Desinfeccion

CHAPTER 14

DISINFECTION
Charles N. Haas, Ph.D.
LD Betz Professor of Environmental Engineering Drexel University Philadelphia, Pennsylvania

Disinfection is a process designed for the deliberate reduction of the number of pathogenic microorganisms. While other water treatment processes, such as filtration or coagulation-flocculation-sedimentation, may achieve pathogen reduction, this is notgenerally their primary goal. A variety of chemical or physical agents may be used to carry out disinfection. The concept of disinfection preceded the recognition of bacteria as the causative agent of disease. Averill (1832), for example, proposed chlorine disinfection of human wastes as a prophylaxis against epidemics. Chemical addition during water treatment for disinfection became acceptedonly after litigation on its efficacy (Race, 1918). The prophylactic benefits of water disinfection soon became apparent, particularly with respect to the reduction of typhoid and cholera. While significant progress is being made in controlling the classic waterborne diseases, newly recognized agents have added to the challenge. These include viruses (Melnick et al., 1978; Mosley, 1966), certainbacteria (Campylobacter, Palmer et al., 1983; Yersinia, Brennhovd et al., 1992; Reasoner, 1991; or Mycobacteria, Geldreich, 1971; Iivanainen et al., 1993; Reasoner, 1991; for example), and protozoans (Giardia, Brown et al., 1992; Le Chevallier et al., 1991; Miller et al., 1978; Reasoner, 1991; Renton et al., 1996; Rose et al., 1991; Cryptosporidium, Bridgman et al., 1995; Centers for Disease Controland Prevention, 1995; Gallaher et al., 1989; Goldstein et al., 1996; Hayes et al., 1989; Le Chevallier et al., 1991; Leland et al., 1993; Mac Kenzie et al., 1994; Miller, 1992; Reasoner, 1991; Richardson et al., 1991; Rose et al., 1991; Rush et al., 1990; Smith, 1992). Occasional outbreaks of drinking-water-associated hepatitis have also occurred (Nasser, 1994; Rosenberg et al., 1980). In addition,new viral agents are continually being found to be capable of waterborne transmission. The state of disinfection practice in the United States in the late 1980s was summarized in a survey of the AWWA Disinfection Committee (Haas et al., 1992). Most water utilities continue to rely on chlorine or hypochlorite as their primary disinfection chemicals (Table 14.1), although increasing numbers areusing ammonia (for pre- or postammoniation) or chlorine dioxide or ozone. With the increasing concern for removing and inactivating some of the more resistant pathogens, such as Giardia and Cryptosporidium, while minimizing disinfection by-products, options other than
14.1

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CHAPTER FOURTEEN

TABLE 14.1 Water Utility Disinfection Practices According to 1989 AWWA Survey (N = 267) Noammonia Chlorine alone Gas Hypochlorite Chlorine + ClO2 Ozone Other 67.42% 5.99% 3.37% 0.37% 0.75% Ammonia 19.85% 0.75% 1.50%

Source: Haas et al., 1992.

traditional chlorination are gaining popularity. This chapter will cover the use of chlorine, as well as the major alternative agents, for the purpose of disinfection.

HISTORY OF DISINFECTION
Chlorine Chlorine gas was first prepared byScheele in 1774, but chlorine was not regarded as a chemical element until 1808 (Belohlav and McBee, 1966). Early uses of chlorine included the use of Javelle water (chlorine gas dissolved in an alkaline potassium solution) in France for waste treatment in 1825 (Baker, 1926) and its use as a prophylactic agent during the European cholera epidemic of 1831 (Belohlav and McBee, 1966). Disinfection of waterby chlorine first occurred in 1908 at Bubbly Creek (Chicago) and the Jersey City Water Company. Within two years, chlorine was introduced as a disinfectant at New York City (Croton), Montreal, Milwaukee, Cleveland, Nashville, Baltimore, and Cincinnati, as well as other smaller treatment plants. Frequently, dramatic reductions in typhoid accompanied the introduction of this process (Hooker,...