Impact of storage period on biomethane potential of agricultural residues with insights from scientific mapping and storage methods

Agricultural residues are widely recognized as key feedstocks for biogas production. However, due to their seasonal harvest characteristics, they require effective storage strategies to obtain high-quality raw materials and ensure the continuous operation of biogas plants. Crop residue preservation and storage for anaerobic digestion remain a relatively underexplored field, with limited global advancements and an insufficiently consolidated understanding of its impact on biomethane potential (BMP). This study presents a comprehensive review combining bibliographic, scientometric, and qualitative analyses to evaluate global research trends and critically assess storage methods influencing BMP. Bibliographic data retrieved from the Scopus database were analysed to identify major contributing journals, authors, countries, and most frequently used keywords, followed by a detailed evaluation of preservation techniques. The analysis indicates a steady increase in research output since 2014, with dominant contributions from European countries and growing participation from Asia and other regions. Ensiling and co-ensiling emerge as reliable and cost-effective strategies that can enhance methane yield by improving substrate biodegradability with reported BMP improvements ranging from approximately 16–35% during medium-term storage conditions. Densification methods such as pelleting and briquetting improve storage and handling without adversely affecting BMP, while alkaline pre-treatment significantly enhances methane production through lignin disruption and increased cellulose accessibility, resulting in BMP enhancement of approximately 21–71% depending on biomass type and treatment conditions. Integrated approaches combining storage and pre-treatment methods show strong potential for further optimization, with storage temperature identified as a key operational factor. However, significant gaps remain, including the lack of standardized methodologies, long-term studies, and climate-specific storage protocols. This review provides a consolidated understanding of current research and highlights directions for developing efficient and sustainable biomass storage strategies for enhanced biogas production.