NOVELTY - A pressurized sewage gas is contacted with high-pressure water. The carbon dioxide and hydrogen sulfide are separated from pressurized sewage gas, and methane is purified. The high-pressure water containing carbon dioxide and hydrogen sulfide is pressure-reduced. The carbon dioxide and hydrogen sulfide are separated from water. The separated carbon dioxide and hydrogen sulfide, and an oxygen-containing gas are supplied to a biodesulfurization column (16). The hydrogen sulfide in the mixed gas is decomposed by the microorganisms.    USE - Desulfurization of sewage gas used as fuel for gas engine of electric power generation, gas turbine, fuel cell and steam boiler.    ADVANTAGE - The method enables desulfurization of the sewage gas efficiently, with simplified installation, and provides purified methane. The deposit of sulfur adhered to the filler layer in the biodesulfurization column is washed with the high-pressure water.    DETAILED DESCRIPTION - A sewage gas discharged by methane fermentation of an organic waste is compressed and pressurized with a compressor. The pressurized sewage gas is supplied to an absorption tower (4), and the pressurized sewage gas is contacted with high-pressure water. The carbon dioxide and hydrogen sulfide are separated from pressurized sewage gas which dissolves carbon dioxide and hydrogen sulfide in the pressurized sewage gas in high-pressure water, and methane is purified. The high-pressure water containing carbon dioxide and hydrogen sulfide from the absorption tower is pressure-reduced. The carbon dioxide and hydrogen sulfide are separated from the high-pressure water. The separated carbon dioxide and hydrogen sulfide, and an oxygen-containing gas are supplied to a biodesulfurization column having a filler layer (15) to which microorganisms which decompose hydrogen sulfide is adhered. The hydrogen sulfide in the mixed gas is decomposed by the microorganisms. The high-pressure water containing carbon dioxide and hydrogen sulfide is supplied to biodesulfurization column, and the filler layer is washed by the bubble of carbon dioxide and hydrogen sulfide which are formed out of the high-pressure water. An INDEPENDENT CLAIM is included for de-sulfuring apparatus of sewage gas, which has compressor to compress and pressurize sewage gas, absorption tower, separation unit to separate carbon dioxide and hydrogen sulfide from high-pressure water, biodesulfurization column and high-pressure water supply unit.    DESCRIPTION OF DRAWING(S) - The drawing shows the schematic view of the de-sulfuring apparatus of sewage gas. (Drawing includes non-English language text)    Mist separator (1)    Hydrogen-sulfide densitometer (2)    Absorption tower (4)    Filler layer (15)    Biodesulfurization column (16)