Enhanced sludge dewaterability via ozonation catalyzed by sludge derived biochar loaded with MnFe2O4: Performance and mechanism investigation

In order to develop an efficient and environmental-friendly alternative for enhancing dewatering performance of waste activated sludge (WAS), the sludge derived biochar loaded with MnFe2O4 (MnFe2O4@SBC) was firstly prepared for catalyzing ozonation of sludge. The optimal condition was determined to be pH = 6, O3 dosage = 60 mg/g VS and MnFe2O4@SBC dosage = 600 mg/g VS, under which the capillary suction time (CST) and specific resistance to filtration (SRF) of WAS declined from 98.3 ± 1.0 s and 1.1 ± 0.03 × 1014 m/kg to 18.3 ± 0.8 s and 0.32 ± 0.03 × 1014 m/kg, respectively. The water content (Wc wt.%) of sludge cake declined from 87.1 ± 0.98% to 68.1 ± 0.87%. The mechanism for enhanced dewatering performance of WAS by MnFe2O4@SBC was systematically clarified. Firstly, the circulation of valence states for Fe and Mn on the surface of MnFe2O4@SBC was found promoting the conversion of O3 into highly active free radicals and the generation of hydroxyl radicals (·OH). Secondly, the density functional theory (DFT) calculation firstly manifested that O3 molecules were easier to be activated and dissociated into ·OH groups on the surface of MnFe2O4 phase. With the above promotion of ·OH generation, the inner part of sludge flocs especially the protein in extra-cellular polymers (ECPS) was destructed strongly, with significant release of bound water and the decrease in water bound energy. The organic biopolymers with negative charges were diminished followed by the increased zeta potential and enlarged particle size, resulting in the enhanced dewatering performance of WAS. This study illustrated the rationality and validity of the new strategy for enhanced sludge dewatering in both practice and theory, shedding light on the further development of sludge dewatering technology.