Carbon dioxide radical reducing nitrate to nitrogen gas in a UV/Fe(III)-oxalate system. (April 2021)

• Record Type: Journal Article
• Authors: Chen, Jialin; Zhang, Ruina; Chen, Dong; Liu, Jianyong; Chen, Shanping
• Is Part Of: Journal of water process engineering. Volume 40(2021)
• Publication Date: 2021-04
• Subjects: Carbon dioxide radical -- Nitrate reduction -- UV/Fe(III)-oxalate system -- Selectivity -- Nitrogen gas; Water-supply engineering -- Periodicals; Saline water conversion -- Periodicals; Seawater -- Distillation -- Periodicals; Sanitary engineering -- Periodicals; Sewage -- Purification -- Periodicals; 627
• DOI: 10.1016/j.jwpe.2021.101934
• Languages: English
• ISSNs: 2214-7144

Abstract

Graphical abstract: Highlights: NO3 − reduction by C O2 - using a UV/Fe(III)-oxalate system was first proposed. The performance and mechanism of NO3 − reduction were investigated. Low CO2 − level is beneficial to improve selectivity to N2 . Abstract: The generation process for the highly reductive carbon dioxide radical ( CO2 − ) in the Fe(III)-oxalate system is enhanced under UV irradiation and used in nitrate (NO3 − ) reduction with improved product selectivity to nitrogen (N2 ). The combination of Fe(III) and residual oxalate forms Fe(III)-oxalate complexes again for an Fe(II)/Fe(III) species cycle and achieves generation of CO2 − radical continually. The electron paramagnetic resonance (EPR) spectrum demonstrates the existence of CO2 − radicals in this process. Some of the important control factors, such as initial concentrations of ferric ions (Fe(III)) (0.5, 1, 2, and 3 mM), NO3 − (14, 21, and 42 mg N/L), oxalate (3, 7, and 10 mM), and pH values (2, 3, 4, 5, and 6), are systematically assessed for NO3 − reduction efficiency and N-species selectivity. Among all the control factors mentioned, pH is a key parameter with an important role in the NO3 − reduction process. Excellent NO3 − reduction efficiency (∼90 %) was achieved at pH 3 in the presence of 1 mM Fe(III) and 10 mM oxalate under UV irradiation for 120 min. High Fe(III) and oxalate concentrations promote NO3 − removal. In addition, there was an increase in the NO3 − removal amount with a greater initial NO3 − concentration. About 60 % of NO3 − can be selectively reduced to N2 with low selectivity to NO2 − (∼3.4 % of total N) and NH4 + (∼15.7 % of total N). In general, the UV/Fe(III)-oxalate system provided an alternative way to improve NO3 − removal performance and selectivity to form N2 in water and wastewater remediation processes.