Redding’s Stillwater Treatment Facility Wins Small Plant of the Year

Northern Sacramento Valley, Resource Recovery, Technology and Innovation
City of Redding

Stillwater Wastewater Treatment Facility
Population served:  29,000
Built 1992 / Major expansion 2014

Flow rates

Average dry weather flow: 4 million gallons per day (MGD)
Peak flow: 14.4 MGD

  • Conventional activated sludge
  • Liquid treatment
    • Screening; activated sludge treatment with secondary clarification, filtration, and chlorination/de-chlorination.
    • Tertiary treatment by traveling bridge sand filters
    • Approximately 2.5 million gallons per month of recycled water is sent to a nearby customer.
  • Solids treatment
    • Aerobic digestion followed by belt-filter-press dewatering.
    • Biosolids are disposed of at a sanitary landfill. The facility is under contract with companies to build a resource recovery system where pyrolysis machines will turn digested sludge into a useful biochar at net zero energy.

The facility recently developed an in-house Safety Program that includes twenty-two SOPs. The entire program is broken down into weekly, monthly, and quarterly safety inspections. Safety work orders are generated in the City’s Cartegraph software program and as a result accurate record keeping is employed.

The Public Works Division has a dedicated full time “Safety Specialist.” She does an outstanding job monitoring and ensuring Cal/OSHA requirements are carried out.


In the past, the Stillwater Treatment Plant has experienced exceedances regarding effluent coliform numbers. Our operations staff has worked hard to reduce exceedances. By monitoring coliform and maintaining a 2.5 to 2.7 PPM of free chlorine at our outfall, we have successfully reduced violations.

Additional recent improvements include: replacing chemical scrubbers; new chlorine dosing system and integrated SCADA alarm monitoring system to monitor for leaks; replacing odor scrubbers in the biosolids building; developing a valve exercise program; adding a full time maintenance mechanic; adding brass equipment tags for asset management to over 900 pieces of equipment; adding additional recycled water pumps to deliver more water to customers; and more.

“We take pride in our facility. The appearance of a wastewater treatment plant speaks volumes about the quality of operations. The weirs on our clarifiers are clean, the landscaping is top notch and the grounds are clean. We take pride in our plant, and our staff takes pride in their work.“
– George Coughran, Public Works Wastewater Utility Supervisor, City of Redding

Plant of the Year Award

The Plant of the Year award recognizes accomplishments in compliance, innovative practices, cost effectiveness, and superior plant performance in small, medium and large categories.

  • Small (Less than 5 MGD)
  • Medium (Greater than or equal to 5 MGD and less than or equal to 20 MGD)
  • Large (Greater than 20 MGD)

Applications are now being accepted at