Electrochemical Shortcut Denitrification Coupled with Chemical Diazotization for Low‐Carbon Nitrate Wastewater Treatment

Efficient treatment of nitrate (NO₃ ^-) wastewater with low carbon emission is a tough challenge because traditional multiple-effect evaporation and biological denitrification are carbon-intensive, especially in the case of NO₃ ^- concentration higher than 1000 mg-N L^-1. In this study, we demonstrate a low-carbon and high-energy-efficiency denitrification strategy by coupling electrochemical shortcut denitrification (NO₃ ^--to-NO₂ ^- conversion) with chemical diazotization (ESD-CD), where NO₃ ^- is first electrochemically reduced to NO₂ ^- by an oxide-derived Cu foam electrode, which then reacts with sulfamate (NH₂SO₃ ^-) via chemical diazotization to rapidly generate N₂. For 5000 mg-N L^-1 simulated NO₃ ^- wastewater, the ESD-CD achieved 98.8% NO₃ ^- removal efficiency, 99.9% N₂ selectivity, and 95.3% Faradaic efficiency. Impressively, its energy consumption was as low as 9.97 kWh kg-N^-1, and its denitrification rate reached an unprecedented record of 24.87 g-N m^-2 h^-1. Driven by photovoltaic cells, the ESD-CD process maintained stable performance in treating industrial NO₃ ^- wastewater (3085.2 mg-N L^-1) with over 96.6% NO₃ ^- removal efficiency and 99.2% N₂ selectivity, and also reduced operational costs by 64.4% and 74.9%, and CO₂ emissions by 79.5% and 93.3% in comparison with biological denitrification and multiple-effect evaporation, underscoring the promising potential of coupling selective electrochemical NO₃ ^- reduction with chemical diazotization for sustainable treatment of high-concentration NO₃ ^- wastewater.