Detailed Study of Odor from Pig Buildings to Improve Understanding of Biotrickling Filter Performance

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Abstract. Recently, bioreactors, such as biotrickling filters, have been used to reduce odor and gas emissions from livestock facilities. Considerable efforts have already been made over the years to evaluate and improve the efficiencies of bioreactors used for this purpose; however, no study has yet been published that attempts to provide a thorough assessment of the performance of bioreactors in eliminating most (if not all) of the gases exhausted from swine facilities. Thus, this study was conducted to obtain a better understanding of the performance of biotrickling filters in treating swine odors by conducting a comprehensive evaluation of their overall performance in removing odor and gaseous components. Evaluating the performance of biotrickling filters using persistent gaseous components, i.e., those that remain in the treated air and contribute to the malodor, helps identify areas of the treatment system that can still be potentially improved. The gaseous components monitored were ammonia (NH3), hydrogen sulfide (H2S), and volatile organic compounds (VOCs). Samples were collected from two four-week trials using three laboratory-scale pig chamber and biotrickling filter systems. The NH3 and H2S concentrations were measured using non-dispersive infrared and ultraviolet fluorescence analyzers, respectively, while VOCs were collected using adsorption tubes and analyzed by a gas chromatograph coupled with a mass spectrometer and an olfactory detection port (GC-MS-O). Samples for odor measurement were also collected and analyzed using a dynamic olfactometer. Linear regression and odor index were used to identify the odorants that had the largest odor impacts. Odor index is an integrated parameter that expresses the combined contributions of odor intensity and hedonic tone to the perceived odor. Of the 176 VOCs identified in the samples, the odor components that had the largest odor impacts included butanoic acid, 3-methylbutanoic acid, 2-methylbutanoic acid, 2-methylpropionic acid, pentanoic acid, p-cresol, 2,3-butanedione, and dimethyl sulfide. However, most of these substances were almost completely eliminated in the biotrickling filters, except p-cresol and dimethyl sulfide. This implies that optimizing the removal of poorly water-soluble components, such as p-cresol and dimethyl sulfide, could further improve the performance of biotrickling filters in treating swine odors. Keywords: Biotrickling filters, Removal efficiency, Swine odor components.