What is Biogas?

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What is Biogas?

What is Biogas?

Biogas is predominantly a mixture of methane and carbon dioxide.
It is the methane which is used to generate power. Depending upon the starting conditions, biogas also includes small quantities of water vapour, hydrogen sulphide, ammonia, hydrogen (H2), nitrogen (N2) and traces of volatile fatty acids and alcohols.


Biogas process

Biogas is produced in a digester using the 4-stage process of biochemical, anaerobic digestion: hydrolysis, acidogenesis, acetogenesis and methanogenesis. Carbohydrates, fats and proteins are transformed into methane (50–70%) and carbon dioxide (25–40%). Fermentation is complete when the substrate has passed through all the stages. Each of these stages features a specific physiological bacterial population.

The key process parameters are temperature and the time spent by the substrate in the fermenter (hydraulic residence). Most agricultural biogas plants operate at a mesophilic temperature (35–42 °C). The residence time depends on the substrate type, and varies between 20 and 70 days.

Anaerobic digestion can be used to transform almost all types of organic matter into biogas. The only exceptions are plant materials, such as wood, with a high lignin or cellulose content. Organic waste (sewage sludge, manure, municipal and industrial waste), agricultural by-products and energy crops such as maize, sunflowers, grains and grass, are used as raw materials in modern biogas plants. The various plants have differing energy contents and per hectare yields. The most efficient plant is maize which is grown for energy generation. Other plants are also used, and possibly for other purposes. Sorghum, for example, can be used both as a feed material or an energy fruit. This makes it very attractive for developing countries such as India. The wide range of potential input materials reduces the need for the monocultures demanded by other biomass technologies (biodiesel and bioethanol).

Biogas can be used in a myriad of ways: the gas can be used in a co-generation unit to produce electricity, for heating, or as fuel. As the gas is produced on an ongoing basis and can be stored, it can be used to cover both basic power demand as well as peak loads.

Biogas is also suitable for decentralised heat and power generation. In contrast to wind power and solar power, electricity can be fed into the grid in a decentralised and controlled manner, even under unfavourable network conditions.



As a renewable source of energy, biogas offers several technological, ecological and economic advantages. Energy can be generated 365 days a year, at all times of the day and night. As a result of this availability, biogas plays an important role in the mix of renewable energy from water, sun and wind. In addition to helping achieve climate protection goals, biogas helps reduce reliance on energy imports. Decentralised power generation also guarantees sustainable local development.

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