Bacterial removal of chromium (VI) and (III) in a continuous system

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Bacterial removal of chromium (VI) and (III) in a
continuous system

• Cabrera, et al. 2007
• Biodegradation
• 18505-513

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Goals of Research

• Evaluate capacity of Acidithiobacillus species to
  reduce chromium (VI)
• Investigate a continuous flow system to treat an
  electroplating waste with high chromium (III) and
  (VI)

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Acidithiobacillus

• Chemolithotrophic, aerobic, Gram-negative rods
• use reduced sulfur compounds as e- donors
• can also utilize Fe2 and metal sulfides
• Acidophiles
• optimum pH 2-4
• Common reactions
• H2S 2O2 SO42- 2H
• S0 H2O 1.5 O2 SO42- 2 H

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Acid Mine Drainage
Carol Stoker NASA
D. Hardesty, USGS Columbia Environmental Research
Center.
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Chromium

• Trivalent chromium Cr(III)
• occurs naturally in soils and plants
• essential nutrient for metabolism
• less toxic and less mobile than Cr(VI)
• Hexavalent chromium Cr(VI)
• inhibits formation of rust
• byproduct of industrial processes
• mobile in groundwater
• EPA MCL for TOTAL Cr 100 ?g/L (100 ppb)

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Conclusions

• Acidithiobacillus cells can reduce Cr(VI)
• A. ferrooxidans had a higher reduction capacity
• A continuous flow system allowed for Cr(VI)
  reduction and Cr(III) solubilization
• Acidithiobacillus present a feasible technology
  for removal of Cr from solid residues