NOVELTY - Continuous synchronous bioremediation of an aqueous contaminated liquid involves circulating contaminated liquid through electrolytic cell (20a) to introduce a controlled amount of dissolved oxygen and hydrogen into the contaminated liquid. The dissolved hydrogen is used as an electron donor by methanogenic bacteria and to in situ generate methane, and by anaerobic bacteria including methanogens.    USE - For continuous synchronous bioremediation of an aqueous contaminated liquid, e.g. ground water (claimed).    ADVANTAGE - The invented method minimizes or eliminates the addition of organic carbon source to diminish the competition between methanotrophic bacteria and heterotrophic bacteria for oxygen.    DETAILED DESCRIPTION - Continuous synchronous bioremediation of an aqueous contaminated liquid including a contaminant requiring reductive and oxidative steps for its biodegradation involves providing a bioreactor (10) containing a coupled single phase anaerobic(methanogenic)/aerobic(methanotrophic) biofilm (38) having an anaerobic (methanogenic) zone located at a central core area of the biofilm, and a juxtaposed aerobic (methanotrophic) zone at a surrounding peripheral area of the biofilm, in fluid communication with the anaerobic (methanogenic) zone, and including a decreasing gradient of oxygen concentration from the aerobic (methanotrophic) zone to the anaerobic (methanogenic) zone toward the core area, and an electrolytic cell for hydrolyzing water, in fluid communication with the bioreactor; circulating the contaminated liquid through the electrolytic cell to together introduce a controlled amount of dissolved oxygen and hydrogen into the contaminated liquid, and continuously cycling the oxygenated and hydrogenated contaminated liquid through the bioreactor, where dissolved hydrogen is used as an electron donor by methanogenic bacteria and to in situ generate methane, and by anaerobic bacteria including methanogens; and dissolved oxygen is used as an electron acceptor by aerobic, including methanotrophic bacteria, and methane is used by methanotrophic bacteria, to remediate the contaminated liquid, respectively by reductive and oxidative steps. An INDEPENDENT CLAIM is also included for an apparatus for the continuous synchronous bioremediation of an aqueous contaminated liquid including a contaminant requiring reductive and oxidative steps before its biodegradation comprising bioreactor containing a coupled single phase anaerobic(methanogenic)/aerobic(methanotrophic) biofilm; inlet (12) in the bioreactor for influent contaminated liquid; first outlet (14) in the bioreactor for effluent treated liquid; second outlet in the bioreactor for effluent gas; conduit (18) outside of the bioreactor for connecting the inlet and the first outlet to define a closed loop including the bioreactor; electrolytic cell for hydrolyzing water associated with the conduit for together introducing oxygen and hydrogen into the conduit, where a controlled amount of oxygen and hydrogen is dissolved in the liquid outside of the bioreactor; and pump for continuously cycling contaminated liquid through the apparatus, where dissolved hydrogen is used as an electron donor by methanogenic bacteria and to in situ generate methane, and by anaerobic bacteria, including methanogens, and dissolved oxygen is used as an electron acceptor by aerobic, including methanotrophic bacteria and methane is used by methanotrophic bacteria, to remediate the contaminated liquid, respectively by reductive and oxidative steps.    DESCRIPTION OF DRAWING(S) - The figure is a schematic view of a bioelectrolytic methanogenic/methanotrophic coupling within a bioreactor system.    Bioreactor (10)    Inlet (12)    Outlet (14)    Conduit (18)    Cell (20a)    Biofilm (38)