The West Point Treatment Plant processes about 100 million gallons of wastewater each day, and up to 440 million gallons during heavy rains. While the plant’s operators are working hard to keep the treatment process flowing smoothly, a momentary lapse of power supply quality can bring vital equipment operations to a hard stop.
That’s why in February 2021, King County Executive Dow Constantine signed an emergency declaration and the King County Council authorized up to $65 million to provide West Point with more reliable power. The team behind the West Point Treatment Plant Power Quality Improvement Project has been working diligently since then to identify an innovative, sustainable supplemental power solution.
Short “voltage sags” make a big impact
Most power disruptions are in the form of voltage sags from the city power supply. To put it simply, a voltage sag is similar to the lights flickering in our homes.
Voltage sags may last only 11 or 12 seconds, but an interruption in power quality will cause wastewater pumps to turn off to protect themselves from long-term damage and requires plant operators to restart the equipment. During that time, the mixture of stormwater and wastewater flowing into the plant will be re-directed through an emergency bypass pipe and discharged directly into Puget Sound. The plant operates this way by design to protect the plant from flooding. The power quality improvement project underway is designed to supplement the power flowing to equipment to keep the voltage consistent even in the case of a voltage sag.
Innovative solution emerges: Online, uninterruptible power system
As part of this project, the technical team examined five feasible technologies to address voltage sags and support short-term outages. They also assessed several approaches which involved creating alternate power sources independent of Seattle City Light or setting up batteries that could kick in when voltage sags occur.
The battery option, or uninterruptible power supply (UPS), stood out as the clear solution: It addresses voltage sags and supports short-term outages. The team also considered multiple variables, including each solution’s noise level, cost, space needed, time needed, and response time (the time between when the technology senses the sag to the time voltage is fully restored).
The UPS will work like a laptop computer with its charger plugged into the wall. The charger is continuously supplying power to the laptop’s battery, which is in turn supplying power to the laptop. When the power goes out (or the charger is unplugged), the laptop works without interruption because it’s getting power from its battery. At the West Point Treatment Plant, engineers are designing a system based on the same principles. The region’s power system will keep the batteries charged and during momentary voltage sags they’ll keep the treatment plant’s systems going until full power is restored.
The project team had to identify a location not only for the battery system, but also necessary support features, such as fire suppression, maintenance access, heating, ventilation, and air conditioning. West Point has a smaller footprint than similarly scaled plants and is limited in its opportunities to expand because of King County’s commitments to the surrounding community to contain the plant’s growth. After exploring whether to place the new equipment in multiple locations on-site, they decided to use a single building to save space.
Compared with the other potential solutions considered, UPS has a short timeline and could be installed by 2024. The project team is working nimbly and with great urgency to put this solution to work, while ensuring safety and sustainability.
About West Point Treatment Plant
West Point treats wastewater from homes and businesses in Seattle, Shoreline, north Lake Washington, north King County, and parts of south Snohomish County. Seattle’s combined stormwater/wastewater sewer system also flows into West Point.
Over the next 10 years, King County will invest more than $660 million at West Point Treatment Plant to protect worker and public safety, the environment, and ratepayer investments through improving system reliability and increasing efficiency.
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