To solve such problems that an amine compound or its derivative is used in a form adhered to a support but there is a limit in the amount possible to adhere of the amine compound or its derivative, much labor is required in the adhesion of the amine compound or its derivative and there is considerable difference in the adhesion effect of an amine to be dispersed by the mixing ratio, amount or kind of the amine.

Sewage is passed through a dispersion prepared by dispersing a micronized emulsified oil treating agent 341 and an oil adsorbing material 342 having a definite size in a weight ratio of 1:1-10.