Ultrasonic enhanced Fe-C/PDS system for sludge dewatering and carbon source release: synergy of oxidation and cracking processes

The effective dewatering of waste activated sludge (WAS) and the utilization of resources are crucial for the sustainable development of wastewater treatment plants. Ultrasonic (US) collaborative iron-carbon (Fe-C) activated peroxydisulfate (PDS) coupling system was constructed to investigate the transformation of physicochemical properties and explore the mechanisms during the cracking and oxidation of WAS. The ultrasonic enhanced Fe-C/PDS system, which exhibited excellent oxidation capacity under the conditions of PDS, Fe-C, and ultrasonic power levels at 0.12 g/g TS, 0.3 g/g TS, and 0.3 W/mL. The water content of the sludge cake was reduced to 61.71 %, while the specific resistance to filtration was lowered to 1.12 × 10¹² m/kg (decreased by 88.2 %). Furthermore, ultrasonic improved the WAS cracking capacity with a satisfying SCOD production (630.64 mg/L) and a dramatic reduction of 9.16 % in volatile solids. Compared to Fe-C/PDS, the addition of ultrasonic enhanced the leaching of Fe, released carbon source and promoted the formation of various reactive oxidative species to degrade bound EPS. The contribution of O₂⁻and¹O₂was 37.00 % and 43.17 %, indicating the oxidation process of free radicals and non-free radicals in Fe-C/PDS/US system. Additionally, the concentration of short-chain fatty acids was increased by 96.7 %, which significantly accelerating the quality of carbon source suitable for recycling. The positive improvement of sludge physicochemical properties revealed the disintegration-degradation synergistic effect of the Fe-C/PDS/US systems. These findings provide a novel strategy for effective disposal and reduction in WAS while also offering valuable insights into resource utilization.