Pyrolysis-based treatment of persistent organic pollutants in wastewater sludge: A critical review

Persistent organic pollutants (POPs) pose a critical environmental threat due to their chemical stability, toxicity, and long-term accumulation in wastewater treatment sludge. This review examines the occurrence and ecotoxicological relevance of POPs in wastewater sludge and evaluates the potential of emerging pyrolysis technologies as a sludge treatment strategy with benefits for environmental sustainability, water quality, and the preservation of aquatic ecosystems. POPs are widely reported in sludge generated during wastewater treatment; for example, pharmaceuticals range from 21 to 4251 ng g −1 and polychlorinated biphenyls from 26 to 94 ng g −1 . Pyrolysis can reduce sludge volume and generate value-added products such as biochar, bio-oil, and biogas. Pyrolytic treatment achieves removal efficiencies of over 90% for various POPs, while biochar derived from pyrolysis shows removal efficiencies exceeding 95% for endocrine-disrupting compounds. Despite these advantages, the performance of pyrolysis depends strongly on temperature, residence time, and heating rate, while the sustainability depends on energy demand and gas management requirements. Emerging approaches, such as co-pyrolysis with agricultural residues, enhance treatment efficiency while simultaneously lowering treatment costs to around $29 per ton of treated sludge and reducing net CO 2 emissions (up to −32.5 kg CO 2 ton −1 ). When appropriately controlled and supported by suitable regulatory frameworks, pyrolysis stands out as a technically viable and environmentally sound alternative for large-scale treatment of POP-contaminated wastewater sludge. • Persistent organic pollutants (POPs) are found in wastewater sludge, posing serious ecological and health risks. • POPs in wastewater sludge can reach 35,000 ng g −1 . • Pyrolysis effectively degrades POPs, achieving removal efficiencies >90%. • Co-pyrolysis reduces treatment costs to $29 t −1 and CO 2 emissions by 32.5 kg t −1 . • Pyrolysis contributes to Sustainable Development Goals by improving water quality and safety.