Fe(III) oxides are ubiquitous electron acceptors for anaerobic bioremediation, although their bioavailability was limited due to the passivation of secondary mineralization products. Here we found the solid S0 can be added to improve their bioavailability. Using lepidocrocite (γ-FeOOH), acetate and Geobacter sulfurreducens PCA as representatives of Fe(III) oxides, intermediate of pollutant degradation and microbes, a 6 times higher amount of FeOOH reduction in the presence of S0 was observed with a time needed for S0 reduction shortened by half. The bioreduction of S0 activated the reduction of FeOOH, while the product (conductive FeS) may have bridged electron transfer across the cell membrane and periplasm. The proportion of excessive Fe(II) produced from Fe(III) was quantified as a direct bioreduction (26 %), with an abiotic FeOOH reduction to FeS (20 %) and an FeS-conducted FeOOH bioreduction (54 %), which highlight the key role of gradually formed FeS from S0 in the bioreduction of FeOOH. Our results showed that S0 can be an effective additive for the bioremediation of environments with abundant Fe(III) oxides, which has broader implications for elemental biogeochemical cycling.
Keywords: Bioremediation; Elemental sulfur; FeS; Ferric oxide; Geobacter.
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