Rates of Nitrate and Perchlorate Removal in a 5-Year-Old Wood Particle Reactor Treating Agricultural Drainage

A 5-year-old wood particle reactor treating agricultural tile drainage in southern Ontario was monitored for its ongoing ability to treat both nitrate (NO3-) and perchlorate (ClO4-). Prior to sampling undertaken in the fifth year of operation, a highway safety flare containing ClO4- was immersed in the inlet pipe elevating influent ClO4- concentrations to up to 33.7 mu g/L. ClO4- removal rates were inhibited in the presence of more than 1 to 2 mg/L NO3--N, but increased rapidly to about 60 mu g/L/d upon NO3- depletion. Nitrate removal rates, measured subsequently in the sixth and seventh years of operation, varied with temperature in the range of 2 to 16 mg N/L/d, but remained similar to rates measured in the second year. Additionally, no deterioration in the hydraulic conductivity (K) of the coarse core layer (0.5 < K < 5 cm/s) was detected over the monitoring period. These results demonstrate that coarse wood particle media can deliver stable NO3- removal rates and can remain highly permeable over a number of years. The media can also provide high removal rates for other redox sensitive contaminants such as ClO4-. The ability to directly measure the reactor flow rate, in this case via an outlet pipe, greatly simplified the task of estimating hydraulic properties and reaction rates.