Resource Recovery, Environmental Risks, and Conversion Technologies: A Thematic Overview of Sewage Sludge Management Research

<ns3:p>Sewage sludge (SS) management has evolved from conventional disposal practices toward resource-oriented and environmentally conscious solutions. This study investigates the thematic structure of global SS research, with a focus on green technological pathways for resource recovery and the environmental risks associated with SS utilisation. A systematic bibliometric approach was adopted using the Web of Science Core Collection, targeting publications from 2015 to 2024 that included the terms “sludge” AND (“recycl*” OR “reuse” OR “treatment” OR “reduc*” OR “management”) within their titles, abstracts, or keywords. The final dataset consisted of 12,666 eligible articles that met all screening criteria. VOSviewer (version 1.6.20) was used for science mapping, including keyword co-occurrence and cluster analysis. Six thematic clusters were identified, representing dominant research trajectories: (i) microbial processes for nutrient recovery, (ii) biological conversion to bioenergy, (iii) thermochemical transformation and material reuse, (iv) heavy metal bioavailability and ecological risk, (v) emerging contaminant (EC) fate and mitigation, and (vi) dye removal mechanisms. Results indicate a shift toward circular-economy-aligned SS management, emphasising bioconversion, hydrothermal technologies, and biochar valorisation. Research gaps relate to large-scale deployment, EC remediation, and commercialization constraints. The findings provide a structured knowledge base for guiding future research, policy formulation, and investment in sustainable sludge-to-resource systems.</ns3:p>