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Biofilters can reduce herbicides in drainage water          Send a link to a friend

[FEB. 6, 2006]  URBANA -- A University of Illinois student has received top honors for research showing that a biofilter made from wood chips can significantly reduce the concentration of herbicides in water flowing through field tiles.

Paul Davidson, who did the research as a senior in agricultural and biological engineering, won the Undergraduate Student Paper Competition from the Water Environment Federation in Washington, D.C., as well as the regional competition in Rochester, Minn. He was also awarded first place in the 2005 Undergraduate Student Poster Competition of the American Society of Agricultural and Biological Engineers in Tampa, Fla.

Earlier research from the U of I had shown that a wood chip biofilter reduced the concentration of nitrogen (nitrate-N) in water draining from field tiles. Under normal conditions, bacteria in the soil naturally break down nitrates. A biofilter provides an organic carbon source, such as wood chips, which the bacteria feed upon. This allows the bacteria population to grow. And more bacteria break down more nitrates.

Davidson wanted to know if concentrations of herbicides, such as atrazine and alachlor, were also reduced with the use of a biofilter. So he placed the biofilter in a number of soil columns, and over a six-week period he applied six different combinations of the three chemicals, using different soil types and placing the filters at different depths. Two soil columns had no biofilter.

While there was little difference in the columns with no biofilter, runoff from the columns with biofilters showed a significant reduction in not only nitrate-N, but atrazine and alachlor as well. Nitrate-N was reduced from 25 parts per million to 0, atrazine went down from 25 parts per billion to 0.5, and alachlor went down from 25 parts per billion to 0.

"Depth made a slight difference but nothing significant," said Davidson, "so biofilters placed at any depth should have satisfactory results."  Reductions in the contaminants were also consistent across soil types.

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Davidson was also intrigued by some results of his study that he feels should be reviewed and investigated further.

He found that when all three contaminants were mixed in combination and applied in the presence of only the biofilter, the nitrate-N still showed a significant reduction in concentration, from 25 to 4.6 parts per million, and atrazine and alachlor both reduced from approximately 25 parts per billion to 3.27 and 2.41 parts per billion, respectively.

This finding could affect the method of application for agricultural chemicals.

"We need to run the tests again to confirm those results," Davidson said. "But if it's true that the nitrate-N concentration is reduced in the presence of atrazine and alachlor, you'd want to wait a length of time between applying your anhydrous and applying your atrazine or alachlor. Otherwise, they would react with your fertilizer and you would reduce the effectiveness of your fertilizer."

Prasanta Kalita, a professor of ag and bio engineering, had high praise for the young researcher.

"Paul worked night and day on this project," said Kalita. "We like to encourage the brilliant students in this type of study. Not everyone has the dedication to do research like this."

"I've never conducted research or written a research paper," Davidson said, "so this definitely helped me prepare for grad school. It was a great experience."

[University of Illinois College of Agricultural, Consumer and Environmental Sciences news release]

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