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You are here: » » Municipal Wastewater Treatment Project

Project Details

Industry
Municipal

Installed power
600 kW backup power system

Fuel type
Natural Gas

Location
Houston, TX

Problem

A municipal wastewater treatment project was originally designed around a 350 kW generator, but by the time the actual equipment was installed, the electrical load had changed significantly. Blowers increased from 30 HP to 60 HP, the main motor increased from 150 HP to 300 HP, and the system had no soft starters or VFDs in place. Once WPP evaluated the installed equipment and startup conditions, it became clear that the system would require an 800 kW natural gas generator to handle the load as designed. That meant a major cost increase for the municipality and a more expensive long-term power solution.

Objective

Reassess the project’s actual operating conditions and identify a more practical backup power solution that would:

  • Support reliable wastewater operations during outages
  • Reduce generator size without compromising performance
  • Lower upfront project cost
  • Improve long-term motor performance and operating efficiency

Solution

WPP reviewed the installed equipment, startup conditions, and generator sizing requirements, then redesigned the system around variable frequency drives (VFDs) and soft starters. By reducing inrush current and controlling how motors started and ran, WPP was able to lower the required generator size from 800 kW to 600 kW. This approach helped the municipality avoid unnecessary generator cost while also improving how the system would operate over time.

Result

The redesign delivered measurable savings and a more efficient long-term solution:

  • Generator size reduced from 800 kW to 600 kW
  • Approximate $175,000 reduction in generator cost
  • Approximate $100,000 net savings after adding VFDs and soft starters
  • Lower startup stress on motors and related equipment
  • Longer motor and bearing life
  • Reduced annual utility costs through more efficient motor operation

Background

Municipal wastewater systems have to keep critical equipment running reliably, even when utility power is interrupted. In this type of environment, generator sizing is closely tied to the actual behavior of pumps, blowers, and motors during startup, not just their nameplate ratings.

In this project, the original generator design no longer matched field conditions by the time the equipment was installed. The blower size had doubled, the main motor had also doubled, and the system still lacked the motor controls needed to reduce startup demand. As a result, the municipality was facing a much larger generator requirement than originally expected.

For public-sector projects, that kind of shift can create more than just a design problem. It can drive up equipment cost, increase scrutiny around project budgets, and create long-term operating inefficiencies if the system is not reevaluated carefully.

Water treatment plant aerial view

Challenges

This project involved several issues that made a simple generator replacement the wrong answer.

Equipment Changes Increased the Load

The installed equipment no longer matched the assumptions behind the original generator design. Larger motors and blowers created significantly more startup demand than the system was expected to handle at the outset.

Startup Conditions Drove Generator Size Up

Without soft starters or VFDs, the motors were creating high inrush current during startup. That pushed the required generator size all the way to 800 kW, substantially increasing project cost.

Generator Cost Needed to Be Controlled

Because the project involved a natural gas unit, upsizing the generator came with a significant price jump. The municipality needed a solution that protected performance without simply accepting a much higher capital cost.

Long-Term Operability Still Mattered

This was not just a one-time sizing exercise. The municipality also needed a system that would be practical to operate over time, with better motor control, less mechanical stress, and improved efficiency.

WPP’s Response

Re-Evaluating the System Instead of Just Upsizing the Generator

Rather than treating a larger generator as the only option, WPP stepped back and reviewed how the system was actually operating. The team evaluated the installed motors, blower loads, and startup conditions to understand what was driving the generator requirement.

Reducing Inrush Current with VFDs and Soft Starters

WPP identified an opportunity to reduce startup demand by incorporating variable frequency drives and soft starters into the design. This allowed the motors to start in a more controlled way, lowering inrush current and reducing the amount of generator capacity needed to support the system.

Delivering a More Cost-Effective Backup Power Solution

With those motor controls in place, WPP was able to reduce the required generator size from 800 kW to 600 kW. That change cut generator cost by approximately $175,000. Even after accounting for the added cost of the VFDs and soft starters, the municipality still realized approximately $100,000 in net savings.

Improving Long-Term System Performance

The redesign also created longer-term operating benefits. By improving how the motors started and ran, the system reduced wear on motors and bearings and supported lower annual utility costs through more efficient operation.

Built for Better Long-Term Value

For municipalities, backup power decisions are about more than getting through the next outage. They also affect project budgets, long-term maintenance, and how efficiently critical infrastructure operates over time.

In this case, WPP helped the customer avoid an unnecessarily large generator by taking a closer look at how the system was designed to run. The result was a more practical solution for a wastewater application: lower capital cost, better motor control, and a backup power system better aligned with actual operating conditions.

That is the value of getting the design right before moving forward. In municipal infrastructure, a second look at generator sizing and motor control strategy can make a six-figure difference.

 

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