Assessment of the stability of chromium in remedied soils by Pannonibacter phragmitetus BB and its risk to groundwater

摘要

Purpose Acid rain can accelerate the acidification of the chromium-contaminated soils, resulting in chromium releasing into soil solution and causing ecological risk. The current study aims to investigate the release of chromium in the remedied soils by Pannonibacter phragmitetus BB under the simulated acid rain leaching and to assess its risk to groundwater. Materials and methods P. phragmitetus BB was utilized to remedy the Cr(Ⅵ)-contaminated soils at two levels (80 and 1,276 mg kg~(-1)) by the column leaching experiment, and the chemical remediation with ferrous sulfate was used as a control. The remedied soils by P. phragmitetus BB and ferrous sulfate were leached under the simulated acid rain to evaluate the release of chromium. Furthermore, the risk of chromium release from the remedied soils to the groundwater was assessed by a fuzzy comprehensive evaluation method. Results and discussion The average concentrations of water-soluble Cr(Ⅵ) in the remedied soils by P. phragmitetus BB were reduced to less than 5.0 mg kg~(-1). Under leaching situation with the simulated acid rain, the release of total chromium and Cr(Ⅵ) from the remedied soils by P. phragmitetus BB and ferrous sulfate declined rapidly with the extended leaching time. However, the release amounts of total chromium and Cr(Ⅵ) from the remedied soil by P. phragmitetus BB more efficiently deceased as compared with that by ferrous sulfate remediation. Carbonate-bounded, exchangeable, and organics-bonded chromium were the major chromium-releasing sources under the simulated rain leaching. After microbial remediation with P. phragmitetus BB and chemical remediation with ferrous sulfate, the risk grades of the remedied soils to groundwater declined from classes 11 to 5 and 6, respectively. Conclusions The risks of the remedied soils by both microbial remediation with P. phragmitetus BB and chemical remediation with ferrous sulfate to groundwater effectively decreased and microbial remediation more significantly declined the chromium risk to groundwater than chemical remediation.