Difference between revisions of "Biogas Reactor"

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Output1=Treated Sludge|Output2=Effluent | Output3=Biogas | Output4= | Output5=
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|english_link=Anaerobic_Biogas_Reactor
 
|french_link=Réacteur_anaérobie_à_Biogaz
 
|spanish_link=Reactor Anaerobico de Biogas
 
 
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<br>
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----
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<br>
  
[[Image:Icon_anaerobic_biogas_reactor.png |right|95px]]
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[[Image:Icon_anaerobic_biogas_reactor.png |right|80px]]
'''An Anaerobic Biogas Reactor is an anaerobic treatment technology that produces (a) a digested slurry to be used as a soil amendment and (b) biogas which can be used for energy. Biogas is a mix of methane, carbon dioxide and other trace gasses that can be easily converted to electricity, light and heat (see [[Biogas as source of energy]]).'''
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'''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.'''
  
An Anaerobic Biogas Reactor is a chamber or vault that facilitates the anaerobic degradation of blackwater, sludge, and/or biodegradable waste. It also facilitates the separation and collection of the biogas that is produced. The tanks can be built above or below ground. Prefabricated tanks or brick-constructed chambers can be built depending on space, resources and the volume of waste generated.
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[[Image:Anaerobic_digestion.PNG|thumb|right|200px|Biogas reactor in Vietnam (for credits, click the picture)]]
  
[[Image:Anaerobic_digestion.PNG|thumb|right|150px|Biogas reactor in Vietnam (for credits, click the picture)]]
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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.
  
The residence time of the fluid in the reactor should a minimum of 15 days in hot climates and 25 days in temperate climates. For highly pathogenic inputs, a residence time of 60 days should be considered. Normally, Anaerobic Biogas Reactors are not heated, but to ensure pathogen destruction (i.e. a sustained temperature over 50°C) the reactor should be heated (although in practice, this is only found in the most industrialized countries).
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===Design Considerations===
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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.
  
Once waste products enter the digestion chamber, gases are formed through fermentation. The gas forms in the sludge but collects at the top of the reactor, mixing the slurry as it rises. Biogas reactors can be built as fixed dome or floating dome reactors. In the fixed dome reactor 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 will flow back down into the digestion chamber. The pressure generated can be used to transport the biogas through pipes.  
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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).
  
In a floating dome reactor, the dome will rise and fall with the production and withdrawal of gas. Alternatively, the dome can expand (like a balloon). Most often biogas reactors are directly connected to indoor (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 and can be built behind the house or buried underground. Sizes can vary from 1,000L for a single family up to 100,000L for institutional or public toilet applications.
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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.
 
 
The slurry that is produced is rich in organics and nutrients, but almost odourless and partly disinfected (complete pathogen destruction would require thermophilic conditions). Often, a biogas reactor is used as an alternative to a conventional septic tank, since it offers a similar level of treatment, but with the added benefit of biogas. Depending on the design and the inputs, the reactor should be emptied once every 6 months to 10 years.
 
  
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<br>
 
{{procontable | pro=
 
{{procontable | pro=
- Generation of a renewable, valuable energy source. <br> - Low capital costs; low operating costs. <br> - Underground construction minimizes land use. <br> - Long life span. <br> - Can be built and repaired with locally available materials. <br> - No electrical energy required. <br> - Small land area required (most of the structure can be built underground). | con=
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- Generation of renewable energy <br>
- Requires constant source of water. <br> - Requires expert design and skilled construction. <br> - Gas production below 15°C is not economically feasible. <br> - Digested sludge and effluent still requires treatment
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- Small land area required (most of the structure can be built underground) <br>
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- No electrical energy required <br>
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- Conservation of nutrients <br>
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- Long service life <br>
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- Low operating costs
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| con=
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- Requires expert design and skilled construction <br>
 +
- Incomplete pathogen removal, the digestate might require further treatment <br>
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- Limited gas production below 15 °C
 
}}
 
}}
  
==Adequacy==
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===Appropriateness===  
 
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This technology can be applied at the household level, in small neighbourhoods or for the stabilization of sludge at large wastewater treatment plants. It is best used where regular feeding is possible. Often, a biogas reactor is used as an alternative to a [[Septic Tank | Septic Tank]] (S.9), 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.
This technology is easily adaptable and can be applied at the household level or a small neighbourhood (refer to Technology Information Sheet T15: Anaerobic Biogas Reactor for information about applying it at the community level).
 
  
Biogas reactors are best used for concentrated products (i.e. rich in organic material). If they are installed for a single household that is using a significant amount of water, the efficiency of the reactor can be improved significantly by also adding animal manure and biodegradable organic waste.
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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.
  
Depending on the soil, location, and size required, the reactor can be built above or below ground (even below roads). For more urban applications, small biogas reactors can be installed on the rooftops or in a courtyard. To minimize distribution losses, the reactors should be installed close to where the gas can be used. Biogas reactors are less appropriate for colder climates as gas production is not economically feasible below 15°C.
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===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.
  
==Health Aspects/Acceptance==
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===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.
  
The digested slurry is not completely sanitized and still carries a risk of infection. There are also dangers associated with the flammable gases that, if mismanaged, could be harmful to human health.
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===References and external links===
  
The Anaerobic Biogas Reactor must be well built and gas tight for safety. If the reactor is properly designed, repairs should be minimal. To start the reactor, active sludge (e.g. from a septic tank) should be used as a seed. The tank is essentially self-mixing, but it should be manually stirred once a week to prevent uneven reactions.
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* CMS (1996). [http://www.fao.org/3/ae897e/ae897e00.htm Biogas Technology: A Training Manual for Extension. FAO/TCP/NEP/4451-T]. Consolidated Management Services, Kathmandu, NP.
  
Gas equipment should be cleaned carefully and regularly so that corrosion and leaks are prevented. Grit and sand that has settled to the bottom should be removed once every year. Capital costs for gas transmission infrastructure can increase the project cost. Depending on the quality of the output, the gas transmission capital costs can be offset by long-term energy savings.
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* GTZ (1998). Biogas Digest. [https://www.susana.org/en/knowledge-hub/resources-and-publications/library/details/525?pgrid=1 Volume I], [https://www.susana.org/en/knowledge-hub/resources-and-publications/library/details/526 Volume II], [https://www.susana.org/en/knowledge-hub/resources-and-publications/library/details/1717 Volume III], [https://energypedia.info/images/1/17/Biogas_gate_volume_4.pdf Volume IV]. Information and Advisory Service on Appropriate Technology (ISAT). Deutsche Gesellschaft für Technische Zusammenarbeit (GTZ) GmbH, Eschborn, DE.
  
==Acknowledgements==
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* Mang, H.-P. and Li, Z. (2010). [https://www.susana.org/en/knowledge-hub/resources-and-publications/library/details/877 Technology Review of Biogas Sanitation. Draft – Biogas Sanitation for Blackwater, Brown Water, or for Excreta Treatment and Reuse in Developing Countries]. Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbH, Eschborn, DE.
{{:Acknowledgements Sanitation}}
 
  
==References and external links==
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* Ulrich, A. (Ed.), Reuter, S. (Ed.), Gutterer, B. (Ed.), Sasse, L., Panzerbieter, T. and Reckerzügel, T. (2009). [https://wedc-knowledge.lboro.ac.uk/resources/books/DEWATS_-_Chapter_01.pdf Decentralised Wastewater Treatment Systems (DEWATS) and Sanitation in Developing Countries. A Practical Guide]. WEDC, Loughborough University, Leicestershire, UK.
  
* Food and Agriculture Organization (FAO) (1996). Biogas Technology: A Training Manual for Extension. Consolidated Management Services, Kathmandu. Available: http://www.fao.org
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* Vögeli, Y., Lohri, C. R., Gallardo, A., Diener, S. and Zurbrügg, C. (2014). [https://www.eawag.ch/fileadmin/Domain1/Abteilungen/sandec/publikationen/SWM/Anaerobic_Digestion/biowaste.pdf Anaerobic Digestion of Biowaste in Developing Countries. Practical Information and Case Studies]. Eawag (Department Sandec), Dübendorf, CH.
  
* ISAT (1998). Biogas Digest Vols. I–IV. ISAT and GTZ, Germany. Available: http://www.gtz.de
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===Acknowledgements===
 
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{{:Acknowledgements Sanitation}}
* Koottatep, S., Ompont, M. and Joo Hwa, T. (2004). Biogas: A GP Option For Community Development. Asian Productivity Organization, Japan. Available: http://www.apo-tokyo.org
 
 
 
* Rose, GD. (1999). Community-Based Technologies for Domestic Wastewater Treatment and Reuse: options for urban agriculture. IDRC, Ottawa. pp 29–32. Available: http://idrinfo.idrc.ca
 
 
 
* Sasse, L. (1998). DEWATS: Decentralised Wastewater Treatment in Developing Countries. BORDA, Bremen Overseas Research and Development Association, Bremen, Germany.
 

Latest revision as of 22:38, 23 September 2020

English Français Español भारत മലയാളം தமிழ் 한국어 中國 Indonesia Japanese
Applicable in systems:
1, 6 , 7 , 8 , 9
Level of Application
Household XX
Neighbourhood XX
City XX

 

Inputs
Sludge, Organics, Blackwater, Brownwater


Level of management
Household XX
Shared XX
Public XX

 

Outputs
Sludge, Biogas
Anaerobic biogas reactor.png




Icon anaerobic biogas reactor.png

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.

Biogas reactor in Vietnam (for credits, click the picture)

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.

Contents

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.


Advantages Disadvantages/limitations
- Generation of renewable energy

- Small land area required (most of the structure can be built underground)
- No electrical energy required
- Conservation of nutrients
- Long service life
- Low operating costs

- Requires expert design and skilled construction

- Incomplete pathogen removal, the digestate might require further treatment
- Limited gas production below 15 °C


Appropriateness

This technology can be applied at the household level, in small neighbourhoods or for the stabilization of sludge at large wastewater treatment plants. It is best used where regular feeding is possible. Often, a biogas reactor is used as an alternative to a Septic Tank (S.9), 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 and external links

  • GTZ (1998). Biogas Digest. Volume I, Volume II, Volume III, Volume IV. Information and Advisory Service on Appropriate Technology (ISAT). Deutsche Gesellschaft für Technische Zusammenarbeit (GTZ) GmbH, Eschborn, DE.

Acknowledgements

Eawag compendium cover.png

The material on this page was adapted from:

Elizabeth Tilley, Lukas Ulrich, Christoph Lüthi, Philippe Reymond and Christian Zurbrügg (2014). Compendium of Sanitation Systems and Technologies, published by Sandec, the Department of Water and Sanitation in Developing Countries of Eawag, the Swiss Federal Institute of Aquatic Science and Technology, Dübendorf, Switzerland.

The 2nd edition publication is available in English. French and Spanish are yet to come.