Stockton Mine Acid Mine Drainage and Its Treatment using Waste Substrates in Biogeochemical Reactors
Thirteen acid mine drainage (AMD) sites were monitored at Stockton Coal Mine near Westport, New Zealand to identify and quantify contaminants of concern and delineate their spatial and temporal variability. Metals (primarily Fe and Al) were the key contaminants and measured at concentrations exceeding off-site compliance targets or the Australia and New Zealand Environmental and Conservation Council (ANZECC) water quality guidelines. Dissolved metal concentrations ranged from 0.05-1430 mg/L Fe, 0.200-627 mg/L Al, 0.0024-0.594 mg/L Cu, 0.0052-4.21 mg/L Ni, 0.019- 18.8 mg/L Zn, <0.00005-0.0232 mg/L Cd, 0.0007-0.0028 mg/L Pb, <0.001-0.154 mg/L As and 0.103- 29.3 mg/L Mn and pHs ranged from 2.04-4.31. Results of mesocosm-scale treatability tests showed that biogeochemical reactors (BGCRs) incorporating mussel shells, pine bark, wood fragments (post peel) and compost increased pH to >6.7 and sequestered ≥98.2% of the metal load from Manchester Seep AMD at the maximum recommended loading rates determined during this study (0.8 mol total metals/m3 substrate). An average of 20.0 kg/day (7.30 tonnes/year) of metals could be removed from Manchester Seep AMD employing BGCRs. Currently, this AMD is effectively treated further downstream by the Mangatini fine limestone dosing plant; however, in the interest of assessing more cost-effective technologies, this research investigated BGCRs as a passive treatment option.