UV Reactor Validation: Implications of Non-ideal Reactor Behavior

Ultraviolet (UV) disinfection has been recognized as a viable and often preferred technology for the disinfection of drinking water and wastewater. UV reactor validation has become a key issue. Recently proposed NWRI/AWWARF and EPA guidelines promote the bioassay approach to reactor validation. The bioassay approach is recommended over analytical and numerical models. Analytical models, which provide an average dose estimate, have been shown to be inadequate for a number of reasons. Primarily, UV reactor performance is significantly impacted by the reactor specific hydraulics, which these models do not account for; and lamp output, a key input to these models, is extremely difficult to measure correctly. It is especially difficult to account for changes in low pressure and amalgam lamp output for varying water temperatures. Experimental evidence shows poor correlation between average dose calculations and measured bioassay dose under varying flow and water quality conditions. Numerical models utilize Computational Fluid Dynamics (CFD) and UV light intensity models to predict reactor performance. While these models can be accurate when used by skilled and experienced professionals, they require significant validation and/or calibration against bioassay data. Bioassay validation is the only true test of reactor performance.