Stirring with the Sun

Solar-powered mixing technology helps an Ohio treatment plant cut electric bills, avoid capital costs and improve treatment performance

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The village of St. Henry, Ohio, was outgrowing its wastewater treatment plant. Bucking the trend among farming communities in the state, the village was growing as industries such as turkey processing expanded.

Despite its good fortune, this community of 2,700, about 40 miles northwest of Dayton, faced fiscal constraints. When village officials learned that a wastewater treatment plant upgrade would cost almost $500,000 and add $49,000 in annual energy costs, they looked for alternatives.

Ultimately, instead of adding energy-intensive aeration equipment, the village saved $100,000 in capital costs by adding solar-powered circulation equipment from SolarBee Inc. to the existing aerated lagoon system. The reconfigured plant saves $20,000 annually in utility costs.

More aeration

The new equipment thoroughly mixes the ponds and significantly reduces energy consumption, according to Stan Sutter, public utilities supervisor. “The problem with the old system was that it was undersized,” he says. “We needed more aeration, and we needed a new cell for extra storage capacity.”

The plant staff considered installing a diffuser blower system that would replace the existing surface aerators. In that configuration, three large blowers would force air through a common header along the whole outside of the lagoon. “But the blower system would have increased our horsepower by 30 percent and our utility bill as well,” Sutter says. “We were determined to solve our problems without all that extra expense.”

The St. Henry staff and consulting engineers decided to reconfigure the first aeration pond, reduce mechanical aeration run time, and add solar-powered circulation to mix the ponds thoroughly, in the process reducing odors.

High efficiency

The SolarBee technology combines solar power with long-distance, near-laminar-flow circulation to provide radial, horizontal and vertical pond mixing. The mixers help conserve dissolved oxygen by mixing and distributing oxygen-saturated surface water throughout the pond, replacing 20 to 40 hp of grid-powered aeration per unit.

The mixing efficiency means the plant can offload a large portion of its energy-intensive aeration and mixing, while significantly reducing BOD, TSS and ammonia. Near-laminar-flow circulation also minimized odor and reduced sludge buildup.

The circulation equipment is designed around pumps that can move up to 10,000 gpm, or 14.4 mgd. Because of the hydraulic design, the system needs only 36 watts to power a 1/2 hp direct-drive motor with 90 percent or higher efficiency. Three 80-watt photovoltaic panels charge an onboard battery, allowing the units to run around the clock on solar power.

Reconfiguring the treatment plant meant dividing the first 8-acre rectangular lagoon into two sections. This concentrates treatment in a small, total-mix, high-solids lagoon and essentially creates an activated sludge basin without the expense of building one, Sutter observes.

In section A of the first pond, eight aerators and one SolarBee unit concentrate the aeration and provide deeper mixing. About 800 to 1,000 mg/l of CBOD runs through the first cell, and about 100 mg/l of CBOD leaves the pond after a three-day detention time.

After the first pond, the system returns to a facultative process. During the day, the gentle and continuous mixing of the circulation unit brings nutrients to the surface, promoting the growth of algae that produce energy-free dissolved oxygen at up to 250 pounds per acre per day.

A high pH also occurs near the surface. The high-oxygen and high-pH water is continuously and thoroughly mixed throughout the pond instead of being mostly underutilized as in all-natural ponds. The higher dissolved oxygen throughout the pond helps reduce BOD by 70 to 90 percent.

Green payback

In total, seven SolarBee units and 11 aerators mix and aerate the lagoons to meet permit requirements. A newly installed fourth pond provides an additional 67 million gallons of storage.

By the time wastewater reaches the fourth pond, there is not enough carbon, ammonia or phosphorous to cause permit problems, or to support algae growth high enough to result in BOD and TSS problems. Aeration run-time has been cut by 60 percent and the utility bill by $20,000 per year.

To Sutter, that’s a green payback. “Green goes hand in hand with operational cost savings,” he says. “We’re not consuming nearly as much power as we were originally looking at. In fact, we’ve decreased our horsepower rather than increasing it, and any time we can use fewer resources, it benefits the entire community.”

With a renewed wastewater treatment system designed with an eye on holding down costs, St. Henry is prepared to accommodate population growth, host new industries, and meet stringent regulatory requirements.

About the author

Michael Christensen is the North U.S. Regional Manager for SolarBee Inc., a manufacturer of solar-powered equipment for water treatment applications. He can be reached at 866/553-5590 or mikec@solarbee.com.



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