Hierarchical net-zero-liquid discharge approach for sustainable salt recovery and carbon footprint reduction in steel wastewater treatment

To reconcile the resource recovery and decarbonization trade-off in industrial wastewater treatment while meeting the United Nations Sustainable Development Goals, this study deciphers the operational mechanisms of globally representative steel-industry net-zero-liquid discharge (NZLD) system (220 m3/h) to propose a hierarchical four-stage framework. We reveal that Cl-/SO42- competition dynamically regulates nanofiltration membrane selectivity, while establishing quantitative links between oxygen atom signatures of dissolved organics and product purity. An experimentally-derived salinity-driven trade-off emerges: high salt levels enhance ion separation but suppress organic degradation due to radical scavenging. Life cycle impact assessment pinpoints carbon hotspots and demonstrates an 81.8% footprint reduction via renewable electricity. Under modelled scenarios, scaling this framework to treat China’s annual 1.50 billion m3 applicable Na+/Cl-/SO42--dominated high-salinity wastewater could potentially recover 1.43 billion m3 water, 8.11 million tonnes NaCl, and 5.09 million tonnes Na2SO4, saving USD 3.68 billion annually. This strategy provides a transferable blueprint for low-carbon resource recovery globally. Huaqiang Chu and colleagues propose a hierarchical four-stage framework based on a full-scale facility to optimize net-zero-liquid discharge and resource recovery from industrial wastewater. They reveal salinity-driven trade-offs between membrane separation and organic degradation, while renewable electricity reduces the system’s carbon footprint by 81.8%.