Multi-spectroscopy reveals selective oxidation for ultrafiltration membrane fouling control in wastewater reuse

Wastewater reuse, a key technology for addressing water scarcity, is of significant importance for achieving Sustainable Development Goal 6 (Clean Water and Sanitation). However, achieving efficient and stable reuse, particularly in the field of ultrafiltration (UF) technology, remains a global challenge due to membrane fouling issues. Here we propose a novel metal-free UF pretreatment in which nitrogen-doped carbon nanofiber (N-CNF) activates peroxymonosulfate (PMS), selectively degrading hydrophobic, high molecular weight fractions of effluent organic matter (EfOM). Heterogeneous two-dimensional correlated spectroscopy (fluorescence EEM vs Fourier transform infrared spectroscopy (FTIR), size exclusion chromatography vs FTIR) elucidated the transformation mechanisms of EfOM, demonstrating preferential degradation of aromatic, phenolic, and amide-rich compounds via electrophilic attack. Fourier transform ion cyclotron resonance mass spectrometry further confirmed the breakdown of unsaturated aromatic formulas, along with increased oxidation state and a compositional shift toward more hydrophilic, lower molecular weight species. The pretreatment doubled the UF permeate flux and significantly reduced reversible and irreversible resistance (80.2 % and 69.0 %), while delaying the formation of cake layer. Life cycle assessment indicated lower environmental impacts for the N-CNF/PMS-UF compared with direct UF and UF with other pretreatments due to improved process efficiency and reduced resource consumption. These findings may provide a reliable strategy for wastewater reuse.