Alkaline pretreatment optimization for Pinus roxburghii needle biomass employing response surface methodology for bioethanol production by separate hydrolysis and cofermentation

ABSTRACT

Production of bioethanol from lignocellulosics can cater to the supply of renewable fuel to transport sector besides being environment friendly. In the present work, bioethanol production potential of Pinus roxburghii needle biomass (PNB) has been studied by optimizing the thermochemical pretreatment method using alkaline conditions (NaOH) firstly by one variable at a time (OVAT) approach, followed by Response Surface Methodology (RSM) with central composite design (CCD) tool. Total reducing sugar (TRS) yield was enhanced from 22.4 g/L (OVAT) to 32.4 g/L using design of experiment (DoE) approach. Effect of pretreatment on PNB was studied by FTIR, phloroglucinol staining and estimation of phenolics which indicated lignin removal. Enzymatic hydrolysis was done by the action of commercial enzymes cellulase and pectinase with loading of 5U/g biomass. The TRS yield was further enhanced to 67.95 g/L after enzymatic hydrolysis. Using separate hydrolysis and cofermentation (SHCF) approach for fermentation of PNB hydrolysate, 28.75 g/L bioethanol was obtained when combined cultures of Saccharomyces cerevisiae (MTCC-36) and Pichia stipitis (NCIM-3498) were used.