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Biogas know-how

Biogas from A to Z

Ammonia (NH3 )

Nitrogenous gas, produced from the decomposition of nitrogenous compounds, such as protein, urea and uric acid.

Anaerobic bacteria

Microorganisms that live and reproduce in an environment where free or dissolved oxygen is absent.

Anaerobic degradation

Degradation of organic substances by anaerobic bacteria, partly under release of biogas.

Base substrate

Farm manure intended for anaerobic digestion.


Product of anaerobic biodegradation of organic substrates. Contains approx. 45-70 % methane, 30-55 % carbon dioxide, small amounts of nitrogen, hydrogen sulphide and other trace gases.

Biogas plant

Plant for the production, storage and utilisation of biogas, including all facilities and buildings serving the operation. The production is based on the fermentation of organic substances.

Buffer capacity

The buffer capacity is the amount of substance of a strong acid that is necessary to change the pH value to a defined value ( e.g. pH 5  ).

Combined heat and power plant (CHP)

Unit for generating electrical and thermal energy based on an engine and a generator coupled to it.


Organic residues other than farmyard manures and energy crops intended for anaerobic digestion.

C/N ratio

Ratio of carbon (C) to nitrogen (N). The C/N ratio in the material to be digested is important for an optimal digestion process (ideally: 13/30). The C/N ratio in the digested material allows a statement to be made about the availability of nitrogen during fertilisation (ideally approx. 13).

Carbon dioxide

Colourless, incombustible, slightly sour-smelling gas which, along with water, is the end product of all combustion processes.


Biogas produced in the fermenter is saturated with water vapour and must be dehydrated before it can be utilized in the CHP unit. The targeted condensation takes place via an adequately laid earth line into a condensate separator or via drying of the biogas.

Combined heat and power generation

Simultaneous conversion of input energy into electrical (or mechanical) energy and into heat intended for energy use (useful heat).



The decomposition of org. compounds consisting of many atoms into simpler compounds or molecules by biotic and abiotic processes. In biotic decomposition, decomposition takes place through biological processes (e.g. enzymes or microorganisms); in abiotic decomposition, decomposition takes place through chemical (e.g. slow oxidation, combustion, transformation) or physical (e.g. UV radiation) processes.


The property of a substance to be able to be transformed by biochemical, chemical or physical reactions. The end products of the reactions are either other compounds (metabolites) or, in the case of complete mineralisation, CO2 , H2O, NH3.

Degree of degradation

The degree of biological or chemical degradation of organic compounds.


Process step (biological or chemical) for precipitating hydrogen sulphide from biogas.

Digester (reactor, tank, fermenter)

Container in which the microbiological degradation of the substrate takes place with simultaneous biogas formation

Digestate storage (slurry storage)

Container or earth basin in which liquid manure, slurry as well as digestate is stored before further use.

Dry matter content (DM)

Anhydrous fraction of a mixture of substances after drying at 105 °C.


Emitting e.g. smoke, gases, dust, waste water or odours into the environment. However, noises, vibrations, light and heat can also be emitted.


FOS/TAC means the titrimetric determination of Volatile Organic Acids (FOS) in relation to the Carbonate Buffer Capacity (Total Inorganic Carbon, TAC).

Fermentation residue

Residue of biogas production, output of the digester.

Full load hours

Period of full utilisation of a plant when the total hours of use and the average utilisation rate within one year are converted to a utilisation rate of 100%.


Grease separator

Plant for separating non-emulsified organic oils and fats contained, for example, in wastewater of restaurants, canteens, slaughterhouses and processing plants of the meat and fish industry, margarine factories and oil mills (cf. DIN 4040).

Gas storage

Room or area in which the gas storage tank is located.

Gas storage

Gas-tight container or membrane bag in which the biogas is temporarily stored.


Process step for the reduction and/or elimination of pathogens and/or phytopathogens, usually by thermal and/or pressure processes. Also called pasteurization

Hydrogen sulphide (H2S)

Flammable, highly toxic gas with an unpleasant pungent odour of rotten eggs, which is perceptible only in low concentrations

Hydraulic retention time

Average residence time of the substrate in the digester


The quantity supplied to and processed by a plant per unit of time.



The heat transfer coefficient, also known as the k-value, is a measure of the quality of thermal insulation. It indicates the heat flow that passes through a square metre of a building component at a temperature difference of one degree Celsius. The smaller the k-value, the lower the heat loss.

Membrane roof

Attachment on the fermentation tank in which biogas is collected and extracted

Methane (CH4)

Colourless, odourless and flammable gas. Burns to form carbon dioxide and water. Methane is one of the most important greenhouse gases and is the main component of biogas, sewage gas, landfill gas and natural gas. Methane forms explosive mixtures with air.

Nitrogen oxides

The gases nitrogen monoxide (NO) and nitrogen dioxide (NO2) are summarised under the term NOx (nitrogen oxides). They are produced in all combustion processes (especially at high temperatures) as a compound between the nitrogen in the air and the oxygen, but also by oxidation of nitrogenous compounds contained in fuel.

Organic dry matter content (oDM)

Portion of a mixture of substances reduced by the water content and the inorganic substance, usually determined by drying at 105 °C and subsequent incineration at 550 °C.

Organic loading rate

Organic fraction of the material introduced into the digester, related to the usable digester space volume per time unit; unit: kg oDM/m³*d.


Pre-treatment process step (e.g. crushing, separation of impurities, homogenization, chopping...)

Potentially explosive atmospheres

Spatial areas in which a hazardous explosive atmosphere may occur due to local and operational conditions.


Renewable raw materials (German: NaWaRo)

Collective term for biomass used for materials and energy (not feed and food). This usually refers to raw materials produced by agriculture and forestry, such as wood, flax, rapeseed, sugars and starch from beet, potatoes or maize, which after processing are used for further material or energy purposes.

Solids input

Process for introducing non-pumpable substrates or substrate mixtures directly into the fermenter.

Sulphur dioxide (SO2)

Colourless, pungent-smelling gas produced when sulphur is burnt or sulphides are roasted. Its aqueous solution is sulphurous acid (H2SO3).


Organic and biodegradable material intended for fermentation with the aim of biogas production.