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| Very High Gravity Ethanol Production Under Different Aeration Schemes |
| ZI Li-han, LIU Chen-guang, WANG Na, YUAN Wen-jie, BAI Feng-wu |
| School of Life Science and Biotechnology, Dalian University of Technology, Dalian 116023, China |
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Abstract Under very high gravity (VHG) ethanol fermentation, aeration is an essential operation parameter for yeast cell to improve the performance of ethanol production. Flocculating yeast was used to convert 300 g glucose/L medium under 5 aeration schemes, including non-aeration, controlled-aeration regulated by redox potential (ORP) at -150 mV and -100 mV, constant aeration by pumping air at the rate of 0.05 vvm and 0.2 vvm. ORP was monitored under all conditions and taken as a criterion to distinct anaerobic, microaerobic and aeraobic conditions. The results showed that anaerobic fermentation produced the least ethanol (119±1.5 g/L) and left the highest glucose in 72 h. Microaerobic fermentation achieved the accurate air supply depending on the real-time cell oxygen demand, which lead to higher ethanol concentration (131±1.8和125±1.7 g/L). Aerobic fermentation brought about a quick biomass formation, and corresponding fast substrate utilization. However, too large aeration rate like 0.2 vvm caused the low yield (decreased by 12.2%) due to the huge formation of biomass and by-product such as glycerol. On the other hand, the lost of ethanol by air flow was highest under this condition. Moreover, it was observed that the flocculation quantified was promoted by increasing the air supply. In order to undertake a comprehensive evaluation for ethanol production and flocculation characteristic under different aeration schemes, a series of radar plots were illustrated based on data normalization. Constant aeration at 0.05 vvm was the preferable aeration condition thanks to its performance balance at all investigated aspects.
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Received: 04 March 2013
Published: 25 June 2013
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