Abstract
Batch microcosms were setup to determine the impact of different sized zero valent iron (Fe0) particles on microbial sulfate reduction during the in situ bio-precipitation of metals. The microcosms were constructed with aquifer sediment and groundwater from a low pH (3.1), heavy-metal contaminated aquifer. Nano (nFe0), micro (mFe0) and granular (gFe0) sized Fe0 particles were added to separate microcosms. Additionally, selected microcosms were also amended with glycerol as a C-source for sulfate-reducing bacteria. In addition to metal removal, Fe0 in microcosms also raised the pH from 3.1 to 6.5, and decreased the oxidation redox potential from initial values of 249 to −226 mV, providing more favorable conditions for microbial sulfate reduction. mFe0 and gFe0 in combination with glycerol were found to enhance microbial sulfate reduction. However, no sulfate reduction occurred in the controls without Fe0 or in the microcosm amended with nFe0. A separate dose test confirmed the inhibition for sulfate reduction in presence of nFe0. Hydrogen produced by Fe0 was not capable of supporting microbial sulfate reduction as a lone electron donor in this study. Microbial analysis revealed that the addition of Fe0 and glycerol shifted the microbial community towards Desulfosporosinus sp. from a population initially dominated by low pH and metal-resisting Acidithiobacillus ferrooxidans.
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