Effects of biomass growth on gas pressure drop in biofilters

The effects of biomass accumulation and distribution on air pressure losses in biofilters were experimentally studied. Two bench-scale biofilters, one packed with inert porous pellets (Nova Inert) and the other with wood chip s, were operated under similar conditions with excess nutrients to treat an airstream containing methanal, at loading rates of 100-150 g methanol/m(3) bed/h. Localized biomass accumulation in the biofilter beds was the key fa ctor increasing the pressure drop, which was caused by local bed clogging d ue to biomass growth. The highest pressure drops in the beds (wood chips: 2 ,600 Pa/m; Nova Inert: 550 Pa/m) occurred in sections where there were high biomass levels with high water content. The pressure drop varied nonlinear ly with the amount of accumulated biomass and the amount of methanal consum ed. Sixfold higher pressure drops were measured in the wood chip biofilter than in the Nova Inert biofilter because of more biomass growth and bed com paction. A model, based on the Ergun equation, was developed to predict bio mass-affected porosity and pressure drop as a function of the biomass conce ntration in a bed packed with spherical pellets. A comparison of the experi mental and the predicted pressure drops showed that the model provided good estimates of biomass-affected porosity and pressure drop in the biofilter packed with spherical porous pellets with even biomass distribution.