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.
The Laguna County Sanitation District (LCSD) Water Reclamation Plant has a design capacity of 3.7 mgd which produces filtered-disinfected water to meet California Title 22 unrestricted re-use criteria summarized in Table 1. There are two treatment streams in the plant. One is the 3.2-mgd wastewater treated effluent, which undergoes primary clarification, biofiltration, secondary clarification, and microfiltration. The second flow (0.5 mgd) contains high total dissolved solids (TDS) that is generated as a result of home water softener use within LCSD. The high-TDS flow is split from the influent during hours of high TDS concentration and is treated in a separate treatment train consisting of screening, membrane bioreactors (MBR), followed by reverse osmosis (RO) filtration. The effluent from each process train (low and high TDS flows) is combined and conveyed to the UV disinfection system as shown in Figure 1.
Disinfection of the tertiary treated wastewater is accomplished by the in-line Aquionics Model 7500 medium-pressure UV system that was installed at the LCSD WWTP with a capacity to treat 3.7-mgd of tertiary effluent. A total of 4 UV banks were installed. However, only three will be in operation at one time, with the fourth bank acting as standby.
The validation testing on the full-scale, 3.7-mgd Aquionics UV Disinfection System was carried out to satisfy the NWRI/AWWARF guidelines and to confirm that the UV system disinfects the water and aids in producing recycled water suitable for irrigation and meets requirements for unrestricted public access pursuant to Section 60304(a) of the California Code of Regulations, Title 22, Water Recycling Criteria.