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South Treatment Plant

Learn about current and future capital projects at South Plant that will increase efficiency, improve reliability, and protect the environment.

To ensure that the County’s regional sewer system keeps pace with growth and continues to meet regulatory requirements, it is important that we maintain and update our infrastructure through capital projects. These improvements also help us increase efficiency, improve system reliability, and protect community health and the environment.

FLUSH FACT: Between 2021 and 2026, South Plant is slated to invest in improving reliability, resiliency to climate change, and efficiency in its capital projects.


  • The wastewater treatment process produces gasses. Our biogas system captures these gases and converts them into energy for heat and other uses.
  • Work will occur through 2024. 

King County staff person with hard hat in front of industrial panel. Biogas from the digesters at South Plant can be sent to the co-generation system to be converted into electricity and heat.

  • Living in the Pacific Northwest puts us at risk of large seismic events. These upgrades will help protect the plant so that wastewater treatment processes can continue even in the event of an earthquake.
  • Work will occur through 2027
  • We want to be good neighbors. This project is allowing us to modify and refurbish our odor control system to reduce the amount of odor that escapes the plant.
  • Work will occur through 2022.
  • We want to keep our workers safe and reduce smells escaping the plant. This project will improve ventilation and reduce ammonia odors on-site and for neighbors.
  • Work will occur through 2025.
  • This project is replacing a generator that is at the end of its useful life. We want to be prepared in the event of a power loss to run essential equipment so that you can keep flushing your toilet.
  • Work will occur through 2024. 
  • We are constantly working to ensure compliance with safety and health codes.
  • Work will occur through 2023. 
  • We are testing out ways to safely produce Class A biosolids from wastewater for use in public spaces and home gardens. Currently, WTD produces Class B biosolids that require permits and are used on commercial farms and forests.
  • Work will occur through 2023. 

A view of three trailers (used by King County to haul Loop Biosolids)Loop trucks—you may recognize them driving around our region.

  • Dissolved air flotation tanks are used to remove grease and oil from wastewater. Some components in our tanks have aged and require rehabilitation or replacement.
  • Work will occur through 2026. 
Contact us

For more information about capital projects at South Treatment Plant, please contact Demmelash Adera, Community Services,, 206-263-2340.

24 hour emergency and odor reporting:   206-263-1760
Administration:  206-263-1810

1200 Monster Road S.W.
Renton, WA 98057

Directions and map

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