Energy-efficiency retrofits pay off even for mature facilities.
Just ask Nicholas Menninga, general manager of the Downers Grove Sanitary District. His desire to spend less on electricity for the district's 50-year-old, 11-mgd plant spawned upgrades that have cut average power usage by one-third: from 2,294 to 1,527 kWh/million gallons treated.
Aeration represents up to three-quarters of a facility's energy usage, so his target was the activated sludge aeration system. Consulting firm Baxter & Woodman Inc. was commissioned in 2006 to identify improvements that resulted in a $1.4-million project that:
- replaced medium-bubble diffusers and turbine aeration equipment with fine-bubble diffusers
- replaced several shallow aeration tanks with a deeper tank converted from sludge processing use
- added an automated control system, and
- added a single-stage centrifugal blower, the first of its kind in Illinois, and one of the first nationwide.
The high-speed blower rotates at 30,000 rpm on a magnetic bearing, making it a highly efficient alternative to conventional multistage centrifugal blowers. "This is the first technology using a variable frequency drive to maintain the efficiency of the blower," says Derek Wold, wastewater department manager for Baxter & Woodman. He visited a 9.5-mgd plant in De Pere, Wis.,, which in 2004 installed the model S9000-1-H-5 high-speed technology (HST) integral turbo compressors manufactured by High Speed Technology Oy Ltd., a Finnish company, and reports a 35% reduction in energy costs; and he recommended the same unit for Menninga's project.
"Just a few years ago, there were one or two manufacturers producing this type of blower," Wold says. "Now there are five players in the market." One U.S. company, Texas-based Houston Service Industries, also makes a high-speed turbo blower.
The project is expected to pay for itself in about five years. Until now, it wasn't cost-effective to retrofit older plants with energy-efficient blowers, but Menninga and Wold expect the technology to help facilities of all sizes save money.
"If you're running a conventional activated sludge facility with multistage blowers, you're going to see a savings within five to 10 years," says Wold, who obtained a $250,000 Illinois Clean Energy Community Foundation grant that helped fund the project.Established a decade ago with a $225-million endowment provided by Commonwealth Edison, the independent foundation supports projects that demonstrate energy efficiency and use of renewable energy.
"There's so much money to go after for anything energy-related-especially with the economic stimulus," he adds. "You just have to do your homework."