Nine years ago, one of the first bioreactors in Iowa was installed on Mike Bravard’s farm near Jefferson, Iowa. Last week, that bioreactor was reconditioned, all in an effort to make water cleaner for people downstream. Water quality data at this site in central Iowa has shown the practice reduces nitrate levels by 20% to 60%. In fact, over its first seven years of use, the bioreactor removed 1,500 lbs. of nitrogen at a cost of $6 to $8 per lb. of nitrogen removed. Chris Hay, senior environmental scientist at the Iowa Soybean Association, in his presentation at the event, reported that with recent improvements in design and available materials, those costs of removal are moving to under $3 per lb. of nitrogen removed.
“We’re happy with its performance to date overall,” says Harry Ahrenholtz with Agriculture’s Clean Water Alliance. “We projected a 10- to 15-year lifetime use, but now with the recharge and the improved uniformity of the newly introduced wood chips it should last another 10 to 15 years.”
A bioreactor is a trench filled with wood chips through which drainage water is routed. Denitrifying bacteria in the wood chips convert nitrate in the drainage water into inert nitrogen gas, reducing the amount of nitrate delivered to the outlet.
Ahrenholtz says there are about 40 bioreactors in Iowa now. The ACWA worked closely with Iowa State University and the project was primarily funded by Agriculture’s Clean Water Alliance and the Sand County Foundation. The Bravard and subsequent bioreactor demonstrations resulted in USDA recognizing the value of the practice. Cost-share funding is now available for these types of projects.
Bravard’s bioreactor is 50 ft. x 25 ft. and treats about 70 acres. It’s landscape-specific, meaning you need underground tile and other factors to ensure the science works as needed. Edge-of-field practices like this one, along with controlled drainage, saturated buffers, wetlands and other practices will provide nitrogen loss reduction in the range of 40% to 50%.
The initial cost of the bioreactor was about $10,000; the recharge was about half the cost of the original installation.
Mike Bravard and his son, Lucas, hosted a group of interested farmers and journalists recently to show their recharged bioreactor.
Harry Ahrenholtz (left), chairman of Agriculture’s Clean Water Alliance; and Roger Wolf, director of environmental programs and services for the Iowa Soybean Association, help field-day attendees understand bioreactor practices.