Mathematical modeling of ethanol production from glycerol by Enterobacter aerogenes concerning the influence of impurities, substrate, and product concentration

The application of biodiesel derived crude glycerol for ethanol production using Enterobacter aerogenes TISTR 1468 involved multiple interactions among substrate (glycerol), impurities (methanol) and product (ethanol and acetic acid). A mathematical model based on Monod and Luedeking-Piret models were established to simulate the cell performance in the presence of inhibitors. The Monod model was modified by adding the inhibition factors in terms of critical concentration (C-Ac* < C-EtOH* < C-MeOH* < C-Gly*) and its inhibition degree (ni) (n(Gly) > n(MeOH)( )> n(Ac) > n(EtOH) with the values of 119.06, 13.33, 1 and 0.0383, respectively). The Luedeking-Piret model confirmed that ethanol and acetic acid were predominantly growth-associated products. Glycerol up to 24.31 g/L and 31.32 g/L were optimum for cell growth and ethanol productivity, respectively. The cell performance was affected by methanol even at its lowest concentration tested (7.92 g/L). The applicability of the new two-phase growth model during the growth phase and stationary phase in the crude glycerol medium was validated and proved accurate (r(2) > 0.98).