Bioethanol production from delignified rice straw by using a novel crude recombinant enzyme cocktail in pre-saccharification simultaneous saccharification and fermentation process

Abstract

This study highlights the problem of differences in the optimum temperatures for the operation of enzymatic saccharification and fermentation processes for lignocellulosic bioethanol production. Therefore, to address this problem, the pre-saccharification simultaneous saccharification and fermentation (PSSF) was carried out for bioethanol production from deep eutectic pretreated rice straw using crude recombinant bacterial enzyme cocktail and the process was statistically optimized by Central Composite Design approach. The three variables viz. pre-saccharification time, enzyme dosage and fermentation temperature were considered for maximizing the ethanol yield and productivity. Statistical analysis of PSSF optimization inferred that low pre-saccharification time (9.6–15 h) and crude enzyme dosage (above 60 FPU/g) significantly influence higher ethanol yield and productivity. Statistical optimization resulted in optimum conditions: 12.2 h pre-saccharification time, crude enzyme dosage (83.7 FPU/g), fermentation temperature (33.7°C) with predicted ethanol yield, 0.35 g/g and productivity, 0.63 g/L/h. The validation of the PSSF process at bioreactor-level in 1.0 L working volume under optimized conditions gave ethanol yield, 0.37 g/g and productivity, 0.82 g/L/h resulting in an overall yield of 182 L ethanol/tonne raw-RS. This study shows the applicability of crude recombinant enzyme cocktail preparation and the modeled PSSF process as a promising industrial approach for bioethanol production using rice straw.