Dissimilatory sulfate-reducing bacteria in sulfide mineral diagenesis: In vitro, geologic systems and bioreactors

Sulfide mineral formation and diagenesis is ubiquitous in anoxic, sulfate rich environments. At ambient temperature and pressure, bacterially catalyzed diagenesis of FeS to FeS₂ by sulfate reducing bacteria occurred more rapidly and efficiently than chemical FeS₂ formation, presumably due to the high surface: volume ratio of the bacterial systems. The bacterial surface served as a matrix for nucleation and growth of pyrite. Further, these μm-sized biogenic crystals were several orders of magnitude larger than those originating abiotically. Bacteria have been implicated in ancient sulfide deposit formation, and pyrite formed within coal may be of biogenic origin also. Pyrite discs within coal were composed of aggregates of crystals, suggesting that sulfide mineral diagenesis had initiated at multiple nucleation sites, prior to the compaction forces that occur during coal formation. Fossilized bacteria on the disc surfaces appeared as halos using reflected light microscopy, but were morphologically lenticular by scanning electron microscopy. In vitro sulfide mineral diagenesis promoted by sulfate reducing bacteria showed in-filling of the bacterial cell during mineral diagenesis that is needed for the formation and preservation of the described microfossil structures. Sulfate reducing bacteria can utilize sulfate from acid mine drainage and precipitate metals from solution under anaerobic, circumneutral conditions. This, coupled with diagenesis, led to a chemical and biogeochemical treatment process design utilizing a bioreactor to treat synthetic acid mine drainage. A 2 liter fluid phase continuous flow bioreactor using a mixed culture consortium of SRB was designed with a retention time of 2.5 days to treat synthetic acid mine drainage of pH 2. Synthetic acid mine drainage was prepared with Fe(II) and sulfate concentrations of 30 and 300 ppm respectively, and was fed into the bioreactor after supplementation with reducing agent, neutralizing agent and growth medium. Efficiencies of sulfate and total Fe removal from the AMD averaged 95.6% and 90.7% respectively, over 10 days. The bacterially catalyzed transformation of FeS to FeS ₂ was quantified by scanning electron microscopy-energy dispersive spectroscopy. Sulfate reducing bacteria are crucial in the biogeochemical cycles of the planet and may be exploited in engineered systems for acid mine drainage remediation.