Investigation of airflow through a compost-based biofilter

grantor: University of TorontoBiofiltration involves venting off-gases containing low concentrations of volatile organic and/or inorganic contaminants through a biologically active medium. In this research, the relationships between air pressure drop, particle size, gas-filled porosity, airflow rate, and moisture content were investigated for compost and wood chip biofilters. This research can be applied in developing biofilter design and operating strategies for reduced air pressure drop through the biofilter. Experiments were carried out in a 200-L downflow biofilter equipped with 28 air pressure transducers. Different mixtures of compost and wood chips were evaluated in this research. Empty bed contact times ranged from 25 to 230 s and the gas-filled porosities of the media were estimated through tracer testing using methane gas. Equivalent diameters for the compost and wood chip mixtures were determined based on the screening analysis of the compost and wood chips. Darcy's law and the Modified-Ergun equation were successfully used to model gas flow through the various mixtures. The surface area and Reynolds number for transition from laminar to inertial flow were also estimated for the media. Tracer testing data were analyzed assuming a pulse input of methane as well as by considering two methane concentration profiles through the biofilter. The tracer testing data were also analyzed using a physical non-equilibrium model for advective-dispersive gas transport through the biofilter. Tests were performed to examine the effect of varying the moisture content on the air pressure drop across the biofilter for the compost-based media. Due to the fact that the compost structure was moisture dependent it was found that adjusting the diameter of the compost aggregates was necessary to account for variation in the air pressure drop as the moisture content changed.Ph.D