BIOTRICKLING FILTER TECHNOLOGY FOR TREATING ETHANOL EMISSIONS FROM BAKERIES

The management of volatile organic compounds in bakery exhaust gases (mainly ethanol) was identified as a high priority problem by the American Bakers Association in conjunction with their member companies. 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). The biotrickling filter employed in the pilot study used a synthetic fibrous support media to immobilize the biofilm. In addition, bench-scale studies were conducted to determine the effectiveness of the support media and develop initial estimates of biotrickling filter performance.Ethanol concentrations were monitored at three locations: (1) the gas inlet to the first biotrickling filter stage; (2) the gas outlet from the first biotrickling filter stage and at the entrance to the second stage; and (3) exit gas from the second stage of the biotrickling filter. 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.