On the Drying Dynamics in Biofilters

To a large extent the performance of biofilters relies on the presence of suitable amounts of water in order to provide conditions needed for microbiological degradation of pollutants to take place. In many cases breakdown of filtration performance occurs due to inappropriate water contents in the filter material. The present study focuses on the drying dynamics within such filters, which are modeled as wetted porous media. Analyzing the governing equation of gas flow and water content reveals that such systems are prone to exhibit instable behavior. Small variations in the initial conditions e.g. slight inhomogeneities in moisture or porosity are likely to be amplified during operation until breakdown occurs. The time constants for such coupled drying processes are analyzed within a 1-D modeling approach. Furthermore, details of flow heterogeneity and drying are investigated by means of two and three dimensional models, which are solved by means of COMSOL Multiphysics.