Enhancement of dewaterability and heavy metals solubilization of waste activated sludge conditioned by natural vanadium-titanium magnetite-activated peroxymonosulfate oxidation with rice husk

In this work, natural vanadium-titanium magnetite-activated peroxymonosulfate (VTM-PMS) oxidation coupled with rice husk (RH) as skeleton builder (VTM-PMS-RH) was employed to enhance sludge dewaterability for the first time. The optimal dosages of PMS, VTM, and RH were 200 mg/g total suspended solids (TSS), 1 g/g TSS, and 200 mg/g TSS, respectively. Under optimal conditions, capillary suction time (CST) reduction and water content of sludge cake (W-C) were 82.1% and 72.9% after VTM-PMS conditioning, respectively, which further reached the values of 94.8% and 63.4% when coupled with RH treatment. Cycle experiments demonstrated that VTM reusability in VTM-PMS system for dewatering sludge was desirable. Based on sludge physicochemical properties after conditioning (i.e., extracellular polymeric substances (EPS), zeta potential, dissolved organic carbon (DOC), total nitrogen (TN), and volatile suspended solids (VSS) reduction), VTM-PMS oxidation shows the merits of EPS degradation, sludge disintegration, and charge neutralization. In addition, the transformation behaviors of heavy metals (HMs) in sludge after conditioning were investigated according to total HMs contents, speciation distribution, and leaching tests. Through conditioning, total HMs contents (Cu, Zn, Cr, and Pb) in liquid phase increased while were adverse in solid phase. The leaching toxicity reductions were 78%, 83%, 60%, and 100% for Cu, Zn, Cr, and Pb, respectively, obtained by VTM-PMS-RH conditioning. Meanwhile, the chemical speciation distribution of HMs in sludge was changed and transformed into more stable forms, as well as the environmental risk of HMs decreased. These results suggest that VTM-PMS-RH process has a synergistic contribution to the environmental risk reduction of HMs and their immobilization enhancement. Therefore, VTM-PMS-RH process is a promising alternative for sludge conditioning in terms of the enhancement of dewaterability and HMs solubilization.