To reduce the quantity of an amphoteric organic high molecular flocculant to be added by using the amphoteric organic high molecular flocculant made of a copolymer composed of monomers expressed by specific formulae as a 2nd flocculant in a method for granulating and flocculating by adding a 1st and the 2nd flocculant to a sewerage.
In the treatment of the sewerage, after the 1st and the 2nd flocculants are successively added to the sewerage and mixed, the sewerage is granulated and flocculated and the treated water is taken out. In such a case, the amphoteric organic high molecular flocculant made of the copolymer composed of the monomer expressed by formulae I-IV, in which total content of the monomers I and II is 15-40mol%, the ratio of the monomer I to total content of the monomers I and II is 0.1-0.5 and the content of the monomer III is 5-10mol%, is used as the 2nd flocculating agent. In the formulas, each of R1 and R3 expresses an alkyl group, each of R2 and R4 expresses an alkyl group or a benzil group, each of R5 and R6 expresses hydrogen or methyl group, X expresses an anion and M expressed hydrogen or an alkali metal.
MIYAHARA KENICHI
NAGANO KIMIHIRO
