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Journal of Energy Bioscience 2025, Vol.16 http://bioscipublisher.com/index.php/jeb © 2025 BioSciPublisher, an online publishing platform of Sophia Publishing Group. All Rights Reserved. Sophia Publishing Group (SPG), founded in British Columbia of Canada, is a multilingual publisher. BioSciPublisher, operated by Sophia Publishing Group (SPG), is an international Open Access publishing platform that publishes scientific journals in the field of life science. Sophia Publishing Group (SPG), founded in British Columbia of Canada, is a multilingual publisher. Publisher Sophia Publishing Group Edited by Editorial Team of Journal of Energy Bioscience Email: edit@jeb.bioscipublisher.com Website: http://bioscipublisher.com/index.php/jeb Address: 11388 Stevenston Hwy, PO Box 96016, Richmond, V7A 5J5, British Columbia Canada Journal of Energy Bioscience (ISSN 1925-1963) is an open access, peer reviewed journal published online by BioSciPublisher. The Journal is committed to publishing and disseminating significant original achievements in the related research fields of energy biosciences. All papers chosen for publication should be innovative research work, covering the collection and identification of bio-energy materials, the genetic improvement and breeding of bio-energy organisms, the extraction methods and techniques of biomass energy, the application of biomass energy, and other related research fields. All the articles published in Journal of Energy Bioscience are Open Access, and are distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. BioSciPublisher uses CrossCheck service to identify academic plagiarism through the world’s leading plagiarism prevention tool, iParadigms, and to protect the original authors’ copyrights.
Journal of Energy Bioscience (online), 2025, Vol. 16, No.4 ISSN 1925-1963 https://bioscipublisher.com/index.php/jeb © 2025 BioSciPublisher, an online publishing platform of Sophia Publishing Group. All Rights Reserved. Sophia Publishing Group (SPG), founded in British Columbia of Canada, is a multilingual publisher Latest Content Bioenergy Production from Rapeseed Straw: A Feasibility Study Tianxia Guo, Kaiwen Liang Journal of Energy Bioscience, 2025, Vol. 15, No. 4, 163-171 Case Study on Energy Crop Development: Sweet Potato for Biogas in Rural China Zhang Qian, Wenzhong Huang Journal of Energy Bioscience, 2025, Vol. 15, No. 4, 172-181 Insights into Increasing Biomass Yield in Energy Maize Xiaojing Yang, Han Liu Journal of Energy Bioscience, 2025, Vol. 15, No. 4, 182-192 Strategies for Enhancing Energy Utilization Efficiency of Sorghum Haimei Wang Journal of Energy Bioscience, 2025, Vol. 15, No. 4, 193-204 Engineering C4 Photosynthetic Pathway into Wheat: Progress and Prospects Zhongying Liu, Wei Wang Journal of Energy Bioscience, 2025, Vol. 15, No. 4, 205-215
Journal of Energy Bioscience 2025, Vol.16, No.4, 163-171 http://bioscipublisher.com/index.php/jeb 163 Systematic Review Open Access Bioenergy Production from Rapeseed Straw: A Feasibility Study Tianxia Guo 1, Kaiwen Liang 2 1 Cuixi Academy of Biotechnology, Zhuji, 311800, Zhejiang, China 2 Agri-Products Application Center, Hainan Institute of Tropical Agricultural Resouces, Sanya, 572025, Hainan, China Corresponding email: tianxia.guo@cuixi.org Journal of Energy Bioscience, 2025, Vol.16, No.4 doi: 10.5376/jeb.2025.16.0016 Received: 15 May, 2025 Accepted: 22 Jun., 2025 Published: 03 Jul., 2025 Copyright © 2025 Guo and Liang, This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Preferred citation for this article: Guo T.X., and Liang K.W., 2025, Bioenergy production from rapeseed straw: a feasibility study, Journal of Energy Bioscience, 16(4): 163-171 (doi: 10.5376/jeb.2025.16.0016) Abstract Rapeseed straw is a common type of agricultural waste. We want to see if it can be used for bioenergy, such as ethanol, biogas and protein, etc. In the experiment, we pre-treated the straw with water heat, dilute acid and mechanical methods. This way, its structure would become easier to decompose and the subsequent conversion efficiency would also be higher. Under the best conditions, the ethanol output can reach 12.2 g/L, and the methane output can reach up to 365 N mL/g of volatile solids. The remaining by-products can also be used to produce proteins or some valuable chemicals. We also attempted mechanical crushing and anaerobic digestion of straw and livestock manure together, which can increase gas production and energy recovery. However, the high ash content, high chlorine content and high sulfur content of straw still pose challenges. By improving pretreatment and process combinations, there is an opportunity to increase energy output and reduce greenhouse gas emissions. The aim of this study is to provide data and scheme references for the utilization of rapeseed straw in the field of sustainable energy. Keywords Rapeseed straw; Bioenergy; Biological refining; Pre-treatment; Sustainability 1 Introduction With the increasing global demand for renewable energy, the reuse of agricultural waste is becoming increasingly important. Rapeseed straw is the main by-product left after rapeseed harvest, and its quantity is very large. In the past, people often burned directly in the fields. This not only wasted resources but also polluted the air and increased greenhouse gas emissions (Passoth and Sandgren, 2019; Abbasi-Riyakhuni et al., 2025). Therefore, finding more efficient utilization methods, especially in the field of bioenergy, is beneficial to both environmental protection and economic development. Although rapeseed straw has a high potential for biomass energy, it has a high lignin content and a compact structure, making it difficult to decompose. This will reduce the efficiency of biological transformation and is also a major challenge for industrial utilization. Research has found that if proper pretreatment is not carried out, straw is difficult to be enzymatically hydrolyzed and fermented, thereby affecting the output of fuels such as ethanol, biogas, biodiesel, and some high-value chemicals. There are still many problems in terms of its physicochemical properties, pretreatment methods, transformation processes and economic feasibility (Lopez-Linares et al., 2015; Passoth and Sandgren, 2019; Stolarski et al., 2024; Abbasi-Riyakhuni et al., 2025). This review mainly sorts out and analyzes the new progress of rapeseed straw in bioenergy production, with a focus on introducing pretreatment technologies, conversion routes (such as ethanol, biogas, biodiesel, etc.), energy output and by-product utilization, etc. The technical and economic conditions of different processes will also be compared to identify their advantages and problems, and future development directions will be proposed to provide references for the high-value utilization of agricultural waste and the green energy industry (Luo et al., 2011; Lopez-Linares et al., 2015; Kuglarz et al., 2018; Elsayed et al., 2020; 2022; Yang et al., 2024). 2 Rapeseed Straw as a Biomass Resource 2.1 Production potential Rapeseed (Brassica napus L.) is one of the common oil crops in the world, and there is a large amount of straw. At the current planting level, rapeseed can produce approximately 4.2 tons of dry straw per hectare (Elsayed et al.,
Journal of Energy Bioscience 2025, Vol.16, No.4, 163-171 http://bioscipublisher.com/index.php/jeb 164 2022; Malať ak et al., 2024). In some places, the figure would be between 2.8 and 4.5 tons per hectare (Malať ak et al., 2024). So much straw provides sufficient raw materials for the production of biofuels, biogas and biochar, etc. (Karaosmanoglu et al., 1999; Elsayed et al., 2022; Malať ak et al., 2024; Suchocki, 2024) (Figure 1). Figure 1 Brassica napus (Adopted from Suchocki, 2024) 2.2 Composition and properties Rapeseed straw is mainly composed of cellulose, hemicellulose and lignin, with an approximate ratio of 1:2:0.8 (lignin: cellulose: hemicellulose), and also contains some ash (Hou et al., 2023). It has a high content of cellulose and hemicellulose, and is very suitable for saccharification and biofuel conversion (Hou et al., 2023; Yang et al., 2024; Tang et al., 2025). The carbon-nitrogen ratio of rapeseed straw is approximately 153.82, and the pH value is around 6.05. All these will affect its effect in anaerobic digestion and microbial decomposition (Witaszek et al., 2025). Its high calorific value is approximately 17.36 MJ/kg, with a high carbon content. After pyrolysis, the oxygen content will significantly decrease, which is beneficial for improving fuel quality (Malať ak et al., 2024). However, its ash and chlorine content is not low either. Attention should be paid during combustion or pyrolysis (Hou et al., 2023; Malaťak et al., 2024). 2.3 Seasonality and availability The output and supply of rapeseed straw are mainly related to the harvest season. Generally, a large amount of straw is produced in a concentrated manner after the summer harvest (Malať ak et al., 2024). Rapeseed has a large planting area in Europe, China and other places. The straw resources are abundant and concentrated, which is convenient for collection and large-scale utilization (Malať ak et al., 2024; Suchocki, 2024). In addition, the distribution of straw in the field and the way it is collected will also affect its cost and sustainability in energy utilization (Elsayed et al., 2022; Suchocki, 2024). 3 Technological Pathways for Bioenergy Production 3.1 Thermochemical conversion Thermochemical conversions include incineration, gasification and pyrolysis. slow pyrolysis (slow pyrolysis) can turn rapeseed stalks into biooil and biochar. Studies have found that under the conditions of 650 °C and a heating
Journal of Energy Bioscience 2025, Vol.16, No.4, 163-171 http://bioscipublisher.com/index.php/jeb 165 rate of 30 °C/min, pyrolysis of rapeseed straw and stems can achieve the highest liquid yield, and bio-oil has the potential as fuel (Karaosmanoglu et al., 1999). Biochar has a high carbon content and good reactivity, and can be used as clean solid fuel (Karaosmanoglu et al., 2000). However, the high content of chlorine, sulfur and ash in straw will bring some problems in thermochemical utilization (Stolarski et al., 2024) (Figure 2). Figure 2 Thermophysical characteristics of the straw types under study, mean values of the three harvest years (Adopted from Stolarski et al., 2024) Note: (a) Moisture content; (b) ash content; (c) fixed carbon content; (d) volatile matter content; (e) higher heating value; (f) lower heating value; a, b, c, d, e, denote homogeneous groups for the straw type, separately for each attribute; error bars denote standard deviation (Adopted from Stolarski et al., 2024) 3.2 Biochemical conversion The main biochemical transformations include anaerobic digestion and fermentation. Rapeseed straw can produce biogas through anaerobic digestion, and the output of methane is affected by the size of raw material particles and the carbon-nitrogen ratio. Mechanical pretreatment can make the gas production efficiency higher (Witaszek et al., 2025). When producing bioethanol, pretreatment with dilute acid combined with enzymatic hydrolysis can yield very high glucose and ethanol (ethanol yield can reach 122~125 kg/Mg of straw), and the by-products can be further fermented to produce high-value chemicals such as succinic acid (Lopez-Linares et al., 2015; Kuglarz et al., 2018; Tan et al., 2020). By using the integrated biorefining process, ethanol, biogas and fungal protein can be produced simultaneously, greatly improving the energy recovery rate (Luo et al., 2011; Abbasi-Riyakhuni et al., 2025).
Journal of Energy Bioscience 2025, Vol.16, No.4, 163-171 http://bioscipublisher.com/index.php/jeb 166 3.3 Pre-treatment technologies Rapeseed straw has a compact structure and a high content of lignin, so effective pretreatment must be carried out first to enhance the efficiency of enzymatic hydrolysis and fermentation. Common methods include hydrothermal, dilute acid, alkaline, steam blasting and combined chemical pretreatment. Hydrothermal pretreatment (120 °C ~180 °C) can significantly increase the specific surface area and porosity of straw, making it easier for enzymes to enter and thereby increasing the yields of ethanol and methane (Abbasi-Riyakhuni et al., 2025). Dilute acid and steam blasting can release cellulose, increase saccharification rate and ethanol yield (Lopez-Linares et al., 2015; Kuglarz et al., 2018; Tan et al., 2020). Combined pretreatment (such as organosilicon surfactant combined with H2O2- p-toluenesulfonic acid) can efficiently remove lignin and hemicellulose, with the maximum saccharification rate reaching 87.3% (Yang et al., 2024). Mechanical pretreatment (such as crushing and adjusting particle size) can also improve the effect of anaerobic digestion (Witaszek et al., 2025). 4 Environmental and Socioeconomic Considerations 4.1 Environmental benefits Producing bioenergy from rapeseed straw has obvious benefits for the environment. Compared with fossil fuels or direct incineration, this utilization method can significantly reduce greenhouse gas (GHG) emissions (Wang et al., 2018; Shi et al., 2023; Fang et al., 2024). Through comprehensive biorefining, straw can be converted into various fuels such as ethanol, biogas and biodiesel. This can not only increase energy output, but also reduce pollution (Luo et al., 2011; Elsayed et al., 2020; Abbasi-Riyakhuni et al., 2025). The results of life cycle assessment show that, compared with crops such as sunflowers, rapeseed bioenergy systems have higher ecological efficiency and produce less greenhouse gases per unit of economic value (Forleo et al., 2018). In addition, replacing energy crops with crop residues such as straw can reduce the consumption of land and water, which is helpful for promoting sustainable agriculture (Fang et al., 2024). 4.2 Economic factors Rapeseed straw also has certain economic advantages. The comprehensive biorefining model shows that if the entire rapeseed processing plant produces multiple biofuels simultaneously, the energy recovery efficiency can reach 60%, while the traditional biodiesel process is only 20% (Luo et al., 2011). Regional forecasts indicate that the profits of this industry are considerable, and some places can net a profit of 2.2 billion US dollars in 15 years (Wang et al., 2018). The economic benefit per kilogram of greenhouse gas emissions brought by rapeseed is higher than that of sunflower, indicating that its economic return is better when the environmental impact is relatively small (Forleo et al., 2018). Furthermore, this industry can also bring about many job opportunities. The regional bioenergy sector alone is expected to create 166,000 new job opportunities (Wang et al., 2018). 4.3 Policy and regulatory support Policies and regulations have a significant impact on the development of rapeseed straw bioenergy. The government's planning, support and supervision will directly affect farmers' choices in straw management and energy utilization. Setting clear straw utilization targets, establishing standardized markets, promoting agricultural mechanization and land consolidation can all increase the collection rate and utilization rate of straw (Del Valle et al., 2022). Encouraging the collection and transformation of crop straw instead of open-air burning or leaving it in the fields is crucial for achieving environmental and economic benefits (Wang et al., 2018; Del Valle et al., 2022). These policy measures can help make better use of biomass resources and also contribute to achieving the sustainable development goals. 5 Challenges and Limitations 5.1 Technical challenges There are many technical challenges in producing bioenergy from rapeseed straw. Rapeseed straw is a kind of lignocellulosic biomass with a very tight structure and is not easy to decompose. If no pretreatment is carried out, it is difficult for enzymes and microorganisms to enter, and the transformation efficiency will be very low (Passoth and Sandgren, 2019; Wang et al., 2023; Abbasi-Riyakhuni et al., 2025). High-temperature hydrothermal, dilute acid, physical plus chemical methods can significantly increase the yield of enzymatic hydrolysis and
Journal of Energy Bioscience 2025, Vol.16, No.4, 163-171 http://bioscipublisher.com/index.php/jeb 167 fermentation, but they will make the process more complex and the cost higher (Tan et al., 2020; Wang et al., 2023; Abbasi-Riyakhuni et al., 2025). Fermentation with high solid content may also encounter problems such as moisture control, uneven mixing and inhibitor accumulation, thereby affecting the output of fuels such as ethanol (Tan et al., 2020). In anaerobic digestion and the refining of multi-process products, the stability of the process and the treatment of by-products are also technical difficulties that need to be solved (Luo et al., 2011; Elsayed et al., 2020; Abbasi-Riyakhuni et al., 2025). 5.2 Economic risks The economic feasibility of bioenergy from rapeseed straw is influenced by multiple factors. The high cost of pretreatment and enzymes is a major economic bottleneck for industrialization (Passoth and Sandgren, 2019; Wang et al., 2023). The collection, transportation and storage of straw all require a large amount of infrastructure, which is difficult for small-scale farmers or small enterprises to afford. Straw may also compete for resources with feed, building materials and other uses, pushing up raw material prices and affecting project profits. Market price fluctuations, unstable policy subsidies, and long payback period of investment will also increase investment risks (Forleo et al., 2018; Ren et al., 2019). 5.3 Policy and infrastructure gaps Insufficient policies and infrastructure are also the main obstacles to promoting bioenergy from rapeseed straw. At present, in many places, the ban on straw burning mainly relies on administrative orders, but there is a lack of long-term and effective economic incentives and supervision mechanisms. Therefore, the resource utilization rate of straw is not high (Ren et al., 2019; Del Valle et al., 2022). The regional facilities for straw collection, transportation, storage and processing are not yet complete. There is no unified planning and a lack of large-scale investment. It is difficult for farmers and local governments to complete them alone (Ren et al., 2019). The existing policies are rather fragmented in terms of fiscal subsidies, carbon trading, market access, etc., and lack a stable feedback mechanism, making it difficult to support the sustainable development of the industry (Ren et al., 2019; Del Valle et al., 2022). Therefore, to promote the long-term development of rapeseed straw bioenergy, it is necessary to improve the policy system, increase infrastructure construction, and optimize resource allocation. 6. Case Study: Bioenergy Production from Rapeseed Straw in [Selected Region] 6.1 Project background The Yangtze River Basin is an important major rapeseed production area in China. There are many winter fallows fields here, and the output of rapeseed straw is also very large. In order to develop renewable energy and reduce the pollution caused by straw burning, the local area has carried out a feasibility study on producing bioenergy from rapeseed straw. Using fallow land in winter to grow rapeseed and collect straw not only makes full use of the land, but also provides a stable source of raw materials for the bioenergy industry (Liu et al., 2018). 6.2 Feedstock supply chain The area of fallow land in the Yangtze River Basin is approximately 24.93 million hectares, with an annual rapeseed output of about 46.41 million tons. The straw resources are concentrated and abundant. The collection of straw mainly relies on mechanical harvesting and transportation, and is combined with farmers' cooperatives and bioenergy enterprises, forming a relatively complete supply chain system. Due to the obvious seasonality of straw, it is necessary to arrange storage, transportation and pretreatment reasonably in order to ensure year-round production (Liu et al., 2018; Stolarski et al., 2024). 6.3 Technology adopted The local area mainly adopts biochemical conversion technologies, including anaerobic digestion (biogas production), bioethanol fermentation and biodiesel production. Before conversion, straw needs to be mechanically crushed and pre-treated with thermochemical or dilute acid to enhance the availability of cellulose, and then undergo enzymatic hydrolysis and fermentation. Some projects also attempted to use black soldier fly larvae to process straw and livestock manure together, and simultaneously produce biogas, protein and fat to achieve resource utilization of waste (Elsayed et al., 2020; Tan et al., 2020; 2022; Abbasi-Riyakhuni et al., 2025).
Journal of Energy Bioscience 2025, Vol.16, No.4, 163-171 http://bioscipublisher.com/index.php/jeb 168 6.4 Performance outcomes After optimized pretreatment of rapeseed straw, the methane yield in anaerobic digestion can reach 132.9-365 Nm³/ ton of volatile solids, the ethanol yield can be as high as 12.2 g/L, and the biodiesel yield is approximately 689.4 kg/ hectare. The energy output efficiency (EROEI) is between 1.52 and 1.84, and the greenhouse gas reduction effect is significant, reducing 23.28 million tons of carbon dioxide equivalent annually (Liu et al., 2018; Elsayed et al., 2022; Abbasi-Riyakhuni et al., 2025; Witaszek et al., 2025) (Figure 3). Figure 3 Graphical abstract of the research methodology for straw processing in biogas production (Adopted from Witaszek et al., 2025) 6.5 Economic viability In the Yangtze River Basin, bioenergy enterprises have a relatively solid foundation for development, and nearly 600 related enterprises can be located here. With abundant raw materials, stable energy output, coupled with policy subsidies and carbon reduction benefits, the overall economic performance of the project is quite good. Products such as biogas, ethanol and biodiesel can also replace some fossil energy and improve the economic benefits of rural areas (Felten et al., 2013; Liu et al., 2018). 6.6 Lessons learned (1) The costs of straw collection and logistics are high, and the supply chain needs to be optimized. (2) The high cellulose and high ash content characteristics of straw pose certain challenges to equipment and processes, and the pretreatment and fermentation technologies need to be continuously improved. (3) Multi-production and collaborative processing can enhance resource utilization and economic benefits. (4) Policy support and market mechanisms are very important for the long-term development of the project (Liu et al., 2018; Stolarski et al., 2024). 7 Future Perspectives 7.1 Technological innovations To make efficient use of rapeseed straw, continuous technological improvements are needed. In recent years, the bio-refining technology has developed rapidly, which can convert rapeseed straw into a variety of products such as ethanol, biogas, succinic acid and fungal protein. Hydrothermal pretreatment, dilute acid pretreatment and
Journal of Energy Bioscience 2025, Vol.16, No.4, 163-171 http://bioscipublisher.com/index.php/jeb 169 enzymatic hydrolysis techniques can significantly increase sugar yield and fuel output, and also enhance energy recovery efficiency (Luo et al., 2011; Kuglarz et al., 2018; Passoth and Sandgren, 2019; Abbasi-Riyakhuni et al., 2025). In addition, biotransformation methods such as black soldier fly larvae can simultaneously produce biodiesel and protein, enabling more efficient utilization of waste (Elsayed et al., 2020; 2022). In the future, the energy utilization technology of rapeseed straw will be further upgraded by improving microbial strains, optimizing enzyme preparations and enhancing the value of by-products (Passoth and Sandgren, 2019; Aragonés et al., 2022). 7.2 Integration with circular economy The energy utilization of rapeseed straw is highly consistent with the concept of circular economy. By using biorefining and polyproduction models, not only can energy, chemicals and feed be obtained simultaneously, but also waste and pollution can be reduced (Luo et al., 2011; Passoth and Sandgren, 2019; Aragonés et al., 2022; Abbasi-Riyakhuni et al., 2025). By-products such as organic fertilizers, protein feed and biochar can recycle nutrients, improve soil and increase carbon sinks (Ren et al., 2019; Cowie, 2020). Next, it is necessary to enhance the full life cycle assessment, improve the indicator system for recycling, and maximize the environmental, economic and social benefits (Cowie, 2020; Arsic et al., 2023). 7.3 Policy directions Policies are of great significance for the sustainable development of rapeseed straw bioenergy. Current subsidies, tax incentives, carbon trading and other measures have promoted industrialization, but there is still room for improvement in the cost of second-generation biofuels (Ren et al., 2019; Wang et al., 2022). Future policies can focus on: improving the infrastructure for straw collection and supply chains, promoting cross-regional mechanized operations and logistics optimization; Establish diversified incentive mechanisms to encourage high-value utilization of by-products and carbon reduction; Combining the goals of circular economy and carbon neutrality, formulate a long-term and stable policy system to achieve a win-win situation for agriculture, energy and the environment (Ren et al., 2019; Cowie, 2020; Wang et al., 2022; Arsic et al., 2023). 8 Concluding Remarks Existing research indicates that it is feasible to use rapeseed straw as a raw material for bioenergy, and there are many ways to utilize it. After physical, chemical or biological pretreatment, rapeseed straw can be converted into various energy sources such as bioethanol, biodiesel, biohydrogen and methane. The energy recovery efficiency can reach up to 60%, which is much higher than the 20% of the traditional biodiesel process. Comprehensive utilization of straw can not only increase energy output but also reduce greenhouse gas emissions, with the reduction rate ranging from 9% to 29%. At the same time, it can also enable agricultural waste to be utilized at a higher value. In terms of policy, efforts can be made to promote the industrialization of rapeseed straw bioenergy, improve the collection, transportation and subsidy mechanisms, and encourage the adoption of multi-product bio-refining models to reduce emissions and drive rural economic development. In terms of research, the pretreatment process can be further improved, such as hydrothermal/dilute acid combined with alkali treatment, mechanical crushing, etc., to enhance the saccharification rate and conversion efficiency. At the same time, attention should be paid to the utilization of by-products and the assessment of environmental impacts. In terms of industry, it is suggested to take an integrated approach, combining multi-product integration such as biodiesel, ethanol and biogas, and exploring coordinated development with industries like livestock and poultry breeding and protein feed, so as to enhance economic and environmental benefits. Rapeseed straw bioenergy is not only an effective way to reuse agricultural waste, but also can play a role in mitigating climate change, optimizing the energy structure and promoting the green transformation of rural areas. Its diverse energy products and emission reduction advantages make it an important part of the sustainable energy transition. In the future, with technological progress and policy support, its position in the global renewable energy system is expected to be further enhanced.
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Journal of Energy Bioscience 2025, Vol.16, No.4, 172-181 http://bioscipublisher.com/index.php/jeb 172 Case Study Open Access Case Study on Energy Crop Development: Sweet Potato for Biogas in Rural China Zhang Qian, Wenzhong Huang Biomass Research Center, Hainan Institute of Tropical Agricultural Resouces, Sanya, 572025, Hainan, China Corresponding email: wenzhong.huang@hitar.org Journal of Energy Bioscience, 2025, Vol.16, No.4 doi: 10.5376/jeb.2025.16.0017 Received: 22 May, 2025 Accepted: 30 Jun., 2025 Published: 11 Jul., 2025 Copyright © 2025 Qian and Huang, This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Preferred citation for this article: Qian Z., and Huang W.Z., 2025, Case study on energy crop development: sweet potato for biogas in rural China, Journal of Energy Bioscience, 16(4): 172-181 (doi: 10.5376/jeb.2025.16.0017) Abstract This study mainly talks about how sweet potatoes are used as energy in rural China, especially for biogas production. In addition to being a common food and industrial raw material, sweet potatoes can actually be used as energy crops. Studies have found that different varieties of sweet potatoes vary greatly in their gas production and methane production capabilities. Some varieties, such as Laranjeiras and BRS Cuia, can produce more biogas, which shows that sweet potatoes are still reliable as energy. In southern China, people can rotate sweet potatoes with corn. This method can bring energy benefits, economic benefits and environmental benefits at the same time. In this way, you can increase net energy output, make more money, and reduce greenhouse gas emissions. If sweet potatoes are fermented with animal manure, more biogas will be produced, which is more cost-effective. This is very helpful for the development of a circular economy in rural areas. If the sweet potato waste is treated with heat treatment before fermentation, it can also produce a lot more gas. This also makes the fermentation process faster and shorter. As an energy crop in rural areas, sweet potatoes not only allow farmers to use their own energy, reduce damage to the environment, but also increase income. For promoting sustainable development in rural China, sweet potatoes are a promising choice. Keywords Sweet potato; Energy crops; Biogas; Rural sustainable development; China 1 Introduction As the demand for energy in rural China grows, it is important to find a sustainable and cost-effective energy solution. In many rural areas, the supply of traditional energy cannot keep up, pollution is serious, and the cost of energy is high. Therefore, it is particularly urgent to develop local renewable energy, which can not only improve the living conditions of farmers, but also help drive economic development (Tang et al., 2022). Biogas is a relatively clean energy source. It can not only solve the problem of insufficient energy in rural areas, but also make good use of agricultural waste, reduce environmental pollution, and reduce greenhouse gas emissions. This is very helpful for achieving sustainable development in rural areas (Tang et al., 2022; Montoro et al., 2025). Sweet potato (Ipomoea batatas L.) is a common food and industrial crop in China, and its production is also high worldwide (Liu, 2011). In recent years, sweet potatoes have been considered suitable for energy production, especially for biogas production, due to their high yield, strong adaptability and rich biomass (De Paula Batista et al., 2019; Tang et al., 2022). Studies have found that different sweet potato varieties and planting methods perform well in terms of biomass yield, energy efficiency and reduction of greenhouse gas emissions. Especially in southern China, the economic and environmental benefits of growing sweet potatoes are obvious (Tang et al., 2022). In addition, if sweet potato waste is first treated by thermochemical methods, it can produce more biogas and methane, which also makes the energy value of sweet potatoes higher (Catherine and Twizerimana, 2022). This study mainly wants to systematically see whether sweet potatoes can be promoted as a biogas energy crop in rural China. We will do several things: first, evaluate the gas production capacity and energy efficiency of different sweet potato varieties and sweet potato waste; second, see if it has any benefits in terms of economy, environment and emission reduction; third, study how to optimize the sweet potato biogas production process and how to promote this practice. We hope that these analyses can provide some scientific support for the development of renewable energy in rural China and give policymakers some useful suggestions.
Journal of Energy Bioscience 2025, Vol.16, No.4, 172-181 http://bioscipublisher.com/index.php/jeb 173 2 Energy Crop Development in China: Background and Policy Context 2.1 National energy strategy China's energy structure has always been dominated by coal. With the continuous development of the economy and the growing population, the demand for energy is also increasing. This has also brought about energy security issues and greater environmental pressure. In order to reduce the impact of climate change, China has proposed the goals of "carbon peak" and "carbon neutrality", and actively promoted the adjustment of energy structure and strived to increase the proportion of renewable energy use. Among various renewable energy sources, biomass energy is a very important one. It is rich in resources, renewable, and basically does not emit carbon. These characteristics make it a good choice to replace fossil energy such as coal and oil, and also help reduce greenhouse gas emissions (Wang et al., 2024). The development of biomass energy is not only helpful for carbon reduction, but also protects the ecological environment and enhances energy security (Sang and Zhu, 2011; Wang et al., 2024). 2.2 Policy support for biogas and bioenergy The Chinese government has always attached great importance to the development of bioenergy and has issued many relevant policies. The Renewable Energy Law implemented in 2005 is a very important starting point. It provides legal support for the development of biomass energy and explicitly encourages the use of methods such as biogas, biopower generation, and biofuels (Wang et al., 2024). The national and local governments also promote rural biogas projects and other bioenergy construction through subsidies, tax cuts, and technical research. These policies also encourage the good use of straw, energy crops, etc. to improve utilization efficiency (Zhang and Lis, 2020; Wang et al., 2024). These practices not only promote the development of bioenergy, but also help improve the rural energy structure and increase farmers' income (Zhang and Lis, 2020). 2.3 Role of energy crops in rural development In rural China, energy crops play many important roles. First, these crops can be grown on marginal land or unused arable land, which will not affect food planting and improve land use efficiency (Wang et al., 2017; Fu et al., 2022; Wang et al., 2024). Planting energy crops can bring new sources of income to rural areas, allowing farmers to earn more and is also conducive to adjusting the agricultural structure (Zhang and Lis, 2020; Fu et al., 2022). Furthermore, the development of energy crops can also reduce straw burning, reduce greenhouse gas emissions, and benefit the rural ecological environment (Sang and Zhu, 2011; Fang et al., 2024; Wang et al., 2024). When these crops are combined with renewable energy technologies such as biogas and power generation, they become a key force in promoting green and low-carbon development in rural areas (Fu et al., 2022; Fang et al., 2024; Wang et al., 2024). 3 Biogas Technology and Feedstock Dynamics 3.1 Principles of biogas production The production of biogas mainly relies on a technology called "anaerobic digestion" (AD). This process is carried out in the absence of oxygen, and microorganisms decompose organic matter and finally produce gases such as methane and carbon dioxide. This decomposition process is generally divided into several stages, including hydrolysis, acidification, acetic acid production and methane production. In the end, not only usable biogas can be obtained, but also a "digestion residue" can be obtained, which can be used as fertilizer (Catherine and Twizerimana, 2022; Montoro et al., 2025) (Figure 1). This technology can process a lot of agricultural waste, such as feces, straw, kitchen waste, etc. It can not only reduce environmental pollution, but also turn waste into energy and resources, realizing "turning waste into treasure" (Zhang et al., 2015; Liu et al., 2023). 3.2 Common feedstocks in China In rural China, the raw materials used to produce biogas are mainly some common agricultural wastes, such as cow dung, pig dung, corn stalks and kitchen garbage (Zhang et al., 2015; Li et al., 2021; Liu et al., 2023). Among them, livestock and poultry manure is more common, mainly because it contains a lot of organic matter and is easier to decompose. However, the source of this type of raw material is affected by the scale of breeding and the
Journal of Energy Bioscience 2025, Vol.16, No.4, 172-181 http://bioscipublisher.com/index.php/jeb 174 season, and it is not always available stably (Li et al., 2021). Although there are a lot of corn stalks, they contain a high amount of cellulose and lignin, which are difficult to decompose and produce gas slowly. Moreover, this kind of stalk is troublesome to collect and transport, and the cost is high (Zhang et al., 2015; Sun et al., 2022; Liu et al., 2023). Kitchen garbage also has certain potential, but its composition is too complex and the collection system is not perfect, so it is difficult to use on a large scale (Zhang et al., 2015). In addition, the winter in the north is too cold, and the low temperature will reduce the biogas production, which also affects the use effect of traditional raw materials (Yan et al., 2022). Figure 1 Biogas production setup 3.3 Need for diversification Because traditional raw materials have many problems, such as low gas production, large seasonal changes, and difficult collection, people began to consider finding some new alternative raw materials. Sweet potato is a very promising choice. It has high yield and strong adaptability, and there are a lot of starch and sugar in the root tubers, which have high energy value and are very suitable for producing biogas (De Paula Batista et al., 2019; Montoro et al., 2025). Studies have found that if sweet potatoes or sweet potato waste are pretreated first, it can not only increase the production of biogas and methane, but also shorten the fermentation time. Moreover, if it is used together with livestock and poultry manure for synergistic fermentation, it will produce more gas and have higher economic benefits (Catherine and Twizerimana, 2022; Montoro et al., 2025). At present, many rural areas in southern China grow sweet potatoes, and the planting foundation is good. If sweet potatoes are promoted as a new biogas raw material, it will not only solve the problem of single type and seasonal shortage of traditional raw materials, but also make rural energy more abundant and sustainable (De Paula Batista et al., 2019; Tang et al., 2022). 4 Agronomic and Economic Suitability of Sweet Potato 4.1 Agronomic characteristics Sweet potato is a crop suitable for energy production, and it has many obvious advantages. First of all, it has high yield and low soil requirements, and can grow well even on poor land. This makes it easy to promote in rural areas. In addition, its short growth cycle allows it to be planted several times a year, and the land utilization rate is also higher. Through the improvement of breeding technology, as well as scientific fertilization and irrigation methods, sweet potatoes are now performing better and better under difficult conditions such as drought (Tedesco et al., 2023). 4.2 Comparative yield analysis Studies have found that the biomass yield and biogas production capacity of sweet potatoes are similar to those of other common energy crops, and some varieties even exceed cassava and corn. For example, some sweet potato varieties can produce about 2 900 liters of biogas per hectare, indicating that its methane production is very good .
Journal of Energy Bioscience 2025, Vol.16, No.4, 172-181 http://bioscipublisher.com/index.php/jeb 175 The reducing sugar and water content in sweet potatoes affect the production of biogas. Some good varieties are more advantageous in converting biomass into energy (De Paula Batista et al., 2019). 4.3 Cost and input analysis Growing sweet potatoes does not require much labor and fertilizer, which is very suitable for rural areas with more manpower but less funds. If local fertilizers can be used, healthy seedlings can be selected, and some biological and physical methods can be used to prevent insects and diseases, the cost of planting can be further reduced and the income can be increased. Now high-resolution remote sensing technology can also be used to help, which can manage the work in the field more accurately, increase production, and make better use of land (Tedesco et al., 2023). 4.4 Byproduct utilization In addition to being used for fermentation to produce biogas, sweet potatoes also have many by-products that can be used. For example, its starch can be used as food or industrial raw materials, and the residue after fermentation can also be used to feed livestock. In this way, resources are more fully utilized. This multi-use approach not only increases the overall value of the sweet potato industry, but also contributes to the sustainable development of the rural economy (Tedesco et al., 2023). 5 Environmental and Sustainability Assessment Sweet potato is a high-yield root crop with low soil requirements. It has great potential for use as biomass energy in rural China. If it is used to produce biogas, whether it is good for the environment needs to be considered from multiple aspects, such as greenhouse gas emissions, land use, biodiversity, water and fertilizer consumption, and the impact of the entire life cycle. 5.1 Greenhouse gas mitigation potential Using sweet potato fermentation to produce biogas can reduce greenhouse gas emissions. On the one hand, rural energy such as coal, firewood and liquefied gas can be replaced by sweet potato biogas, reducing dependence on carbon energy. On the other hand, biogas residue and biogas liquid can be returned to the fields, which can reduce the use of chemical fertilizers and reduce N2O emissions caused by nitrogen fertilizers. Some studies have estimated that each ton of sweet potato can produce about 60 to 80 cubic meters of biogas. If a farmer uses 1 ton of sweet potato to produce biogas per year, it can reduce about 180 to 250 kilograms of carbon dioxide equivalent. Compared with straw, sweet potatoes are more suitable for small-scale household use and have higher fermentation efficiency (Hou et al., 2017; Sun et al., 2022). 5.2 Land use and biodiversity considerations Sweet potatoes are often planted on sloping land, dry land, or in the gaps between crop rotations. This way, they will not compete with major food crops for land, and both food and energy can be obtained. It can also have a good yield on marginal land, and is suitable for promotion in some mountainous areas in southwest and central China, which is very helpful for the development of rural ecological agriculture. It should also be noted that sweet potatoes should not be planted too intensively. If they are planted too singly, biodiversity may be affected. Therefore, it is recommended to use mixed cropping or crop rotation when planting sweet potatoes, and also consider combining them with local ecological protection plans, so that the agricultural system can be more stable (Zhang and Qiu, 2018; Li et al., 2025). 5.3 Water and nutrient requirements Compared with water-intensive crops such as corn, sweet potatoes require less water. It also has strong adaptability to rainfall and soil, and is a relatively water-saving energy crop. It does not require high fertilizers, mainly phosphorus and potassium, and has less demand for nitrogen, which can also reduce water pollution caused by too much nitrogen fertilizer. Some studies have put forward several suggestions, such as: the water consumption per hectare of sweet potato planting should not exceed 3 500 cubic meters; organic fertilizer substitution should reach at least 40%; nitrogen fertilizer use should be controlled at no more than 80 kilograms
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