NOVELTY - Combination of a biogas fermenter and a multi-stage self-regulating ultrasonic disintegration system for liquid media, is claimed. The biogas fermenter comprises e.g. a feeding device, a viewing window, preferably portholes or slits in the upper half of fermenter, sensors, an outlet nozzle, flush ports, and outlet and/or agitators to reduce or dissolve the floating layer. The ultrasonic disintegration system comprises e.g. at least one substrate line, at least one conveyor, at least one sonotrode, devices for testing or measuring parameters of liquid, and devices for connecting to a container.    USE - The combination is useful for increasing population density of active bacteria and Archaea using multi-stage self-regulating ultrasonic processing of liquid media in biogas fermenter, to produce biogas at mesophilic- and thermophilic (greater than 50 degrees C) temperature conditions (claimed).    ADVANTAGE - The combination is safe, economical and environmentally friendly, and has self degradation control.    DETAILED DESCRIPTION - Combination of a biogas fermenter and a multi-stage self-regulating ultrasonic disintegration system for liquid media, is claimed. The biogas fermenter comprises (a) a feeding device for introducing a fermentation substrate into a floating layer, (b) a viewing window, preferably portholes or slits in the upper half of fermenter, (c) sensors for remotely controlling the upper half of the fermenter, (d) a sensor connecting piece and/or nozzles for sampling the fermenter substrate, (e) an outlet nozzle for removing incompletely degraded substrate of layers, (f) flush ports contained above or in the floating layer to introduce incompletely degraded material back into the fermentation cycle, and (g) outlet and/or agitators contained in at least one duplicate to reduce or dissolve the floating layer with respect to their dimension. The ultrasonic disintegration system comprises (i) at least one substrate line (14), (j) at least one conveyor (15), (k) at least one sonotrode (16) located within the substrate line or on outer side of the substrate line, (l) devices for testing or measuring parameters of a liquid, and (m) devices for connecting to a container. An INDEPENDENT CLAIM is also included for increasing the population density of active bacteria and Archaea using multi-stage self-regulating ultrasonic processing of liquids in biogas fermenter by the above device, comprising (i) introducing a coarse fiber material having a density lower than the liquid with the substrate, where the floating layer is formed on or below the upper substrate liquid level of the biogas fermenter, and immobilizing the methanogenic microorganisms, (ii) ultrasonically processing within the substrate line, (iii) measuring the parameters of the liquid within the substrate line at measuring nozzle, and (iv) controlling the pump using measured parameters, where the intensity is increased or reduced or backwashing is initiated.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic representation of the ultrasonic disintegration system (Drawing includes non-English language text).    Substrate line (14)    Conveyor (15)    Sonotrode (16)    Slide (19)    Container wall (20)