Improving the efficiency of wood chip bioreactors for removing nitrate from drainage water
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Date
2017
Authors
Whyte, Katie Anne
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Abstract
Wood chip bioreactors can be installed at subsurface drainage outlets in order to decrease the concentration of nitrate (NO3-) discharged to receiving waters. A laboratory column study was conducted to determine NO3-N removal in wood chip bioreactors under saturated and unsaturated conditions. Nitrate-N was added at a concentration of 100 mg/l to columns filled with wood chips and effluent samples were collected daily for NO3-N analysis. Once the denitrifying bacteria communities had established in the bioreactors, NO3-N removal under saturated conditions (85.4 and 92.8%) was significantly higher (p < 0.0001) compared to unsaturated conditions (2.8 and 21.4%). Using these results, in-field wood chip bioreactor sizing was determined for four different daily precipitation rates in southern Manitoba. The bioreactors were designed to maintain saturated conditions. The bioreactor volume was based on a three-day hydraulic retention time (HRT) to attain NO3-N removal for the chosen precipitation values.
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Keywords
Subsurface agricultural drainage, Tile drainage, Nitrate reduction, Denitrification, Edge-of-field bioreactors, Wood chip bioreactors