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The objective of this research was to assess the potential for naturally occurring particlesin surface water to protect microorganisms from ultraviolet (UV) disinfection. This study consideredindigenous coliform bacteria as surrogates for common pathogens when assessing thevulnerability of UV system performance to particulate matter. The similarity in sizebetween the surrogates and pathogens such as Cryptosporidium oocysts may allow theseresults to be extrapolated in terms of the ability of UV to treat unfiltered surface water.Some UV inactivation studies are performed by seeding cultured microorganisms into awater sample. Since seeded microorganisms will not necessarily associate with particlesin the same way as indigenous microorganisms, such studies provide only a preliminaryassessment of the impact of particulate matter on the UV dose-response of indigenousorganisms in their natural particle-association or clumping state.Due to the low population density of microorganisms in surface water (typically 100CFU / 100 mL) compared with wastewater and the volume of water typically exposed toUV light via a collimated beam apparatus, there are practical limits to UV inactivationstudies using microorganisms indigenous to surface water. However, UV inactivationstudies in wastewater have yielded information on the inactivation kinetics and protectionby particles of coliform bacteria. For example, in wastewater, protection of coliformbacteria is typically linked with particles greater than 10 m in nominal diameter (Quallset al., 1983; Emerick et al., 2000; Jolis et al., 2001). Whether such protection by naturalparticles can be expected in unfiltered surface water is unclear. Includes 16 references, table, figures.

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Edition: Vol. - No. Published: 11/01/2006 Number of Pages: 9File Size: 1 file , 340 KB