Microbial removal of alkanes from dilute gaseous waste streams: mathematical modeling of advanced bioreactor systems

Many industries generate volatile organic compounds (VOCs) in dilute streams which must be removed before being released into the environment. Mathematical models for biological filters which can remediate waste streams are useful both as predictive tools and as a means to better understand the fundamental processes involved. Optimization of the system also necessitates a better understanding of the mechanisms by which biofilters work and can be approached through modeling and maximizing appropriate conditions for removal. In a trickle-bed bioreactor, VOCs (n-pentane and isobutane) were passed over a biofilm-coated packing which degraded the VOCs. Bacterial growth was controlled via liquid nutrient-limited media trickled through the reactor. Results from this trickle-bed system were analyzed by applying a simple mathematical model to accurately describe the processes which are believed to play important roles. The model was based on a two-step process: mass transfer in which the VOCs diffuse into the liquid biofilm, and kinetics by which VOCs are degraded by the biofilm. Modeling results revealed that both kinetic and mass transfer resistances were significant under typical operating conditions.