Assessment of Wood Chips and Agricultural Residues as Denitrifying Bioreactor Feedstocks for Use in the Canadian Prairies

Highlights Performance of denitrifying bioreactors in Alberta was evaluated. Barley straw was more effective in reducing nitrate compared to wood chips. Hydraulic retention time, feedstock, and season are the primary factors affecting nitrate removal. Abstract. This study evaluated the performance of pilot-scale denitrifying bioreactors (LWD: 6 × 0.6 × 1m) filled with different carbon substrates, including barley straw, hemp straw, and woodchips, for removing dissolved nitrogen from simulated subsurface drainage at two representative geographic locations in Alberta. In this study, the bioreactors were tested under varying hydraulic retention times (4, 8, and 12 h) in the spring, summer, and fall of one year. Tracer studies were conducted to evaluate flow and dispersion characteristics. The mean of nitrate removal efficiency ranged from 19% to 87% during the spring, 44% to 95% during the summer, and 21% to 68% during the fall. We found that barley straw was more effective in reducing nitrate (45% to 95%) compared to wood chips (19% to 54%). This study is the first testing of the effect of different biomass types and hydraulic residence times on bioreactor performance in the Canadian prairies (Alberta) and will allow agricultural producers and regulators to assess the suitability of these systems within the region. Keywords: Bioreactor, Denitrification, Water quality, Wood chips, Agricultural residues, Subsurface Drainage.