Abstract
Ethanol fermentation requires oxygen to maintain high biomass and cell viability, especially under very-high-gravity (VHG) condition. In this work, fermentation redox potential (ORP) was applied to drive the aeration process at low dissolved oxygen (DO) levels, which is infeasible to be regulated by a DO sensor. The performance and characteristics of flocculating yeast grown under 300 and 260 g glucose/L conditions were subjected to various aeration strategies including: no aeration; controlled aeration at −150, −100 and −50 mV levels; and constant aeration at 0.05 and 0.2 vvm. The results showed that anaerobic fermentation produced the least ethanol and had the highest residual glucose after 72 h of fermentation. Controlled aerations, depending on the real-time oxygen demand, led to higher cell viability than the no-aeration counterpart. Constant aeration triggered a quick biomass formation, and fast glucose utilization. However, over aeration at 0.2 vvm caused a reduction of final ethanol concentration. The controlled aeration driven by ORP under VHG conditions resulted in the best fermentation performance. Moreover, the controlled aeration could enhance yeast flocculating activity, promote an increase of flocs size, and accelerate yeast separation near the end of fermentation.
Highlights
Ethanol fermentation requires oxygen to maintain high biomass and cell viability, especially under very-high-gravity (VHG) condition
There is controversy regarding fuel ethanol production by fermenting starch-based feedstock, which can otherwise be consumed by humans, there is no doubt that ethanol is the most utilized bio-energy all around the world[1]
This work investigated the effects of various aeration strategies on VHG ethanol fermentation and yeast flocculating characteristics by using an ORP sensor instead of a traditional dissolved oxygen (DO) probe
Summary
Ethanol fermentation requires oxygen to maintain high biomass and cell viability, especially under very-high-gravity (VHG) condition. The performance and characteristics of flocculating yeast grown under 300 and 260 g glucose/L conditions were subjected to various aeration strategies including: no aeration; controlled aeration at −150, −100 and −50 mV levels; and constant aeration at 0.05 and 0.2 vvm. The controlled aeration driven by ORP under VHG conditions resulted in the best fermentation performance. The formation of yeast flocs helps this yeast strain enduring ethanol toxicity, which makes it suitable to propagate under VHG conditions[4]. The stressful environment encompassing VHG fermentation results in incomplete glucose utlization at the end of fermentation (aka, stuck fermentation), leading to slow yeast growth and low yeast viabilty.
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