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

The microwave-assisted alkali salt (NaCl, MgCl 2 , and KCl) in combination with H 3 PO 4 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–H 3 PO 4 pretreatment system which is in line with maximum saccharification per biomass of 79% using commercial xylanase and cellulase enzyme cocktail (Com CK –XylCell). Comparable saccharification per biomass of 74% was obtained with in-house xylanase and cellulase enzyme cocktail (Cr CK –XylCell). The simultaneous saccharification and fermentation by KCl–H 3 PO 4 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 Com CK –XylCell and Cr CK –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 H 3 PO 4 can serve as a cost-effective and environment friendly pretreatment method for high production of sugar and ethanol.