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SDSU Extension Testing Woodchip Bioreactors to Reduce Nitrate Runoff

Most South Dakota counties and the Legislature hesitate to stand in the way of the total industrialization of the prairie with sensible drainage regulations. But if our leaders don't want to stand in the way of wetland extinction, perhaps they'll at least look at reducing the pollution impacts by requiring field tile drainage systems to include woodchip bioreactors. No, we're not burning pine trees for electricity; we're using wood chips to filter and breakdown pollutants from field drainage.

Excavation for woodchip bioreactor. Photo by SDSU Extension, 2013.
Excavation for woodchip bioreactor. Photo by SDSU Extension, 2013. (Click for SDSU Extension article and larger photos.)

South Dakota State University scientists are testing five bioreactors at demonstration sites near Baltic, Montrose, Arlington, Beresford, and Canton. A bioreactor is a long trench, maybe a couple hundred feet long and four to six feet deep. The trench can be as narrow as three feet deep, but the SDSU Extension test bioreactors appear to be a good twelve feet wide. The SDSU scientists lay plastic to hold water in the trench, then fill it with wood chips. The trench is re-covered with topsoil and reseeded.

The big result SDSU Extension highlights is a reduction of nitrates by 30 to 70 percent. Nitrates come from natural and synthetic fertilizers and make downstream lakes unlivable with explosive algae growth. The woodchips become home to bacteria that eat the carbon and breathe out the nitrogen, which escapes to the atmosphere instead into hungry algae at your favorite fishing hole.

The Minnesota Department of Agriculture says bioreactors can support limited field operations and crop growth, minimizing the productivity impact.

So consider this, county commissioners and state legislators: if we can require factories to install smokestack scrubbers to protect air quality, how about we require farmers install bioreactors as drain tile scrubbers to protect water quality?


  1. Jeff Barth 2013.09.09

    Minnesota has a program, along with the NRCS, to help farmers pay for the installation of bio-reactors. There are many other technologies being developed that also remove contaminants.
    Also remember that folks in the city do not need permission to pump out their basements from their downstream neighbors and often that water has other chemical toxins. The city of Sioux Falls has dumped raw sewage into the Big Sioux too.
    (PS- Don't use wood chips from pine trees in your bio-reactor)

  2. caheidelberger Post author | 2013.09.09

    No pine chips? Why not, Jeff?

  3. Jeff Barth 2013.09.09

    The professor said that the bacteria does not like pine sap. You also don't want bark, leaves or twigs (from any tree) as they block the water flow through the reactor.

  4. interested party 2013.09.09

    Charcoal from pine works just fine.

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