City of Sultan


Established in the late 1880’s, the City of Sultan has a rich heritage as a logging, mining and agricultural community. To accommodate a growing population, City administrators knew infrastructure upgrades at its Wastewater Treatment Plant  were needed. In addition, its Booster Pump Station, which serves potable water to City residents and fire system, as well as backwash to the potable water treatment facility, was not able to maintain system pressure during peak flow events, its electrical generator was undersized, and the building itself was at the end of its useful life. The City initiated two projects, the first to upgrade its Wastewater Treatment Plant, followed by upgrades to resolve the issues at its Booster Pump Station.

Key objectives: Wastewater Treatment Plant
The City’s key objectives for its Wastewater Treatment Plant were to avoid capital costs that would be required to maintain its aging infrastructure, to reduce energy costs by using more efficient equipment and improving processes, and to maximize operational efficiencies. The City also wished to upgrade its controls system for the benefit of plant operators, and improve exterior lighting quality and safety.

Key objectives: Booster Pump Station
The City also sought to avoid costs associated with maintaining the antiquated equipment at its Booster Pump Station. For the continued health and safety of its residents, the City wanted a redundant potable water system that would ensure the facility maintained code requirements and reduced the risk of system failure. In addition, the City wished to increase capacity to help meet peak demand, reduce energy costs and extend the life of its systems.


Project I: Wastewater Treatment Plant
After working with Trane to complete a city-wide Preliminary Audit, the City selected the company to implement an Investment Grade Audit (IGA) of its Wastewater Treatment Plant through the State of Washington Energy Savings Performance Contracting (ESPC) program administered by the Department of Enterprise Services. During the IGA, Trane identified opportunities to improve the treatment process and increase energy efficiency. Relying on the Trane Building Advantage™ portfolio of energy services, Trane presented a solution that maximized grant and utility incentive dollars, improved system operation and addressed capital improvement needs. IGA data was used to prioritize proposed energy conservation measures (ECMs) and used to project energy savings to assist in obtaining grant dollars from the Department of Commerce and energy conservation incentives from Snohomish PUD to enable the project.

Maximizing energy and process efficiency
A dissolved oxygen (DO) sensor was installed in the oxidation ditch and integrated into the plant’s SCADA system to provide operators with accurate DO levels. Programmable logic controller (PLC) programming was completed to automatically control mixer and aerator speed to maintain a constant DO  level in accordance with demands of the biological process.  By allowing operators to set two anoxic cycles per day instead of one, the programming changes will enhance present and future operations. It maximizes energy and process efficiency, while providing aeration to meet required levels and mixing in oxidation ditches. The heat pump was replaced with a new pump correctly sized for present and future operations.  Twenty-three yard lights and wall packs were replaced with LED fixtures, and five fluorescent fixtures were retrofit with T-8 lamps and electronic ballasts to improve exterior lighting quality and safety, while maximizing energy efficiency.

Project II: Booster Pump Station
Trane began with an Investment Grade Audit (IGA) to identify and prioritize ECMs for implementation. The project consisted of process and efficiency improvements to increase peak capacity and system reliability, replace aging equipment and generate energy/operational savings. Five booster pumps were installed to replace end of life equipment, and an abovegrade metal building was constructed to improve the potable
water system infrastructure and increase capacity to meet current peak demand conditions. To further increase capacity and provide redundancy, an emergency generator was added adjacent to the building. The improvements help maximize energy efficiency while meeting water demands of two zones, and supplement flows required during a fire event. The SCADA system was expanded to improve flow monitoring and alarming, and aesthetic improvements were implemented.


City of Sultan Wastewater Treatment Plant and Booster Pump Station upgrades are helping to ensure the continued health and safety of area residents and accommodate the needs of a growing population. Results include:

Wastewater Treatment Plant

  • Utility cost savings of more than $7,700/yr, with annual
    reduction in energy use of more than 92,000 kWh.
  • Snohomish PUD incentives estimated at more than $16,000
    and Department of Commerce grants of nearly $196,600.
  • Capital replacement cost avoidance of more than $84,000.

Booster Pump Station

  • Utility cost savings of more than $2,700/yr, with stipulated
    energy use reduction of 30,786 kWh/yr.
  • Snohomish PUD utility incentives estimated at $6,800.
  • Maintenance and operational cost reductions estimated at
    $12,500/yr for three years.