The hydrolyzed substrate (in some instances, the non-hydrolyzed one) is contained into high volume anaerobic digesters where their decomposition process is proceeded by maintaining the required temperate, and the biogas produced during the final stage methanogenesis process. The biogas usually contains its main component methane (45-70 %) and carbon dioxide (50-25 %). Usually There is small but undesirable amount of aggressive gasses (hydrogen sulfide, ammonia, etc.) and other ballast gasses (oxygen, nitrogen, etc.) that can be introduced due to some technological peculiarities.

The quantity and volume of digesters is calculated for each separate biogas plant considering the raw material composition, seasonal supply fluctuations, location and local peculiarities. Usually there are installed two or three digesters to ensure their reserve during repairs or cleaning. Moreover, smaller digesters are easier to operate and their size can be smaller and easier to integrate into the surroundings.