Biological treatment of hazardous air pollutants from corn-to-biofuel dry mill production facilities
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Development of renewable energy sources such as ethanol has become a priority to meet growing energy demands. In the United States, the majority of ethanol is produced at dry mill facilities that convert corn to ethanol; these facilities can be a major emission source for volatile organic compounds (VOCs). Biofiltration is a promising VOC control technology but its effectiveness for the VOC mixtures emitted from ethanol production facilities has yet to be determined. The main goal of this research was to evaluate the feasibility of using biofiltration to treat ethanol plant air pollutants. To accomplish this, microbial degradation of four representative pollutants (formaldehyde, acetaldehyde, ethanol and acetic acid) was examined first in simplified batch reactors and then in a laboratory-scale biofilter system. The batch data indicate that, at a neutral pH, an enriched microbial consortium was capable of completely degrading formaldehyde, acetaldehyde and ethanol, and the Monod model was successfully utilized to describe single substrate degradation kinetics for these pollutants. However, the consortium only partially degraded acetic acid. In binary substrate experiments, acetaldehyde degradation was not significantly affected by either ethanol or formaldehyde. However, acetaldehyde inhibition of ethanol degradation was observed and inhibition kinetics were necessary to describe the observed ethanol removals. Formaldehyde degradation was inhibited in the presence of acetaldehyde and/or ethanol; however, further research will be required to identify the inhibtion. The biofilter study was performed to investigate the effects of pollutant loading, substrate mixtures and low pH on system performance. The results indicate that it is feasible to achieve greater than 97% overall removal efficiency at a short contact time of 5 seconds under neutral pH conditions. The level of substrate inhibition observed in the batch experiments was not evident in the biofilter experiments. However, low pH conditions gradually decreased the biofilter performance with a more significant impact on acetaldehyde, a result that was supported by batch data. Finally, a numerical model that integrated degradation kinetics was able to describe the biofilter performance under the test conditions. This research demonstrates that biofiltration has the potential to be a viable VOC treatment technology at corn-derived ethanol production facilities.