Gas characteristics before and after biofiltration treating odorous emissions from animal rendering processes

Studies of odour-control biofilters at two animal rendering plants were conducted. Biofilter influent and effluent gases were characterized using a gas chromatograph-mass spectrometer (GC-MS) and a GC fitted with an odour sniffing port. Overall odour-removal performance of the biofilters was evaluated using forced-choice dynamic-dilution olfactometers. GC-MS analysis revealed that the biofilter influent gases at each plant contained about 300 compounds. About 20% of these compounds were identified, and included hydrocarbons, ketones, heterocyclics, aldehydes, aromatics, carobxylic acids, esters, sulphur compounds, nitriles, an amine and an amide. About 20 identified compounds were present in both biofilter influent gases. The influent gas at Plant 1 contained more straight chain hydrocarbons, while the influent gas at Plant 2 contained more sulphur compounds and esters. Sensory evaluation of the gas samples using the GC-odour port technique indicated that about 45 compounds in the biofilter influent gases were odorous at Plant 1, and about 30 were odorous at Plant 2. A variety of odour characters was observed in the two biofilter influent gases. The biofilters reduced the concentration of most of the odorous compounds to levels that were not detectable by the GC-odour port analysis. The rendering process gases had odour concentrations of between 59,000 and 1,000,000 OU m(-1). The biofilters reduced the odour concentration by 82-99% and also reduced the "offensiveness" of the odour. Uneven gas distribution affected biofilter odour-removal performance.