Journal of Energy Bioscience 2025, Vol.16, No.5, 263-272 http://bioscipublisher.com/index.php/jeb 267 5 Environmental and Economic Benefits 5.1 Environmental sustainability Life cycle assessment (LCA) shows that the net energy ratio of sweet potato bioethanol is 1.48, and the net energy gain is 6.55 MJ/L. This means it uses energy more efficiently than fossil fuels (Wang et al., 2013; Sanni et al., 2022). The use of sweet potato ethanol and biogas can help cut greenhouse gases and lower the need for oil and other nonrenewable energy. Compared with corn or cassava, sweet potato makes better use of land. It can still grow well on poor soil or marginal land, so it does not take land away from food crops (Sheikha and Ray, 2017; Sanni et al., 2022). Sweet potato waste can also be reused. After anaerobic digestion treatment, the residue can be converted into organic fertilizer and energy (Weber et al., 2020; Montoro et al., 2025). This not only reduces waste but also helps to recycle useful materials. Even so, the production of sweet potato biofuel still brings some environmental problems, such as eutrophication and acidification. The use of fertilizer and pesticide, and the steam used in production, may cause water and air pollution. Studies show that steam use, crop yield, and fertilizer input are key factors that affect the environmental results (Wang et al., 2013). To make the process greener, we can replace coal with clean energy and promote precise fertilization in farming. The liquid and solid leftovers from biogas production can also go back to the fields as organic fertilizer, reducing chemical fertilizer use (Montoro et al., 2025). 5.2 Economic opportunities The sweet potato industry brings jobs and supports other related industries like energy and environmental protection (Weber et al., 2020). In places such as Brazil and China, making bioethanol and biogas from sweet potatoes increases the value of crops and helps improve rural areas and technology (Montoro et al., 2025). Farmers can earn money not just from selling the roots but also from using vines and residues to make other products (Sheikha and Ray, 2017). A sweet potato biorefinery can make ethanol, biogas, and liquor at the same time. This brings more income sources. In many cases, the projects show good net present value (NPV) and internal rate of return (IRR). Some projects can get back the investment in only one year (Weber et al., 2020). Using co-digestion can increase biogas output and raise profits by about 60% compared to using only animal manure (Montoro et al., 2025). These projects not only make money but also create new jobs and improve local economies. 5.3 Cost-benefit analysis Economic studies show that sweet potato ethanol factories can reach a return on investment (ROI) of 41.96% when working at 80% of capacity. This is higher than sorghum and only slightly lower than cassava. The break-even price is about $3.27 per gallon. When the selling price is higher, the project makes a profit (Sanni et al., 2022). If the factory produces ethanol and liquor together, profits can grow even more. In some cases, the net present value goes over $1 million, and the internal rate of return reaches 51%, with the payback period just over one year (Weber et al., 2020). For biogas projects, using co-digestion and by-products helps improve cost-effectiveness. Over half of these projects can reach a positive net present value (Montoro et al., 2025). The main factors that affect cost and profit include the price of raw materials, yield, energy use, process efficiency, and the sale of by-products (Wang et al., 2013; Sanni et al., 2022; Montoro et al., 2025). Steam use and the type of energy are also very important. Using clean energy and better technology can lower costs (Wang et al., 2013). Using sweet potato residues and vines adds extra income and spreads the cost of materials and treatment (Weber et al., 2020; Montoro et al., 2025). Compared with sugarcane, sweet potato projects may have lower profit per unit, but they are better for the environment and for society.
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