Self-cycling fermentation strategy for efficient bioethanol production from wheat straw by Kluyveromyces marxianus

The economic feasibility of lignocellulosic ethanol production depends on obtaining high yields and productivity. This condition requires extensive research to identify strategies that maximize yield and productivity in lignocellulosic ethanol production. Self-cycling fermentation (SCF) has been shown to increase ethanol productivity. To validate whether the SCF system could enhance productivity during ethanol fermentation, we simulated the process using experimental results obtained from six cycles in a stirred bioreactor and compared the outcomes with separate hydrolysis and fermentation (SHF) and simultaneous saccharification-fermentation (SSF) for ethanol production from wheat straw using Kluyveromyces marxianus SLP1. The volumetric ethanol productivity (Q_p) was 1.11 g/Lh, 1.13 g/Lh, and 0.42 g/Lh for SCF, SHF, and SSF, respectively. The system with the highest global productivity (Q_g) was SCF with 0.65 g/Lh. Moreover, the estimated annual ethanol productivity for SCF (P_SCF) improved by 21.7% compared with SHF and by 3.1-fold improvement over SSF. This result confirms that SCF can be an effective strategy for increasing productivity during lignocellulosic ethanol production. However, the SCF system is limited by the physiological states of the yeasts.