NOVELTY - Device for biosynthesis of methane, comprises: a reactor vessel (1) comprising at least one filling body (2) which is mounted in reactor interior (10) and which comprises a surface for colonization of methanogenic microorganisms; an inlet for substrate input, a gas outlet (11) at a first end of the reactor vessel, an inlet for gas supply (3) and a substrate input (6) at a second end of the reactor vessel. The substrate guiding and the gas guiding occur in the reactor interior in countercurrent manner. The filling body colonized with the methanogenic microorganisms is axially movable.    USE - The method is useful for: purifying and enriching methane from carbon dioxide or carbon monoxide-containing biogas mixture; and storing excess energy from wind turbines and/or solar systems (all claimed).    ADVANTAGE - The device: comprises filling bodies which provide high flow-through, stability and large surface area for colonization by microorganisms (claimed); and achieves high methane enrichment.    DETAILED DESCRIPTION - Device for biosynthesis of methane, comprises: a reactor vessel (1) comprising at least one filling body (2) which is mounted in reactor interior (10) and which comprises a surface for colonization of methanogenic microorganisms; an inlet for substrate input, a gas outlet (11) at a first end of the reactor vessel, an inlet for gas supply (3) and a substrate input (6) at a second end of the reactor vessel. The substrate guiding and the gas guiding occur in the reactor interior in countercurrent manner. The filling body colonized with the methanogenic microorganisms is axially movable via a lifting platform arranged on the container bottom in the interior of the reactor vessel. An INDEPENDENT CLAIM is also included for biosynthesis of methane using methanogenic microorganisms, comprising (a) inoculating a surface of at least one filling body of a reactor with methanogenic microorganisms, (b) introducing substrate from one end of the reactor into the reactor interior and then passing hydrogen through the filling body with the substrate, such that the substrate comes into contact with the microorganisms, (c) discharging the substrate channeled via the filling body from the reactor, (d) introducing carbon dioxide or carbon monoxide-containing gas and the hydrogen gas from another end of the reactor and then allowing it to flow through filling body, such that the gases come into contact with the substrate, filling bodies and microorganisms, and (e) recovering the process gas from the reactor.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic representation of a bioreactor comprising storage container.    Reactor vessel (1)    Filling body (2)    Gas supply (3)    Substrate input (6)    Gas outlet (11)