Model-based estimation of optimal temperature profile during simultaneous saccharification and fermentation of Arundo...

A kinetic model fitted to enzymatic hydrolysis of Arundo donax was coupled to a fermentation kinetic model derived from simultaneous saccharification and fermentation (SSF) experiments at different temperatures for the determination of optimal temperature profile (between 36 and 45°C) using iterative dynamic programming (IDP). A sensitivity analysis of enzyme kinetic model not only facilitated model reduction in terms of number of parameters, but also enabled artifacts from parameter estimations to be identified. In separate fermentation experiments conducted at 35, 40, 45, and 50°C using ∼40 g/L background glucose in fiber-free liquid fraction of Arundo it was found that growth was possible at 40°C, but the fermentation capacity was completely lost after 12 h at 50°C. The final ethanol concentration obtained after 120 h in isothermal SSF experiments at 36, 39, 42, and 45°C were 10.6, 13.7, 14.2, and 12.5 g/L, respectively. The predicted optimal temperature profile in SSF determined by iterative dynamic programming was (i) gradual decrease from 40 to 37.5°C until 16 h, (ii) a linear increase upto 45°C until 80 h, and (iii) gradual decrease by 1°C until 120 h. Experimental results were in good agreement with the model predictions. The ethanol concentration after 72 h obtained in the optimal case was 13.6 g/L in comparison to 9.1, 12.2, 12.6, and 11.6 g/L for ISO-SSF at 36, 39, 42, and 45°C, respectively. Moreover this value was 95.8% of the final value achieved at the end of 120 h, indicating that the process times could be significantly shortened by using non-isothermal SSF.