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19 June 2018

Anaerobic Digestion (General)

Author/Compiled by
Dorothee Spuhler (seecon international gmbh)
Executive Summary

Biogas sanitation is the treatment of waste and wastewater by a process called anaerobic digestion. During anaerobic digestion, the organic matter in the waste and wastewaters is transformed to biogas, a mix of methane (CH4) and carbon dioxide (CO2) and a nutrient rich sludge. Biogas can be transformed into heat or power and has therefore a large potential as a renewable energy source. The nutrient-rich sludge can be composted and used as fertilising soil amendment in agriculture. Typical biogas sanitation technologies are biogas settlers, upflow anaerobic sludge blanket (UASB) reactors, anaerobic baffled reactors (ABRs) and anaerobic filters for municipal wastewaters; and biogas reactors (batch, fed-batch PFR or CSTR) for the treatment of slurries and solid organic wastes from agriculture and industry.

Advantages
Production of renewable energy (heat, light, electricity)
Reduction of greenhouse gas emissions through methane recovery
Reduction of solids to be handled (e.g. less excess sludge)
Transformation of organic wastes into high quality fertilizer
Improvement of hygienic conditions through reduction of pathogens, worm eggs and flies
Process stability (high-loads can be treated but anaerobic sludge can also be preserved for prolonged periods without any feeding)
Relatively low construction costs
The space requirements of anaerobic treatment are lower than for aerobic wastewater treatment systems
Disadvantages
Experts are required for the design, construction and maybe even operation (complexity generally rises with scale)
Temperature dependent
Reuse of produced energy (e.g. transformation into heat and power) needs to be established
Sludge may require further treatment (e.g. aerobic composting, humification using sludge drying beds, etc.)
High sensitivity of methanogenic bacteria to a large number of chemical compounds
Requires seeding (start-up can be long due to the low growth yield of anaerobic bacteria)
In Out

Blackwater, Brownwater, Faecal Sludge

Biogas

Biogas sanitation technologies are based on the collection of waste and wastewater in airtight chambers in which anaerobic digestion transforms the organic matter into biogas and nutrient rich slurry. The produced biogas can be recovered and used directly for cooking and lighting or it can be transformed into heat in a gas heater system or into combined heat and power (CHP) in cogeneration plants thereby replacing other fuel sources (MES et al. 2003; JENSSEN et al. 2004; WRAPAI 2009) (factsheets on conversion of biogas to electricity on small and large scale, or on direct use of biogas). The biogas can also be upgraded to natural gas quality, compressed and used to power motor vehicles. Methane (CH4) is the valuable component under the aspect of using biogas fuel. 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). The remaining sludge is biologically more or less stable and rich in nutrients, which makes it a valuable soil conditioner and fertiliser.

 

Overview scheme of biogas sanitation systems. Source: MUENCH (2008)

Overview scheme of biogas sanitation systems. Source: MUENCH (2008)

Anaerobic digestion is a well-established treatment technology suited for wastewater or wastes containing high levels of organic matter. Anaerobic waste and wastewater treatments are cheaper and simpler to operate than aerobic processes, as there is no need for energy for the aeration system and the reduction of the sludge volumes is relatively high as a large fraction of the organic matter is volatilised into the biogas. Moreover, the collection of the biogas reduces the emission of greenhouse gases to the atmosphere and gives a source of renewable energy.

Anaerobic digestion is one of the oldest technologies used for waste treatment (MUELLER 2007). The industrialisation of anaerobic digestion began in 1859 with the first plant in Bombay, India. These early biogas plants were based on a simple waste dumping pond, which was covered to collect the gas. This type of plant is still used to day for the treatment of some very diluted wastes (BURKE 2001).

 Covered anaerobic waste stabilisation pond (WSP) with biogas collection. Source: H.P. MANG

Covered anaerobic waste stabilisation pond (WSP) wit h biogas collection. Source: MANG (n.y.)

 Small-scale biogas reactor for the treatment of market waste (left); large-scale anaerobic lagoon with biogas recovery for the treatment of waste from swine stock farming (middle); and treatment of excess sludge from a municipal waste water treatment plant in egg-shaped completely mixed reactors (right). Source: MIKLED (n.y.), gfn.unizar

Small-scale biogas reactor for the treatment of market waste (l eft); large e-scale anaerobic lagoon with biogas recovery for the treatment of waste from swine stock farming (middle); and treatment of excess sludge from a municipal waste water treatment plant in egg-shaped completely mixed reactors (right). Source: MIKLED (n.y.); GFN UNIZAR (n.y.)

 

 

 

 

 

 

 

In developing countries, mainly basic agricultural small-scale biogas reactors have been promoted. In more industrialised countries, anaerobic digesters were continuously improved and more sophisticated equipment and operational techniques emerged resulting in the use of large-scale closed tanks and heating and mixing equipment (MUELLER 2007). Today, the interest in biogas as a renewable, green energy is soaring facing the global energy and climate crisis. Electricity and fuel pricing as well as grid access are the key factors for the dissemination of biogas plants (BRUYN 2006). Almost any organic waste can be transformed to energy by anaerobic digestion and various technologies are available, depending on the substrate and the context.


Factsheet Block Title
Main applications of biogas sanitation
Factsheet Block Body
  • Small-scale agricultural biogas reactors for the treatment of animal manure. Kitchen or garden wastes can be co-treated or reactors are can be linked to toilets as safe sanitation option (see the factsheet biogas digesters small-scale)
  • Large-scale biogas reactors for the treatment of slurries form agriculture and industry and organic solid waste (see the factsheet biogas digesters large-scale and anaerobic treatment of organic solid waste). These types of reactors are also used for the treatment of excess sludge from large municipal wastewater treatment plants.
  • Small-scale and decentralised biogas reactors for the treatment of organic solid waste in developing countries (still relatively new, see the factsheet anaerobic treatment of organic solid waste).
  • Anaerobic settlers for the treatment of municipal wastewater (domestic and industrial), faecal sludge (sludge and liquid) and sewage: biogas settlers or modified septic tanks, anaerobic baffled reactors (ABRs), anaerobic filters (AFs), up flow anaerobic sludge blanket reactors. These pre-settling units are often used in decentralised wastewater treatment systems (DEWATS).
Factsheet Block Title
Classification of biogas sanitation systems
Factsheet Block Body

 Classification of biogas treatment technologies. Source: SPUHLER 2010

Classification of biogas treatment technologies. Source: SPUHLER (2010)

Anaerobic biogas reactors can be divided into “high-rate” systems, involving biomass retention and “low-rate” systems without biomass retention.

High-rate systems are characterised by a relatively short hydraulic retention time (HRT), but long sludge retention time (SRT). Typical high-rate systems are biogas settlers, ABRs, AFs and UASB reactors, used for the pre-treatment (e.g. biogas settler) and treatment (e.g. ABRs, AFs and UASB) of rather heterogeneous flows such as municipal wastewater. In high-rate systems, the sludge is retained and transformed into biogas, while the liquor flows out of the tanks for further treatment and/or disposal.

Low-rate systems are characterised by a relatively long hydraulic HRT, which is equal to the SRT as the sludge and liquid enter and leave the tank in a more or less homogeneously mixed slurry. Low-rate systems are suited for all kinds of biodegradable slurries (e.g. animal manure, excess sludge from municipal wastewater plants, mixed organic solid wastes). Typical low-rate anaerobic biogas digesters are batch reactors, fed-batch reactors (accumulation systems), plug-flow reactors (PFR) or continuously stirred tank reactors (CSTR) (see the factsheets biogas digesters small and large scale) and biogas reactors for the treatment of organic solid waste).

The process used for all these technologies is basically the same: anaerobic digestion. However, depending on scale and type of waste stream to be treated, complexity of design, construction and operation varies strongly.

Factsheet Block Title
Anaerobic digestion
Factsheet Block Body

Anaerobic digestion is the degradation of organic material by microbial activity in the absence of air transforming it into biomass and biogas, a mixture of methane (CH4), carbon dioxide (CO2) and some trace gases:

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

Typical composition of biogas. Sources: YADAVA & HESSE (1981); FAO (1996); PIPOLI (2005); GTZ (2009)

The process is generally carried out in four stages: hydrolysis; fermentation and acidification; acetogenesis, and methanogenesis. To achieve this sequence of four steps, various bacteria (e.g. fermenting, acetogenic and methanogenic bacteria) need to work together. None of these types of bacteria is able to produce biogas products alone (ISAT/GTZ 1999).

 Anaerobic digestion: complex organic molecules, proteins and fats are broken down in a four-step process in to a mixture of methane (CH4) and carbon dioxide (CO2) and some trace gases. The biogas can be collected and the CH4 be used as a combustible. Source: SPUHLER 2010

Anaerobic digestion: complex organic molecules, proteins and fats are broken down in a four-step process in to a mixture of methane (CH4) and carbon dioxide (CO2) and some trace gases. The biogas can be collected and the CH4 be used as a combustible. Source: SPUHLER (2010)

Hydrolysis describes the cleavage of a chemical compound through the reaction with water. Thereby, a hydrogen atom (H) is added to one part of the split chain, while the remaining hydroxyl group of the water (OH) is added to the other. Hydrolysis is the first step of anaerobic digestion in which insoluble complex molecules such as carbohydrates and fats are broken down to short sugars, fatty acids and amino acids.
Fermentation is the second step of anaerobic digestion. Fermentative bacteria transform sugars and other monomeric organic products from hydrolysis into organic acids, alcohols, carbon dioxide (CO2), hydrogen (H) and ammonia (NH3).

Acetogenesis is the third step of anaerobic digestion. Products from fermentation (organic acids, alcohols) are converted into hydrogen (H2), carbon dioxide (CO2) and acetic acid (CH3COOH). To produce acetic acid, acetogenic bacteria need oxygen and carbon. For this, they use the oxygen solved in the solution or bounded-oxygen. Hereby, the acid-producing bacteria create an anaerobic condition, which are essential for the methane-producing microorganisms responsible for the further step.

Methanogenesis is the fourth and final step of anaerobic digestion. Methanogenic bacteria (methanogens), which are strictly anaerobic, transform the acetic acid, carbon dioxide and hydrogen into a mixture of methane (CH4, 50–75 %), carbon dioxide (CO2, 50-75 %) and varying quantities of nitrogen, hydrogen sulphide and other components. This mixture is called biogas (PIPOLI 2005; GTZ 2009).

Factsheet Block Title
Important process parameters
Factsheet Block Body

For the digestion to be effective, it should operate as a finely balanced, living system – carefully controlled and closely monitored – in order to create optimal conditions for the growth of the bacteria responsible for anaerobic digestion. Therefore, several factors should be considered for design and processing of biogas treatment units. The most important of these parameters are described below.

Temperature: mesophilic and thermophilic digestion

Temperature is one of the most important parameters influencing the performance of anaerobic digestion processes. Anaerobic digestion is theoretically possible between approximately 3 to 70 °C (ISAT/GTZ 1999). As in all other microbial processes, the rate of metabolism increases along with the temperature: the higher the temperature, the shorter the retention time (WERNER et al. 1989). Depending on the temperature, the digestion process will be more or less long and therefore, temperature is directly linked to the retention time.
The following types of digestion are distinguished according to the temperature in the digester (SASSE 1988): psychrophilic digestion (10-20 °C); mesophilic digestion (20-35 °C); and thermophilic digestion (50-60 °C, HRT > 8 days). The conventional operational temperature levels for anaerobic digesters are mesophilic and thermophilic. Thermophilic processes produce more biogas in shorter time but require higher input energy to obtain operation temperatures. Further, at higher temperature, not only methane production can be increased but also the generation of free ammonia, which can have an inhibitory effect on the digestion performance (ISAT/GTZ 1999). Therefore, mesophilic systems are generally more interesting. If the temperature of the biomass is below 15°C, gas production will be so low that the biogas plant is no longer economically feasible.

The optimal pH-level

There are two groups of bacteria in terms of pH optima, namely acidogens and methanogens. The best pH range for acidogens is 5.5 – 6.5 and for methanogens is 7.8 – 8.2 (MANG n.y.). The operating pH for combined cultures is 6.5-7.5 (MES et al. 2003). Since methanogenesis is considered as a rate-limiting step, pH close to neutral is optimum. Generally, pH is self-regulating and there is now need for adjustment. However, in the case of dysfunction of a system, an inappropriate pH may be the reason for the disturbed microbial process (MES et al. 2003).

Content of total solids (TS): dry (high-solid) and wet (low-solid) fermentation

Low-rate digesters can be designed to operate either in a high-solids (dry) or low-solids (wet) digestion process. High-solids digesters have TS contents above 20%, whereas below 20%, the digestion process is called wet. The most often, low-rate processes for the treatment of excess sludge, faecal sludge and agricultural or industrial slurries are wet processes. Wet (also low-solids) digesters can transport material through the system using standard pumps that require significantly lower energy input. Dry processes have the advantage to require less space, but they are somehow more complex and relatively new, however they have a large potential for the treatment of municipal organic solid waste. The TS content of high-rate systems after separation of the sludge from the liquid is generally similar to the one of slurries for wet digestion, but the concept of dry and wet mode is not applicable to high-rate anaerobic systems.

Mixing

For a well operating system, mixing has to be provided by mechanical stirring, gas circulation (bubbling) or displacement under gravity (MUELLER 2007). Intensive mixing is important for the process to allow the bacteria the contact with every degradable material. Mixing therefore improves the processing rate of reactor system (MUELLER 2007).

Methane production potential: COD and anaerobic biodegradability

In all kinds of biogas technologies, it is the chemical oxygen demand (COD), which is generally used to quantify the amount of organic matter in waste streams and predict the potential for biogas production. Another very useful parameter to evaluate substrates for anaerobic digestion is the anaerobic biodegradability and hydrolysis constant. The total anaerobic biodegradability is measured by the total amount of methane produced during a retention time of at least 50 days (MES et al. 2003).

Reactor set-up: batch or continuous

The most common forms of low-rate biogas reactors are batch reactors, plug-flow reactors (PFR) and continuously stirred tank reactors (CSTR). High-rate reactors a mixed concept: continuous mode for liquid and batch mode for settled sludge. Wet systems often also apply fed batch reactors (accumulation systems, MES et al. 2003).
Batch systems are the only systems that allow controlling accurately the hydraulic or solid residence time (HRT and SRT). But as the batch needs to be opened and emptied regularly, odour emissions can occur. In continuous reactors (PFR and CSTR) the HRT/SRT are determined by dividing the volume of the reactor by the flow.

One-stage and multi-stage processing

One-stage digestion, where all the process takes place in a single reactor, saves costs and is easier to operate. Small-scale plants in general are designed as one-stage processes. Large-scale plants however, often apply two- or multi-stage processes. The idea of multi-stage processes is that the digestion is mediated by a sequence of bio-chemical reactions, which do not necessarily share the same optimal environmental conditions. The systems involve separation of hydrolysis and acidogenesis from acetogenesis and methanogenesis phases (MES et al. 2003). This allows to more accurately control the main process factors (oxygen, temperature and pH) influencing the performance of the digestion bacteria. This is particularly interesting where heating is applied to improve the methanogenesis process as the volume to be heated is considerably lowered, resulting in an energy savings.

Applicability

Anaerobic digestion can be used for almost any kind of organic waste. It is particularly interesting where there is a demand for biogas as a renewable energy source and where the remaining fertilising sludge can be reused for food or crop production.

Small-scale biogas reactors for the household level treatment of animal manure, kitchen waste and toilet products have been widely disseminated in southern countries, mainly in Asia. Large-scale plants are used mainly in industrialised countries for the treatment of waste slurries from agriculture and industry or the treatment of excess sludge from municipal wastewater treatment. There are also technologies for the treatment of organic solid wastes at small-, community- and large-scale level.

Library References

Dairy Waste Anaerobic Digestion Handbook. Options for Recovering Beneficial Products from Dairy Manure

This manual provides an introduction to the anaerobic digestion of dairy manure. The operation and waste management practices of Idaho dairies, the anaerobic digestion and the anaerobic digestion processes suitable for dairy waste, the typical design applications for different types of dairies and finally the cost and benefits of the facilities are discussed.

BURKE, P.E. ; Dennis, A. ; (2001): Dairy Waste Anaerobic Digestion Handbook. Options for Recovering Beneficial Products from Dairy Manure, Olympia: Environmental Energy Company

Biogas Technology - A Training Manual for Extension

This manual contains a complete set of training materials on various topics around the large-scale dissemination of domestic (agricultural) biogas systems, including a system approach to biogas technology, biogas programmes, reuse of slurry, subsidy and institutional financing, quality standards and monitoring and evaluation issues.

FAO (1996): Biogas Technology - A Training Manual for Extension, Support for Development of National Biogas Programme (FAO/TCP/NEP/4451-T) . Consolidated Management Services Nepal (P) Ltd. and Food and Agriculture Organization of the United Nations (FAO) URL [Accessed: 19.04.2010]

Technology Review of Biogas Sanitation

This document provides an overview and introduction on biogas sanitation (anaerobic digestion) for blackwater or for brown water, or excreta treatment for reuse in developing countries. The main technologies discussed are biogas settlers (BSs), biogas septic tanks, anaerobic baffled reactor (ABRs), anaerobic filter (AFs) and upflow anaerobic sludge blanket reactors (UASBs).

MANG, H.-P. ; LI, Z. ; (2010): Technology Review of Biogas Sanitation, (= Technology Review ). Eschborn: Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbH URL [Accessed: 17.06.2013]

Biogas Basics

The information service on biogas technology has been developed and produced on the behalf of the GTZ project Information and Advisory Service on Appropriate Technology (ISAT). Volume I tells you all you need to get an overview on biogas sanitation systems, from history over process and operation parameters to social, political and cultural issues.

ISAT ; GTZ (1999): Biogas Basics, (= Biogas Digest , 1 ). Information and Advisory Services on Appropriate Technology (ISAT) and German Agency for Technical Cooperation GmbH (GTZ) URL [Accessed: 19.04.2010]

Overview of anaerobic treatment options for sustainable sanitation systems

PDF presentation about condominium-level biogas digesters for the transformation of human faeces. Biogas basics as well as two case studies (from Germany and India) are presented.

MUENCH, E. (2008) Overview of anaerobic treatment options for sustainable sanitation systems, In: BGR Symposium "Coupling Sustainable Sanitation and Groundwater Protection". . URL [Accessed: 23.04.2010]

Biogas Plants in Animal Husbandry

This guide addresses the planners and providers of stock-farming and agricultural-extension services in developing countries. It is intended to serve as a source of information on the potentials of and prerequisites for biogas technology: a decision-making and planning aid for the construction and dissemination of biogas plants: a book of reference for information on practical experience and detailed data.

WERNER, U. ; STOEHR, U. ; HEES., N. ; (1989): Biogas Plants in Animal Husbandry, German Appropriate Technology Exchange (GATE) and German Agency for Technical Cooperation (GTZ) GmbH

Document 8, Data Management Document, Appendix S 06 - Energy Research

This document provided by Waste Refinery Australia Project Association Inc. contains information on biogas, different types of cogeneration (CHP) and district heating. Additionally there are also facts and information on hydronics and gas flare.

WRAPAI (2009): Document 8, Data Management Document, Appendix S 06 - Energy Research, Australia: Waste Refinery Australia Project Association Incorporated (WRAPAI)

Chapter 4. Methane production by anaerobic digestion of wastewater and solid wastes

This chapter is part of a publication, commissioned by the Netherlands Agency for Energy and the Environment (Novem) on the status and perspectives of research and development in the field of high-tech biological production of methane and hydrogen. Chapter 4 gives a short but precise introduction the technological aspects of waste treatment by anaerobic digestion and the reuse of the produced biogas.

MES, T.Z.D. de ; STAMS, A.J.M. ; ZEEMAN, G. ; (2003): Chapter 4. Methane production by anaerobic digestion of wastewater and solid wastes, REITH, J.H. ; WIJFFELS, R.H. ; BARTEN, H. (2003): Biomethane and Biohydrogen. Status and perspectives of biological methane and hydrogen production. ,58-94 .

Biogas Plants

This rather old document still gives a good overview on biogas technology. It is intended to help designers of a biogas plant to be able to distinguish between valid and invalid solutions.

SASSE, L. ; (1988): Biogas Plants, German Appropriate Technology Exchange (GATE) and German Agency for Technical Cooperation (GTZ) GmbH URL [Accessed: 15.05.2012]

The Development and Use of Biogas Technology in Rural Areas of Asia (A Status Report 1981). Improving Soil Fertility through Organic Recycling

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, Food and Agriculture Organization (FAO) and United Nations Development Program (UNEP)

Anaerobic Methods of Waste Treatment

This technical factsheet describes the treatment of wastes through anaerobic digestion and biogas production at large-scale in a very comprehensive way. The treatment of different wastes, including sewage sludge, agricultural and industrial wastes or solid municipal wastes, is emphasised.

Naturgerechte Technologien (2000): Anaerobic Methods of Waste Treatment, (= Technical Information, W2e ). German Agency for Technical Cooperation GmbH (GTZ) and German Appropriate Technology Exchange (GATE) URL [Accessed: 20.04.2010]
Further Readings

Technology Review of Biogas Sanitation

This document provides an overview and introduction on biogas sanitation (anaerobic digestion) for blackwater or for brown water, or excreta treatment for reuse in developing countries. The main technologies discussed are biogas settlers (BSs), biogas septic tanks, anaerobic baffled reactor (ABRs), anaerobic filter (AFs) and upflow anaerobic sludge blanket reactors (UASBs).

MANG, H.-P. ; LI, Z. ; (2010): Technology Review of Biogas Sanitation, (= Technology Review ). Eschborn: Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbH URL [Accessed: 17.06.2013]

Biogas Basics

The information service on biogas technology has been developed and produced on the behalf of the GTZ project Information and Advisory Service on Appropriate Technology (ISAT). Volume I tells you all you need to get an overview on biogas sanitation systems, from history over process and operation parameters to social, political and cultural issues.

ISAT ; GTZ (1999): Biogas Basics, (= Biogas Digest , 1 ). Information and Advisory Services on Appropriate Technology (ISAT) and German Agency for Technical Cooperation GmbH (GTZ) URL [Accessed: 19.04.2010]

Biogas - Application and Product Development

The information service on biogas technology has been developed and produced on the behalf of the GTZ project Information and Advisory Service on Appropriate Technology (ISAT). Volume II emphasises the design and operation of biogas plants.

ISAT ; GTZ (1999): Biogas - Application and Product Development, (= Biogas Digest , 2 ). Information and Advisory Services on Appropriate Technology (ISAT) and German Technical Cooperation (GTZ) GmbH URL [Accessed: 19.04.2010]

Biogas - Costs and Benefits and Biogas – Programme Implementation

This information service on biogas technology has been developed and produced on the order of the GTZ project Information and Advisory Service on Appropriate Technology (ISAT). Volume III discusses the micro- and macro-economic viability of biogas sanitation systems.

ISAT ; GTZ (1999): Biogas - Costs and Benefits and Biogas – Programme Implementation, (= Biogas Digest , 3 ). Information and Advisory Services on Appropriate Technology (ISAT) and German Agency for Technical Cooperation GmbH (GmbH) URL [Accessed: 19.04.2010]

Biogas Production in Climates with long cold Winters

This study analyses the feasibility and potential production of biogas in countries with a cold climate, with emphasis on Romania, Kyrgyzstan, Georgia, Kazakhstan and Armenia. The results are compared with China, Nepal and Bolivia. The study also carefully reviews existing literature before suggesting the same technology for the colder target communities. It also contains recommendations on whether to use the plants on household or community level afterwards.

BALASUBRAMANIYAM, U. ; ZISENGWE, L.S. ; MERIGGI, N. ; BUYSMAN, E. ; (2008): Biogas Production in Climates with long cold Winters, Wageningen: Wageningen University URL [Accessed: 20.04.2010]

Dairy Waste Anaerobic Digestion Handbook. Options for Recovering Beneficial Products from Dairy Manure

This manual provides an introduction to the anaerobic digestion of dairy manure. The operation and waste management practices of Idaho dairies, the anaerobic digestion and the anaerobic digestion processes suitable for dairy waste, the typical design applications for different types of dairies and finally the cost and benefits of the facilities are discussed.

BURKE, P.E. ; Dennis, A. ; (2001): Dairy Waste Anaerobic Digestion Handbook. Options for Recovering Beneficial Products from Dairy Manure, Olympia: Environmental Energy Company

Anaerobic Versus Aerobic Treatment in the USA

This study evaluated the feasibility of using anaerobic pre-treatment before aerobic polishing treatment for high-strength industrial wastewater (BOD values ranging form 200 to 5000 mg/L). The results indicated an economic feasibility at water strengths above 1000 mg/L, but treatability evaluation would be required for every specific industrial wastewater to confirm the technical feasibility.

ECKENFELDER, W.W. ; PATOZKA, J.B. ; PULLIAM, G.W. (1988) Anaerobic Versus Aerobic Treatment in the USA, In: Proceedings of the 5th International Symposium of Anaerobic Digestion. ,105-114 . URL [Accessed: 05.08.2010]

Technology Review of Biogas Sanitation

This document provides an overview and introduction on biogas sanitation (anaerobic digestion) for blackwater or for brown water, or excreta treatment for reuse in developing countries. The main technologies discussed are biogas settlers (BSs), biogas septic tanks, anaerobic baffled reactor (ABRs), anaerobic filter (AFs) and upflow anaerobic sludge blanket reactors (UASBs).

MANG, H.-P. ; LI, Z. ; (2010): Technology Review of Biogas Sanitation, (= Technology Review ). Eschborn: Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbH URL [Accessed: 17.06.2013]

Biogas: GP Option for Community Development

This document contains a short review on biogas technology and an overview on the green productivity concept and community development. It also contains a detailed construction manual for fixed-dome biogas plant at the household level for the digestion of animal dung. An operation manual is also given and wide information on biogas appliances, such as cooking stoves and reuse of remaining compost from the digesters.

KOOTTATEP, S. ; OMPONT, M. ; HWA, T.J. ; (2004): Biogas: GP Option for Community Development, Asian Productivity Organization (APO) URL [Accessed: 21.05.2010]

Anaerobic treatment of municipal wastewater treatment

Technical information on the advantages and main technologies of anaerobic digestion treatment for wastewaters in developing countries.

NATURGERECHTE TECHNOLOGIEN ; Bau- und Wirtschaftsberatung (TBW) GmbH (2001): Anaerobic treatment of municipal wastewater treatment, (= Technical Information W3e ). German Agency for Technical Cooperation GmbH (GTZ) and German Appropriate Technology Exchange (GATE) URL [Accessed: 11.03.2010]

Anaerobic Methods of Waste Treatment

This technical factsheet describes the treatment of wastes through anaerobic digestion and biogas production at large-scale in a very comprehensive way. The treatment of different wastes, including sewage sludge, agricultural and industrial wastes or solid municipal wastes, is emphasised.

Naturgerechte Technologien (2000): Anaerobic Methods of Waste Treatment, (= Technical Information, W2e ). German Agency for Technical Cooperation GmbH (GTZ) and German Appropriate Technology Exchange (GATE) URL [Accessed: 20.04.2010]
Case Studies

Biogas Systems

During the last years a number of biogas systems have been installed as part of sanitation systems. Issue 9 of Sustainable Sanitation Practice (SSP) on „Biogas systems“ shows successful examples. The first paper presents results from a study in Kerala, India, for digesters on a household level. The second paper shows the results of a long-term implementation program for biogas systems in Lesotho. The third paper presents first results of a digester constructed in a small village in Morocco.

MUELLEGGER, E. ; LANGERGRABER, G. ; LECHNER, M. (2011): Biogas Systems, (= Sustainable Sanitation Practice , 9 ). EcoSan Club URL [Accessed: 24.10.2011]

Anaerobic Digestion of Biowaste in Developing Countries

This book published by Eawag/Sandec compiles existing and recently generated knowledge on anaerobic digestion of urban biowaste at small and medium scale with special consideration given to the conditions prevailing in developing countries. Written for actors working in the waste and renewable energy sector, the book is divided into two parts: Part 1 focuses on practical information related to the anaerobic digestion supply chain (substrate-, process-, and product chain), and Part 2 presents selected case studies from around the world.

VOEGELI, Y. ; LOHRI, C.R. ; GALLARDO, A. ; DIENER, S. ; ZURBRUEGG, C. EAWAG (2014): Anaerobic Digestion of Biowaste in Developing Countries, Practical Information and Case Studies. Duebendorf: Swiss Federal Institute of Aquatic Science and Technology (Eawag) URL [Accessed: 03.03.2013]
Training Material

Technology Review of Biogas Sanitation

This document provides an overview and introduction on biogas sanitation (anaerobic digestion) for blackwater or for brown water, or excreta treatment for reuse in developing countries. The main technologies discussed are biogas settlers (BSs), biogas septic tanks, anaerobic baffled reactor (ABRs), anaerobic filter (AFs) and upflow anaerobic sludge blanket reactors (UASBs).

MANG, H.-P. ; LI, Z. ; (2010): Technology Review of Biogas Sanitation, (= Technology Review ). Eschborn: Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbH URL [Accessed: 17.06.2013]

Biogas Basics

The information service on biogas technology has been developed and produced on the behalf of the GTZ project Information and Advisory Service on Appropriate Technology (ISAT). Volume I tells you all you need to get an overview on biogas sanitation systems, from history over process and operation parameters to social, political and cultural issues.

ISAT ; GTZ (1999): Biogas Basics, (= Biogas Digest , 1 ). Information and Advisory Services on Appropriate Technology (ISAT) and German Agency for Technical Cooperation GmbH (GTZ) URL [Accessed: 19.04.2010]

Overview of anaerobic treatment options for sustainable sanitation systems

PDF presentation about condominium-level biogas digesters for the transformation of human faeces. Biogas basics as well as two case studies (from Germany and India) are presented.

MUENCH, E. (2008) Overview of anaerobic treatment options for sustainable sanitation systems, In: BGR Symposium "Coupling Sustainable Sanitation and Groundwater Protection". . URL [Accessed: 23.04.2010]

Biogas Sanitation Systems

This PDF-presentation gives a good introduction to biogas sanitation as a sustainable and ecological sanitation approach. Basic principles and main features are illustrated. Some design considerations are also addressed.

MANG, H. P. ; (2005): Biogas Sanitation Systems, (= Ecological sanitation course ). Beijing: Chinese Academy of Agricultural Engineering

Biogas Technology - A Training Manual for Extension

This manual contains a complete set of training materials on various topics around the large-scale dissemination of domestic (agricultural) biogas systems, including a system approach to biogas technology, biogas programmes, reuse of slurry, subsidy and institutional financing, quality standards and monitoring and evaluation issues.

FAO (1996): Biogas Technology - A Training Manual for Extension, Support for Development of National Biogas Programme (FAO/TCP/NEP/4451-T) . Consolidated Management Services Nepal (P) Ltd. and Food and Agriculture Organization of the United Nations (FAO) URL [Accessed: 19.04.2010]

Biogas Handbook. Consolidation of Information

This handbook, even though it dates back to 1982, is quite comprehensive. It explains the theory of biogas productions, factors affecting plant designs, and operation of plants. Details of several popular biogas plant designs, construction and operation and maintenance are given. Designs of biogas utilisation devices and their operation requirements for use in lighting and cooking and as a fuel for prime movers are also included. The use of digested slurry as a source of organic fertilizer is discussed. Technical problems faced in the construction and operation of biogas plants and appliances are identified along with the causes and known solutions.

MAZUMDAR, A. ; (1982): Biogas Handbook. Consolidation of Information, Paris: United Nation Educational, Scientific and Cultural Organization (UNESCO)

Biogas Plants

This rather old document still gives a good overview on biogas technology. It is intended to help designers of a biogas plant to be able to distinguish between valid and invalid solutions.

SASSE, L. ; (1988): Biogas Plants, German Appropriate Technology Exchange (GATE) and German Agency for Technical Cooperation (GTZ) GmbH URL [Accessed: 15.05.2012]

Improved Biogas Unit for Developing Countries

This booklet reflects seven years of experience of the Biogas Extension Service (BES) of CAMARTEC (Centre for Agricultural Mechanization and Rural Technology) in Arusha/Tanzania, which was carried out in cooperation with the GTZ from 1983 to 1986. It is meant as a teaching aid in agricultural colleges and as a reference book for professionals working in the field of rural biogas extension.

SASSE, L. ; (1991): Improved Biogas Unit for Developing Countries, German Appropriate Technology Exchange (GATE) and German Agency for Technical Cooperation (GTZ) GmbH URL [Accessed: 25.04.2010]
Awareness Raising Material

…And Sewage, Too

This column by Rose George published in the New York Times emphasises the enormous potential wastewaters have as a renewable energy source.

GEORGE, R. (2010) …And Sewage, Too, In: The New York Times. ,25 . URL [Accessed: 29.04.2010]

Asia hits the gas

Biogas technology is already working extremely well on a large scale in several Asian countries. This article reports on some of these successes and recent up-scaling initiatives, and makes a plea for a global conference on biogas.

NES, W.J., van (2006) Asia hits the gas, In: Renewable Energy World. 1 ,102-111 . URL [Accessed: 24.04.2010]

Links between Sanitation, Climate Change and Renewable Energies

This factsheet of Sustainable Sanitation Alliance describes the impact of greenhouse gases on climate change and focuses on the advantages of renewable energies. Therefore many different technologies like production of biogas or short-rotation-plantations are mentioned.

SUSANA (2009): Links between Sanitation, Climate Change and Renewable Energies, Eschborn. (= SuSanA fact sheet 09/2009 ). Sustainable Sanitation Alliance (SuSanA) URL [Accessed: 05.09.2010]

Waste? Not

Critical article on conventional end-of-pipe wastewater approaches, introducing some alternatives such as biogas digester, arborloos or the fossa alterna.

TUHUS-DUBROW (2008) Waste? Not, In: The Boston Globe. . URL [Accessed: 21.02.2010]

Biogas in cities - A New Trend?

This paper investigates whether anaerobic digestion could also be suitable to treat organic household waste in urban and peri-urban areas to alleviate the she solid waste crisis in cities of the developing world.

VOEGELI, Y. ; ZURBRUEGG, C. (2008) Biogas in cities - A New Trend?, In: Sandec News. 9 .

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