Lignocellulosic ethanol production employing immobilized Saccharomyces cerevisiae in packed bed reactor

• EHB were used up to 40 repeated fermentation batches with 97% ethanol yield.
• In continuous mode, 82 g L−1 ethanol with ≈30 g L−1 h−1 productivity was obtained.
• Using rice straw enzymatic slurry, ≈25 g L−1 h−1 ethanol productivity was observed.
• REH without detoxification makes ethanol production economical and sustainable.

Most of ethanol production processes are limited by lower ethanol production rate and recyclability problem of ethanologenic organism. In the present study, immobilized co-fermenting Saccharomyces cerevisiae GSE1618 was employed for ethanol fermentation using rice straw enzymatic hydrolysate in a packed bed reactor (PBR). The immobilization of S. cerevisiae was performed by entrapment in Ca-alginate for optimization of ethanol production by varying alginic acid concentration, bead size, glucose concentration, temperature and hardening time. Remarkably, extra hardened beads (EHB) immobilized with S. cerevisiae could be used up to repeated 40 fermentation batches. In continuous PBR, maximum 81.82 g L−1 ethanol was obtained with 29.95 g L−1 h−1 productivity with initial glucose concentration of 180 g L−1 in feed at dilution rate of 0.37 h−1. However, maximum ethanol concentration of 40.33 g L−1 (99% yield) with 24.61 g L−1 h−1 productivity was attained at 0.61 h−1 dilution rate in fermentation of un-detoxified rice straw enzymatic hydrolysate (REH). At commercial scale, EHB has great potential for continuous ethanol production with high productivity using lignocellulosic hydrolysate in PBR.