NOVELTY - Biological methane conversion device comprises a mixing chamber for mixing hydrogen and exhaust gas, a biological oxygen reduction tank with a wastewater discharge port, installed on wastewater inlet port, a first diffusing pipe for reducing oxygen, a first screen for passing gas, a biological carbon dioxide reduction tank for discharging carbon dioxide, an electronic control valve for adjusting hydrogen dosage, installed on hydrogen line, a carbon dioxide concentration measuring unit installed on exhaust gas line, and a controller for controlling hydrogen dosage.    USE - The device is useful for reducing carbon dioxide in exhaust gas using fixed media (claimed).    ADVANTAGE - The device reduces oxygen in the exhaust gas, measures the concentration of carbon dioxide and hydrogen, and controls the pH lowering phenomenon of the carbon dioxide reduction tank.    DETAILED DESCRIPTION - Biological methane conversion device comprises either: (a) a mixing chamber (110) for mixing hydrogen supplied from a hydrogen line and exhaust gas supplied from an exhaust gas line, (b) a biological oxygen reduction tank (120) provided with a wastewater discharge port for discharging internal processed wastewater, installed on the outer upper portion of a wastewater inlet port, which supplies processed wastewater inside the biological oxygen reduction tank and is installed on the outer bottom portion of the biological oxygen reduction tank, (c) a first diffusing pipe for generating fine bubbles and reducing oxygen in exhaust gas by injecting exhaust gas and hydrogen through a supplying pipe connected to the lower part of the mixing chamber, provided with a vertical cylindrical enclosure type fixed media and hydrogenotrophic methanogens inside the biological oxygen reduction tank, (d) a first screen for passing gas and fixing the fixed media, installed on the inner upper portion of the biological oxygen reduction tank and on the upper portion of the first diffusing pipe from the inner bottom of the biological oxygen reduction tank, (e) a biological carbon dioxide reduction tank (130) for discharging methane converted from carbon dioxide present in the exhaust gas through the top of the a discharge pipe and supplying reduced oxygen through a connecting pipe connected between the upper and lower portion of the biological oxygen reduction tank, (f) an electronic control valve (140) for adjusting hydrogen dosage according to external control and is installed on the hydrogen line, (g) a carbon dioxide concentration measuring unit (150) for measuring carbon dioxide concentration present in the exhaust gas and is installed on the exhaust gas line, and (h) a controller for controlling certain percentage of hydrogen dosage by adjusting the electronic control valve; or (a), (i) a biological oxygen and carbon dioxide reduction tank provided with the waste water discharge port for discharging internal processed waste water and is installed at the bottom of a second screen and the wastewater inlet port supplying processed wastewater inside the reduction tank and is installed on the outer bottom of the reduction tank, (ii) a diffusing pipe for generating fine bubbles, discharging methane converted form carbon dioxide in the exhaust gas through the top of discharge pipe and for reducing oxygen in the exhaust gas by injecting exhaust gas and hydrogen through the supplying pipe connected to the bottom of the mixing chamber, arranged on the inner bottom of the reduction tank and provided with the fixed media and hydrogenotrophic methanogens formed in vertical cylindrical enclosure type inside the reduction tank, (d) the first screen for passing gas and fixing the fixed media at the bottom of the reduction tank and is installed on top of the diffusing pipe from the inner the bottom of the reduction tank, (iii) the second screen for passing gas and fixing the fixed media at the bottom of the reduction tank, (iv) a third screen for passing gas and fixing the fixed media at the bottom of the reduction tank and is arranged spaced apart from the upper portion of the second screen, (v) a fourth screen for passing gas and fixing the fixed media at the inner upper part of the reduction tank, (f), (g) and (h).    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic representation of the biological methane conversion device for reducing carbon dioxide in exhaust gas using fixed media.    Mixing chamber (110)    Biological oxygen reduction tank (120)    Carbon dioxide reduction tank (130)    Electronic control valve (140)    Carbon dioxide concentration measuring unit (150)