Chromium(VI) reduction by Pseudomonas fluorescens LB300 in fixed-film bioreactor

The potential for Cr(VI) reduction in a bench-scale, fixed-film bioreactor system was investigated using a Cr(VI) reducing bacterial species, Pseudomonas fluorescens LB300. The bench-scale reactor was packed by glass beads and was operated to steady-state conditions with near complete removal of Cr(VI) under a range of influent Cr(VI) concentrations (30-100 mg/L) and hydraulic retention times (3.6-14.2 min). Cr(VI) over-loadings were observed when the bioreactor system was operated at 200 mg Cr(VI)/L under a 14.2 min hydraulic retention time and at 50 mg Cr(VI)/L under a 3.6 min hydraulic retention time. The system recovered in both cases after reducing Cr(VI) loadings by lowering influent Cr(VI) concentration to 10 mg/L. Cr(VI) reduction was carried out by biological mechanisms through both attached and suspended biomass. Control studies using Cr(VI) showed that abiotic Cr(VI) reduction in the bioreactor was insignificant. Nearly all the influent Cr(VI) reduced in the reactor was recovered in the form of Cr(III) in the effluent.