In 1995, Microbial Technologies conducted laboratory and field investigations to develop a wetland treatment system, on behalf of United Keno Hill Mines Ltd. Although design criteria existed for wetlands treating acid mine drainage in the Eastern United States, there were none for zinc removal, or for wetlands located this far North.
As a first task, a pilot-scale wetland was constructed to treat a portion of the adit discharge. A cleared site located below the adit was excavated for this purpose. Plants (Carex aquatilis) were obtained from a donour site and transplanted into this area. The site was fertilized and kept wet, and plants soon began to grow (see Photo 1, 74 Kb).
This pilot wetland measures 9 x 18.5 m, for a surface area of 167 m². In this photograph, mine water is fed to the wetland from the upper right corner (by the white pail) and is discharged in the lower left corner.
Mine water was introduced into the wetland when it was fully grown. Concentrations of zinc at its inlet and outlet were measured, to determine the rate of zinc removal. A typical result is shown in the figure below.
The figure shows that zinc concentrations were reduced as the water flowed through the wetland, from an initial concentration of 25 mg/L (ppm) to approximately 5 ppm. This is a removal rate of 80%, which is reasonably good. However, it still leaves more zinc in the discharge than desired. Ideally, the zinc concentrations would be reduced to 0.5 ppm, or less.
Bear in mind that the pilot wetland was not initially optimized. After all, this is the object of the test work! Further testing was necessary to obtain these design criteria.
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