PURPOSE: To use the treated water of gas liquor cyclically and effectively by collecting dust from the recovered gases from blast furnaces, converters, etc. by using concd. gas liquor from recovered gases from coke furnaces and bringing said gas liquor into contact with the produced gases from the blast furnaces, converters, etc.

CONSTITUTION: The gases recovered from a coke furnace 1 are condensed to gas liquor 2 which is fed by the 1st tank 7 and a pump 71 to a wet dust collector 8. In the collector 8, the polluting materials in the gas liquor are brought into contact with the active and porous dust in the recovered gases, and are modified from the state wherein said materials exist in the condensed gas liquior by adsorption, decomosition, complex formation, etc. The gas liquor after the dust collection is fed from the collector 8 to a thickener 9, where the gas liquor is settled and purified. The supernatant liquid of the thickener 9 is sucked by a pump 91 and is returned into the 1st tank 7.