Continuous removal of Cr(VI) from aqueous solution catalysed by palladised biomass of Desulfovibrio vulgaris

Growth-decoupled cells of Desulfovibrio vulgaris NCIMB 8303 can be used to reduce Pd(II) to cell-bound Pd(0) (Bio-Pd-0), a bioinorganic catalyst capable of reducing hexavalent chromium to less toxic Cr(III), using formate as the electron donor. Magnetic resonance imaging showed that Bio-Pd-0, immobilized in chitosan and agar beads, is distinguishable from the surrounding gel and is evenly dispersed within the immobilization matrix. Agar-immobilized Bio-Pd-0 and 'chemical Pd-0' were packed into continuous-flow reactors, and challenged with a solution containing 100 muM Cr(VI) (pH 7) at a flow rate of 2.4 ml h(-1). Agar-immobilized chemical Pd-0 columns lost Cr(VI) reducing ability by 160 h, whereas columns containing immobilized Bio-Pd-0 maintained 90% reduction until 680 h, after which reduction efficiency was gradually lost.