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Transportation & Public Works - News

Posted on: June 30, 2022

Laguna Treatment Plant Ultraviolet Disinfection Improvements Project


A new $68 million ultraviolet (UV) light disinfection system will be installed at Santa Rosa Water’s Laguna Treatment Plant located on Llano Road in Santa Rosa. The new UV system will replace the existing system originally installed in 1997. UV disinfection is the final step in producing Title 22 recycled water at the plant that by exposing the tertiary treated water to multiple banks of UV lights. At full capacity, the new system will be one of the largest UV disinfection systems in the United States. 

The existing UV system is being replaced because it has exceeded its life expectancy, which has led to a reduced treatment capacity that no longer meets the operational needs of the plant. Complete replacement is necessary due to the age of the system and the difficulty of procuring replacement parts, many of which have had their manufacturing discontinued. Construction of the new system is expected to be complete in early 2025. The existing system will remain operational until construction is complete.

The new system is critical to meet the needs of the approximately 236,100 residents and businesses the plant serves in Santa Rosa, Rohnert Park, Cotati, Sebastopol, and unincorporated potions of Sonoma County.  The new UV system will have the capacity to treat 70 million gallons of water per day (MGD), enough water to fill roughly 106 Olympic sized swimming pools.

The UV disinfection process is superior to other methods of disinfection, such as chlorine disinfection, UV does not require the storage, transport, or potential exposure to harmful chemicals, nor does it create harmful disinfection by-products that remain in the recycled water after the disinfection process is complete. 

In addition to the new UV disinfection system, and Effluent Diversion Pumping Station will be constructed with a pumping capacity of 35 MGD. This pump station will allow staff to divert water that does not meet permit limitations to the beginning of the plant for retreatment, thereby alleviating the risk of contaminating the City’s Recycled Water storage ponds.

How the UV Disinfection System Works

The UV disinfection system at the plant is the final step in recycling water for beneficial reuse. The upstream treatment processes remove inorganic and organic material by screening, clarifying, biological oxidation, and filtration systems. Although the upstream processes are effective at greatly reducing contaminants within the water, these processes have limited ability to inactivate pathogenic organisms.  Treated effluent will flow through multiple banks of UV lamps where pathogenic organisms within the effluent are exposed to UV light. The UV light damages the DNA of the organisms to the point of non-repair, effectively killing them and thereby disinfecting the recycled water. Disinfection is a necessary final component of the treatment process to produce recycled water that is safe for reuse in urban and agricultural irrigation, as well as recharging the steamfields for Calpine’s geothermal power plant.

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