Bioreactors encouraged as a means of removing nitrates

ANKENY — A bioreactor might sound like a complicated machine. It isn’t.

At least the one on display at the Iowa Soybean Association’s July 1 water quality open house didn’t seem elaborate. It’s a simple mechanism that pumps water through wood chips in a way that removes nitrates from runoff before sending it downstream.

Such a tool could be a valuable part of the battle to get nitrates out of water that is leaving farms and ranches and into rivers and lakes used for drinking water. The Des Moines Water Works lawsuit against Sac, Buena Vista and Calhoun counties is based largely on the amount of nitrates sent downstream.

On July 24, the soybean association, Iowa Learning Farms, the Monroe County Soil and Water Conservation District and the Agri Drain Corporation are putting on a bioreactor field day in southern Iowa. A bioreactor is being installed at the Tom Dykstra Farm, located just south of Eddyville in Wapello County.

The model on display earlier this month at the ISA’s Ankeny campus rested on a couple of tabletops. Environmental Projects Manager Keegan Kult conducted a full-motion demonstration of a water bioreactor, showing how many elements can be captured using a wood-chip type of device.

Fields that are already set up with a low-lying central water collection point, with, for example, a ditch or a drain tile network, are already partly set up for bioreactors. The arrangements vary in size, but most bioreactor units alone are about the size of a large trunk or box.

The unit is then typically partially buried underground, with a door or access panel facing up, although it could be above ground. Water is then fed through it via drainage pipes.

The wood chips end up eating the nitrates. A variety of wood chips can be used, but it should be a kind that soaks up water, rather than repels it, Kult said.

The flow of the water is powered by gravity, although valves and intake can be adjusted based on need for more or less flow. Kult said major adjustments to settings can be made about three times per year.

“We’re really not worried about what that water does until a couple weeks before you get in there in the spring to treat fields,” Kult said. “Then, you can change it again after all your field operations are done, and then again in the fall. You can do it more often if you like, but realistically, there isn’t enough time to see how well the adjustments are working.”

Kult said one of the main reasons bioreactors aren’t on every Iowa farm is cost.

Installation typically costs $2,000 to $3,000, as there aren’t many contractors around who can and will do installations. Some larger projects and units might run a farmer a cost of $5,000. He said the industry is still in its infancy.

While the ISA has been involved with bioreactors since about 2008, and has learned a great deal, the units aren’t the type of devices one can yet purchase at a store and put in as if it were an air conditioner.

There are no bioreactors set up in Jasper County, according to Watershed Coordinator Terry McNeely of Clean Water Iowa. A goal for the Van Zante Creek Watershed, which runs across southern Jasper County, is to establish a bioreactor there soon.

“Most current bioreactor designs are successful at reducing the amount of nitrate in drainage areas from 30 to 80 acres,” McNeely said. “To date, most bioreactors in Iowa are about 100 to 120 feet long and 10 to 25 feet wide. Typically, no land is taken out of production for a bioreactor. Because bioreactors tend to have an orientation that is long and narrow, they fit well in edge-of-field buffer strips and grassed areas.”

McNeely said the wood chips are, by themselves, a once-in-a-generation investment. The bioreactor itself could last much longer.

“The lifespan of a bioreactor is estimated to be 15 to 20 years, after which the woodchips would be replaced to continue effectively treating water,” McNeely said.

The July 24 field day at the Dykstra farm is meant to show many in the public one of the ways farmers are combating the amount of nitrates released into watersheds. Kult will be joined by Dykstra, the host farmer, and two water quality specialists at the event.

Reservations should be made by Thursday. Send an email to McNeely at ilf@iastate.edu or call 515-294-8912.

Contact Jason W. Brooks at 641-792-3121 ext. 6532 or jbrooks@newtondailynews.com