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Wastewater treatment process

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.

Diagram showing wastewater sources (from homes, businesses and industries), local sewer pipes (maintained by local sewer agencies), regional sewer pipes and pumps (maintained by King County), regional wastewater treatment plants, recycled and reused products (energy recovery, bisolids recycling, recycled water) and the clean water that flows back to Puget Sound. Source: Ratepayer Report, pages 4 and 5

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:

Learn more about wastewater treatment

Visit the wastewater education and tours site to learn about our programs, education resources and events, and how you can help the environment.