This article is part of the article on BLEENS - Biogas, Liquefied Petroleum gas, Electricity, Ethanol, Natural gas, and Solar.
Biogas is produced by the anaerobic digestion of organic materials such as manure, sewage sludge, organic waste from households, industry waste, and also energy crops. It is composed mainly of methane (40-70%) and carbon dioxide (30-60%). However, it also contains small traces of other compounds such as hydrogen sulphide, nitrogen, hydrogen, methylmercaptans and oxygen . The energy content of the biogas is directly proportional to the methane content in the biogas (higher methane content is equivalent to higher energy output) . 1 m3 of purified biogas contains 6.5 KW of energy and is equivalent to the following fuels   :
- 1.7 L of bioethanol = 1 m3 of purified biogas
- L of gasoline =1 m3 of purified biogas
- 0,97 m3 of natural gas= 1 m3 of purified biogas
- 1 Kg firewood = 0.25 m³ biogas
- 1 Kg dried cow dung =0.1 m³ biogas
- 1 Kg Charcoal = 0.65 m³ biogas
- 1 L LPG = 1.05 m3 of biogas
- 1 kg LPG = 2.1 m3 of biogas
- 1 L of Kerosene = 1.60 m³ biogas
Biogas can be produced in both large scale digesters as well as in small scale digesters in households. This article focuses only on small scale digesters for household level.
Source / Production of Biogas
Figure 1: Potential of biogas production from different organic materials. It is expressed as m3 of biogas produced per 1t of dry organic mass.
Biogas can be produced from a variety of organic materials as mentioned above. The organic matter is fed to an air-tight tank called biodigester. The bacteria then decompose the organic compounds to produce biogas. The rich -slurry that is left in the digester during biogas production can be used as fertilizer. The biogas is collected at the top and the slurry at the bottom has to be removed regularly. See this article for more information about the different types of biodigesters
. For a small households, digester of 1 m3 is suggested while for a typical farm plant 10 m3 is needed and more than 1,000 m3 for a large installation 
Technically, biogas is feasible in all climatic conditions but the cost of biogas production increases with a decrease in temperature, making it economically not viable in cold climate (mean temperature below 15°C). This is because in cold climate, an extra heating system has to be installed. For more information, please see this article. A biogas plant has a lifespan of more than 20 years .
The table below shows the biogas potential of different organic components that are easily available in households. As shown in the figure, cow manure, which is the most common organic compound available in farms has the lowest energy content. Compared to cow manure, other farm outputs such as poultry dropping, grass silage, maize silage have higher biogas yield.
As shown in Figure 1, each organic material has different biogas capacity so that determines the quantity required for the biogas production. For an optimal biogas production, it is advisable to mix different available organic components. There is no fixed ratio for mixing but rather depends on the capacity of the digester, the biogas holder, acidity (PH) of the biodigester, carbon-nitrogen ratio of organic substrates etc. See this article for more information.
Assumptions: If a family of 4 members needs 1 m3 of biogas for cooking in a day, then 6 cows with the following factor will yield the required biogas  (Assuming one person requires 0-2 – 0.4 m3 of biogas in a day, only for cooking and then taking the lower value 0.2 m3). This value is based on many assumptions: by simply changing the cow dung output or the retention time in the digester,
the biogas production can be increased or decreased. The biogas feasibility at any farm can also be roughly calculated using the table below:
| No of cows
| Cow dung
| Total cow dung
| Inflow (1:1 mixing with water)
| Retention time
| Digester volume (Vd)
| Yield (Y)
| Volatile solids
| Initial concentration of volatile solids (S) per cow
| Total VS
| Gas yield
For biogas production, the fuel is mostly the organic waste product. So there is no price range for the fuel. However, high investment is needed in the beginning to construct a biogas plant. The investment cost depends on the size of the biogas plant, availability of construction materials, location of construction, labor wages and end-use applications.
According to this publication from SNV in 2014, the cost of installing a household size biodigester vary from: EUR 300-600 in Asian countries and EUR 500-1000 in African countries .
Average cost-benefit of biodigester based on 2013 data from SNV
Average cost of biodigesters based on different regions, according to IRENA
Applicability/which cooking needs are covered with it
Biogas can be used for cooking and lighting in households. For cooking, it can be directly used in conventional low-pressure gas burners. It reduces the cooking time as compared to a traditional cookstove . Biogas provides instant heat upon ignition, so no extra waiting time is required. Conventional cooking appliances can also be used by adopting the biogas burners to ensure proper combustion of the energy. It is also possible to regulate the gas flow-rate to regulate the heat from high to low. This allows to cook all kinds of food, those that required high temperature and those that require slow cooking. There are also biogas ovens that can be used for baking.
Since biogas cannot transfer over long distance, they have to be used where they are produced. There are new concepts such as biogas backpack for transporting over distance, but they are not commercially available everywhere.
Contribution or Conflicts with SDGs
Use of biogas replaces the firewood and charcoal for cooking. This reduces the impact on the environment via reduced deforestation. It also reduces the burden on women who initially had to travel far-off distance to collect firewood. There is also no indoor air pollution, which improves the health of the people as compared to cooking with firewood. The cooking pots also do not have soot on them. This makes it easier for the women to wash them . However, biogas can also increase the burden on women as they might be responsible for the biogas. It is physically demanding to move the biogas feedstock, add water to the digestor and also to transport the slurry to the field.
The slurry from biogas production is used as organic fertilizer improving the soil quality and increasing the crop yield. This management of manure also reduces the potential methane emission as major part of the emitting methane is captured in the biodigester. Methane has a heating factor of 21 times of that of CO2. So, burning biogas reduces methane to CO2 and reduces the greenhouse gas impact. A family sized digester can reduce about 2.5 t C02 annually . While construction underground biodigester, special care has to be taken to not to pollute ground water. The slurry has to be also pre-treated before using as fertilizers to kill any harmful pathogens.
Therefore, use of biogas helps to address SDG 3 (eradicate hunger), SDG 7 (renewables) and SDG 13 (climate change). With regard to SDG 5 (gender equality), it could have both positive and negative direct effect, but it depends on what it the overall impact.
Also see: Environmental Frame Conditions of Biogas Technology
- ↑ 1.0 1.1 “Cooking with Biogas - energypedia.info.” [Online]. Available: https://energypedia.info/wiki/Cooking_with_Biogas. [Accessed: 08-Apr-2019]
- ↑ 2.0 2.1 “Biogas Basics - energypedia.info.” [Online]. Available: https://energypedia.info/wiki/Biogas_Basics. [Accessed: 03-Apr-2019].
- ↑ A. Petersson and A. Wellinger, “Biogas upgrading technologies – developments and innovations,” p. 20.
- ↑ 4.0 4.1 4.2 4.3 J. van Hessen, “An Assessment of Small-Scale Biodigester Programmes in the Developing World: The SNV and Hivos Approach,” p. 51.
- ↑ RENA, “Measuring small-scale biogas capacity and production,” /publications/2016/Dec/Measuring-small-scale-biogas-capacity-and-production. [Online]. Available: /publications/2016/Dec/Measuring-small-scale-biogas-capacity-and-production. [Accessed: 08-Apr-2019].
- ↑ IRENA, “Measuring small-scale biogas capacity and production,” /publications/2016/Dec/Measuring-small-scale-biogas-capacity-and-production. [Online]. Available: /publications/2016/Dec/Measuring-small-scale-biogas-capacity-and-production. [Accessed: 08-Apr-2019].
- ↑ “Amount of biogas to cook for a person?” [Online]. Available: https://www.researchgate.net/post/Amount_of_biogas_to_cook_for_a_person. [Accessed: 01-Jul-2019].
- ↑ IRENA, “Biogas for domestic cooking: Technology brief,” p. 32.
- ↑ Global Alliance for Clean Cookstoves, “Biogas.” [Online]. Available: https://www.cleancookingalliance.org/binary-data/TECHNOLOGY_FUELS/document/000/000/6-1.pdf. [Accessed: 08-Apr-2019].