Reduction and fixation of Cr(VI) by Aspergillus niger along with bentonite-sodium alginate beads

Previous researches had demonstrated that microorganisms were able to reduce Cr(VI), which has been always regarded as a threat to human health. However, reduced Cr(III) exposed to natural environment is still possible to be re-oxidized to Cr(VI). In this present study, the system including Aspergillus niger and bentonite-sodium alginate beads (BSBs) was used to reduce and fix Cr(VI) from aqueous solution by batch mode. The A. niger and BSBs were characterized by spectrophotometry, inductively coupled plasma-optical emission spectroscopy (ICP-OES), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray synchrotron radiation technology. Multiple mechanisms such as interlayer cation-exchange and bioremediation involved in Cr(VI) removal process. The results of spectrophotometry and TEM-EDS revealed the removal of Cr(VI) by A. niger through bioremediation. Also, the interlayer cation-exchange between Cr(III) and BSBs was revealed by ICP-OES, SEM-EDS and X-ray synchrotron radiation technology analysis. Experimental data showed that A. niger cultured in the system could reduce Cr(VI) nearly 100% while cell did not form intracellular Cr-containing minerals with trace amount of Cr in cell, and approximately 0.2 mg·L–1 Cr(III) was fixed per gram of BSBs. This research provided a promising application of BSBs–A. niger system in Cr(VI) remediation where A. niger was capable of reducing Cr(VI) to Cr(III), and then Cr(III) could be immobilized through inter-layer cation-exchange by BSBs.