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DISINFECTION
Citation:
Rice*, E W. DISINFECTION. Chapter 5, Clark, R.M. and Boutin, B.K. (ed.), Controlling Disinfection By-Products and Microbial Contaminants in Drinking Water (EPA/600/R-01/110). USEPA, Cincinnati, OH.
Description:
The primary goal of the disinfection process in drinking water treatment is the inactivation of microbial pathogens. These pathogens comprise a diverse group of organisms which serve as the etiological agents of waterborne disease. Included in this group are bacterial, viral and protozoan species. The disinfection of potable water supplies was first initiated in the early part of the 20th Century, and there have been few developments in the area of public health which have been more effective in the control of infectious diseases. While other unit processes, such as coagulation, clarification, and filtration, may dramatically reduce the number of microbial pathogens, disinfection serves as the final and, in some cases, the only barrier to the entry of these organisms into the finished product water. The disinfection process may be affected by a variety of both physical and biological factors. Temperature and pH are two physical factors which are known to play an important role in the inactivation process for most commonly used disinfectants. In actual practice, turbidity and particle protection are two other physical parameters which influence disinfection efficiency, as well as clumping of individual microorganisms. Resistance to chemical disinfection may vary greatly between the various microorganisms of interest and also between different life-stages of individual species, such as is seen with bacterial endospores or encysted forms of protozoa. Studies of microbial inactivation are often difficult to compare with one another owing to differences in methodological approaches. The role of mixing, the type of bioassays employed to determine viability, the volume of sample analyzed, and the reporting of residual versus initial dosing concentrations of the disinfectant are all factors which may vary greatly from one study to antoerh. Often these parameters are not described in sufficient detail in scientific manuscripts of these studies. Further, dat acollected from field or pilot-scale conditions may show marked differences from the results of laboratory experiments conducted under oxidant demand-free conditions. These discrepancies, along with the need to determine the efficacy of disinfection for new and emerging waterborne pathogens, have spearheaded the USEPA research program on microbial inactivation. The following discussion on potable water disinfection, categorized by individual oxidants, summarizes the microbial inactivation research which has been conducted or sponsored by EPA from 1980 to 1999.