Sustained moderate oxidation system driven by gas-liquid-solid microenvironment under Mn(VII)-Fe(III)/sodium percarbonate (SPC) treatment: Mechanism and application in sludge dewatering

Rapid-strong oxidation systems cause cell lysis and the release of intracellular substances during the degradation of extracellular organic matters (EOM), deteriorating the treatment efficiency of selected technology (such as sludge treatment). To address these shortcomings of rapid-strong oxidation, a sustained moderate oxidation system was proposed and investigated in this study. For establishing sustained moderate oxidation system, sodium percarbonate (SPC) was chosen as the oxidant while potassium permanganate (Mn(VII)) and ferric chloride (Fe(III)) were selected as the catalysts. Results showed that moderate contents of different reactive oxygen species (ROS) were generated continuously under the sustained release of hydrogen peroxide (H₂O₂). Mechanism exploration performed that the oxygen (O₂) bubbles and Mn-Fe flocs formed in Mn(VII)-Fe(III)/SPC system interacted with the reaction solution to jointly construct a gas-liquid-solid microenvironment for efficient generation of ROS. The Mn(II)/Mn(IV) and Fe(III) existed in Mn-Fe flocs effectively adsorbed/coagulated organics. Meanwhile, the existed Mn(II)/Mn(III) promoted the surface oxidation of Mn-Fe flocs and the cycle of Fe(II)/Fe(III) in liquid phase, achieving the directional oxidation of organics on the surface of Mn-Fe flocs. The bubbles of O₂ drove the contact between H₂O₂ and Mn-Fe flocs, and were converted into corresponding ROS with oxidizing properties by obtaining electrons. Compared with direct addition of H₂O₂, Mn(VII)-Fe(III)/SPC increased the organics degradation rate by an additional 14 %. Meaningfully, the potential of sustained moderate oxidation on sludge dewaterability enhancement had been also experimentally confirmed in this study to verify its engineering practicality. The water content decreased from 85 % to 72 % (75.3 % in rapid-strong oxidation group).