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

Studies of odour-control biofilters at two animal rendering plants were con ducted. Biofilter influent and effluent gases were characterized using a ga s chromatograph-mass spectrometer (GC-MS) and a GC fitted with an odour sni ffing port. Overall odour-removal performance of the biofilters was evaluat ed using forced-choice dynamic-dilution olfactometers. GC-MS analysis revea led that the biofilter influent gases at each plant contained about 300 com pounds. About 20% of these compounds were identified, and included hydrocar bons, ketones, heterocyclics, aldehydes, aromatics, carobxylic acids, ester s, sulphur compounds, nitriles, an an-tine and an amide. About 20 identifie d compounds were present in both biofilter influent gases. The influent gas at Plant I contained more straight chain hydrocarbons, while the influent gas at Plant 2 contained more sulphur compounds and esters. Sensory evaluat ion of the gas samples using the GC-odour port technique indicated that abo ut 45 compounds in the biofilter influent gases were odorous at Plant 1, an d about 30 were odorous at Plant 2. A variety of odour characters was obser ved in the two biofilter influent gases. The biofilters reduced the concent ration of most of the odorous compounds to levels that were not detectable by the GC-odour port analysis. The rendering process gases had odour concen trations of between 59,000 and 1,000,000 OU m(3). The biofilters reduced th e odour concentration by 82-99% and also reduced the "offensiveness" of the odour. Uneven gas distribution affected biofilter odour-removal performanc e.