NOVELTY - The method for operating biogas plant with a fermented (1), in which or into which a preconditioned fermentation pulp from biomasses is introduced and biogas is removable from a collection volume, comprises conditioning the biomass to a flow able fermentation pulp and then introducing into a tube or tubular system, which automatically forms the fermentation chamber, where the biomass is present between an inlet zone (2) and a discharge zone (3) of the tube or the tubular system, and influencing the flow velocity in the tubular system.    USE - Method for operating biogas plant with a fermented.    ADVANTAGE - The method is capable of economically operating the biogas plant with high efficiency and less energy requirements.    DETAILED DESCRIPTION - The method for operating biogas plant with a fermented (1), in which or into which a preconditioned fermentation pulp from biomasses is introduced and biogas is removable from a collection volume, comprises conditioning the biomass to a flow able fermentation pulp and then introducing into a tube or tubular system, which automatically forms the fermentation chamber, where the biomass is present between an inlet zone (2) and a discharge zone (3) of the tube or the tubular system, and influencing the flow velocity in the tubular system, so that a dwell time of the biogas of the produced fermentation pulp is controllable in the tubular system. The gas production rate is steadily measured and the control of the dwell time of the biomass or the fermentation pulp takes place in the tubular system dependent of the gas production rate. The tubular system is provided with distributed arranged semi-permeable membranes (7), which guide through the biogas but blocks the passage of the liquid, over which the produced biogas discharges from the tubular system. The liquefied animal rumen or other microbial additives and/or trace elements and/or minerals are introduced into a tubular fermented at an inlet opening or at the distributed arranged injection openings along a tube length. The biogas plant or the tubular fermented is integrated into a coolant circuit of a thermal power plant in a heat-exchanging manner, so that the power plant waste heat is added for supporting the biogas production process. An INDEPENDENT CLAIM is included for a biogas reactor or a biogas plant with a fermented.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic representation of a fermented of a biogas plant as tube meander.    Fermented (1)    Inlet zone (2)    Discharge zone (3)    Tube support (6)    Membranes. (7)