Abstract
Passive biochemical reactors (PBRs) are an effective and promising technology for the treatment of mine drainage with moderate contamination in temperate or semi-arid climates. However, PBR performance is poorly known in northern climates, characterized by low temperatures (<4 °C) and often by high salinities (up to 20 g/L), in addition to the highly variable quality of mine drainage. In the present study, twenty PBRs containing mixtures of zero-valent iron (ZVI) and natural/residual materials (ash, maple chips/sawdust, sand and sludge), in different proportions, were tested in batch mode. The testing was carried out for a period of 57 days, with two mine drainage types [acid mine drainage (AMD) and neutral mine drainage (NMD)], at two temperatures (5 and 22 °C) and two salinities (0 and 25 g/L). The objective was to assess the simultaneous effect of low temperature and high salinity on PBR performance through comparative evaluation of metal and sulfate removal. The results showed that the most promising mixtures for NMD and AMD treatment contained at least 30% cellulosic materials. These mixtures gave satisfactory efficiency of metal (>87%) and sulfate (100%) removal, at 22 °C and for non-saline mine drainage. When salinity increased from 0 to 25 g/L, metal removal (Fe, Ni and Cu) decreased to < 9% and <5% for NMD and AMD, respectively. For sulfate, removal efficiency decreased by over 54% for AMD, but remained high for NMD. At 5 °C, removal efficiency decreased by at least 93% for sulfate and at least 19% for metals. Low temperatures have more detrimental impacts on the efficiency of PBRs. The simultaneous effect of both parameters (low temperature and high salinity) further reduced the performance of the treatment system and was more pronounced for the AMD, with reductions of over 97% for sulfates and over 28% for metals.
Published Version
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