Bioreactor to remove nitrate from tile water

WAVERLY — A new bioreactor will reduce nitrates in tile water draining off Tom Manson's corn field just off Highway 63 northeast of Waverly.

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WAVERLY — A new bioreactor will reduce nitrates in tile water draining off Tom Manson's corn field just off Highway 63 northeast of Waverly.

Sampling tile water before it flows into the bioreactor and again after it has been treated will provide more information on how successful the practice is in reducing nitrates.

Manson is interested in the results.

"It doesn't look like much now that it's built," Manson said, pointing to the mounded soil with water control structures at each end. He will seed the ground to grass this fall.

The project is funded by the Heartland Water Quality Project, a four-state effort led by Iowa State University, said Chad Ingels, Extension watershed specialist. Extension is making a video to document the project.


"It is important that some practices are put out there and farmers take time to evaluate what results are coming out of them," Ingels said. "It will take a lot of practices and a lot of farmers adjusting their management to make the Iowa Nutrient Reduction Strategy work. Bioreactors are one option."

To build the denitrifying bioreactor, an excavator dug a trench 100 feet long, 10 feet wide and four feet deep in a grass strip between the edge of Manson's corn field and Crane Creek at the end of August. The trench was lined with plastic, filled with two semi loads of wood chips, covered with geo-textile fabric and topped with soil.

Drainage water is routed into the bioreactor through an inflow water control structure. Denitrifying bacteria living in the soil use carbon from the wood chips as their food and nitrate from the tile water as part of their respiration process. An outflow water control structure keeps the water in the bioreactor long enough for the bacteria to have time to remove nitrate before the water flows into Crane Creek. The control structures can by-pass the bioreactor during high-flow events.

Manson grows 125 acres of continuous corn which he fertilizes with manure from the 6,000 hogs he finishes each year. About 30 acres drain into the bioreactor.

"They were interested in this field because I use hog manure," Manson said.

He participates in the Crane Creek Watershed Project, a group organized by Ron Lenth, Bremer County Extension coordinator. Lenth has monitored water quality in Crane Creek during several growing seasons. One of his sampling sites is Manson's farm. Crane Creek dumps into the Wapsipinicon River.

"We want to know if a lot of nitrogen is getting into the creek," Manson said. "We also want to know how much a bioreactor reduces that."

Manson's site was selected in part because it's right off Highway 63 and easy to reach. There is a grassy area for parking for field days or tours.


Manson follows a manure management plan, has built terraces and planted windbreaks around his house and hog buildings.

"Around the hog buildings, it helps diffuse the odor," he said.

He has a major waterway that runs from the west side of his farm just about to Highway 63.

"We're a lower farm and back in the 1970s everyone's water was dumping on us," Manson said. "I got the neighbors together and we formed a pooling agreement. We received cost share for half the price of a mutual main and five of us landowners paid the other half. We dump into that and the water outlets at Highway 63.

He farms on the contour some, uses minimum till and knifes in all his manure.

"It all helps keep the soil in place," he said.

Manson is grateful to Lenth for his efforts to bring water quality and nutrient management information to Bremer County farmers.

"Ron was right down in the trench working on those really hot days," Manson said. "He's a super guy."


With all the attention on nutrient reduction, a bioreactor is one of the practices that has the highest potential to reduce nitrates, said Lenth. Bioreactors don't require a large land areal and they don't take land out of production.

Iowa Nutrient Reduction Strategy documents show an average expected nitrate reduction of 43 percent for all water, Ingels said.

"We're getting a lot of questions from farmers," Ingels said. "We want to get more data on what bioreactors might be able to do."

If the nitrate reduction data Lenth gathers from the bioreactor is positive, Manson said there will be more bioreactors built in the area.

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