Biogas Reactor

A biogas reactor or anaerobic digester is an anaerobic treatment technology that produces (a) a digested slurry (digestate) that can be used as a fertilizer and (b) biogas that can be used for energy. Biogas is a mix of methane, carbon dioxide and other trace gases which can be converted to heat, electricity or light.

A biogas reactor is an airtight chamber that facilitates the anaerobic degradation of blackwater, sludge, and/or biodegradable waste. It also facilitates the collection of the biogas produced in the fermentation processes in the reactor. The gas forms in the slurry and collects at the top of the chamber, mixing the slurry as it rises. The digestate is rich in organics and nutrients, almost odourless and pathogens are partly inactivated.

Design Considerations

Biogas reactors can be brick-constructed domes or prefabricated tanks, installed above or below ground, depending on space, soil characteristics, available resources and the volume of waste generated. They can be built as fixed dome or floating dome digesters. In the fixed dome, the volume of the reactor is constant. As gas is generated it exerts a pressure and displaces the slurry upward into an expansion chamber. When the gas is removed, the slurry flows back into the reactor. The pressure can be used to transport the biogas through pipes. In a floating dome reactor, the dome rises and falls with the production and withdrawal of gas. Alternatively, it can expand (like a balloon). To minimize distribution losses, the reactors should be installed close to where the gas can be used.

The hydraulic retention time (HRT) in the reactor should be at least 15 days in hot climates and 25 days in temperate climates. For highly pathogenic inputs, a HRT of 60 days should be considered. Normally, biogas reactors are operated in the mesophilic temperature range of 30 to 38°C. A thermophilic temperature of 50 to 57°C would ensure the pathogens destruction, but can only be achieved by heating the reactor (although in practice, this is only found in industrialized countries).

Often, biogas reactors are directly connected to private or public toilets with an additional access point for organic materials. At the household level, reactors can be made out of plastic containers or bricks. Sizes can vary from 1,000 L for a single family up to 100,000 L for institutional or public toilet applications. Because the digestate production is continuous, there must be provisions made for its storage, use and/or transport away from the site.

Appropriateness

This technology can be applied at the household level, in small neighbourhoods or for the stabilization of sludge at large wastewater treatment plants. The reactors are best used where regular feeding is possible.

Often, a biogas reactor is used as an alternative to a septic tank, since it offers a similar level of treatment, but with the added benefit of biogas. However, significant gas production cannot be achieved if blackwater is the only input. The highest levels of biogas production are obtained with concentrated substrates, which are rich in organic material, such as animal manure and organic market or household waste. It can be efficient to co-digest blackwater from a single household with manure if the latter is the main source of feedstock. Greywater should not be added as it substantially reduces the HRT. Wood material and straw are difficult to degrade and should be avoided in the substrate.

Biogas reactors are less appropriate for colder climates as the rate of organic matter conversion into biogas is very low below 15°C. Consequently, the HRT needs to be longer and the design volume substantially increased.

Health Aspects/Acceptance

The digestate is partially sanitized but still carries a risk of infection. Depending on its end-use, further treatment might be required. There are also dangers associated with the flammable gases that, if mismanaged, could be harmful to human health.

Operation & Maintenance

If the reactor is properly designed and built, repairs should be minimal. To start the reactor, it should be inoculated with anaerobic bacteria, e.g., by adding cow dung or septic tank sludge. Organic waste used as substrate should be shredded and mixed with water or digestate prior to feeding.

Gas equipment should be carefully and regularly cleaned so that corrosion and leaks are prevented. Grit and sand that have settled to the bottom should be removed. Depending on the design and the inputs, the reactor should be emptied once every 5 to 10 years.

References

Further Readings

  • Cover image of a reference book or miscellany.

    TILLEY, E.; ULRICH, L.; LUETHI, C.; REYMOND, P.; SCHERTENLEIB, R.; ZURBRUEGG, C. (2014): Compendium of Sanitation Systems and Technologies (Arabic). 2nd Revised Edition. Duebendorf, Switzerland: Swiss Federal Institute of Aquatic Science and Technology (Eawag). PDF

    This is the Arabic version of the Compendium of Sanitation Systems and Technologies. The Compendium gives a systematic overview on different sanitation systems and technologies and describes a wide range of available low-cost sanitation technologies.

  • Cover image of a reference book or miscellany.

    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]. PDF

    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.

  • Cover image of a reference book or miscellany.

    GREEN, S. (2005): Emerging Biodigester Technology in Honduras: Biophysical Processes and Operation. Montana: University of Montana. PDF

    Master thesis on biophysical and operational aspects of anaerobic bio-digesters in rural Honduras. Bio-digester processes, the operational practices for plastic balloon bio-digesters and a typology of successful bio-digester operation are developed.

  • Cover image of a reference book or miscellany.

    HEEB, F. (2009): Decentralised anaerobic digestion of market waste. Case study in Thiruvananthapuram, India. Duebendorf: Swiss Federal Institute of Aquatic Science and Technology (EAWAG). URL [Accessed: 27.04.2010]. PDF

    Decentralized anaerobic digestion is a promising technology to handle the large organic fraction of the municipal solid waste with the additional benefit of producing biogas as well as fertilizer. In this study a market level biogas plant in Thiruvananthapuram, South India and constructed by a NGO called BIOTECH is monitored and evaluated.

  • Cover image of a reference book or miscellany.

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

    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.

  • Cover image of a reference book or miscellany.

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

    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.

  • Cover image of a reference book or miscellany.

    LEMOS CHERNICHARO, C.A. de (2007): Anaerobic Reactors. London: International Water Association (IWA) Publishing. URL [Accessed: 01.11.2013]. PDF

    Anaerobic Reactors is the forth volume in the series Biological Wastewater Treatment. The fundamentals of anaerobic treatment are presented in detail, including its applicability, microbiology, biochemistry and main reactor configurations. Two reactor types are analysed in more detail, namely anaerobic filters and especially UASB (upflow anaerobic sludge blanket) reactors. Particular attention is also devoted to the post-treatment of the effluents from the anaerobic reactors. The book presents in a clear and informative way the main concepts, working principles, expected removal efficiencies, design criteria, design examples, construction aspects and operational guidelines for anaerobic reactors.

  • Cover image of a reference chapter of a book/miscellany.

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

    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.

  • Cover image of a reference book or miscellany.

    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) . URL [Accessed: 05.08.2010]. PDF

  • Cover image of a reference book or miscellany.

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

    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.

  • Cover image of a reference book or miscellany.

    SANOGO, O. (2008): Dissemination of improved stoves and biogas experiences in Burkina Faso. Institute de Recherche en Sciences Appliquées et Technologie (IRSAT) and Centre National de la Recherche Scientifique et Technologique (CNRST). PDF

    This PDF-presentation was presented a workshop in Ouagadougou entitled South-South cooperation in the field of Biomass energy: Challenge and opportunities. It illustrates how biogas technology was introduced along with cooking stoves and emphasizes technical and organisational lessons learnt.

  • Cover image of a reference book or miscellany.

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

    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.

  • Cover image of a reference book or miscellany.

    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]. PDF

    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.

  • Cover image of a reference book or miscellany.

    SASSE, L. ; BORDA (Editor) (1998): DEWATS. Decentralised Wastewater Treatment in Developing Countries. Bremen: Bremen Overseas Research and Development Association (BORDA). PDF

    Exhaustive report on technological, operational and economic aspects of decentralised waste water treatment systems. Spreadsheet examples support the reader in designing and planning waste water treatment systems components.

  • Cover image of a reference book or miscellany.

    SPERLING, M. von; LEMOS CHERNICHARO, C.A. de (2005): Biological Wastewater Treatment in Warm Climate Regions Volume 1. London: International Water Association (IWA) Publishing. URL [Accessed: 01.11.2013]. PDF

    Biological Wastewater Treatment in Warm Climate Regions gives a state-of-the-art presentation of the science and technology of biological wastewater treatment, particularly domestic sewage. The book covers the main treatment processes used worldwide with wastewater treatment in warm climate regions given a particular emphasis where simple, affordable and sustainable solutions are required. The 55 chapters are divided into 7 parts over two volumes: Volume One: (1) Introduction to wastewater characteristics, treatment and disposal; (2) Basic principles of wastewater treatment; (3) Stabilisation ponds; (4) Anaerobic reactors; Volume Two (also available in the SSWM library): (5) Activated sludge; (6) Aerobic biofilm reactors; (7) Sludge treatment and disposal.

Case Studies

  • Cover image of a reference book or miscellany.

    APEIS (Editor) (2003): Biogas Plants Based on Night Soil. Asia-Pacific Environmental Innovation Strategies (APEIS), Research on Innovative and Strategic Policy Options (RISPO). (=Good Practices Inventory). Sulabh International and Agency for Non Conventional Energy and Rural Technology (ANERT). PDF

    The government of India started its biogas development project in 1981 as one of its programs designed to meet rural energy needs, especially for cooking. One of the solutions to the problem was the introduction of the concept of pay-and-use toilets championed by the Sulabh International Social Service Organisation, a non-profit voluntary organisation pioneering in the field of sanitation in India. The biogas generated is used largely for public lighting. Sulabh community toilets linked to biogas plants are generating energy and fertilizer, and some of them have attached health care facilities as well.

  • Cover image of a reference book or miscellany.

    ASHDEN (Editor) (2005): Domestic biogas for cooking and sanitation. London: The Ashden Awards for Sustainable Energy. URL [Accessed: 13.04.2010]. PDF

    The Biogas Sector Partnership (BSP) in Nepal managed the installation of over 124,000 domestic biogas plants in Nepal between 1992 and 2005. The plants use cattle manure to provide biogas for cooking and lighting. In addition, about 75% of the plants incorporate toilets.

  • Cover image of a reference book or miscellany.

    ASHDEN (Editor) (2006): Fuel, compost and sanitation from biogas in rural China. London: The Ashden Awards for Sustainable Energy. URL [Accessed: 13.04.2010]. PDF

    The Shaanxi Mothers' Environmental Protection Volunteer Association has installed 1,294 biogas plants in rural farming households in the Shaanxi Province of China since 1999. The plants produce biogas from pig and human waste.

  • Cover image of a reference book or miscellany.

    ASHDEN (Editor) (2007): Clean cooking and income generation from biogas plants in Karnataka. London: The Ashden Awards for Sustainable Energy. URL [Accessed: 14.03.2010]. PDF

    SKG Sangha (SKG S) is a non-profit organisation that supplies biogas plants to households in rural areas of South India. The ‘Deenbandu’ design plants are built on-site by local masons and labourers trained by SKGS, with very high quality standards. Plants produce biogas by digesting cow dung, replacing all the fuel wood used for cooking.

  • Cover image of a reference book or miscellany.

    BORDA (Editor) (2008): Decentralized Wastewater Treatment System - DEWATS. Manjuyod Public Market. Bremen: Bremen Overseas Research and Development Association (BORDA) . URL [Accessed: 26.03.2010]. PDF

    The wastewater from Manjuyod’s public market is treated in a decentralized system (DEWATS) composed of four different components: a settling tank; a anaerobic baffled reactor which reduces the BOD/COD content from 20% to 85%; a planted gravel filter; and finally a polishing pond.

  • Cover image of a reference book or miscellany.

    ISAT (Editor); GTZ (Editor) (1999): Biogas - Country Reports. Information and Advisory Services on Appropriate Technology (ISAT) and German Agency for Technical Cooperation GmbH (GTZ). URL [Accessed: 19.04.2010]. PDF

    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 IV summarises over 20 case studies from biogas sanitation as an appropriate technology in developing countries.

  • Cover image of a reference journal article.

    VOEGELI, Y.; LOHRI, C.; KASSENGA, G.; BAIER, U.; ZURBRUEGG, C. (2009): Technical and biological Performance of the ARTI Compact Biogas Plant for Kitchen Waste - Case Study from Tanzania. In: Proceedings Sardinia 2009, Twelfth International Waste Management and Landfill Symposium S. Margherita di Pula, Cagliari, Italy; 5 - 9 October 2009. Environmental Sanitary Engineering Centre (CISA).URL [Accessed: 27.04.2010]. PDF

    With the growing problem of municipal solid waste and the demand for an alternative energy source regarding rising petrol prices, anaerobic digestion technology has also been extended to organic solid wastes instead of animal dung and faecal wastes. This paper evaluates the suitability of a small-scale biogas system as a decentralised treatment option for the organic fraction of market and household solid waste in Dar el Salaam, Tanzania.

  • Cover image of a reference book or miscellany.

    MUELLEGGER, E. (Editor); LANGERGRABER, G. (Editor); LECHNER, M. (Editor) (2011): Biogas Systems. EcoSan Club. URL [Accessed: 24.10.2011]. PDF

    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.

Awareness Material

  • Cover image of a reference book or miscellany.

    WAFLER, M. (2009): Reuse of Energy (Biogas). (PPT presentation). Wien: seecon international GmbH. PDF

    PPT presentation on the advantages of biogas reuse.

  • Cover image of a reference book or miscellany.

    WELL (Editor) (n.y.): Using Human Waste. Loughborough: Water and Environmental health at London and Loughborough (WELL). URL [Accessed: 26.04.2010]. PDF

    This Technical Brief introduces the main issues one needs to consider to both control the process and optimize the benefits gained from using human waste, whilst minimizing the risks.

Training Material

  • Cover image of a reference book or miscellany.

    AKUT (Editor) (2008): Technical Drawing: Cross-Section of a Fixed Dome Biogas Plant (12 m3). Berlin: AKUT Partner. PDF

    Technical drawing showing a design of a fixed dome biogas plant with a volume of 12 m3.

  • Cover image of a reference book or miscellany.

    AKUT (Editor) (2008): Technical Drawing: Cross-Section of a Fixed Dome Biogas Plant (124 m3). Berlin: AKUT Partner. URL [Accessed: 12.05.2014]. PDF

    Technical drawing showing a design of a fixed dome biogas plant with a volume of 124 m3 and a gas storage capacity of 15 m3.

  • Cover image of a reference book or miscellany.

    FAO (Editor) (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]. PDF

    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.

  • Cover image of a reference book or miscellany.

    MANG, H. P. (2005): Biogas Sanitation Systems. Beijing: Chinese Academy of Agricultural Engineering. PDF

    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.

  • Cover image of a reference book or miscellany.

    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]. PDF

    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.

  • Cover image of a reference book or miscellany.

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

    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.

  • Cover image of a reference book or miscellany.

    WAFLER, M. (2008): Training Material on Anaerobic Wastewater Treatment. Aarau: Seecon GmbH. PDF

    This training manual emphasizes basics of biogas technology as well as design principles and technical considerations. A sample design exercise and some technical drawings and sketches are also given.

Important Weblinks