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The LT2ESWTR, expected in 2002, will require public water utilities to achieve varying degrees of Cryptosporidium removal and inactivation depending on their source water quality and their water treatment process train. Ultraviolet (UV) disinfection is very effective against Cryptosporidium, produces negligible disinfection byproducts, and is the lowest cost technology available for achieving Cryptosporidium credits. In this study, the long-term performance of four UV disinfection systems treating finished water was evaluated at three surface water treatment plants over a one-year period. Two of the systems used low-pressure, high-output mercury arc lamps, one used conventional low-pressure lamps, and the last used medium-pressure lamps. All systems were designed to deliver a UV dose of 40 mJ/cm 2 . Water quality evaluations demonstrated that UV transmittance and factors deemed to influence fouling depend on the water source and water treatment used. Dose delivery was assessed using MS2 bioassay. Neither lamp fouling nor seasonal changes in water temperature had a notable impact on dose delivery by the UV reactors. The dependence of UV dose on UV transmittance was dependent on the reactor design. While lamp aging was observed, three of the reactors were able to maintain doses above 40 mJ/cm 2 and one was able to maintain a dose above 30 mJ/cm 2 for several thousands of hours. UV dose, however, did not correlate to UV intensity measured using on-line sensors. Overall, UV sensor readings were difficult to interpret. Unexplainable trending of UV sensor readings were observed indicative of either sensor degradation or sensor window fouling. The study indicates that with an appropriate lamp replacement period, UV systems may be sized to reliably meet a dose target over time. Further, the study indicates a need for improved UV intensity sensor performance and provides evidence supporting the need to use reference sensors to regularly check measurements made by on-line sensors. Includes 10 references, tables, figures.

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Edition: Vol. - No. Published: 06/01/2001 Number of Pages: 20File Size: 1 file , 420 KB