Abstract: A method of treating an oil-containing waste water includes adding, where the waste water has been adjusted to have a pH between eight and twelve and have a temperature not higher than 50° C., a high-cationic flocculant consisting of a high-molecular material selected from among acrylamide-quaternized or salified dimethylaminoethyl acrylate or methacrylate copolymer, and acrylamide-quaternized or salified dimethylaminoethyl acrylate or methacrylate-acrylic acid copolymer, and which constitutes a plurality of polymerized units at least 60 mol % of which have respective cationic functional groups, to the waste water, such that a concentration of the flocculant in the waste water falls between 100 mg/L and 1,000 mg/L, so that at least one fouling component dispersed in the water is flocculated to form a sludge consisting of flocks of the at least one fouling component and thereby separate the at least one fouling component and the water.

Abstract: A method of treating an oil-containing waste water which is produced by washing, with a surfactant, an article bearing at least one fouling component including an oil, and in which the at least one fouling component is finely dispersed in the water by the surfactant, the method including the step of adding, under a condition that the oil-containing waste water has been adjusted to have a pH value greater than eight and smaller than twelve and have a temperature not higher than 50° C.