British Columbia Mine Reclamation Symposium

Performance of a pilot scale wetland for nitrogen removal from coal mine drainage Whitehead, Alan Joseph, 1952-; Malick, James G.; Kelso, Bryan W.; Cann, Jack W.


Nitrate releases from blasting residues at open pit coal mines can be an environmental concern because of potential eutrophication of receiving waters. Cost effective methods have not yet been identified to remove nitrate from large discharges such as occur at surface mines. Earlier studies in Canada and elsewhere have shown that wetlands may be a low-cost option for nutrient and metals removal from mine drainage. As a result of these studies, Environment Canada commissioned a 3-year study to investigate treatment efficiency, wastewater effects on vegetation, and wetland maintenance requirements. The selected study site was an operating coal mine on Vancouver Island, British Columbia. Effluent from the mine's settling pond was dosed with KNO₃ to simulate nitrate enrichment. This paper presents the results of the third year of wetland operation, from December 1989 to March 1991. Mass removal efficiencies of total-N and NO₃-N averaged 96.7 % and 90.2 %, respectively. Peak nitrogen removals occurred during the warm season, although removal in excess of 72 % continued in winter. NH₃-N and NO₂-N often increased through the wetland, although wetland effluent concentrations were within Canadian water quality guidelines. The results support the hypothesis that wetland systems can be effective in mitigating environmental impacts of mining. Key words: wetlands, nitrogen removal, coal mining, pilot scale, Canada.

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