Laboratory scale optimization of alkali pretreatment for improving enzymatic hydrolysis of sweet sorghum bagasse

Abstract

Sweet sorghum has been identified as a promising feedstock for biological conversion to fuels as well as other chemicals. The lignocellulosic stalk of sweet sorghum, called sweet sorghum bagasse (SSB) is a potential source of lignocellulosic biofuel. The primary goal of this study was to determine optimal alkali (lime : Ca(OH)2 and lye : NaOH) pretreatment conditions to obtain higher yield of total reducing sugar while reducing the lignin content for biofuel production from SSB. Biomass conversion and lignin removal were simultaneously optimized through four quadratic models analyzed by response surface methodology (RSM). The optimal conditions for lime pretreatment was 1.7% (w/v) lime concentration, 6.0% (w/v) SSB loading, 2.4 h pretreatment time with predicted yields of 85.6 total biomass conversion and 35.5% lignin reduction. For lye pretreatment, 2% (w/v) alkali, 6.8% SSB loading and 2.3 h duration were the optimal levels with predicted biomass conversion and lignin reduction of 92.9% and 50.0%, respectively. More intensive pretreatment conditions removed higher amounts of hemicelluloses and cellulose. Fourier transform infrared spectroscopy (FTIR) spectrum and scanning electron microscope (SEM) image revealed compositional and microstructural changes caused by the alkali pretreatment.

THE EFFECTIVENESS OF PHYSICAL AND ALKALI HYDROTHERMAL PRETREATMENT <br> IN IMPROVING ENZYME SUSCEPTIBILITY OF SWEET SORGHUM BAGASSE

“…Meanwhile, the result of study conducted by Toquero & Bolado (2014) using wheat straw showed that alkali hydrothermal pretreatment removed 51% of acid insoluble lignin. These suggested that the performance of pretreatment for different types of lignocellulose could be differ widely depending on the composition of biomass and severity of pretreatment conditions, although under same chemical pretreatment (Umagiliyage et al, 2015). The weight loss of biomass caused by alkali hydrothermal pretreatment was the highest than those caused by other pretreatments used in this study.…”

Optimization of Saccharification Conditions of Lignocellulosic Biomass under Alkaline Pre-Treatment and Enzymatic Hydrolysis

“…Glucose concentration (mg/g), xylose concentration (mg/g), the rate of saccharification [35] Potato peel residues t = 30-60 • C, pH = 5-8, substrate concentration 2-10% (w/v), and surfactant concentration 0-1% (v/v) Saccharification yield [30] Sweet sorghum bagasse t = 50 • C, pH = 4.8, τ = 48 h Total reducing sugars, morphological changes [27] Coffee pulp t = 30 • C, τ = 48 h Reducing sugars, total reducing sugars, glucose concentration [29] Coastal bermudagrass t = 55 • C, pH = 4.8, τ = 72 h Total reducing sugars, glucose yield, xylose yield [26] Switchgrass t = 55 • C, pH = 4.8, τ = 72 h Total reducing sugars, concentration of glucose and xylose [37] The appropriate design of combined alkaline pre-treatment and enzymatic hydrolysis allows to obtain high yields of monosugars in hydrolyzates, even close to theoretical ones. Additionally, low concentrations of substances acting as inhibitors are formed, which is beneficial during further fermentation process.…”

“…Biomass conversion, lignin removal, morphological changes [27] Coffee pulp C NaOH = 0-8% w/v; C Ca(OH)2 = 0-8% w/v; t = 121 • C, τ = 16.5-33.4 min; S:L = 1:5 w/v…”

Nitric Acid Pretreatment of Jerusalem Artichoke Stalks for Enzymatic Saccharification and Bioethanol Production

“…lignin. The content of cellulose, the most important component, was comparable to that of other feedstock commonly used for bioethanol production, e.g., 36.3% for corn stover [41], 36.9% for sweet sorghum bagasse [33], 35.8% for rice straw [42], and 38.7% for wheat straw [43].…”