Increasing the stability and efficiency of an electrochemical ammonium separation system via state-of-charge (SoC) control

초록

Ammonium ions in wastewater can induce toxicity in aquatic organisms and accelerate eutrophication. Therefore, the efficient removal of ammonium ions is necessary. The electrochemical ion separation method, based on an electrode with selectivity for ammonium ions, is a promising recovery technique that can efficiently adsorb and desorb ammonium ions. In this system, the electrode is composed of copper hexacyanoferrate (CuHCF) and silver (Ag), and ammonium ions are captured by the CuHCF electrode. However, the stability of the CuHCF electrode is not sufficient for continuous ammonium ion removal. We aim to report an improvement in the stability of this system realized through the use of the state-of-charge (SoC) control method. The stability of the system can be enhanced by using SoC control at only 60 % of the maximum capacity. After 300 cycles, the discharge capacity for the 60 % SoC approach remained at 55.8 %, showing a 10 % improvement in stability compared to the 100 % SoC method (45.8 %). Furthermore, in concentrated solutions with a ratio similar to that of domestic wastewater, the 60 % SoC control strategy exhibited ammonium removal capacity and selectivity comparable to that with 100 % SoC control but with higher energy efficiency (77 % reduction in energy consumption). These results indicate that the state-of-charge (SoC) control method can enhance both the stability and the efficiency of the electrochemical ammonium separation system.

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