Mitigation of Ca, Fe, and Mg loads in surface waters around mining areas using indigenous microorganism strains

In attempting to achieve acceptable minimum concentration levels of excess calcium, iron and magnesium in surface waters around mining areas, experiments conducted at laboratory scale to remove these metals from synthetic solutions (30 ppm and 50 ppm) using indigenous strains of Shewanella sp., Bacillus subtilis sp. and Brevundimonas sp. revealed varying abilities of these microorganisms. B. subtilis and Shewanella sp. absorbed the highest amount (14% Ca, 8% Mg and 8% Fe) of each of the three metals, recorded from solutions containing the metals at 30 ppm concentration, with calcium being most easily removed metal species. The purpose of this study was to investigate a cost-effective solution based on indigenous microorganisms for the bioremediation of toxic metallic species in the mine dumps where small scale mining operations occur. Metal removal from solution decreased when their concentration in solution was at 50 ppm. It was also found that combining the metals in one solution affected the microorganisms’ affinity for the metals thus reducing their removal efficiency. There was also a tendency for microorganisms to release the absorbed metal into solution after a certain period of time, most probably due to an efflux transport mechanism. It was further concluded that the metal removal efficiency is dependent on the biomass, and the percentage removals obtained in this study suggest that we could achieve better removal rates of targeted metals and reduce their concentrations to below recommended values through the optimization of the biomass. The success of this study has prompted a broader research project into the removal of metal species in mine dumps before contamination of water resources occurs so that the water in the disused mine pits is suitable for irrigation, farming and washing.