Simultaneous Saccharification and Fermentation of Low Strength Sodium Hydroxide Pre-treated Rice Straw for Higher Ethanol Yields: Batch and Fed Batch Hybrid Approach

Abstract

Low strength sodium hydroxide pre-treated rice straw was hydrolysed at two different solid loadings i.e. 10 and 15 % (w/v) with in-house cellulases (IC) produced by Aspergillus terreus along with commercial cellulases (CC) by using batch and fed batch hybrid simultaneous saccharification and fermentation process. Optimization of process parameters enhanced the crude cellulase activities i.e. filter paper, β-glucosidase and endoglucanase by 1.6, 2.7 and 2.2 fold in 6 days as compared to activities obtained on a single substrate i.e. rice straw. Out of four fed batch approaches, approach III (A-III) at 10 % solid loading yielded higher ethanol concentrations of 30.55 and 28.66 g L−1 by using thermo tolerant in-house yeast strain Kluyveromyces marxianus at 42 °C. Combination of 9 FPU g−1 substrate and CC plus 30 CBU of commercial β-glucosidase (Cβ) yielded slightly higher theoretical ethanol yields of 92.24 % as compared to 86.54 % obtained from IC+Cβ. Dunnett’s Post Hoc Annova test also proved that CC+Cβ were found to be significant in batch as well fed batch experiments as compared to other combinations tried. Thus, fed batch A-III seems to be an optimistic one to overcome the problems associated with batch mode to achieve higher ethanol yields.