Modeling variations of medium porosity in rotating drum biofilter

Rotating drum biofilters (RDBs) mounted with reticulated polyurethane sponge media has showed high removal efficiencies over a long period of time when used for volatile organic compound (VOC) removal. Due to the accumulation of biomass within the sponge medium, the porosity of a filter bed usually changes dynamically, which makes it difficult to predict and to control. In this paper, the porosity of a multi-layer RDB bed was investigated by a diffusion-reaction model in which biofilm growth and decay were taken into account at the pore scale of the sponge medium. Temporal and spatial changes of porosity were studied under various organic loadings and gas empty bed contact times (EBCTs). The porosity of the biofilter bed was assumed to be a function of biofilm thickness, and all the pores were assumed to be uniform. Toluene was selected as the model VOC. The model was solved using numerical methods through the MATLAB software. Results show that the porosity decreased with increased time of operation, increased toluene loading, or decreased gas EBCT value. The porosity in the outermost medium layer was less than that in the inner medium layers. Toluene removal efficiencies and porosities calculated from this model correlated with the experimental data well. Porosity variation was proposed to be an indicator for prediction of biofilter performance in biofilters as a consequence.