Journal of Energy Bioscience 2025, Vol.16, No.5, 263-272 http://bioscipublisher.com/index.php/jeb 266 Because sweet potatoes have a high sugar content and are rich in water, microorganisms can easily decompose the residue of sweet potatoes and produce methane. Some varieties, such as Laranjeiras and BRS Cuia, have higher biomethane potential (BMP), with gas production exceeding 2,900 liters per hectare (De Paula Batista et al., 2019). However, complex starch structures, especially amylopectin, can reduce enzyme activity and prolong digestion time (Catherine and Twizerimana, 2022) (Figure 2). Figure 2 Biogas production setup (Adopted from Catherine and Twizerimana, 2022) In practical applications, sweet potato residue can be used alone or mixed with livestock and poultry manure for anaerobic digestion. Co-digestion helps balance the carbon-nitrogen ratio, enhance microbial activity and system stability (Montoro et al., 2025). After co-digestion with livestock and poultry manure, biogas production can be increased by approximately 12.65%, methane content can reach 61.92%, and organic matter degradation and nutrient recovery rate are also improved. 4.2 Process optimization Pretreatment is crucial for increasing biogas production because the complex starch structure makes its digestion more difficult. Thermochemical pretreatment (such as using NaOH solution) can break down starch and cellulose, making the material more digestible (Catherine and Twizerimana, 2022). Under the optimal conditions (NaOH 2.9 g/L, 82 ℃, 102 min), biogas production increased by 33.88%, methane content rose from 42% to 64%, and digestion time was shortened from 22 days to 16 days (Catherine and Twizerimana, 2022). Other pretreatment methods, such as grinding, hot water treatment and enzyme pretreatment, are also very common. Both intermittent and continuous anaerobic digesters can be used. Batch reactors are suitable for small-scale or laboratory applications, while continuous stirred tank reactors (CSTR) are more suitable for industrial production with stable output (Catherine and Twizerimana, 2022; Montoro et al., 2025). New systems such as multi-stage reactors and anaerobic membrane bioreactors can further increase methane production and system performance. Process optimization also includes precise control of temperature, pH value and carbon-nitrogen ratio. 4.3 Biogas production and utilization of by-products The biogas production and methane content of sweet potato residue depend on the substrate composition, pretreatment and process parameters. After optimization, the yield can reach 37.8 mL/g (in terms of dry matter), and the methane content can reach 64%, which is much higher than that of untreated sweet potato residue (Catherine and Twizerimana, 2022). Co-digestion further improved these results and demonstrated stable energy conversion (Montoro, Santos, and De Lucas, 2025). Although the biogas production varies among different sweet potato varieties, on the whole, its potential for sustainable utilization is huge (De Paula Batista et al., 2019; Montoro et al., 2025). In addition to biogas, anaerobic digestion can also produce nutrient-rich digestion products and liquid by-products. These by-products can be used as bio-organic fertilizers to recycle nutrients and improve the soil (Montoro et al., 2025). Liquid digests are rich in nitrogen, phosphorus and potassium, making them suitable for crops or gardens. Solid residues can be composted or used to increase soil organic matter and fertility.
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