NOVELTY - The biogas fermentation plant for the production of fermentation gas, comprises an agitation mechanism having counter-displaced agitators and an upper, motorically height-adjustable submersible-pump agitator. The displaced agitators (10a, 10b, 10c) are brought at the fermenter inner wall region within the fermenter and each of which carries an agitating blade (16) at a horizontally aligned agitation shaft. A multiple-agitator unit (7) with a lower- and an upper agitator and another multiple-agitator unit (8)with a middle agitator, are oppositely arranged in the fermenter.    USE - For the production of fermentation gas that is used as heating gas to generate current in internal-combustion engines with electric generators.    ADVANTAGE - The fermentation plant ensures uniform and effective mixing of biomass in the liquid by arranging multiple agitators and increases the production of fermentation gas as well as ensures high safety during the agitating procedure.    DETAILED DESCRIPTION - The biogas fermentation plant for the production of fermentation gas, comprises an agitation mechanism having counter-displaced agitators and an upper, motorically height-adjustable submersible-pump agitator. The displaced agitators (10a, 10b, 10c) are brought at the fermenter inner wall region within the fermenter and each of which carries an agitating blade (16) at a horizontally aligned agitation shaft. A multiple-agitator unit (7) and another multiple-agitator unit (8) are oppositely arranged in the fermenter. The fermenter is designed as a vertical cylindrical section with circular area-shaped diameter or is built in the form of a circular ring in a ring-in-ring arrangement. The multiple-agitator unit comprises a lower- and an upper agitator arranged at a lower region and an elevated region of the fermenter and the oppositely-lying multiple-agitator unit comprises of a middle agitator arranged at a central height range of the fermenter. The upper agitator is implemented as a lateral agitator, which is insertable into the fermenter through a lateral installation opening and the lower agitator is height-adjustably mounted as a submersible-pump agitator at vertically aligned unit carriers (9a, 9b, 9c). The lateral agitator and the submersible-pump agitator and/or the installation opening and the unit carrier are arranged close together. The unit carriers are adjustable and rotatable around their vertical axes. The unit carriers are led upwards through a hood opening in the fermenter cover, up to the region of service shaft attached above the hood opening. The upper agitator is height-adjustable motorically over a controller. During the operation of the biogas facility, the fermenter is filled with a substrate (5) to be fermented to a filling level and the submersible-pump agitator with its agitating blades is completely submerged in the substrate. A level-measuring device is intended, with which the filling level of the substrate is determined and a corresponding level measuring signal is produced as an actual height signal. A control device is intended, to which the level measuring signal is sent and which regulates the level actuator for the submersible-pump agitator in the case of a smaller measured filling level in such a manner that the submersible-pump agitator is lowered and the agitating blades are completely immersed in the substrate.    DESCRIPTION OF DRAWING(S) - The figure shows a biogas fermentation plant:    Substrate; (5)    Multiple agitator unit; (7)    Another multiple-agitator unit; (8)    Unit carriers; (9a, 9b, 9c)    Agitators; (10a, 10b, 10c)    Agitating blade. (16)