Biochar-Assisted Anaerobic Digestion: A Bibliometric Analysis of Publication Trends, Global Collaboration, and Emerging Research Themes

Biochar is widely used to enhance anaerobic digestion (AD) and biogas production, yet bibliometric analyses of this field remain limited. This study analyzes publication trends, scientific productivity, international collaboration, and the evolution of research in biochar-assisted AD. Scopus data were retrieved using TITLE-ABS-KEY [Biochar AND ("Anaerobic Digestion" OR "Anaerobic Digester" OR Biogas OR Biomethane OR "Methane Yield" OR Methanogenesis)]. The search covered publications from January 2012 to October 2025 and was conducted on 16 November 2025. A total of 374 articles were analyzed using Biblioshiny and VOSviewer. Publications grew by 40.74% annually, reaching 85 articles in 2025. China produced the largest share of publications (149 articles; 39.8%), whereas Hong Kong and Ireland showed higher proportions of international collaboration and higher average citations per article. Keyword co-occurrence analysis identified four thematic clusters, whereas conceptual structure analysis identified five. Research focus has shifted from biochar properties and AD performance to microbial interactions and Direct Interspecies Electron Transfer (DIET), with engineered and magnetic biochar emerging as topics of interest. These findings indicate that biochar-assisted AD research is increasingly focused on mechanistic understanding and material development. Future studies should prioritize standardized reporting, pilot-scale validation, techno-economic assessment, and evaluation of biochars derived from local biomass.