NOVELTY - The method for transferring and mixing a biomass slurry in a hydrolyser by hydrolyzing a biomass and transferring and mixing the hydrolyzed slurry in a fermenter using anaerobic processing of biomass into biogas (12), comprises comminuting biomass in a macerator comminuter, mixing the comminuted biomass with a part of reflux containing bacterial cultures in a comminuter tank, recycling the reflux, back to a tank of the macerator, with leachates from a digested slurry separator and with make-up water, and passing the slurry through the macerator comminuter.    USE - The method is useful for transferring and mixing a biomass slurry in a hydrolyser by hydrolyzing a biomass and transferring and mixing the hydrolyzed slurry in a fermenter using anaerobic processing of biomass into biogas including methane, carbon dioxide, hydrogen, hydrogen sulfide and small quantities of other gases.    ADVANTAGE - The method is capable of rapidly and continuously transferring and mixing the biomass slurry with good solubility and less water consumption.    DETAILED DESCRIPTION - The method comprises comminuting a biomass in a macerator comminuter, mixing the comminuted biomass with a part of reflux containing bacterial cultures in a comminuter tank, recycling the reflux, back to a tank of the macerator, with leachates from a digested slurry separator and with make-up water, passing a biomass slurry through the macerator comminuter, and cyclically pumping the comminuted slurry to a horizontal hydrolyser tank until it is filled at 50-70%. The biomass slurry is subjected to mixing in a single zone or in zones of a hydrolyser using slurry streams produced by jet nozzles. The hydrolyzed slurry is pumped in portions to a fermenter whose bottom slopes at an angle of 0.3-0.9% towards an outlet of the slurry to cause a horizontal movement of the slurry during which it is subjected to periodical mixing from the first zone up to penultimate zone by slurry streams produces by jet nozzles. In the fermenter zone, the biomass is continuously introduced in form of a broadening stream in a biogas discharge area. The fermented biomass after exiting the fermenter is split into two streams, where a first stream as a reflux is fed to a fermenter tank (10), a hydrolyser tank and a tank of the macerator comminuter while other stream of the fermented biomass is fed to a digested pulp separator from where a part of leachates is recycled back via a pipeline to the tank of a macerator mill and/or the hydrolyser tank, and biogas flowing out from the fermenter is treated and further processed in a known way. The biomass slurry to be ejected from the jet nozzles is sucked at the bottom of the hydrolyser within that zone in which the respective jet nozzle is located. The biomass stream introduced at the top is directed vertically to a surface of the slurry in the hydrolyser tank. The hydrolysis and fermentation of biomass are performed at an equal elevated pressure of the gases in the hydrolyser and fermenter. The biomass transfer and mixing processes are carried out in hydrolyzers arranged in parallel and in fermenters arranged in parallel or in series. The biomass slurry is further comminuted in an attachment fitted in the transfer pump before the biomass slurry is fed to hydrolyser nozzles. An INDEPENDENT CLAIM is included for a system for transferring and mixing of a biomass slurry in a hydrolyser and in a fermenter.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a fermenter.    Fermenter mixing segment (9)    Fermenter tank (10)    Biomass slurry in fermenter (11)    Biogas (12)    Scrubbing unit. (13)