Light-driven sustainable enhancement of Cr(VI) reduction via the combination of Cr(VI)-reducing bacteria, Paraclostridium bifermentans with CdS nanoparticles

Hexavalent chromium (Cr(VI)) contaminated in soil or water system poses a serious threat to human health. Developing an efficient remediation strategy and treatment method towards Cr(VI) in situ from wastewater is truly under an urgent demand in many countries or regions suffered from this heavy metal threaten. Converting Cr(VI) to Cr(III) with less toxicity by a biological or photocatalytic reduction processing is commonly considered as one of the effective strategies. However, how to effectively enhance the performance of Cr(VI) reduction processing remains a technical challenge. In line with this issue, a novel approach has been proposed to combine a biological and photocatalytic reduction processing together to improve the Cr(VI) remediation. In this system, a novel Cr(VI)-reducing anaerobic bacterium Paraclostridium bifermentans G3 isolated from termite's gut would detoxify Cd(II) to cadmium sulfide (CdS) nanoparticles that could be precipitated in situ on the cell surface to create a CdS-Paraclostridium bifermentans complex. More importantly, with this complex system, the Cr(VI) reduction processing was significantly improved, where Cr(VI) was completely reduced by the complexes in the case of Cr(VI) concentration at 260 mg/L after 90 min under light culture. As a comparison, if the biological agent, P. bifermentans, was applied alone, it would come out a different reduction efficiency at 81.9% of Cr(VI) after 90 min reaction. These results suggested that the proposed complex system of Cr(VI)-reducing bacteria combined with CdS nanoparticles may potentially provide a novel and in-situ approach for a sustainable enhancement of Cr(VI) remediation to wastewater.