The fermentation process integrated with membrane distillation

Ethanol production in tubular bioreactor integrated with the membrane disti llation (MD) system has been investigated. The fermentation of sugar with S accharomyces cerevisiae proceeds with the formation of by-products, which t ends to inhibit the yeast productivity. The removal of by-products front th e fermenting broth by MD process increased the efficiency and the rate of s ugar conversion to ethanol. The fermentation process carried out in the mem brane bioreactor with the yeast concentration of 20 g dm(-3) resulted in th e productivity of 5.5 g EtOH dm(-3) h and the efficiency closed to 95% afte r 20 h. The productivity decreased to 2.6 g EtOH dm(-3) h with the efficien cy below 50%, for the fermentation under similar conditions, but without MD . The separation of alcohol by MD enabled to achieve a higher content of et hanol in the permeate than that in the broth. The enrichment coefficient am ounted to 2-6 were depended on the ethanol concentration in the feed. The p resence of yeast cells in the feed increased the concentration and the temp erature polarization, consequently the ethanol flux through the membrane wa s reduced by ca. 50%. A beneficial effect of carbon dioxide presence in the feed on the ethanol flux was found. The evolution of CO2 bubbles from the fermenting broth enhanced the turbulence in the boundary layer, hence the e thanol transport through the membrane increased. (C) 2001 Elsevier Science BN, All rights reserved.