Effect of product removal by a pervaporation on ethanol fermentation

Ethanol fermentation is inhibited by the products of the reaction and the p roductivity is reduced with increase in the concentrations of products. By removing the products from the fermentor, a high productivity can be mainta ined during fermentation. In this paper, we propose a new method of long-te rm fermentation with minimal wastewater, and evaluate the effect of removal of ethanol by pervaporation (PV) on ethanol fermentation. Three types of f ermentation experiments were carried out; batch fermentation as the standar d process, fed-batch fermentation without PV, and fed-batch fermentation wi th PV. Glucose and immobilized baker's yeast were used for the fermentation s. A module of a hydrophobic porous membrane made of polypropylene (PP) was used for the PV process. Fed-batch fermentation with or without PV was car ried oat for 72 h, and the feed rate (F) was equal to the sum of the produc tion rate (P) and drain rate of broth (W), and was=1 l/12 h. When the remov al ratio (R) was adjusted to 84.4%, the concentration of ethanol in the bro th remained almost constant at 50 g/l, and the apparent rate of ethanol pro duction was 2 times higher than that in fermentation without PV. Total etha nol produced was 780 g, and the conversion efficiency of glucose to ethanol was 96.3% of the theoretical yield. The amount of wastewater was 38.5% of that discharged from the conventional batch process. Furthermore, it was sh own that as the riverse of inhibition constant (1/K-i) approached zero at R =100%, tbe effect of byproducts on tbe fermentation was negligible, thus in dicating that in the presence of PV, the reduced ethanol productivity was o nly due to ethanol inhibition under present conditions.