Improved dewaterability of anaerobically digested sludge by thermally activated persulfate oxidation: Performance evaluation and nutrient release

Wastewater treatment plants (WWTPs) generate large volumes of anaerobically digested sludge, whose high-water content (95–97 wt.%) continues to pose major operational and economic burdens. Although anaerobic digestion reduces sludge organic load, it does not sufficiently improve dewaterability, creating a need for more effective conditioning strategies. In this study, thermally activated potassium persulfate (PS-H) is proposed as an efficient, catalyst-free method to enhance sludge dewatering under moderate mild conditions. Frist of all, a parametric study was conducted by varying oxidant concentration (0.25 – 2.0 mmol g sv -1 ), temperature (25 – 80 °C) and pH 0 (3-9). Under optimal conditions ([K 2 S 2 O 8 ] 0 = 1.0 mmol g sv -1 ; T = 60 ºC; pH 0 = 5), PS-H achieved 54.4% centrifuge weight reduction and a 78.6% decrease in capillary suction time. These improvements clearly surpass those obtained with persulfate alone (10% and 25.6%, respectively), demonstrating a strong synergistic effect between persulfate and thermal activation. Mechanistically, the process promoted a >50% reduction in bound water, a marked decrease in viscosity, and pronounced floc disintegration. The transformation of tightly bound extracellular polymeric substances (EPS) into soluble fractions confirmed the effective structural disruption underlying the enhanced water release. Beyond dewatering performance, the treatment maximized nutrient release into the liquid phase, representing a promising and innovative strategy to simultaneously improve sludge dehydration and foster resource recovery in WWTPs.