Woodchip bioreactors are at the forefront of conservation technology

This edge-of-field practice utilizes biological denitrification

While it may not be evident above ground, below ground is a network of tile connected to a trench of woodchips on Michael Ganschow’s Bureau County, Illinois farm. That trench of woodchips is home to microbes cleaning the drainage water of nitrates before it leaves his corn and soybean fields to nearby surface waters.

The woodchip bioreactor (or denitrifying bioreactor) is considered a new edge-of-field conservation practice that can reduce nitrate levels by 15-60% on 30-80 acres of tile-drained fields.

Ganschow was first introduced to the concept in 2018 as a member of the Illinois Farm Bureau Conservation and Natural Resources Strength With Advisory Team (SWAT). SWAT members are taught to address the state’s nutrient loss reduction goals with a combination of practices; a whole systems approach to conservation farming.

“I looked at utilizing a bioreactor as an edge-of-field practice that I could use on my farm along with nutrient management, cover crops and a variety of different things that I'm implementing to try to help solve this nutrient loss problem,” he says.

How it Works

Bioreactors are being studied and evaluated for their effectiveness through partnerships between university researchers, private landowners and USDA’s Natural Resources Conservation Services (NRCS).

Dr. Laura Christianson at the Department of Crop Sciences, University of Illinois, and her team don’t just sit in the lab running experiments. They are out on research farms across the state building, monitoring, and collecting water samples. “We are really trying to figure out how bioreactors are working and if they’re working for farmers.”

A woodchip bioreactor has two main components: one or more water control structures intercepting an existing tile line, and a trench filled with woodchips. Bacteria live on the woodchips, which serve as a food source and a substrate for the water to flow through. The bacteria convert nitrogen to nitrogen gas as water flows through the trench. The setup is designed so that the tile water can be treated while still properly draining the crop field.

Christianson explains, “With a woodchip bioreactor, denitrification is the exact process that we're trying to get to happen. This natural process that happens in our soils can be considered a loss of nitrogen when it happens in the field. But we do want denitrification to happen inside our bioreactor because that’s how the bioreactor cleans water. It's enhancing the natural process of denitrification.”

Each bioreactor is also designed with a bypass flow pipe connected to the water control structure. The bypass routes water away from the fields and the trench if there is a significant amount of runoff and drainage.

During rainy seasons, nutrient loss increases, but as Ganschow says, “By using these edge-of-field practices, we can take what the weather has given us, to a degree, and we can actually treat water before it gets downstream.”

In a year like 2019, when rainfall and flooding plagued the Midwest, farmers needed the bypass on a bioreactor. “There are simply times where there is just too much water. The bypass will relieve head pressure in extreme circumstances,” explains Ganschow. “At that rate, you're treating some water and you're not treating the rest, but still trying to get a good average out of it.”

How to Get Started

Dr. Ruth Book, Illinois State Conservation Engineer, and her team recognize that as the concept and design process are still being developed, bioreactors are a little experimental. “It’s new enough that we still don’t have all the answers, so the research that Dr. Christianson is doing is vital for our design work,” Book says. “We're out in front of things just a little bit more than usual with the bioreactor. We tend to stick with the tried and true for conservation practice recommendations. So, understand that the bioreactor might not be for everybody right now. It's for those folks who are interested in being the upfront people who want to demonstrate this good stewardship and this new practice to their neighbors.”

Dr. Christianson’s experience points toward a rule of thumb of “10k for 10 years” though costs will vary by site. A bioreactor costs roughly $10,000 and will treat water for about 10 years before the woodchips need to be excavated and replaced.

Financial assistance is available through the state and through federal NRCS, Environmental Quality Incentives Program (EQIP), the Conservation Stewardship Program (CSP), and the Farm Service Agency’s Conservation Reserve Program (CRP).

“In Illinois, we actually have a special statewide Conservation Drainage funding pool in EQIP that allows farmers more likelihood of being funded. With the special funding pool, there is less competition,” says Book.

Book recommends going to your local NRCS office first to learn how a bioreactor could work on your land.

What’s on the Horizon

While Christianson and her team collect data and monitor existing bioreactors, they are also working to develop the next generation of on-farm solutions.

“Where we are with the research right now is figuring out how to design bioreactors to treat 200-400 acres and how to do that well,” explains Christianson. “Scale is also a focus, so how can we make bioreactors smaller but work better? We know right now it’s a trench full of woodchips, but how can we rethink that and maybe have two smaller trenches that can treat more water, rather than just one big trench?”

Ganschow’s bioreactor is one of many that Christianson monitors. When the bioreactor was installed in 2018, Ganschow selected a specific tile outlet where he was already collecting water quality data, which he continues to do today. The bioreactor treats about 17 acres on his farm. He says, “I'm curious to see going forward what the results are going to be out of it. How efficient it will be at catching nutrients that I'm unable to catch through nutrient management or utilizing cover crops.”

Like anyone, Ganschow wants to see the nutrient loss problem resolved. But as he says, “This problem didn't happen overnight and it's not going to be solved overnight either. It's going to take a serious commitment from a lot of operators to make a difference and I believe we're starting to see that push happening in Illinois.”

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