NOVELTY - A sludge-digestion gas treatment equipment is equipped with methane concentrator (10) having carbon dioxide fixing device having solid electrolyte providing anode supplied with ion supply source, and cathode supplied with digestion gas. The power supply of the device carries out separation-fixation in cathode by impressing voltage between the poles of electrode(s), making gaseous carbon dioxide as carbonate.    USE - For treating sludge-digestion gas and recovering carbon dioxide and methane in gaseous phase.    ADVANTAGE - The sludge-digestion gas treatment equipment efficiently and economically recovers carbon dioxide and methane in gaseous phase. The methane concentration in the gas is increased by 90% or more. The energy conversion efficiency in a fuel cell or fuel combustion facility is improved. Production of electric or heat energy is performed stably. The production supply of high concentration methane gas is carried out continuously. Liquid spills are not produced. The equipment is compact and easy to handle. The contacting efficiency of the gas to be treated with carbon dioxide is improved. The equipment contributes to green house gas curtailment countermeasure and global warming countermeasure.    DETAILED DESCRIPTION - A sludge-digestion gas treatment equipment is equipped with a methane concentrator (10), and obtains methane-rich gas which removes carbon dioxide from sludge-digestion gas. The methane concentrator has a carbon dioxide fixing device equipped with a solid electrolyte which provides an anode to which an ion supply source substance is supplied, and a cathode to which the digestion gas is supplied. The power supply of the fixing device carries out separation-fixation in the cathode by impressing a voltage between the anode and/or cathode poles, making carbon dioxide in gaseous phase as carbonate. When the ion supply source substance is a sodium compound, when the solid electrolyte is a sodium ionic conductor or when the solid electrolyte is a lithium ionic conductor, the ion supply source substance is a lithium compound.    DESCRIPTION OF DRAWING(S) - The figure shows the sludge-digestion gas treatment apparatus. (Drawing includes non-English language text).    Methane concentrator (10)    Fuel cell (13)