Journal of Energy Bioscience 2024, Vol.15, No.5, 326-336 http://bioscipublisher.com/index.php/jeb 328 Various pretreatment methods have been explored, including mechanical, chemical, and biological strategies. Mechanical pretreatment involves physical processes such as milling or grinding to reduce the particle size and increase the surface area of the biomass. Chemical pretreatment methods include the use of acids, alkalis, and solvents. For instance, dilute acid (DA) and ammonia fiber expansion (AFEX) are common chemical pretreatments that have been shown to be effective in breaking down the lignin and hemicellulose components of switchgrass (Figure 1) (Tao et al., 2011; Wang et al., 2020). Biological pretreatment involves the use of microorganisms or enzymes to degrade lignin and hemicellulose, making the cellulose more accessible. This method is often combined with other pretreatment strategies to enhance efficiency (Chen et al., 2018; Kothari et al., 2018). Figure 1 SEM images of untreated and pretreated switchgrass: (a) untreated switchgrass; (b) HNO3 pretreated switchgrass; (c) NaOH pretreated switchgrass; (d) C2H5OH pretreated switchgrass at 10 000×magnification (Adopted from Wang et al., 2020) Different pretreatment methods vary in their efficiency and the challenges they present. Chemical pretreatments such as dilute acid and ionic liquid pretreatment have shown high efficiency in reducing lignin content and increasing enzymatic saccharification rates. For example, ionic liquid pretreatment resulted in a 96% glucan yield in 24 hours, significantly enhancing the rate of enzyme hydrolysis compared to dilute acid pretreatment (Li et al., 2010). However, the cost and environmental impact of chemical pretreatments, particularly those involving ionic liquids, can be significant challenges (Li et al., 2010; Smullen et al., 2017). Mechanical pretreatments, while less costly, often require high energy inputs and may not be as effective in breaking down lignin. Biological pretreatments are environmentally friendly but can be slower and less efficient compared to chemical methods (Chen et al., 2018; Kothari et al., 2018). Overall, the choice of pretreatment method depends on a balance between efficiency, cost, and environmental considerations. 3.2 Enzymatic Hydrolysis Enzymatic hydrolysis is a critical step in converting pretreated biomass into fermentable sugars. Advances in enzyme technologies have focused on improving the efficiency and reducing the cost of enzymes. Recent studies have demonstrated the use of engineered enzymes and enzyme cocktails that can more effectively break down cellulose and hemicellulose into simple sugars (Sundar et al., 2014; Wang et al., 2020). For instance, the use of a combination of cellulases and β-glucosidase has been shown to significantly increase glucose yields from pretreated switchgrass (Sundar et al., 2014). Several factors affect the efficiency of enzymatic hydrolysis, including the type of pretreatment used, enzyme loading, and the presence of inhibitors. Pretreatment methods that effectively reduce lignin content and increase cellulose accessibility tend to result in higher enzymatic hydrolysis efficiency (Li et al., 2010; Kothari et al., 2018). Enzyme loading is another critical factor; higher enzyme concentrations generally lead to higher sugar yields, but
RkJQdWJsaXNoZXIy MjQ4ODYzMg==