Predictive mathematical modeling of trickling bed biofilters for elucidating mass transfer and kinetic effects

Mathematical models of varying complexity have been proposed in the open literature for describing uptake of volatile organics in trickling bed biofilters. Many simpler descriptions yield relatively accurate solutions, but are limited as predictive tools by numerous assumptions which decrease the utility of the model. Trickle bed operation on the boundary between mass transfer and kinetic limitation regimes serves as one example in which these models may be insufficient. One-dimensional models may also fail to consider important effects/relationships in multiple directions, limiting their usefulness. This paper discusses the use of a predictive, two-dimensional mathematical model to describe microbial uptake, diffusion through a biofilm, and mass transfer of VOCs from gas to liquid. The model is validated by experimental data collected from operating trickle-bed bioreactors designed for removing sparingly soluble gaseous contaminants. Axial and radial (biofilm) concentration profiles are presented, along with validation results. Operation in regimes in which both mass transfer and kinetic factors play significant roles are discussed, along with predictive modeling implications.