Chromate reduction by immobilized palladized sulfate-reducing bacteria

Resting cells of Desulfovibrio vulgaris NCIMB 8303 and Desulfovibrio desulfuricans NCIMB 8307 were used for the hydrogenase-mediated reduction of Pd(II) to Pd(0). The resulting hybrid palladium bionanocatalyst (Bio-Pd(0)) was used in the reduction of Cr(VI) to the less environmentally problematic Cr(III) species. The reduction of Cr(VI) by free and agar-immobilized Bio-Pd(0) was evaluated. Investigations using catalyst suspensions showed that Cr(VI) reduction was similar (similar to 170 nmol Cr(VI)/h/mg Bio-Pd(0)) when Bio-Pd(0) was produced using D. vulgaris or D. desulfuricans. Continuous-flow studies using D. vulgaris Bio-Pd(0) with agar as the immobilization matrix investigated the effect of Bio-Pd(0) loading, inlet Cr(VI) concentration, and flow rate on the efficiency of Cr(VI) reduction. Reduction of Cr(VI) was highest at a D. vulgaris Bio-Pd(0) loading of 7.5 mg Bio-Pd(0)/mL agar (3:1 dry cell wt: Pd(0)), an input [Cr(VI)] of 100 mu M, and a flow rate of 1.75 mL/h (approx. 3.5 column volumes/h). A mathematical interpretation predicted the activity of the immobilized Bio-Pd(0) for a given set of conditions within 5% of the value found by experiment. Considering the system as an 'artificial enzyme' analog and application of applied enzyme kinetics gave an apparent K, value (Km,pp) of 430 mu M Cr(VI) and a determined value of flow-through reactor activity which differed by 11% from that predicted mathematically. (c) 2006 Wiley Periodicals, Inc.