Trends, advances, and future directions in water hyacinth-based biogas production: A bibliometric review (1994–2024)

Water hyacinth is one of the world's most invasive aquatic plants, yet its high lignocellulosic biomass offers significant potential for renewable biogas production. Although several reviews have examined water hyacinth utilisation, no previous study has provided a dedicated bibliometric assessment of global research trends in water hyacinth-based biogas production. This study addresses this gap by conducting the first bibliometric analysis of three decades (1994-2024) of research using Bibliometrix (RStudio) and VOSviewer. A total of 322 publications, retrieved from the Scopus database following Preferred Reporting Items for Systematic Reviews and Meta-Analyses-based screening, were analysed to evaluate publication trends, influential contributors, collaboration networks, keyword evolution, thematic development, and emerging research directions. In addition, the most-cited studies were synthesised qualitatively to identify technological advances and research priorities. The results show that research output increased substantially after 2017, peaking at 38 publications in 2023. Asia contributed 61.7% of the publications, followed by Africa (16.2%), while India emerged as the leading research hub and international collaborator. Thematic evolution revealed a transition from biomass characterisation and biogas yield optimisation to biomethane, techno-economic assessment, renewable energy integration, and circular bioeconomy applications. The qualitative synthesis further showed that pretreatment, co-digestion, and process optimisation consistently enhanced methane production and process stability. These findings provide a strategic roadmap for researchers, policymakers, and industry by identifying research priorities, strengthening international collaboration, supporting evidence-based policy, and accelerating the sustainable commercial deployment of water hyacinth-based biogas systems within circular bioeconomy and low-carbon energy transitions.