Improved bioethanol productivity through gas flow rate-driven self-cycling fermentation

Abstract

Background: The growth of the cellulosic ethanol industry is currently impeded by high production costs. One possible solution is to improve the performance of fermentation itself, which has great potential to improve the economics of the entire production process. Here, we demonstrated significantly improved productivity through application of an advanced fermentation approach, named self-cycling fermentation (SCF), for cellulosic ethanol production. Results:The flow rate of outlet gas from the fermenter was used as a real-time monitoring parameter to drive the cycling of the ethanol fermentation process. Then, long-term operation of SCF under anaerobic conditions was improved by the addition of ergosterol and fatty acids, which stabilized operation and reduced fermentation time. Finally, an automated SCF system was successfully operated for 21 cycles, with robust behavior and stable ethanol production. SCF maintained similar ethanol titers to batch operation while significantly reducing fermentation and down times. This led to significant improvements in ethanol volumetric productivity (the amount of ethanol produced by a cycle per working volume per cycle time)-ranging from 37.5 to 75.3%, depending on the cycle number, and in annual ethanol productivity (the amount of ethanol that can be produced each year at large scale)-reaching 75.8 ± 2.9%. Improved flocculation, with potential advantages for biomass removal and reduction in downstream costs, was also observed. Conclusion:Our successful demonstration of SCF could help reduce production costs for the cellulosic ethanol industry through improved productivity and automated operation.

High-level production of maltobionic acid from high-maltose corn syrup by genetically engineered Pseudomonas taetrolens

“…In an industrial point of view, the decrease in productivity is a disadvantage because it lengthens the process and thus increases the cost [ [25] , [26] , [27] ]. However, the bulk price of the HMCS ($370/ton) was approximately 94.6-fold lower than that of the pure maltose ($35,000/ton) ( https://www.alibaba.com ).…”

The Influence of Long and Short Cycle Schemes of Self-Cycling Fermentation on the Growth of E. Coli and S. Cerevisiae

“…Control parameters used to establish cycling conditions have included dissolved oxygen (DO), carbon dioxide evolution rate (CER), or oxidation-reduction potential (ORP) (Brown 2001). Mass ow rate of the exit gas has also been used for SCF of S. cerevisiae Superstart TM producing ethanol (Wang et al 2020) and was a direct re ection of CER under anaerobic conditions. In studies of phenol degradation using Pseudomonas putida ATCC 12633 (Hughes and Cooper 1996) and Acinetobacter calcoaceticus RAG-1 ATCC 31012 grown on hexadecane (van Walsum and Cooper 1993), CER patterns were found to mirror DO patterns, and CER maximum aligned with DO minimum.…”

“…It is a semi-continuous, unsteady-state, cyclical mode of operation, in which, following an initial batch growth, cycles are triggered when the depletion of a limiting nutrient occurs (Brown and Cooper 1991;). Many metabolism-and growth-related parameters, including dissolved oxygen (DO), carbon dioxide evolution rate (CER), oxidation-reduction potential (ORP), and exit gas mass ow rate, have served as control parameters to ful ll the automated feedback-control necessary for SCF cycling (Brown 2001; Wang et al 2020Wang et al , 2021. When a pre-established condition of the control parameter is met, SCF cycling is triggered and exactly one half of the working volume is harvested before being replenished with the same amount of fresh medium (Brown and Cooper 1991;).…”

“…Recent SCF works using E. coli ATCC 11303), E. coli CY15050(Storms et al 2012), and engineered S. cerevisiae CEN.PK 113-1A Matα (Agustin 2015) depicted an identical trend -cell count doubled step-wise at the maximum in CER (at the cycle midpoint), but glucose, the limiting nutrient, was only exhausted once the decrease in CER attened (at the end of the cycles). In ethanol fermentation using S. cerevisiae Superstart TM undergoing SCF(Wang et al 2020), glucose was depleted upon the time when CER attened…”

The influence of self-cycling fermentation long- and short-cycle schemes on Saccharomyces cerevisiae and Escherichia coli

“…The increased productivity demonstrated in many SCF studies 1 , 2 , 4 , 6 , 8 , 10 , 11 is strongly related to the operational characteristics of this semi-continuous process. Compared to a conventional batch reactor (BR), SCF cycles have negligible lag or stationary phases.…”