AWWA WQTC58846

AWWA WQTC58846 Comparison of Disinfection Efficiency of Electrochemically or Mechanically Mixed Oxidants with Free Available Chlorine
Conference Proceeding by American Water Works Association, 11/02/2003

Son, Hyunju; Cho, Min; Kim, Jaeeun; Chung, Hyenmi; Sohn, Jinsik; Yoon, Jeyong

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In a small water treatment system, electrochemically produced mixed oxidants by electrolysis ofbrine have shown promise as an alternative disinfectant to free available chlorine (FAC). However,the efficacy and mechanisms of electrochemically mixed oxidants as a disinfectant formicroorganisms such as E. coli and Bacillus subtilis spores have not been reported widely, and thosethat have been reported are controversial in some aspects, particularly in comparison with FAC.Hence, this study was performed to evaluate the efficacy of electrochemically mixed oxidant solutionas a disinfectant in comparison with that of FAC solution on the basis of an equal weight of the totaloxidants per unit volume. In addition, the chemical characteristics of the electrochemically mixedoxidants was examined by evaluating the disinfection efficiency of the mechanically mixed oxidants,which were made by adding small amounts of subsidiary oxidants such as Osub3/sub, ClOsub2/sub and Hsub2/subOsub2/sub toFAC.The major conclusions are as follows: firstly, electrochemically mixed oxidants are approximately20-50% more efficient in inactivating E. coli and Bacillus subtilis spores at certain pH conditions (pH8.2) than FAC. These observations can be explained by the characteristics of the oxidants, such asHOCl, Osub3/sub, ClOsub2/sub, Hsub2/subOsub2/sub, which would be generated by the cathode reduction of oxygen and the anodeoxidation of chloride ion in the electrolytic cell of brine. However, the exact composition of theliquors produced from the electrochemical processes is not well understood because of the lack ofselective analytical methods for detecting the specific oxidants. Secondly, the enhanced disinfectionefficacy of mechanically mixed oxidants was observed in comparison with FAC as they were made byadding a small amount of Osub3/sub or ClOsub2/sub to FAC. These improved results were explained by the effect ofchlorine dioxide and chlorite which can possibly be generated as a result of reaction with an excess ofchlorine and a small amount of ozone generated in electrolytic cell. Includes 30 references, tables, figures.