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

Abstract

Abstract Efficient treatment of nitrate (NO 3 − ) 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 NO 3 − 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 (NO 3 − ‐to‐NO 2 − conversion) with chemical diazotization (ESD‐CD), where NO 3 − is first electrochemically reduced to NO 2 − by an oxide‐derived Cu foam electrode, which then reacts with sulfamate (NH 2 SO 3 − ) via chemical diazotization to rapidly generate N 2 . For 5000 mg‐N L −1 simulated NO 3 − wastewater, the ESD‐CD achieved 98.8% NO 3 − removal efficiency, 99.9% N 2 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 NO 3 − wastewater (3085.2 mg‐N L −1 ) with over 96.6% NO 3 − removal efficiency and 99.2% N 2 selectivity, and also reduced operational costs by 64.4% and 74.9%, and CO 2 emissions by 79.5% and 93.3% in comparison with biological denitrification and multiple‐effect evaporation, underscoring the promising potential of coupling selective electrochemical NO 3 − reduction with chemical diazotization for sustainable treatment of high‐concentration NO 3 − wastewater.