The wet cutter RotaCut has proven the optimal solution countless times whenever foreign matter interrupts the biogas plant operation or long-fiber solid matter in the suspension is causing problems. The integrated heavy material separator (stone catcher) separates out metal parts and stones. At the same time, the wet cutter RotaCut cuts foreign matter such as wood pieces and branches, and is ideal for chopping down fibrous foreign matter such as straw bands. Solid matter composed of long fibers, such as dung, straw and grass silage, as well as long, fresh grass, is finely cutted. In this way, the wet cutter RotaCut protects pumps and other components of the biogas plant from damage caused by foreign matter while also preventing clogging. The reliable treatment of long-fiber fibrous matter with the wet cutter RotaCut simultaneously prevents the formation of floating layers in the digester of the biogas plant. This reduces the suspension's viscosity, which in turn lessens the load on the mixers, reduces power consumption and shortens the needed mixer run time in many biogas plants. The comprehensive model range as well as the numerous features and options enable the cutter to be used in a wide variety of positions within the biogas plant. For instance, the wet cuttter RotaCut can treat both the liquid suspension and/or recirculated material before mashing within the scope of liquid feeding, as well as prepare the freshly mashed suspension as a first step even before the digester. Moreover, the wet cutter RotaCut can be easily integrated anywhere that pumping processes are required within the biogas plant. For example, for transfer from the digester into the post digester and/or into final storage, and for return flow of the recirculated material. However the compact and easy to maintain cutter can also be easily integrated into the pipe system for digester circulation and/or when external heating is used – or additionally for supplying fresh liquid manure upstream of the separator. There is at least one place in every biogas plant to integrate the wet cutter RotaCut.