ADVANCED TREATMENT OF BIOLOGICALLY TREATED WATER

摘要

PROBLEM TO BE SOLVED: To stabilize a sludge blanket layer and to obtain high-quality treated water by providing the subject treatment method with flocculation, solid-liquid separation, sludge return and aeration stages and determining the amount of return sludge so as to attain the amount of a specific relation with the amount of the suspended solids in the return sludge per unit time flowing into a solid-liquid separation stage. SOLUTION: The biologically treated water is fed from a relay tank (raw water) tank 1 to a reaction chamber 2 where an inorganic flocculating agent is added to the water and its pH is regulated. A high-molecular flocculating agent (polymer) is then added to the water in a flocculating tank 3 to execute a flocculation treatment. The flocculation-treated water is then introduced into a sludge blanket type solid-liquid separation tank 4 where the waste water is subjected to a solid-liquid separation. The treated water is discharged to the outside of the system. The separated sludge is partly returned as the return sludge to the relay tank 1 and the balance is discharge to the outside of the system. The amount of the return sludge is set at an amount to attain SA=(SB-SA)×5 to 30 when the amount of the SSs (suspended matter) in the return sludge per unit time is defined as SA and the amount of the SSs per unit time flowing into the sludge blanket type solid-liquid separation tank 4 as SB.