Journal of Energy Bioscience 2025, Vol.16, No.4, 172-181 http://bioscipublisher.com/index.php/jeb 178 easier for farmers to organize themselves. Cooperatives can also help apply for loans, coordinate government subsidies, provide technical services, etc., which is very useful. To make this system smoother, it is also necessary to clearly define the rights and responsibilities of each party and how to divide the benefits. Only in this way can farmers have a greater sense of participation and trust, and cooperatives can cooperate better and move towards standardization (Sheikha and Ray, 2017; Iqbal et al., 2021). 8 Case Study: Rural Biogas Deployment Using Sweet Potato 8.1 Location and demographics: brief description of the study site. This case study was selected from a rural area in China. Most people here are engaged in agriculture, and most farmers are family units. The labor force is mainly middle-aged and elderly people, the population density is neither high nor low, and the crops are mainly food and cash crops, sweet potatoes are one of them (De Paula Batista et al., 2019; Montoro et al., 2025). 8.2 Project design: who led the initiative (government, NGO, private). This biogas project is led by the local government. The government provides policy and technical support, and the agricultural cooperative is responsible for organizing everyone to participate and collecting raw materials. Farmers grow sweet potatoes themselves and process part of the raw materials (Montoro et al., 2025). 8.3 Sweet potato cultivation model: contract farming, subsidies, or cooperative growing. Here, the "cooperative + farmer" approach is adopted to grow sweet potatoes. Farmers and cooperatives sign contracts, the price is set in advance, and the cooperatives also provide planting training. Some places also have planting subsidies to encourage everyone to grow more sweet potatoes and ensure a stable source of raw materials (Montoro et al., 2025). 8.4 Technology used: digesters, pre-treatment, energy use (cooking, lighting). The project uses anaerobic digesters, also known as biogas digesters. Sweet potato waste is first treated with thermochemical treatment before use, such as using NaOH to improve the fermentation effect. The biogas produced is mainly used in farmers' homes, such as cooking and lighting, and some is used to drive some small agricultural machinery (Catherine and Twizerimana, 2022; Montoro et al., 2025). 8.5 Results and lessons learned: 8.5.1 Biogas output vs expectations After thermochemical treatment, the gas production of sweet potato waste increased by about 33.88%, and methane increased by 22%. In addition, the fermentation cycle was shortened from the original 22 days to 16 days. Compared with using only livestock and poultry manure, if it is fermented with sweet potatoes, the gas production can be increased by 12.65%, and the methane ratio can reach 61.92% (Catherine and Twizerimana, 2022; Montoro et al., 2025). 8.5.2 Farmer feedback Most farmers said that the biogas production was relatively stable and sufficient for cooking and lighting. They said that now they no longer had to burn coal or chop wood at home, and life was more convenient (Montoro et al., 2025). 8.5.3 Economic and environmental outcomes This project has greatly increased farmers' income. Using the "co-digestion" method, profits can be increased by 60%. The return of biogas residue and liquid to the fields as fertilizer not only saves money on fertilizers, but also makes the soil better and more environmentally friendly (Montoro et al., 2025). 8.5.4 Key bottlenecks (supply chain, policy, knowledge gaps) However, the project also has some problems. For example, sweet potatoes are seasonal crops, and the supply of raw materials is not stable. Some farmers are not very skilled, and it is difficult to repair biogas equipment when it breaks down. In addition, some subsidy policies are slow to implement, and technical training is not enough, and support in this regard needs to be strengthened (Catherine and Twizerimana, 2022; Montoro et al., 2025).
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