Cr(VI) reduction by bio and bioinorganic catalysis via use of bio-H2: a sustainable approach for remediation of wastes

Use of biologically-produced hydrogen (bio-H-2) as an electron donor for Cr(VI) reduction by native and palladized cells of Desulfovibiio vulgaris NCIMB 8303 was demonstrated. The bio-H-2 was produced fermentatively by Escherichia coli HD701 (a strain upregulated with respect to formate hydrogenlyase expression) using glucose solution or two industrial confectionery wastes as fermentable substrates. Maximum Cr(VI) reduction occurred at the expense of bio-H-2 using palladized biomass (bio-Pd(0)), with negligible residual Cr(VI) remaining from a 0.5 mmol dm(-3) solution after 2.5 h. Use of bio-H-2 as the electron donor for Cr(VI) reduction by agar-immobilized bio-Pd(0) in a continuous-flow system gave 90% reduction efficiency at a flow residence time of 0.7 h, which was maintained for the duration of bio-H-2 evolution by E. coli HD701. This study shows the potential to remediate toxic metal waste at the expense of food processing waste, as a sustainable alternative to landfilling.