Generation of Alkalinity by Stimulation of Microbial Iron Reduction in Acid Rock Drainage Systems: Impact of Natural Organic Matter Types.

To determine the possible role of organic matter in promoting the attenuation of an Acid Rock Drainage (ARD), microcosm-based experiments were performed using ARD sediment which had been stimulated by addition of local plants and different manures. Mineralogical, geochemical, organic geochemical and microbial analyses of the ARD sediment, indicated a predominance of goethite, a substantial amount of organic carbon originating from local sources and a bacterial community comparable to those detected in a range of ARD sites worldwide. After one hundred days of incubation, changes in the mineralogical, organic and microbiological composition of the biostimulated ARD sediments, have demonstrated that the plant additions stimulate microbes that have the potential to degrade this organic matter but do not necessary cause substantial Fe(III)-reduction. Conversely, the greatest observed stimulation of Fe(III)-reduction, associated with an increase in pH to near neutral values, was observed using manure additions. These results demonstrate that adding the optimal natural carbon source offers a potential remediation strategy for sites impacted by acid mine or rock drainage, through the stimulation of biogeochemical processes that can generate alkalinity.