Enhanced Sludge Dewaterability and Pathogen Inactivation by Synergistic Effects of Zero-Valent Iron and Ozonation

In this study, the efficiency of the combined zerovalent iron (ZVI) and ozone (O-3) treatment at a pH of 2 (acid-ZVI-O-3) for simultaneous improvement of sludge dewaterability and pathogen inactivation was investigated. The results showed that the ozone treatment alone deteriorated sludge dewaterability, while the introduction of acid-ZVI into the ozone treatment could significantly enhance the sludge dewaterability. At the optimal conditions with 30 mg O-3 g(-1) of total solid (TS) and 63 mg ZVI g(-1) of TS at a pH of 2, the capillary suction time of conditioned sludge was 1.63 s L g(-1) TS, which was much smaller than those of raw sludge (10.45 s L g(-1) TS), the single ozonation treated sludge (16.07 s L g(-1) TS), and the acid-ZVI-treated sludge (6.98 s L g(-1) TS). The acid-ZVI-O-3 treatment promoted the generation of hydroxyl radicals and showed synergistic effects in removing key hydrophilic substances which would deteriorate sludge dewaterability, i.e., humic acid-like compounds and soluble microbial byproduct-like substances in the tightly bound extracellular polymeric substances (TB-EPSs). Ferric iron was generated therein and worked as a coagulant to agglomerate sludge particles. The enhanced sludge dewaterability was further confirmed by a laboratory-scale diaphragm filter press. Moreover, the acid-ZVI-O-3 treatment showed an effective inactivation of pathogens, which was below the limit specified for class A biosolids, according to the US EPA standard. As such, enhanced sludge dewaterability and pathogen inactivation can be simultaneously achieved with the acid-ZVI-O-3 treatment.