Development of microwave-assisted alkaline pretreatment methods for enhanced sugar recovery from bamboo and corn cobs: Process optimization, chemical recyclability and kinetics of bioethanol production

Abstract

The present study optimized two microwave-assisted alkaline (Na3PO4.12H2O and NaOH) pretreatment methods for the enhancement of sugar recovery from different lignocellulosic substrates (bamboo and corn cobs) with varying structural compositions. Subsequently, the chemical recyclability of the optimized alkaline pretreatments were evaluated on corn cobs. Furthermore, kinetics of microbial cell growth and bioethanol production in simultaneous saccharification and fermentation (SSF) processes were assessed. The optimized Na3PO4.12H2O pretreatment conditions resulted in the maximum reducing sugar yield (0.512 g/g) from corn cobs. Interestingly, the recyclability studies demonstrated that the NaOH-based black liquor resulted in a slightly higher average sugar yield (0.37 g/g) compared to the Na3PO4.12H2O (0.31 g/g) over three pretreatment cycles. Kinetics showed a maximum specific growth rate and maximum potential bioethanol concentration of 0.175 h−1 and 16.928 g/L respectively for the optimized NaOH pretreated corn cobs. The findings from this study provide significant knowledge enhancements pertaining to the use of gold standard, well-known NaOH methods, in addition to the emerging Na3PO4.12H2O alkaline catalyst for the pretreatment of lignocellulosic substrates with varying structural compositions. Moreover, recyclability of Na3PO4.12H2O and NaOH black liquor demonstrated the potential to reduce costs associated with the application of chemicals and fresh water in pretreatment systems. Kinetics of cell growth and bioethanol production elucidates noteworthy indices such as the maximum specific growth rate of the cells, lag time and maximum bioethanol production for lignocellulosic process development and scale-up procedures.