Journal of Energy Bioscience 2024, Vol.15, No.5, 277-288 http://bioscipublisher.com/index.php/jeb 278 lignocellulosic biomass into biofuels, including pretreatment processes, enzymatic hydrolysis, and fermentation techniques. The study will also discuss the socio-economic and environmental benefits of second-generation biofuels, as well as the challenges and future prospects in this field. By providing a comprehensive overview, this study seeks to highlight the importance of advancing second-generation biofuel technologies to achieve a sustainable and renewable energy future. 2 Types of Agricultural Waste and Non-food Biomass Used in Second-Generation Biofuels 2.1 Crop residues Crop residues, such as corn stover, wheat straw, and rice husk, are significant sources of lignocellulosic biomass for biofuel production. Corn stover, which includes the leaves, stalks, and cobs left after harvesting corn, is particularly notable for its high ethanol yield potential. One study estimates that 1 mg of corn stover can produce approximately 280 L of ethanol (Lal, 2008). Similarly, wheat straw and rice husk are abundant agricultural by-products that can be converted into biofuels through processes like pyrolysis, which has shown promising results in terms of bio-oil yield (Biswas et al., 2017). However, the removal of these residues from fields can lead to soil degradation and increased CO2 emissions, highlighting the need for balanced management practices (Lal, 2008). 2.2 Forestry residues Forestry residues, including sawdust and wood chips, are another valuable source of biomass for second-generation biofuels. These materials are by-products of the forestry industry and can be utilized without impacting food production. The use of forestry residues can help reduce waste and provide a sustainable energy source. Studies have shown that these residues can be effectively converted into biofuels, contributing to energy efficiency and reducing carbon emissions (Antízar-Ladislao and Turrion-Gomez, 2008). 2.3 Industrial waste Industrial waste, such as bagasse (the fibrous residue from sugarcane processing) and cotton gin trash, also serves as a feedstock for biofuel production. Bagasse, in particular, is a well-established source of biomass for bioethanol production. Utilizing these industrial by-products not only helps in waste management but also provides an additional revenue stream for industries (Antízar-Ladislao and Turrion-Gomez, 2008). The conversion of these wastes into biofuels can be achieved through various biorefinery techniques, which have been reviewed extensively in the literature (Taghizadeh-Alisaraei et al., 2022; Liang, 2024). 2.4 Dedicated non-food crops Dedicated non-food crops, such as switchgrass and Miscanthus, are specifically grown for biofuel production. These perennial grasses are less fertilizer-intensive and can be cultivated on marginal lands, reducing the competition with food crops. Switchgrass and Miscanthus have been shown to be viable sources of biomass for biofuel production, with the added benefit of improving soil health and reducing nutrient runoff (Femeena et al., 2018). However, the high production costs associated with these crops have limited their widespread adoption (Femeena et al., 2018). 3 Technological Pathways for Second-Generation Biofuel Production 3.1 Thermochemical processes Thermochemical processes are pivotal in converting agricultural waste and non-food parts into second-generation biofuels. These processes include gasification, pyrolysis, and hydrothermal carbonization (HTC). Gasification involves the partial oxidation of biomass at high temperatures (800 ℃~1 300 ℃) to produce syngas, a mixture of hydrogen, carbon monoxide, and other hydrocarbons, which can be further processed into biofuels like bio-methanol and Fischer-Tropsch fuels (Sikarwar et al., 2017). Pyrolysis, on the other hand, thermally decomposes biomass in the absence of oxygen to yield biochar, bio-oil, and syngas. The process parameters such as temperature, heating rate, and reaction time significantly influence the yield and quality of the products (Uzoejinwa et al., 2018; Patra et al., 2021). HTC is particularly effective for wet feedstocks like manure, producing hydrochar with enhanced nutrient content and stability when combined with pyrolysis (Lin et al., 2021).
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