Spokane County Regional Water Reclamation Facility (SCRWRF)

Dye Tracer Test

As part of our state issued NPDES (National Pollutant Discharge Elimination System) Permit, the Spokane County Regional Water Reclamation Facility (SCRWRF) will be conducting a required mixing zone study of the Spokane River.

The study involves a dye tracer test where an environmentally safe red dye will be added to the facility effluent water before it enters the river. The dye will allow water specialists to analyze how the effluent from the facility mixes into the river. The SCRWRF is using Rhodamine WT dye which is not harmful to humans, wildlife, or the environment.

The test is scheduled for Tuesday, August 5, 2025, from 11:00 a.m. until 3:00 p.m. Those conducting the test will use a boat to access different locations and depths of the river to gather data on dye concentrations. A drone will also be used to capture aerial views of the dye mixing.

The effluent enters the Spokane River just east of Spokane Community College. The dye will be best viewed at the intersection of N Havana St and E Upriver Dr, but it will be visible for up to a half-mile downstream for the duration of the testing timeframe.

For more information, please refer to the Effluent Mixing and Dye Tracer Plan of Study, section S10 of the Spokane County NPDES permit, or contact Hannah Thomascall at [email protected] or (509) 477-7575.

Facility Background

In 1999, Spokane County began a Wastewater Treatment Facilities Plan process to evaluate long term regional wastewater needs, and to determine alternatives to meet those needs. Water Reclamation was identified as a fundamental piece of this Wastewater Facilities Plan. On December 1, 2011, and ahead of schedule, the Spokane County Regional Water Reclamation Facility (SCRWRF) began treating wastewater from the incorporated and unincorporated areas of Spokane Valley. The Water Reclamation Program serves the County by providing highly treated water for beneficial reuse and concurrently protects Spokane County's surface and groundwater resources, now and into the future.

The facility is treating to very high standards which help improve water quality in the Spokane River and Spokane Valley-Rathdrum Prairie Aquifer. The facility uses state-of-the-art membrane technology and is designed to meet or exceed current legal requirements for phosphorus removal. Phosphorus removal is crucial for the health of the river and aquifer. For more information on the high standards that SCRWRF is treating to, the NPDES permit, and NPDES permit fact sheet are linked below:

⇒ SCRWRF NPDES Permit ⇒ NPDES Permit Fact Sheet

See here for a description to compliment the process video:

The Spokane County Regional Water Reclamation Facility (SCRWRF) treats around 7 million gallons of wastewater from Spokane Valley everyday using a membrane bioreactor process before discharging the cleaned water to the Spokane River.

00:20 - First, underground sewer pipes send raw influent (wastewater) to the headworks building where a 3-mm band screen filters out solids and trash, called screenings, that have made their way to the facility. These screenings get chopped up, rinsed, and compacted before being sent to the Waste-to-Energy facility.

00:54 - Common items that come to the facility through the sewer system include cotton balls, cotton swabs, paper towels, tissues, medications, and even small toys! All of these items are examples of what not to flush.

01:12 - After the large trash is removed, the aerated grit basin removes small, heavy particles that arrived at headworks in the influent. Grit is made up of sand, small gravel, coffee grounds, eggshells, and other materials. The grit is rinsed and sent to the Waste-to-Energy facility along with the screenings.

01:25 - Various systems throughout the plant are connected through ventilation that pulls odorous air into the odor control system. A biofilter that utilizes microbes and woodchips which help to reduce the smells from these processes.

01:37 - Next up after headworks, the influent is sent through the primary clarifiers, which are used to remove organic solids and phosphorus from the wastewater.

02:26 - After treatment in the primary clarifiers, the influent moves to an aeration basin, where biological treatment helps to reduce organic solids while also removing nitrates and ammonia. This stage represents the bioreaction step in the wastewater treatment process.

03:34 - Organic solids, now referred to as sludge, travel from the primary clarifiers and the aeration basins to the solids treatment facility where moisture is removed, and the sludge is thickened. It gets sent through a process to remove water by means of gravity belt thickeners and centrifuges.

04:04 - Sludge is stabilized and reduced in aerobic digesters. The solids that have been through digestion and dewatering are then trucked offsite to be composted.

04:38 - The site collects and stores the methane gas produced as a by-product of the anaerobic digestion. This gas is used to provide up to 15% of the power for the entire facility. Any excess methane that cannot be utilized is burned to reduce its harmful impact to the environment.

04:48 - Operators use a SCADA system to run and monitor the entire facility. Real-time measurements are visible through the SCADA system, and each pump and tank can be controlled remotely using the SCADA system.

05:37 - SCRWRF has a state-certified lab on-site that is used to analyze critical water parameters at different stages of the process.

05:47 - Once treated for solids, the remaining wastewater then travels to the membrane tank, while the extracted solids are sent to solids treatment facility. In the membrane tank, membrane filters are then used to filter smaller particles out while letting larger water molecules through. The residue that is too large to be filtered is returned to the aeration basin.

07:27 - The water that has been pulled through the membrane filters is sent to the chlorine contact basin for final disinfection. Once the water has been disinfected, the chlorine is removed.

07:47 - Once the treatment process is complete, the water is then pumped back into the Spokane River through an outfall. Each drop of water takes approximately eight hours to make its journey from wastewater to river water.