Wastewater treatment process
The process used at our three regional treatment plants provides secondary treatment (preliminary, primary and secondary treatment, and disinfection).
The graphic below shows the basic steps in the treatment process.
Note: Stormdrains are connected to the sewer system only in the combined sewer system in parts of Seattle.
King County treatment plants
Besides our principal work of treating wastewater, we provide odor control, investigate and assess new wastewater treatment technologies, and strive to be a good neighbor during construction.
To find out more about King County's wastewater system:
- View an overview of standard and advanced wastewater treatment processes.
- Visit the home pages for the regional Brightwater, South, and West Point treatment plants, and the local Carnation and Vashon treatment plants.
- View facts at a glance about the King County Regional Wastewater System, including:
- local sewer utilities
- service area
- sewer rate
- annual budget
- system and treatment plant facts and data (for most recent year available).
- View King County wastewater (NPDES) permits (for discharged treated wastewater) issued by the Washington State Department of Ecology.
- Learn about the history of King County's regional wastewater treatment utility.
- View division brochures and other resources.
- Visit the industrial waste program site to learn how King County regulates the wastewater discharge to our system by businesses and industries.
- Visit the resource recovery site to learn how King County recovers and recycles beneficial resources from the wastewater treatment process.
- Learn about WTD's environmental, social, and economic sustainability practices.