Upload
phunghanh
View
227
Download
1
Embed Size (px)
Citation preview
VISVESVARAYA TECHNOLOGICAL UNIVERSITY
“Jnana Sangam”, Belgaum-590018
Student Project Programme- 39S_BE_0239
A Project report on
“OPTIMISATION OF FOOD-WASTE BASED BIOGAS DIGESTER
AND ITS IMPLEMENTATION IN RURAL AREAS”
Submitted to the Visvesvaraya Technological University, Belgaum.
In partial fulfilment for the award of the degree of
BACHELOR OF ENGINEERING IN CIVIL ENGINEERING
For the Academic year- 2015-2016
Submitted By
MR. BLESSON USN: 4SF12CV020
MR. NIRMITH ASHOK BANGERA USN: 4SF13CV027
MR. KOUSHIK M USN: 4SF13CV056
MR. ARTHIK RAI USN: 4SF13CV022
SPP coordinator Project Guides
Dr. Manjappa S. Dr. Prasanna Kumar. C Ms. Rashmishree K. N.
Director, Research and
Consultancy
Sahyadri College of Engineering
and Management
Associate Professor
Department of Electronic
and Communication
Engineering
Assistant Professor
Department of Civil
Engineering
Sahyadri College of Engineering and Management
Adyar, Mangalore-575007
SAHYADRI COLLEGE OF ENGINEERING AND MANAGEMENT
Adyar, Mangalore-575007
DEPARTMENT OF CIVIL ENGINEERING
CERTIFICATE
Certified that the project work entitled “OPTIMISATION OF FOODWASTE BASED
BIOGAS DIGESTER AND ITS IMPLEMENTATION IN RURAL AREAS” carried out
by MR. BLESSON S(4SF12CV020), MR. NIRMITH ASHOK
BANGERA(4SF13CV027), MR KOUSHIK M(4SF13CV056) and MR. ARTHIK
RAI(4SF13CV022) are bonafide students of Department of Civil Engineering,
Sahyadri College of Engineering and Management in partial fulfilment for the award of
Bachelor of Engineering in Civil Engineering of the Visvesvaraya Technological
University, Belgaum during the year 2015-2016. It is certified that all correction/suggestions
indicated for Internal Assessment have been incorporated in the Report deposited in the
department library. The project report has been approved as it satisfies the academic
requirements in respect of Project work prescribed for the said Degree.
Prof. Purushothama C T Dr. U M Bhushi
Head of the Dept. Principal
Dr. Prasanna Kumar. C Ms. Rashmishree. K.N
Project guide Project guide
OPTIMISATION OF BIOGAS PRODUCTION BY THREE STAGED DIGESTER
ACKNOWLEDGEMENT
The gratified feeling that we share at the completion of our project work is the
courtesy of those who were involved in our efforts to bring out a successful project
“OPTIMISATION OF FOODWASTE BASED BIOGAS DIGESTER AND
ITS IMPLEMENTATION IN RURAL AREAS”.
We salute our esteemed institution Sahyadri, Adyar which will shape us to
effective engineers of tomorrow. We express our deep sense of gratitude to
department of CIVIL Engineering, which is providing us a homely atmosphere to
develop our all-around skills.
We are grateful to Dr. U M Bhushi, Principal, SCEM, for having extended all
facilities to make this project a grand success.
Our sincere thanks to our respected SPP Coordinator Dr. S Manjappa, Director of
Research and Consultancy, SCEM for his valuable suggestions and providing all
facilities to carry out the project.
We are also grateful to Prof. Purushothama C T, Head of the department, Civil
engineering, and Prof. Umesh S, head of the department, M.Tech Civil, SCEM for
their constant support throughout the project.
We are grateful to Dr. Prasanna Kumar. C, Associate Professor, Department of
E&C Engineering and Ms. Rashmishree K. N., Department of Civil Engineering,
SCEM for their co-operation and guidance at each stage of the project.
Our sincere gratitude to Dr. Gautham P Jeppu, for his guidance and support
throughout the project. His encouragement and inspiration was guiding source
throughout the project work. We are also thankful to Dr. Savitha M, Ms. Sharadha,
(Department of Chemistry, SCEM), Mrs. Ranjini(Headmistress, Govt. School,
Nekkilady), Mrs. Sevrin(Asst. Teacher, Govt. School, Nekkilady) and Edison
Project Team for helping us throughout the project.
Finally we are ever grateful to our parents, teaching and non-
teaching staff members of civil engineering department and
friends for their encouragement, suggestions and help.
OPTIMISATION OF BIOGAS PRODUCTION BY THREE STAGED DIGESTER
Sahyadri College of Engineering and Management Page 2
INDEX
Chapters Title Page No. 1. Introduction 3-5 2. Literature Review 6-8
3. Biogas 9-12 4. Design of Digester 13-16 5. Principles for the production of biogas 17-20 6. Tests, observation and results 21-23
7. Conclusion 24 8. Scope for future work 25 9. References 26-27
OPTIMISATION OF BIOGAS PRODUCTION BY THREE STAGED DIGESTER
Sahyadri College of Engineering and Management Page 3
CHAPTER-1
INTRODUCTION
1.1 GENERAL
Due to scarcity of supply of petroleum and coal and its threats by emissions
has led to research throughout the world in different corners to get access to the
new sources of energy, like renewable energy resources. Solar energy, wind
energy, different thermal and hydro sources of energy, biogas etc. are all renewable
energy resources. But, biogas is distinct from other renewable energies because of
its characteristics of using, controlling and collecting organic wastes and at the
same time producing fertilizer and water for use in agricultural irrigation. Biogas
neither has any geographical limitations nor does it require any advanced
technology for producing energy. It is very simple to use and apply.
A biogas plant is an anaerobic digester that produces biogas from animal,
food waste or plant waste. Biogas can provide a clean, easily controlled source of
renewable energy from organic waste materials for a small labour input, replacing
firewood or fossil fuels (which are becoming more expensive as supply falls
behind demand). Biogas is generated when bacteria degrade biological material in
the absence of oxygen, in a process known as anaerobic digestion. Since biogas is
a mixture of methane (also known as marsh gas or natural gas, CH4) and carbon
dioxide it is a renewable fuel produced from waste treatment. Food waste is the
best feedstock for biogas production. It is 20times more efficient than conventional
methods of using cow dung and pig wastes.
Biogas does not require any new technology as it is a natural process. But the
optimisation of production can be made by availing proper environment
conditions. Environmental factors temperature, pH, alkalinity, agitation etc. greatly
affect the production of biogas. The mesophilic temperature favours the reaction.
Experiments are made on use of higher temperatures that is thermophilic
temperature for production of biogas and are found effective. Constant stirring
increases the rate of production as the bacteria gets exposed to large area for
decomposing. The pH plays an important role as it should be maintained moderate
for the survival of bacteria.
OPTIMISATION OF BIOGAS PRODUCTION BY THREE STAGED DIGESTER
Sahyadri College of Engineering and Management Page 4
Considering all these factors a new technique digester designed to optimise
the biogas production. Three staged digester improves agitation process. The pH
was regulated and temperature was monitored to influence bacterial fermentation.
Three staged digester not only provides complete utilisation of food waste. But
also provides stirring effect.
1.2 AIM OF THE STUDY
The main objective of the project was to design a prototype and to study the
efficiency on using a three staged digester for production of biogas with food waste
and also to study the feasibility of implementation in rural areas as a community
reactor.
The project intended in comparing the production of normal digester with the
three staged digester. The aim was to develop a design of biogas digester for a
school in rural area, a community reactor to propose a disposal management
system for food waste.
1.3 OBJECTIVES
The objectives of our project are listed below-
To design two prototype biogas digesters and test them for biogas
production from food waste.
To study the production of biogas with normal digester and a three staged
digester.
To quantify the biogas produced with both normal and three staged digester
and thus obtaining the biogas yield at constant percentage of feedstock for
both prototypes.
To optimize the production of biogas using higher temperature with heat
exchanger.
To regulate the pH of slurry in the digester and thus promoting bacterial
activity.
To obtain the efficiency of using a three staged digester over normal
digester.
To survey a rural area and develop a design a biogas digester design by
considering yield and food waste produced.
OPTIMISATION OF BIOGAS PRODUCTION BY THREE STAGED DIGESTER
Sahyadri College of Engineering and Management Page 5
1.4 METHODOLOGY
1. A normal biogas digester was designed and it was fed with constant
feedstock of 0.2% the size of the digester.
2. The gas produced was quantified daily and the conditions like pH and
temperature were regulated.
3. The yield per 100L size of the digester was calculated.
4. A new technique three-staged digester was designed and even that was fed
constantly with 0.2% the size of the digester.
5. The yield produced was quantified daily and yield for 100litre size of the
digester were calculated.
6. From the results the optimisation by using the three staged digester were
studied.
7. A survey was made on quantity of food waste produced in Nekkilady
village, near Uppinangady.
8. The quantity of LPG cylinders used and the waste produced in college were
studied.
9. Based on the results a digester was designed for the school which would
replace the use of LPG completely.
1.5 SOURCES OF INFORMATION
ARTI
HANDBOOK OF BIOGAS UTILIZATION.
ENCYCLOPEDIA OF PHYSICAL SCIENCE AND TECHNOLOGY.
BIOGAS THESIS
JOURNALS
DOCUMENTS FROM OFFICE OF THE SCHOOL.
OPTIMISATION OF BIOGAS PRODUCTION BY THREE STAGED DIGESTER
Sahyadri College of Engineering and Management Page 6
CHAPTER-2
LITERATURE REVIEW
2.1 INTRODUCTION
Food waste is a very good feedstock for biogas production. It is 20 times
more efficient than the conventional methods of using cow dung. Multi-stage
anaerobic digestion has the advantage of achieving superior performance compared
with single-stage conventional digestion. The multi-stage process is capable of a
higher volatile solids (VS) reduction with shorter residence times, production of
biogas of higher quality, and elimination of foaming. The purpose of stirring is to
distribute the nutrients in the biogas digester uniformly, to form a suspension of
liquid and solid parts, to avoid sedimentation of particles, to ensure uniform heat
distribution, to prevent foam formation and to enable gas lift from the fermentation
substrate at high dry matter (DM) contents.
2.2 ARTI
Appropriate Rural Technology of India, Pune (2003) has developed a
compact biogas reactor which uses waste food rather than any cow dung as
feedstock, to supply biogas for cooking. Dr. Anand Karve (ARTI) developed a
compact biogas system that uses starchy or sugary feedstock (waste grain flour,
spoilt grain, overripe or misshapen fruit, nonedible seeds, fruits and rhizomes,
green leaves, kitchen waste, leftover food, etc.). Just 2 kg of such feedstock
produces about 500 g of methane, and the reaction is completed with 24 hours. The
conventional biogas systems of cattle dung, sewerage, etc. use about 40 kg of
feedstock to produce the same quantity of methane and it requires about 40 days
for completing the reaction. Thus, from the point of view of conversion of
feedstock into methane, the system developed by Dr. Anand Karve is 20 times as
efficient as the conventional system, and from the point of view of reaction time, it
is 40 times as efficient. Thus, overall, the new system is 800 times as efficient as
the conventional biogas system.
2.3 SHALINI SINGH
Shalini Singh (2000) studied the increased biogas production using microbial
stimulants. They studied the effect of microbial stimulant aquasan and teresan on
biogas yield from cattle dung and combined residue of cattle dung and kitchen
waste respectively. The result shows that dual addition of aquasan to cattle dung on
OPTIMISATION OF BIOGAS PRODUCTION BY THREE STAGED DIGESTER
Sahyadri College of Engineering and Management Page 7
day 1 and day 15 increased the gas production by 55% over unamended cattle dung
and addition of teresan to cattle dung kitchen waste (1:1) mixed residue 15%
increased gas production.
2.4 WASTEWATER INNOVATION- TDS-BIO-06-2015
Anaerobic digestion, a widely used biological process for treating wastewater
solids, refers to the process of converting organic matter into methane and carbon
dioxide through the help of anaerobic bacteria. There are three distinct steps during
anaerobic digestion, with each performed by a different group of microorganisms:
Hydrolysis,
Volatile acid fermentation
Methane formation.
Temperature and the amount of time the process is allowed to react define the
efficiency of each step. Multi-stage anaerobic digestion systems can be utilized for
all wastewater treatment systems, either new installations or retrofits. The only
requirement needed would be that the solids delivered to the system should be of
acceptable levels of concentration. For most wastewater solids and for all loading
rates, multi-stage anaerobic digestion has the advantage of achieving superior
performance compared with single-stage conventional digestion. The performance
increase is achieved even with smaller digester volumes because of the higher
loading rates that can be achieved with multi-stage digesters. The multi-stage
process is capable of a higher volatile solids (VS) reduction with shorter residence
times, production of biogas of higher quality, and elimination of foaming.
2.5 LISSENS
Lissens (2004) completed a study on a biogas operation to increase the total
biogas yield from 50% available biogas to 90% using several treatments including:
a mesophilic laboratory scale continuously stirred tank reactor, an up flow biofilm
reactor, a fiber liquefaction reactor releasing the bacteria Fibrobacter succinogenes
and a system that adds water during the process. These methods were sufficient in
bringing about large increases to the total yield. However, the study was under a
very controlled method, which leaves room for error when used under varying
conditions.
2.6 HANS–JOACHIM NAGELE, JANA SONDERMAN
A unique probe sampling system has been developed that allows probe
sampling from the top of the concrete roof into different parts and heights of the
digester. The samples were then analysed in the laboratory for natural fatty acids
concentrations. Three different agitation setups were chosen for evaluation at
continuous stirring and feeding procedures. The results showed that the analysis
OPTIMISATION OF BIOGAS PRODUCTION BY THREE STAGED DIGESTER
Sahyadri College of Engineering and Management Page 8
approach for agitator optimization through direct measurement of the nutrients
distribution in the digester is promising. The type of the agitators and the agitation
regime showed significant differences on local concentrations of organic acids,
which are not correlated to the dry matter content. Simultaneous measurements on
electric energy consumption of the different agitator types verify that by using the
slow-moving incline agitator with large propeller diameters in favour of the fast-
moving submersible mixer with smaller propeller diameters, the savings potential
rises up to 70% by maintaining the mixing quality.
2.7 JANTSCH AND MATTIASSON
Jantsch and Mattiasson (2004) discuss how anaerobic digestion is a suitable
method for the treatment of wastewater and organic wastes, yielding biogas as a
useful by-product. However, due to instabilities in start-up and operation it is often
not considered. A common way of preventing instability problems and avoiding
acidification in anaerobic digesters is to keep the organic load of the digester far
below its maximum capacity. There are a large number of factors which affect
biogas production efficiency including: environmental conditions such as pH,
temperature, type and quality of substrate; mixing; high organic loading; formation
of high volatile fatty acids; and inadequate alkalinity.
2.8 TALEGHANI AND KIA
Taleghani and Kia, (2005) outlined the economic, and social benefits of
biogas production.
The economic benefits were as follows:
1. Treatment of solid waste without long-term follow-up cots usually due to soil
and water pollution.
2. Increased local distribution of fertilizer, chemical herbicides, and pesticide
demand. Generation of income through compost and energy sales
(biogas/electricity/heat) to the public grid.
3. Improved soil/agriculture productivity through long-term effects on soil
structure and fertility through compost use.
4. Reduction of landfill space and consequently land costs.
The social and health effects associated with biogas include:
1. Creation of employment in biogas sector.
2. Improvement of the general condition of farmers due to the local availability of
soil improving fertilizer.
3. Decreased smell and scavenger rodents and birds.
OPTIMISATION OF BIOGAS PRODUCTION BY THREE STAGED DIGESTER
Sahyadri College of Engineering and Management Page 9
CHAPTER- 3
BIOGAS
3.1 COMPOSITION OF BIOGAS
BIOGAS is produced by bacteria through the bio-degradation of organic
material under anaerobic conditions. Natural generation of biogas is an important
part of bio-geochemical carbon cycle. It can be used both in rural and urban areas.
Table 3.1- Composition of biogas.
Component Concentration (by volume)
Methane (CH4) 55-60 %
Carbon dioxide (CO2) 35-40 %
Water (H2O) 2-7 %
Hydrogen sulphide (H2S) 20-20,000 ppm (2%)
Ammonia (NH3) 0-0.05 %
Nitrogen (N) 0-2 %
Oxygen (O2) 0-2 %
Hydrogen (H) 0-1 %
3.2 CHARACTERISTICS OF BIOGAS
Composition of biogas depends upon feed material also. Biogas is about 20%
lighter than air has an ignition temperature in range of 650 to 750 °C. Biogas is an
odorless & colorless gas that burns with blue flame similar to LP gas. Its calorific
value is 22 Mega Joules (MJ) /m3 and it usually burns with 60% efficiency in a
conventional biogas stove. Biogas digester systems provides a residue organic
waste, after its anaerobic digestion(AD) that has superior nutrient qualities over
normal organic fertilizer, as it is in the form of ammonia and can be used as
manure. Anaerobic biogas digesters also function as waste disposal systems,
particularly for human wastes, and can, therefore, prevent potential sources of
environmental contamination and the spread of pathogens and disease causing
bacteria. Biogas technology is particularly valuable in agricultural residual
treatment of animal excreta and kitchen refuse (residuals).
OPTIMISATION OF BIOGAS PRODUCTION BY THREE STAGED DIGESTER
Sahyadri College of Engineering and Management Page 10
3.3 FACTORS AFFECTING YIELD AND PRODUCTION OF BIOGAS
Many factors affecting the fermentation process of organic substances under
anaerobic condition are,
The quantity and nature of organic matter
The temperature
Acidity and alkalinity (pH value) of substrate
The flow and dilution of material
Table 3.2 GENERAL FEATURES OF BIOGAS
Energy Content 6-6.5 kWh/ m3
Fuel Equivalent 0.6-0.65 l oil/ m3 biogas
Explosion Limits 6-12 % biogas in air
Ignition Temperature 650-750 °C
Critical Pressure 75-89 bar
Critical temperature -82.5 °C
Normal Density 1.2 kg/ m3
Smell Bad eggs
3.4 PROPERTIES OF BIOGAS
1. Change in volume as a function of temperature and pressure.
2. Change in calorific value as function of temperature, pressure and water vapor
content.
3. Change in water vapor as a function of temperature and pressure.
3.5 MECHANISM OF BIOGAS FERMENTATION
A) Group of biogas microbes: Fig-3.1
Biogas microbes
Non methane Methane
Fermentative bacteria Hydrogen producing acetogenic
bacteria
OPTIMISATION OF BIOGAS PRODUCTION BY THREE STAGED DIGESTER
Sahyadri College of Engineering and Management Page 11
B) Group of microbes involved in 3 stages of biogas fermentation
1st stage: Fermentative bacteria:-
Saccharides amino acids Fatty acids
Fig. 3.2
2nd
stage: - Hydrogen producing acetogenic bacteria
Fig. 3.3
3rd
stage: - Methane producing bacteria
Fig. 3.4
3.6 BENEFITS OF BIOGAS TECHNOLOGY
Production of energy.
Transformation of organic wastes to very high quality fertilizer.
Improvement of hygienic conditions through reduction of pathogens.
Environmental advantages through protection of soil, water, air etc.
Micro-economic benefits by energy and fertilizer substitutes.
Macro-economic benefits through decentralizes energy generation and
environmental protection.
Cellulose decomposing
bacteria
Protein decomposing
bacteria
Fat decomposing
bacteria
Hydrolyze and Ferments organic substance
Volatile acid (H2 & CO2)
Decompose the substance
produced in 1st stage
Acetic bacteria
Convert the substance
produced in 1st & 2nd stage
CH4 & CO2
OPTIMISATION OF BIOGAS PRODUCTION BY THREE STAGED DIGESTER
Sahyadri College of Engineering and Management Page 12
3.7 COMPARISON WITH THE CONVENTIONAL SYSTEMS
The current practice of using low calorie inputs like cattle dung, distillery
effluent, municipal solid waste, or sewerage, makes methane generation in
conventional biogas reactors highly inefficient. Through this compact system, it
has been demonstrated that by using feedstock having high calorific and nutritive
value to microbes, the efficiency of methane generation can be increased by
several orders of magnitude. Operating the system on this simple tenet also brings
in many more advantages over the conventional systems: As a result of the higher
efficiency, the size and cost of the new system are also lower. While the
conventional biogas system occupies about 4 cubic meters of space, the compact
ARTI biogas system is about as large as a domestic refrigerator. It is an extremely
user friendly system, because it requires daily only a couple of kg feedstock, and
the disposal of daily just 5 litres of effluent slurry.
OPTIMISATION OF BIOGAS PRODUCTION BY THREE STAGED DIGESTER
Sahyadri College of Engineering and Management Page 13
CHAPTER- 4
DESIGN OF DIGESTER
4.1 SURVEY ON QUANTITY OF FOOD WASTE PRODUCED
Nekkilady, a village nearby Uppinangady, Puttur taluk, Dakshina Kannada
was selected for the study on implementation in rural areas. The study was based
on the area of interest near the Government school of Nekkilady. Nearly 50 houses
were surveyed for the quantity of food waste produced. At an average of
0.5kg/house of food waste is produced daily. One more survey was done on the
amount of food waste produced in the school. There is a production of about 3kg
of food waste per day. Around 2 LPG cylinders are used per month which accounts
to a daily usage 1L of LPG.
OPTIMISATION OF BIOGAS PRODUCTION BY THREE STAGED DIGESTER
Sahyadri College of Engineering and Management Page 14
4.2 FABRICATION OF NORMAL DIGESTER
A prototype metal digester of 24L capacity was fabricated for the
quantification of biogas in single staged digester. It was metal fabricated digester
of dimensions 30cm diameter and height 34cm. the digester had an inlet pipe of
5cm diameter. Outlet pipe of size 4cm was used. The digester was a fixed dome
digester and rubber tubes were used for collection of gas. A gas outlet of 1.25cm
diameter was used.
The digester was initially fed with cow dung for start-up process and after one
week it started giving flammable gas. From seventh day after start-up it was fed
constantly with food waste at 0.2% the size of the digester that is 48g. The gas
produced was quantified daily by water displacement method.
Metal fabricated digester- Prototype of Normal Digester
OPTIMISATION OF BIOGAS PRODUCTION BY THREE STAGED DIGESTER
Sahyadri College of Engineering and Management Page 15
4.3 FABRICATION OF THREE STAGED DIGESTER
A 30L metal fabricated digester with three stages was used as another
prototype. The digester had three compartments occupying same volume. The
digester was proposed in order to offer agitation by offering movement of slurry.
The compartments were separated by three metal sheets welded at the centre to a
metal pipe and at the periphery to the cylinder. The metal sheets had openings for
the flow of slurry the first chamber had the inlet fixed to it. Inlet was a 4cm
diameter metal pipe. The third chamber had the outlet for digested slurry of the
same size as inlet pipe. The openings in the chambers were provided such that after
the complete digestion period in first chamber it would flow to second chamber
and so on to the third chamber. The whole cylinder had cone shaped top for the
allowance of flow of gas to the gas outlet. The gas outlet was of 1.25cm diameter
size.
Chamber 2 Chamber 1
Chamber 3
OPTIMISATION OF BIOGAS PRODUCTION BY THREE STAGED DIGESTER
Sahyadri College of Engineering and Management Page 16
4.4 COMPARISON BETWEEN NORMAL DIGESTER AND THREE
STAGED DIGESTER
The gas produced in both the digesters was quantified. After the 30th
day gas
production was stable. At this point the gas produced for 100L size of the digester
was calculated. The gas production varies with the size of the digester. So the
calculations were made for 100L size of the digester. The three staged digester
provides more time for decomposition and also provides stirring effect.
OPTIMISATION OF BIOGAS PRODUCTION BY THREE STAGED DIGESTER
Sahyadri College of Engineering and Management Page 17
CHAPTER- 5
PRINCIPLES FOR THE PRODUCTION OF BIOGAS
5.1 PRODUCTION PROCESS
A typical biogas system consists of the following components:
I. Manure collection
II. Anaerobic digester
III. Effluent storage
IV. Gas handling
V. Gas use
Biogas is a renewable form of energy. Methanogens (methane producing
bacteria) are last link in a chain of microorganisms which degrade organic material
and returns product of decomposition to the environment.
Fig.5.1 Production Process
OPTIMISATION OF BIOGAS PRODUCTION BY THREE STAGED DIGESTER
Sahyadri College of Engineering and Management Page 18
5.2 PRINCIPLES FOR THE PRODUCTION OF BIOGAS
Organic substances exist in wide variety from living beings to dead
organisms. Organic matters are composed of Carbon (C), combined with elements
such as Hydrogen (H), Oxygen (O), Nitrogen (N), and Sulphur (S) to form variety
of organic compounds such as carbohydrates, proteins & lipids. In nature MOs
(microorganisms), through digestion process breaks the complex carbon into
smaller substances.
There are 2 types of digestion process:
(1) Aerobic digestion
(2) Anaerobic digestion
5.3 AEROBIC DIGESTION
The digestion process occurring in presence of Oxygen is called Aerobic
digestion and produces mixtures of gases having carbon dioxide (CO2), one of the
main “greenhouse gasses” responsible for global warming. The digestion process
occurring without (absence) oxygen is called anaerobic digestion which generates
mixtures of gases. The gas produced which is mainly methane produces 5200-5800
KJ/m3 which when burned at normal room temperature and presents a viable
environmentally friendly energy source to replace fossil fuels (non-renewable).
5.4 ANAEROBIC DIGESTION
It is also referred to as Bio-Methanisation, is a natural process that takes place
in absence of air (oxygen). It involves biochemical decomposition of complex
organic material by various biochemical processes with release of energy rich
biogas and production of nutritious effluents.
Fig. 5.2 Anaerobic Digestion
OPTIMISATION OF BIOGAS PRODUCTION BY THREE STAGED DIGESTER
Sahyadri College of Engineering and Management Page 19
5.5 BIOLOGICAL PROCESS
I. HYDROLYSIS
II. ACIDIFICATION
III. METHANOGENESIS
5.5.1 HYDROLYSIS:
In the first step the organic matter is acted upon externally by extracellular
enzymes, cellulose, amylase, protease & lipase, of microorganisms. Bacteria
decompose long chains of complex carbohydrates, proteins, & lipids into small
chains. For example, Polysaccharides are converted into monosaccharide. Proteins
are split into peptides and amino acids.
5.5.2 ACIDIFICATION:
Acid-producing bacteria, involved this step, convert the intermediates of
fermenting bacteria into acetic acid, hydrogen and carbon dioxide. These bacteria
are anaerobic and can grow under acidic conditions. To produce acetic acid, they
need oxygen and carbon. For this, they use dissolved O2 or bounded-oxygen.
Hereby, the acid-producing bacteria create anaerobic condition which is essential
for the methane producing microorganisms. Also, they reduce the compounds with
low molecular weights into alcohols, organic acids, amino acids, carbon dioxide,
hydrogen sulphide and traces of methane. From a chemical point, this process is
partially endergonic (i.e. only possible with energy input), since bacteria alone are
not capable of sustaining that type of reaction.
5.5.3 METHANOGENESIS: (Methane formation)
Methane-producing bacteria, which were involved in the third step,
decompose compounds having low molecular weight. They utilize hydrogen,
carbon dioxide and acetic acid to form methane and carbon dioxide. Under natural
conditions, CH4 producing microorganisms occur to the extent that anaerobic
conditions are provided, e.g. under water (for example in marine sediments), and in
marshes. They are basically anaerobic and very sensitive to environmental
changes, if any occurs. The methanogenic bacteria belong to the archaebacter
genus, i.e. to a group of bacteria with heterogeneous morphology and lot of
common biochemical and molecular-biological properties that distinguishes them
from other bacteria. The main difference lies in the makeup of the bacteria’s cell
walls.
OPTIMISATION OF BIOGAS PRODUCTION BY THREE STAGED DIGESTER
Sahyadri College of Engineering and Management Page 20
5.6 SYMBIOSIS OF BACTERIA
Methane and acid-producing bacteria act in a symbiotically. Acid producing
bacteria create an atmosphere with ideal parameters for methane producing
bacteria (anaerobic conditions, compounds with a low molecular weight). On the
other hand, methane-producing microorganisms use the intermediates of the acid
producing bacteria. Without consuming them, toxic conditions for the acid-
producing microorganisms would develop. In real time fermentation processes the
metabolic actions of various bacteria acts in a design. No single bacteria are able to
produce fermentation products alone as it requires others too.
OPTIMISATION OF BIOGAS PRODUCTION BY THREE STAGED DIGESTER
Sahyadri College of Engineering and Management Page 21
CHAPTER- 6
TESTS, OBSERVATIONS AND RESULTS
6.1 SURVEY AT RURAL AREA
The place selected for survey was 34th
Nekkilady, Uppinangady, Dakshina
Kannada. The region under consideration of Nekkilady was located. Based on the
documents from school office houses to be surveyed were taken into consideration
the school region covered 1126 houses.
PARTICULARS NUMBERS UNITS
Total number of students in school 77
Number of cylinders used 2 /month
0.067 /day
Waste produced in school 3 kg/day
Number of houses under school 1126
Number of houses surveyed 50
Waste produced in houses 0.5 kg/day
Total Quantity of food waste 25 kg
28 kg/day
The volume of digester required 14 m3
The digester produces sufficient gas for the complete replacement of LPG. In
addition to this extra gas is produced which can be used for other purposes. The
system can also be used to generate sufficient electricity to run the school. Design
calculations are given below.
6.2 COMPARISON BETWEEN NORMAL AND THREE STAGED
DIGESTER
GAS PRODUCED FOR 100L
DAYS GAS PRODUCED SIZE OF THE DIGESTER
NORMAL THREE STAGED
NORMAL THREE STAGED
1 0.425 0.860 1.771 2.867
2 0.575 1.160 2.396 3.867
3 0.865 1.750 3.604 5.833
4 1.000 2.000 4.167 6.667
5 1.150 2.300 4.792 7.667
6 1.250 2.500 5.208 8.333
OPTIMISATION OF BIOGAS PRODUCTION BY THREE STAGED DIGESTER
Sahyadri College of Engineering and Management Page 22
7 1.300 2.550 5.417 8.500
8 1.450 2.800 6.042 9.333
9 2.200 3.800 9.167 12.667
10 3.000 5.800 12.500 19.333
11 3.800 7.700 15.833 25.667
12 4.675 9.300 19.479 31.000
13 4.800 9.700 20.000 32.333
14 5.000 10.200 20.833 34.000
15 5.600 11.200 23.333 37.333
16 5.700 11.500 23.750 38.333
17 5.850 11.750 24.375 39.167
18 6.000 12.050 25.000 40.167
19 7.000 14.000 29.167 46.667
20 7.500 15.100 31.250 50.333
21 8.100 16.300 33.750 54.333
22 8.800 17.650 36.667 58.833
23 8.900 17.800 37.083 59.333
24 9.000 18.200 37.500 60.667
25 9.100 18.300 37.917 61.000
26 9.500 19.100 39.583 63.667
27 10.000 20.200 41.667 67.333
6.3 REPRESENTATIVE GRAPH
FIG- 6.1- Graph showing the production of gas daily
0.000
5.000
10.000
15.000
20.000
25.000
0 5 10 15 20 25 30
Gas
pro
du
ced
in L
Days
GAS PRODUCTION
Normal Digester
Three stagedDigester
OPTIMISATION OF BIOGAS PRODUCTION BY THREE STAGED DIGESTER
Sahyadri College of Engineering and Management Page 23
6.4 DESIGN OF BIOGAS DIGESTER FOR SCHOOL.
PARTICULARS UNITS
Volume of the digester required (28kg food waste) 14 m3
Total volume (assuming volume of partition walls) 15 m3
Depth of the digester 2.5 M
Inner diameter of the digester 2.7 M
3 M
Assuming 0.15m thick concrete cylinder Total volume 3.3 M
Gas collector dome volume 8.4 m3
As storage cylinders shall be used provide
Provide 30% size of the collector dome
2.52~
2.6
m3
Diameter shall be little less than the digester 2.4 M
Depth of collecting dome 1.72 M
6.5 COST ANALYSIS
Particulars Quantity Unit
Earthwork involved 23.95 m3
Cost involved in earthwork (Rs. 350/m3) 8382.5 Rs
Concrete volume 7.27 m3
Cost of concrete(Rs. 775/m3) 5634.25 Rs
Cost for metal dome 10000 Rs
Miscellaneous (collector system & piping) 30000 Rs
Total cost 54100 Rs
Savings per year (2*12*1000) 24000 Rs/year
Payback duration 2.3 Years
0.000
10.000
20.000
30.000
40.000
50.000
60.000
70.000
80.000
0 5 10 15 20 25 30
Gas
pro
du
ctio
n in
L f
or
10
0L
Dig
est
er
Days
Gas production for 100L size of Digester
Normal Digester
Three stagedDigester
OPTIMISATION OF BIOGAS PRODUCTION BY THREE STAGED DIGESTER
Sahyadri College of Engineering and Management Page 24
CHAPTER- 7
CONCLUSION
• Biogas is a clean renewable source of energy and hence its substitution for
LPG will help in reducing greenhouse gas emissions.
• Food waste is a very good substitute for L P G because India is self-reliant in
food production and crude oil is imported.
• Three staged digester efficiently uses all the waste and produces more gas.
• The production can be increased by 25% if a conventional digester produces
42L of gas, three staged digester produces 67L gas.
• The three staged digester not only provides more time for digestion. But it also
provides stirring effect.
• The new technique digester developed is efficient than conventional reactors.
The effluent is completely digested and the gas production will be optimum.
• The gas produced is sufficient for the use in school for midday-meals. And
extra gas that is produced can be stored and supplied for nearby restaurants or
houses.
• A regular feeding of biogas reactor with proper amount will ensure consistent
release of biogas and ensures uninterrupted production of gas.
• Crushed and blended food improves the liberation of biogas as digestion
becomes easy.
• Underfeeding or overfeeding of reactor should be avoided. Underfeeding keeps
the reactor inefficient and overfeeding increases the pH value of food waste
and reduces the development of microbes.
• Payback period is small. Hence it can be adopted in all the rural places.
OPTIMISATION OF BIOGAS PRODUCTION BY THREE STAGED DIGESTER
Sahyadri College of Engineering and Management Page 25
CHAPTER- 8
SCOPE FOR FUTURE WORK
The scarcity of petroleum and increased use of LPG have given rise for the
alternative fuel technology. And hence the scope of developing a biogas digester is
trending. With the Indian government keen on utilizing renewable resources for
energy production, it is likely that there will be a greater thrust and higher
incentives for concepts such as biogas production from waste. An increasing
awareness among the public regarding sustainable use of resources will only
enhance the production and use of biogas. It can hence be expected that biogas will
have a significant growth in India at all levels of usage (household, municipality
and industry) for both heat generation and electricity production.
It is also possible to earn carbon credits for biogas-based power or heat
generation in India. For instance, in Apr 2008, Andhyodaya, a non-government
agency working in the field of promoting water management and non-conventional
energy and social development distributed the first instalment of the biogas carbon
credit to farmers in the state of Kerala. Andhyodaya had helped construct 15,000
biogas reactors in the state and earned carbon credits. This trend is likely to grow
further.
In sum, India has significant potential for generating heat and electricity from
waste in the form of biogas. While only a portion of the potential has been tapped,
it is likely that more investments in this direction could accelerate exploitation of
this source in future.
The scope also lies in monitoring the factors thus developing a better digester
for effective working of biogas digester. The project can be developed into a better
system by ensuring the proper levels of temperature and pH. The production can be
increased by themophilic temperature. The use of kitchen steam and smoke can be
used to maintain the temperature in rural areas. The gas produced can be purified
in order to increase the calorific value.
OPTIMISATION OF BIOGAS PRODUCTION BY THREE STAGED DIGESTER
Sahyadri College of Engineering and Management Page 26
CHAPTER- 9
REFERENCES
Andreas Lemmer, Hans-Joachim Naegele and Jana Sondermann-How
Efficient are Agitators in Biogas Digesters? Determination of the Efficiency of
Submersible Motor Mixers and Incline Agitators by Measuring Nutrient
Distribution in Full-Scale Agricultural Biogas Digesters-Energies 2013, 6,
6255-6273; doi:10.3390/en6126255
Wilson, T., Potts, L., and Stallings, R. 2005. Review of Full Scale 2-phase
AG Anaerobic Digester Systems Technology: Multi-Stage Anaerobic
Digestion
Biogas Digest Volume II, Biogas - Application and Product Development
Information and Advisory Service on Appropriate Technology
Chen Y., Cheng J. J., Creamer K. S. (2007): Inhibition of anaerobic
digestions process: A review, Bio resource technology; VOL- 99, PP 4044-
4064.
Deublein D. Steinhauser A. (2008): Biogas from waste and renewable
resources: an introduction, Willey, Wienheim.
Dhakal, N.R. (October 12-14, 2003), Use of vegetable and kitchen wastes as
alternative feed stocks for biogas production
Handbook of Biogas Utilization (February 1988), U.S
Haridas A. (2007): Tourism in limbo at Kumbalanghi, The Hindu, 12
September 2007.
Karve .A.D. (2007), Compact biogas reactor, a low cost digester for biogas
from waste starch. http://www.arti-india.org.
Karve of Pune A.D (2006). Compact biogas reactor compact low-cost digester
from waste starch. www.bioenergylists.org.
Ranjeet Singh, S. K. Mandal, V. K. Jain (2008), Development of mixed
inoculum for methane enriched biogas production .
Shalini sing, sushil kumar, M.C. Jain, Dinesh kumar (2000), the increased
biogas production using microbial stimulants.
Harka Man Lungkhimba, Amrit Bahadur Karki and Jagan Nath Shrestha
(2010), Biogas Production from Anaerobic Digestion of Biodegradable
OPTIMISATION OF BIOGAS PRODUCTION BY THREE STAGED DIGESTER
Sahyadri College of Engineering and Management Page 27
Household Wastes, Nepal Journal of Science and Technology 11 167-172 167
Heeb F. (2009): Decentralised anaerobic digestion of market waste, Case study
in Thiruvananthapuram, India, Eawag/Sandec. Switzerland.
Hilkiah Igoni, M. F. N. Abowei, M. J. Ayotamuno and C. L. Eze (2008),
Effect of Total Solids Concentration of Municipal Solid Waste on the Biogas
Produced in an Anaerobic Continuous Digester.
Kale, S.P and Mehele, S.T. kitchen waste based biogas reactor.pdf. Nuclear
agriculture and Biotechnology/ Division.
Kumar, S., Gaikwad, S.A., Shekdar, A.K., Kshirsagar, P.K., Singh, R.N.
(2004). Estimation method for national methane emission from solid waste
landfills. Atmospheric Environment. 38: 3481–3487.
Lohri, C. (2009): Research on anaerobic digestion of organic solid waste at
household level in Dar es Salaam, Tanzania; Bachelor thesis at ZHAW (Zurich
University of Applied Sciences) in collaboration with Eawag, ZHAW,
Wädenswil.
Meres, M., Szczepaniec-Cieciak, E., Sadowska, A., Piejko, K.,
Oczyszczania, M.P., Szafnicki, K. (2004). Operational and meteorological
influence on the utilized biogas composition at the Barycz landfill site in
Cracow, Poland. Waste Management Resource. 22: 195–201.
M. Kaltschmitt, D. Thrän and K. R. Smith, (Academic Press, 2001),
Renewable Energy from Biomass, in Encyclopedia of Physical Science and
Technology, ed. by R. A. Meyers ,Pp. 203-228
Raymond Myles, (November 19-21, 2001) Implementation Of Household
Biogas Reactor by NGOs in India, Practical Experience in Implementation
Household Biogas Technology, Lessons Learned, Key Issues And Future
Approach For Sustainable Village Development .
Robert Jon Lichtman (1983), Biogas Systems in India, VITA/COSTED,
ISBN O-86619-167-4
Salminen E., & Rintala J. (2002): Anaerobic digestion of organic solid
poultry slaughterhouse waste – a review, Bioresource Technology, vol 83, no.
1, pp. 13-26.