NOVELTY - Producing biogas from biomass using anaerobic digestion, comprises feeding biomass as input to a reaction space using mechanical feed equipment while simultaneously advancing biomass contained in the reaction space horizontally as plug flow; separately mixing biomass in each block comprising microbial strain in the reaction space divided into successive blocks for feeding biomass to block-specific microbial strains and transferring biomass forward in the reaction space; and recovering biogas produced as the result of anaerobic digestion of biomass.    USE - Used as method for producing biogas from biomass using anaerobic digestion.    ADVANTAGE - The method is more efficient and faster than prior art methods, since a microbial strain is re-circulated inside the block as reject from the end to the beginning of the block, and reject is removed from the blocks as a bottoms product using a vacuum and The vacuum is advantageously generated using a single pump and applied to a selected block of the valve system, and the temperature of biomass is block-specifically adjusted in each block. The reactor is more efficient than prior art reactors, since the reactor includes equipment for independently monitoring and controlling the inoculation, mixing and heating of each block.    DETAILED DESCRIPTION - Producing biogas from biomass using anaerobic digestion, comprises feeding biomass as input to a reaction space using mechanical feed equipment while simultaneously advancing biomass contained in the reaction space horizontally as plug flow; separately mixing biomass in each block in the reaction space divided into successive blocks for feeding biomass to block-specific microbial strains and transferring biomass forward in the reaction space, in which the number of blocks is at least three each comprising its own main microbial strain; and recovering biogas produced as the result of anaerobic digestion of biomass. The microbial strain of each block is fed in front of the corresponding block and at least in two of these blocks, the feed is reject obtained from the block as high consistency stock. An INDEPENDENT CLAIM is also included for a reactor for producing biogas from biomass using anaerobic digestion, including a frame (12) delimiting a reaction space (14) for biomass (16), where the frame is channel-like and horizontal for plug flow of biomass and the frame has at least three successive blocks (24) including their microbial strains, a mixing equipment (20) for mixing biomass and feeding microbes to biomass as well as transferring biomass forward in the reaction space, a recovery equipment for recovering generating biogas while microbes consume organic material of biomass, where the mixing equipment includes a reject collection and feed system for collecting reject from the blocks and feeding it to at least three blocks as high consistency stock.    DESCRIPTION OF DRAWING(S) - The figure shows a process chart of the reactor for producing biogas from biomass using anaerobic digestion.    Frame (12)    Reaction space (14)    Biomass (16)    Mixing equipment (20)    Blocks (24)