Treatment of acid mine water by sulfate-reducing bacteria; results from a bench scale experiment

Overflowing water from waterfilled mines and open pits in pyrite and coal mine areas is often acid and severely polluted by metals and sulfate. The effect of stimulating bacterial sulfate reduction in such systems in order to improve water quality was examined in a bench scale experiment. Polyacrylate cylinders with a sand bed and a layer of crushed stones at the bottom were filled with acid mine water, supplied with whey to support bacterial growth and incubated for 203 d. After an initial lag phase, pH started to increase, redox potentials dropped and dissolved concentrations of copper, zinc, iron and aluminium were reduced in cylinders supplied with whey. Simultaneously, a black sludge was formed. Acetate tended to accumulate as an undesired waste product. The observations indicate that sulfate-reducing bacteria (SRB) became active in the cylinders and contributed to metal removal. Inoculation with SRB shortened the initial lag phase, but was not necessary to initiate the sulfate-reduction process. The in situ treatment concept may be useful in relatively small and well defined mine water systems, where the process can be governed properly.