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Case Histories : Wastewater

SolarBee : Oregan WWTP Receives State Award
By Mary Jones
Feb 29, 2012
  E-mail article
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Dickinson, ND -- SolarBee™ solar-powered mixers installed in the St. Helens, OR, wastewater treatment plant have helped reduce aeration horsepower over 60 percent and save the city over $100,000 compared to the previous year. Because of these significant savings, the city received the Oregon Leaders Award for Industrial Energy Efficiency at the 4th Annual NW Industrial Energy Efficiency Summit in Portland in January. St. Helens was one of six organizations honored for innovation and improving efficiency.

St. Helens (population 13,000) and the town’s major industry, Boise Paper, share the wastewater treatment plant and even the EPA-required NPDES (National Pollutant Discharge Elimination System) permit along with it. The two organizations work together closely to meet mutual goals, the main one being to operate the plant as effectively and cost-efficiently as possible.

Toward this goal, a recent project to reduce the cost of aeration in the 42-acre secondary lagoon led to the installation of solar-powered, long-distance circulation mixers from SolarBee, Inc. The city and the mill not only cut their energy costs, but the project also qualified for a $70,000 rebate from their serving electric utility, Columbia River PUD, with support from the Bonneville Power Administration’s Energy Smart Industrial (ESI) program

Secondary lagoon is focus of energy-reduction project

Built in 1970, the wastewater treatment plant was sized to meet the needs of the city and Boise Paper, which for 40 years operated as both a pulp and paper mill. A three-acre primary lagoon received loading from the city and smaller industries; a 40- acre secondary lagoon received effluent from the city's primary pond and from the mill’s primary clarifier.

To maintain adequate mixing, 24 mechanical surface aerators in the secondary lagoon ranged from 50 to 150 hp and operated approximately 2100 hp/day. The aerators were alternated to maintain thorough mixing; between six and seven ran constantly, and a SCADA control system rotated the aerators automatically depending on the level of dissolved oxygen.

However, in 2010, Boise shut down its pulp processing operations and today operates solely as a paper mill. Flow decreased from 35 million gallons a day to five million gallons a day. BOD (biochemical oxygen demand) went from 50,000 to 1,500 pounds a day.

As a result, the cost of aerating the larger lagoon skyrocketed. “Despite the significant reduction in loading, we had a great system and didn’t want to have to block off part of it because we weren’t using it,” said Aaron Kunders, superintendent of the St. Helens wastewater treatment plant.

Solar-powered circulation provides biggest savings

When the mill reduced its loading on the wastewater treatment plant, the focus changed from maintaining the aerators to reducing the electricity required to run them. “Boise Paper was working on a variety of energy reduction projects,” said Alison Dean, environmental engineer with Boise Paper, “including reducing energy at the wastewater treatment plant. We had been able to decrease aeration down to the point where mixing was the limiting factor. The secondary treatment lagoon was still expensive to operate, and we searched for ways to reduce those costs.”

Engineers at Cascade Energy Engineering, a BPA ESI program implementation partner, conducted a study at the request of Columbia River PUD, to consider energy-saving solutions at the plant. They considered three options in their study report:

1. Replace a portion of the existing surface aerator propeller blades to a lower pitch. This would reduce aeration power but also reduce mixing.

2. Replace a portion of the existing surface aerators with aspirating aerators. This would provide adequate aeration, but would create only localized mixing due to the small impellers used.

3. Replace a portion of the existing surface aerators with solar-powered mixers. This would reduce the runtime of existing aerators or the number of aerators while also improving mixing.

According to the study, the lower-pitched propeller blades would save 119,553 kW/yr; the aspirating aerators would save 91,747 kW/yr; and the solar-powered mixers would save 1,375,518 kW/yr.

Solar-powered mixers cut more than 50 percent of aeration horsepower

“To me, the choice was obvious,” said Kunders. “Due to the energy savings and the resources available through the ESI program, Columbia River PUD was able to provide a 70 percent rebate for the cost of the mixers. It brought the price so far down that our payback was two years. In two years we have a payoff and in four years we make that money back. Instead of these other little projects we were thinking of, this one cost a lot more up front, but it also has the biggest return.”

Seven SolarBee SB10000 v18 mixers are now installed in the second lagoon, spaced about four acres apart. Each SolarBee mixer can displace between 30 and 60 hp of aeration.

SolarBee mixers, available in solar-powered and energy-efficient grid-connected models, can supply most of the mixing energy required in any treatment pond—including partial- and total-mix systems and activated sludge basins—reducing the hours that the aeration system must operate. SolarBee’s patented long-distance circulation technology creates a near-laminar flow pattern that completely mixes the water column and improves distribution of dissolved oxygen. Active mixing also helps control odors, meet NPDES discharge permits, and improves BOD, TSS, ammonia and sludge reduction.

“Right now we’re saving over 50 percent of horsepower,” said Kunders. “We were at 550 hp/day before we added SolarBee mixers, and now we’re at approximately 250 hp. Plus, we’re getting nearly complete mixing at up to 20 feet deep in the 28-foot secondary lagoon. Typical aerators only mix the top five to six feet. And we’re not done turning off the aerators. We take them down in stages. We can still turn them off a little bit more but we don’t want to upset the lagoon. At first we were saving 40 percent, now we’re saving over 50 percent. Down the road we may turn them off more, but probably not until fall. During the summer, we take more advantage of the algae in the water. It’s producing oxygen so we bring up everything from the bottom to mix with the oxygen.”

Successful results prompt installation in city’s primary lagoon

The success of the project prompted the city to install two more SolarBee mixers in the primary lagoon, which receives loading from the city and a few smaller industries. “The two additional SolarBees will cause us a little more maintenance because there’s a lot more debris in that lagoon—rags and stuff—but we’re hoping to shut off at least one aerator a day throughout the year,” said Kunders.

Kunders says that the biggest payoff of the project is for taxpayers. “The cost for all these SolarBee mixers was offset so the cost doesn’t have to go to our taxpayers. Instead of paying 100 percent of it, the city probably paid 10 percent of it (between the rebate and the mill’s contribution), which is incredible. The citizens got a great deal on it.”

With the wastewater treatment plant now redesigned for cost-efficient operation, St. Helens is poised for industrial growth, and the local economic development association is actively seeking industry. The partnership has paid off for residents, city and mill—and for the community’s future economic well-being.

Source: http://www.solarbee.com/

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