title: Variation of fermentation redox potential during cell-recycling continuous ethanol operation.
abstract: Fermentation redox potential was monitored during cell-recycling continuous ethanol operation. The cell-recycling system (CRS) was operated using two hollow fibre (HF) membranes (pore sizes 0.20 and 0.65μm) at three dilution rates (0.02, 0.04 and 0.08h-1). Saccharomyces cerevisiae NP 01 were recycled in the fermenter at a recycle ratio of 0.625. Aeration was provided at 2.5vvm for the first 4h and then further supplied continuously at 0.25vvm. As steady state was established, results showed that the fermentation redox potential was lower for processes employing CRS than those without. At the same dilution rates, the sugar utilization and ethanol production with CRS were higher than those without CRS. The highest fermentation efficiency (87.94g/l of ethanol, ∼90% of theoretical yield) was achieved using a 0.2-μm HF membrane CRS at a dilution rate of 0.02h-1. It was found that 7.53-10.07% of the carbon derived from glucose was incorporated into the yeast. Further, at the same dilution rates, yeast in the processes with CRS incorporated less carbon into ethanol than in those grown without CRS. This result suggests that processes involving CRS utilize more carbon for metabolite synthesis than biomass formation. This indicated that the processes with CRS could utilize more carbon for metabolite synthesis than biomass formation.
authors.affiliation: Graduate School, Khon Khon University, Khon Kaen 40002, Thailand.
authors.forename: Arthit
authors.initials: A
authors.lastname: Thani
authors.affiliation: Department of Chemical and Biological Engineering, University of Saskatchewan, Saskatoon, SK S7N5A9, Canada. Electronic address: yenhan.lin@usask.ca.
authors.forename: Yen-Han
authors.initials: YH
authors.lastname: Lin
authors.affiliation: Department of Biotechnology, Faculty of Technology, Khon Kaen University, Thailand.
authors.forename: Pattana
authors.initials: P
authors.lastname: Laopaiboon
authors.affiliation: Department of Biotechnology, Faculty of Technology, Khon Kaen University, Thailand. Electronic address: lakcha@kku.ac.th.
authors.forename: Lakkana
authors.initials: L
authors.lastname: Laopaiboon
mesh_terms: D018533:Biomass; D019149:Bioreactors; D018929:Cell Culture Techniques; D000431:Ethanol / Q000032:analysis / Q000378:metabolism; D005285:Fermentation / Q000502:physiology*; D010084:Oxidation-Reduction; D015003:Yeasts / Q000166:cytology / Q000378:metabolism
chemical_list: D000431:Ethanol
keywords: Cell-recycling system; Continuous fermentation; Fermentation efficiency; Hollow fibre membrane