Ethanol fermentation coupled with complete cell recycle pervaporation system: Dependence of glucose concentration

Abstract

A membrane bioreactor system comprised of a fermenter and a flat pervaporation module was developed for continuous ethanol fermentation by Saccharomyces ccrevisiue. In order to obtain the guidelines for high sugar concentration fermentation, the dependence of glucose concentration on the coupled system was investigated. Fed by 158 and 29Og glucose/l, the improvement in productivity was obtained with 1. 58 and

A review of pervaporation for product recovery from biomass fermentation processes

“…For example, Pichia stipitis CBS 5773 experiences ethanol inhibition at 2 wt% ethanol, which is several times lower than the concentration of ethanol found to inhibit Saccharomyces cerevisiae 42. As a result, organisms which are highly sensitive to the produced solvent but which otherwise possess superior performance characteristics (for example, thermotolerance) could be employed if the solvent concentration is depressed using a separation technology. Increasing the concentration of viable cells in the fermentor will increase the solvent productivity of the fermentor, all other variables being equal 41, 56, 71, 74, 75, 79, 89, 96. For example, Nakao et al observed a 200–300% increase in fermentor ethanol productivity (mass of ethanol produced per unit of reactor volume per unit of time, ie kg m −3 h −1 ) when pervaporation was coupled directly with a fermentor 79.…”

“…Since pervaporation removes water along with produced ethanol, cell density will increase upon application of pervaporation, although this increase will be small compared to that achieved using other approaches like filtration 75. Unfortunately, few studies in which product separation technologies have been mated to fermentors actually monitored the concentration of viable cells; without this information the true increase in productivity cannot be assessed. Integrating a solvent recovery unit with a fermentor enables the use of more concentrated substrate solutions which increases the productivity of the fermentor and reduces the amount of water processed in the system 20, 24, 33, 43, 54, 56, 61, 93, 105. Taylor et al were able to feed a 550 g dm −3 glucose solution to a fermentor while maintaining the ethanol concentration in the fermentor at about 5 wt% by removing the ethanol via a gas stripping process 33.…”

“…Unfortunately, each of the first three trends may also lead to undesirable consequences such as higher levels of non‐alcohol inhibitors 38, 56, 66, 71, 86, 89. These inhibitors may include organic acids (such as formic, acetic, citric, butyric, and lactic acids), organic compounds (such as acetaldehyde, ethyl acetate, methanol, isobutanol, methyl butanol, furfural, 5‐hydroxymethylfurfural), and salts (such as NaCl, MgCl 2 ) 10, 20, 56, 71, 76, 86. By increasing fermentor productivity, higher amounts of substrate are fed/consumed per unit volume of the fermentor.…”

“…Increasing the concentration of viable cells in the fermentor will increase the solvent productivity of the fermentor, all other variables being equal 41, 56, 71, 74, 75, 79, 89, 96. For example, Nakao et al observed a 200–300% increase in fermentor ethanol productivity (mass of ethanol produced per unit of reactor volume per unit of time, ie kg m −3 h −1 ) when pervaporation was coupled directly with a fermentor 79.…”

“…From an analysis of ethanol production from biomass, Lynd concluded that the energy usage and cost of distillation is not a primary constraint to the competitiveness of such a process 12. However, the advantages of distillation over competing separations technologies for biofuel recovery fade as the scale of the operation is reduced, thereby opening the door for other technologies such as gas stripping,9, 10, 30–43 liquid–liquid extraction,34–39, 44, 45 vacuum stripping,35, 36, 38, 46–51 membrane distillation,52, 53 vacuum membrane distillation (VMD),31, 34, 54, 55 sorption,34–38 and pervaporation 34–39, 56–89. In this paper, the potential for using pervaporation in the recovery of liquid biofuels from dilute fermentation broths will be reviewed.…”