Boosting seawater denitrification in an electrochemical flow cell

• Published in: Water research (Oxford) 2024-11, Vol.266, p.122384, Article 122384
• Main Authors: Li, Ding, Jiang, Shuang-Cheng, Xie, Jia-Fang, Zhang, Jian, Zheng, Ying-Lian, Zhao, Quan-Bao, Yu, Han-Qing
• Format: Article
• Language: English
• Subjects: ammonia; anodes; catalysts; cathodes; China; chlorides; chlorine; Denitrification; Electrochemical Techniques; Electrochemical-chemical tandem reaction process; electrochemistry; Electrodes; Flow cell; mariculture; marine science; nanosheets; Nitrate removal; Nitrates; nitrites; Nitrites - chemistry; nitrogen; Nitrogen - chemistry; On-demand active chlorine generation; seawater; Seawater - chemistry; Seawater denitrification; total nitrogen; Waste Disposal, Fluid - methods; wastewater; Water Purification - methods
• ISSN: 0043-1354; 1879-2448; 1879-2448
• DOI: 10.1016/j.watres.2024.122384

•Seawater denitrification is achieved by tandem reaction in a designed flow cell.•The single-pass mode achieves 89.6 % denitrification from simulated seawater.•On-demand generation of active chlorine is realized under ultra-high Cl- provision.•NO2- and NH3 can also be removed in the flow cell under ultra-concentrated Cl-.•Actual seawater attains 85.5 % denitrification with the designed flow cell. Nitrogen compounds in current seawater treatment processes typically are converted to nitrate, threatening seawater quality and marine ecology. Electrochemical denitrification is a promising technique, but its efficiency is severely limited by the presence of excess chloride ions. In this work, a flow-through cell went through an on-demand chlorine-mediated electrochemical-chemical tandem reaction process was designed for efficient seawater denitrification. Equipped with ultrathin cobalt-based nanosheets as the cathode catalyst and commercial IrO2-RuO2/Ti as the anode, the newly designed flow-through cell achieved nitrate removal efficiency that was about 50 times greater than the batch cell and nearly 100 % N2 selectivity. Moreover, nitrite and ammonia can also be removed with over 93 % efficiency in total nitrogen (TN) removal. Furthermore, the concentration of active chlorine in the effluent could be adjusted within two orders of magnitude, enabling on-demand release of active chlorine. Finally, this flow-through cell reduced the TN of actual mariculture tailwater (40.1 mg N L-1 nitrate) to only 5.7 mg N L-1, meeting the discharge standard for aquaculture tailwater of Fujian, China. This work demonstrates the paradigm of deep denitrification from ultra-concentrated chlorine ion wastewater using an on-demand active chlorine-mediated electrochemical-chemical tandem reaction process. [Display omitted]