Performance evaluation of four field-scale denitrification wood chip bioreactors treating agricultural tile drainage water in a cold climate.

Field-scale wood chip based denitrification bioreactors were installed in St. John’s Research and Development Centre, in Newfoundland and Labrador to reduce the amount of nitrate in agricultural drainage water. Denitrification is a microbially-catalyzed reaction which occurs in the system when microbes use the wood chip as a carbon source to convert nitrate to nitrogen gas. Although it is a well-known technology that a denitrifying bioreactor can maintain high nitrate-removal efficiency, there is a question about how well these systems perform under cold vs warm temperature conditions. The key objective of this study is to assess the performance of wood chip bioreactors (WB) in a cool maritime climate. Four bioreactors filled with similar sized Black spruce wood chips (25-40 mm) received drainage water from 12 experimental plots (22 x 60m). Four forage mixture treatments were planted using an incomplete Latin square design with 3 blocks. Water from the tile drains was collected in a containment tank (1.0 m L x 1.0 m W x 0.4m H) and then routed to wood chip bioreactor for nitrate treatment. In 2016, tile drainage water samples were collected from the inflow and outflow of the bioreactor. Nitrate- N analysis was analyzed with Ion Chromatograph (Model: 881 Compact IC Pro, Manufacturer: Metrohm). The inflow NO3-N concentrations were 49.9, 47.7, 20.4 and 54.4 mgL-1 for WB 1-4, respectively. Reductions in NO3-N were 24.5, 21.3, 3.7 and 2.5 mgL-1 for WB 1-4, respectively. This study showed good overall performance of the bioreactor under cool conditions and all bioreactors tested reduced NO3-N by a similar amount.