Inactivation of enteric microbes in water by electro-chemical oxidant from brine (NaCl) and free chlorine L.V. Venczel, C.A. Likirdopulos, C.E. Robinson and M.D. Sobsey Dept of Environmental Sciences and Engineering, University of North Carolina, CB #7400, McGavran- Greenberg Hall, Chapel Hill, North Carolina 27599-7431, USA (E-mail: Mark_Sobsey@unc.edu) Abstract Oxidant solutions of mostly free chlorine can be electrochemically produced on-site from brine (NaCl) solution and used to disinfect water at the household or community level. In this study electrochemical oxidant (ECO) from brine and free chlorine were evaluated under laboratory conditions for inactivation of test microbes. Purified suspensions of Escherichia coli, the rugose strain of Vibrio cholerae, Clostridium perfringens spores, MS2 coliphage and Cryptosporidium parvum oocysts were treated with 2 mg/L or 5 mg/L solutions of ECO or free chlorine at 5°C and 25°C and pH 6, 8, and 10 (pH 7 and 25°C only for C. parvum oocysts) for contact times <60 min. Under nearly all conditions, inactivation kinetics were more rapid for E. coli, V. cholerae, C. perfringens spores and MS2 coliphage with ECO than with free chlorine. ECO reduced E. coli, V. cholerae and MS2 by >4 log 10 within 30 min and C. perfringens spores by >2 log 10 within 10 min at pH 8 and 25°C. Contrary to previous results, however, C. parvum oocysts were not inactivated by ECO, and the reasons for this difference are uncertain. The on-site electrolytic generation of oxidants from brine provided a convenient and inexpensive disinfectant containing free chlorine that was effective against many enteric microbes, for the treatment of household and community drinking-water supplies worldwide. However, the effectiveness of such oxidants for inactivating C. parvum oocysts was variable and sometimes ineffective. Keywords Cryptosporidium; disinfection; electrochemical oxidant; microbes; water Introduction Disinfection is the final, and in some cases the only, barrier against waterborne pathogens. Yet the availability of chemical disinfectants is limited in many parts of the world, due to lack of production facilities, transportation limitations and high cost. It has been known for many decades that chlorine, perhaps mixed with other oxidants, can be generated on-site by the electrolysis of a solution of sodium chloride (brine). Using direct-current electrical energy, such an oxidant disinfectant can be produced on-site at a low cost in remote locations and used to disinfect both community and household water supplies. The elec- trolytic generator uses a cell consisting of titanium electrodes coated with Group VIII metal oxides separated into anodic and cathodic compartments. As “dimensionally stable anodes”, they are highly resistant to corrosion and have a low potential for over-voltage. This design allows for the production of chlorine and perhaps other aqueous oxidants at the positive anode, and reductants at the cathode by the electrolysis of the brine solution. The actual concentration and proportion of chlorine and perhaps other oxidant species is a func- tion of the cell design and anode material, as well as the purity and concentration of salt. Water quality, such as pH, organic matter and temperature, also will influence the presence of different oxidant species. The objectives of this study were to compare the inactivation kinetics of V. cholerae, MS2 coliphage, E. coli, and C. perfringens spores and C. parvum oocysts exposed to an electrolytic oxidant solution or sodium hypochlorite and to deter- mine disinfection efficacy when applied to waters differing in pH, temperature, and humic acid content. Water Science and Technology Vol 50 No 1 pp 141–146 © IWA Publishing 2004 141 Downloaded from http://iwaponline.com/wst/article-pdf/50/1/141/421371/141.pdf by guest on 25 April 2021