Assessment of Process Limiting Factors During the Biofiltration of Odorous VOCs in a Full-Scale Composting Plant

The removal efficiency (RE) profile of a complex mixture of volatile organic compounds (VOCs) was characterized in a full-scale biofilter treating odorous emissions from a composting plant in an urban environment. The biofilter was composed of two similar units packed with mixtures of pine bark and wood chips, and were operated in parallel. Up to 48 different VOCs were identified by gas chromatography-mass spectrometry (GC-MS) and individual RE values were calculated by comparing influent and effluent GC-MS chromatograms. Multivariate correlations on RE, the partition coefficients between octanol/water (K-OW), octanol/air (K-OA) and water/air (K-WA), as well as biodegradability and toxicity estimates, were established by Principal Component Analysis (PCA). Biofilter RE values were positively and negatively correlated to K-OA and to K-WA, respectively, indicating that hydrophobic volatile compounds were more efficiently removed than the hydrophilic ones. Instead, RE was poorly correlated with estimates of the VOCs fast aerobic biodegradation. Substrate mass transfer (adsorption on the hydrophobic packing/biomass), rather than biodegradation rates, appears to be the main process governing the efficiency in conventional air biofilters applied for the treatment of odorous emissions.