Drop-In Deliverance

A new mixer and reactor save on energy and chemicals at a wastewater treatment lagoon in Indiana.
Drop-In Deliverance
Floats on either side support the fusion aerator/mixers.

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Dense algae and high pH levels plagued the lagoon at the Wingate (Ind.) Wastewater Treatment Plant in summer. Since 2007, nitrogen averaged 18.9 mg/L to 30 mg/L every January through March, exceeding the 7.2 mg/L winter discharge limit.

"An engineer at the Indiana Department of Environmental Management (IDEM) recommended building a mechanical treatment plant, but our 260 residents can't afford a $2 million facility," says town superintendent and Class 1 operator Ramon Knutti. "Even covering the lagoon with a $750,000 blanket was out of the question."

Then Knutti met Jim Bradley from Bradley Environmental in Ladoga, Ind. Bradley was looking for an opportunity to test his fusion aerator and Bobber moving-bed biological reactor. He offered to provide the equipment for free if Knutti would participate in monitoring how it worked.

The IDEM approved the pilot project and waived enforcement. The Wingate plant is the only one in the world using the technology, which solved all the issues and operated as designed.

Gallant efforts

Septic tanks service homes in Wingate; effluent flows by gravity through 4-inch sewers to two lift stations. The east station pumps to the center of town, then effluent gravity-feeds to the west station, which pumps it to the 35,000 gpd (design) wastewater treatment facility. Flows average 20,000 to 22,000 gpd.

The 14-foot-deep lagoon had two 5 hp surface aerators in the 492,000-gallon primary cell, and one 3 hp unit in the secondary and tertiary cells, each 233,000 gallons. Weekly, Knutti added one pound of enzymes to the lift stations and a pound each to the treatment cells to accelerate the process.

"Once temperatures fell below 39 degrees F, the enzymes didn't do anything, but I felt more comfortable adding them year-round to compensate for minimum sludge and low bacteria numbers," Knutti says. When algae turned the water deep green, Knutti applied a contact killer. "I used 10 gallons per cell at $95 per gallon and treated them twice a year," he says. "The effect was minimal."

During summer, he also increased chlorine from 0.8 ppm to 1.8 ppm to help kill algae in the contact tank. Then he added the chemical in winter to monitor its effect on ammonia. "I needed 300 ppm chlorine to remove 30 ppm ammonia, and that was too expensive," he says. "It also was dangerous to my discharge stream."

Searching for a better algae killer, Knutti found EarthTec algicide/bactericide, a biologically active form of copper ion from Supreme Turf Products. "It costs $29 per gallon and worked better," he says. "While it didn't kill all the algae, I now could see down into the water. That hadn't happened before."

The equipment

While waiting for the aeration system to arrive, Knutti installed an electric meter at the lagoon to monitor usage. "Other than that, we used the same electrical hookups that were in place for the surface aerators," he says.

Knutti, Bradley and Bill Blythe, lead biologist for Bradley Environmental, set six 1 hp fusion pumps three to a row and 15 feet apart in the first cell, and one in the third cell. The second cell received six 1 hp reactors for nitrification. Dual stainless steel cables anchored to eyebolts screwed into the shore prevent the units from drifting.

"We experimented with the best position for the aerators," says Knutti. "At one point, the primary cell short-circuited due to heavy rains. Moving the two middle aerators closer together solved the problem."

The fusion pump mixer/aerator pulls 600 gpm into the 8-inch inlet pipe from any depth or direction. One enclosed propeller lifts the flow, and a second propeller at the air/water interface creates a vacuum, drawing in oxygen at 1.5 lb/hp/hr. After mixing, eight adjustable outlets disperse the oxygenated water to any depth or location in the lagoon. With floats, the pump measures 40 inches high, 80 inches long, and 48 inches wide.

"Our intake pipes are 7 feet deep so as not to disturb the sludge blanket," says Knutti. "We set the discharge outlets to release toward the surface and outward, ensuring complete mixing from top to bottom and side to side."

The reactor, a 6-foot sphere, sits beneath the fusion pump. Inside the ball is 50 cubic feet of Kaldnes media, plastic wheels 3/8-inch in diameter and 1/4-inch wide. One cubic foot of media equals 260 square feet of surface area; 65 percent of it is protected to prevent the biofilm from being scraped away when the media is agitated.

The pump fills the ball with water and creates the air/water interface. As oxygenated water cascades down through the floating wheels, it replenishes oxygen, transfers nutrients, and cleans the media. The water is dispersed back to the lagoon through the adjustable outlets. The reactor with floats measures 144 inches long, 48 inches wide, and 96 inches high.

Pioneering study

Knutti, Bradley and David Denman from the IDEM Operator Assistance Program monitored the system since it was activated in September 2011. "No one has done a study from lagoon system to lagoon system," says Knutti. "We're testing everything to see what processes happen where." Purdue University professor Ernest R. Blatchley, P.E., published the initial study, available at www.bradleyenvironmental.com.

One fact the team learned is that the sludge layer varies from 12 to 24 inches deep to almost none. They are still investigating why. The system also lowered alkalinity from exceeding the pH 9 limit in summer to averaging 8.2 to 8.5.

The reactors provided the needed nitrification. "This past winter (2011-12), the water temperature was 33 degrees F, as cold as it ever gets," says Knutti. "Even then, ammonia levels averaged 2.5 mg/L." They were 0.02 to 0.04 mg/L in the summer of 2012.

The new system is also energy efficient. The plant's electric bill went from $910 to $550 per month, an annual savings of $4,320. Knutti saved an additional $6,240 annually by discontinuing the algicide/bactericide and the enzymes. With most of the algae gone, he also stopped increasing chlorine in the contact tank in summer.

"Lagoons are an extremely efficient, effective, inexpensive treatment process for small towns," says Knutti. "I believe this technology can save them, as the capital and operating costs are one-tenth the cost of mechanical plants."


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