Insolubilization of hexavalent chromium in cement waste soil by anaerobic microorganisms

Chemical treatment by reducing agents is the most popular method for insolubilization of hexavalent chromium in construction waste soil containing cement. However, with the use of such chemical agents, there are some risks of secondary pollution through the elution of other heavy metals. This study aims to insolubilize hexavalent chromium by activation of anaerobic microorganisms utilizing a fermentation accelerator, instead of using chemical agents. When the accelerator was added to hexavalent chromium contaminated soil in anaerobic conditions, the amount of hexavalent chromium eluted from the treated soil was decreased to below the level of the environmental standard value in Japan and its pH was reduced by pH 8. Oxidation-reduction potential of the sludge was also decreased and its microorganism flora changed. These results indicated that anaerobic microorganisms could contribute to insolubilize the hexavalent chromium. Nucleotide sequence analysis suggested that the anaerobic microorganism activated in the soil could be a sort of microorganisms belonged to Exiguobacterium. which are capable of surviving in a high pH environment containing cement. Additionally, the treated soil that was subjected to shaking in acid or alkali did not elute the hexavalent chromium either. Hexavalent chromium was effectively insolubilized in the cement sludge.