Research landscape and emerging pathways of sewage sludge application for soil carbon sequestration

The agricultural application of sewage sludge offers potential for enhancing soil fertility and promoting soil organic carbon (SOC) sequestration, but also poses environmental risks due to the presence of pollutants. Given the growing volume of research and the complexity of its environmental implications, a systematic understanding of how this field has evolved is urgently needed. To clarify the evolution, research priorities, and knowledge gaps in this domain, this study conducted a systematic bibliometric analysis of 3794 articles published from 1991 to 2024. Results revealed exponential growth in publications, with a marked shift in research focus after 2010. China, the United States, and Spain were identified as leading contributors. Keyword co-occurrence and citation analyses revealed three dominant thematic clusters: 1) sludge stabilization and soil property improvement, 2) contaminant risk and remediation strategies, and 3) SOC dynamics and sequestration mechanisms. Highly cited studies highlighted the potential of composted and pyrolyzed sludge in enhancing SOC while mitigating ecological risks. However, most evidence remains limited to laboratory conditions, with a paucity of long-term field trials under realistic agronomic scenarios. Future research should address methodological limitations and strengthen interdisciplinary integration for balancing SOC sequestration goals with environmental safety in sludge-based agricultural practices.