Bibliometric and bibliographic review of sewage sludge by pyrolysis

The growing global generation of sewage sludge, estimated at approximately 200 million tons per year, has intensified the need for sustainable and efficient management strategies. In this context, emerging trends point to a transition from conventional waste treatment to integrated resource recovery systems. Accordingly, pyrolysis has emerged as a promising thermochemical route for converting sewage sludge into value-added products while minimizing environmental impacts. Recent advances demonstrate that pyrolysis enables the recovery of key resources in the form of biochar, bio-oil, and non-condensable gases, depending on operating conditions, particularly temperature (400–700 °C). Biochar, typically containing more than 50 wt.% carbon and exhibiting high surface area, has gained attention for applications in soil amendment, carbon sequestration, and as a functional material for adsorption and catalysis. Bio-oil, with a calorific value ranging from 15 to 25 MJ·kg −1 , is being explored as a renewable energy carrier and chemical feedstock, while non-condensable gases (e.g., CO, CO 2 , CH 4 , H 2 ) enable partial energy self-sufficiency of the process. However, challenges remain regarding contaminant management (e.g., heavy metals), product standardization, and process scale-up. For provide a comprehensive understanding, a systematic review of the literature published over the last decade (2015–2025) was conducted using the Scopus database, resulting in a final dataset of 500 documents. Furthermore, a comprehensive review of research articles on technologies for converting sewage sludge using thermochemical processes and the byproducts generated was carried out. Overall, this review identifies current trends, research gaps, and future perspectives in sewage sludge pyrolysis and its conversion into value-added co-products, supporting sustainable resource recovery and contributing to the transition toward low-carbon energy systems.