Evaluation of Woodchip Bioreactor Denitrification Kinetics

Agricultural subsurface drainage is a water management practice used to remove excess water in poorly drained soil. The use of fertilizers combined with subsurface drainage practice affects negatively surface water quality due to nutrient loss. Woodchip bioreactors have previously been used as a technology for removing nitrate from agricultural subsurface drainage. Understanding the mechanism that governs nitrate removal in woodchip bioreactors is crucial for field bioreactor design and application. The objective of this project is to determine woodchip bioreactor denitrification kinetics parameters under different operating conditions including hydraulic retention time, temperature and influent nitrate concentrations. Laboratory column experiments were conducted with influent nitrate concentrations varying from 50 mg N/L to 3 mg N/L at a HRT of 12 hours. The integrated Michaelis Menten equation was used to determine the denitrification kinetics parameters. The half saturation constant was found to be 2.17 mg N/L and the maximum nitrate removal rate was 0.86 mg N/L/H at 22 degree Celsius. The woodchips bioreactor achieved a denitrification rate ranging from 3.02 g NO3 - N/m3/d to 9.80 g NO3 - N/m3/d. At 5 degree Celsius, the bioreactor had a half saturation of 0.58 mg N/L and a maximum removal rate of 0.045 mg /L/H with denitrification rate ranging from 0.52 g N/ m3 /d to 0.28 g N/ m3 /d. At HRTs of 24 hours and 6 hours with an influent nitrate concentration of 10 mg N/L, a 98.70 % and 29.4 % percentage removal was achieved respectively. Nitrite accumulation was observed in all experiments with the highest nitrite effluent concentration of 1.4 mg N/L, observed at 50 mg N/L under 12 hours HRT. The results of this study a better understanding of denitrification kinetics in woodchip bioreactors