EFFECTS OF DIFFERENT CHEMICAL PRETREATMENTS ON CELL WALL COMPOSITION AND ASH CONCENTRATION OF SWEET SORGHUM BAGASSE FOR BIOETHANOL PRODUCTION

Pretreatment is one of the key processes in lignocellulosic bioethanol production, which is needed to improve accessibility of enzymes to cellulose. This study was conducted to investigate the effects of different chemical pretreatments on cell wall composition and ash concentration of sweet sorghum bagasse. 9 different pretreatment methods used in the study can be categorized into 3 different methods such as dilute sulphuric acid (1, 1.5 and 2 % H2SO4 w/v), dilute sodium hydroxide (1, 1.5 and 2 % NAOH w/v) and sequential dilute sulphuric acid and sodium hydroxide (1 % H2SO4 w/v + 0.5 M NAOH, 1.5 % H2SO4 w/v + 0.5 M NAOH and 2 % H2SO4 w/v + 0.5 M NAOH). According to results, while 2 % H2SO4 w/v + 0.5 M NAOH gave the highest cellulose (91.51 %) and lowest lignin (1.7 %) concentrations, the lowest cellulose (65.11 %), hemicellulose (0.4 %), and highest lignin concentrations (23.42 %) were provided by 1.5 % H2SO4 w/v among pretreatments. Cellulose, hemicellulose and lignin contents of sweet sorghum bagasse after sodium hydroxide pretreatments ranged from 76.72 to 79.88, 11.75 to 14.62, and 2.05 to 4.11 %, respectively. The most appropriate cell wall composition for enzymatic hydrolysis was derived from sequential dilute sulphuric acid and sodium hydroxide pretreatments due to the fact that they provided the highest cellulose (90.68 – 91.51 %), lowest lignin (1.7 – 3.41 %) and desirable hemicellulose (1.10 – 1.82 %) contents. However, enzymatic hydrolysis must be done to learn which method enables the highest fermentable sugar production.