Impact of Organic Substrate on No Oxidation in Biofilters Final rept

摘要

This project complemented a project funded by the California Energy Commission's Energy Innovations Small Grant (EISG) program. The EISG project examined the feasibility of using a commercial carbon-foam packing to enhance the specific surface area on which the biofilm develops in an aerobic biofilter. The enhanced surface area would reduce the mass-transfer limitation in the removal of nitric oxide (NO) from exhaust streams. The specific objectives of this study were to: determine the effects of organic addition on the biofilm, and to determine the role of heterotrophic microorganisms in enhancing NO removal. In this project, enhanced aerobic biodegradation of NO as a result of organic substrate addition was not conclusively observed. The explanations of such an observation provided by the authors of the earlier study appear to be unsubstantiated. Our alternate explanation for high removal efficiencies observed at EBCTs of a few minutes is that abiotic oxidation occurs rapidly in both the gas and aqueous phases when the NO concentration exceeds about 100 ppm. Although enhanced removal of NO was observed when glucose was added in the present study, the weight of evidence suggests that NO removal was most likely a result of reduction rather than oxidation to nitrate. As a practical matter, the ratio of carbon consumed to nitrogen removed for high removal of NO in the present study was greater than one order of magnitude. That ratio is consistent with other studies of NO reduction by bacteria and fungi under overall aerobic conditions.