DYNAMIC MATHEMATICAL-MODEL FOR THE BIODEGRADATION OF VOCS IN A BIOFILTER - BIOMASS ACCUMULATION STUDY

Although biofiltration is a firmly established technology for the cont rol of emissions of volatile organic compound (VOCs), more fundamental research is still needed. This work uses a mathematical model describ ing the dynamic physical and biological processes occurring in a packe d trickle-bed air biofilter to analyze the relationship between biofil ter 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 achiev ing removal efficiencies over 99% and 97% for 4.1 and 6.2 kg COD/m(3) day toluene loading, respectively. Experimental results showed that as biomass accumulates in the reactor, the available area for the contam inant to diffuse into the biofilm decreases causing a drop in removal efficiency. This effect is specially important for biofilters where th ere is a high degree of biomass accumulation that significantly affect s biofilter performance. In response to these observations, a new appr oach for the calculation of the biofilm specific surface area of the r eactor 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 fla t parallel plates in the third model. The first two models, spheres an d pipes, were proven superior in their ability to explain the system p erformance. The effect of contaminant solubility on biofilter performa nce was also analyzed.