1. Anaerobic Digestion of Solid Waste
Dorothee Spuhler, seecon gmbh

2. Copy it, adapt it, use it – but acknowledge the source!
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Copy it, adapt it, use it – but acknowledge the source!
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3. Contents
Concept
How can Digestion of Green Waste optimise SSWM
Design Principals
Examples of Applications
Applicability
Pros’ and Con’s
References

4. 1. Concept
Background
Anaerobic digestion is a natural process which occurs when organic material is kept in the absence of air. Thereby, the organic material is transformed into biogas, a renewable and green energy.
In developed countries, this process has been evolved over the past twenty years, resulting in more and more complex large-scale biogas plants including heating and multiple stage processes.
So far, several million conventional biogas plants, using predominantly animal manure as feedstock, have been successfully installed in rural areas of developing countries. (VOEGELI & ZURBRUEGG 2008)
Anaerobic digestion, as a controlled and voluntary process for the reduction and reuse of green wastes has a large potential to give answer to the soaring crisis of increasing municipal solid wastes for instance in urban and peri-urban areas of the developing world. (VOEGELI & ZURBRUEGG 2008)

5. Anaerobic Digestion of Green Waste (1/2)
1. Concept
Anaerobic Digestion of Green Waste (1/2)
Anaerobic Digestion takes place in airtight reactors.
The organic fraction of the wastes is transformed into a mixture of CH4, CO2 and some trace gases (biogas).
The produced biogas can be used either directly for cooking, heating or lightening
It can also be transformed into combined heat and power (CHP) in cogeneration plants
Biogas can also be compressed and sold as fuel (e.g. for vehicles), much like natural gas.
With time the reactors fill up and digested sludge (sludge which organic fraction was already converted to biogas) accumulates in the bottom.
Nutrients remain in the sludge is a well-balanced fertiliser and can be used in agriculture as a rich soil amendment.

6. Anaerobic Digestion of Green Waste
1. Concept
Green Waste
Coocking
Lightning
Electricity
Fuel
Biogas
Heating
Fertiliser
Agriculture
Anaerobic Digestion of Green Waste
D. SPUHLER (2010), Pictures from: [Accessed: ]

7. Anaerobic Digestion of Green Waste: Small-scale
1. Concept
Anaerobic Digestion of Green Waste: Small-scale
Biogas
Soil amendement
Food
Energy
D. SPUHLER (2010). Pictures from: //gardening.ygoy.com/wp-content/uploads/2009/10/how-to-plant-a-decorative-vegetable-garden0.jpg; [Accessed: ]

8. Anaerobic Digestion of Green Waste: Large-scale
1. Concept
Anaerobic Digestion of Green Waste: Large-scale
Source: HOLLIGER (2008)

9. The example of Kristianstad (Sweden)
1. Concept
The example of Kristianstad (Sweden)
Co-digestion of waste and manure
Food production at farms
Re-use of nutrients
Re-use of energy
Green waste from households and industries

10. 1. Concept What is Green Waste?
[Accessed: ]
Garden refuses
1. Concept
What is Green Waste?
Market waste
[Accessed: ]
Green waste is any kind refused material which is biodegradable and has a high fraction of organic matter, which can be transformed into biogas. Some examples…
[Accessed: ]
Refuses from the food industry
Waste from agriculture
[Accessed: ]
Kitchen refuses
[Accessed: ]
[Accessed: ]
Organic fraction of municipal waste
[Accessed: ]
Some industrial wastes

11. 1. Concept
What is Biogas ?
Biogas is a mixture of methane and carbon dioxide.
The properties of biogas are similar to the ones of natural gas.
Biogas is the common name for the mixture of gases released from anaerobic digestion.
Typically biogas is composed of:
Methane is the valuable part of the biogas. Biogas that contains about 60 to 70 % of CH4 has a calorific value of about 6 kWh/m3 what corresponds to about half an L of diesel oil. (ISAT/GTZ 1999, Vol. I)
Methane (CH4)
50 to 75 %
Carbon Dioxide (CO2)
25 to 50 %
Hydrogen (H)
5 to 10 %
Nitrogen (N2)
1 to 2 %
Hydrogen sulphide (H2S)
Traces
Sources: YADAV & HESSE (1981); FAO (1996); PIPOLI (2005); GTZ (2009
Source: MUENCH (2008)

12. What is Anaerobic Digeastion ? (1/2)
1. Concept
What is Anaerobic Digeastion ? (1/2)
Degradation of organic material by bacteria. In the absence of air (anaerobic). Four stages:
Hydrolisis
Cleavage of a chemical compound through the reaction with water.
Insoluble complex molecules are bracken down to short sugars, fatty acids and amino acids.
Fermentation (Acidogenesis)
Products from hydrolysis are transformed into organic acids, alcohols, carbon dioxide (CO2), hydrogen (H) and ammonia (NH3).
Acetogenesis
Organic acids and alcohols are converted into hydrogen (H2), carbon dioxide (CO2) and acetic acid (CH3COOH). Therefore, oxygen is consumed and anaerobic conditions are created
Methanogenesis
Methanogenic bacteria (methanogenesis), transform the acetic acid, carbon dioxide and hydrogen into biogas.

13. What is Anaerobic Digestion ? (2/2)
1. Concept
What is Anaerobic Digestion ? (2/2)
D. SPUHLER (2010)

14. What is a anaerobic digester ?
1. Concept
What is a anaerobic digester ?
Source: HOLLIGER (2008)
1. Airtight chamber, filled with green waste
2. Anaerobic digestion takes place
3. Sludge settles on the bottom
4. Gas bubbles to the top where it is collected
Reaction temperature is > 35 to 55 °C: mesophilic or thermophilic range
Either continuous or in batch mode:
Batch: filled and left for digestion; After the hydraulic retention time (HRT) emptied and filled again for a new cycle
Continuously-stirred tank reactor (CSTR): continuous in/out flow and mixing
Plug-flow reactor: the sludge moves through the reactor much like a train to a tunnel, with a velocity corresponding to the minimal HRT
The liquid phase can be re-circulated to maintain optimal moisture conditions

15. Examples: Small-scale digesters
1. Concept
Source: F. HEEB
Examples: Small-scale digesters
Household floating-drum digesters
[Accessed: ]
Portable reactors form the Indian NGO BIOTECH
[Accessed: ]

16. Examples: Large-scale digesters
1. Concept
Source: BRUYN (2006)
Examples: Large-scale digesters
[]Accessed:
Source: BRUYN (2006)
Source: BRUYN (2006)

17. Examples: Biogas Appliances
1. Concept
Examples: Biogas Appliances
M. WAFLER
Biogas cooking stove
Chang Mai
Biogas boiler
Mini biogas generator
Large combined heat and power (CHP) Cogeneration plant
Biogas lamp

18. 2. How the Digestion of Green Waste optimises SSWM
Anaerobic digestion is a promising answer to the soaring crises of municipal waste explosion and thus prevent the pollution of water sources and the evnvironment
Biogas is an renewable energy and has the potential to replace other fuel sources. Biogas contributes to prevent and lower greenhouse gas emission.
Green Waste
Coocking
Lightning
Electricity
Fuel
Biogas
Heating
Fertiliser
Agriculture
Digested sludge can substitute chemical fertiliser and enhance food production
Sustainable development:
Improved health
Improved economy

19. Basics: Process Parameters
3. Design Principals
Basics: Process Parameters
The biogas yield depends on the process and the substrate.
Substrate:
High COD (Chemical Oxygen Demand) = High potential of biogas generation
Process:
Anaerobic digestion = Biological system of bacteria
Optimal conditions required that bacteria feel wealthy…
Temperature
Performance
Retention time pH
Wide range, but methanogenesis requires neutrality ( )
Multistage process for better pH and temperature control
Total solid (TS) and moisture
Wet digestion (TS < 20 %): easier to maintain, good fluidity
Dry digestion (TS > 20 %): sophisticated but safes space

20. The ARTI compact biogas plant
4. Examples of Applications
The ARTI compact biogas plant
Source: HEEB (2009)
Developed in 2003
ARTI = Appropriate Rural Technology Institute
2000 plants currently used in Maharashtra, India (WRAPAI 2009)
Some have been constructed in Tanzania (VOEGELI & LOHRI 2009)
Floating-drum design:
2 conventional polyethylene tanks (0.75 and 1 m3). (MUELLER 2007)
Standard plumber piping.
The smaller tank is the gasholder and the larger holds the mixture of decomposing feedstock and water
Inlet and an overflow
Overflow liquid is mixed with the feedstock and back recycled into the plant to maintain optimal moisture condition. (MUELLER 2007)
A pipe takes the biogas to a collection balloon or directly to the kitchen.
Source: VOEGELI & LOHRI (2009)

21. 4. Examples of Applications
The BIOTECH Plant (1/2)
BIOTECH is a nodal agency of the Ministry of Non-Conventional Energy Sources in Kerala, South India. (MUELLER 2007)
Domestic plants: 1 m3 for a 3 to 5 member-family meets about 50 % of cooking needs. (MUELLER 2007)
Decentralised treatment of market waste, municipal solid waste or slaughterhouse waste: Biogas used for public street lightning and distributed into households
Source: HEEB (2009)
Source: HEEB (2009)
Source: HEEB (2009)

22. 4. Examples of Applications
The BIOTECH Plant (2/2)
Conventional floating-drum reactor
Liquids are mixed with incoming feedstock and re-circulated
A baffle in the middle increases solids retention
Source: HEEB (2009)
Schematic plan of a BIOTECH market level plant. a) Inlet tank for feedstock. b) Digester tank. c) Effluent tank. d) Effluent storage tank. e) Effluent pump. f) Gasholder drum. The drum is stabilized by a guide pole in the middle and is floating in a water jacket outside the digester. g) Biogas pipe. h) Gas Scrubber. i) Biogas generator j) Drainage connection for excess effluent. (HEEB 2009)

23. 4. Examples of Applications
The KOMPOGAS Plant
Thermophilic dry digestion process developed in Switzerland
Organic wastes come from municipalities with source separation or from food industry
Horizontal plug-flow reactors
Propellers move the sludge trough the reactor and keep particles in suspension. (OSTREM 2004)
Retention time is 20 days. (MES et al. 2003)
Biogas is transformed in a CHP unit providing 100 % of the facility needs as well as additional electricity for sale. In some cases, the biogas is upgraded to natural gas standards for use in vehicles or input to the natural gas network. (OSTREM 2004)
Both liquid and solid effluents are commercialised fertilisers

24. Large-scale Plant in Thailand for Municipal Waste (1/2)
4. Examples of Applications
Large-scale Plant in Thailand for Municipal Waste (1/2)
In Thailand, where the development of alternative sources is critical to energy sustainability as the government has set 2011 as the target date for 80 % of the nation’s total energy, representing an estimated 1,900 MW, to be generated from renewable energy sources. (MUELLER 2007)
This has given large rise to various large-scale biogas projects.
The Rayong Municipality has constructed plant for the treatment of the organic fraction of the municipal solid waste (MSW) with a capacity of 60 tons of waste per day.
Two systems:
Digesters: converts waste to biogas and fertilizer
A biogas-fired cogeneration process (CHP)
MUELLER (2007)
MUELLER (2007)

25. Large-scale Plant in Thailand for Municipal Waste (1/2)
4. Examples of Applications
Large-scale Plant in Thailand for Municipal Waste (1/2)
SourcE: MUELLER (2007)
a wet fed-batch high-solids
Process: Wet fed-batch high-solids digestion
Feedstock: Organic MSW and refuses from the food industry.
Capacity: 60 tons per day
Output: 5800 tons organic fertilizer and electricity of about 5 million kWh. (MUELLER 2007)

26. 5. Applicability
Anaerobic digestion can transform almost any biodegradable waste into biogas (e.g. green waste).
The anaerobic treatment of organic solid waste is applicable everywhere where there is a need for biogas and waste treatment and the technical conditions allow the installation of a plant.
Small-scale (biogas generation for cooking and lightening) – low-cost and relatively low-tech:
Household-level
Community-level
Institutional-level
Large-scale – high-tech, requires expert design:
Industrial plant connected to the public power and heat grid.
Low-tech (un-heated plants), however, are only adapted to areas where temperature does not fall short of for any substantial length of time.

27. 6. Pros’ and Cons’
Disadvantages:
Small- and middle-scale anaerobic technology for the treatment of solid waste in middle- and low-income countries is still relatively new
Experts are required for the design and construction, depending on scale may also for operation and maintenance
Reuse of produced energy (e.g. transformation into, fire/light, heat and power) needs to be established
High sensitivity of methanogenic bacteria to a large number of chemical compounds
Sulphurous compounds can lead to odour
Advantages:
Generation of biogas and fertilizer (almost complete retention of the fertiliser nutrients (N, P and K)
Reduction of greenhouse gas emissions through methane recovery
Combined treatment of different organic waste and wastewaters
Reduction of solids to be handled (e.g. less excess sludge)
Good pathogen removal depending on temperature
Process stability (high-loads can be treated but anaerobic sludge can also be preserved for prolonged periods without any feeding)

28. 7. References
BRUYN, J. de, HOUSE, H., RODENBURG, J. (2006): Ontario Large Herd Operators European Anaerobic Digestion Tour Report. Germany, Denmark and the Netherlands August 21 to 29, Ontario Ministry of Agriculture, Food and Rural Affairs
FAO (1996): Biogas Technology - A Training Manual for Extension. Consolidated Management Services Nepal (P) Ltd. and Food and Agriculture Organization of the United Nations (FAO) Available at: [Accessed: ]
GTZ (2009): Biogas sanitation for black water or brown water, or excreta treatment and reuse in developing countries. Draft Version.(=Technology review). Eschborn: German Agency for Technical Cooperation GmbH (GTZ) and Sustainable Sanitation Alliance (SuSanA) Available at: [Accessed: ]
HEEB, F. (2009): Decentralised anaerobic digestion of market waste. Case study in Thiruvananthapuram, India. Duebendorf: Swiss Federal Institute of Aquatic Science and Technology (EAWAG). Available at: [Accessed: ]
HOLLIGER, C. (2008): Microbiologie et Biotechnologie Environnementale. Enseignements au 2iE. Swiss Federal Institute of Technologies (EPFL)
ISAT/GTZ (1999): Biogas Basics. (=Biogas Digest, Volume I). Information and Advisory Services on Appropriate Technology (ISAT) and German Agency for Technical Cooperation GmbH (GTZ). Available at: [Accessed: ]
MES, T.Z.D. de, STAMS, A.J.M, REITH, J.H., ZEEMAN, G. (2003): Chapter 4. Methane production by anaerobic digestion of wastewater and solid wastes. In: REITH, J.H., WIJFFELS, R.H., BARTEN, H.(Eds.) (2003): Biomethane and Biohydrogen. Status and perspectives of biological methane and hydrogen production. Dutch Biological Hydrogen Foundation and the Netherlands Agency for Energy and the Environment (Novem). Available at: [Accessed: ]
MUELLER, C. (2007): Anaerobic Digestion of Biodegradable Solid Waste in Low- and Middle-Income Countries. Swiss Federal Institute of Aquatic Science (EAWAG), Department of Water and Sanitation in Developing Countries (SANDEC) [Accessed: ]
MUENCH, E. (2008): Overview of anaerobic treatment options for sustainable sanitation systems. In: BGR Symposium „Coupling Sustainable Sanitation and Groundwater Protection“ 14 – 17 Oct 2008, Hannover, Germany. Eschborn: German Agency for Technical Cooperation (GTZ) GmbH Available at: [Accessed: ]
OSTREM, K. (2004): Greening Waste: Anaerobic Digestion for treating the organic Fraction of Municipal Solid Wastes. Master theis. Colombia: The Fu Foundation of School of Engineering and Applied Science, Columbia University
PIPOLI, T. (2005): Feasibility of Biomass-based Fuel Cells for Manned Space Exploration. In: Proceedings of the Seventh Eurpean Space Power Conference, Stresa, Italy. 9 to 13 May VOEGELI & LOHRI 2009)
VOEGELI, Y., ZURBRUEGG, C. (2008) Biogas in cities - A New Trend?. In: Sandec News, Vol. 9/2008. Duebendorf: Swiss Federal Institute of Aquatic Science (EAWAG)
WRAPAI (2009): Document 8, Data Management Document, Appendix S 06 - Energy Research. Australia: Waste Refinery Australia Project Association Incorporated (WRAPAI) Available at: [Accessed: ]
YADAVA, L. S., HESSE, P. R. (1981): The Development and Use of Biogas Technology in Rural Areas of Asia (A Status Report 1981). Improving Soil Fertility through Organic Recycling. (=Project Field Document No. 10.). Food and Agriculture Organization (FAO) and United Nations Development Programme (UNEP)

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