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King County Washington home

Improvement projects

Find information about capital improvement projects at South Plant.

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

Capital projects

Loop Compost Pilot - 2026

  • During treatment, we remove solid, organic material from wastewater. These are called biosolids. Biosolids are full of nutrients. The biosolids produced at WTD treatment facilities is called Loop®. It is a sustainable alternative to chemical fertilizer. Currently, WTD produces Class B biosolids. These require permits and are used on commercial farms and forests.

This project is testing out ways to safely produce Class A biosolids from wastewater. Class A biosolids can be used in public spaces and home gardens.

  • Timeline: Work is currently happening and will occur through 2026.
    • Loop trucks—you may recognize them driving around our region

           Loop trucks—you may recognize them driving around our region.

 Essential services standby generator replacement – 2026 

  • 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 is currently happening and will occur through 2026.  

Digester Circulation Pump Replacement – 2027

  • For our digesters to function, pumps need to circulate water in the tanks. The current pumps are at the end of their useful life. This project will replace the pumps with more energy efficient equipment that will also reduce water usage.
  • Work is currently happening and will occur through 2027.

 

Biogas and heat system improvements - 2028

    • The wastewater treatment process produces gasses. Our biogas system captures these gases and converts them into energy. Then we do two things with it. Usually, we sell the extra energy back to the natural gas marketplace. However, when our power demands get too high for the power grid to support, we can use the system to power our plant. This project will provide necessary improvements to make this system more efficient. 
    • Work is currently happening and will occur through 2028. 

Biogas from the digesters at South Plant can be sent to the co-generation system to be converted into electricity and heat.

Biogas from the digesters at South Plant can be sent to the co-generation system to be converted into electricity and heat. 

Dewatering building truck loading bay ventilation improvements – 2029

  • After solid waste is removed from the water, it is compressed to squeeze out as much water as possible. We then load it onto trucks to take to other facilities. During this process, 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 is currently happening and will occur through 2029.  

Influent pump station seismic upgrades – 2029

  • 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 2029

Dewatering building truck loading bay ventilation improvements – 2026

  • 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 2026. 

Essential services standby generator replacement – 2026

  • 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 2026. 

Dissolved air flotation tank rehabilitation – 2029

  • 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 2029.