Formation and degradation mechanisms of CX3R-type oxidation by-products during cobalt catalyzed peroxymonosulfate oxidation: The roles of Co3+ and SO4·-.

Sulfate radical (SO 4 ·-)-based advanced oxidation processes (AOPs) attract increasing attention in the control of micropollutants. However, SO 4 ·- can react with other chemicals present in water and result in undesired oxidation by-products (OBPs) generation. The formation and degradation mechanisms of CX 3 R-type OBPs during cobalt catalyzed peroxymonosulfate (Co2+/PMS) oxidation were investigated. In the formation of CX 3 R-type OBPs, both Co3+ and SO 4 ·- could convert chloride to free chlorine that then reacted with natural organic matter, leading to the formation of CX 3 R-type OBPs. The concentrations of trichloromethane, chloral hydrate, dichloroacetonitrile, dichloroacetamide and trichloroacetamide after 15 min reaction were 9.8, 3.9, 1.2, 5.9 and 22.3 nM, respectively. Compared to SO 4 ·-, Co3+ played a more significant role in the CX 3 R-type OBP formation and calculated toxicity values of CX 3 R-type OBPs. CX 3 R-type OBPs could not only be formed but also be degraded at the same time during Co2+/PMS oxidation. As for the degradation of CX 3 R-type OBPs, both Co3+ and SO 4 ·- could transform CX 3 R-type OBPs to chloride. Compared to Co3+, SO 4 ·- played a more important role in the degradation of CX 3 R-type OBPs and the conversion from chloride to final by-product chlorate. The adverse effects that results from Co3+ need more attention in SO 4 ·--based AOPs application. ga1 • The formation and degradation pathways of CX 3 R-type OBP were proposed. • Co2+/PMS promotes CX 3 R-type OBP formation compared to PMS. • Co3+ outweighs SO 4 ·- in CX 3 R-type OBP formation. • SO 4 ·- plays a significant role in CX 3 R-type OBP degradation. • Co3+ makes great contributions to toxicity of treated water. [ABSTRACT FROM AUTHOR]