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Conservation Choices: Denitrifying Bioreactor

Denitrifying Bioreactor

Denitrifying BioreactorWhat it is

An edge of field structure containing a carbon source, such as wood chips, installed to reduce the concentration of nitrate-nitrogen in subsurface agricultural drainage flow via enhanced denitrification.

How it helps

  • Bioreactors help improve water quality by reducing the nitrate-nitrogen content of subsurface agricultural drainage flow.

Planning ahead

  • Do water samples show there is a need to reduce nitrate-nitrogen concentration in subsurface drainage flow?
  • Do you have a good location at the edge of a field near an outlet pipe for a bioreactor?

Tech Notes

A bioreactor should be designed to:

  • treat peak flow from a 10-year, 24-hour drain flow event.
  • treat at least 15% of the peak flow from the drainage system.
  • treat at least 10% of the peak flow from the drainage system if systematic monitoring will be taking place through NRCS.
  • use locally proven criteria that will result in the treatment of at least 60% of the long-term average annual flow from the drainage system.
  • achieve at least a 30% annual reduction in the nitrate-nitrogen concentration of water flowing through the bioreactor.

Media Chamber:

  • Use a medium for a carbon source that is reasonably free from dirt, fines, and other contaminants. Distribute the media within the bioreactor for a uniform flow path.
  • Use geotextile or plastic lining for the bottom, sides, and top of the bioreactor to prevent migration of soil particles into the bioreactor.
  • Design the bioreactor for an expected life of at least 10 years.

Water Control Structures:

  • Design water control structures to provide the required capacity and hydraulic retention time.
  • Evenly distribute and collect water in the upstream and downstream ends of the media chamber.
  • Allows for completely draining the media chamber to facilitate management and maintenance.


  • NRCS will provide an operation and management plan to the landowner.

Iowa Practice Standard