title: Removal of ultrafine and fine particulate matter from air by a granular bed filter.
abstract: The removal efficiency of granular filters packed with lava rock and sand was studied for collection of airborne particles 0.05-2.5 microm in diameter. The effects of filter depth, packing wetness, grain size, and flow rate on collection efficiency were investigated. Two packing grain sizes (0.3 and 0.15 cm) were tested for flow rates of 1.2, 2.4, and 3.6 L/min, corresponding to empty bed residence times (equal to the bulk volume of the packing divided by the airflow rate) in the granular media of 60, 30, and 20 sec, respectively. The results showed that at 1.2 L/min, dry packing with grains 0.15 cm in diameter removed more than 80% (by number) of the particles. Particle collection efficiency decreased with increasing flow rate. Diffusion was identified as the predominant collection mechanism for ultrafine particles, while the larger particles in the accumulation mode of 0.7-2.5 microm were removed primarily by gravitational settling. For all packing depths and airflow rates, particle removal efficiency was generally higher on dry packing than on wet packing for particles smaller than 0.25 microm. The results suggest that development of biological filters for fine particles is possible.
authors.affiliation: Department of Civil and Environmental Engineering, University of Southern California, Los Angeles 90089-2531, USA.
authors.forename: Fethiye
authors.initials: F
authors.lastname: Ozis
authors.forename: Manisha
authors.initials: M
authors.lastname: Singh
authors.forename: Joseph
authors.initials: J
authors.lastname: Devinny
authors.forename: Constantinos
authors.initials: C
authors.lastname: Sioutas
mesh_terms: D000393:Air Pollutants / Q000302:isolation & purification*; D005374:Filtration; D055593:Geological Phenomena; D005844:Geology; D010316:Particle Size; D012822:Silicon Dioxide
chemical_list: D000393:Air Pollutants; D012822:Silicon Dioxide