Nitrate Removal From Subsurface Drainage By Denitrifying Bioreactor

Denitrifying bioreactors are an edge-of-field best management practice that reduce nitrate in runoff and subsurface drainage waters with minimum surface foot print and management requirements. The objectives of this study included evaluating a 173 m3 wood chip bioreactor for nitrate reduction and removal rates, the effects on phosphorus, and the impacts of the bioreactor\u27s physical characteristics on effective nitrate reduction During periods of flow, weekly water samples were collected for lab analysis of nitrate+nitrite (nitrate-N), total nitrogen (TN), soluble reactive phosphorus (SRP), and total phosphorus (TP) and measurements were made of water temperature, dissolved oxygen, pH, oxidation reduction potential, temperature, water levels, and flow. Nitrate-N concentrations were reduced on average by 94% in 17 observed drainage events, influent nitrate-N concentrations from 9.4 mg N/L to effluent 0.58 mg N/L SRP concentrations increased as water moved through the bioreactor. Influent SRP concentrations averaged 0.02 mg P/L (0- 0.16 mg P/L) and effluent concentrations averaged 1.29 mg P/L (0.03- 5.52 mg P/L). Physical characteristic data of the bioreactor displayed conditions conducive for denitrification to occur however o quantitative relationships could be made between physical characteristics of the bioreactor and its effective nitrate reduction