The City of Selah wastewater facilities consist of a sewage collection system and a wastewater treatment facility. The sewage collection system consists of approximately 110,000 linear feet (LF) of pipe, with a majority of the pipe being 8-inch diameter. The wastewater treatment facility was originally constructed in 1936, with upgrades and expansions in 1949,1968,1975, and 1987. Today, the plant is an activated sludge plant operated in an extended aeration configuration. The wastewater flow averaging 1.2 MGD travels through the treatment plant beginning at the influent building, where wastewaters are screened to Ecology standards and pumped to the two aeration basins for biological treatment. Aeration basin effluent gravity flows through 2 clarifiers and then UV disinfection prior to discharge to Selah Ditch. Solids that settle in the clarifiers are either pumped back to the aeration basins (return activated sludge) for use in treating influent waste or are removed from the process (waste activated sludge) by pumping to the aerobic digester, where solids undergo additional biological decomposition and stabilization. Sludge is removed from the aerobic digester by being pumped to our Biosolids facility where it is stored and metered into a centrifuge where polymer is added to help separate the solids from the water. The water is sent back to the lagoon and solids sent to a dryer where it is dried to CLASS A standards. The product after drying is sent to a Beneficial Use Facility where they land apply or compost to further breakdown and utilize as a fertilizer product.
The industrial pretreatment facility, for the treatment of food processing waste was constructed in 1985. After being treated in the 6 MG Pretreatment Lagoon, the effluent is discharged to the main Selah wastewater treatment facility and mixed with the domestic wastewater, where they undergo the treatment process.
A new facility is being designed to better accommodate growth and future treatment requirements.
Selah’s facility is manned Monday through Friday 6AM -3:30PM by 5 Certified Operators with varied levels of certification ranging from level II to level IV, 2 years of experience to 25 years of experience! They work together to provide professional and responsible operation of the Selah Waste water Facility.