Batch digesters are fed at start-up and then monitored for gas production. Once the methanogens run out of food, biogas production ceases. This type of digester is generally a lab scale digester used to investigate the biogas production potential of various feed stocks. A typical batch system consists of a reactor, which contains the seed and feed material, and a means of collecting and measuring the biogas produced. The amount of gas produced can be a measure of the potential for that particular feedstock to produce biogas.
Digesters operating in industry are much more likely to be routinely fed.
These digesters also include a reactor and a gas collection system. However, the reactor is usually fed either continuously, daily, weekly, or at some intermediate time interval. As the digester is fed, an equivalent volume must be removed from the reactor in order to maintain a constant level. The routinely fed digesters can generally be classified as one of two types. Dispersed growth digesters allow the bacteria to flow with the digester solution.