KAREN TAKATANI
Persistence of E.coli O157:H7, S. typhimurium, and Coliphage MS2 in a Model Home Water System after Ultraviolet (UV) Disinfection Treatment
Environmental Health, MS
Preceptor: J. Scott Meschke, PhD
Drinking waters comes from two primary sources: groundwater (wells and springs) and surface water (rivers, lakes, and reservoirs.) In the United States, 80% of the community water systems use groundwater as the primary source, but these systems serve only 34% of the population [US EPA, 1997]. This is because most large community water systems (serving 10,000 or more people) rely on surface water while smaller water systems use groundwater.
Most community water systems treat their water to remove pathogens. This process- called disinfection- is usually accomplished by adding a chemical to the water in conventional water treatment processes. Common disinfectants are chlorine, chloramines, chlorine dioxide, and ozone. These chemicals work by causing damage to the cell membrane of bacteria or the lipoprotein envelope of viruses. Chemical disinfectants leave a lasting residual in the treated water which helps to minimize the regrowth of pathogens and other bacteria in water distribution systems. One disadvantage of chemical disinfection is these chemicals may react with natural and man-made organic matter in water to create harmful byproducts such as trihalomethanes. There is some evidence trihalomethanes may cause DNA damage in humans, a precursor to cancer, and epidemiological evidence indicates trihalomethanes cause elevated risks of bladder cancer [Geter et al., 2004; Morris et al., 1992]. An emerging alternative to chemical disinfection is ultraviolet (UV) light disinfection. This is a physical disinfection process which uses UV irradiation, and does not produce any known disinfection by-products. It is very effective on pathogens, particularly on chlorine-resistant microorganisms such as Cryptosporidium parvum and Giardia lamblia [Shin et al., 2001].
