Coremoval of Ca and Organics: In Situ Hardness-to-Catalyst Upcycling Enabling Nonradical Ozonation for Sustainable Water Purification

Heterogeneous catalytic ozonation, an efficient and promising technology, is often hindered by the resource-intensive nature of complicated catalyst preparation. This challenge is particularly acute in treating industrial wastewater, which faces the twin challenges of salt scaling and salt-inhibited oxidation. Herein, we propose a transformative hardness-to-catalyst strategy to achieve water softening and catalytic ozonation, termed the in situ crystallization-catalyzed ozonation process (ICCOP). Through the minimalist crystallization of inherent calcium into CaCO₃, organics degradation exhibited significantly accelerated reaction kinetics, as the ICCOP improved O₃ utilization efficiency and enhanced electron transfer. Surface atomic oxygen (*O) was identified as the dominant reactive oxygen species, with Ca atoms on the (1 0 4) plane of CaCO₃ as the active sites. Practically, the ICCOP yielded effective decontamination of intricate fracturing flowback wastewater (FFW), achieving enhanced organics and Ca removal within a unitary reactor. Life cycle assessment (LCA) quantifiably demonstrates that the ICCOP markedly reduced CO₂ emissions and environmental impact, owing to significant savings in chemicals and electricity, underscoring its strong sustainability advantages. This work deciphers a previously uncharted mechanistic role of Ca crystallization in catalyzing nonradical ozonation for enhanced organics degradation. Crucially, ICCOP emerges as a paradigm-shifting technology for waste-to-resource conversion, pioneering sustainable water remediation.