Department of Crop Sciences University of Illinois at Urbana-Champaign logo

Agronomy Day 2007

Home Welcome (Hoeft) Welcome (Dunker) Field Tour Presentations Tent Displays Credit & Thanks Sponsors

Removing Tile Drain Nitrates With Biofiltration: Let The Bugs Do The Work!

tour c
Richard Cooke Richard Cooke
Associate Professor
Department of Agricultural
and Biological Engineering
217-333-0944;
rcooke@illinois.edu
Malia Appleford Malia Appleford
PhD Student
Department of Agricultural
and Biological Engineering
217-244-8196;
applefor@illinois.edu
Paul Davidson Paul Davidson
PhD Student
Department of Agricultural
and Biological Engineering
217-244-8196;
pdavidso@illinois.edu

Application of inorganic nitrogen fertilizers can cause significant nitrate leaching from soils. In agricultural fields with subsurface drainage, this leached nitrate creates elevated nitrate levels in tile drainage water. These high nitrate concentrations can cause algae blooms that remove oxygen and kill fish in surface waters (eutrophication). Elevated nitrates in drinking waters have also been implicated in increased cancer risks and diseases like blue baby syndrome. Currently, there is a hypoxic (oxygen-deficient) zone the size of New Jersey in the Gulf of Mexico that is mostly attributed to agricultural nitrogen use in the Mississippi Valley.

fig 1

To help remove nitrates leached into tile drains, we have developed a biofiltration technology that works at the end of the tiles themselves. Biofiltration is a method in which contaminants in a fluid are removed by the metabolism of stationary microorganisms as the fluid flows past. Our biofilters (or bioreactors) consist of a of buried trench with woodchips through which the tile water flows before entering a surface water body. Microorganisms from the soil colonize the woodchips. These microorganisms “eat” the carbon from the woodchips and “breathe” the nitrate from the water. Just as humans breathe in oxygen and breathe out carbon dioxide, these microorganisms breathe in nitrate and breathe out nitrogen gas, which exits the biofilter into the atmosphere. Through this mechanism, called the denitrification pathway, nitrate is removed from the tile water before it can enter surface waters.

Ten biofilters are now in use in agricultural fields throughout Illinois, and control of nitrates overall from these biofilters is promising. During ordinary flow periods, more than 60% of the nitrate is removed from tile drains.

fig 2

The systems are easy to construct, inexpensive, and almost maintenance free. Each system consist of a diversion structure to channel the water through the woodchips, and a capacity control structure that can be adjusted to control how fast the water flows through the woodchips.

Our understanding of the bioreactor system is incomplete. Firstly, although the chemistry of the denitrification pathway is well-documented, the identity and community dynamics of microorganisms participating in denitrification in tile drain bioreactors is unknown, apart from our findings that both bacterial and fungal species are important to the process. The performance of particular media (woodchip) types is also unclear. While a “black box” approach is sometimes sufficient for effective engineering design, in this case a better understanding of the microbial community and factors that influence it may lead to enhanced control and performance of bioreactors. We are therefore using molecular biology tools such as FISH (fluorescence in-situ hybridization) to identify the microbial species contributing to denitrification in the biofilter and to compare the microbial communities from different biofilters. We are also conducting experiments to determine the effectiveness of different media types in removing nitrate and other common tile pollutants like pesticides, ammonia, and phosphate. Our preliminary research suggests that hardwood chips perform better than softwoods and that pesticides may also be removed from tile water by the biofilter system.