Chromate reduction by Microbacterium liquefaciens immobilised in polyvinylalcohol

A polyvinyl alcohol-based immobilisation technique has been utilised for en trapping the newly-isolated chromate-reducing bacterium, Microbacterium liq uefaciens MP30. Three immobilisation methods were evaluated: PVA-nitrate, P VA-borate and PVA-alginate. Chromate reduction was studied in batch and con tinuous-flow bioreactors, where the beads maintained integrity during conti nuous operation. PVA-borate and PVA-alginate cell beads showed a higher rat e and extent of chromate reduction than PVA-nitrate cell beads in batch exp eriments. With the former 100 muM Cr(VI) was removed within 4 days, while o nly 40 muM Cr(VI) was removed using the latter, and with no increase in Cr( VI) removal subsequently. Cell activity was maintained during immobilisatio n but the rate of Cr(VI) removal by immobilised cells was only half that of an equivalent mass of free cells. Using PVA-alginate cell beads in a conti nuous-flow system, chromate removal was maintained at 90-95% from a 50 muM solution over 20 days without signs of bead breakdown.