Evaluation of UV System Performance and Challenges of UV Validation Testing at the Laguna County Sanitation District

The Laguna County Sanitation District (LCSD) Water Reclamation Plant, with a design capacity of 3.7 mgd, produces tertiary water that was designed to meet California Title 22 unrestricted re-use criteria. The disinfection in LCSD is provided by an in-line Aquionics Model 7500 medium pressure UV system containing four UV banks. California Department of Health and Services (CDHS) require that all UV systems be validated according to the National Water Research Institute and American Water Works Association Research Foundation UV Disinfection Guidelines (NWRI/AWWARF 2003), before distributing reclaimed water to the end users. A set of laboratory and field testing has been performed to demonstrate the efficacy of the UV equipment. The early test results were, however, not in total compliance with DHS requirements. In two of the five collimated beam tests, the majority of the data (more than 20 percent) did not fall within the “check curves” established by the NWRI/AWWARF guidelines. CDHS directed LCSD to perform two additional collimated beam and full-scale tests to fully satisfy NWRI/AWWARF requirements. With the few changes and adjustments in testing procedure, the UV disinfection system satisfied the requirements for DHS approval. This paper discusses key challenges and presents lesson learned during this validation testing.