Mixing It Up

A portable aeration system provides immediate and long-term energy savings for an Alabama city’s treatment pond
Mixing It Up
The control box for the aerators cycles them on and off. The two light-green canisters each contain two air filters on suction pipes.

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Discharge from a textile plant in Monroeville, Ala., paid 90 percent of operating costs for the Hudson Branch Wastewater Treatment Plant. The 2 mgd (design) activated sludge extended aeration facility ran two 125 hp propeller-type aerators in its 11-foot-deep wastewater pond. Power usage averaged $12,500 per month.

When the textile plant closed in 2009, Hudson Branch installed a baffle curtain in the pond, cutting its capacity in half. With flows averaging 250,000 gpd, operators cycled the active aerator on and off. Although running it 10 hours per day lowered utilities to $4,000 per month, it was too expensive to run for the influent coming into the headworks.

“In 2008, an aerator broke down and Randy McGuffin of DO2E Waste Water Treatment leased a floating mixer and aerator to us for 60 days,” says superintendent Darlene Johnson. McGuffin later installed two single-flow high-volume 5 hp floating aerators, and two 2 hp high-volume floating mixers in the active half of the lagoon. They lowered the utility bill to $1,300 after one month.

 

Green and white team

The prewired and pre-plumbed DO2E aerators (dissolved oxygen enhancers) installed in four hours. “They float on the water and are held in place by guide wires,” says Johnson. “Randy plugged them in, hooked up the air hoses, and we were good to go.”

The staff electrician stepped down the three-phase power to single-phase for the mixers and mounted a control box for the aerators. The original aerators remained in the pond as backups.

The mixers each have two green sponsons. Suspended between them eight to 10 inches below the water is an air manifold and stationary diffuser head. Each mixer moves up to 1.3 mgd and transfers 2.75 lb O2/hp-hr. Each mixer is driven by a 3 hp regenerative air blower producing 1.5 psi and 125 cfm of air flow, drawing eight to 12 run amps while reducing sludge buildup by up to 60 percent.

The single-flow high-volume aerators move 12.6 mgd, diffuse 245 cfm at 50 inches Hg and transfer 3.70 lb O2/hp-hr. The blower injects air through a multichambered manifold at the bottom of the units to draw up the solids.

Released at a specific depth within a confined space, coarse bubbles provide velocity while fine bubbles maximize oxygen transfer. The resulting turbulence creates a surface current of 8 knots for 100 feet while reducing sludge buildup by 75 percent.

 

Substantial savings

The marine-grade mixers and aerators have no moving parts, reducing maintenance costs by up to 90 percent. “Timers cycle the units on for three hours and off for five,” says Johnson. “When they run, the aerators push the solids to the outfall and into the clarifiers.

“I budgeted $58,900 for utilities this year with an average of $4,900 per month for electric,” says Johnson. “Based on what we’re saving, we should see a return on our investment in 18 months, and save tens of thousands of dollars over the lifetime of the equipment.”



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