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Microbial Reduction of Hexavalent Chromium under Vadose Zone Conditions
Author(s) -
Oliver Douglas S.,
Brockman Fred J.,
Bowman Robert S.,
Kieft Thomas L.
Publication year - 2003
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq2003.3170
Subject(s) - hexavalent chromium , vadose zone , biostimulation , environmental chemistry , chemistry , chromium , nitrate , bioremediation , nutrient , microcosm , soil water , contamination , environmental science , soil science , ecology , organic chemistry , biology
Hexavalent chromium [Cr(VI)] is a common contaminant associated with nuclear reactors and fuel processing. Improper disposal at facilities in arid and semiarid regions has contaminated underlying vadose zones and aquifers. The objectives of this study were to assess the potential for immobilizing Cr(VI) using a native microbial community to reduce soluble Cr(VI) to insoluble Cr(III) under conditions similar to those in the vadose zone, and to evaluate the potential for enhancing biological Cr(VI) reduction through nutrient addition. Batch microcosm and unsaturated flow column experiments were performed. Native microbial communities in subsurface sediments with no prior Cr(VI) exposure were shown to be capable of Cr(VI) reduction. In both the batch and column experiments, Cr(VI) reduction and loss from the aqueous phase were enhanced by adding high levels of both nitrate (NO − 3 ) and organic C (molasses). Nutrient amendments resulted in up to 87% reduction of the initial 67 mg L −1 Cr(VI) in an unsaturated batch experiment. Molasses and nitrate additions to 15 cm long unsaturated flow columns receiving 65 mg L −1 Cr(VI) resulted in microbially mediated reduction and immobilization of 10% of the Cr during a 45‐d experiment. All of the immobilized Cr was in the form of Cr(III), as shown by XANES analysis. This suggests that biostimulation of microbial Cr(VI) reduction in vadose zones by nutrient amendment is a promising strategy, and that immobilization of close to 100% of Cr contamination could be achieved in a thick vadose zone with longer flow paths and longer contact times than in this experiment.