Wastewater Treatment Plant Facility

Your Collection System:
The City of Granite Falls Wastewater Collection System is comprised of over 187 Manholes and over 11 miles of Polyvinyl Chloride (PVC) pipe, with some sensitive areas utilizing Ductile Iron Pipe (DIP). The Wastewater is conveyed through pipes primarily comprised of 8” with some 10” and 12” to the Wastewater Treatment Plant located at 501 West Wallace Street.

The Treatment process:
Wastewater entering the Treatment plant is first met by chemicals to adjust the PH, then as part of the Pretreatment process it is ran through a Velocity Settling Basin. This slows the wastewater down to around 1FT/S (Foot Per Second) allowing inorganics like rocks and debris that could potentially damage pumps later in the process to settle for removal, while keeping beneficial organics suspend. After the Velocity Settling Basin, the wastewater is then ran through a Fine Screen to remove rags and other solids before entering a device that introduces the new wastewater to older wastewater known as Mixed Liquor Suspended Solids (MLSS). MLSS is contained in an Aeration Basins that adds air to the MLSS to keep a diverse group of important microscopic bugs alive. After mixing new and old wastewater, the newly formed MLSS is pumped to one of two Secondary Clarifiers. Clarifiers are large Basins that allow the MLSS to settle while also allowing Effluent (wastewater in route to leave the Plant) to exit to. The Effluent flows through a series of final settling basins before flowing through two banks of UV (Ultraviolet) lights. The UV lights inactivate any potential pathogens (disease causing bugs) before exiting the plant. After settling in the Clarifier the MLSS is then pumped into a holding tank where it is again pumped through dewatering devices. Water from the dewatering process is then pumped back to the Velocity Settling Basin to start the process over again. The solids portion from the dewatering process, which is referred to as Class A “Biosolids”, is mixed with Alder sawdust and Hogfuel (ground up stumps) and held on site for up to 4 weeks. At that point, the “Compost” mix is permitted to leave the Treatment Plant for yard and landscaping proposes.

Throughout this entire process State Certified Wastewater Operators employed by the City run a multitude of complex tests, to ensure that all state required standards are achieved.

Fats, Oils, and Grease that enter the Collection System can have adverse effects on the ability of the system to transport Wastewater to the Treatment Plant. F.O.G enters the system from restaurants and homes that dump Grease down the drain. Once the liquid F.O.G enters the system it begins to cool and solidify. Over time, larger masses of F.O.G build up and can restrict pipes or break lose and completely block portions of the collection system, creating the potential for sewer backups that may enter homes, streets, or waterways. Please do your part. Dump cooking grease into empty cans, allow them to harden and dispose of in the trash.


Additional Information:

Wastewater System Basemap
Department of Ecology Biosolids Page
Department of Ecology Wastewater Treatment Page
Sewer Collection System Smoke Testing