Passive biological treatments have been proposed as an efficient and cost effective treatment of metal bearing water discharged from mine sites after closure. However, concerns are typically expressed around biological treatments and their suitability in northern, colder climates, as few examples of passive treatment systems operating under cold conditions have been documented so far. In this study, four laboratory scale anaerobic bioreactors were monitored for over one year for their capacity to reduce metal concentrations at ambient laboratory temperature, then at 6°C and 3°C. As, Cd, Cu, Se and Zn concentrations in the effluent were compared and contrasted with discharge limits in application at the Bellekeno Mine, Yukon Territory. Removal efficiencies in the range of 90 to 100% were observed in the four reactors and for the five metals studied, suggesting that sulfate-reducing bacteria native from the Yukon stayed active under cold conditions. In addition, integration of biochar in the composition of a bioreactor had a positive effect on the treatment efficiencies at the lower temperatures. This finding suggested that addition of a reactive material in the composition of the bioreactor substrate might help reduce the impact of the cold climate on the treatment system by taking advantage of metal adsorption mechanisms, which allows for continued metals removal during changes in temperature.
