| 摘要 |
PROBLEM TO BE SOLVED: To provide a waste water treatment apparatus capable of efficiently removing not only BOD but also nitrogen and phosphorus without adding treatment facilities other than existing standard activated sludge waste water treatment facilities. SOLUTION: A waste water treatment apparatus is equipped with a first sedimentation basin 1 for separating waste water into water and sludge, an oxygen-free tank 4 for stirring separated water from the first sedimentation basin 1, an aerobic tank 5 for aerating the mixed liquid from the oxygen-free tank 4, a circulating means 10 for circulating the mixed liquid of the aerobic tank 5 to the oxygen-free tank 4 and a final sedimentation basin 9 for separating the outflow liquid from the aeration tank 5 into treated water and sedimented sludge. A gravitational concn. tank 22 concentrates the sludge separated in the first sedimentation basin 1 and the sedimented sludge separated in the final sedimentation basin 9. The conc. sludge from the gravitational concn. tank 22 is returned to the non-oxygen tank 4 through a conc. sludge return pipeline 24.
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