Microwave-assisted pretreatment using alkali metal salt in combination with orthophosphoric acid for generation of enhanced sugar and bioethanol

Abstract

The microwave-assisted alkali salt (NaCl, MgCl2, and KCl) in combination with H3PO4 pretreatment of rice straw followed by enzymatic hydrolysis with in-house and commercial enzyme cocktail (cellulase and xylanase) was investigated. The effect of pretreatment on the structure and composition of RS was investigated using XRD and FTIR analysis, and the result suggested strategic structural changes in the RS structure. The maximum CrI of 51.3% was obtained with KCl–H3PO4 pretreatment system which is in line with maximum saccharification per biomass of 79% using commercial xylanase and cellulase enzyme cocktail (ComCK–XylCell). Comparable saccharification per biomass of 74% was obtained with in-house xylanase and cellulase enzyme cocktail (CrCK–XylCell). The simultaneous saccharification and fermentation by KCl–H3PO4 pretreated system of RS resulted the maximum sugar yield of 30.6 and 26.9% and ethanol yield of 12.2 and 11.9 g/L using ComCK–XylCell and CrCK–XylCell cocktail, respectively, along with Saccharomyces cerevisiae MTCC 173. The hydrolysis of pretreated RS pulp using in-house enzyme cocktail resulted in high sugar and ethanol yield suggesting that the studied alkali metal in combination with weak acid such as H3PO4 can serve as a cost-effective and environment friendly pretreatment method for high production of sugar and ethanol.