Coupling weak magnetic field and zero-valent iron-activated persulfate oxidation process activation for improving dewaterability of waste activated sludge

Zero-valent iron (ZVI) activated persulfate (S₂O₈²⁻) oxidation offers an alternative strategy for enhancing sludge dewatering. However, the slow corrosion/dissolution and precipitations of oxide iron layer of ZVI particles limit it real applications. In this study, weak magnetic field (WMF) was coupled with zero-valent iron (ZVI)-activated persulfate (S₂O₈²⁻) oxidation at the different initial pH levels to enhance waste activated sludge (WAS) dewatering ability. The use of WMF can avoid the precipitation of ferric (hydr) oxides and accelerate the dissolution of ZVI particles, with the concentration of Fe(II) increased from 10.0 ± 8.8 to 222.0 ± 118.0 mg/L. The lowest CST/CST₀ value of 0.27 ± 0.00 was observed at the ZVI/S₂O₈²⁻ dosage of 1.5/1.2 mmol/g-VS when coupled with WMF of 25 mT, lower than that without WMF (0.59 ± 0.03). The improved ZVI corrosion and subsequent liberation of Fe(II) provoked the SO₄⁻· production from S₂O₈²⁻ and thus enhanced the sludge dewaterability greatly by disrupting the extracellular biopolymers and cells. Our results show that the application of WMF can be feasible for ZVI/S₂O₈²⁻ oxidation to improve sludge dewatering performance. ZVI/S₂O₈²⁻ oxidation cannot only avoid rapid free radical consumption and introduction of other anions to a certain extent, but also is more environmentally friendly when coupled with WMF than with thermal and acid-wash pretreatment.