AWWA JAW64489

This research was undertaken to identify the residual risk of Cryptosporidium infection, even with ultraviolet (UV) disinfection, and provide rational guidance for the application of mitigation measures to maximize UV disinfection system reliability and maintain compliance with the Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR). The most significant findings include: seemingly minor increases in UV disinfection system downtime significantly reduce the net disinfection credit; the LT2ESWTR allowance for 5% off-specification operation is too lenient for filtered water systems in bins 3 and 4 and unfiltered surface water systems; and, power quality mitigation measures are recommended except in certain bin 2 cases. Recommended steps to increase UV disinfection system reliability include providing redundant equipment, standby power, active series compensators, and an uninterruptible power supply. By following the guidance suggested, utilities can more effectively plan, design, build, operate, and finance UV disinfection systems to ensure maximum reliability and LT2ESWTR compliance. Includes 8 references, tables, figures.