Oxygen mass transfer characteristics in a membrane-aerated biofilm reactor

Immobilization of pollutant-degrading microorganisms on oxygen-permeable me mbranes provides a novel method of increasing the oxidation capacity of was tewater treatment bioreactors. Oxygen mass transfer characteristics during continuous-flow steady-state experiments were investigated for biofilms sup ported on tubular silicone membranes. An analysis of oxygen mass transport and reaction using an established mathematical model for dual-substrate lim itation supported the experimental results reported. In thick biofilms, an active layer of biomass where both carbon substrate and oxygen are availabl e was found to exist. The location of this active layer varies depending on the ratio of the carbon substrate loading rate to the intramembrane oxygen pressure. The thickness of a carbon- substrate-starved layer was found to greatly influence the mass transport of oxygen into the active biomass laye r, which was located close to, but not in contact with, the biofilm-liquid interface. The experimental results demonstrated that oxygen uptake rates a s high as 20 g m(-2) d(-1) bar(-1) can be achieved, and the model predicts that, for an optimized biofilm thickness, oxygen uptake rates of more than 30 g m(-2) d(-1) bar(-1) should be possible. This would allow membrane-aera ted biofilm reactors to operate with much greater thicknesses of active bio mass than can conventional biofilm reactors as well as offering the further advantage of close to 100% oxygen conversion efficiencies for the treatmen t of high-strength wastewaters. In the case of dual- substrate-limited biof ilms, the potential to increase the oxygen flux does not necessarily increa se the substrate (acetate) removal rate. (C) 1999 John Wiley & Sons, Inc. B iotechnol Bioeng 62: 183-192, 1999.