AWWA ACE58214

Recently the use of low levels of medium- and low-pressure ultraviolet (UV) light for successful inactivation of Cryptosporidium parvum oocysts has generated tremendous excitement in the water industry. While these findings have been corroborated by numerous independent studies at the bench-scale level, there is little experience in the U.S. with full scale disinfection of finished water, using UV light. Concerns exist with respect to the reliability of UV technology and, in addition to biodosimetry experiments to validate reactor performance for organism inactivation, additional issues include determination of the performance efficiency of the reactors, effects of suspended metals or other water characteristics on lamp sleeve fouling, effectiveness and reliability of lamp cleaning mechanisms, UV measurement sensors' stability, costs associated with retrofitting UV systems into existing water treatment plants, operation and maintenance costs associated with employment of UV disinfection, impact of lamp aging on delivery of target UV doses and impact of UV on disinfection byproduct (DBPs) formation or degeneration. Although it is anticipated that experience with UV disinfection will provide information on some of these issues, certain parameters need to be investigated before water utilities can commit to using UV disinfection as one of the multiple barriers for protection of public health from waterborne disease causing organisms. To address some of these operational issues, American Water, has been actively involved in ascertaining the long-term feasibility of applying UV for treatment of finished water. A 12 inch diameter 4 x 1 KW, closed chamber UV reactor was installed after granular activated carbon filtration at the Pennsylvania American Water treatment plant at Hayes Mine and was operated continuously with a finished water flow rate of 600 gpm. Over a 12 month period, various chemical (THM, HAA, UV254, DOC, TOC, metals, nitrate, nitrites) and physical measurements (lamp voltage, current, sensor measurements) were monitored. Also parameters such as power consumption and other operational issues associated with reactor function (i.e. frequency of power outages, failing components, etc.) were recorded. Reactor validation studies were performed using Bacillus subtilis spores, MS2 bacteriophage and Deinococcus radiodurans as a biodosimetry surrogates and utilized various lamp configurations as well as lamp age. Includes 7 references, figures.