ACTIVE SLUDGE SETTLING METHOD

PROBLEM TO BE SOLVED: To provide a method for preventing outflow of activated sludge, which introduces a mixed liquid into a settling tank to perform settling separation in an activated sludge process of introducing waste liquid into an aeration tank retaining activated sludge to be biologically treated, and can immediately cope with the sludge when settleability of the sludge is lowered and surely promotes settling of the activated sludge in a waste liquid treatment process of returning a part of separated sludge to the aeration tank.SOLUTION: A waste liquid treatment method of returning a part of separated sludge to an aeration tank includes adding a blended composition containing water-in-oil emulsion (A) of polyvinyl amine having a specific composition and physical property value and water-in-oil emulsion (B) of a cationic or amphoteric water-soluble polymer having a specific composition and composition to a path from the aeration tank leading to a settling tank, and thereby enables settling treatment having a better efficiency compared to that of a conventional settling agent.SELECTED DRAWING: None 【課題】活性汚泥を保持する曝気槽に排液を導入して生物処理する活性汚泥法において、混合液を沈殿槽に導いて沈殿分離し、分離汚泥の一部を曝気槽に返送する排液処理方法において、汚泥の沈降性が低下した場合に即対応可能であり、しかも確実に活性汚泥の沈降を促進する方法を開発すること。【解決手段】分離汚泥の一部を曝気槽に返送する排液処理方法において、特定の組成と物性値を有するポリビニルアミンの油中水型エマルジョン（Ａ）と、特定の構造及び組成を有するカチオン性あるいは両性水溶性高分子の油中水型エマルジョン（Ｂ）を含有する配合組成物を曝気槽から沈殿槽に至る系路に添加することで、従来の沈降剤に比べて効率が良い沈降処理が可能となる。【選択図】 なし