Impact of UV disinfection on microbially available phosphorus, organic carbon, and microbial growth in drinking water.

UV irradiation at a wavelength of 253.7 nm (UV(254)) is commonly used for drinking water disinfection. UV radiation is known to convert organically combined phosphorus to orthophosphate and to degrade natural organic matter. We studied if UV disinfection increases the amount of microbially available forms of organic carbon and phosphorus in drinking waters with different characteristics, and if these changes in water chemical quality could enhance the microbial growth in drinking water. The UV(254) dose (15-50 mWs/cm(2)) used in waterworks reduced the concentration of assimilable organic carbon and the sum of the molecular size fractions. The release of microbially available phosphorus needed higher doses (204 mWs/cm(2)) of UV(254) radiation. Of bacteria in drinking water, 90% were inactivated with UV(254)-irradiation doses below 50 mWs/cm(2). A high dose (501 mWs/cm(2)) of UV(254) radiation inhibited the microbial growth in water.