Inhibition effect of secondary metabolites accumulated in a pervaporation membrane bioreactor on ethanol fermentation of Saccharomyces cerevisiae

The secondary metabolites accumulated in a pervaporation membrane bioreactor during ethanol fermentation were mostly composed of acetic acid, lactic acid, propionic acid, citric acid, succinic acid and glycerol. The inhibition effect of these compounds at a broad concentration range was studied through ethanol fermentation by Saccharomyces cerevisiae. An increasing concentration of the secondary metabolites led to longer lag time and a reduction of cell growth. The specific cell growth rate, cell yield, ethanol productivity were only 0.061 h−1, 0.024, 0.47 g L−1 h−1 respectively, when the medium contained 3.12 g of acetic acid, 10.23 g of lactic acid, 2.72 g of propionic acid, 1.35 g of citric acid, 2.26 g of succinic acid and 49.25 g of glycerol per liter (a concentration level in pervaporation membrane bioreactor at later fermentation period). By increasing pH of the medium to 6.0–8.0, the inhibition of these secondary metabolites could be greatly relieved.