Wastewater Treatment Plant VFD Upgrades

Problem

The City of Payette’s wastewater treatment plant operated six 60-horsepower surface aerators at full load throughout the year. This constant-speed operation limited the City’s ability to adjust aeration rates based on dissolved oxygen levels and seasonal mixing requirements. As a result, the facility experienced higher-than-necessary energy consumption and operating costs.

The City identified the need for improved process control to better match aeration output to treatment demands while maintaining reliable, continuous wastewater treatment operations. Any upgrades also needed to be compatible with existing equipment and implemented through a public works contracting process.

Solution

HECO Engineers provided electrical engineering design and construction-phase services to support installation of variable frequency drives (VFDs) on six existing surface aerators at the wastewater treatment plant.

Key actions included:

• Preparing plans and specifications for installation of six VFD units, associated load reactors, mounting equipment, wiring, conduit, and related electrical components.

• Designing the system to integrate with existing aeration motors and allow variable-speed operation based on dissolved oxygen levels and seasonal treatment needs.

• Supporting the City during bidding and contract execution through use of standard public works contract documents.

• Serving as the City’s representative during construction, including review of contractor submittals, applications for payment, and coordination with the contractor.

• Providing construction administration and observation services to verify that the work was completed in accordance with the contract documents.

The design and construction process was completed while maintaining ongoing wastewater treatment plant operations.

Results

Following installation of the VFDs, the City transitioned from constant full-load aerator operation to variable-speed control tailored to treatment demands. This operational change has resulted in measurable reductions in energy use and operating costs.

As of January 2026, documented results include:

• Approximately 217,877 kilowatt-hours of energy savings per year.

• Nearly $18,000 in annual electric cost reductions.

• Energy savings equivalent to the electricity usage of approximately 20 homes per year.

• Cumulative cost savings totaling $39,217.86 to date.

The cumulative savings figure is expected to change over time as additional operational savings are realized.

Improving Wastewater Treatment Efficiency

Through targeted electrical upgrades and construction-phase support, HECO Engineers helped the City of Payette improve operational flexibility at its wastewater treatment plant while achieving documented energy and cost savings. The project demonstrates how focused infrastructure improvements can support efficient municipal operations and long-term utility management goals.