Journal of Energy Bioscience 2024, Vol.15, No.5, 326-336 http://bioscipublisher.com/index.php/jeb 329 also increase costs (Sundar et al., 2014). Additionally, the presence of inhibitors such as furans and phenolic compounds, which can be released during pretreatment, can negatively impact enzyme activity and reduce conversion efficiency (Wang et al., 2020). 3.3 Fermentation techniques Fermentation is the final step in the production of cellulosic ethanol, where fermentable sugars are converted into ethanol by microorganisms. The choice of microbial strains and optimization of fermentation conditions are crucial for maximizing ethanol yields. Ethanol-producing strains such as Saccharomyces cerevisiae and engineered Escherichia coli have been widely used. Recent studies have also explored the use of novel wild yeast strains, such as Scheffersomyces parashehatae, which have shown promising results in fermenting both pentose and hexose sugars (Antunes et al., 2021). Process optimization involves adjusting parameters such as temperature, pH, and nutrient availability to enhance microbial activity and ethanol production. Simultaneous saccharification and fermentation (SSF) is a commonly used process that combines enzymatic hydrolysis and fermentation in a single step, reducing the overall processing time and costs (Wang et al., 2019; Wang et al., 2020). One of the main challenges in the fermentation of lignocellulosic biomass is the presence of lignin, which can inhibit microbial activity and reduce fermentation efficiency. Lignin-derived compounds, such as phenolics, can be toxic to fermenting microorganisms, leading to lower ethanol yields (Wang et al., 2019; Wang et al., 2020). Strategies to overcome this challenge include the use of pretreatment methods that effectively reduce lignin content and the development of microbial strains that are more tolerant to lignin-derived inhibitors (Wang et al., 2019; Antunes et al., 2021). 4 Technological Evaluation and Optimization 4.1 Process integration The integration of pretreatment, hydrolysis, and fermentation processes is crucial for optimizing the production of cellulosic ethanol from switchgrass. Various pretreatment methods such as dilute acid, ammonia fiber explosion (AFEX), and liquid hot water (LHW) have been evaluated for their efficiency in breaking down the lignocellulosic structure of switchgrass to release fermentable sugars (Tao et al., 2011; Martín and Grossmann, 2012). Enzymatic hydrolysis follows these pretreatments to convert the released sugars into glucose and xylose, which are then fermented to produce ethanol. The choice of pretreatment significantly impacts the overall yield and efficiency of the process. For instance, dilute acid hydrolysis followed by molecular sieves for dehydration has been identified as an optimal flowsheet, reducing energy consumption and cooling needs (Martín and Grossmann, 2012). Additionally, the co-fermentation of pentoses and hexoses using novel yeast strains has shown promise in maximizing ethanol yield from both C5 and C6 sugar streams (Antunes et al., 2021). Energy and water consumption are critical factors in the sustainability of cellulosic ethanol production. Advanced bioconversion technologies, such as multieffect columns and heat integration, have been employed to minimize energy usage (Martín and Grossmann, 2012). Studies have shown that the production of ethanol from switchgrass can lead to significant energy savings and reduced greenhouse gas emissions compared to fossil fuels (Laser et al., 2009; Jin et al., 2019). Water use is another important consideration, with integrated process designs aiming to optimize water recycling and reduce overall consumption. For example, the use of liquid hot water pretreatment has been found to be effective in reducing water usage while maintaining high ethanol yields (Larnaudie et al., 2019; Larnaudie et al., 2021). 4.2 Lifecycle assessment Lifecycle assessments (LCA) of switchgrass ethanol production have demonstrated favorable energy balances and significant reductions in greenhouse gas (GHG) emissions. Switchgrass ethanol has been shown to produce 540% more renewable energy than the nonrenewable energy consumed during its production (Schmer et al., 2008). Additionally, GHG emissions from switchgrass ethanol are estimated to be 94% lower than those from gasoline,
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