Dual-anode electrochemical strategy enables simultaneous carbon and nitrogen removal from biologically treated...

Cost-effective removal of refractory organic matter and nitrate (NO₃^-) from biologically treated landfill leachate remains a significant challenge. Here we developed a dual-anode electrochemical system including a mixed metal oxide (MMO) anode and an iron (Fe) anode to achieve simultaneous removal of carbon and nitrogen. Compared to single-MMO anode and single-Fe anode systems, the dual-anode configuration exhibited a synergistic enhancement, achieving a chemical oxygen demand (COD) removal efficiency of 86.5 %, surpassing the sum of the two individual systems. The generation of high-valent iron-oxo species (Fe^IV=O) in the dual-anode system was confirmed via electron paramagnetic resonance (EPR) spectroscopy and probe experiments. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) analysis revealed that Fe^IV=O plays key role in inducing the structural transformation of dissolved organic matter (DOM), shifting it toward higher O/C and lower H/C ratios, thereby promoting flocculation and enhancing DOM removal. In addition, Fe(II) released from the Fe anode effectively scavenged reactive chlorine species, which mitigated the re-oxidation of NO₃^- reduction intermediates and suppressed the formation of chlorinated byproducts. A mathematical model was developed based on continuous-flow experiments with synthetic wastewater, and subsequently applied to predict COD and NO₃^- removal under varying operational conditions for landfill leachate treatment.