In-situ utilization of EPS improves the directional oxidation ability of Fe(III)/H₂O₂ and enhances sludge dewaterability

Inefficient sludge dewatering can result in high costs for sludge treatment and disposal, as well as increased pollution of the environment. In this study, we constructed a double oxidation–reduction (Redox) cycle system of Fe(II)/Fe(III) and Fe(II)-extracellular polymeric substance (EPS)/Fe(III)-EPS by utilizing EPS in situ and collaborating with Fe (III) and H₂O₂ so as to regulate the performance of Fenton oxidation for efficiently enhancing the dewaterability. Results displayed the specific resistance to filtration (SRF) reduced from 34.1 ± 2.4 × 10¹² m/kg to 16.2 ± 1.5 × 10¹² m/kg with only 0.15 mmol Fe(III)/g VSS and 1.46 mmol H₂O₂/g VSS. Notably, the formation of relative stable Fe(III)-EPS complex was found under the interval addition of Fe(III) and H₂O₂. Four types of reactive species (hydroxyl radical (•OH), singlet oxygen (¹O₂), superoxide radical (O₂^•-) and Fe(IV)) which could effective destroy EPS structure during conditioning process, were generated after the addition of H₂O₂. It effectively promoted the transition from intracellular oxidation to extracellular oxidation under Fenton oxidation conditions, which reduced negative effects of cell lysis under excessive oxidation during sludge conditioning. The structure of EPS damaged significantly during the oxidation process, leading to the effective conversion of bound water to free water. Meanwhile, the existence of dissociative Fe(III) promoted the aggregation of sludge flocs, generating large channels or pores for sludge water to discharge, and then improving the dewaterability. Overall, [Fe(III)-EPS]/H₂O₂ treatment as an efficient sludge conditioning method can provide guidance for sludge dewaterability enhancement in urban sludge treatment and disposal.