Nashua research farm studying bioreactor

By Jean Caspers-Simmet

NASHUA, Iowa —A bioreactor built a little over a year ago at Iowa State University’s Northeast Research Farm near Nashua will help researchers decide how best to build such structures to remove nitrogen from subsurface agricultural drainage water.

Farmers got to see the bioreactor and its water monitoring equipment at a recent field day on the research farm.

Chad Ingels, ISU Extension Watershed Project specialist, explained that the bioreactor’s purpose is to reduce nitrates in water to improve its quality.

“Water flows into the bioreactor from the tile line, through the woodchips, and back out to a tile line,” Ingels said. “Anaerobic bacteria feed off the carbon from the woodchips that fill the bioreactor and convert nitrates into a gaseous form of nitrogen by using the oxygen part of the nitrate. It functions similar to a wetland in this respect.”

Finished Biofilter

The bioreactor is placed near a tile outlet or further into a field. Most are conveniently placed in a waterway or grass strip. A water control structure diverts tile water into the bioreactor, but when tile water flow exceeds capacity it allows water to bypass the bioreactor.

The Nashua bioreactor is 120 feet long, up to 15 feet wide and 3.5 feet deep. In cross section it is trapezoidal-shaped, wider at the top than the bottom. It is filled with two semi-loads of wood chips, the food source for bacteria. Landscape fabric is placed over the top of the wood chips and a foot of soil is layered over that.

Cost varies depending on the drainage area being treated, Ingels said. Costs will likely exceed $2,500 for woodchips, control structures, backhoe work and tiling supplies. The Nashua bioreactor cost $15,000, but at least half of that amount was water monitoring equipment, which generally wouldn’t be needed, Ingels said.

The Nashua bioreactor includes two large black culverts not ordinarily a part of a bioreactor. These are used for viewing and research purposes.

The Coldwater/Palmer Watershed Council sponsored installation of the bioreactor after approaching the research farm board and researchers about the need for evaluating the efficiency of bioreactors in northeast Iowa.

The Nashua structure will be used to gather data about bioreactors, how they are constructed and if they are effective. The limited information that is available shows anywhere from 10 percent to 90 percent nitrate removal depending on many variables — including age, Ingels said.

The life expectancy of a bioreactor is estimated to be 10 years, although more research is needed on that as well.

ISU researchers are measuring the amount of water flowing through the bioreactor and monitoring the amount of nitrate in the water going into and out of the Nashua bioreactor. They will also study the degradation of the wood chips.

“This is the most fully equipped site in Iowa to gather the information we need,” Ingels said.

Research farm superintendent Ken Pecinovsky said there is a nitrate removal wetland about a mile away from the bioreactor, which he hopes that they can monitor if research dollars can be found. In addition, the bioreactor is near the farm’s extensive nitrogen water monitoring site.

“This is a nice complement to that work,” Pecinovsky said.

Link to orginal article: http://www.agrinews.com/nashua/research/farm/studying/bioreactor/story-2733.htm

Filling Bioreactor