Excess sludge conditioning with ultrasound/ozone and its effect on the anaerobic anoxic oxic process in a municipal wastewater treatment plant

Abstract Impact of ultrasonication and ozonation pre-treatment on the sewage sludge and ultrasonication–ozonation integrated with anaerobic anoxic oxic system were investigated. According to response surface methodology, the optimal conditions were determined for an ozone dosage of 0.14 g·O3/g·SS and an ultrasonic intensity of 1.61 W/mL, which corresponded to a maximum sludge reduction ratio of 68.1%. When the residence time of broken sludge was 30 min and the reflux ratio was 60%, the broken sludge returned to the anaerobic or anoxic zone had little effect on chemical oxygen demand and improved total phosphorus removal rate of the anaerobic anoxic oxic system effluent. The broken sludge was returned to the anoxic zone, the removal rate of total nitrogen in the effluent of the anaerobic anoxic oxic system could be increased by 13.2%. The broken sludge backflow improved the sedimentation performance of the anaerobic anoxic oxic system sludge, which had little to do with reflow methods. The broken sludge reflowed to the anaerobic zone reduced the sludge production of the anaerobic anoxic oxic system by 51.3%.