Sulfide enhances the Fe(II)/Fe(III) cycle in Fe(III)-peroxymonosulfate system for rapid removal of organic contaminants: Treatment efficiency, kinetics and mechanism.

The activation of peroxymonosulfate (PMS) by Fe(II) or Fe(III) for environmental decontamination is severely limited by the low conversion rate from Fe(III) to Fe(II). Here, we found that this puzzling problem could virtually be solved by introducing trace amounts of S. With the addition of 0.2 mM S, the bisphenol A (BPA) degradation efficiency and total organic carbon (TOC) removal in PMS/Fe(III) system were improved by 3.8 and 6.0 times, respectively. Meanwhile, the k and PMS utilization efficiency also markedly increased by 650% and 160%, respectively. The constructed PMS/Fe(III)/S system exhibited a good applicability to a wide pH range (3.2 ~ 9.5) and high resistance to humic acid, Cl and NO. The main reactive oxidant species in PMS/Fe(III)/S system were identified by scavenging experiments, electron paramagnetic resonance measurement, chemical probe approach, and O isotope-labeling technique. The identification results revealed that FeO was the primary reactive oxidant species, while •OH, SO, O and O were also involved in the degradation of BPA. Finally, the generalizability of PMS/Fe(III)/S system was evaluated by varying the target pollutants, oxidants, and reducing S species. The construction of PMS/Fe(III)/S system provides some insights into the treatment of organic wastewaters containing S, e.g., from refineries and tanneries.