Comparison of strategies for the simultaneous saccharification and fermentation of cashew apple bagasse using a thermotolerant Kluyveromyces marxianus to enhance cellulosic ethanol production

Simultaneous saccharification and fermentation (SSF) is a promising process for the bioconversion of lignocellulosic biomass. Furthermore, an efficient approach to reduce the capital costs for the production of bio-based products is the use of high glucan loading. Therefore, in this study, a comparison of SSF strategies were investigated aiming to enhance ethanol production from acidic-alkaline pretreated cashew apple bagasse (CAB-OH) by Kluyveromyces marxianus ATCC36907 at high glucan loading. An ethanol concentration of 58 g/L was achieved with 15% CAB-OH using batch SSF, resulting in an 81.2% overall ethanol yield. Prehydrolysis of 12 h, prior to SSF, did not significantly increase the overall ethanol yield. Fed-batch SSF, using high loadings of solids, was also investigated. Ethanol concentrations of up to 67 g/L could be produced from CAB-OH (20% w/v) by adding fresh substrate every 4 h during the first 48 h of SSF (10% initial and 2.5% of feeding), achieving an overall ethanol yield of 81%. In the fed-batch mode, the amount of enzyme was lower than used in batch and this process allowed higher ethanol concentrations and similar yield. No major differences in fed-batch performance, considering ethanol concentration and yield, were observed for the different feeding amounts, around 68 g/L and 80.7%, respectively.