Spectroscopic Characterization and the pH Dependence of Bactericidal Activity of the Aqueous Chlorine Solution

tion dates back to the mid 18th century. Chlorinated lime and chlorine gas have since been used for conventional disinfection of municipal drinking water for the prevention of epidemic diseases such as cholera and typhoid.1–3 Generation of chlorine by electrolysis of aqueous NaCl solution had come into use by the end of the 19th century. The advantage of the electrolysis is that transportation and storage of potentially hazardous chemicals are not needed. In recent years, compact equipments designed for the electrolysis of aqueous NaCl solution have become available commercially. The acidic solution generated in the anode chamber of the equipment, which will hereafter be designated as acidic electrolyzed water (EW), has been widely used in medical applications such as for the prevention of the infection of methicillin resistant Staphylococcus aureus (MRSA). Acidic EW has also been used for various agricultural purposes, such as sterilization of vegetables. Significant attention is now being paid to acidic EW for disinfection of drinking water in military or refugee camps in remote areas. The microbicidal activity of the aqueous solution of chlorine has not been fully understood in a quantitative way. The aim of the present study is to establish the chemical basis of the microbicidal activity of the aqueous solution of chlorine. An attempt was made successfully to establish the chemical basis of the microbicidal activity of the chlorine solution. Raman and ultraviolet spectral measurements were used along with conventional chemical analyses to follow the pH dependence of the chemical equilibrium of the solution. A semi-quantitative bioassay system using suspension culture of bacteria was designed for statistical treatment of the inhibitory effects to bacterial growth. The discussion of the microbicidal activity of acidic EW will be based on the results obtained using E. coli and B. subtilis.