Enhanced primary sludge sonication by heat insulation to reclaim carbon source for biological phosphorous removal

Abstract Ultrasound pretreatment is a potent step to disintegrate primary sludge (PS). The supernatant of sonicated PS is recycled as an alternative carbon source for biological phosphorus removal. In this study, we investigated the role of temperature on PS disintegration during sonication. We found that a temperature of 60 °C yielded a dissolution rate of about 2% soluble chemical oxygen demand (SCOD) as compared to 7% SCOD using sonication at the specific energy (SE) of 7359 kJ/kg TS. Using the SE of 6000 kJ/kg TS with heat insulation during sonication, the SCOD dissolution rate of PS was similar to the result at the SE of 7051 kJ/kg TS without heat insulation. Upon treatment with sonication, the PS released low concentrations of Cu and Zn into the supernatant. The phosphorus-accumulating organisms (PAOs) used the supernatant of sonicated PS as the carbon source. Supplementation with the diluted sonicated PS supernatant (SCOD ≈ 1000 mg/L) in anaerobic phase resulted in the release of phosphorus (36 mg/L) and the production of polyhydroxyalkanoates (PHAs) (0.36 g PHA/g SS). Compared with sodium acetate, higher polyhydroxyvalerate (PHV) faction in the polyhydroxyalkanoates (PHAs) was observed in the biomass when incubated with sonicated PS as the carbon source. This work provides a simple pathway to conserve energy and to enhance efficiencies of ultrasonic pretreatment and the recovery of carbon source from the sludge for improving the phosphorus removal in the ENR system.