Development of a sulfate-reducing biological process to remove heavy metals from acid mine drainage

The feasibility of using sulfate-reducing bacteria to remove heavy metals f rom aqueous streams such as acid mine drainage was evaluated using three an aerobic reactors: an upflow anaerobic sludge blanket (UASB) reactor, a pack ed filter reactor, and a filter reactor that was partially packed with floa ting plastic pall rings. The packed filter reactors removed more than 99% o f the influent metals. The performance of the partially packed reactor was superior based on effluent metal and sludge concentrations. Although the UA SB reactor reduced the concentration of dissolved iron, the effluent concen tration of total suspended solids remained greater than 18 g/L. This elevat ed solids concentration indicated that the UASB reactor was not operating a s an effective clarifier, and, as a result, UASB reactor operation was disc ontinued after 4 months. The packed filter reactors were operated in parall el and received influent containing a combination of heavy metals. By withd rawing sludge from the bottom of these reactors, the accumulation of solids such as metal precipitates and biomass was controlled. The effluent concen trations of most metals were low, often less than drinking water standards, with the exception of manganese.