FT-ICR MS analysis of DOM transformation in steel wastewater zero-liquid discharge systems

Sustainable water management in the iron and steel industry necessitates effective treatment of high-salinity wastewater, with zero liquid discharge (ZLD) systems emerging as a critical solution. However, molecular-level transformations of dissolved organic matter (DOM) during the terminal evaporation-crystallization stage remain rarely understood, constraining system optimization. Herein, we systematically investigate DOM transformation mechanisms in three industrial high-salinity brines—coking, cold rolling, and comprehensive wastewater—during mechanical vapor recompression (MVR) treatment at full-scale steel plants. Integrating 3D fluorescence spectroscopy with ultra-high-resolution mass spectrometry, we elucidate wastewater-specific transformation pathways and molecular redistribution patterns. MVR treatment induces pronounced compositional shifts: CHO compounds decrease by 3–5 % while CHONS compounds increase by 4–6 %, driven by sulfate-mediated C S and N S bond formation. Coking wastewater DOM undergoes decarboxylation (20–25 % of transformations), shifting toward oxidized unsaturated states. Cold-rolling wastewater favors oxidation pathways, generating saturated oxidation products. Comprehensive wastewater, with elevated ammonia nitrogen (31 %), suppresses oxidation and produces reduced saturated compounds via amide bond formation. These molecular insights directly inform targeted optimization strategies: elevated drying temperatures prevent salt discoloration, wastewater-specific anti-scalants mitigate fouling, and tailored evaporation parameters maintain crystallization stability. This study establishes a molecular foundation for evidence-based ZLD system design, advancing water conservation in water-intensive industries. • MVR functions as a thermochemical reactor inducing DOM molecular reorganization. • Sulfate enrichment drives C-S/N-S bond formation in high-salinity brine DOM. • 54–66 % of DOM molecules are eliminated while recalcitrant species are generated.