Research Projects

Project at a Glance

Project Status: complete

Title: Impact of organic substrate on NO oxidation in biofilters

Principal Investigator / Author(s): Chang, Daniel P. Y.

Contractor: UC Davis

Contract Number: 00-311


Research Program Area: Emissions Monitoring & Control

Topic Areas: Stationary Sources


Abstract:

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 overall goals of the ARB-funded project were to verify and understand a postulated improvement in the effectiveness of the NO-oxidizing biofilm through addition of an organic substrate (glucose). A report had appeared in the literature [Chou and Lin, 200l] at about the time that the EISG project was initiated, indicating that relatively rapid removal of high concentrations of nitric oxide (NO) was possible through the addition of glucose. The empty-bed contact time (EBCT) required to achieve about 80 percent removal was reported to have decreased to about 2 minutes for NO present at about 1000 ppmv. The specific objectives of this study were to: * determine the effects of organic addition on the biofilm * 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.


 

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