TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Components: The fermenter comprises a heating device, which heats the fermentation mass to a predetermined temperature above 30 degrees C, preferably 42 degrees C or alternatively 53 degrees C. The thermal conductivity is adjustable at least in individual portions of the partition wall such that the biomass in the mixing tank is heated by heat transfer from the fermentation mass through the partition wall to a predetermined temperature below 25 degrees C, preferably above 15 degrees C. The partition wall is formed as a concrete wall, and the portions of the partition wall are formed with adjustable thermal conductivity of hollow bodies, preferably tubes inserted in the concrete wall. The conductivity is adjusted by changing the liquid-filled pipe lengths and correspondingly changing the gas, preferably air-filled pipe lengths. The inserted pipe is formed as many adjacently arranged U-shaped tube sections, where the U-legs extend vertically and are respectively provided above for introducing, blowing or sucking water. The fermenter and the mixing tank comprise a common continuous concrete floor (7). The fermenter and the mixing tank comprise at least one common concrete side wall continuously extending transversely to the partition wall. The mixing tank, the fermenter and two partial areas of a rectangular concrete trough, which is arranged in a hole, are formed in the planar view. The height of the mixing tank is smaller than the height of the fermenter. A first cover of the mixing tank is provided with a closable charging shaft in the region of the ground surface and a connection for introducing slurry. A second cover of the fermenter lies slightly above the ground surface. The covers of the mixing tank and the fermenter are at least partially designed as a concrete floor. A container is arranged on the second cover of the fermenter. The biogas plant comprises a combustion device, preferably a motor, a generator driven by the combustion device for generation of electricity and a heat duct, which is connected to the combustion device. The heat duct supplies the heating device of the fermenter with heat. A cover unit with a gas reservoir is arranged on the second cover of the fermenter. The biogas passes via short wiring connections from the biogas outlet arrangement into the gas storage and from gas storage to the combustion device. An agitator, preferably an agitator with agitator elements, which are rotating around a vertical axis, is arranged in the fermenter and in the mixing tank, preferably at least in the central region. The discharge device comprises a discharge duct and a discharge pump, which is connected to the discharge duct in the fermenter. An inlet is arranged from the fermenter in the discharge duct in a predetermined height range, preferably 2/5 total height of the fermenter filled with the fermentation mass, where a maximum of the fermented fermentation mass is present at this level.