Dewaterability improvement and environmental risk mitigation of waste activated sludge using peroxymonosulfate activated by zero-valent metals: Fe0 vs. Al0

Abstract

The stabilization and dewaterability of waste activated sludge (WAS) are essential factors for downstream disposal or reuse. Herein, two types of zero-valent metals, zero-valent iron (Fe0) and zero-valent aluminum (Al0), were compared for their ability to activate peroxymonosulfate (PMS) during the WAS conditioning process, with the effects of PMS activation by these two metals on WAS dewaterability and the potential environmental risks evaluated. Results showed that compared to Al0/PMS treatment, Fe0/PMS treatment achieved superior WAS dewaterability and reduced operational costs. Using PMS combined with Fe0 and Al0 treatments under optimal conditions, the water content (Wc) of dewatered sludge decreased to 55.7 ± 2.7 wt% and 59.4 ± 1.3 wt%, respectively. Meanwhile, application of the Fe0/PMS treatment system reduced the total annual cost by approximately 33.1%, compared to the Al0/PMS treatment. Analysis of the dewatering mechanism demonstrated that in the Fe0/PMS treatment, Fe3+/Fe2+ flocculation played an important role in the enhancement of WAS dewatering, while sulfate radical (SO4•−) oxidation was the dominant factor for WAS dewaterability improvement in Al0/PMS treatment. The greater enhancement of WAS dewaterability by Fe0/PMS treatment, was mainly attributed to more efficient reduction of hydrophilic extracellular polymeric substances (EPS) and an increase in surface charge neutralization. Environmental risk evaluation results indicated that Fe0/PMS and Al0/PMS treatments both effectively alleviated the environmental risks of heavy metals and faecal coliforms in dewatered sludge. Overall, this study proposes a novel perspective for the selection of an optimal PMS activator in sludge treatment.