Ethanol Fermentation Process in Series with Gel Immobilized Cells and Integrated with Membrane

The production of fuel alcohol by using the inexpensive and renewable sugar of biomass as raw material is one of the most effective methods to solve energy crisis in the world. The continuous ethanol fermentation with mixed substrates consisting of glucose and xylose was conducted in two fixed columns connected in series and packed with calcium alginate beads encapsulating immobilized yeast cells of Saccharomyces cerevisiae and Pachysolen tannophilus, respectively. The porous PDMS membranes were used to separate the volatile compounds from the fermentation liquid by pervaporation. Since these volatile compounds inhibit the viability of the yeast cells, the elimination of these compounds increases the productivity and yield of ethanol from sugar fermentation. When the fermentation system was operated at the dilution rate of 0.321 h-1, the effluent containing glucose of 0.134 g·L-1 and xylose of 4.92 g·L-1 is steadily produced; the yield of ethanol is 0.457 g(ethanol)·g-1(sugar), it is equivalent to 92.64% of its theoretical value (0.4933 g(ethanol)·g-1(sugar)), and the ethanol productivity reaches 10.996 g·L-1·h-1. From above results, it can be concluded that the novel fermentation process of using immobilized yeast cells matching with PDMS membrane could increase the concentration of yeast cells and the conversion rate of sugar by decreasing the fermentation inhibition caused by the ethanol product.