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 from aqueous streams such as acid mine drainage was evaluated using three anaerobic reactors: an upflow anaerobic sludge blanket (UASB) reactor, a packed filter reactor, and a filter reactor that was partially packed with floating plastic pall rings. The packed filter reactors removed more than 99% of the influent metals. The performance of the partially packed reactor was superior based on effluent metal and sludge concentrations. Although the UASB reactor reduced the concentration of dissolved iron, the effluent concentration of total suspended solids remained greater than 18 g/L. This elevated solids concentration indicated that the UASB reactor was not operating as an effective clarifier, and, as a result, UASB reactor operation was discontinued after 4 months. The packed filter reactors were operated in parallel and received influent containing a combination of heavy metals. By withdrawing sludge from the bottom of these reactors, the accumulation of solids such as metal precipitates and biomass was controlled. The effluent concentrations of most metals were low, often less than drinking water standards, with the exception of manganese.