Inactivation of Microorganisms in Water by Ozone and Chlorine

For preventing the spread of water-born diseases, disinfection has already become an essential part in drinking water treatment plant. Chlorine disinfection is the most popular disinfection method because of its cheap, simple, and efficient properties. On the other hand, Ozone is a very strong and fast-reacting oxidant without byproduct, as considered as a potential disinfection method. Our current study was to evaluate the inactivation efficiency of ozone and chlorine on microorganisms in water. By culture and non-culture（flow cytometry with fluorochrome, FCM/FL）methods, the influences of microorganism species, microorganism concentrations, ozone and chlorine concentrations, and exposure time on inactivation efficiencies of ozone and chlorine were evaluated.
By culture method, it was found that the resistant abilities of tested microorganisms to both ozone and chlorine were as follows：endospore of Bacillus subtilis＞Penicillium citrinum spores＞Candida famata＞Escherichia coli. For ozone disinfection, the importance of the evaluated parameters were ozone concentration > species > exposure time > microbial concentrations. For chlorine disinfection, the importance was species, chlorine concentration, exposure time and microbial concentrations. Under the USEPA standards, the suggested doses could not provide efficient disinfection for spore type microorganisms.
It is known that microorganism could be still viable when they lose their ability to grow on culture medium. In comparison with non-culture method, it was clearly demonstrated that inactivation efficiencies of ozone and chlorine on microorganisms were overestimated by culture method.