Impact of Influent Pipe Configuration on UV Reactor Performance: Is the Elbow Truly the Worst Case Hydraulic Condition?

A study has been performed to investigate the impact of upstream piping configurations on the UV disinfection performance. In this study, experimental biodosimetry and numerical simulations were performed on a pilot-scale monochromatic reactor with and without an upstream elbow piping configuration. In addition, simulations using a validated numerical model were performed on a full-scale polychromatic reactor with an upstream straight pipe configuration and two alternate elbow configurations. These three piping configurations were compared with elbow configuration tested during validation of the reactor.The results of the pilot scale tests showed that the placement of an elbow upstream from a UV reactor reduced the log inactivation compared to the same reactor placed downstream of a straight pipe configuration. The numerical model of the two upstream configurations agreed well with the experimental biodosimetry results. The lower log inactivation was caused by a shift in the fluence distribution to a lower fluence region due to the change in hydraulic characteristics and path taken by the microorganisms. Simulations of the full-scale reactor showed that not all influent elbow configurations lead to a reduction in the log inactivation compared to the straight pipe configuration. Consequently, the upstream elbow configuration may not universally represent the worst case hydraulic condition. It may be important to use a validated CFD UV model to simulate the actual site specific hydraulic conditions to determine the UV disinfection performance, since it will be cost prohibitive for validation facilities to exactly mimic all site specific WTP conditions.