Verification of model for adsorption and reduction of chromium(VI) by Escherichia coli 33456 using chitosan bead as a supporting medium

A non-steady-state mathematical model system for the kinetics of adsorption and reduction of Cr(VI) by Escherichia coli (E. coli) biofilm on chitosan bead (EBCB) process was derived. The mechanisms in the model system included Cr(VI) adsorption by chitosan beads, Cr(VI) bioreduction by E. coli cells and Cr(VI) mass transport diffusion. Batch kinetic tests were performed to determine surface diffusivity of Cr(VI), adsorption parameters for Cr(VI) and biokinetic parameters of E. coli 33456. Experiments were conducted using an EBCB reactor system with high recycled rate to approximate a completely-mixed flow reactor for model verification. The experimental results indicated that E. coli biofilm bioregenerated the chitosan beads after E. coli biofilm has grown significantly. Cr(VI) reducing efficiency by E. coli was about 84% when Cr(VI) concentration in the influent was 5 mg/L at a steady-state condition. The concentration of suspended E. coli cells reached up to 10 mg/L while the thickness of attached E. coli cells was estimated to be 150 μm at a steady-state condition by model prediction. The comparisons of experimental data and model simulation show that EBCB model system for Cr(VI) adsorption and reduction can predict the experimental results well.