[Performance and mechanism of excess sludge reduction in an OSA (oxic-settling-anaerobic) process].

The possible factors of sludge reduction such as sludge decay, energy uncoupled metabolism, anaerobic oxidation with low sludge production were discussed in an OSA (oxic-settling-anaerobic) process. It has been confirmed that sludge decay included hydrolysis and acidogenesis of dead microorganism and particle organic carbon adsorbed in sludge flocs and endogenous metabolism. The concentrations of SCOD, NH4(+)-N, TP in supernatant were increased gradually during sludge anaerobic treatment in the batch experiments. Soluble protein were increased up to 33.09 mg/L, exceeding carbohydrate change after 16 h anaerobic sludge treatment in the OSA batch experiment. It proved sludge lysis and hydrolysis in the OSA process. Endogenous SOUR in the OSA batch test was achieved 8 mg/(g h), more than 1.7 multiples as that in the CAS batch test. Higher endogenous metabolism promoted sludge reduction in the OSA process. Sludge decay is the decisive cause in OSA process, accounting for 66.7% of sludge production reduction. By batch experiments, it has been validated energetic uncoupling in OSA system since microorganisms were exposed in alternative anaerobic and aerobic environment. It accounts for about 7.5% of sludge production reduction. SCOD released from anaerobic sludge tank in the OSA process is used as the substrate for cryptic growth. The substrate is used for anoxic denitrifying, anaerobic phosphorus release, sulfate reduction and methane production. These anaerobic reactors have lower sludge production than aerobic oxidation when consumed SCOD is equivalent, which may lead to approximately 23.5% reduction of sludge production in the OSA system. It has been concluded that multiple causes result in minimization of excess sludge in OSA system.