NOVELTY - Biological process for producing methane gas comprises: providing an electromethanogenic reactor (10) having an anode (12), a cathode (16) and many methanogenic microorganisms disposed on the cathode; and providing electrons and carbon dioxide to the methanogenic microorganisms, where the methanogenic microorganisms reduce the carbon dioxide to produce methane gas.    USE - The biological process is useful for: producing methane gas (claimed); wastewater treatment, renewable energy production, and carbon capture. The energy produced by the biological process is useful for running combustion engines and also as green and sustainable fuel for the benefit of society.    ADVANTAGE - The biological process: provides methane gas in high yield (96%) when compared to other methods; does not require hydrogen, organic carbon sources and metal catalysts; and is environmental friendly. The efficiency of carbon dioxide capture by electromethanogenesis is high compared to conventional methods.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) a biological process for producing methane gas, comprising either providing an electromethanogenic reactor containing exoelectrogenic microorganisms and methanogenic microorganisms, providing an organic material oxidizable by an oxidizing activity of the exoelectrogenic bacteria, thus electrons are produced and transferred to the anode and to the methanogenic microorganisms and providing carbon dioxide to the methanogenic microorganisms, where the methanogenic microorganisms reduce the carbon dioxide to produce methane gas, or inserting an anode and a cathode in a methanogenic reactor comprising methanogenic microorganisms, providing electrons to the methanogenic microorganisms and increasing the efficiency of the methanogenic reactor to produce methane gas; and    (2) an electromethanogenic reactor comprising an anode and a cathode comprising methanogenic microorganisms.    DESCRIPTION OF DRAWING(S) - The figure shows the schematic diagram of the electromethanogenic reactor.    Electromethanogenic reactor system (10)    Anode (12)    Cathode (16)    Conduit (17)    Power source (18)