Catalytic reduction of nitrate in secondary effluent of wastewater treatment plants by Fe⁰ and Pd–Cu/γ–Al₂O₃

Total nitrogen, in which NO₃⁻ is dominant in the effluent of most wastewater treatment plants, cannot meet the requirements of the Chinese wastewater discharge standard (<15 mg/L), making nitrate (NO₃⁻) elimination attract considerable attention. In this study, reductant iron (Fe⁰) and γ–Al₂O₃ supported palladium–copper bimetallic catalysts (Pd–Cu/γ–Al₂O₃) were innovatively used for the chemical catalytic reduction of nitrate in wastewater. A series of specific operational conditions (such as mass ratio of Pd:Cu, catalyst amounts, reaction time and pH of solution) were optimized for nitrate reduction in the artificial solution, and then the selected optimal conditions were further applied for investigating the nitrate elimination of secondary effluent of a wastewater treatment plant in Beijing, China. Results indicated that a better catalytic performance (74% of nitrate removal and 62% of N₂ selectivity) could be obtained under the optimal condition: 5 g/L Fe⁰, 3:1 mass ratio (Pd:Cu), 4 g/L catalyst, 2 h reaction time and pH 5.1. It is noteworthy to point out that nitrogen gas (N₂) predominated in the byproducts without another system to treat ammonium and nitrite. Therefore, the chemical catalytic reduction combining Fe⁰ with Pd–Cu/γ–Al₂O₃ could be regarded as a better alternative for nitrate removal in wastewater treatment.