In the standard process of biogas production, the bioorganic material is processed before being fed into the biogas plant. The plant consists of a mixer, two digesters and a gas storage. The digesters are also called fermentation tanks and are the crucial components of the plant since they provide the anaerob conditions in which the bacteria generate biogas. The substrates have to be constantly heated and stirred in order to ensure their homogenity and the consistent discharge of gas. The gas holder is normally an airproof steel container that, by floating like a ball on the fermentation mix, cuts off air to the digesters (anaerobiosis) and collects the gas generated. In one of the most widely used designs, the gas holder is equipped with a gas outlet, while the digesters are provided with an overflow pipe to lead the sludge out into a drainage pit.