Embed Size (px)
Citation preview
MESTRADO INTEGRADO EM ENGENHARIA DA ENERGIA E DO AMBIENTE
Aula N
MUNICIPAL SOLID WASTESLandfilling and composting
Santino Di Berardino
2
RSU-INTRODUCTION
The problem of solid waste arises in this century. The strong economic growth and social development of man, the search for comfort and improvement of the standard of living of the population, have increased the production of waste vertiginously.
Until about 50 years ago organic wastes were largely recycled and processed within the material transformation cycle, either for animal feed or for land application.
The products were mostly sold in bulk, without packaging; the containers and the paper bag replaced the plastic bags. There was no abundance and diversification of the products generated by the consumption society, and the life cycle of each product was much longer.
3
Urban Solid Wastes - URS
Urban Solid wastes are today one of the major source of pollution of our society and one of the major source of organic matter Biomass.
They can cause Pollution in its various forms: water (liquid drainage) , air (gas emissions) and soil
They are one of the greatest scourges on earth.
It is an indicator of the standard of living in society: the greater the amount of waste produced by a man in a community, the higher his or her living standard.
4
Characteristics of solid waste
Its composition is non-uniform. It contains several materials with different characteristics.
Differs from one city to another due to customs and living standards.
The specific mass of food waste varies between 0.2 ton / m3 and 0.45 ton / m3 and presents an average of 0.23 ton / m3, according to the country.
In Portugal the production of garbage is very variable. the maximum capitation in large cities (about 1.0 kg / d) and minimum in rural areas (Mação: 0.458 kg / d).
In the European Union average capitation is 0.850 kg / day, while each Lisbon produces 0.910 kg per day.
5
Composition and Characteristics of USW
Organic Fraction of HouseholdGarbage - residues of kitchen ofresidences and restaurants, made oforganic materials such as: vegetables,fish, meats, etc. containing highhumidity and subject todecomposition. Their share of totalwaste varies between 20 and 40%.
Fuel materials: Plastics, paper, wood,etc. Participation in the total of 20 to40%. Inert materials such as sand, ash,glass, metals, ceramics, etc.Participation in the total of 20 to 40%.
6
EU Country Waste production Comparison (kg per capita)
Energia da biomassa
7
Organic waste disposal solutions
Today only three disposal solutions are accepted:
Incineration and cinder landfilling (large scale solution)
Land application for Agriculture after conversion bycomposting.
Landfilling. Very popular solution. has a low hierarchylevel, now is being restricted by by EU directive1999/31/EC
8
Sustainability of Landfills
8Source: WASTE INCINERATION (2010) and AFRICAN DEVELOPMENT BANK (2002)
Landfilling is the least preferred method in the hierarchy of integrated solid waste management.
9
Directive on landilling
the European Directive 1999/31/EC defining national targets on the reduction of biodegradable waste in landfilling.
By 2010, reduce biodegradable municipal waste land-filled to 75% of the level produced in 1995.
By 2013, reduce biodegradable municipal waste land-filled to 50% of the level produced in 1995.
By 2020, reduce biodegradable municipal waste land-filled to 35% of the level produced in 1995.
10
Solid Waste Treatment and Disposal
The treatment, the disposal or re-use of solid waste plays a key role in protecting public health and maintaining the hygienic conditions necessary for a healthy environment.
There are nowadays some treatment processes that prepare the solid waste to be received by nature or to be reused. Some treatment processes are both treatment and final destination of waste, while others are specific.
Typically, cities that experience rapid population and / or economic growth produce solid waste in quantities that are far greater than their treatment capacity and disposal.
11
Landfilling
Landfill is a site for the disposal
of waste materials by burial. It is the oldest form
of waste treatment historically refuse was just
left in piles or thrown into pits: DUMPING
Energia da biomassa
12
Types of Landfills
• Open Dump: Waste is discharge open without
any management-
• Basic Landfill: Waste is discharged in a pit and
covered every day
• Engineered Landfill: Liner, cover, leachate
treatment and gas extraction (energy production
or flared)
• Bioreactor Landfill: Acceleration of
decomposition and creation of a conditions for
microbiological activities -> produced gas is used
for energy production.
12
13
Treatment and Health Aspect
13
Open Dump
Basic Landfill
Engineered Landfill
Bioreactor Landfill
health
and e
nviro
nm
enta
l pro
tectio
n
slow decomposition; spreading of waste, pathogens and odour; no liner, no cover
better decomposition; cover avoids
spreading of waste and breeding of
insects; leaching may occur
advanced decomposition; cover; liner;
leachate, stormwater and gas
management.
acceleration of decomposition; cover;
liner; leachate and stormwater
management; energy production
14
Landfill
Basic landfill improved waste Dumping by
buryng and covering to promote anaerobic
digestion, waste reduction and stabilization.
Anaerobic digestion takes place and avoids
emissions and bad odours and generates
methane.
This Landfill have been the most common
method of organized waste and remain so in
many places around the world. In EU is
decreasing
Energia da biomassa
15
Sanitary Landfill
Landfill or controlled landfill is also a process of treatment and disposal of solid waste. The process work at natural conditions. Anaerobic digestion start spontaneously
The organic part of the waste decomposes into biogas, which can be collected and used.
Solid waste, when disposed in landfills, is scattered, compacted and covered with soil with a layer of about 15 cm thick, with daily frequency.
16
Sanitary Landfill - Biogas evolution
Biogás is produced during 30 -40 years
In the early period acidification occurs.
17
Sanitary Landfill coverture
In the basic systems the last layer of covering of the garbage is at least 60 cm thick and should be above the final projected level of the landfill because, over time, and with the decomposition of the landfill, there will be rebates, serving this height difference, to counterbalance the sinking caused by repression.
Modern systems are provided with plastic andmembranes layers to avoid the methane and leachateescape
18
Engineered Landfills in Contrast
to Open Dumps
18
Source: LATROBE CITY COUNCIL (2005)
Cover layer avoids spreading of
waste, pathogens, odour
Gas extraction well control and
reuse of biogas (mainly CO2 and
CH4) for energy production
Liner system avoids a
contamination of ground water
Leachate system collection and
treatment of fluid effluent
Groundwater monitoring on-
going information about the
groundwater quality
It is not an open dump, it is an
engineered facility in order to
protect the environment and
human health!
19
Why is used?
Low cost solution, with no by-products and requiring the minimum of equipment and specialized labor.
Suitable for small and medium-sized communities.
In the case of large cities or metropolitan areas careful planning, operation and maintenance is required.
The land where the landfill is made is not recovered. So landfilling should be applied in erosion or degraded areas without possibility of recovery and in need of landfills.
The application of landfills is conditioned by the availability of land with adequate characteristics and is impossible to be applied to unstable or porous soils.
20
Escavation-Execution Methods
The method of implementation of the landfill depends on the amount of waste, the work area available and the weather conditions.
According to the topographic conditions of the site chosen for the execution of the landfill, it can be carried out below or above the natural level of the land.
the sanitary landfill can be realized as:
Landfill in single trench
Landfill in double trench
Sanitary landfill on ramp
Landfill in an area or workbench
21
Landfill escavation
22
Landfills Escavation
23
Biogas extraction from landfill
24
Santitary landfills
25
Biogas use for electricity
Workshop CCI, lisboa 27 de novembro de
2008
Santino Di Berardino
Amarsul
26
Electricity production
27
Basic Landfill (Emergency
Landfill) (HARVEY et al. 2002)
• Pit should be
backfilled with
excavated soil every
day.
• Site should be agreed
with local population
and authorities.
• Site should be
fenced.
• At least 1 km
downwind from the
nearest dwellings.27Source: HARVEY et al. (2002)
28
Engineered Landfill (UNEP 2002)
• The capacity is planned and the site is chosen
based on an environmental risk assessment
study.
• Gas is flared or used for energy production.
28Source: UNEP (2002)
29
SUSTAINABLE LANDFILL CONCEPT
The concept of sustainability implies the controlled use of natural resources, so as to ensure that the needs of the present do not jeopardize the evolution of future generations.
In order to transfer this concept to landfills, it can be assumed that the application of the materials in the landfills must be such that, at the end of a given period, the landfill is in equilibrium with the environment, thus regenerating its capacity. Taking into account that a generation lasts about 30 years, this is the agreed time period for the area in which the landfill has been placed to recover its properties and return in balance with nature.
This implies that, after 30 years, emissions, whether gaseous or liquid, do not exceed acceptable levels for the receiving medium where they converge. Such emissions shall not in any way constitute a restriction on human health or the environment.
So the sustainability reach implies that the residual emissions from these sites are considered to be marginal and that the insulation protections, both above and below the landfill, should no longer be useful. This situation defines the end of posthumous treatment. Further involvement with the site will depend on its end use, but this should be minimized in a manner comparable to maintaining a park.
30
Landfill Classification
Landfills can also be classified into three categories, according to the type of waste:
1 - Landfills with biodegradable organic matter: requires degradation treatment
2 - Landfills with hazardous materials: requires immobilization treatment.
3 - Landfills with inert inorganic materials: requires control of solubility.
31
Sustainability of Landfill
Each type of landfill requires the application of a specific processing. The first two types of landfills can be converted into the third,
In landfills, controlling the solubility and flow of contaminants, in line with the provisions of the Directive on landfills for aggregates, it can be considered a sustainable landfill with negligible emissions. It must have no impact on drinking water.
In landfills where organic matter predominates, its transformation into a landfill requires the control and acceleration of degradation of organic matter.
In the case of landfills with hazardous materials, their restoration requires the use of techniques to immobilize toxic compounds.
32
DESENVOLVIMENTO DE UM ATERRO SUSTENTÀVEL
A possibilidade de tornar um aterro com matéria orgânica num aterro de inertes é tentadora é atractiva. Na Holanda, um país com escassos recursos territoriais, este tema tem tido grande relevância.
A fundação dos aterros sustentáveis (Sustainable landfillFoundation) [6] [8], definiu o conceito do “aterro-bioreactor”, como um sistema dotado de procedimentos operacionais de excelência, que incluem a implementação de medidas mais eficazes para o controlo do biogás, a injecção de água ou de ar, a colocação de coberturas permeáveis. Esta entidade tem publicado diversos manuais e livros sobre este tema.
33
Acelerated landfills
Sustainability implies that the decomposition of M. O will end within 30 years. Existing new technological systems allow to achieve the following:
The acceleration of decomposition and stabilization of organic matter.
The recovery and extension of the use, avoiding new landfills.
The reduction of gaseous and liquid emissions.
The renewal and reuse of completed landfills
34
Increasing biodegradation: landfill-bioreactor
Some techniques based on different biological criteria allow to reduce potential emissions, the duration of the landfill closure phase, and can be applied either to landfills in operation or to end-of-life landfills, with leachate recycling and possible treatment abroad and on-site aeration ("in situ") [9].
Leachate infiltration has the ability to increase the biological reactions within the landfill due to the increased water content and also increase the leaching of substances out of the landfill by diluting and increasing the water flow.
Its implementation lies in operating a landfill that receives biodegradable waste as a bioreactor and provides several advantages. The acceleration of the process allows to manage the period of production of the useful biogas, reduces the load of the leachates and reduces the environmental risks. The biogas yield is substantially higher than in conventional landfills and, consequently, provides higher revenues from the use and sale of energy.
The bio-reactor can play a very important role in reducing emissions and in achieving the objectives envisaged at European level [6] by significantly intervening in the carbon cycle [15].
35
Others solutions
In addition to the recirculation of the leachate inside the landfill, it is possible to intercalate a reactor outside the landfill, where it is possible to create adequate conditions to improve the performance. According to experience gained by INETI, a high yield reactor can provide inoculum for degradation to the interior, substantially increase the rate of degradation of the landfill and the degree of degradation, since fermentation conditions can be suitably controlled. The leachate treatment system inserted in the circuit may be anaerobic, aerobic or anaerobic plus aerobic, according to the scheme described in figure 3.
Figure 3: Supplementary treatment scheme with external reactors In an initial phase the treatment will be of the anaerobic type, since it allows the
activation of the embankment and the recovery of the biogas. The anaerobic process allows the degradation of more complex organic compounds in relation to the anaerobic processes. When the landfill is in the final stage, the treatment could be supplemented or replaced with an aerobic reactor, possibly with pure oxygen aeration.
These technologies allow the control of degradation, provide more favorable conditions for the biological process and constitute a powerful instrument for the control of the quality of the landfill. On the other hand, the reactors to be carried out do not involve large investments, and can be carried out in Portugal in prefabricated material, in a scheme similar to that indicated in photograph 1.
36
Bioreactor Landfill)
36
• Acceleration of biologic decomposition (organic fraction).
• Promoting conditions necessary for the microorganisms (moisture
content).
• Liquids must be added (leachate, stormwater, sewerage sludge).
• Gas is collected to produce
electrical energy.
• Design includes liner, cover,
leachate system, groundwater
monitoring.
• Systems: aerobic, anaerobic,
aerobic-anaerobic, facultative
(to control high ammonia
concentration).Source: WM (2004)
37
Acelerated landfills – Leachate recirculation
38
Increased biodegradation:aerated landfill
The other available technology, based on on-site aeration, uses aerobic stabilization to accelerate biological degradation reactions within the landfill. Emissions are significantly reduced compared to anaerobic conditions after a relatively short treatment period of about a few years, due to the higher rate of degradation of the aerobic community, which has more energy to effect the oxidation.
To force in the ambient air is used a compressor that compresses the air in aeration wells placed in the embankment, while the air penetrates in its interior by convection and diffusion. According to the rate of application and duration of aeration most of the landfill or almost the entire landfill can be in aerobic conditions accelerating its degradation.
At the same time as aerating, an equivalent amount of gas is extracted from the landfill from other extraction holes. This gas must be subjected to appropriate treatment (biological and / or chemical physical) and cooled, before being dispersed into the atmosphere. On-site aeration was used in three landfills in Germany, with the aim of reducing and controlling emissions before the final closure of the landfill
39
Aerated landfill
40
Treatment of Leachate
40
Without proper cleaning, leachate will cause environmental problems.
Potential methods for treatment:
•Recirculation of leachate through the landfill
•Disposal off-site to sewer for treatment as an admixture with domestic
sewage
•Physical-chemical treatment
•Membrane filtration
•Reverse osmosis
•Anaerobic biological treatment
•Aerobic biological treatment
•Constructed wetlands
Design of a vertical flow constructed wetland. Source: MOREL &
DIENER (2006)
41
Treatment of Leachate-evaporation
42
Landfill Operation and Maintenance
Requires dedicated operators.
Waste has to be covered each day.
Proper leachate management.
Cover must be resistant to erosion.
Once capacity is reached,
the bottom (cover layer) has to be controlled regularly to avoid toxic ffluents/emissions.
Bioreactor landfills require a more complex set of O&M
42
43
Urban Solid Waste Sector
As solid waste can be transported by truck its management can be favorably planned at regional or multi-municipal scale. Tis requires:
Implementation of regional bodies responsible for MSW management
Implementation of European and national legislation on waste,
Realization of the most efficient management structure,
change of attitude of the society on the environment
Evolution of the technology of treatment of Solid Waste allowing Elimination and control all basic sanitation and environmental issues related to solid waste, which must be treated and disposed of safely.
44
Landfilling was widely employed for the disposal
of municipal solid waste.
• Depending on the community/city (financial,
knowledge, interests)
• Enough land must be available.
• Compared to other discharge possibilities costs are
lower.
• Landfill should always be lined, correctly covered
and maintained to avoid a contamination of the
environment and to minimise health risks for locals.
44
45
Pro e contra
Advantages:
• An effective disposal method if
well-managed.
• A sanitary disposal method if
managed effectively.
• Energy production and fast
degradation if designed as a
bioreactor landfill.
Disadvantages:
• Fills up quickly if waste is not reduced and
reusable waste is not collected separately
and recycled.
• A reasonable large area required.
• Risk of groundwater contamination if not
sealed correctly or the liner system is
damaged.
• High costs for high-tech landfills.
• If the management is bad, there is a risk
that the landfill degenerates into an open
dump.
• After the end of disposal the landfill needs
still O&M and monitoring for the next 50 to
100 years.
45
46
Measures to control the production of biogas.
In landfills, emissions can be reduced and more biogas can be obtained by altering the planning of material and cover placement work.
Methane collection efficiency can be achieved over the life of the landfill varying from 50 to 60% using conventional biogas extraction and control technology, which is based on the construction of biogas wells during and after the operation of the system. Following these procedures, biogas extraction normally begins after reaching the final height of the cells, which may take three to five years from the start of the refuse placement.
Given that biogas begins to be produced about six months after the deposition and reaches its maximum value two years later, most of the methane produced is lost during the initial phase of the formation of the landfill.
Operational control of biogas should involve the implementation of operational procedures and sequences of more accurate work. In particular, the installation of the biogas extraction system and the placing of the cover should be done by partial areas and much earlier, in order to make possible the extraction of biogas in a period of less than a year. With these procedures it is possible to increase the biogas collection efficiency to about 90%.
If these excellent operational control measures, which are based on the preventive installation of biogas collection and extraction infrastructures and compartment accelerated sealing, are implemented, the emissions and the environmental impact of the landfill bioreactor are much lower than the methodology practiced traditionally.
47
Sustainable Land Use of Landfills
Restoration of landfill sites is a key component of a sustainable land use system. There are numerous sites contaminated with landfills whose restoration constitutes a new investment opportunity. The future "Soil Framework Directive (SFD)", which is being drafted, is creating a lot of expectations as it is expected to define key principles for preventing restrictions, preserving soil functions, maintaining their properties and enabling their use sustained [7].
This topic is complex and involves fundamental considerations about the concepts of soil, waste and contaminated land, which should be defined, specified and included in the relevant legislation. The concept of "soil" implies a material or substrate that should be restored until it has the natural biological functionalities. However, this definition may not be appropriate for landfills when there is a lot of inert filler material and the soil is intended for urban use.
The recovery of contaminated landfills entails adequate framing in terms of the legal status of soils and residues, the relationships between contaminated soil and waste, the reuse of contaminated soil and the conditions under which contaminated soil should be left on site .
48
Validity of Landfills
The important role that Aterro still plays in the context of environmental management technologies can not be disregarded, a component that can not be completely eliminated.
Landfills are the best technology solution for certain types of waste such as those contaminated by asbestos [3], waste from soil restoration and inorganic sludge.
Landfills are also used as a resource solution in temporary situations of insufficient capacity or failures of the main processing units. Therefore, bearing in mind that the current Directive provides for the gradual reduction of the organic matter to be disposed of in landfills, it is immediately apparent that this system will be used for many years in tune and coordination with other methods used in the modern treatment management and final destination of the waste.
On the other hand, without any interference in environmental policy and the promotion of the highest hierarchical solutions, market actors will still continue to deal with both new and end-of-life landfills, which will require care. For this reason it makes perfect sense to introduce measures to improve landfills and make them sustainable.
49Congress Bioenergy-Guimarães 6-9 April 2008
Santino Di Berardino
Solid waste sector –in Portugal
Initial urgent objective: Elimination, until 2000, of all open dumps and control of all basic sanitary and environmental issues related with solid wastes, which are now already treated and disposed safely.
Implementation of regional entities in charge of MSW management
Appearance of European and national legislation about waste,
Achievement of more efficient management framework,
the change of attitude of society concerning the environment
Evolution of Solid Waste treatment technology allowed:
50
Solid Waste operators in charge for waste management in Portugal
28 de Maio de 2015
51Congress Bioenergy-Guimarães 6-9 April 2008
Santino Di Berardino
Collection and treatment in Portugal
In 2002 the total production of municipal solid wastes (MSW) was 4.7 Million of tons [7].
Organized collection and removal is carried out for 100 % of the total MSW produced.
About 67 % of the cycle of production, collection and disposal ends at controlled sanitary landfills, the more popular method of MSWT.
Incineration is the solution adopted in large high density urban centres (in Lisbon, Porto and Madeira) : 1 million/ton/year (20.9%).
Organic waste recovery and composting quite practiced, accounting 8.4% of the total. A small portion of the wastes (3.4%) was processed at sorting units.
The average per capita generation rate in 2002 was 1.32 kg/capita/day [7].
52Congress Bioenergy-Guimarães 6-9 April 2008
Santino Di Berardino
MSW amounts by methods of disposal in continental Portugal, 2002.[5]
0,0E+00
5,0E+05
1,0E+06
1,5E+06
2,0E+06
2,5E+06
3,0E+06
3,5E+06
4,0E+06
4,5E+06
5,0E+06
(to
n.)
ton./year 3193560 992429 300412 159621 4646022
Sanitary
landfill
Incineration
plant
Organic
Waste Sorting plant Total
53Congress Bioenergy-Guimarães 6-9 April 2008
Santino Di Berardino
Situation
Source separate collection is improving, to accomplish the recycling targets for 2011.
Sanitary Landfilling is the main method for MSW. In the majority of landfill sites, gas energy recovery is not practiced. Only In two
large sanitary landfill, controlled by the Empresa Geral do Fomento (AGF), today the Power electricity production from landfill gas is 9,9 MW [8].
in May 2002, the European Directive 1999/31/EC was transposed, defining national targets on the reduction of biodegradable waste in landfilling.
In 2007 the Law DL - N 225/2007, introduced feed-in tariff from renewable fonts, including biomass and residues and SW, propitiating financial facilities and promoting AD plants implementation for MSW.
EGF company is planning for 2008/2012 the construction of several digesters to replace landfilling, with a power electricity capacity of 42 MW (from biogas), including 27 MW from hydrogen Biomethane production [6].
Additional 35 MW presumably can be produced by the other company acting on SW management.
54
Composting
When no agricultural land is available close to the facility and it is unviable digestate composting is recommendable option.
Allows more easy storage and transportation as well as provides better safe and hygienic product.
This solution implies additional capital and operational costs and its revenue are strongly dependent from the market demand, making uncertain its cost-effectiveness.
55
Existing landfills and adequacy to the directive
This solution represents a major development in relation to open-air discharges but is at the bottom of the hierarchy of treatment and recovery systems as defined by Directive 94/62 / EC - on landfills, classifying the prevention, reuse and recycling at higher levels compared to treatment and final disposal, even when carried out in situations of high sanitary and environmental control.
In most national landfills, the recovery of the gas and its use for the production of energy is not carried out.
Recent legislation has more seriously considered the recovery and potential use of biogas which, because of its calorific value, can provide interesting revenues and benefit the environment by reducing greenhouse gas emissions.
56
Landfills with biogas recovery
In October 2005 there were 4 landfills that practiced the recovery and use of biogas in Portugal with a total installed capacity of 4.9 MW, related to the companies Suldouro, Valorlis, Amarsul and Algar. [15]
More recent data [2009] indicate that in AMARSUL landfills and others controlled by the General Development Company (EGF) there is an installed electrical power of 9.9 MW.
The energy currently produced from landfills is 10 MW [8], being the largest source of biogas in the country.
57
Landfills with biogas recovery in PORTUGAL
58
Replacing landfills
Decree-Law 152/2002 of the Ministry of the Environment (transposition of European Directive 1999/31 / EC) establishes the procedures for the licensing and reduction rates of organic matter to be applied and restricts the application of biodegradable organic matter in landfills toilets.
The replacement of the sanitary landfills provided for in this Decree-Law leads to a significant increase in the hierarchy of treatment and removal methods, promotes anaerobic digestion, increasing the production and use of biogas and the environmental control of emissions.
The materials rejected by our civilization should not be placed underground. In each specific case, an alternative, accessible, viable and more environmentally sensitive use should be considered and envisaged.
9 MW. The energy currently produced from landfills is 10 MW [8], being the
largest source of biogas in the country.
59
Methods of Treatment in Portugalof MSW in 2002 and 2016
60
Organic valorization of GARBAGE
The biological decomposition of the organic matter transforms the organic fraction of the wastes into humus relatively stable and suitable for the fertilization of the soil, being carried out under aerobic or anaerobic conditions and at mesophilic or thermophilic temperatures.
The processes of decomposition of the organic matter of the anaerobic type of waste is defined as anaerobic digestion whereas in an aerobic regime the decomposition takes the current name of composting.
61
Organic valorization of GARBAGE
The composting takes place in an aerobic regime, avoiding the anaerobic decomposition as it presents drawbacks: excessive humidity, bad smell, drainage loss, longer fermentation period. It requires less investment but does not produce energy, being preferred in small scale systems.
Nowadays, AD is applied in large systems, followed by composting (ETVO)
Garbage is one of the substrates for anaerobic digestion, with excellent functioning systems.
62
Composting Description
In simple composting, it is sought the stabilization of the solid residues that are: disintegrated, mixed, aerated and dehydrated. The process is fast, requiring only a few days to complete it. The aerobic fermentation process is very easy to be adapted to the most various local conditions.
The process can be carried out in a natural way, by pre-grinding the residues and fermenting them in feathers of 1.50 m to 1.80 m in height, ventilated periodically by stirring the contents or can be carried out in an accelerated way in aerated units with system forced.
The microorganisms responsible for the fermentation process use the carbon in the waste as a source of energy and nitrogen as a nutrient for cell growth and are sensitive to changes in temperature.
During growth, high temperature develops in the medes, which may reach about 60 ° C. This temperature value provides a faster growth of the microbial species and the decrease of the pathogenic organisms.
63
Windrow composting
The windrow should have a trapezoidal section with a height ranging from 1.20 m to 1.80 m and base width from 2.40 m to 3.60 m and be laid on compacted or paved ground. The height of the lairage is very important because if it is too low, the material will lose heat and moisture quickly, and if it is too high, the material will not lose heat, become excessively hot, and compress itself due to its own weight, reducing the pores and becoming anaerobic.
Energia da biomassa
64
Process Description
For balanced growth of microorganisms, the carbon / nitrogen ratio and pH value must be controlled, which can not fluctuate above certain limits.
The decomposition is terminated when the compound is stabilized and does not generate heat and can be applied without restriction in agriculture if the C / N value is equal to or less than 20.
Garbage grinding allows for better aeration, better moisture control and more favorable spread of bacteria. Before grinding, the waste is sorted and homogenized to accelerate the decomposition process
65
Process Description
It can be made with residues that have humidity, from 30% to 85%, provided that an adequate aeration is provided, to avoid anaerobic conditions, producing bad smells and polluting liquids.
High moisture content in the mass decreases the volume of air contained in the interstices, favoring the appearance of anaerobic conditions.
If the waste contains less than 40% moisture, the microorganisms do not have enough water for the metabolism, inhibiting their activities. Therefore, water must be added to the fermenting material when the moisture is lowered by 40%, and the water withdrawn when the humidity exceeds 60%.
66
Process Operation.
During decomposition, the material should be periodically flipped in order to facilitate aeration, ensuring natural and rapid stabilization, without damaging the aerobic thermophilic process. Revolving can be performed manually or mechanically.
As the decomposition progresses, the area necessary for the formation of the medas decreases. Turning the outer faces of the median to the center, a uniform decomposition is achieved. The high temp. from the interior of the meda eliminate pathogenic bacteria, or insect eggs that live on the cold outer surface. The moisture content determines the frequency and number of turns.
67
Process Operation.
.
There is usually no need to inoculate the waste with bacteria to develop the process as they exist in the urban waste. The time to process development varies with the nature of the waste, its C / N ratio and the method used. The decomposition time increases with increasing C / N.
C / N between 18 and 25, time from 6 to 8 days;
C / N between 20 and 50, time 16 days.
The C / N ratio also has an important effect on the soil, because if this value is higher than 20, the microorganisms remove nitrogen from the soil in order to use the carbon still available. This will cause a delay in the plant's use of the nitrogen that is diverted to the life cycle of soil bacteria.
When considering the decomposition practically complete, the value of the C / N ratio should be between 12 and 20. The appearance of the ready-to-use compound is dark gray to brown and, to improve its appearance, grinding and bagging.
68
Process application
The composting process has the undeniable advantage of transforming polluting waste into a useful by-product in agriculture and land preparation, which are particularly interesting in the profile of the demand for sustainable growth.
The process itself is fairly simple to carry out and manage, requiring simple machinery. However, the time required for the stabilization of the compost and the relatively large area of land are factors which may restrict its adoption.
Pretreatment of separation of other products, grinding and homogenization are relatively expensive and difficult to apply in systems with small size.
The existence of a market capable of absorbing the fertilizer produced by composting is the main factor influencing the decision to adopt this solid waste transformation process.
69
Product use
Around the urban centers, there is always the possibility of using the product, depending on a campaign of clarification with the farmers, convincing them of the advantages of organic fertilization.
However, these campaigns have not always led to the expected results. For example, in the Lisbon area the sale of compost has not had a favorable penetration, weighing the disfavor of this product on its not always homogeneous quality, and the presence of aggregates that can progressively damage agricultural soils. Acceptance in the North has been much better.
To help dispose of the product, the municipality itself may consume some of the compost, fertilizing parks, public gardens, etc. Residences, industrial and commercial complexes that have gardens or yards are also potential consumers.
70
Process application
The composting process is used in combination with anaerobic digestion being applied to valorize the digestate.
All the modern AD central have a composting unit for organic valorization.
Digester efluent is mixed with green wastes and grass.
