Many paired t‐tests showed—at a 95 percent confidence level—no evidence that UV treatment increased BDOC or AOC.The effects of low‐pressure mercury‐vapor ultraviolet (UV) irradiation at 254 nm on the biological regrowth potential of two surface water and two groundwater sources are reported. Because of possible effects of the pending Ground Water Rule, UV disinfection is being studied as an alternative to chlorination. Water samples to be tested were separated into hydrophilic and hydrophobic fractions. The concentration of biodegradable dissolved organic carbon (BDOC) was measured in nonfractionated and fractionated water samples collected before and after UV treatment at a dosage of 130 mW·s/cm2. Two methods were compared in these analyses: a 30‐day BDOC and a 5‐day assimilable organic carbon (AOC) test. Many paired t‐tests showed (at a 95 percent confidence level) no evidence that UV treatment increased BDOC or AOC. Because results differed in water from different sources, utilities considering UV treatment should evaluate the potential for biological regrowth in their own distribution systems.
