Denitrification beds and walls

Professor Louis Schipper from Waikato University talks about a simple design approach to remove nitrate from groundwater or surface water discharges. He also explains the differences between denitrification walls and beds.

Jargon alert

Denitrification is part of the nitrogen cycle. It is a process where bacteria in soil break down nitrate and convert it into atmospheric nitrogen gas.

Transcript

PROFESSOR LOUIS SCHIPPER

Denitrification beds and walls are an approach that we have been developing over the last decade or so, and it’s essentially a simple approach for removing nitrate from either groundwater or from surface discharges. Essentially, they contain woodchips or sawdust, which provide an energy source for bacteria that grow on the woodchips naturally, and they convert nitrogen into nitrogen gas and release that back up into the atmosphere where it’s essentially harmless.

Denitrification walls are essentially for treating groundwater. They’re trenches that have been dug down below the water table and then sawdust is added, and that material’s returned back into the trench, and that intercepts groundwater with nitrate in it.

A denitrification bed is a large container filled with woodchips and you pump nitrate-containing effluent or discharges from drainage from underneath agricultural land into one end of that bed and it stays fully saturated. And the woodchips slowly degrade with time and support denitrifying bacteria, which convert the nitrogen coming in with the effluent to nitrogen gas. So one, a denitrification wall is for treating groundwater, and a denitrification bed is for treating pipe flow of effluent.

We are seeing them particularly being taken up in the mid-west of the US, in the corn belt, and then also on the east coast of the US. And in both of these areas, they are trying to protect large parts of the sea, surface water bodies like the Gulf of Mexico or the Chesapeake Bay area, and so people are starting to put in these denitrification beds particularly to try and reduce nitrate pollution of surface waters.

Acknowledgements: Professor Louis Schipper, University of Waikato Anna Carter