NOVELTY - The operating method for wet fermentation in a single-step, actively-operated biogas plant, comprises feeding fermentable materials continuously/batch-wise, quasi-continuously into a fermenter (3) by metering mechanism (2) acting as a solid substance metering device, removing a substrate with a dry substance from the fermenter by displacement/pumping methods, supplying the substrate to a separator (8), and regulating the dry substance of the substrate present in the fermenter. The plant operates according to a flow mechanism.    USE - For wet fermentation in a single-step, actively-operated biogas plant.    ADVANTAGE - The operating method is simple, cost effective and improves the environmental compatibility of the plant.    DETAILED DESCRIPTION - The operating method for wet fermentation in a single-step, actively-operated biogas plant, comprises feeding fermentable materials continuously/batch-wise, quasi-continuously into a fermenter (3) by metering mechanism (2) acting as a solid substance metering device, removing a substrate with a dry substance from the fermenter by displacement/pumping methods, supplying the substrate to a separator (8), and regulating the dry substance of the substrate present in the fermenter. The plant operates according to a flow mechanism. A partial separation of the substrate discharged from the fermenter into a substrate-solid portion and a -liquid portion takes place. Regenerating raw materials are metered as fermentable materials. The actual dry substance proportion in the substrate of the fermenter is measured over a probe and the measured value is led as an electrical 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 means of 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 is presets a valve smaller than or equal to 15.5 %. The substrate for the separator is discharged from the fermenter that is directly downstream to the metering mechanism and/or a post-fermenter (5) that is downstream to the fermenter. The quantity of control liquid is fed back directly into the fermenter and/or indirectly over preliminary pit acting as a storage tank and/or as mashing-up pit. 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 separator. The separator contains a pouring from bio solids as solid filters, over which the removed substrate is led and below which the separated substrate-liquid portion is collected for the further processing. The control algorithm exhibits a differential fraction and/or is combined with a control mechanism for a speedy rough adjustment. A part of the substrate-solid portion is separated by the separator that is fed back over the metering mechanism into the fermenter. The whole of the separated substrate-solid portion is automatically fed to the fermenter over the metering mechanism and the residual quantity of the substrate-liquid portion is automatically fed back or discharged to a final waste disposal (4).    DESCRIPTION OF DRAWING(S) - The drawing shows a biogas plant:    Metering mechanism; (2)    Fermenter; (3)    Waste disposal; (4)    Post-fermenter; (5)    Separator. (8)