Upcycling waste sewage sludge into superior single-atom Fenton-like catalyst for sustainable water purification

The worldwide generation of waste sludge emanating from municipal wastewater treatment plants amounts to 80–90 million tons of dry matter annually and continues to escalate, posing a substantial economic and environmental challenge for society. Although waste sludge offers a tantalizing resource to be harnessed, highly efficient and effective strategies for its repurposing remain elusive due to its complex compositions and low concentration of recoverable metallic elements. Here we devise a straightforward methodology for adept transformation of waste sludge into high-value single-atom catalysts (SACs) for water purification. This process involves in situ upcycling of trace redox-reactive transition metals present in sludge into single-atom speciation by carbon, nitrogen, sulfur, phosphorus, silicon and aluminium via the formation of reactive anchoring sites and selective chemical bonds. Sludge-derived SACs demonstrate remarkable reactivity, stability and selectivity in Fenton-like degradation of various contaminants. Structural analyses and density functional theory calculations reveal that co-coordinated iron single atoms act as the principal reactive sites in the catalysts. In addition, other single-atom transition metals with distinct coordination structures form and contribute to catalytic performance. Furthermore, we employ life cycle assessment and payback period analysis to conduct an evaluation of sludge upcycling to SACs with considerations of environmental impacts and production costs at an industrial level. Compared with conventional incineration, the overall life cycle impacts of our upcycling approach on human health, ecosystems and resources are much lower and exhibit a greater potential for reduction of emissions. This innovative technology promises financial benefits, obviates the substantial economic burdens of sludge disposal and charts a new trajectory for waste sludge disposal, promoting the genesis of more sustainable wastewater and waste management frameworks. The transformation of waste sludge from municipal wastewater treatment plants into valuable resources is fraught with challenges due to its complex composition. The approach proposed here efficiently upcycles trace redox-reactive transition metals present in sludge into single-atom catalysts, offering the dual benefit of effective sludge disposal and enhanced water purification.