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Two biofilters were operated to treat a waste gas stream intended to simulate off-gases generated during the manufacture of reformulated paint. The model waste gas stream consisted of a five-component solvent mixture containing acetone (450 ppm v ), methyl ethyl ketone (12 ppm v ), toluene (29 ppm v ), ethylbenzene (10 ppm v ), and p-xylene (10 ppm v ). The two biofilters, identical in construction and packed with a polyurethane foam support medium, were inoculated with an enrichment culture derived from compost and then subjected to different loading conditions during the startup phase of operation. One biofilter was subjected to intermittent loading conditions with contaminants supplied only 8 hr/day to simulate loading conditions expected at facilities where manufacturing operations are discontinuous. The other biofilter was subjected to continuous contaminant loading during the initial start period, and then was switched to intermittent loading conditions. Experimental results demonstrate that both startup strategies can ultimately achieve high contaminant removal efficiency (Ͼ99%) at a target contaminant mass loading rate of 80.3 g m Ϫ3 hr Ϫ1and an empty bed residence time of 59 sec. The biofilter subjected to intermittent loading conditions at startup, however, took considerably longer to reach high performance. In both biofilters, ketone components (acetone and methyl ethyl ketone) were more rapidly degraded than aromatic hydrocarbons (toluene, ethylbenzene, and p-xylene). Scanning electron microscopy and plate count data revealed that fungi, as well as bacteria, populated the biofilters.

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