Impact of zero valent iron/persulfate preoxidation on disinfection byproducts through chlorination of alachlor

Abstract

The occurrence of alachlor in natural drinking water sources raises concerns due to adverse health effects. Advanced oxidation with zero valent iron activating persulfate (ZVI/PS) can degrade alachlor with great potential. But no information was reported about effect of ZVI/PS preoxidation on the generation of disinfection byproducts (DBPs) during the downstream chlorination of alachlor. The objective was to investigate DBP formation through chlorination of alachlor preoxidized by ZVI/PS. The results found that ZVI/PS preoxidation enhanced the DBP formation, compared with original system without any treatment. The longer the preoxidation time of ZVI/PS during the experiment, the more DBPs that were generated. During 48.0 h chlorination time, the produced DBPs increased to a stable value. Nitrate posed almost no impact on the DBP formation in the ZVI/PS system, while chloride significantly decreased DBP formation, which was attributed to the reduction of trichloromethane. During the chlorination process, alachlor could be further oxidized by remaining PS and free chlorine collectively. ZVI/PS had little effect on the DBP formation in the real water matrix. However, it could reduce carbonaceous DBP formation and increase nitrogenous DBP formation when the real water matrix contained 100 μg/L alachlor. The acute toxicity of alachlor solution could be reduced by the ZVI/PS system, while after chlorination the acute toxicity was largely increased due to the formation of DBPs. With increase of PS concentration, the DBP formation decreased in the ZVI/PS preoxidation system and increased in the system with PS alone. In conclusion, application of ZVI/PS in actual water containing alachlor declined DBP generation by augmenting PS concentration which should consider standard limited value of sulfate. Further investigation is needed for high bromide water.