Construction of Ultraviolet Treatment Will Enhance Water Quality

Construction of the Ultraviolet light disinfection treatment technology (UV) is now underway at the Water Resource Recovery Facility (WRRF). Similar to the City’s investment in Membrane Bioreactor Technology (MBR), the addition of UV is the result of a rigorous technical analysis. UV will replace the current tertiary treatment process that uses chlorine to disinfect the wastewater before releasing it to San Luis Obispo Creek or distributing it throughout the City as recycled water. The construction is part of the comprehensive SLO Water Plus upgrade that will continue through 2023.

MBR and UV disinfection are commonly used in combination with one another in advanced water treatment systems. UV is a disinfection method that destroys disease-causing organisms in wastewater. The UV light destroys the genetic material of microorganisms, which prevents them from reproducing. UV is the last step in the WRRF treatment train before the water is conveyed by gravity to the recycled water storage tank or cooled for release to the creek.

In the SLO Water Plus design stage, the City explored several treatment technologies that would help the WRRF fulfill evolving water quality requirements while setting the stage for potable reuse in the future. The analysis included years of piloting various treatment technologies, as well as tours of facilities equipped with similar treatment processes. Ultimately, UV was identified as the preferred technology, providing the City with several key benefits, as described below.

Minimized System Footprint

An overarching objective of the SLO Water Plus upgrade design was to optimize the WRRF’s existing footprint. Smaller footprints offer several opportunities, from reduced operational costs to space for future expansion as the City’s needs change. Because the MBR process produces such clean water, UV demands a relatively small footprint as compared to other disinfection technologies. Further, the technology is modular, allowing for incremental expansion as capacity demands change. This adaptability aligns well to the City’s future water reuse goals, as described below.

Reduced Treatment Biproducts and Improved Water Quality

Unlike conventional treatment methods — such as tertiary treatment that uses chlorine to disinfect — UV disinfection does not use chemicals in the treatment process. As a result, disinfection byproducts are minimized, and dissolved solids and salts are significantly reduced in the treatment process.

The inclusion of UV will allow the City to exceed regulatory water quality discharge requirements, supporting the health of San Luis Obispo Creek and area wildlife. Because UV does not rely on chemicals or biological conditions, it is a comparatively stable treatment process. That means a more consistent, high-quality effluent will be produced.

Enhanced Operations and Safety

The handling of treatment chemicals (such as chlorine) presents some common operational and safety challenges for facilities like the WRRF, particularly with traditional treatment methods. The adoption of UV helps minimize these challenges because it doesn’t require these chemicals. The UV system will be automated to maintain operation in the case of an emergency event.

Adaptability for Potable Water Reuse

One of the most notable benefits of choosing UV technology is that it advances the City’s goal to expand its recycled water program, ultimately moving towards potable water reuse to supplement the community’s water supply. In combination, the City’s investments in MBR and UV treatment technologies will significantly reduce the scope of future potable reuse expansion.

Construction of the UV system is currently underway and is expected to be completed by May of 2022.