An $11 million ultraviolet disinfection system was installed at the Kailua Regional Wastewater Treatment Plant.

The City and County of Honolulu’s Department of Environmental Services said Tuesday the new UV disinfection system is now operating after undergoing a two-month testing and commissioning process without failure.

The treatment process starts by removing large objects (cloth, cans, sticks, rags, rocks, batteries, fish heads, etc.) with big screens and gravity helps settle paper products that shouldn’t be flushed. A mechanical rake or screen collects the waste, and a hopper compacts it to remove excess water, before the waste is taken to the landfill. Next, wastewater is sent to large open-air settling tanks, where the water settles and heavier solids sink to the bottom (primary sludge) and oil and grease (scum) float to the top. Revolving arms in the tanks slowly scrape the solids from the bottom and top, while microorganisms break down the organic waste.

Now, the wastewater is ready for the last step: disinfection. Some treatment plants use chlorine, but the Kailua Regional Wastewater Treatment Plant now has the more advanced UV light system disinfection process. In this system, the water flows through a closed channel, passing under UV lamps that kill or weaken bacteria before being discharged into the ocean. 

“The upgrade strengthens the protection of our shoreline in a way that is clean and efficient for Kailua’s long-term future,” said Dr. Roger Babcock, Director of Environmental Services in a news release. “Residents can rest assured knowing we are using the latest technology to care for our ocean.”

ENV was required by regulators to install the UV disinfection system by Dec. 31, 2025.

The Kailua Regional Wastewater Treatment Plant processes an average of 10.77 million gallons of wastewater per day. Water-quality sample data collected at seven stations in Kailua Bay near the WWTP can be viewed here.