NOVELTY - The operating procedure for wet fermentation in a single-step, actively-operated biogas plant, comprises feeding fermentable materials continuously or batch-wise, quasi-continuously into a fermenter (3) containing a substrate by a metering mechanism (2), removing the substrate by displacement/pumping method, supplying the substrate from the metering mechanism and/or a post-fermenter (5) to a separator (8), and feeding the substrate-solid portion (7) from the separator, continuously or batch-wise to the metering mechanism by conveyance unit. The substrate has a dry substance proportion.    USE - For wet fermentation in single-step, actively-operated biogas plant.    ADVANTAGE - The operating method is a simple and economical, ensures continuous wet fermentation and improves the environmental compatibility of the plant by using regenerating raw materials.    DETAILED DESCRIPTION - The operating procedure for wet fermentation in a single-step, actively-operated biogas plant, comprises feeding fermentable materials continuously or batch-wise, quasi-continuously into a fermenter (3) containing a substrate by a metering mechanism (2), removing the substrate by displacement/pumping method, supplying the substrate from the metering mechanism and/or a post-fermenter (5) to a separator (8), and feeding the substrate-solid portion (7) from the separator, continuously or batch-wise to the metering mechanism by conveyance unit. The substrate has a dry substance proportion. The biogas plant operates according to a flow mechanism and comprises the fermenter, an upstream metering mechanism for fermentable materials and a downstream separator, with which a partial separation of the substrate discharged from the fermenter into a substrate-solid portion and a -liquid portion takes place. A screw-type and/or a conveyor-screw-type separator and/or a centrifuge separator and/or a belt-type filter press are used as the separator. The separator exhibits a separation tank, with a pouring of bio-solids as solid filter, over which the removed substrate is led. The substrate-solid portion is retained to a large extent in the pouring and is collected for further processing. The pouring with the substrate-solid portion is continuously or batch-wise metered directly and/or over the metering mechanism with a fresh pouring. The separator is also a solid metering mechanism and the entire meterable biomass is used as pouring. The bound liquid portions are set free by the fermentation process. Regenerating raw materials are metered as fermentable materials. The substrate from the fermenter is discharged directly to the metering mechanism and/or a post-fermenter that is downstream to the fermenter. From the separated substrate-liquid portion, 20 % of the total liquid quantity is led back by a pumping mechanism/valve arrangement into the fermenter, and the remaining substrate- liquid portion is transferred into the post-fermenter or into a final waste disposal and/or on to open spaces. The actual dry substance proportion in the substrate is measured over a probe and the measured value is led as an electrical actual signal to an automatic controller. The desired dry substance proportion is adjusted by an electrical pre-set signal, and after evaluation of a control deviation by a control algorithm, an adjusting signal is sent from the automatic controller to a control- correcting element for the provision and supply of the quantity of the control liquid. The dry substance proportion of 10-15.5 % is adjusted by an electrical pre-set signal. The partial quantity of the separated substrate-liquid portion is fed back optionally as a quantity of control liquid directly into the fermenter and/or indirectly over a storage tank and/or a mashing-up pit.    DESCRIPTION OF DRAWING(S) - The drawing shows a biogas plant:    Metering mechanism; (2)    Fermenter; (3)    Post-fermenter; (5)    Substrate-solid portion; (7)    Separator. (8)