DENITRIFICATION OF AGRICULTURAL DRAINAGE USING WOOD-BASED REACTORS

Two denitrification reactor designs, utilizing alternate layers of fine and coarse wood particles, were monitored for their ability to achieve passive, maintenance-free nitrate removal in agricultural tile drainage. A lateral flow design was tested over a 26-month period on drainage from a cornfield in southern Ontario, and an upflow design was tested over a 20-month period on drainage from a golf course, also in southern Ontario. At the cornfield site, flow through the reactor averaged 7.7 L/min at an average influent NO3 concentration of 11.8 mg N/L, and removal averaged 3.9 mg N/L. At the golf course site, flow through the reactor averaged 7.8 L/min at an average influent NO3 concentration of 3.2 mg N/L, and removal averaged 1.7 mg N/L. Areal removal rates averaged 2.5 g N/m2/d in the cornfield reactor and 0.95 g N/m2/d in the golf course reactor, and are about an order of magnitude higher than rates reported for other passive treatment systems such as constructed wetlands even though average operating temperatures were relatively low (7°C to 9°C). Mass balance calculations indicate that carbon consumption from denitrification was <2% per year; thus, these reactors have the potential to operate for a number of years without the need for media replenishment. Both reactors were successful in achieving maintenance-free operation during all seasonal conditions, including unassisted startup after drought and freeze periods. Reactors such as these have the potential for a range of applications in agricultural settings because of their low cost and low maintenance characteristics. They are most usefully applied in the treatment of base flows rather than peak flows and can be readily used in combination with other treatment systems such as constructed wetlands.