Chemical aspects and by-products of electrolyser J. Cho*, H. Choi*, I.S. Kim* and G. Amy** *Department of Environmental Science and Engineering, Kwangju Institute of Science and Technology, Oryong-dong 1, Puk-gu, Kwangju 500-712, Korea **Department of Environmental Engineering, University of Colorado at Boulder, Boulder, CO 80309, USA Abstract The electrolyser is a disinfection device consisting of a series of porous graphite plates through which water flows while low voltage and current are applied. This electrolyser had been demonstrated successfully for efficient microbial (coliform bacteria, bacteriophage, Giardia, and Cryptosporidium) inactivation before this study. In this study, chemical aspects were evaluated in terms of the formation of disinfectants and/or oxidants as well as disinfection by-products (DBPs) during the disinfection by the electrolyser. Experiments were performed under constant electrolyser conditions but variable water quality conditions (electrolyte type and concentration, dissolved organic carbon, bromide ion (Br – ) and, to an extent, pH). It was shown that disinfectants and (chlorinated or ozonated) DBPs could be measured successfully for the effluent samples from the electrolyser. Chlorination by-products did not pose any problem in compliance to drinking water regulations, while bromate and chlorate (ozonation by-products) were shown to be formed at levels near their respective regulation levels, but only under extreme water quality conditions. Keywords Electrolyzer; disinfectants; disinfection by-products; chlorination; ozonation Background Drinking water regulation in the USA has become increasingly stringent recently and this trend will likely continue into the future. Recent regulations have been focused on disinfec- tion by-products (DBPs). A nationwide study is re-examining the occurrence of DBPs indi- rectly through total organic carbon (TOC) measurements in finished waters under the Information Collection Rule (ICR). Most utilities will attempt to reduce DBPs by reducing TOC prior to disinfection. Other strategies to minimize DBP formation include reducing disinfectant dose and using alternative oxidants such as chlorine dioxide and ozone. Many of the DBPs are suspected carcinogens including bromate, trihalomethanes (THMs; sum of four species (chloroform, bromoform, bromodichloromethane and dibromochloro- methane)) and haloacetic acids (HAAs). The Disinfectant–Disinfection By-Product (D/DBP) Rule proposes to set maximum contaminant levels (MCLs) for three disinfec- tants, two inorganic DBPs and ten organic DBPs. Table 1 summarizes the DBPs which will be regulated by the D-DBP Rule (which may have implications for the electrolyser); the existing and proposed MCLs are of most relevance. Chlorine has been the most common disinfectant used in the USA. Chlorine can react with organic compounds forming tri- halomethanes and HAAs among other DBPs. Chlorate and chlorite are DBPs of chlorine dioxide (ClO 2 ). Recent regulations have been proposed for controlling the amount of disinfectant resid- ual. Table 2 shows the proposed regulations for chlorine, chloramines and chlorine dioxide as part of the D/DBP Rule. Ozone, hydrogen peroxide and other alternative disinfectants are not currently regulated. Bromate is a DBP which has recently been identified as a carcinogen. Bromate forma- tion occurs during a series of reactions between ozone and bromide ion (Br – ). Trace amounts of bromide ion can be found in most natural waters. The average bromide ion concentration in the USA is reported to be approximately 100 μg/l. Water Science and Technology: Water Supply Vol 1 No 4 pp 159–167 © IWA Publishing 2001 159 Downloaded from https://iwaponline.com/ws/article-pdf/1/4/159/108980/159.pdf by guest on 31 May 2020