Author : Mehraj U Din Dar 1
Date of Publication :17th August 2017
Abstract: Subsurface agricultural drainage can allow large gains in agricultural productivity in the Midwestern United States. There is, however, concern about pollutants moving through these systems. One specific water quality concern is nitrate, a form of nitrogen that moves readily through the soil and often can be present in high amounts in clear drainage waters. The water quality of our local streams, rivers, and lakes can be negatively impacted by nitrate in tile drainage. Moreover, because many streams and rivers in this region lead to the Mississippi River, nitrate in mid-western agricultural drainage also contributes to the hypoxic zone (or Dead Zone) in the Gulf of Mexico. Fortunately, there are a number of practices that can reduce the amount of nitrate in drainage water. Woodchip bioreactors are a new option to reduce the amount of nitrate in drainage before it gets to local surface waters. This technology describes key questions relevant to this innovative approach to water quality. A woodchip bioreactor is made by routing drainage water through a buried trench filled with woodchips. Woodchip bioreactors also are known as DE nitrification bioreactors, a name that is slightly more descriptive of the actual process occurring inside the bioreactor. DE nitrification is the conversion of nitrate (NO3-) to nitrogen gas (dinitrogen, N2) that is carried out by bacteria living in soils all over the world and also in the bioreactor. These good bacteria, called denitrifiers, use the carbon in the woodchips as their food and use the nitrate as part of their respiration process. Because these bacteria also can breathe oxygen, providing anaerobic conditions through more constantly flowing tile water helps ensure that the bacteria utilize the nitrate. Providing these denitrifiers an ample supply of carbon to eat and giving them anaerobic conditions in the bioreactor offers them a perfect environment to remove nitrate from drainage, and in this way we can get rid of the nitrate from the drainage water which ultimately joins other water bodies and can create serious health hazards like the most coveted Blue baby Syndrome. A typical woodchip bioreactor can treat 30 to 80 acres of nitrate infested fields with an annual nitrate load reduction of about 10 percent to greater than 90 percent depending on the bioreactor
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