Dynamic Mathematical Model for the Biodegradation of VOCs in a Biofilter: Biomass Accumulation Study

Abstract

Although biofiltration is a firmly established technology for the control of emissions of volatile organic compound (VOCs), more fundamental research is still needed. This work uses a mathematical model describing the dynamic physical and biological processes occurring in a packed trickle-bed air biofilter to analyze the relationship between biofilter performance, biomass accumulation in the reactor, and mathematical description of the packed bed porous media. In this study a biofilter packed with pelletized support media was used to treat toluene achieving removal efficiencies over 99% and 97% for 4.1 and 6.2 kg COD/m3 day toluene loading, respectively. Experimental results showed that as biomass accumulates in the reactor, the available area for the contaminant to diffuse into the biofilm decreases causing a drop in removal efficiency. This effect is specially important for biofilters where there is a high degree of biomass accumulation that significantly affects biofilter performance. In response to these observations, a new approach for the calculation of the biofilm specific surface area of the reactor as a function of biomass growth was developed. Three models of the reactor porous medium were analyzed. The medium was represented as a bed of equivalent spheres in the first model, as an equivalent set of parallel pipes in the second model, and as an equivalent set of flat parallel plates in the third model. The first two models, spheres and pipes, were proven superior in their ability to explain the system performance. The effect of contaminant solubility on biofilter performance was also analyzed.