Free radical destruction of haloacetamides in aqueous solution Jun Xu, William J. Cooper and Weihua Song ABSTRACT Haloacetamides are disinfection byproducts (DBPs) formed through chlorine/chloramine disinfection processes in drinking waters and have been recently highlighted in the US national Reconnaissance Survey. These species occur at low concentrations, but have been determined to have high cytotoxicity and mutagenicity and therefore may represent a human health hazard. Advanced oxidation/reduction processes (AO/RPs) which utilize free radical reactions are new alternatives to degrade these species. This study reports the absolute bimolecular reaction rate constants for 12 haloacetamides with •OH radical and hydrated electron. The •OH radical reaction rates varied from 5.18 × 10 7 to 1.14 × 10 10 M À1 s À1 , and hydrated electron reaction rates varied from 5.00 × 10 9 to 3.64 × 10 10 M À1 s À1 . Results obtained using an ion chromatograph indicated that ARPs are suitable for dehaloliazation of haloacetamides. These data are required for both evaluating AO/RPs for the destruction of these compounds and for studies of their fate and transport in surface waters where radical chemistry may be important in assessing their lifetime. Jun Xu Weihua Song (corresponding author) Department of Environmental Science and Engineering, Fudan University, Shanghai, 200433, China E-mail: wsong@fudan.edu.cn William J. Cooper Urban Water Research Center, Department of Civil and Environmental Engineering, University of California, Irvine, California, 92697-2175, USA Key words | advanced oxidation/reduction processes, haloacetamides, hydroxyl radical, solvated electron INTRODUCTION Disinfection byproducts (DBPs) formed in water treatment processes during disinfection react with bromide and iodide and/or natural organic matter present in the raw water. Initial attention has been given to the carbonaceous disinfection byproducts (C-DBPs), particularly trihalo- methanes (THMs) and haloacetic acids (HAAs) since the 1970s (Bellar et al. ; Rook ). Late in that decade the United States Environmental Protection Agency (USEPA) started to regulate THMs at 100 μgL À1 (ppb) due to a cancer risk. Recently emerging nitrogenous disinfection byproducts (N-DBPs) have raised public concerns due to several reasons. First, alternative disinfectants, such as chloramines, are increasingly being used by water utilities, often to reduce the formation of THMs and HAAs. However, use of chlora- mines can increase the formation of certain N-DBPs (Seidel et al. ). Secondly, water scarcity is likely to force utilities to consider utilization of source water impaired by municipal wastewater effluents or algal blooms, which are enriched in dissolved organic nitrogen compounds. These can be considered as organic precursors for N-DBPs (Mitch & Sedlak ; Zhang et al. ). Thirdly, while N- DBPs typically occur at lower concentration than regulated C-DBPs, many N-DBPs are of greater health risk (Bond et al. ). Comparison of data from in vitro mammalian cell tests demonstrated the N-DBPs are all far more cytotoxic and genotoxic than the non-nitrogenous THMs and HAAs (Richardson et al. ; Bond et al. ). Therefore, N- DBPs were cited as research priorities by the USEPA (Bond et al. ). The removal of trace levels of N-DBPs from waters remains a major challenge in water treatment (Chu et al. ). One potential approach is the use of advanced oxi- dation or reduction processes (AO/RPs) that generate radicals that directly destruct contaminants. AO/RPs usually involve the formation of the hydroxyl radical 212 © IWA Publishing 2014 Water Science & Technology: Water Supply | 14.2 | 2014 doi: 10.2166/ws.2013.184 Downloaded from https://iwaponline.com/ws/article-pdf/14/2/212/415481/212.pdf by guest on 09 June 2020