The city of Spokane is evaluating suppliers that responded to its request for qualifications to build a filtration membrane as part of its estimated $80 million to $100 million upgrade of the Riverside Water Park Water Reclamation facility, says city spokeswoman Marlene Feist. 

The city sent out the request on July 23, Feist says, and submissions were due on August 18. The city will evaluate the responses and chose the top two suppliers, which then will provide pilot filtration units for a six- to 12-month testing period. One of the suppliers ultimately will be chosen to supply the membrane system for the entire plant, Feist says. 

The upgrade also will include the construction of a third solids digester at the facility this fall, Feist says. The city approved in July an $11 million contract with Ferndale, Wash.-based IMCO General Construction Inc. to build the digester and remove an older, unused one. The third digester will enable the plant to meet regulations, Feist says, as well as enable the city to do maintenance on the other two digesters. 

At this time there aren’t any cost estimates for the pilot or the full-scale membrane system, Feist says. The upgrade is expected to begin as early as 2016. 

The overall upgrade is expected to increase the level of phosphorus removed from the effluent from 90 percent to 99 percent, Feist says.

The final membrane filtration system will be designed to treat an average of 50 million gallons of wastewater a day, Feist says. Mainly, the new system will reduce the level of phosphorus that’s discharged into the Spokane River in effluent, she says. 

“It will also reduce other pollutants, such as PCBs (polychlorinated biphenyl) and heavy metals,” Feist says. 

The plant currently has preliminary, primary, and secondary treatment levels. The new system will add an additional level, she says. 

In the preliminary level of treatment, rocks, grit, and other large debris are removed. In the primary level, solids settle to the bottom of the effluent and oils float to the top; both are removed at this stage. The secondary level separates and removes smaller particles from the water.

“This is going to add tertiary, or third, level of treatment, which will remove more pollutants,” Feist says. In the tertiary level, the water will flow through the membrane system to remove the pollutants. 

Next, the water is disinfected before being released into the river. While the water is going through these treatments, Feist says, the digesters are being used to process all the removed solids and oils. The processed solids are dried out and spread on fields where grain for livestock is grown; Feist says the city handles about 6,500 tons a year. 

The upgrade is part of the larger $310 million Integrated Clean Water Plan, which the city adopted in May. In addition to the water treatment plant upgrade, the plan includes work to reduce overflows from sanitary and stormwater sewers and reduce the amount of stormwater reaching the river from storm sewers.