Mechanistic insights into promoted dewaterability, drying behaviors and methane-producing potential of waste activated sludge by Fe²⁺-activated persulfate oxidation

Sludge management represents a critical challenge because of complex compositions and poor dewaterability. Fe²⁺-activated persulfate oxidation (Fe²⁺/S₂O₈²⁻) is an effective, and widely investigated method for enhancing sludge dewatering. However, the potential effects of Fe²⁺/S₂O₈²⁻ on sludge drying efficiency, anaerobic biodegradation behaviors and potential recycling of sludge residua are not yet well-known. In this study, a new sludge disposal route (step i: enhanced dewatering via Fe²⁺/S₂O₈²⁻, and step ii: drying-incineration or anaerobic digestion) was proposed and appraised comprehensively. Results showed that Fe²⁺/S₂O₈²⁻ oxidation destroyed extracellular polymeric substances, lysed sludge cells and enhanced the dewaterability greatly. Capillary suction time and mechanical filtration time at 2.0/1.6 mmol-Fe²⁺/S₂O₈²⁻/g-VS decreased by 88.0% and 79.6%, respectively. Moreover, 89.8% of micro-pollutants (e.g., methylbenzene, ethylbenzene, p-m-xylene and o-xylene) in sludge were removed. Besides, the pretreatment was able to alter sludge drying behaviors and methane-producing potential. Pretreated sludge exhibited faster drying rate and shorter lag-time for methane production. Incineration residua of dewatered sludge could be re-coupled with S₂O₈²⁻ as the conditioner to enhance sludge dewaterability, thereby reducing the chemical input and disposal cost. This study provides a novel, self-sustainable strategy for sludge management, reutilization and final safe disposal.