Role of Carbon Fractionation and Microbial Inoculum in Bioremediation of Acid Mine Drainage

Abstract

Acid mine drainage (AMD) from abandoned mines is a threat to Nevada’s limited water supply and requires cost-effective, passive remediation techniques. Mining activities expose mineral surfaces to oxidation, which accelerates the release of acidity, sulfate, and metal ions found in the AMD. Sulfate-reducing bacteria (SRB) can be used to treat AMD by reducing sulfate, increasing pH, and precipitating metals as metal sulfides. SRB require an external electron donor, supplied from short-chain organic compounds, and an electron acceptor in the form of sulfate. The process releases hydrogen sulfide and bicarbonate that treat the AMD by forming insoluble metal sulfides and alkalinity. The goal of this work was to develop a low-cost, passive bioremediation process to treat AMD originating from Perry Canyon, located in Washoe County, Nevada. Several locally available waste organic materials were characterized by carbon fractionation, and two mixtures with the same carbon profile but originating from different sources were created to use as an organic substrate for sulfate-reducing bioreactors. Microbial communities from two different soil types and in dairy manure were used to inoculate the bioreactors. Twelve bioreactors were constructed and operated for 12 months to evaluate SRB remediation as a function of carbon source and inoculum. It was found that the inocula source impacts bioremediation startup, while the carbon source impacts bioremediation efficiency.