South Treatment Plant

[4] The plant received $6 million worth of upgrades in 2013, alongside numerous other improvements to the local wastewater system.

Recycled water from the plant undergoes tertiary treatment with a sand filter, while the rest of the effluent is pumped into Puget Sound through a 12-mile (19 km) pipe.

[6][7][8] At Duwamish Head the transfer line's effluent enters two underwater pipes that take it 1.9 miles (3.1 km) offshore where it is diffused through 168 ports into the water of Elliott Bay at a depth of 607 feet (185 m).

[14] In 2004, King County installed a 1 MW molten carbonate fuel cell at the South Treatment plant as a demonstration project in cooperation with the United States Environmental Protection Agency.

At the time, it was the largest fuel cell of this kind in the world and operated on either internally produced or purchased gas.

[16] In addition to wastewater treatment, the facility has an educational role, with public tours and a demonstration garden.

[18] The plant also has to handle large inflows from the King County system during heavy rainstorms; it uses a special treatment process for this.