Effects of Solid-Phase Organic Carbon and Hydraulic Residence Time on Manganese(II) Removal in a Passive Coal Mine Drainage Treatment System

Passive treatment is a cost-effective method for Mn(II) removal from coal mine drainage via microbial oxidation and abiotic sorption/oxidation by Mn oxide (MnOx). Emplacement of solid-phase carbon within passive treatment systems to slowly release organic carbon has been proposed to enhance microbial Mn(II) removal. We tested the effects of wood chips as a solid-phase carbon source on Mn(II) removal efficiency. Both softwood (white pine) and hardwood (red oak) digestion solution (10 mg C/L) inhibited Mn(II) removal due to dissolution and coating of the reactive MnOx surface. Our results indicate that wood chips would not be a suitable solid-phase organic amendment for Mn removal. A strong linear correlation was observed between hydraulic residence time and Mn(II) removal rate.