Weak magnetic field accelerates chloroacetamide removal by zero-valent iron in drinking water

摘要

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.