The superiority of this technology is already apparent from the wide diversity of suitable substrates. Bulk materials with a high dry-substance content can be digested without need for any complex pre-treatment of the fermentation material. The principle is quite simple: in the absence of air and following inoculation by previously fermented material the biological waste begins to digest immediately resulting in the production of biogas. The process is a single-step fermentation process that employs batch operation. Single step in this sense means that the various degradation reactions (hydrolysis acidification and methanization) constitute one process step.