Sequential synergy of ultrasonication and powdered activated carbon in sludge dewatering: RSM-driven optimization and mechanistic insights

This study optimized the synergistic use of powdered activated carbon (PAC) and ultrasonication (US) for sludge dewatering via response surface methodology. Results identified optimal conditions (43% PAC, 9.3 W/L US, 43 s) and revealed that treatment sequence critically determined performance. US followed by PAC achieved a sludge cake moisture content of 63.52% and specific resistance to filtration of 2.293 × 1011 m/kg, improving raw sludge values by 35.5% and 97.2%, respectively. Conversely, the reverse sequence degraded efficiency. SEM indicated that US pretreatment disrupts extracellular polymeric substances, releasing bound water, while subsequent PAC creates permeable channels. This sequence-dependent synergy underscores the importance of operational optimization for energy-efficient conditioning, offering a viable strategy to reduce sludge disposal costs and environmental footprint, despite persisting challenges like PAC cost and reactor design.