Redox potential driven aeration during very-high-gravity ethanol fermentation by using flocculating yeast

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.

The establishment of a marine focused biorefinery for bioethanol production using seawater and a novel marine yeast strain

“… 36 claimed that fermentations conducted in stressful environments involving very high gravity medium results in incomplete utilisation of glucose at the end of fermentation. In addition, the stressful condition leads to slow yeast growth and low cell viability that will lead to a lower ethanol production 36 . However, ethanol yields were very similar in seawater-based media containing up to 20% glucose using our marine yeast ( S. cerevisiae AZ65) investigated in this study.…”

“…Ethanol yield in this study could have been enhanced by supplying a low amount of air or oxygen during the fermentation (micro-aerobic condition). Liu et al ., (2016) found that supplying low amounts of oxygen during a very high gravity ethanol fermentation enhanced the yield and productivity of ethanol 36 . Oxygen advances cell recovery through the TCA cycle and respiration pathway by retaining vital cellular components during synthesis and carbon utilisation.…”

Enhancement of ethanol production in very high gravity fermentation by reducing fermentation-induced oxidative stress in Saccharomyces cerevisiae

“…However, the potential of these candidate antioxidants for application in VHG ethanol fermentation is needed to be evaluated. In addition to antioxidant supplementation, optimal aeration has been reported to be essential to achieve high ethanol yield under VHG fermentation conditions, due to its role in maintaining a proper oxygen supply and a stable redox environment 34 . However, aeration will also increase oxygen solubility in fermentation media, thereby potentially enhancing ROS production.…”

Integrated Process for Bioenergy Production and Water Recycling in the Dairy Industry: Selection of Kluyveromyces Strains for Direct Conversion of Concentrated Lactose-Rich Streams into Bioethanol

“…This is a common industrial setup in sugarcane ethanol production in Brazil, where high cell density fermentation is achieved through yeast recycling [33]. Moreover, it is generally accepted that yeast cell viability is lower under anaerobic conditions [34], and, in particular, K. lactis is unable to grow under strict anaerobiosis, although it can ferment and grow under oxygen-limiting conditions, e.g., below 1% air saturation [35].…”