A percolation biofilm-growth model for biomass clogging in biofilters

Biomass accumulation has been recognized as a limiting factor in the operation of biofilters. As the biofilm thickens, portions at the base may no longer be exposed to contaminants and oxygen. Smaller pores are filled with biomass so that air no longer flows into them. As pores are blocked, air may be prevented from reaching some pores even when they are not filled. Eventually blockage becomes sufficiently widespread so that increasing head loss and decreasing removal efficiency require that the system be shut down. Optimization necessitates a better understanding of the mechanisms by which biofilter clogs. Percolation theory was developed for application to similar problems in other fields such as oil recovery and catalyst bed design. In this work, a numerical percolation model of the blockage process was developed for application to biofilters. It allows comparison of pore blockage histories for various pore size distributions, and predicts biomass accumulation, head loss, and treatment efficiency as a function of time, as well as total time until blockage prevents further operation.; A model was developed and applied to two theoretical biofilters having log-normal pore size distribution with mu= 4 and 7. It was also used to simulate two bench-scale biofilters with experimentally determined pore size distributions.; This model accounts for biomass growth and its impact on head loss, contaminant removal and channeling in the biofilter. It will be useful in biofilter design, particularly in the choice of appropriate packing. A complete understanding of the clogging process, and ultimately its control, would increase biofilter efficiency and broaden the range of applications.; Finally, the removal efficiency of granular filters packed with lava rock and sand was studied for collection of airborne particles 0.05 to 2.5mum in diameter in anticipation of the possibility that either inert granular filters or biofilters could be used for treatment of fine particles. The effects of filter depth, packing wetness, grain size and flow rate on collection efficiency were investigated. Packed-bed granular filters were proved effective for removal of fine and ultrafine particles from air.