NOVELTY - The method for increasing concentration of methane biogas from biogas plant, comprises supplying hydrogen and a liquid hydrolyzate in a methane level of a two-stage biogas process or supplying the hydrogen to a methane reactor (3) above the hydrolyzate, and diverting the hydrolyzate at the lower end of the methane reactor so that the methane reactor is dived into process technology in a lower column (32) flow throughable with hydrolyzate that represents the part of the methane reactor between inlet and outlet of the hydrolyzate and in an upper column (31).    USE - Method useful for increasing concentration of methane biogas.    ADVANTAGE - The method ensures increasing of the concentration of methane biogas with high efficiency and quality in economical manner.    DETAILED DESCRIPTION - The method for increasing concentration of methane biogas from biogas plant, comprises supplying hydrogen and a liquid hydrolyzate in a methane level of a two-stage biogas process or supplying the hydrogen to a methane reactor (3) above the hydrolyzate, and diverting the hydrolyzate at the lower end of the methane reactor so that the methane reactor is dived into process technology in a lower column (32) flow throughable with hydrolyzate that represents the part of the methane reactor between inlet and outlet of the hydrolyzate and in an upper column (31), which represents the part of the methane reactor between gas supply and gas discharge. The lower column of the methane reactor contains immobilized acetotrophe methanogens, which are formed through the biogas from the hydrolyzate, and the upper column of the methane reactor contains suspended and/or immobilized hydrogenotrophic methanogens. The hydrogen is supplied at the lower end of the upper column in fine distribution and flows through upper column towards top. The biogas formed in the lower column is led into the upper column. The carbon dioxide present in the upper column with the hydrogen is converted to methane through suspended and/or immobilized hydrogenotrophic methanogens. The hydrogen supplied to the methane reactor is regained itself by ion exchange, electrolysis or chemical and biochemical reactions from the methane level. The hydrogen supplied to the methane reactor is regained from hydrolysis gas (2) of a mesophilic, thermophilic or hyper-thermophilic operated hydrolysis of the total biogenic feedstock or a fraction. The hydrogen and the carbon dioxide are supplied from hydrolysis gas so that the hydrogen in the resulting biogas is 3 vol.%. INDEPENDENT CLAIMS are included for    (1) a methane reactor for producing biogas; and    (2) a biogas plant for two-stage production of biogas.    DESCRIPTION OF DRAWING(S) - The figure shows a plant for increasing concentration of methane biogas (Drawing includes non-English language text).    Hydrolysis reactor (1)    Hydrolysis gas (2)    Methane reactor (3)    Upper column (31)    Lower column. (32)