The purified biosuspension is temporarily stored in a suspension tank. It decouples the treatment section from the actual fermentation so that the latter can take place independently of the working rhythms of the waste reception.

The organic suspension is fermented in fully mixed fermenters, usually single-stage and mesophilic fermentation at 35 - 38 °C. The design of the fermenter and its mode of operation depend on the type of feedstock and the project-specific requirements for microbiological degradation and biogas yield. The design of the fermenter and its mode of operation depend on the type of feedstock and the project-specific requirements for microbiological degradation and biogas yield.