NOVELTY - The method for thickening of fermentation substrate from a biogas plant, comprises pumping a substrate quantity from a fermenter (1), separating a part of the liquid from the pumped substrate quantity, introducing the concentrated substrate in a collection container (2) and leading the substrate quantity by a filtering device (10) with a filter tube (14), which is provided in its tubular jacket with liquid permeable recesses and is surrounded by an external chamber (17) formed between the filter tube and the external housing.    USE - Method for thickening of fermentation substrate from a biogas plant (claimed).    ADVANTAGE - The method can able to thicken the subjected fermentation substrate with simply manufactured technical devices and simple regulation measures in economical manner.    DETAILED DESCRIPTION - The method for thickening of fermentation substrate from a biogas plant, comprises pumping a substrate quantity from a fermenter (1), separating a part of the liquid from the pumped substrate quantity, introducing the concentrated substrate in a collection container (2) and leading the substrate quantity by a filtering device (10) with a filter tube (14), which is provided in its tubular jacket with liquid permeable recesses and is surrounded by an external chamber (17) formed between the filter tube and the external housing. A part flowing in the filter tube is subjected as main flow with a low dry material portion and a part of the substrate quantity flowing through the external chamber is subjected as part flow with a high dry material portion. The part flow and the main flow of the substrate quantity are 30-100% and 70-0% respectively. The part flow with a dry material content of 15% and the main flow with a dry material content of 4% are subjected in a dry material content of 15% of the substrate led to the filtering device. The flow rates are regulated in dependent upon a measured pressure in the external chamber and/or in the filter tube of the filtering device. The part flow and the main flow are occasionally led back in the fermenter. The main flow is occasionally introduced in a buffer, reverses the flow direction of the main flow and is conveyed by a reversible rotary piston pump. The buffer is arranged in an upper region of the fermenter. The part flow is conveyed by a rotary piston pump. The subjected fermentation substrate is pressed in as a basic flow rate by the rotary piston pump in the filtering device and the thickened part flow is pressed out by the reversible rotary piston pump from the filtering device. The conveying capacities of the pumps are regulated to each other, so that an adjusting pressure difference is minimized itself between the inner- and the outer side of the filter tube. An INDEPENDENT CLAIM is included for a filtering device for thickening of fermentation substrate from a biogas plant.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic block view of a method for thickening of fermentation substrate from a biogas plant.    Fermenter (1)    Collection container (2)    Filtering device (10)    Filter tube (14)    External chamber. (17)