| 摘要 |
An aerobic treatment process is operated to reduce overall oxygen requirements, to maintain general pH balance and to produce a low-coliform solids effluent. From the system's clarifier a slurry of concentrated solids is moved to a premix basin, where the slurry is vigorously aerated for a sufficient time to raise microbial activity and dissolved oxygen content. The aerated, microbially active sludge is then moved to a gravity thickener basin, in which solids are allowed to settle to the bottom without aeration, to establish a quiescent state in the settled sludge and also an anoxic stage. This causes the sludge to be denitrified by microbial action, raising and stabilizing the pH of the sludge. Separated supernatant liquid is decanted and removed from the gravity thickener. The sludge is moved into an aerobic digester, where the sludge is aerated and nitrification occurs but using less aeration than normally required in a digester, due to the effect of anoxic/aerobic phases. A portion of the slurry in the aerobic digester basin is recycled back to the premix basin. Another important aspect is the use of two digesters, only one in loop with the premix and thickener at any one time, with each digester being taken out of the loop and isolated when a solids content of about 25,000 to 35,000 mg/L (2+E,fra 1/2+EE % to 3.5%) is achieved in that digester. The isolation results in a significantly lowered coliform content in the effluent sludge.
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