Targeted degradation pathways via Fe⁰ regulation for enhanced organic nitrogen removal from printing and dyeing wastewater

Printing and dyeing wastewater (PDW) is a major source of dissolved organic nitrogen (DON), posing environmental risks such as algal blooms. This study explores the enhancement of DON removal from PDW using a Fe⁰-integrated hydrolysis acidification (HA)-aerobic-anoxic system. The Fe⁰-assisted group (G-Fe) achieved 77.4 % DON removal, outperforming the control one (G-Bio, 61.8 %). G-Fe effectively eliminated high-risk DON fractions, including low-molecular-weight, hydrophilic and bioavailable components, significantly lowering their concentrations in the final effluent compared to G-Bio. Fe⁰ promoted microbial-derived DON production during HA section, which was intensively removed in later phases. Based on the results of Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), Fe⁰ was found to direct DON degradation pathways that are more specific and focused. The improved deamination contributed to superior DON removal; the strengthened dealkylgroup and oxygenation pathways increased hydrophilic DON generation in aerobic step, which were effectively removed via co-precipitation with iron oxides in subsequent anoxic stage. Fe⁰ decreased microbial diversity but enriched more functional strains like Acinetobacter, Leucobacter, and Ellin6067, capable of resisting toxicity and degrading complex pollutants. Additionally, Fe⁰ upregulated key metabolic pathways, including amino acid biosynthesis and TCA cycle, aiding microbial adaptation to stress. These findings underscore the potential of Fe⁰ to enhance DON removal and mitigate PDW-related environmental risks, offering a novel approach for advanced PDW treatment.