Journal of Energy Bioscience 2025, Vol.16, No.4, 172-181 http://bioscipublisher.com/index.php/jeb 176 per hectare. These practices can turn sweet potato biogas production into a "low-input, high-efficiency" green circular agricultural system. 5.4 Lifecycle assessment (LCA): Summary of existing LCA studies on sweet potato-based biogas. Many studies have used the life cycle assessment (LCA) method to analyze the environmental impact of sweet potato biogas systems. From sweet potato planting to transportation, fermentation and final utilization, the carbon emissions in the whole process are much lower than those of corn and wheat straw. Chen et al.'s study in Hunan found that the carbon emissions per unit energy of biogas made from sweet potatoes were 17.6 grams CO2-eq/MJ, which is 85% lower than coal and 65% lower than liquefied gas. Moreover, its energy return ratio (EROEI) is also over 1.8, indicating that it is also cost-effective in terms of energy utilization. Other studies have pointed out that if some optimization measures are added to the system, such as returning biogas residue to the fields or improving water-saving irrigation technology, carbon emissions can be further reduced by 20%. These results show that LCA is very sensitive to management methods and can bring more benefits if used properly (Yang et al., 2024). 6 Technology Integration and Processing Chain 6.1 Harvesting and storage: post-harvest handling challenges Sweet potato is a good raw material for biogas production, but its tubers contain a lot of water and reducing sugars. These components affect the yield of biogas. Different sweet potato varieties have different water absorption, decay speed, yield and quality. These differences also make post-harvest storage and processing difficult. Varieties with high water and sugar content are more likely to deteriorate. Therefore, after the sweet potato is harvested, appropriate methods should be adopted for storage and transportation to reduce losses and maintain the quality of the raw materials (De Paula Batista et al., 2019). 6.2 Pretreatment techniques: crushing, hydrolysis, ensiling The structure of sweet potato tubers is relatively complex, and it also contains a lot of starch, especially high content of amylopectin, which will affect its hydrolysis efficiency during anaerobic fermentation. To solve this problem, some thermochemical pretreatment methods can be used, such as alkali solution (NaOH), heating treatment, and controlling the treatment time. Studies have found that after this pretreatment, the gas production of sweet potato waste can be increased by 33.88%, and the methane ratio increased from 42% to 64%. At the same time, the time required for fermentation was shortened from 22 days to 16 days. In addition to heat treatment, physical or biological treatments such as crushing and silage can also make sweet potatoes easier to decompose and extend their shelf life (Catherine and Twizerimana, 2022). 6.3 Co-digestion opportunities: sweet potato mixed with manure or other substrates If sweet potatoes and livestock and poultry manure are fermented together, it will be more efficient than fermenting them separately. This "co-digestion" method not only increases gas production, but also makes the entire system more cost-effective. Studies have shown that co-digestion can increase gas production by 12.65%, organic matter degradation rate by 15.48%, and methane content can reach 61.92%. At the same time, the fertilizer produced by fermentation is also more nutritious, with nitrogen, phosphorus, and potassium contents of 1.24%, 3.09%, and 3.11%, respectively. In terms of economics, co-digestion can also increase profits by 60%, greatly improving the return on investment (Montoro et al., 2025). 6.4 Biogas yield efficiency: performance metrics from trials and pilot plants Different sweet potato varieties vary greatly in gas production. Some varieties, such as BRS Cuia and BRS Rubissol, can produce 2 906.5 liters of biogas per hectare. But varieties like Bela Vista only produce 398.2 liters/hectare. If combined with optimized pretreatment and co-digestion, the methane content can be stabilized at 61.92%. The gas production efficiency per unit of volatile solids can also reach 0.449 cubic meters/kilogram (De Paula Batista et al., 2019; Catherine and Twizerimana, 2022; Montoro et al., 2025).
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