Biogas– A Renewable Energy for Sustainable Future

Biogas is one of the key renewable sources of energy next to solar and wind. After all, biogas can be produced in a particularly environmentally responsible and CO2 neutral way from sustainable raw and energy-rich waste materials that are available at a regional level. Biogas utilizes the natural energy present in organic matter.

Biogas Production

Biogas plants predominantly process energy-rich vegetation, such as grass silage, maize and sugar beet, as well as solid manure and slurry, organic waste, sugar industry effluent. In addition, it also process food leftovers or by-products from the food processing industry, can be fermented. Biogas is produced by means of anaerobic digestion, i.e. the microbiological decomposition of organic materials in a humid environment under exclusion of air (anaerobic milieu). The biogas plant’s principle of operation is based on bringing about a controlled biological breakdown process (digestion/fermentation) which converts the organic biomass into its constituents such as water, carbon dioxide and methane. The methane can be used as fuel in CHP modules, where it generates power and heat. If the biogas is upgraded, it can also be fed into the gas mains to supply decentralized CHP modules with biogas. One cubic meter of methane contains a calorific value of approx. 10 kWh

Biogas Composition

The end-product is combustible biogas, a mixture that mainly consists of methane CH4 (50-75 %), carbon dioxide CO2 (25-45 %) and small proportions of water as well as trace gases, such as hydrogen sulphide H2S, oxygen 02, nitrogen N, ammonia NH4 and hydrogen H.

Biogas Process

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Organic materials ferment at temperatures between 0 ºC und 70 ºC under the exclusion of air – provided a humid environment- and under the effect of methanogenic bacteria (methanococcus and methanobacterium species). During the digestion process, the carbon in the substrates is converted into biogas in four phases. These four phases are divided into hydrolysis (first phase), acidification (second phase), acetogenesis (third phase) and methanogenesis (fourth phase).

Unlike composting, which represents a rotting process, digestion does not generate heat but combustible methane gas. Neutral carbon dioxide, water and trace gases, such as hydrogen sulphide, ammonia, elementary nitrogen, hydrogen and oxygen, are also generated.

The principle of anaerobic digestion is widespread. Among others, it occurs in sea muds, rivers and lakes, swamps and marshes, unventilated soil layers, landfill sites, slurry and sewage pits or rice farming. Depending on where anaerobic digestion occurs, it is referred to as marsh gas, fermentation gas, sewage gas, mine gas, landfill gas or, in the agricultural sector, biogas.

The density of biogas is 1.21 kg/m³ with an average methane content of approx. 60 % and carbon dioxide content of approx. 35 %, as well as trace gases (O2, H2S, NH4, etc.).

Biogas – A Substitute for Natural Gas

In principle, the methane in biogas is chemically equivalent to natural gas and it is the main energy-bearing component. One cubic meter of biogas with a methane content of 60 % corresponds to an energy value of approx. six kilowatt hours. The average heating value of one cubic meter of biogas is therefore equivalent to approximately 0.6 litres of heating oil. Prior to being fed into the public network, the biogas is upgraded, i.e. undesirable components are removed and the biogas is “methane-optimized”.

Biogas Digestate – An Agricultural Fertilizer

The digestate remaining after digestion (biomass and minerals that have not decomposed) has outstanding fertilizing properties and can be used in arable farming.

Biogas Advantages

•  It supplies power, heat, cooling and gas in one
•  It is available all year round – 24/7 – and can be stored.
•  It is independent of the weather and can, therefore, be made available on demand
•  Processed biogas can be used in all vehicles converted to natural gas without problems, and it can be filled in tanks and transported in bottles or pipelines.