The oxic‐settling‐anoxic (OSA) system operated as a sequencing batch reactor was studied. Sludge was interchanged between the aerobic and anaerobic reactors, and the number of daily interchange times was changed from 1 to 4 during the experiments. When the sludge was interchanged
1 time/d, the reduction of excess sludge mass was only 52.8%. When the sludge was interchanged 4 times/d, the reduction of excess sludge mass was 77.4%; reductions in the total chemical oxygen demand, total solids, and total volatile solids of both the anaerobic sludge and the aerobic settled
sludge were the greatest; and more soluble iron was released from the anaerobic sludge. The water quality of the final effluent in the two systems was close. The investigation showed that interchange times are important in improving sludge reduction efficiency, and the parameter should be
regarded as an important operating factor in the OSA process.
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