Courtesy of Benjamin Benschneider

The $467-million Brightwater Treatment Plant serves as the hub of the $1.8-billion Brightwater Regional Wastewater System, which includes 13 miles of conveyance tunnels, a reclaimed water distribution system, a marine outfall into Puget Sound and an offsite pumping station.

Brightwater provides membrane bioreactor treatment for flows up to 57 million gallons per day, reclaimed water production, full-solids handling and comprehensive odor control. It is the largest membrane bioreactor of its kind in North America, forming the heart of the King County, Wash., system.

Construction documents consisted of 5,000 drawings organized into contract packages. They were developed using 3-D modeling to help county staff and contractors more easily review building equipment and piping layouts.

The design team of CH2M HILL/Brown and Caldwell balanced strict environmental requirements throughout the project. The goal was to return the site to a pre-development stormwater runoff condition and protect a nearby salmon-bearing stream, so surface water was closely monitored during construction. That was a healthy challenge, given the excavation of 1 million cu yd of dirt. The project team created an integrated stormwater management system—incorporating flow interception, settling basins, groundwater under drains, detention basins and treatment wetscapes—to protect the site.

The plant's processing capabilities, especially during peak flows, include a split-flow liquids treatment that precedes the membrane bioreactor. The process treats base flows up to 57 mgd through the membrane bioreactor, and direct flows above 57 mgd and up to 130 mgd, through chemically enhanced primary clarification.

This allows the use of more cost-effective membrane technology to treat base flows and achieve environmental benefits while maintaining the capacity to treat extreme wet-weather flows. The system produces a higher effluent quality and reduces annual mass discharge of biochemical oxygen and total suspended solids into Puget Sound.

Brightwater Treatment Plant, Woodinville, Wash.

Key Players

General Contractor: Kiewit Infrastructure; Hoffman Construction Co., Seattle

Owner: King County Dept. of Natural Resources and Parks, Wastewater Treatment Division, Woodinville, Wash.

Design Team: CH2M HILL/Brown and Caldwell, Bellevue, Wash.

Submitted by Brown and Caldwell

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