Tuesday, April 20, 2010
11-14
Effects of ammonia impurity in syngas on ethanol production via fermentation
Biomass is an attractive energy feedstock because it is an abundant, domestic, renewable resource that can be converted to liquid transportation fuels. Currently, most of the ethanol research is centered on fermenting sugars obtained from biomass. An alternative process is fermentation of biomass-generated syngas --more carbon in the biomass can be converted to end products. For this process, most research uses “clean” syngas instead of biomass syngas. However, there is a great difference in the compositions between the “clean” syngas and biomass syngas—the latter contains several impurities such as benzene, hydrogen sulfide, ammonia, etc. Therefore, an understanding of the effects of impurities from syngas on ethanol production will provide critical information regarding the need for efficient gas cleaning processes for commercialization.
From available syngas compositions, ammonia can range from 2800-4000 ppm. Since ammonia is very soluble in culture media, ammonium ion can accumulate during the fermentation process. This work will present the effects of ammonia impurity on cell growth, enzyme activity, and ethanol production. Initially, NH4OH was used as the ammonia ion source for bottle batch studies, ranging from 0 to 500 mM. Key findings include: (a) cell growth rate was substantially inhibited with increasing [NH4+]; (b) the acetic acid to ethanol conversion mechanism was inhibited; and (c) hydrogenase activity was inhibited at low [NH4+]. The results of batch studies were confirmed in continuous gas flow bioreactors with pH control. Furthermore, K3PO4 was used as a substitute for NH4OH to obtain an insight into the root cause of cell growth inhibition. It was found that osmolarity likely plays a key role in the cell growth mechanism. In addition, media absorption efficiency for ammonia was also obtained under different mass flow rates for fixed media volume in order to assess the effect of ammonia on industrial fermentation processes.
From available syngas compositions, ammonia can range from 2800-4000 ppm. Since ammonia is very soluble in culture media, ammonium ion can accumulate during the fermentation process. This work will present the effects of ammonia impurity on cell growth, enzyme activity, and ethanol production. Initially, NH4OH was used as the ammonia ion source for bottle batch studies, ranging from 0 to 500 mM. Key findings include: (a) cell growth rate was substantially inhibited with increasing [NH4+]; (b) the acetic acid to ethanol conversion mechanism was inhibited; and (c) hydrogenase activity was inhibited at low [NH4+]. The results of batch studies were confirmed in continuous gas flow bioreactors with pH control. Furthermore, K3PO4 was used as a substitute for NH4OH to obtain an insight into the root cause of cell growth inhibition. It was found that osmolarity likely plays a key role in the cell growth mechanism. In addition, media absorption efficiency for ammonia was also obtained under different mass flow rates for fixed media volume in order to assess the effect of ammonia on industrial fermentation processes.
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See more of The 32nd Symposium on Biotechnology for Fuels and Chemicals (April 19-22, 2010)
See more of General Submissions
See more of The 32nd Symposium on Biotechnology for Fuels and Chemicals (April 19-22, 2010)