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When Bart Sexton leaves his position as Oneida County’s solid waste department head on Dec. 10, he will leave behind him a legacy of ecological innovation that includes a project to treat wastewater leachate by using a hybrid poplar forest.

The project, which was originally developed from research conducted by Rhinelander DNR ecologist Jill Zalesny for a doctoral thesis while she was a student at Iowa State, combines cutting-edge technology from the USFS Northern Research Station in Rhinelander with a practical approach to dealing with contaminated wastewater produced by the Oneida County landfill.

“We’re basically using wastewater to grow trees faster,” said Sexton.

Zalesny’s research project involved three greenhouse experiments in which she fed eight varieties of hybrid poplars with clean water and leachate from the county landfill and compared them to trees fed with clean water and fertilizer. Three of the hybrid poplar varieties fared better with the leachate than with fertilizer.

Wastewater leachate is the liquid contaminant produced when rainwater filters through the landfill. The landfill is lined and the leachate is collected and transported by pipes into collection pools. Disposing of the leachate, in the past, has involved hauling it away to a wastewater treatment plant, a process that produces a significant carbon footprint.

Sexton saw Zalesny’s research as the chance to implement a photoremediation program for the county’s contaminated effluents. Photoremediation is the fancy name for letting the trees process the leachate through photosynthesis. Hybrid poplars developed by USFS researchers are the fastest-growing trees available, which makes them perfect for photoremediation.

“Because they’re so fast-growing, they are absorbing things quicker out of the soil and they need more water. Both of those attributes make them suitable for taking out contaminants,” said Sexton.

A hybrid poplar can take up 30 gallons of water and nutrients in a day, Sexton said, and it can also process large amounts of nitrates, ammonias, and volatile organic chemicals that are potential groundwater contaminants.

“The tree can either break that stuff down or it can be released into the atmosphere,” said Sexton. “We save on trucking and treatments costs and we reduce carbon emissions.”

Zalesny’s research showed that certain hybrid poplar varieties thrive on leachate because of valuable trace nutrients like boron that are present in the landfill. The Rhinelander landfill, as a result of the study, now uses hybrid poplars to contain contaminated wastewater at its facility.

The Oneida County solid waste department has used the experiment to create a treatment process for the effluent runoff created by the paper sludge it takes in from Wausau Paper’s Rhinelander production facility.

Sexton planted a 2.5 acre hybrid poplar forest on a hill above the paper sludge composting field in 2001. The paper sludge sits on a 5-acre bed of asphalt and as it breaks down, the water runoff is channeled into a holding tank. The landfill processes up to 4,000 tons of paper sludge each year. The effluent is full of nitrates and phosphorous that could contaminate the groundwater, but they are ready food for the poplar plantation up the hill. When the weather report shows no rain, Sexton’s crew pumps the effluent to the poplars.

Even though six of the last seven summers have seen drought conditions, the poplars are growing fast and cleaning wastewater as they grow. The trees are now over 30-feet tall and seven-inches in diameter at the stump. The forest at the county dump has attracted deer, voles, fishers, and even a pair of indigo buntings. If life gives you a heap of trash, plant a paradise.

Meanwhile, down the hill the treated paper sludge, absent of its contaminants, makes a perfect base for a topsoil compost when mixed with sand. Last year the compost sold out in October.

Treating leachate through photoremediation is just one of Sexton’s many innovative ways to ensure the solid waste department plans for the well-being of future generations.

“We’re leaving a lot of things for future generations to deal with and landfills are just one example,” Sexton said.

As a county enterprise fund, solid waste must earn its keep each year, and the recent drop in prices for recyclables has threatened the department’s budget.

Sexton hopes prices will rebound soon, so that his successor at the Oneida County landfill will have the chance to maintain the solid waste department’s reputation as a site for innovation and the advancement of ecological principles.

“We’re not in it for the money,” Sexton said. “We really are trying to work towards a greater good.”

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