wet science center
our career site

Budd Inlet Treatment Plant

The heart of LOTT's system is the Budd Inlet Treatment Plant. Wastewater flowing to the plant currently comes from almost 90,000 homes, apartments, and commercial/industrial connections served by the sewer utilities of Lacey, Olympia, and Tumwater. From homes and businesses, the wastewater flows through a series of underground pipes to the plant. The treatment plant is located at the north end of Adams Street, between downtown Olympia and the Port of Olympia.

About 11.5 million gallons of wastewater flow through the Budd Inlet Treatment Plant on an average day. During the wet months, flows average nearly 15 million gallons per day due to stormwater inputs from older storm drains in downtown Olympia. During the wettest month, flows reached an average of 33.8 million gallons per day (mgd) due to large storm events, but this rate of flow is very unusual.


Treatment Process Overview

LOTT offers the highest level of wastewater treatment on Puget Sound, treating to an advanced secondary standard. Both physical and biological processes are used to clean LOTT's wastewater as it moves through a series of cleaning stages:

  • Screening – First, a mechanical screening process removes large materials such as sticks, rocks, rags, toys, and countless other untreatable items.
  • Primary Treatment – Additional solid material and its related pollutants are removed from the wastewater by allowing them to float to the surface or sink to the bottom of large tanks. "Floaters and sinkers" are removed and processed in solids handling.
  • Secondary Treatment – The plant provides an environment, which allows naturally present bacteria to consume and break down additional pollutants.
  • Nitrogen Removal – The treatment process at the Budd Inlet Plant includes removal of nitrogen from the water (April to October) to prevent the nitrogen from feeding excessive algae growth after the treated water is discharged.
  • Disinfection – The final treatment step is disinfection with ultraviolet light, which turns any remaining pathogens sterile.
  • Discharge – The cleaned water is discharged into Budd Inlet through an outfall off the north end of the Port peninsula.

As the wastewater is cleaned, remaining solid material is removed.

  • Thickening – The material removed in the primary and secondary treatment processes is sent to the solids handling building to a Dissolved Air Flotation Thickener, which concentrates the sludge and separates it from the liquid before it goes to the digesters.
  • Digestion – The thickened sludge is fed to the two primary digesters. The sludge is heated, mixed, and held for at least 15 days to further reduce pathogens. This process also produces methane gas, which provides heat and power for plant processes.
  • Dewatering – The digested sludge is sent to a centrifuge for dewatering after its pathogens have been sufficiently reduced. This machine spins to create centrifugal force, which further separates liquids from the solids. The final product, called biosolids, leave the machine and is carried via screw conveyor to a biosolids hauling truck.
  • Hauling and Beneficial Use – The resulting biosolids are trucked to Lewis County where they are used to fertilize pasture land, forests and dry-land wheat.

get adobe reader