Journal of Energy Bioscience 2025, Vol.16, No.5, 263-272 http://bioscipublisher.com/index.php/jeb 265 3.3 Ethanol output and efficiency The output of ethanol depends on the variety, starch content and process parameters. Each kilogram of dry sweet potato residue can produce 210-226 grams of ethanol with a concentration of 79-113 grams per liter (Wang et al., 2016; Gou et al., 2023). The theoretical yield can reach 4 800~10 000 liters per hectare (Lareo et al., 2013; Rizzolo et al., 2021) (Figure 1). The net energy ratio can reach 1.48, and the energy gain is 6.55 megajoules per liter (Wang et al., 2013). The key factors include starch content, enzyme type, strain activity and pH value. Cleaner energy use and better crop management can enhance energy and environmental efficiency (Costa et al., 2018). Figure 1 Conversion process of sweet potato into ethanol (Adopted from Rizzolo et al., 2021) 3.4 Pilot and commercial applications China has built several pilot projects and commercial chemical plants for sweet potato ethanol, promoting the energy transition in rural areas (Zhang et al., 2011; Wang et al., 2016). Brazil and India are also carrying out similar work, with a focus on breeding and technological innovation (Rizzolo et al., 2021). The key to success lies in stable raw materials, simplified production processes and the utilization of by-products. Although sweet potato ethanol has a lower environmental impact than some fuels, problems such as water eutrophication and gas emissions still exist (Wang et al., 2013; Costa et al., 2018). Centralized production, green planting and policy support will contribute to the sustainable development of this industry. 4 Sweet Potato Residue Produces Biogas 4.1 Anaerobic digestion potential Sweet potato residue is an agricultural waste rich in starch, cellulose and soluble sugar, and has huge potential for biomass energy. There are differences in the contents of moisture, reducing sugar and organic matter among different varieties of sweet potato roots and residues, which will affect the ease of decomposition and gas production during anaerobic digestion (De Paula Batista et al., 2019).
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