Biofiltration Of Ethanol Emissions From Bakery Operations

By Dr. Rakesh Govind and James Fang

The management of volatile organic compounds in bakery exhaust gases was identified as a high priority problem by the American Bakers Association in conjunction with their member companies. Biotrickling filter technology was evaluated among other approaches and was selected for a pilot study to control ethanol emissions from a bakery oven exhaust gas stream. Biofilters and biotrickling filters use microbial populations in biofilms that grow on support media to degrade or transform contaminants in the air. The biotrickling filter employed in the pilot study used a synthetic fibrous support media to immobilize the biofilm. A pilot study was conducted from September 1997 to February 1998, to assess the performance of biotrickling filter technology in treating organic emissions from bakery ovens. Bench-scale studies were conducted to determine the effectiveness of the support media and develop initial estimates of biotrickling filter performance. Pilot studies were performed with USEPA's trailer mounted two-stage biotrickling filter system, at flowrates in the range of 1.8-3.0 standard cubic meters per minute (65-104 standard cubic feet per minute). Removal efficiencies in the range of 80% to 100% were measured experimentally, and averaged 91% over the duration of the study. The pilot-scale biofilter produced removal efficiencies exceeding 80% for about 99.6% of its operating time. The pressure drop across the bed was less than 6.4 millimeters (0.25 inches) of water. The test further revealed that the biotrickling filter was quite robust; it responded quickly to changes in inlet concentration and exhibited a recovery time of less than 150 minutes after a nine day shutdown period. Preliminary economic analysis of the biotrickling filter system, from a Reasonably Available Control Technology (RACT) perspective, showed that the tested biotrickling filter technology is cost-effective for treating ethanol emissions from a bakery oven.