WATER PURIFICATION METHOD AND WATER PURIFICATION APPARATUS

To provide a water purification method and a water purification apparatus capable of adding a polymer coagulant without excess or shortage and stably and continuously obtaining a high coagulation sedimentation treatment effect.SOLUTION: A water purification method includes: a coagulation treatment S1 where an inorganic coagulant is injected into raw water and suspended matter in the raw water is coagulated; a coagulation sedimentation treatment S2 including a coagulation treatment S21 forming coagulation flocks by performing the coagulation treatment in the presence of a polymer coagulant to the raw water containing the inorganic coagulant and a solid-liquid separation treatment S22 obtaining coagulation sedimentation sludge or sludge slurry by performing the solid-liquid separation of the coagulation flocks; a return treatment S3 where at least a part of the coagulation sedimentation sludge is returned to the coagulation treatment as separated sludge or the sludge slurry is returned to the coagulation treatment; and a polymer coagulant addition treatment S4 adding the polymer coagulant in the return treatment S3. In the water purification method, the determination of the addition amount of the polymer coagulant is based on the sludge weight of the separated sludge or the sludge slurry and a predetermined polymer coagulant addition rate.SELECTED DRAWING: Figure 1 【課題】高分子凝集剤を過不足無く添加でき、高い凝集沈殿処理効果を安定して継続的に得ることが可能な浄水処理方法及び浄水処理装置を提供する。【解決手段】原水に無機凝集剤を注入して原水中の濁質を凝結させる凝結処理Ｓ１と、無機凝集剤を含む原水に対して高分子凝集剤の存在下で凝集処理を行うことにより凝集フロックを形成させる凝集処理Ｓ２１、及び、凝集フロックを固液分離し、凝集沈殿汚泥又は汚泥スラリを得る固液分離処理Ｓ２２を含む凝集沈殿処理Ｓ２と、凝集沈殿汚泥の少なくとも一部を分離汚泥として凝集処理へ返送するか、又は汚泥スラリを凝集処理へ返送する返送処理Ｓ３と、返送処理Ｓ３において高分子凝集剤を添加する高分子凝集剤添加処理Ｓ４と、を有し、分離汚泥又は汚泥スラリの汚泥重量と予め設定した高分子凝集剤添加率とに基づいて、高分子凝集剤の添加量を決定する浄水処理方法である。【選択図】図１