Water Reclamation Facility: Tertiary Treatment Improvements
City of Post Falls, ID

The Post Falls Water Reclamation Facility (WRF) is undergoing a capacity expansion coupled with technological improvements to improve the water quality that is produced. Phase 1 of the project included new headworks, influent flow equalization, and biosolids handling improvements.

The Phase 2 Tertiary Treatment Improvements project includes an upgrade to the City’s WRF to address environmental regulations improving the treatment process to remove phosphorous and oxygen demanding materials from the reclaimed water, which will maintain compliance with the City’s IPDES permit, before returning it to the Spokane River through upgraded outfall piping and diffuser. The project will also set the City up with advanced filtration and disinfection facilities to generate a “Class A” effluent for irrigation use on their community forest property in the future.

At a construction budget of $38 Million, Phase 2 includes both secondary and tertiary improvements to increase the capacity of the facility to an average day capacity of 5.21 mgd peak day capacity of 8.76 mgd, as well as targeting improved biological and physical treatment to reduce effluent CBOD to <10 ppm, total nitrogen to <10 ppm, and total phosphorus below 50 ppb.

 Phase 2 project elements include:

Secondary Biological Nutrient Reduction (BNR):

  • Conversion of the existing Oxidation Ditches (OD 1 to 4) from an A-0 process to A-2-0 BNR process to recover alkalinity and for total nitrogen reduction
  • Equipment modifications and capacity additions to the existing Biological Nutrient Reduction Facilities to increase Anoxic Capacity in Oxidation Ditch 5 and overall BNR capacity in Oxidation Ditch 6
  • New secondary clarifier no. 8 and RAS Pumping.

Advanced Tertiary Improvements:

  • Secondary effluent pump station to tertiary treatment
  • Tertiary clarification pretreatment including rapid chemical mixing/coagulation, flocculation basins, and inclined plate settlers.
  • Open-platform pressurized membrane filtration system
  • In-channel UV Disinfection system for both river discharge and Class A reuse

Support System Improvements

  • Recycled utility water pump station and Class A reuse pumping (future)
  • Plant drain pump station
  • Upgraded 30-inch river outfall piping and diffuser constructed through a CM/GC alternative delivery project.