the
biogas, if their demand is close to the average biogas production rate, since they then may
experience shortages. See section 6.4 for a more in-depth discussion.
Conclusion
Daily loading of the digester is to be preferred, whenever possible, since it results in a
more stable BPR. Waiting one week between digester loadings results in a high variation
of the BPR.
6.2.2 Developing a Communal System
6.2.2.1 Who Loads? Who Empties? And When? (Operation)
For the management of slurry flow in communal systems, it is of great importance to
clarify who is in charge of loading and emptying the digester, and when they are to do so.
The task can be shared or done by one person who is compensated in some way. In Pasir
Angling, the newly installed communal system (PA1) was loaded by a man in one of the
households. He was the also the one who dug the hole for the digester, prior to the
installation. Complaints of low BPR and shortage of biogas in the gas holders of the
communal system, led to the realization that the suggested LR to reach an RT of 30 days,
was not being followed. The required loading rate would be 256.7 l of influent slurry per
day (See Table 4.2 in section 4.1.2). The actual loading rate was as little as 120 l slurry
every 3 days. This leads to an RT of 192.5 days. This is an RT that will lead to a very low
SE of the digester and biogas shortages in the households. This will create unnecessary
strains on the relationship between the households connected to the biogas system, when
deciding how to distribute the scarce biogas resource.
The low LR was not due to a shortage of dung or water as input. Several reasons for the
unwillingness to change the LR were identified. The person loading the digester was
afraid that the pressure of the digester would become too high if they increased the LR.
This is understandable, since the pressure does increase while the digester is being loaded.
However, the pressure in the digester is quickly stabilized to the pressure (in cm WC) that
is set on the pressure valves, as the biogas flows through the pressure valves and into the
gas holders. Another reason was the fact that it would be much more time consuming to
switch to the suggested LR. The person loading the digester had limited amount of time
and did not want to spend more time than necessary on operating the biogas system.
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The fact that the low and infrequent loading of the digester was the main cause of the low
production rate was communicated a number of times to the users. They did however not
change the LR to the suggested rate. After about a month they had increased the LR to
240 l of slurry every 3 days, leading to an RT of 96.25 days. This will definitely increase
the BPR and lead to a better SE. However, it will still not be making full use of the biogas
systems potential.
An underlying reason of the unwillingness to change the LR, may also be the lack of
understanding of the complex dynamics of the biogas production process. This is quite
clear from a statement from one of the users of the communal biogas system in Pasir
Angling:
“When we need more biogas, we load more dung into the digester”
This statement disregards the sensitivity (e.g. due to scum formation) of the process and
the delays inherent to the process of biogas production. Finding simple ways of raising an
understanding of the biogas production process and communicating the need for
continuous and stable loading should be developed.
6.2.2.2 Location and Ownership of Dung (Installation and Operation)
The cow pen providing the dung for the communal system in Pasir Angling (PA1) was not
located far away from the digester. The low loading rate discussed above, was not due to
the distance of transporting the slurry. Nevertheless, the location of the cow pen in
relation to a communal biogas system does of course matter, since the workload of the
person or persons in charge of loading the digester will increase with increased distance.
This said, if there is a large demand for a biogas system in a household, but no cow pen
close by, the high labour requirements may still be outweighed by the benefits of having
biogas. In Cireyod for example, one of the dairy farmers involved in installing a
communal biogas system, owned cows in a cow pen several hundred meters away. The
dung was to be transported from the cow pen to the digester using a wheel-barrow.
The ownership of dung may become an issue in a communal biogas system since the
contributions and benefits become clearer than in single-family systems (where a dairy
farmer may be happy to give away dung to the owner of a biogas system just to be rid of
it).
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6.3 Gas Flow Management
The key issue of gas flow management is mainly connected to the operation and
maintenance of a biogas system. In this section a closer look is taken at the issues of users
adjusting the pressure valve and the process of checking and fixing leaks. In terms of the
development of a communal system, the regulation of gas flow (using both manual valves
and pressure valves) and the effects that water and leaks in the pipes can have on gas flow
distribution. Key findings and suggestions from this section are also summarized and
synthesized in Chapter 7.
6.3.1 Improved Single-Family Systems
6.3.1.1 Adjusting the Pressure Valve (Operation)
The pressure in the biogas system is regulated by changing the height of the water column
(WC) in the pressure valve. The recommended height is 3 cm in order to maintain a
sufficient pressure in the digester and a flow of biogas to the gas holder. A common
finding in the villages, where biogas systems had been installed, was that the users
adjusted the height of the WC quite frequently. The tendency was to decrease the height
of the WC to only a few millimetres height (even after resetting the height to 3 cm they
would change it back). When asked the reason for doing so, it turned out to be that they
were afraid that the pressure in the digester was too high and that it may explode. It did
not help much to say that the digester should hold up to at least a pressure of 15 cm WC
(which we had investigated through experiments). They also believed that the gas flow
would increase by decreasing the height of the water column (which is understandable
since it actually will increase during a short period of time just as the change is made).
6.3.1.2 Leaks and Checking for Leaks (Maintenance)
If the WC is set to 3 cm height and the pressure in the digester is visibly low, there is a
leak somewhere in the system. To check if there is a leak in the digester, the gas pipe
leading to the pressure valve and gas holder should be closed off and the digester
observed. If the pressure does not increase visibly within an hour or so there is either a
leak in the digester or in the connection between the gas pipe and the digester. If
however, the pressure in the digester increases when it has been closed off from the rest
of the system, the leak may be located somewhere in the gas pipe or in the pressure valve
itself.
Finding a leak can be quite difficult. If a leak in the digester is suspected, using water with
a foaming-agent (such as soap) and rubbing it on the digester should help to detect the
leak (look for bubbles). Increasing the pressure in the digester (if possible) also helps since
the leak then will produce more bubbles. Even small holes can lead to significant leaks,
and are the hardest ones to detect. If a leak in a gas pipe is suspected, it should be closed
off from the rest of the biogas system and a manometer used to detect pressure drops in
the gas pipe. A manometer can easily be constructed using a plastic tube, a piece of
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plywood, two rulers, a rubber plug and some copper pipes (See United Nations (1984) for a
design). The manometer we constructed can be seen in Figure 6.5. The manometer should
be inserted into the end of the gas pipe that is closest to the pressure valve. Before it is, the
pressure in the pipe should be increased by introducing more air into it using either lung
power or an air filled plastic bag. The manometer will indicate a certain pressure at the
time of insertion. Try to get at least a pressure of 15 cm WC. If there is a large leak in the
gas pipe, this will be easy to detect by a quickly decreasing WC. If the leak is smaller but
still significant, it will be more difficult, since some leakage is usually difficult to avoid. If
the WC does not decrease in a period of three minutes, or decreases only slightly (no more
than 1 cm) the leak is probably not significant. If the decrease in pressure is greater than
this, soapy water should be put on the gas pipe, joints and fittings to see if a leak can be
detected. Try to maintain a high pressure in the gas pipe while doing this. Figure 6.5
shows the materials needed and process of checking for leaks.
Figure 6.5: Leak detecting set, using soapy water to find leaks in digesters and gas holders, using the
manometer to check for leaks in gas pipes.
6.3.1.3 Fixing Leaks and Holes (Maintenance)
Depending on the size and location of the leak, there are different ways to mend it. A
small leak can be fixed by applying a small amount of sun-activated soft-polyethylene
repair paste, over the leak. If the leak is slightly larger, applying a piece of heavy-duty
tape, before applying the paste, may be a good idea. A large hole, especially when it is in a
filled digester, can be very difficult to fix. Nevertheless, even a hole caused by a person
stepping into the digester, can be fixed. As can be seen in Figure 6.6, a piece of wood is
needed to close the hole. The piece of wood needs to stay inside the digester which may
have slight implications for the BPR and the functioning of the biogas system.
Figure 6.6: Steps in fixing a major hole.
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Checking for, detecting and fixing leaks can be an arduous task once the biogas system is
installed and operating. Therefore it is highly suggested to check for leaks in all parts of
the biogas system during installation.
6.3.2 Developing a Communal System
The issue of gas flow management is of central importance to the development of a
communal biogas system. Each household connected to the system must be able to obtain
a sufficient amount of biogas to fulfil their cooking needs throughout the day.
When installing a communal system, the distance between the digesters and households
need to be taken into account, since this will affect not only the total cost of the system,
but also the way that the gas flow should be managed. In section 5.3.2 we saw that the
pressure drop in gas pipes increases with increasing pipe length and gas flow and decrease
with increasing pipe diameter. The magnitude of this pressure drop and its importance for
gas flow management remains uncertain, since theory and the experiments did not
correspond well. However, if there is a large difference in the length of the gas pipes
leading to the connected households, a difference in the pressure drops (and thus gas flow)
can be expected.
One way to solve the distribution of gas flow would be to install all pressure valves at the
exact same distance from the digester, and make sure the height of all WC are the same.
However, the pressure valves are usually installed next to the gas holders since it is more
practical to have them next to each other. Furthermore, the high sensitivity of gas flow to
changes in the WC height (see experiment in section 5.3.2), makes this solution sub-
optimal.
In section 5.3.2, different ways of regulating the gas flow were investigated. Using
pressure valves proved to be difficult whereas using manual valves seemed to be more
promising. In Pasir Angling, the use of manual valves to regulate was implemented on the
communal biogas system with a large long tubular digester and two connected households
(PA1). They had experienced low gas production and problems with uneven distribution
between the two households for a number of weeks after the system was installed. Manual
valves were then installed on each gas pipe, close to the digester (see Figure 6.7).
The regulation of gas flow was then managed by leaving only one manual valve open at a
time. When the first gas holder had been filled, the corresponding manual valve was
closed and the other one opened. This seems to be working well but requires that
someone remembers to manage this distribution on a daily basis. An alternative to this
would be to leave both manual valves open at the same time, but at an appropriate
“openness” (as was investigated in the experiment in section 5.3.2). If the distribution of
gas flow between the two households appears to be very uneven and not adapted to the
demand of the involved houses, the “openness” of the valves can be adjusted, until an
appropriate distribution is achieved.
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Figure 6.7: One of the two installed manual valves and the pressure valve (installed later) between the
vertical (PA2) and horizontal digester (PA1) of the communal system in Pasir Angling.
When a vertical cylindrical digester (PA2) was installed and connected to the communal
biogas system (PA1) in Pasir Angling, a third way to regulate gas flow was introduced.
Digester PA2 was producing more biogas than was demanded from the household it was
connected to prior to being connected to digester PA1. The two houses connected to PA1
were still experiencing a shortage of biogas. Therefore a pressure valve was installed in the
gas pipe connecting the digesters, which ensured that the excess gas from PA2 would flow
to the other two households (see Figure 6.7). The gas could not flow in the other direction
however. As long as the BPR of PA2 and the demand of the households do not change too
much, this solution should be fine. However, if they do change, it may be necessary to
either switch the direction of the pressure valve or replace it with a manual valve.
Water collecting in the gas pipes can lead to difficulties in gas flow management since
they can hinder the gas flow. It can easily be avoided by making sure there are no points
on the way from the digester to the gas holder where water can collect in the gas pipe.
Leaks in the gas pipes, joints, connections and pressure valves can also complicate the
management of gas flow in a communal system (on how to detect and fix leaks, see section
6.3.1). Users in one of the households connected to the communal system in Pasir Angling
have noticed that an increase in the height of the WC in their pressure valve, leads to
decreased biogas in their gas holder. The major explanation for this decrease is most likely
that the biogas instead is flowing to the other gas holder. However, there may be a
number of other factors also contributing. If leaks exist, more biogas can escape when the
pressure is increased in the system. Dips in production (on both an hourly and daily basis)
and the time it takes to build up pressure in the digester after changing the WC height,
can also result in a perceived lower flow to the gas holder in the short term.
The question of who should manage the regulation of gas flow in a communal system
needs to be addressed from case to case. If only one person is in charge, he or she needs to
be in constant communication with the people in all connected households to see if they
are receiving sufficient amounts of biogas for their cooking needs. Having a group of
people (e.g. one from each household) sharing the responsibility of managing the
regulation may be a good solution. However, if each household is in charge only of their
own gas flow, this may lead to big problems. E.g. if each household keeps lowering the
85
WC of their pressure valve, the pressure in the digester will in the end become too low -
i.e. a race to the bottom. The risk of this outcome is especially high when the total biogas
demand of the households is larger than the current BPR of the digesters (i.e. during
biogas scarcity).
6.4 Balancing Biogas Production and Demand
Balancing biogas production and demand is the ultimate goal of a well-functioning biogas
system (as can be seen in the decision making diagram and conceptual framework in
Figure 2.8 in section 2.4). Achieving this goal is dependent on a number of factors,
including the issues discussed above: gas flow management, slurry flow management, the
shape of the digesters and their location in relation to the households. Furthermore, it is
also dependent on the amount and sizing of the digesters. This is in turn dependant on the
available supply of dung, water, labour, finances and the anticipated biogas demand of the
households (see figure 2.8 again). This section will present important results from
measurements and observations of systems that are in use.
The anticipated biogas demand from a household, determining the supply of needed
inputs, the sizing of a biogas system, and the balancing of biogas production and demand
through iteration, are investigated and presented in this section. The same issues are
looked at in terms of the development of a communal system. Key findings and
suggestions from this section are also summarized and synthesized in Chapter 7.
6.4.1 Improved Single-Family Systems
6.4.1.1 Anticipated Biogas Demand (Operation)
When a biogas system is to be dimensioned, it is important to not only know the
technically feasible BPR from a specific design (which was determined in section 5.4.1),
but also the anticipated biogas demand from the household in question. This section
therefore aims to answer how much biogas is needed daily, for a family of three to be able
to meet their cooking needs. More specifically the aim is to answer the following two
questions:
1. How much time per day does a family spend on cooking with biogas and at what
times during the day?
2. How efficient is the biogas stove, i.e. how many liters of biogas is used per hour?
Background and Theory
The available literature provides us with a number of different approximations of the
biogas demand of a family, as well as the efficiency of biogas stoves. Table 6.1 provides us
with an overview.
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Reference Demand
Biogas consumption [l] Time [min]
Equivalent [l/day/3 person family]
Equivalent [min/day/family]
A,B, C 1 meal, 1 person 150-300
1125-2250 B,C 2 meals, 5 person 1500-2400
1125-1800
D 1 meal
100
250
E 3 meals, 1 person 200
500 F 3 meals, 4 person 1000
625
F 1 person, 1 day 300
900
Table 6.1: Anticipated biogas consumption according to various earlier studies. Reference key is as follows:
A: Kossman & Pönitz, 1984a, B: Kossman & Pönitz, 1984b, C: Werner et al. 1989, D: Gustavsson, 2000, E: An
et al., 1997, F: United Nations, 1984.
The “equivalent”-columns in Table 6.1, are calculated as to be able to compare with the
system observed in Lembang (digester C). An assumption in this calculation is that a
person will eat approximately 2.5 meals per day, which leads to 7.5 meals per 3 person
family. This assumption is based on the observation (of households in Lembang) that no
more than 3 (and often only 2) meals were cooked per day, even when the supply of
cooking-fuel was plentiful. Another assumption is that the amount of biogas needed for
three people is three times the amount needed for one person. This is probably a
somewhat faulty assumption and the resulting anticipated demands thereby a bit higher
than reality (see section 6.4.2 for a more valid assumption which includes a decreasing
marginal demand with increasing household size).
Methods and Materials
The two question required different approaches:
1. The time spent on cooking with biogas in a household with three people was recorded
during a period of 24 days (Wawa‟s family using biogas from digester C). The start and end
time of each use of the stove was recorded as well as the type of food cooked.
2. To determine the stove efficiency two experimental methods were used. The first
method entailed using a biogas stove connected to the water displacement apparatus (WD
unit C) to determine the amount of gas used per time unit. The flame was adjusted using a
manual valve in order to resemble the flame that is used (on average) in “real life”
cooking. Three measurements were conducted - one when cooking water, one when
cooking rice and one when steaming rice. These are three of the most common uses of the
biogas stove and hence a representative simulation. The other method entailed connecting
the stove to a filled biogas holder with a known volume of 500 liters. The gas holder was
then emptied while cooking (adding weights to increase pressure and adjusting the flame
depending on the needs, as is done in real life) and the time to empty the gas holder was
recorded.
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Results
1. Time spent on Cooking
On 3 out of the 24 days, the biogas stove was not used at all due to various reasons (short
trips, visits with neighbours). The average time spent on cooking on the 21 days that the
stove was used, was 2.33 hours per day (2 hours and 20 minutes). If all days are counted,
the average time spent on cooking was 2.04 hours per day (2 hours and 2 minutes). The
average amount of times to cook per day was 2.14 (or 1.88 if all days are counted). Almost
all of the cooking was performed in the morning between 5 and 10 AM (47.9 % ) or in the
afternoon between 2 and 6 PM (45.3 %). Figure 6.8 provides an overview and example of
an anticipated variation of biogas demand during a day.
Figure 6.8: Variation of cooking demand in a household with 3 people. The measurements are taken during
a period of 24 days.
2. Biogas stove efficiency
Using method 1 (with the stove connected to WD unit C) the efficiency of the stove was
387.9 l/h. This is an average of three measurements (399.68+436.8+327.36)/3 = 387.9 l/h)
which were from cooking water, cooking rice and steaming rice.
Using method 2 (with the stove connected to a gas holder of known volume) the
efficiency of the stove was 333.33 l/h. This efficiency was calculated based on the
observation that the time to empty the gas holder which had a volume of 500 l was 1 hour
and 30 minutes (500/1,5 = 333.33 l/h).
Analysis
With a daily biogas stove usage of 2 hours and 20 minutes (for a family of three) and a
stove efficiency of 387.9 l/h (method 1) or 333.3 l/h (Method 2) the anticipated average
biogas consumption is:
Cooking time
Morning (5-10 AM)
Midday (10 AM-2 PM)
Afternoon (2-6 PM)
Evening (6-10 PM)
maximum 235 120 120 115 7
minimum 53 25 0 0 0
Average 139,9 67 9,14 63,43 0,33
0
50
100
150
200
250
co
okin
g t
ime
[m
in]
Variation of cooking times
maximum
minimum
Average
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Method 1: 387,9*2,33= 903,8 l
Method 2: 333,3*2,33= 776,6 l
Average of method 2 and 3: (903,807+776,589)/2= 840.5 l
If we look at the maximum and minimum daily usage of the biogas stove during the
experimental period we get a maximum and minimum daily usage:
Maximum value recorded (235 minutes / day) = 3 hours 55 minutes:
Method 1: 387.9*(3+55/60) = 1519.3 l
Method 2: 333.3*(3+55/60) = 1305.4 l
Minimum value recorded (53 minutes /day):
Method 1: 387.9*(53/60) = 342.6 l
Method 2: 333.3*(53/60) =294.4 l
Literature (see Table 6.1) anticipates a demand somewhere between 500 l and 2,250 l to
cook 2.5 meals per day for a family of three. The results of our experiments, with an
anticipated demand between 294 l and 1,519 l, are a bit lower than these values. The
lower values could be partly attributed to the fact that the calculations for the literature
assumed that the demand for 1 person could be multiplied with a factor 3 to get the
demand for a household with three people. Whatever the main reason, since the results of
the experiments are highly contextual, the values from our measurements are the ones to
be used when planning a biogas system in the Lembang area.
Conclusion
The biogas demand for a family of three, varies quite a bit from day to day, and also
depends on the way that the biogas stove is used. The maximum anticipated demand is
1,519 l per day and the minimum demand is 294 l per day. The average biogas demand is
between 777 l and 904 l per day (average 840.5 l per day). Almost all cooking is either
done in the morning (5-10 AM) or in the afternoon (2-6 PM), 47.9 % and 45.3 %
respectively.
6.4.1.2 Determining the Supply of Needed Inputs (Installation)
Besides determining an anticipated biogas demand, it is important to identify the supply
of inputs that exist in the area, before installing a biogas system. The required inputs were
identified in Figure 2.8 in section 2.4. Here is a brief explanation of their meaning:
Cow dung: The amount of cows in the area and the amount of dung per day from each
cow must be approximated.
Water: Water (both fresh and grey) must be available and affordable.
Labour: The person/people who are to operate and maintain the biogas system must have
the time and will to do so. The installation will also require continuous work for a number
of days.
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Space: The required space to be able to install a biogas system that will produce enough
biogas to meet the demand of the household, must exist.
Financial: The cost of the materials and construction must be able to be covered by the
household that is installing a digester.
6.4.1.3 Sizing the Biogas System and Cow Dung Required (Construction and Design)
With a maximum anticipated demand of 1,519 l per day and a minimum demand of 294 l
per day, it is quite hard to determine an average anticipated demand that should be used
when sizing a biogas system. If the digester is made to small there is a risk that the
demand will not be met and the users will need to compliment the biogas systems with
other ways of cooking.
Making the digester to large can be at least as detrimental to its functionality. If the
digester is over-sized there is a risk that it will take up more land than needed and require
more dung, water, labour or finances than are available, and thereby leading to a low SE
of the biogas system.
A conservative rule of thumb, when sizing a biogas digester (which we will call “digester
sizing, example 1”), is to be able to, under optimum conditions and operation, daily
produce an amount of biogas equal to the maximum anticipated biogas demand per day.
So for our case, if we assume that we want an RT of 30 days, that the PE is 136.8 l/ kg TS
(from measurements in section 5.4.1, taken during the coldest time of year) and that it can
be improved to 150 l / kg TS, by insulating the digester with rice husks (10 % increase -
results from section 5.4.1), we will need the following size of a digester for a family of
three:
Biogas production rate (process efficiency): 150 l / kg TS
Demand (maximum): 1500 l per day
Required LR (kg TS /day): 1500 / 150 = 10 kg TS
TS (average) = 16.34 %
Required LR (kg dung/day) = 10 / 0.1634 = 61.2 kg dung/day.
Required liquid volume of digester: (61.2*2) * 30 = 3672.0 l
In other words, with this calculation, approximately three cows (producing 20 kg dung
each daily) are needed to fulfil the maximum daily demand of a family of three. The liquid
volume of the digester needed is 3.67 m3.
A less conservative rule of thumb (digester sizing, example 2), is to size the digester so that
it will be able to produce an amount of biogas daily, that is at least equal to the anticipated
average demand. With an RT and the same assumed BPR as above, we will need the
following size of a digester for a family of three:
Bigas production rate (process efficiency): 150 l / kg TS
Demand (Average): 840 l per day (average of method 1 and 2)
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Required LR (kg TS /day): 840 / 150 = 5.6 kg TS
TS (average) = 16.34 %
Required LR (kg dung /day) = 5.6 / 0.1634 = 34.3 kg dung/day.
Required liquid volume of digester: (34.3*2) * 30 = 2058.0 l
In other words, with this calculation, less than two cows (producing 20 kg dung each
daily) are needed to fulfil the average daily demand of a family of three. The liquid
volume of the digester needed is 2.06 m3.
When a seemingly appropriate size and dimension of a digester has been chosen, the
required amount of inputs to this system should be compared to the available supply in
the area. This may alter the choices since a lack of dung, water, labour, space or finances
may require a smaller system and abundance of these inputs may motivate a larger system.
For approximate values of the required supply of inputs for a biogas system for a family of
three, see section 7.3.1.
Besides finding an appropriate size of the digester, it is important to size the gas holder
correctly. The gasholder must be designed to:
- cover the peak consumption rate (i.e. not be emptied)
- hold the biogas produced during the longest zero-consumption period
Practical experience shows that 60 % of the maximum daily production should be able to
be stored in the gas holder (Werner et al., 1989). For the two sizes of digesters above, the
size of the gas holders should be at least 900 l (0.6*1500) and 504 l (0.6*840).
6.4.1.4 Balancing Biogas Production and Demand (Through Iteration)
Some knowledge of the variation of demand from a household during a day, is of great use
when trying to make sure the biogas production from a system will be sufficient to meet
the demand at all times. We have assumed that for most households, the time that the
biogas is mostly used, is in the morning (5-10 AM) and in the afternoon (2-6 PM) (just as
in Wawa‟s household).
“Digester sizing, example 2” is used as a case study to see if the anticipated demand will be
met by the production rate.
Liquid volume of digester: 2058 l
Volume of gas holder: 504 l
Production rate: 840 l/ day = 840 / 24 = 35 l / hour
Consumption rate: 840 l /day
Let us say that we start with an empty gas holder at 6 PM on day 1. There is almost no
biogas consumption during the evening (only 0.23 % of total consumption), and the next
time the digester will be used is in the morning (at 5 AM on day 2). This will result in a
gas holder which will have 385 l (35*11) at this time. This means that the 504 l gas holder
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volume is large enough to cover the longest no-consumption period. If 47.9 % of biogas
consumption takes place during 5 and 10 AM on day 2, this will mean that 402 l
(0.479*840) must have been produced by 10 AM. From 5 AM to 10 AM another 175 l
(35*5) has been produced. At 10 AM there should therefore be (385+175-402) 158 l left in
the gas holder. Between 10 AM and 2 PM on day 2, around 55 l (0.0653*840) will be
consumed and 140 l (35*4) will have been produced which means the gas holder will
contain 243 l (158 + 140 – 55) at 2 PM. If 45.3 % of biogas consumption takes place
between 2 PM and 6 PM, this will mean that 380.5 l (0.453*840) is consumed and the
production is 140 l (4*35) which means the gas holder will contain 2.5 l (243+140 -380.5)
at 6 PM on day 2. A visualization of the consumption, production and biogas in the gas
holder during the 24 hour period can be seen in Figure 6.9.
Figure 6.9: Assumed biogas production, consumption and amount of biogas in the gas
holder for an imaginary biogas system for a household of three people, during a 24 hour
period. In reality the gas production is of course not constant as is assumed in this
simulation.
This is good news. The biogas demand will be able to be met at all times during this 24
hour period. However, this calculation is based on the assumption that the production
rate and consumption rate actually are the same. If the daily consumption rate increased
or the production rate decreased for any reason, a biogas shortage could easily be the
result. Over-sizing the digester by around 20 % may be a good idea for this reason.
The production rate may decrease as a result of sub-optimal slurry flow management
(infrequent loading) or gas flow management (e.g. unfixed leaks). However, since the
measurements we did were taken at the coldest time of the year, the production rate will
most likely be higher during all other times of the year. The calculated biogas production
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may therefore actually be a good approximation of the annual average production rate of a
real system in use.
When a biogas system has been installed and is operating, the challenge of making sure
biogas production stays above demand at all times, remains. Decreasing the biogas demand
(e.g. by increasing the efficiency of biogas stove use) and changing the times of
consumption, is one way. The other way is to increase production rates through
improving slurry flow management and gas flow management. E.g. if dung is abundant,
the LR can be increased, leading to a higher SE and daily BPR (in l /day).
Balancing biogas production and demand is hence an iterative process. It should start
during the planning phase and continue as long as the biogas system is operating.
6.4.2 Developing a Communal System
6.4.2.1 Anticipated Biogas Demand (Operation)
For practical reasons, the anticipated biogas demand can be assumed to be the same for all
households with three people. Many times, a household will include a larger amount of
people. Four to six people is a fairly common size of a household in the Lembang area.
However, households of only two people also exist. When it comes to anticipating the
biogas demand of households with a different amount of people in them, some
approximations must be made. The biogas demand per person will most likely decrease
with a growing amount of people in the household. If the average demand of a family of
three is assumed to be 840 l (from measurements in section 6.4.1), the following values
could be good approximations for households of different sizes:
Household with 2 people: 600 l / day (300 l /person)
Household with 3 people: 840 l /day (280 l/person)
Household with 4 people: 1060 l/day (265 l /person)
Household with 5 people: 1260 l /day (252 l / person)
Household with 6 people: 1440 l/day (240 l /person)
These values are important to take into consideration when designing a communal
system. Before the system is sized and dimensioned, the amount of people in the involved
households must be counted, and the total biogas demand be calculated.
The anticipated variation of demand during the day, of the involved households, is just as
important to consider. If the families‟ usage coincides, a biogas shortage can easily occur, if
the system is not designed and operated to handle such a peak in demand. On the
contrary, if the families‟ usage of biogas turns out to be at quite different times of the day,
the system can have a smaller size (and BPR) and still manage to cover the demand of all
households at all times.
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6.4.2.2 Determining the Supply (Installation)
Determining the supply of inputs available in the area, where a communal system is to be
built, is the same procedure as for a single-family system, except that more attention will
have to be paid to who contributes with the inputs and that a fair agreement can be
reached.
6.4.2.3 Amount of Digesters, Their Size and Required Dung (Construction and Design)
The amount of digesters that should be used for a communal system will depend on the
amount of households and people involved, as well as the size, shape and location of the
available land. If more than two households or ten people are involved, it is probably a
good idea to construct more than one digester.
The communal system in Pasir Angling (PA1) was initially meant to provide biogas for
two households using one longer tubular digester. Five people were living in one of the
households and two people in the other. With the assumptions made above about biogas
use, we would get an average daily biogas demand of 1860 l (600 l + 1260 l).
Due to the difficulties of regulating gas flow and the potential arguments resulting from a
shortage in a communal system, it may be a good idea to size the digester so that it can
produce slightly more than the average anticipated demand. However, it should not be
made larger than what is appropriate considering the amount of input (dung, water,
labour, space and finances) available. A rule of thumb could be to size a communal system
to be able to produce 20 % more than the anticipated average biogas demand. This gives
us the following size, and dung requirements of a communal system using one longer
tubular digester, providing biogas to two households (with five and two people in them):
Production rate (process efficiency): 150 l / kg TS
Demand (Average): (1260+600)*1.2 l per day = 2232 l per day
Required LR (kg TS /day): 2232 / 150 = 14.88 kg TS
TS (average) = 16.34 %
Required LR (kg dung /day) = 14.88 / 0.1634 = 91.1 kg dung/day.
Required liquid volume of digester: (91.1*2) * 30 = 5466 l
This production rate hence requires cow dung from four to five cows (producing 20 kg of
dung each per day) and a digester with a liquid volume of about 5.47 m3. This can be
compared to the actual liquid volume of the communal digester in Pasir Angling which is
7.70 m3. It seems as if the digester is over-sized - the users are not loading the digester
enough and the production rate is therefore low (see slurry management, section 6.2.2). It
may have been a good idea to have made the digester slightly smaller from the beginning.
Now that it already is installed however, the only thing to do is to encourage a higher LR
and maybe even connect another household to the digester (since the potential to produce
more biogas from the current size of the digester exists).
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As was the case with the communal system in Pasir Angling (PA1 and PA2) digesters can
be connected to the system at a later time, as more households show an interest in
installing biogas. The size of the added digester should be calculated with the additional
anticipated demand of the new households, the BPR of the currently connected digesters
and the demand of the already connected households in mind. There is no specific limit to
the amount of digesters that can be added to a communal system, but there should be a
discussion whether the connection is worthwhile and necessary. Many times, a single-
family system may be a better solution. Also, the more digesters that are added to a
system, the more difficult the regulation of gas flow becomes.
6.4.2.4 Balancing Production and Demand (Based on Observations in the Villages)
(Operation)
A few weeks after the communal biogas system had been installed in Pasir Angling, the
users exclaimed: “Now that we have biogas, we no longer need to collect firewood!”.
However, a month later, the same people had experienced a number of shortages in biogas
supply. After filling the digester, there was usually enough biogas for both households for
a while, but between fillings (they only filled every three days) other cooking fuels were
used (mostly firewood and sometimes kerosene) to cover the shortages of biogas.
Especially the household with two people were experiencing a lack of biogas during this
period.
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7: Key Findings and Suggestions
Chapter 7 summarizes the key findings from chapter 5 and 6 and provides suggestions in
terms of the development of a communal biogas system. As can be seen in Figure 2.3 (in
section 2.4), this chapter also aims to answer the three research questions formulated in
section 2.3. Section 7.1 aims to answer research question 1, section 7.2 research question
2, and section 7.3 research question 3.
7.1 Improving Single-Family Systems - Key Findings
The research question (formulated in section 2.3) that this section aims to answer is:
How can the construction and design of all polyethylene plastic biogas systems (including
single-family systems) be improved in terms of their appropriateness and functionality in
the Indonesian rural setting? (Research Question 1)
The experiments and observations documented in Chapter 5 and 6 resulted in a number of
key findings for all polyethylene plastic biogas systems. Each finding belongs to one of the
four technical and operational issues (introduced in section 2.4), and are listed below.
Some of the findings are quite contextual but most of them can still be assumed to be valid
for other similar rural areas in Indonesia and other tropical countries.
Digester Dimension (5.1.1) / Available Space and Alternative Uses of the Land (6.1.1)
Shorter digesters and vertical digesters are not as efficient at producing biogas as
the standard longer digester. A shorter digester with a length/diameter ratio of 1.4
has a PE and SE that is approximately 12.6 % lower than that of a standard digester
with length/diameter ratio of 3.33. A vertical digester with length/diameter ratio of
1.4 has a PE and SE that is approximately 7.2 % lower than that of a standard
digester. (from 5.1.1)
The “Space efficiency” (l of biogas produced per m2 digester area) of vertical
digesters, is much higher than for horizontal digesters. A vertical digester (with
length/diameter ratio 1.4) produces almost twice as much biogas per m2 as a
horizontal digester (with the same length/diameter ratio) and more than twice as
much as a longer horizontal digester (with length/diameter ratio 3.33). (from 6.1.1)
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Slurry Management (6.2.1)
The frequency of which a digester is loaded has little impact on the average BPR of
a biogas system, but has a large impact on the variation of the BPR. A digester that
is loaded daily will have a small variation of the BPR (the minimum BPR recorded
was 91.3 % of average BPR, maximum 108.4 %) while a digester that is loaded
weekly will have a very large variation (the minimum being as little as 65.3 % of
the average BPR and the maximum 134.1 %). This is a very important finding
which has great implications on the process of sizing systems and to make sure that
the biogas production will be able to meet the biogas demand, at all times. (from
6.2.1)
The quicker flow of slurry through vertical digesters and digesters of shorter
dimension, may lead to lower average BPR‟s and disruption of the biogas
production process. Further research into this phenomenon must be done. (from
6.2.1)
Gas Flow Management (6.3.1)
The inclusion of pressure valves in the biogas system helps ensure a continuous
and one-way flow of biogas from the digester to the gas holder. The height of the
WC in the pressure valve is often played with, leading to an unnecessary variation
in the flow of biogas in the system. (from 6.3.1)
Checking for, detecting and fixing leaks can be an arduous task once the biogas
system is installed and operating. Therefore it is highly recommended to check for
leaks in all parts of the biogas system during installation. (from 6.3.1)
Technically Feasible Biogas Production (5.4.1) / Balancing Biogas Production and Demand (6.4.1)
The average amount of biogas that can be produced daily from a polyethylene
tubular digester is 136.8 l/kg TS. This is 13-29 % higher than the production rates
found in literature for all types of biogas systems, under similar operating
conditions. (from 5.4.1)
Insulating the polyethylene digester with rice husks can increase the PE of the
biogas system with around 10 %. Insulating the polyethylene digesters with soil
does not change the magnitude of the PE. However, both ways of insulating the
digester decrease the variability of the PE between night and day. (from 5.4.1)
The average daily amount of time spent on cooking with a biogas stove in a
household with three people was 2 hours and 20 minutes. The amount of time
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ranged from 53 minutes to 3 hours and 55 minutes. Most of the cooking took place
in the morning (47.9 %) and in the afternoon (45.3 %). (from 6.4.1)
Depending on the way that the biogas stove is used, it will require between 333.3
and 387.9 l per hour. (from 6.4.1)
To be able to meet the demand from a family of 3 people, a digester with a liquid
volume between 2058.1 and 3672.0 l is required. The corresponding dung required
is between 34.3 and 61.2 kg of dung per day (to reach an RT of 30 days) which can
be supplied by 2-3 cows. (from 6.4.1)
The stove efficiency could in theory be increased by adding air to the biogas before
burning the gas. However, experiments showed no significant improvement in
burning efficiency.
7.2 Developing a Communal System
This section addresses research question 2 and the corollary research question 2*, which
were formulated in section 2.3:
Is it possible to develop a well functioning communal system with polyethylene plastic
digesters, with due consideration to key operational and technical issues of a biogas
system? (Research Question 2)
What are the difficulties of developing a communal biogas system and how could they be
overcome? (Research Question 2*)
In Chapter 5 and 6, experiments and observations which specifically addressed issues
relevant to the development of communal systems, were conducted. The result was that
communal polyethylene biogas systems can and should be developed. However, there
were a few issues which are listed below under section 7.2.1. Several of these issues have
also been identified by earlier research for all types of small scale communal biogas
systems (see e.g. United Nations, 1984)
7.2.1 Difficulties and How they Can Be Overcome
The difficulties of developing a communal system and their potential solution can be seen
in Table 7.1.
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Difficulty Potential solution(s)
There may not be a suitable space available for a communal system with only one large digester
Build several digesters of different dimension (including digesters with higher space efficiency) and connect their gas pipes
Realize and maintain a fair distribution of gas flow between the households
Regulate the gas flow using manual valves. (Not appropriate to regulate only with pressure valves)
The pressure drop in the gas pipes is too large leading to low flow rates
- Increase the diameter of the gas pipe - Limit the distance from the households to the
digester - Adjust the WC of the involved pressure valve
The owner of the land or dung does not want to contribute to a communal system by offering this input.
Develop some sort of agreement between the involved parties or build single-family systems instead. The latter solution is probably a better solution if the social capital, and the will to contribute to the common good, is low.
Table 7.1: Summary of issues related to the development of communal systems and their potential solution.
7.2.2 Other Key Findings
Besides the difficulties mentioned above, a few other key findings related to the
development of communal systems were:
Connecting the slurry flow between digesters in a communal system (in order to
decrease the amount of time to load the digester and being more flexible in terms
of the space that can be used) does not seem to work well. (from 5.2.2)
The size of the digester does not influence the PE or SE of the system significantly.
They can be assumed to be the same for all digesters of similar dimensions, no
matter their size (as long as the LR and RT are the same). (from 5.4.2)
7.3 When to Build a Communal System
This section addresses research question 3, which was formulated in section 2.3:
Under which circumstances should a communal system be built instead of a single-family
system? (Research Question 3)
The decision of whether a communal or a single-family system is to be installed, must be
based on an evaluation of the local conditions and how they relate to the requirements for
installing, operating and maintaining the respective systems (see section 7.3.1, 7.3.2 and
7.3.3). The potential advantages of installing a communal system should also be weighed
against the problems that may arise (see section 7.3.4).
Section 7.3.1, 7.3.2 and 7.3.3 addresses the corollary research question 3*:
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What are the criteria and requirements when installing, operating and maintaining a
single family system, and what are they for a communal system? (Research Question 3*)
While section 7.3.4 addresses the corollary research question 3**:
What are the potential advantages of installing communal systems and what are problems
that could arise? (Research Question 3**)
7.3.1 Requirements for the Installation, Operation and Maintenance of a Single-Family System
Biogas Demand
There needs to be a demand for biogas in at least one household, in order to be able to
motivate the construction and installation of a single-family biogas system. The
magnitude of the demand will depend on the amount of people in the household and their
cooking routines.
Required Supply of Inputs (Installation)
Besides determining an anticipated biogas demand, it is important to identify the supply
of inputs that exist in the area, before sizing, designing and installing a biogas system. The
relevant inputs were presented in figure 2.8 in section 2.4 and further explained in section
6.4.1. For a single-family system providing biogas for 3 people, the following approximate
amounts will be needed (based on the discussion in section 6.4.1):
Cow dung: Around 40 kg per day.4 If the dairy cows produce around 20 kg of dung per
day, 2 cows are enough.
Water: Around 40 l is enough, to be mixed with the 40 kg dung, which leads to a daily
influent slurry volume of around 80 l.
Labour: Dependant on the distance between the cow pen and the digester. No more than
30 minutes per day should be needed for the operation and maintenance of the biogas
system (includes loading, emptying, fixing leaks).
Space: The space required will depend on the chosen shape and orientation of the
digester. A standard digester will require an area of 6 m length and 1 m width (6m2). A
vertical cylinder digester requires a circular area with a diameter of about 2 m (3.14 m2).
The space required per user is hence 2 m2 and 1.05 m2, respectively for the two systems.
Financial: The cost of the materials for a single-family system is no more than Rp.
1,000,000 (100 USD). The cost of construction and help during installation is around Rp.
300,000 (30 USD). The cost per user is hence Rp. 433,333 (43.3 USD).
4 Based on “digester sizing example 2” in section 6.4.1, with 20% extra margin added.
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Available Space and Alternative Uses of the Land
The space identified for building a single-family system must be located no more than 25
m away from the household‟s kitchen and a cow pen must exist in the vicinity. Preferably
the space is owned by the household that will be using the biogas, and the effluent slurry
should not end up on anyone else‟s land. Alternative uses of the surrounding land (by
humans and other animals) may continue but precautionary steps must be taken to ensure
that the biogas system is protected from physical damage.
Gas Flow Management
The WC in the pressure valve should be set to 3 cm height to ensure that pressure
is maintained and biogas flows continuously to the gas holder.
Leaks in the digester, gas pipes, gas holders and other system components should
be avoided to the highest extent possible. If a leak is suspected, the biogas system
should be checked and encountered leaks fixed.
Slurry Management
The digester must be loaded frequently (preferably daily) with an amount of
slurry, appropriate to the RT required to reach a production rate, that will meet
the biogas demand of the household.
Dung must be transported from the cow pen to the digester, preferably on a daily
basis.
The digester must be emptied at the same frequency that it is loaded, and the
effluent slurry taken care of (e.g. dried on spot).
At the installation of the biogas system, the digester must be inoculated with a
mixture of digested slurry, fresh dung and water. The water/dung ratio should be
around 1, and can be slightly lower for digesters which have a shorter distance
between input and output.
Balancing Biogas Production and Demand
Demand from the household must be able to be covered at all times.
Enough dung, water and manual labour must be available (supply sufficient) to
reach production rates that are required.
The sizing of the digester and gas holder must be appropriate to the determined
demand and supply.
7.3.2 Requirements for the Installation, Operation and Maintenance of a Communal System
Biogas Demand
There needs to be a demand for biogas in at least two households that are located
relatively close to each other (no further than 50 m apart), in order to motivate the
construction and installation of a communal biogas system. The magnitude and variation
of demand will depend on the amount of people in each household, their cooking routines
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and the relationship between the two houses cooking routines (in terms of when they
cook).
Required Supply of Inputs (Installation)
For a communal system consisting of one digester and providing biogas for two families
with a total of seven people, the following approximate amounts will be needed (based on
the discussion in section 6.4.2):
Cow dung: Around 90 kg per day. If the dairy cows produce around 20 kg of dung per
day, five cows are enough.
Water: About 90 l is enough, to be mixed with the 90 kg dung, which leads to a daily
influent slurry volume of around 180 l.
Labour: Dependant on the distance between the cow pen and the digester. No more than
40 minutes per day should be needed for the operation and maintenance of the biogas
system (includes loading, emptying, fixing leaks, regulation of gas flow).
Space: The space required will depend on the chosen shape and orientation of the
digester. A standard horizontal digester with a liquid volume of 5466 l (calculated size that
is needed to reach the wanted production rate), a total volume of 7709 l, and a
length/diameter ratio of 5.5 (standard) will require a space of 6.7 m length and 1.2 m
width (8.0 m2). The space required per user is in this case 1.14 m2.
Financial: The cost of the materials is no more than Rp. 1,300,000 (130 USD). The cost of
construction and help during installation is around Rp. 300,000 (30 USD). The cost per
user is hence Rp 228,571 (22.9 USD).
Available Space and Alternative Uses of the Land
The available space for installation of the biogas digester needs to be in an appropriate
place in relation to the households that are to be connected and a cow pen must exist in
the vicinity. The distance between the digester and the kitchens of all households needs to
be no larger than 25 m. The owner or owners of the land where the communal system is
to be installed need to be willing to contribute with this resource. Having households that
have people from the same family will increase the chance that this will be the case. More
rural and remote villages also seem to have a greater sense of community and appreciation
of communal solutions, making the issue of land ownership less relevant than in more
urban villages.
Gas Flow Management
The gas flow should be distributed appropriately and fairly among the households
connected to the communal system. Preferably, a manual valve is installed on each
gas pipe leading to a household. To facilitate the regulation of the gas flow, the
manual valves should all be placed close to each other and close to the digester (or
digesters).
The regulation of the gas flow should be performed by one or more of the users on
a daily basis. The magnitude and timing of the anticipated demand from each
household should be taken into consideration.
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The pressure valves on each gas pipe can be set to 3 cm WC. The levels do not have
to be exactly the same for all pressure valves, since the difference in the length of
the gas pipes will lead to different pressure drops anyways. The regulation of gas
flow can be managed solely with the manual valves.
Leaks in the digester, gas pipes, gas holders and other system components should
be avoided to the highest extent possible. If a leak is suspected, the biogas system
should be checked and encountered leaks fixed. Besides being a waste of biogas,
leaks in one or more of the gas pipes or pressure valves can lead to major
difficulties in distributing the gas flow.
If the communal system consists of more than one digester, the gas flow between
the two digesters must be managed. If one of the digesters is known to
overproduce, a pressure valve (a one-way valve) can be installed. In other cases, a
manual valve can be installed.
Slurry Management
The digesters connected to the communal system must be loaded frequently
(preferably daily) with an amount of slurry, appropriate for the RT required to
reach a production rate, that will be able to meet the total biogas demand of the
households.
Dung must be transported from the cow pen to the digester by one or more of the
users, preferably on a daily basis.
The digesters need to be emptied as frequently as they are loaded and the effluent
be taken care of (e.g. dried on spot).
At the installation of the biogas system, the digesters must be inoculated with a
mixture of digested slurry, fresh dung and water. The water/dung ratio should be
around 1, and can be slightly lower for digesters which have a shorter distance
between input and output.
Balancing Biogas Production and Demand
Maximum demand must be able to be covered at all times, which will depend on
the involved household‟s cooking routines (when they cook).
Enough dung, water and manual labour must be available to reach production rates
that are required. It may be a good idea to be clear on who contributes with these
necessary inputs and how they can be compensated (if they perceive it as being
unfair), especially in more urban villages.
The amount of digesters and gas holders and their sizing must be appropriate to the
determined demand and supply.
7.3.3 Required Inputs – A Comparison Between Communal and Single-Family Systems
A comparison between the required inputs of a single-family system and a communal
system is summarized in Table 7.2.
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Required Input Single-family system
(3 people) Communal system (7 people, 2 households)
Cow dung (cows) [kg/day] 40 (2) 90 (4-5)
Water [l/day] 40 90
Labour [min/day/person] 10 (30/3) 5.7 (40/7)
Space [m2/person] 2.0 (6,0/3) 1.14 (8,0/7)
Financial [USD/person] 43.3 (130/3) 22.9 (160/7)
Table 7.2: Summary of the required inputs to single-family systems and communal systems.
As can be seen in Table 7.2, a communal system with one large digester is more efficient
in terms of cost per person and space required, than a single family system. Communal
systems with several smaller digesters will be less cost- and space efficient than a
communal system with one or more larger digesters. However, often the size and shape
of the available space will put constraints on the design of the communal system.
7.3.4 Potential Advantages of Installing a Communal System and Some of the Problems that May Arise
The installation of a communal system can lead to several advantages over having single-
family systems. However, there are also a number of disadvantages and problems that can
arise. The potential advantages and disadvantages are summarized in Table 7.3.
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Potential advantages Comments
Decreases the amount of labour needed for slurry management
Fewer digesters per household leads to less labour per person. Connecting the slurry flow between digesters may lead to even further reductions but may lead to other complications.
Decreases the amount of land needed (increases the space efficiency)
Using larger digesters leads to less space needed per person (that is reliant on the biogas system)
Decreases the costs per person (increases the cost efficiency)
Less material per person (that is reliant on the biogas system), is needed.
The PE and SE of the biogas system does not change significantly with increased size of the digester
As long as the LR and the RT is kept constant.
Can increase the social capital, social equity and cooperation in a village
As long as the right preconditions exist and conflicts are prevented well in advance
Potential disadvantages and problems that may arise
Comments
Biogas shortages may be more frequent and have larger implications
The biogas demand, and it’s variation during the day, can be more difficult to predict for a communal system than for a single-family system since there are more people and households involved. This can easily lead to either an over sizing or under-sizing of the biogas system, which both may lead to biogas shortages (from lack of inputs and from lack of production capacity, respectively).
A too low LR may create a shortage of biogas and problems of fairly distributing the scarce biogas resource
A solution must include increasing the user’s knowledge of the biogas process and the importance of frequent loading and other O&M (e.g. by constructing simulation games teaching about delays etc.).
Communal biogas systems can lead to conflicts, if managed badly.
Who contributes with what resources? Who is to be in charge of O&M? Who regulates the gas flow?
Table 7.3: Potential advantages and disadvantages of communal systems compared to single-family systems.
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8. Biogas in Lembang
Chapter 8 delves back into the issues first presented in the Background chapter
(specifically sections 2.1 and 2.2) in the light of the results of this study. Section 8.1 looks
at the potential for diffusion of biogas in Lembang while section 8.2 presents some recent
developments and takes a look into the future of the biogas initiative.
8.1 Potential for Diffusion of Biogas in Lembang
8.1.1 Economics of a Dairy Farmer, Vegetable Farmer and Biogas Owner
As has been mentioned before, the economic situation of vegetable farmers in the
Lembang area, is unstable and vulnerable to changes in the global economy. Dairy farmers
have a more stable income and capital but, just like vegetable farmers, usually lack
sufficient funds and cash flow to be able to finance the construction and installation of a
polyethylene biogas system in one payment. Dairy farmers will also obviously have higher
operation and maintenance costs than vegetable farmers, as cows require a large amount
of both water and fodder. During certain times of the year, water can be quite scarce and
hence more expensive, and feed for the cows (mostly grass-cuttings are used) is becoming
increasingly difficult to get a hold of (see section 8.1.5).
A financing scheme used for many years in the Indonesian culture is one of revolving
funding. A number of families join forces and support, in this case, the construction and
installation of one biogas system at a time. This way, each family‟s costs are spread out
over a longer time-period. This can of course be applied to both communal and single-
family systems (in fact, it was implemented in all of the installations discussed in this
paper).
Besides the potential economic benefits of replacing fossil-based cooking fuels with biogas
(see section 8.1.2) the effluent slurry can be economically valuable as a fertilizer (either as
a product to be sold or directly used as a fertilizer on their own fields). A kg of chemical
fertilizer cost between Rp. 11,000 and 12,000 (1.1 to 1.2 USD). In the village of Cicalung, a
50 liter bag of semi-dry effluent slurry from a biogas digester sold for Rp.10,000 (1 USD).
This can be compared to a 20 liter bag of Chicken manure which sold for between Rp.
5,000 and 6,000 (0.5 to 0.6 USD).
8.1.2 Biogas Compared to Other Fuels
Kerosene, liquid petroleum gas and fuel-wood currently make up more or less all of the
cooking fuels used in the Lembang area. A comparison of biogas to these fuels is of crucial
importance in understanding the potential and limits of diffusion of biogas in the area. A
comparison should preferably include the factors in Table 8.1.
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Cost Current subsidy (and potential future development of subsidy) Time to bring 1 l of water to a boil Energy content Security (in use) Reliability (of supply) User friendliness Way to obtain the fuel (time consumed, difficulty)
Table 8.1: Important factors to consider in a comparison between biogas and other cooking fuels.
Unfortunately a full comparison as lined out above was not conducted within the scope of
this thesis project. However, as was mentioned before, as subsidies on kerosene have
decreased greatly and fuel-wood is becoming scarcer, biogas will become a more and more
attractive option.
Even after a polyethylene biogas system has been installed, observations show that people
will keep using other fuels sporadically and as a compliment as long as they are cheap
enough and available. For instance, they may need to cook two things at once or like the
way something tastes when it is roasted over a wood fire.
8.1.3 Small-Scale vs. Large-Scale
Besides the biogas initiative which this Master‟s thesis is a part of, there are a number of
organisations and companies that have shown interest, or may become interested in
developing biogas in the Lembang area.
There are a few medium sized companies (CTL and MTN) that have their own small-scale
biogas systems which they have installed in a number of different areas on Java. They use
a blue polyethylene plastic which is bought from a factory and not available in local
agricultural supply stores. The prices of the CTL biogas systems are slightly higher than
the digesters researched in this paper and the prices of the MTN biogas systems
considerably higher.
A larger Indonesian energy company (Indogas) have shown interest in building a large-
scale biogas plant in Lembang that would be able to process much of the daily produced
cow dung in the area. The cow dung would be collected and transported to the biogas
plant (for a fee) where it would be processed and converted to fertilizer and biogas that in
turn would be sold back to the farmers. This may be a quick way to help solve the waste
and sanitation issues associated with cow dung, but may be less favourable from a
perspective of poverty alleviation and empowerment of poorer farmers.
The dairy farmers cooperative of northern Bandung (KPSBU) have ear-marked a
considerable amount of money for the development of biogas systems in the Lembang
area, but have yet to find an initiative which they wish to support.
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A Dutch funding agency (HIVOS) has decided to promote biogas development in
Indonesia by constructing 8000 biogas systems. They are looking for 3 larger areas where
they can implement their project (Lembang may be on their list).
In an evaluation of the appropriateness of a certain design and scale of a biogas technology
in the Lembang area, the list of considerations in Table 8.2 should be looked at. Of course,
the choice and importance of these considerations is subjective and will vary between the
various actors in the area (the farmers, the initiators of the biogas initiative, the actors
mentioned above).
How well does the scale and design of the biogas system perform..
as a solution to the waste and sanitation issue? as a solution to meeting energy needs? as a solution to agricultural issues (fertilizer etc.)? as a solution to poverty alleviation and more empowered farmers? as a solution to a more resilient and cooperative society?
Table 8.2: Considerations when deciding on an appropriate scale and design of biogas systems in Lembang.
8.1.4 Two Diffusion Models for Small-Scale, Polyethylene Biogas Systems in Lembang
Different worldviews, values, experience, visions and goals among the actors involved in a
project can lead to conflicting interests and misunderstandings.
Two partly conflicting diffusion models that were favoured by different actors in the
biogas initiative in Lembang were, what we can call, the cash-economy model and the
alternative model. The cash-economy model aims to promote a diffusion with centralized
production of biogas systems and slightly more decentralized installation and maintenance
capacity. The alternative model aims to promote a diffusion where farmers diffuse the
technology to each other.
A comparison between these two models (see Table 8.3) highlights many interesting
aspects of technology diffusion and the appropriateness of using either a standard business
model or a more community-oriented model. The question of funding and use of revenue
is of course of central importance but will not be discussed further here. The comparison
also exemplifies the advantages and disadvantages of trying to work either within or
outside predominant socio-economic structures. It also shows that there are different
ways to work within the system (e.g. using local, traditional funding mechanisms vs.
larger, newer ones).
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Diffusion model Cash Economy model Alternative model
Main goal Integrate the initiatives with Business as usual models. Put the biogas systems on the market.
Create a non-cash economy system which ensures that the introduction of biogas technology will improve social equity and create closed material-cycles in Lembang.
A few characteristics Sees the dung as a resource Construction of digesters done by professionals (local entrepreneurs). Installation and maintenance done by either professionals or local technicians (depending on difficulty) Funding from economic cooperatives and other funders (local, national and international) Controlled diffusion
Sees the dung as waste (communal problem) Construction, installation and maintenance of digesters done by local technicians Funding using only traditional mechanism of rotating funds Less controlled diffusion
Potential advantages Quicker diffusion, successes and failures can lead to insights that can be applied to other areas
Increased community capital and cooperation, empowered farmers, localized resource flows
Potential risks May increase the gap between the rich (dairy farmers) and the poor (vegetable farmers). Trickle-down effect may be non-existent or insufficient. Loss of resources from the Lembang area – farmers in the Bandung/Jakarta area have higher purchasing power than the poor vegetable farmers in Lembang Farmers vulnerability to fluxes in the global financial system remains
Resistance from people who are not familiar with the alternative system and not sure that any alternative to cash economy can work. Alternative socio-economic systems are fairly uncommon and hence little is known about how they may function within and relate to the global financial system. More frequent failures and difficult to diffuse improvements to the technology resulting from experience/research etc.
Table 8.3: Main goal, characteristics and risks of two diffusion models.
It should be noted that the above diffusion models do not necessarily have to be
completely opposed, and there may be common ground that could be found where the
models may complement each other.
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8.1.5 Limits to Expanding Biogas in Lembang
With more than 12,000 cows in the Lembang area, and using the calculations done in
section 6.4, between 18,000 and 20,000 people (or about 10 % of the total urban and rural
population of Lembang area) would be able to rely solely on biogas for their cooking
needs, if enough biogas systems were installed. If all these systems were constructed,
installed and functioned well, there is a great chance that the increased popularity and
demand for biogas systems in turn drives an expansion of dairy farming in the area. The
carrying capacity of the region (in terms of the amount of cows) should be taken into
consideration should biogas technology become very popular, since waste management
and availability of cow-feed otherwise may become major issues.
The amount and quality of available feed for dairy cows is already an issue in the Lembang
area. The feed is mainly king-grass and men often travel by motorcycle and pick-up trucks
in order to find feed - sometimes long distances (e.g. to Subang which is around 1 hour
away). This indicates a shortage and another cost for the cow farmers (in time and fuel).
Women often collect grass for the cows from the side of the road, where many of the
pesticides and chemical fertilizers from the fields end up and where the pollution from
the road is the highest. Together with the fact that the cows are stabled and do not move
around, one should investigate the quality of the milk that is produced under these
circumstances.
Figure 8.1 shows a casual loop diagram which conveys some of the dynamic relationships
between key factors in the diffusion of small-scale, polyethylene biogas systems in the
Lembang area (including negative feedback loops highlighting the limits of expanding
biogas technology).
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Figure 8.1: Casual loop diagram of dynamic relationships between key factors in the future of biogas
systems in the Lembang area.
8.2 Recent Development and a Look Ahead
8.2.1 Multiple Problems with Digesters5
Unfortunately, ten months after the biogas system installations in Pasir Angling, Cireyod
and Pengkolan commenced, many of the digesters had stopped working. All four biogas
systems in Cireyod and four out of five systems in Pasir Angling were no longer producing
any biogas. The one biogas system still producing biogas in Pasir Angling (PA3) was doing
so at a very low rate. The two biogas systems in Pengkolan were still functional. Having
more than 70 % of the installed digesters not working after such a short time is of course
not acceptable and also problematic for the perception of the technology. Technical
problems with the designs, a lack of local capacity to maintain and operate the systems
and a lack of community involvement have all contributed to this unfortunate outcome.
Both the vertical digester design (such as PA2) and the shorter horizontal design (such as
PA3, Ci2 and Ci3) seem to be problematic. In the case of the vertical digesters the flow of
slurry does not seem to function well. Sedimentation occurs and the constructed stirrers
are not able to solve the issue. The pressure in the digester is not large enough to push the
slurry out of the digester. In the case of the shorter horizontal design the problems
5 Based on email conversations with Any Sulistyowati and David Sutasurya from 2009-12-19 to 2010-02-15
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identified in section 6.2.1 seemed to have been realized for all installed digesters of this
design. Other factors (primarily when the systems are installed), such as the location (and
height) of the inlet and outlet pipes may also be significant. These outcomes may mean
that these two designs are much less suitable than previously laid out in chapters 5, 6 and
7. However, before we dismiss them, there are a number of other factors that could be
contributing just as much (or more) to the problems observed.
There is an apparent lack of local capacity and understanding of both how to operate and
maintain the systems. Holes in the digester plastic from animals, is one of the major
reasons that so many of the biogas systems have failed. This problem was quite quickly
understood by the users and preemptive measures have been taken to protect the
digesters. A bit trickier is acquiring an understanding of the biogas process and the
measures needed to maintain a high production rate. As was shown in section 6.2.1, a
sufficient amount of slurry needs to be added to the digester, preferably on a daily basis. A
daily loading of the digester will lead to much more stable production rates and will also
decrease the chance of a collapse of the biogas production process.
In some cases, a low participation of the community in the construction and installation of
the biogas systems may also be a contributing factor to the lack of local capacity which
was mentioned in the previous paragraph – and therefore also contributing to the
dysfunction of the biogas systems.
8.2.2 Moving Ahead
In response to the multiple problems with the biogas systems, the biogas team has created
a new agreement with the involved communities that says that the biogas team will:
fix the broken digesters as long as the community is involved and engaged in the
process (including a person willing to become a local biogas technician)
replace the vertical digesters and horizontal, shorter digesters with digesters of the
standard design - if the designs are proved to not be functional. The problem will
be analyzed in cooperation with the community.
give priority to the users that have managed to make payments for the
construction and the installation of the biogas system, on time.
The communities accepted the agreement and the process of repairing existing digesters is
underway in both Pasir Angling and Cireyod. More digesters will be installed, but not
before the existing ones are fixed and working.
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8.2.3 Further Needed Research
In addition to the agreement constructed by the biogas team, further research could help
to avoid further problems for the biogas initiative in Lembang as well as contribute to the
fairly limited literature on the implementation of family-sized, plug-flow, polyethylene
biogas systems in rural areas of tropical regions such as Java. A few suggestions for future
research in Lembang:
Redo the experiment on digester dimension (see section 5.1.1) but with a much
longer experimental period to see if production is maintained after several months
(experiments seemed to indicate that the production rate of the vertical digester
(A6) and the shorter horizontal digester (A5) was falling after about a month and
the observations in the field also indicate problems with these designs).
Investigate the effect of stirring on slurry flow and biogas production (different
designs, which designs and dimensions of digesters require stirrers? Frequency and
amount of stirring).
Design a new experiment with connecting digesters, maybe just two and make
connections large and the slope between the digesters a little larger. Investigate if
scum formation can be avoided and flow maintained.
Further gas flow experiments. Design an experiment using larger pipe diameters to
see if there still is a big difference in distribution when the pipe lengths are varied.
Other relevant and interesting experiments that could be done but that not are
directly connected to the scope of this paper include:
Reusing effluent (at least the ”liquid part” of it) since water is scarce at times.
Further polyethylene strength tests.
Varying the retention time and loading rate (frequency and amount) and
investigating it‟s effect on biogas production.
Seasonal variations (do the same one month long experiments 4 times in a year)
Using different feed (e.g. rumput, tree-leaves, rice stems etc.) for the cows.
How does this affect manure/biogas quality (TS, CH4-content etc.)? How does it
affect biogas production rates?
Experiments with fertilizer (different drying times, how much nutrition in
effluent (access to lab probably required). This is important since there is a
large need for fertilizer in Lembang and much is imported at the moment.
Besides this research educational tools could also be of great benefit to the biogas
initiative. As has been mentioned before, simple ways (e.g. through games based on
systems thinking)6 that can be used to improve the understanding of the characteristics of
a complex process such as anaerobic digestion, and how to properly operate and maintain
it, are very much needed. Any further efforts should be concentrated on developing such
tools.
6 For an excellent collection of such games, see Booth-Sweeney & Meadows (2010).
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9. Conclusions
In Lembang, a farming community on western Java, family-sized, plug-flow, polyethylene
biogas systems fed with cow dung, are being used as an integrated solution to issues
related to energy, agriculture and waste management. Through simple, on-farm research
and observation, a number of key problems have been addressed and improvements made
to the design. Due to the large supply of cow dung in the area, and the potential to spread
the benefits of the technology beyond the homes of dairy farmers, the feasibility of
developing a communal, polyethylene biogas system for several households, has been
investigated. Experiments on small model-digesters were combined with observations of
full-scale biogas systems in use. Measurement equipment and techniques were
constructed and developed, in order to measure biogas production and other relevant
process parameters. Results indicate that a communal system can be an appropriate
choice, but only under a certain set of circumstances.
9.1 Polyethylene Biogas Systems in the Indonesian Rural Setting
Through the work with this Master‟s thesis a number of key insights where gained about
the construction and design of polyethylene plastic biogas systems, in terms of their
appropriateness and functionality in the Indonesian rural setting:
Alternative digester dimensions can seem attractive due to their at first, perceived,
higher space efficiency. In the long run however, they seem to be much less
functional compared to the standard, horizontal design.
The average biogas production rate recorded in the experiments in Cicalung, are
higher than in the reviewed literature. Insulating the digesters with rice husks
increases the biogas production rate further.
In a three-person household, the biogas stove is on average used a little more than
2 hours a day and mostly in the mornings and afternoons. The biogas stove uses
around 330-380 l /hour. For a family of three, dung from 2-3 cows is therefore
needed.
Digester loading frequency has a somewhat deceptive effect on the biogas
production rate of a system. In the short run, the total production rate is the same
for weekly and daily loading. However, in the long run and too ensure a steady
supply of biogas, daily loading is much to prefer compared to weekly loading.
Checking for leaks in the digester and fixing them is an arduous task and it is
highly recommended that this is done before installation.
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9.2 Communal Biogas Systems in the Indonesian Rural Setting
Results indicate that a well functioning communal biogas system with polyethylene
digesters, can and should be developed. However there are some major issues that need to
be overcome. First and foremost, there is the issue of fairly distributing the gas to the
connected households. This is especially crucial when the biogas production rate of the
system is low compared to the demand of the households. Results indicate that manual
valves are the most appropriate for regulating gas flow. The size of the digester does not
seem to affect the efficiency of the system (whereas dimension does, as was mentioned
above). For communal systems it is therefore recommended that the amount of digesters
are minimized (and their size maximized) as this is more space- and cost-efficient than
building many small ones. Furthermore, there is the issue of land availability. In many
villages it is difficult to find a space large enough for a communal system as well as owners
who are willing to give up their land for communal purposes. This issue seems to be more
prominent in more urbanized areas. Communal systems may therefore be easier to
promote and diffuse in more rural areas. Lastly, it should be noted that connecting the
slurry flow between digesters does not seem to be a good idea.
9.3 Communal or Single-Family?
The decision of whether a communal or a single-family system is to be installed, must be
based on an evaluation of the local conditions and how they relate to the requirements for
installing, operating and maintaining the respective systems. The difference between a
communal system and a single-family system in terms of required inputs (cow dung,
water, labour, space and financial) can be approximated in order to make a decision easier.
In general, communal systems require less labour, less available space and are more cost
efficient but require the same amount of dung and water per person as single-family
systems. Gas flow management is obviously more difficult for a communal system as the
manual valves need to be adjusted so that all households‟ biogas demands are met.
Balancing biogas production and demand in a communal biogas systems, is not an easy
task. Several households, with different cooking routines lead to higher variability and
uncertainty in biogas demand. Increasing digester size and the gas buffer may be a
solution to this problem but this requires more inputs (of dung, water labour, space and
finances). The question of who will manage the gas flow as well as the slurry flow (mainly
the loading and emptying of the digesters) is another issue for communal systems.
Besides decreasing the costs, required labour input and the space required, a communal
biogas system may potentially also increase the social capital, social equity and
cooperation in a village. However, biogas shortages may be more frequent and have larger
implications in a communal system. If the loading rate is too low or infrequent, it will
create a shortage of biogas and lead to problems of fairly distributing the scarce biogas
resource among the households. This could potentially lead to conflicts and a decrease in
social capital and trust.
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9.4 Potential for Diffusion of Biogas in Lembang
The many challenges facing the rural population in and around Lembang are
interconnected and complex in nature. The issue of energy security and energy systems
must be looked upon in a broad context that includes issues of waste management,
agricultural inputs, pollution, forest management, poverty and current socio-economic
structures.
The economic situation of both dairy farmers and vegetable farmers is unstable and
vulnerable to changes in the global economy. Since sufficient available funds to finance
the construction and installation of a biogas system, often are lacking, a system of
revolving funding has been used in this project. This can help to facilitate the diffusion of
the technology. The potential for diffusion of biogas in the Lembang area can only be
estimated if it is set in its rightful context and compared to competing energy technologies
for cooking (kerosene, liquid petroleum gas and fuel-wood). A comparison should include
factors such as cost, subsidies, reliability, user friendliness, security and other benefits
(such as free fertilizer, cleaner burning, less time consuming maintenance etc.).
The potential for diffusing biogas technology in Lembang also needs to be seen in the light
of the carrying capacity of the region in terms of dairy farming. The area is already
heavily stressed and could probably not support any significant amount of additional
cows. Furthermore, calculations show that only about 10 % of the current cooking needs
in the Lembang area could be met if all cow dung was used to produce biogas. Hence, a
future energy system for cooking will have to consist of much more than just biogas.
In this paper, the scale of biogas technology discussed is mainly from single-family to
small communal systems (2-4 households). It should be noted that other organisations and
companies have shown interest in developing larger scale biogas systems in the Lembang
area. In comparing advantages and disadvantages of large- and small scale systems it is
hoped that consideration will be given to the technology‟s ability to solve issues of waste,
sanitation and energy but also to its ability to alleviate poverty, empower farmers as well
as strengthen the communities‟ resilience and cooperative nature.
For small-scale polyethylene biogas systems, two different diffusion models have been
presented in this paper. The “cash economy” model promotes an integration of the biogas
initiative with business as usual scenarios – basically putting the technology on the
market. The “alternative” model aims to create a non-cash economy system which ensures
that the introduction of biogas technology will improve social equity and create closed
material-cycles in the region. There are advantages and risks with both models and
choosing one does not necessarily discredit the value of the other. They do not necessarily
have to be exclusive and there may be advantages (but also risks) of combining them.
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9.5 Recent Developments and a Look Ahead
Unfortunately, ten months after the biogas system installations in Pasir Angling, Cireyod
and Pengkolan commenced, many of the digesters had stopped working. Many of the
issues and risks identified through the research for this paper ended up being realized.
Care should be taken when using the results in chapter 5, 6 and 7. The experimental
periods in chapter 5 should be made much longer and many of the experiments could be
refined in other ways. The observations made in Chapter 6 could also be complemented
by continued investigation into the problems that can arise when the technology is
introduced into a community. There is still much to learn about these issues and much
research still to be done. An interdisciplinary and participatory approach is highly
recommended in order to grasp the complex nature of these issues and make the results of
the research useful to the participating communities. Developing educational tools (e.g.
games based on systems thinking) that aim to increase the understanding of the process of
biogas production, and how to manage it, is also highly encouraged.
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Acknowledgements
This Master‟s thesis project is the result of a large number of people‟s generous and
unselfish contributions and support– both in Indonesia and Sweden.
First of all, I would like to deeply thank Any Sulistyowati for inspiring me and inviting
me to come to Indonesia. Her warm welcome and flawless coordination of my stay in
Bandung was also very much appreciated, as have been the continuing discussions and
comments on my thesis long after my return to Sweden. David Sutasurya at YPBB was
instrumental in helping me to organize the research and focus on relevant and useful areas
of inquiry. He also made sure that I was very well incorporated into the biogas team as
well as other YPBB activities.
Bambang Boedi Cahyono (Yono) and Wawa Wahyudi were my two closest colleagues,
mentors and friends in the field. Without their great support, knowledge, high spirits and
incredibly innovative solutions to problems we were faced with, this thesis would have
been significantly more difficult, if not impossible, to complete. Many of the staff and
volunteers at YPBB were also very helpful and instrumental in making my time in
Indonesia as good as it possibly could have been. I wish to extend my great thanks to
Gundil Gundala, Yulia Nadya, Rima Putri Agustina, Jessi Fam, Kandi Sekarwulan, Ade
Dan Dom and Dody Alfajr for translation help, organizing trips, helping out with
fieldwork, great company and many more things that unfortunately do not fit onto this
page. I would like to thank PESAT staff for their great work with community
development and for letting me take part in several village meetings. In Cicalung - besides
Wawa and Yono – Dede Mulyana, Wawan Sumpena, Ano, Aep Saepuloh, Dadan and
Anang Kmot were very helpful (and patient) in introducing me to the construction,
installation and maintenance of polyethylene biogas systems. I would also like to thank
Bapak Atang for providing our digesters with cow dung. I have a hard time finding words
to express my gratitude to Wawa and his family, who took me into their home and made
me a part of their family. I would also like to thank Ingrid Somorjai whom I unfortunately
did not get to know until my last few weeks in Indonesia. To all my Indonesian friends:
Terima Kasih. Hatur Nuhun.
The fieldwork for this Master‟s Thesis was made possible by the financial support of The
Swedish International Development Cooperation Agency (SIDA) under their program for
Minor Field Studies (MFS). I would like to thank SLU Omvärld at the Swedish University
of Agricultural Sciences (SLU) for their choice to support my project proposal. The
Department of Energy and Technology at SLU generously accepted to provide me with
supervision. A great many thanks to my supervisor Sven Smårs who provided me with key
contacts, crucial advice and measuring equipment prior to my departure to Indonesia, and
who has remained supportive throughout the work with this Master‟s Thesis. I would also
like to extend my thanks to the head of the department, Professor Per-Anders Hansson,
who in an early stage helped me to improve my project proposal and to narrow the scope
of the research questions. My faculty examiner, Professor Kjell Aleklett, has shown great
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support and interest from the very start. I am very grateful to have had an examiner who
has shown such genuine interest in my work and asked me to report back to his research
group, Global Energy Systems, a number of times throughout the work with the project.
A great many thanks to Kjell and his colleagues in the research group. A great many
thanks also to my fellow student Caroline Nielsen, who has read my thesis a number of
times and given me valuable feedback.
During my preparation before leaving for Indonesia, Lena Rhode at the Swedish Institute
of Agricultural and Environmental Engineering (JTI) and Johnny Ascue at the
Department of Microbiology at SLU generously provided me with simple measuring
equipment that proved to be very useful for my fieldwork in Indonesia. Mathias
Gustafsson and Thomas Reg Preston provided me with very useful and relevant advice on
literature as well as feedback on my project proposal.
Lastly, I would like to thank Alan AtKisson, Junko Edahiro and Riichiro Oda for their
support and friendship. Alan also for introducing me to Any and Junko and Riichiro for
supporting and believing in the biogas initiative. As with many of the above mentioned
people, this Master‟s Thesis would not have been possible were it not for them.
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Glossary
Ammonia (mineralized nitrogen, NH3) concentration in slurry: The concentration of
ammonia is a good indicator (among several others) of the fertilizer qualities of slurry.
Due to plants‟ ability to directly make use of Ammonia it is also known as plant-available
nitrogen. See also Fertilizer Value.
Anaerobic digestion: Phenomena by which organic matter is transformed into methane
(or another reduced organic compound, e.g. ethanol or lactic acid) in the absence of air
(oxygen). See Methanogenesis.
Anticipated biogas demand: The expected amount of biogas to be consumed in a
household (or households) connected to a biogas system, at different times of the
day/week/year. The anticipated biogas demand is important to approximate when sizing
and constructing a biogas system.
Biogas digester: See section 3.3.2 for description.
Biogas flow: Is the amount of biogas to pass by a certain point in the gas pipe per unit time
(here in m3/hour).
Biogas production rate (BPR): Is here defined as the amount of biogas (measured in litres)
that a biogas system produces every hour.
Biogas stove: See section 3.3.2 for description.
Biogas stove efficiency: Is here defined as the amount of biogas used by the stove each
hour. This then has to be compared to the work actually performed during this amount of
time (e.g. heating a pot of water of known volume from 25 to 100°C) in order to eliminate
the unknown variable of how the biogas stove is actually used. See also section 6.4.1.
Communal biogas system: Is here defined as a system that provides more than one
household with biogas for cooking.
C/N ratio: Mass ratio of carbon to nitrogen in a material.
Daily biogas production rate (BPRd): The amount of biogas (measured in litres) that a
biogas system produces daily.
Daily input volume of slurry (Vi): The volume of influent slurry which is loaded into a
digester each day, measured in litres.
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Digester stirrer: A stirring device that is constructed and installed in a way so that the
slurry in a digester can be mixed . The inclusion of this device was beleived to be
especially important in vertical digesters and horizontal digesters of the shorter kind.
Effluent: Waste-end product, usually liquid, of an industrial or microbial process. Any
liquid discharged from a source into the environment.
Einhorn fermentation saccharometer: Is a instrument that can be used to measure the
methane content of biogas. A solution of lye (NaOH) and a syringe is also needed. See
section 4.2.4.
Experimental period: The total number of days that an experiment is run.
Fertilizer value (TKN, COD and NH3-concentration): Besides Ammonia concentration,
Total Kjeldahl Nitrogen (TKN) and Chemical Oxygen Demand (COD) are two useful
indicators of the fertilizer value of a material. TKN is a the total nitrogen content exluding
nitrates and COD is the mass of oxygen needed to oxidise one unit material using a
chemical process.
Fixed dome digester design: A digester design which usually is constructed out of
masonry, concrete or ferro-cement and buried in the ground. The digester volume is
constant leading to a gas pressure that is dependent on the production and consumption
levels of the system. The design is particularly common in China and Nepal.
Floating drum digester design: A design with a cylindrical or dome-shaped digester (out of
brick, concrete or quarry-stone) and a moving, floating gas-holder, or drum (out of steel
sheets). The gas-holder floats either directly in the fermenting slurry or in a separate
water jacket. The design is particularly common in India.
Four key technical and operational issues: Available space and alternative uses of the land,
Slurry management, Gas flow management and Balancing biogas production and demand were the four most important technical and operational issues identified by the biogas
project team when it comes to improving single-family systems as well as developing a
communal biogas system.
Friction constant of pipe material: Is a constant which varies depending on pipe material
and is used to calculate the pressure drop in a pipe. See section 5.3.2.3 for further
explanation.
Gas holder: See section 3.3.2 for description.
Gas pipes: See section 3.3.2 for description.
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Hydrometer: Is a instrument that measures a liquid„s density - In our case the slurry used
in a biogas system. See section 4.2.3.
Inlet bucket with stirrer: See section 3.3.2 for description.
Influent: Material, usually a liquid, which enters a process, such as anaerobic digestion.
Liquid volume of digester (Vl): The volume of slurry in a digester, measured in litres.
Loading rate (LR): Is here defined as the amount of substrate loaded daily (measured in kg
TS/day) per liquid digester volume (measured in m3).
Manometer: Is a instrument that measures pressure in a gas or liquid in relation to the
atmospheric pressure. See section 6.3.1.
Manual valve: A valve that can and must be operated manually.
Measurement period: The number of days that measurements are conducted.
Mesophilic: That which takes place at temperatures ranging from 20 and 40°C. Mesophilic
is descriptive of (biological) processes taking place at room temperature or slightly above,
say between 25 and 40°C. Mesophilic methanogenesis occurs optimally at 35°C.
Methane (CH4) content of gas: The percentage of methane in the biogas is a good
indication of the quality of the gas since it is through the combustion of methane to
carbon dioxide that heat is produced.
Methanogen: Micro-organism able to produce methane from organic matter in the
absence of air. See Methanogenesis.
Methanogenesis: A process by which organic matter is transformed into methane by
micro-organisms in the absence of air. When considered sensu-stricto, methanogenesis is
only the final step of the global process of anaerobic digestion during which acetate,
dihydrogen and bicarbonate are transformed into methane, carbon dioxide and water.
Because methane is produced, the process is called methanogenic. Methanogenesis is
mediated be archaea called methanogens.
Mika kardus: A semi-hard transparent plastic material used to create a light-weight top for
a water displacement apparatus.
Mulsa: A plastic film used in agriculture to retain heat and moisture in the soil around
crops
122
Nitrogen meter: Is a instrument that measures the concentration of plant-available
nitrogen in wet and dry manure. See section 4.2.5.
Openness of manual valve: Is here defined as the extent to which the manual valve is open
and calculated as the ratio between the current area of the hole in the valve and the area
of the hole when the manual valve is fully open.
Plug-flow: Characterises a continuous process in the digester, where slurry moves from
end to the other and where plugs are used to regulate when the digester is loaded and
emptied.
Polytethylene biogas systems: Is here defined as a system with a soft polyehtylene plastic
digester as well as the additional parts defined in section 3.3.2.
Polytethylene digester: A cylinder-shaped digester made of soft polyethylene plastic.
Polytethylene tubular digester: A horizontal, long, cylinder-shaped digester made of soft
polyethylene plastic.
Pressure drop in gas pipes: Due to friction, the pressure of a gas decreases as it moves
along in a pipe. The magnitude of the pressure drop depends on a number of parameters
including gas flow, pipe diameter, pipe length and pipe material. See section 5.3.2.3 for
further explanation.
Pressure valve: See Section 3.3.4 for description.
Process efficiency (PE): Is here defined as the amount of biogas (measured in litres)
produced per unit influent (measured in kg TS).
Process temperature: the average temperature of the slurry in the digester.
Retention time (RT): In a continuously fed, plug-flow digester, the RT is defined as the
average amount of days that a unit of substrate will remain in the digester.
Safety valve: See section 3.3.2 for description.
Saung: A bamboo structure covered with transparent polyethylene plastic.
Scum formation: A hard layer that can form on the top of the slurry which can hinder the
biogas that is formed to escape from the substrate.
Single-family biogas system: Is a system that provides only one household with biogas for
cooking.
123
Slurry: A liquid mixed with a large proportion of solid material. In our case, water mixed
with cow dung.
Space efficiency: Is a parameter that is used in this thesis to relate the biogas production
rate of a system to the amout of space used. It is here defined as the ratio between the
daily average biogas production and the area required by the digester.
Stabilisation period: The number of days after innoculation required for a biogas system to
reach a stabile biogas production rate.
Starter: Is already digested slurry which is used to get the process of anaerobic digestion
going.
Substrate: Starting material of a biological (microbial) process. Also called feedstock.
System efficiency (SE): Is here defined as the ratio of the amount of biogas produced daily
(BPRd) and the digester's liquid volume (Vl).
Technically feasible biogas production: The maximum amount of biogas that can be
produced from a biogas system, given certain conditions which are constant (temperature,
retention time, loading frequency). The technically feasible biogas production is crucial to
know when sizing a biogas system, so that it can be compared to the anticipated biogas
demand.
Total volume of digester (Vt): Total volume of digester, measured in litres.
TS-content: The Total Solids (TS) content of the substrate is the mass which remains
when the water content is removed (by heating). Also known as dry matter content.
Tubular plastic digester: A horizontal, long, cylinder-shaped digester made of either soft
or hard plastic.
Vertical digester: A digester with a vertical orientation as a opposed to the standard
horizontal one.
VS-content: The Volatile Solids (VS) content of the substrate is the mass which is
removed when the dry matter is heated (from 105°C to 550°C) and is essentially equal to
the organic matter content.
Water column (WC): Is a unit of pressure which is measured by the height (often in cm)
of a maintained and contained column of air (or in our case biogas) which is immersed in
a container of water. The pressure valves used in this thesis are constructed in a way that
the water column is clearly visible.
124
Water displacement technique: A relatively simple way to measure gas production. The
basic principle is to let biogas fill a light-weight bucket of known volume, turned up-side-
down and floating in a larger, water-filled bucket. As more biogas enters the light-weight
bucket, it rises, and the volume of the produced biogas per unit time can be calculated
(since the volume of the light-weight bucket is known).
125
References
Aleklett, K., Höök, M., Jakobsson, K., Lardelli, M., Snowden, S. & Söderbergh, B., 2010.
The Peak of the Oil age – analyzing the world oil production Reference Scenario in World
Energy Outlook 2008. Energy Policy, 38(3), pp.1398-1414.
An, B.X., Rodriguez, L., Sarwatt, S.V., Preston, T.R. & Dolberg, F., 1997. Installation and
performance of low-cost polyethylene tube biodigesters on small scale farms. World Animal Review. [Online] Available at: http://www.fao.org/docrep/w5256t/w5256t06.htm
[Accessed 6 December 2008].
An, B.X., 2002. Biogas technology in developing countries: Vietnam case study.
Proceedings Biodigester Workshop March 2002. [Online] Available at:
http://www.mekarn.org/procbiod/an.htm [Accessed 12 November 2008].
Badan Pusat Statistik (BPS), 2007. National Socio-Economic Survey. [Online] Available at:
http://dds.bps.go.id/eng/index.php?news=625 [Accessed 13 May 2010].
Booth Sweeney, L. & Meadows, D., 2010. The Systems Thinking Playbook - Exercises to Stretch and Build Learning and Systems Thinking Capabilities. White River Junction:
Chelsea Green Publishing Company.
Botero, R. & Preston, T.R., 1986. Low-cost biodigester for production of fuel and fertilizer from manure. Cali: CIPAV. (unpublished manuscript, in Spanish).
Cahyono, B.B., 2009. Dicussion about dairy farming in Lembang. [Conversation] (Personal
communication, 7 March 2009).
Cortsen, L., Lassen, M. & Nielsen, H.K., 1997. Evaluation of small scale biogas digesters in Turiani, Nronga and Amani, Tanzania. Copenhagen: DSR.
Daly, H., 1997. Beyond Growth: The Economics of Sustainable Development. Boston:
Beacon Press.
Ek, F., 2007. Produktion av Biogas på Gården. Helsingfors: ProAgria Svenska
lantbrukssällskapets förbund.
Gustavsson, M., 2000. Biogas Technology – Solution in Search of Its problem: A Study of Small-Scale Rural Technology Introduction and Integration. Ph. Lic. Thesis, Department
of Interdisciplinary Studies, Human Ecology Section, Göteborg University.
Hansen, J. 2009. Storms of My Grandchildren: The Truth About the Coming Climate Catastrophe and Our Last Chance to Save Humanity. New York: Bloomsbury USA.
126
Hardin, G., 1968. The Tragedy of the Commons. Science, 162(3859), pp. 1243-1248.
Heinberg, R., 2007. Peak Everything – Waking Up to the Century of Decline in Earth„s Resources. Forest Row: Clairview.
Jackson, T., 2009. Prosperity without Growth? – The transition to a sustainable economy.
[pdf] London: Sustainable Development Commission Reports & Papers. Available at:
http://www.sd-commission.org.uk/publications.php?id=914 [Accessed 8 May 2010].
Kossman, W. & Pönitz, U., 1999a. Biogas Digest Volume 1: Biogas Basics. Information and
Advisory Service on Appropriate Technology and GTZ.
Kossman, W. & Pönitz U., 1999b. Biogas Digest Volume 2, Biogas – Application and Product Development. Eschborn: Information and Advisory Service on Appropriate
Technology (GTZ project).
Kossman, W. and Pönitz, U., 1999c. Biogas Digest Volume 4, Biogas – Country Reports. Eschborn: Information and Advisory Service on Appropriate Technology (GTZ project).
Kounnavonga B., 2008. Effect of mixing on gas production in plug flow tubular plastic biodigesters. MEKARN MSc Miniproject. [Online] Available at:
http://www.mekarn.org/msc2008-10/miniprojects/minpro/boun.htm [Accessed December
6 2008].
Lonely Planet, 2007. Indonesia. 8th ed. London: Lonely Planet Publications Pty Ltd.
Meadows, D.H., Randers, J., Meadows, D.L. & Behrens, W.W., 1972. The Limits to growth: A report for the Club of Rome's Project on the Predicament of Mankind. New
York: Universe Books.
Meadows, D.H., Randers, J. & Meadows, D.L., 2004. Limits to Growth: The 30-Year Update. White River Jct.: Chelsea Green Publishing.
Nyns, E-J., 1985 Biomethanation Processes. In W. Schönborn, ed. Biotechnology - Volume 8 Microbial degredations. Weinheim:VCH Verlagsgesellschaft, 1986, Chapter 5.
Nörretranders, T., 1994. Världen Växer – En bok om slumpens historia.
Stockholm:Bonnier Alba AB.
Olstrom, E., 1990. Governing the Commons – The Evolution of Institutions for Collective Action. Cambridge: Cambridge University Press.
127
Pound, B., Bordas, F. & Preston, T.R., 1981. Characteristics of production and function of
a 15 cubic metre Red-Mud PVC biogas digester. Tropical Animal Production 6, pp. 146-
153.
Rockström, J., Steffen, W., Noone, K., Persson, Å., Chapin, F.S., Lambin, III, E., Lenton, T.
M., Scheffer, M., Folke, C., Schellnhuber, H., Nykvist, B., De Wit, C. A., Hughes, T., van
der Leeuw, S., Rodhe, H., Sörlin, S., Snyder, P. K., Costanza, R., Svedin, U., Falkenmark,
M., Karlberg, L., Corell, R. W., Fabry, V. J., Hansen, J., Walker, B., Liverman, D.,
Richardson, K., Crutzen, P. & Foley, J. 2009. Planetary Boundaries: Exploring the Safe
Operating Space for Humanity. Ecology and Society 14(2): 32.
Rogers, E.M., 2003. Diffusion of Innovations. 5th ed. New York: Free Press.
Sasse, L., 1988. Biogas Plants. Eschborn: German Appropriate Technology Exchange
(GATE).
Smårs, S., 2009. Dicussion about C/N ratio and biogas production. [Conversation]
(Personal communication, 25 September 2009).
Sulistyowati A. & Sutasurya, D., 2008. Challenges for Supplying Energy for The Poor – Lessons from Indonesia. [Unpublished paper]
Tainter, J. A., Allen, T. F. H., Little, A. & Hoekstra, T. W., 2003. Resource transitions and
energy gain: contexts of organization. Conservation Ecology, 7(3): 4, [Online] Available at:
http://www.consecol.org/vol7/iss3/art4/ [Accessed 9 May 2010].
Thu Hang, B.P., 2003. Effect of dimension of plastic biodigester (width:length ratio) on gas
production and composition of effluent. Livestock Research for Rural Development 15(10):2003. [Online] Available at: http://www.mekarn.org/msc2003-
05/miniprojects/webpage/hangctu.htm
[Accessed 25 January 2008].
Thy, S., 2003. Management and utilization of biodigesters in integrated farming systems.
MSc Thesis, MEKARN-SLU. [Online] Available at: http://www.mekarn.org/msc2001-
03/theses03/santhlitrevapr27.htm [Accessed 27 January 2008].
Thy, S, Preston, T.R. & Ly, J., 2003. Effect of retention time on gas production and
fertilizer value of biodigester effluent. Livestock Research for Rural Development 15(7):
2003. [Online] Available at: http://www.cipav.org/lrrd/lrrd15/7/sant157.htm [Accessed 2
December 2008].
128
Thy, S., Buntha, P.,Vanvuth, T., Preston, T.R., Khang, D.N., Soukanh, K., Phouthone, B.,
Mikled, C. & Sopharoek, N., 2005. Effect of length: diameter ratio in polyehtylene
biodigesters on gas production and effluent composition. Livestock Research for Rural Development 17(11): 2005. [Online] Available at:
http://www.lrrd.org/lrrd17/11/sant17120.htm [Accessed 12 November 2008].
United Nations, 1984. Updated Guidebook on Biogas Development – Energy Resources Development Series No. 27. New York:United Nations.
United Nations Department of Economic and Social Affairs (UNDESA), 2009. A Global Green New Deal for climate, energy and development. [Online] Available at:
http://www.un.org/esa/dsd/resources/res_pdfs/publications/sdt_cc/cc_global_green_new_
deal.pdf [Accessed 9 May 2010].
Van Chinh, B., Viet Ly, L., Huu Tao, N. & Giang Phuc, N., 2002. Biogas technology transfer in small scale farms in Northern provinces of Vietnam. Proceedings Biodigester
Workshop March 2002. [Online] Available at:
http://www.mekarn.org/procbiod/chinh.htm [Accessed 12 November 2008].
Wahyudi, W, 2009. Dicussion about dairy farming in Lembang. [Conversation] (Personal
communication, 10 March 2009).
Wellinger, A., 1999. Process design of agricultural digesters. Ettenhausen: Nova Energie
GmbH. [Online] Available at:
http://homepage2.nifty.com/biogas/cnt/refdoc/whrefdoc/d14prdgn.pdf
[Accessed 12 November 2008].
Werner, U., Stöhr, U. & Hees, N., 1989. Biogas plants in animal husbandry. Eschborn:
German Appropriate Technology Exchange (GATE).
Örtenblad, H., 2000. Anaerobic Digestion: Making Energy and solving modern waste problems. AD-NETT Report.
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