Fermenter for producing biogas from organic material

A fermenter for producing biogas from organic fermentation material, having:

• a) a fermentation chamber with an essentially round base surface to receive the fermentation material for anaerobic processing;
• b) arranged, in a peripheral region of the fermentation chamber, filling means for the fermentation material to be fermented;
• c) arranged, above the fermentation chamber, an unpressurized gas store with gas discharging means;
• d) stirring means;
• e) a settling chamber with an overflow rim and, in its lower region, a fixed-bed reactor composed of porous solid material through which a volume of passive biomass must pass before being removed from the settling chamber;
• and
• f) pumping means for the continuous or batchwise removal of fermentation material from the fermentation chamber and the introduction thereof into the settling chamber in a region situated below the overflow rim, said pumping means being capable of introducing a volume of fermentation material into the settling chamber that is greater than the volume of passive biomass removed from the settling chamber such that active biomass can be displaced upward and run over the overflow rim to be returned to the fermentation chamber.