Colby Hunt, an Illinois farmer and McDonough County Farm Bureau president, is always looking to continue his family's tradition of conservation. His latest completed project is a woodchip bioreactor that has been installed as an edge-of-field conservation practice, according to an article from Farm Week Now

"We always want to do what we are doing even better, so we put in the bioreactor to improve our stewardship efforts," he says. "My grandpa and dad started no-tilling and strip-tilling in the 1980s. They were also believers that every year you don't use field till is a year you 'pay' for it. So, since we have good draining soils, this was a way to replace a pond and silted-in dam."

Hunt started the project in 2017 and completed it in fall 2021. It looks like a row of woodchips spread in the grass strip along the edge of a field. The 15-foot by 60-foot woodchip bioreactor filters 0.117 cubic feet of water per second (approximately seven-eighths of a gallon and about 75,000 gallons per day) to prevent nitrates from flowing from the field. To help this, a control structure redirects water into the bioreactor, allowing wood chips become a nutrient for bacteria. The bacteria turns nitrate in the water into a process called denitrification. In addition, excess water moves past the bioreactor, and a dirt berm near it pushes surface water away. 

Luciano Alves de Oliveria, an ag engineering researcher at the University of Illinois, says water must be in the bioreactor for at least 3 hours so microbes can function. 

"From October to May, water spent an average of 5 hours in the bioreactor," Alves de Oliveria says. "The autosampler collected 80 samples during that time that showed a 5.6 pound-per-acre nitrate reduction and 22% efficiency, which is what we expected. During winter, nitrates were reduced 60-70% and in spring, 15-20%. We are working on designs to improve efficiency even more.”

According to researchers, the "sweet spot" for a woodchip bioreactor is 40 acres. It requires an open, grassy area with minimal surface inlets to prevent crop residue from getting into the structure. Woodchips should last about 10 years before needing replacement.

Learn more about the project in this video

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