Bioreactors
Filter excess nitrates from tile drainage water with natural processes using woodchip bioreactors.
Fighting Nutrients in the Trenches
A bioreactor is a buried trench filled with a carbon source like woodchips that filter tile drainage water. As water passes through the bioreactor, microbes use the carbon source to convert nitrate in the drainage water into harmless nitrogen gas, resulting in cleaner water for your community. Bioreactors are the second best edge-of-field option after saturated buffers.
Low Maintenance, High Impact
A bioreactor is an innovative water conservation strategy that has big impacts downstream, while minimally impacting farmers.
Small footprint
The area of a bioreactor is small, typically covering less than 0.05 acres. This makes it an excellent option for farmers who want to protect production acres.
No changes to crop management
Bioreactors are used at the edge of a field, so they do not change in-field land management practices.
No farm loss
Because they work well in existing filter strips, bioreactors usually require no land to be taken out of production.
Low maintenance
The woodchips last 10-15 years, requiring very little maintenance. After 10 years, they have to be recharged, a process that is usually covered with cost share.
Highly efficient
Over their lifespan, bioreactors have a better cost to impact ratio than cover crops. But they’re best used in conjunction with other practices.
How It’s Done
Most of the time, bioreactors are installed through a local “batch and build.” Batch and build is exactly like it sounds – local conservation professionals batch construction of several bioreactors in one neighborhood. This makes it more time and cost efficient. They’re 100% paid for and landowners may even receive a small payment. The group organizing the program does all the behind-the-scenes work so it takes very little landowner time – often just an afternoon to sign paperwork.
Benefits at a Glance
On average, one biroeactor removes 43% of nitrogen from water
It lasts 10-15 years before maintenance is needed!
Though phosphorus (P) is not the primary goal, it can also remove 16% of P from water
Because a bioreactor retains water for 4-8 hours, it reduces streamflow by 5%.
Myth vs Fact:
Myth or fact? bioreactors do not cause drainage issues in the field.
Fact!
In the case of heavy rain, there’s a bypass pipe that allows water to flow quickly to the outlet so it doesn’t back up into the field.
Myth or fact? bioreactors are effective even though they drain quickly without treatment during heavy rain events.
Fact!
Bioreactors still treat 40-60% of a drainage area’s water! That’s because peak flow doesn’t happen every day. Bioreactors are one of the most cost effective tools in the Iowa NRS.
Already have a bioreactor of saturated buffer? Check out this booklet that’s a straightforward guide to keeping your edge of field practice operating as designed.
Bioreactor Components
- Excess water drains and moves through the tile main.
- Inflow structure diverts water into an underground trench of woodchips. If there is heavy rain, it can immediately go through the bypass flow pipe.
- Denitrifying bacteria in the woodchips transform nitrate into nitrogen gas as water continues movin toward the outlet.
- An outflow structure controls the speed at which water leaves the bioreactor.
- Finally, it exits the field and into a local ditch or waterway.
Want to be part of the action?
We rcommend contacting somone at the Iowa Department of Agriculture and Land Stewardship’s Water Resources Bureau.
Cost-Share Options
The best way to get an edge-of-field practice installed is to sign up during a “batch and build” process. Learn more about batch and build in the video below.
Check with your local USDA Service Center for more cost share opportunities in your area.
Partner Spotlight
Our partner nonprofit, Agriculture’s Clean Water Alliance, led the installation of the first bioreactor in Iowa. They also monitored the bioreactors outflow to prove its effectiveness. This was critical in creating the first practice standard – a requirement for cost share. The bioreactor was placed in Mike Bravard’s farm in Greene County in the Raccoon River Watershed in 2008 and was “recharged” in 2017. You can check out pictures of the installation here. Read about the process in the 25-year anniversary ACWA annual report.
More Resources
Here are more helpful resources on watershed planning:
Clean Water Iowa shares success stories and videos showing how bioreactors are constructed
Applying Woodchip Bioreactors for Improved Water Quality publication (Iowa State University) has infographics that illustrate how bioreactors work
Woodchip Bioreactors: Removing Nitrate from Field Tile Lines video (Iowa State University) explains how bioreactors filter out pollutants from tile drainage water