Biofilm development in a membrane-aerated biofilm reactor: Effect of flow velocity on performance

The effect of liquid flow velocity on biofilm development in a membrane-aer ated biofilm reactor was investigated both by mathematical modeling and by experiment, using Vibrio natriegens as a test organism and acetate as carbo n substrate. It was shown that velocity influenced mass transfer in the dif fusion boundary layer, the biomass detachment rate from the biofilm, and th e maximum biofilm thickness attained. Values of the overall mass transfer c oefficient of a tracer through the diffusion boundary layer, the biofilm, a nd the membrane were shown to be identical during different experiments at the maximum biofilm thickness. Comparison of the results with published val ues of this parameter in membrane attached biofilms showed a similar trend. Therefore, it was postulated that this result might indicate the mechanism that determines the maximum biofilm thickness in membrane attached biofilm s. in a series of experiments, where conditions were set so that the active layer of the membrane attached biofilm was located close to the membrane b iofilm interface, it was shown that the most critical effect on process per formance was the effect of velocity on biofilm structure. Biofilm thickness and effective diffusivity influenced reaction and diffusion in a complex m anner such that the yield of biomass on acetate was highly variable. Consid eration of endogenous respiration in the mathematical model was validated b y direct experimental measurements of yield coefficients. Good agreement be tween experimental measurements of acetate and oxygen uptake rates and thei r prediction by the mathematical model was achieved. (C) 2000 John Wiley & Sons, Inc.