UV Wastewater Disinfection Seminar

Sand Island WWTP: Primary Effluent Ultraviolet (UV) Disinfection

by Dr. Victor Moreland, WRRC Researcher

Abstract
Ultraviolet (UV) light is used for disinfecting many types of water: drinking water, recycled water, secondary effluent; including low quality waters like primary effluent and combined sewer overflows. Low quality waters are often thought to be challenging for UV because they have low UV transmittance (UVT), but with proper reactor design, UV can be successfully applied. UV has now been installed at Honolulu's Sand Island WWTP; an example of successful reactor design and equipment implementation for treating a low quality wastewater. The project's success is due to the methodology used: a) bench-scale reactor performance comparison of chlorine disinfection and UV; b) pilot-scale reactor performance testing; and c) full-scale reactor performance testing to verify pilot-scale results. These three phases are required because there is limited data existing for similar applications.

The bench scale work compared chlorine and UV disinfection for the specific low quality water to be treated, determining the dose requirements for both disinfectants and also quantifying the relevant water quality parameters over time. UV was selected for piloting, using the bench scale work to give the performance targets for disinfection. Piloting was important to test UV reactor designs specifically suited to the low quality wastewater. The challenge for UV disinfection is to get UV energy into the water, especially in low quality wastewaters with low UVT as a higher percentage of light is absorbed. To eliminate dark zones that are less than optimally disinfected, UV reactor designs can employ narrower lamp spacing, but this leads to head loss and associated disinfection problems. Alternatively, hydraulic devices can be used with wider spacing to exchange water between high and low intensity regions and to eliminate head loss problems. These reactor design principles were tested and evaluated at the pilot scale, found to be applicable, and implemented into the full scale UV reactor. Effluent from the full scale reactor was microbiologically tested to verify the pilot results.

The presentation will describe the history of the project in terms of the three phases of testing that ensured the proper UV disinfection limit, the proper UV reactor design and verification of the full scale UV disinfection system performance.

This presentation illustrates what is needed in the partnership between researcher, designer, equipment manufacturer, contractor, and customer. The largest non-technical challenge was overcoming the belief held by all of the people representing various organizations that “You can’t disinfect primary effluent with UV”.

Event Sponsor
Water Resources Research Center, Manoa

More Information
Philip Moravcik, 956-3097, morav@hawaii.edu

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