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For questions about the Reclaimed Water Program, please contact Jo Sullivan

For questions about the Reclaimed Water Comprehensive Plan, please contact Doug Marsano

Wastewater Treatment Division 
King Street Center
201 S. Jackson St., Suite 505
Seattle, WA 98104-3855

Get Directions to our office location in Seattle, Washington.

Overview of standard and advanced wastewater treatment processes

Most of King County's wastewater flows to one of two regional treatment plants where the wastewater flows through a series of treatment processes that remove waste from the water and protect public health and the environment.

primary secondary disinfection advanced

Standard wastewater
treatment process

Typically, wastewater treatment begins with primary treatment where solids are separated from liquids. This happens in sedimentation tanks.

The next phase is called secondary treatment. It is also called biological treatment because oxygen is added to activate the living microorganisms (such as bacteria) that eat the dissolved organic material still in the wastewater. We use an 'activated sludge' treatment process where the organisms are maintained at a very high level to accelerate the consumption process.

After secondary treatment, King County disinfects the treated wastewater and returms it to the environment.

Advanced
treatment

Some of the water treated at the regional treatment plants is reclaimed. Reclaimed water must be treated beyond secondary treatment to meet Washington State Departments of Health and Ecology Class A standards.

This advanced treatment involves an additional filtration step to remove any remaining solids and an extended disinfection process.