How the humble wood chip cleans water around the world – sciencedaily

Australian pineapple, Danish trout and corn farmers in the American Midwest are not often grouped under the same agricultural umbrella. But they and many others who raise crops and animals face a common problem: excess nitrogen in the drainage water. Whether it flows to the Great Barrier Reef or the Gulf of Mexico, the nutrient contributes to harmful algal blooms that starve fish and other organisms for oxygen.

But there is a simple solution that significantly reduces the amount of nitrogen in drainage water, regardless of the production system or location: denitrifying bioreactors.

“Nitrogen pollution from farms is significant all over the world, from corn and bean farms here in Illinois to sugarcane and pineapple farms in Australia to the various ditch-lined farms in Belgium. It’s really exciting that bioreactors are bringing us together around a potential solution, ”says Laura Christianson, assistant professor in the Department of Crop Sciences at the University of Illinois and lead author of a new review article accepted for publication in American Society of Agricultural and Biological Engineers (ASABE) Transactions.

Denitrifying bioreactors come in many shapes and sizes, but in their simplest form, they are trenches filled with wood chips. Water from fields or aquaculture facilities flows through the trench, where bacteria living in crevices in the wood chips transform the nitrate into a harmless gas that escapes into the air.

This field-edge conservation practice has been studied for at least a dozen years, but most of what scientists know about nitrogen removal rates is based on laboratory replicas and experimental facilities. on a smaller scale. The USDA National Resource Conservation Service released a set of standardized bioreactor guidelines in 2015, in part based on Christianson’s early work in the field, and more and more American farmers are adding bioreactors. . They are also spreading to other countries.

The ASABE article is the first to synthesize the data available from full-size bioreactors on operating farms around the world.

“After you have gathered all the data, the message is that the bioreactors are working. We’ve shown a 20-40% reduction in nitrate from bioreactors in the Midwest, and now we can say bioreactors around the world are pretty consistent with that, ”Christianson says.

She adds that bioreactors, like all conservation practices, have their limits, but nitrous oxide emissions are not one of them.

“People are concerned that we are just transferring nitrate into the water for nitrous oxide, which is a greenhouse gas. We don’t know the whole story of nitrous oxide with bioreactors yet, but we can confidently say that they don’t create a huge nitrous oxide problem, ”she says. “They just aren’t.”

Christianson says farmers frequently ask her questions about water monitoring in bioreactors, so she and her coauthors detail the process in the ASABE article. She has also partnered with the Illinois Farm Bureau to create a series of step-by-step videos on how to test the water.

“For surveillance, there are two parts. You need to know how much water is flowing through the bioreactor and how much nitrogen is in the water, ”she says.

The short videos, which are aimed at non-researchers such as farmers and water quality volunteers, break down the process into five steps. Christianson notes that his students, postdoctoral fellows, and lab staff all came together to create the series.

The videos are available at

Christianson, who may be the world’s greatest bioreactor cheerleader, admits the surveillance guidelines and video series are a little self-serving.

“We’ve included recommended monitoring approaches so that more people build them, and then more people monitor them. And then we’ll have more data to show how well bioreactors work and how we can improve them. ”

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