Bioreactors are essentially subsurface trenches filled with a carbon source, mainly wood chips, through which water is allowed to flow just before leaving the drain to enter a surface water body. The carbon source in the trench serves as a substrate for bacteria that break down the nitrate through denitrification or other biochemical processes. Bioreactors provide many advantages:

• They use proven technology

• They require no modification of current practices

• No land needs to be taken out of production

• There is no decrease in drainage effectiveness

• They require little or no maintenance

• They last for up to 20 years