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City of Oak Harbor Meets Tomorrow’s Wastewater Requirements Today

UV disinfection systems help the city reduce costs and stay compliant

The city of Oak Harbor, a population of 23,000+, is situated on the northern portion of Whidbey Island, approximately two-hours drive north of Seattle, and is accessible by both land and ferry. Located in the rain shadow of the Olympic Mountains, Whidbey Island experiences half the annual rainfall of Seattle.​


The city of Oak Harbor's two aging wastewater treatment facilities were operating near full capacity, making it impossible to keep up with future water quality standards. Therefore, a solution was needed that would deliver long-term reliable service, support the city’s future growth initiatives, help enhance public spaces, while also providing an opportunity to reclaim valuable resources from their wastewater. Ultimately, giving their wastewater multiple uses.​

Upgrading both treatment facilities was considered, although the cost of doing so, while being restricted in using their current infrastructure, did not meet future growth requirements. As a result, a plan to build a new wastewater treatment facility was chosen. The new facility would provide the city with the opportunity to create a custom solution that would meet not only their quality and quantity of water but reduce the city’s overall operating costs.


For this project, Carollo Engineers worked closely with the City of Oak Harbor to replace the two treatment facilities, located in an environmentally sensitive area, with a single MBR facility, handling a peak flow rate of 4.5 MGD. The city chose to add validated UV systems to provide an additional barrier for the MBR treated effluent water, improving water quality and ensuring that the effluent coliform levels meet the required discharge permit level. UV is a proven and safe barrier that can inactivate bacteria, viruses, and other microorganisms.

Two UVLW-20800-20 ETS-UV™ units were selected for this project. The UVLW model​ is a multilamp, low-pressure, high output amalgam treatment solution. The lamps are positioned parallel to flow in a non-uniform configuration and the chamber has been designed with a unique hatch for easy access, making it ideal when performing routine maintenance. This generator is known for its low head loss, high output lamp and advanced design features. The unit’s flexible design, energy savings and easy to operate full plant integration PLC system makes it the best solution for the City of Oak Harbor’s Clean Water Facility Project.

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