Wastewater Treatment Plant Upgrade

The Lake Stevens Sewer District replaced its existing 2.4 mgd wastewater treatment facility (WWTF) with a new membrane bioreactor (MBR) WWTF to remove the existing facility from the floodplain and to meet population growth demands over the next 20 years.

The new MBR plant, called the Sunnyside WWTF due to its location along Sunnyside Boulevard in the Lake Stevens area, was constructed on a new 10-acre upland site. The design has a Phase I capacity of 5.0 mgd with a plan for phased expansion to 10.4 mgd. The project was designed for construction in phases to allow for the optimum match between the customer base and capital costs.

The project also included construction of a new pump station, 12-inch-diameter force main, and 24- and 36-inch-diameter gravity interceptors to convey flows to the new treatment facility.

The Phase I Sunnyside WWTF includes a headworks building with screening and flow measurement, two primary clarifiers, primary effluent screening, activated sludge basins to provide nitrification and denitrification, membrane bioreactors for filtration of mixed liquor solids, ultraviolet disinfection system sized to meet Class A reclaimed water standards, anaerobic digesters, centrifuge dewatering of biosolids, and odor control facilities. The project also included a new administration and laboratory building, membrane equipment building, and vehicle maintenance building.