UV disinfection system downtime: Effects and mitigation

Abstract

Off‐specification operation and downtime are important considerations in designing system reliability in ultraviolet (UV) light disinfection systems. This research analyzed the residual risk of Cryptosporidium infection from surface water supplies—after implementation of UV disinfection—and the corresponding UV disinfection system reliability requirements. The author concluded that achieving a maximum downtime of 0.01% (4.4 min/month) is unrealistic, even with standby power and an uninterruptible power supply. Furthermore, starting from 0.01% downtime, seemingly minor increases in downtime significantly reduce the net disinfection credit and result in diminishing returns, regardless of the validated UV disinfection system credit. Providing redundant equipment, standby power, active series compensators, and uninterruptible power supplies can increase UV disinfection system reliability. Judicious application of these and other mitigation measures will help maximize the effectiveness of UV disinfection for regulatory compliance.