Determination of physical parameters affecting biofiltration of VOCs

This study dealt with the determination of physical and design parameters affecting the transient behavior of classical biofilters employed in removal of VOCs from airstreams. The column packing material consisted of a mixture of peat and perlite particles (2:3, v:v). The design parameters investigated were the density of the packing material, its porosity, and the void fraction of the filter-bed. The physical parameters investigated were the characteristics of adsorption equilibrium between VOCs and packing material, and the mass transfer coefficients of VOCs to the packing material. The density of the packing material was found to be 0.679 x 106 g-packing/ m3-packing, while its capacity for water holding was 0.601 m3-water/ m3-packing (i.e., 60% porosity). The void fraction of the filter-bed was determined as 0.324 m3-air/ m3-bed. Batch adsorption equilibrium experiments were performed with single and mixtures of two VOCs. With single compounds, it was found that hydrophobic compounds such as benzene and toluene follow an almost linear isotherm (i.e. a Freundlich isotherm with an exponent almost equal to unity). Hydrophilic compounds such as butanol and ethanol were found to follow a clear Freundlich isotherm with an exponent of approximately 0.5. The adsorption equilibrium of mixtures of benzene and toluene vapors was found to follow the Langmuir-Freundlich isotherm which implies that the two VOCs are involved in a competitive interaction. Column experiments with airstreams containing benzene, toluene, and their mixtures were performed in the absence of biological activity. Transient data under various inlet concentrations and air flow rates were used in determining the mass transfer coefficient of VOCs to the packing material. The data were successfully described with a mathematical model