Chloroacetamides (CAMs) as a class of highly toxic nitrogenous disinfection by-products (N-DBPs) have been widely detected in drinking water. It has been reported that weak magnetic field (WMF) could improve the removal ability of zero-valent iron (ZVI) to some pollutants, but CAMs removal by ZVI coupled with WMF has never been studied. This study through oxic batch experiments was executed to investigate the effect of WMF on trichloroacetamide (TCAM) removal by different doses of ZVI under different pH levels and to explore how WMF works on TCAM removal for the first time. The results showed that the WMF improved TCAM removal by ZVI and the strengthening effect of WMF was more significant at lower ZVI dose or higher pH conditions. The formation of trichloroacetic acid indicated the occurrence of TCAM hydrolysis. Chlorine mass balance was observed in TCAM and its potential products, dichloroacetamide, monochloroacetamide, and chloride, indicating these were all the products and a dechlorination process occurred when TCAM contacted with ZVI. By calculating the yields of hydrolytic products and dechlorinated products, it was determined that dechlorination of TCAM was the dominant reaction for TCAM removal by ZVI with and without WMF, while hydrolysis reaction played a minor role. Mechanism analysis showed that the WMF promoted TCAM hydrolysis through impacting the electromigration within the oxide scale and improving the migration of paramagnetic oxygen to the surface of magnetized ZVI. Taken together, ZVI coupled with WMF is a potential effective technology for TCAM removal in effluent of chlorination.

Atmospheric particulate matter (PM) can be scavenged by rainfall and contribute dissolved organic matter (DOM) to rainwater. Rainwater may serve as a part or the whole of drinking water sources, leading to the introduction of PM-derived DOM into drinking water. However, little information is available on the role of PM-derived DOM as a remarkable precursor of CX₃R-type disinfection by-products (DBPs) in rainwater. In this study, samples were collected from ten occurrences of rainfall in Shanghai and batch experiments were executed to explore the contribution of PM-derived DOM to CX₃R-type DBP formation in rainwater and to further understand some of unknowns regarding its characteristics. Results revealed that a part of PM was scavenged by rainfall and the scavenge performance was better for smaller PM. The formation potentials (FPs) of individual CX₃R-type DBP were similar among size-isolated PM. TCM was predominant (around 0.5–4.5 μg-C/mg-C) and TCAA was the secondary (around 0.6–3.2 μg-C/mg-C) among all detectable CX₃R-type DBPs. Based on the PM removal data and DBP FP results, the contribution of PM-derived DOM to CX₃R-type DBP formation in rainwater was modeled. Furthermore, aromatic proteins and soluble microbial product-like compounds were found to be significant compositions, which were reported to be DBP precursors. And low molecular weight (< 10 kDa) DOM derived from total PM and rainwater exhibited higher CX₃R-type DBP FPs. DOM fractions with higher SUVA₂₅₄ and SUVA₂₈₅ values gave relatively higher yields of CX₃R-type DBPs, indicating that aromatic compounds played an important role in DBP formation.

The effective removal of haloacetamides (HAMs) as a group of emerging disinfection by-products is essential for drinking water safety. This study investigated the degradation of 10 HAMs, including chlorinated, brominated, and iodinated analogues, by sodium sulfite (S(IV)) and the mechanism behind it. The results indicated that all HAMs, excluding chlorinated HAMs, decomposed immediately when exposed to S(IV). The reductive dehalogenation kinetics were well described by a second-order kinetics model, first-order in S(IV) and first-order in HAMs. The degradation rates of HAMs increased with the increase of pH and they were positively correlated with sulfite concentration, indicating that the reaction of S(IV) with HAMs mainly depends on sulfite. The rank order and relative activity of the reaction of sulfite with HAMs depends on bimolecular nucleophilic substitution reaction reactivity. The order of the reductive dehalogenation rates of HAMs versus the substitution of halogen atoms was iodo- > bromo- >> chloro-. During reductive dehalogenation of HAMs by sulfite, the α-carbon bound to the amide group underwent nucleophilic attack at 180° to the leaving group (halide). As a consequence, the halide was pushed off the opposite side, generating a transition state pentacoordinate. The breaking of the C-X bond and the formation of the new C-S bond occurred simultaneously and HAM sulfonate formed as the immediate product. Results suggest that S(IV) can be used to degrade brominated and iodinated HAMs in drinking water and therefore should not be added as a quenching agent before HAM analysis to accurately determine the HAM concentrations produced during water disinfection.