Nitrate removal and recovery by capacitive deionization (CDI)

Capacitive deionization (CDI), an emerging technology, has attracted attention recently and has been applied for various purposes. Herein, we investigated the application of a CDI system using activated carbon (AC) electrodes for nitrate removal and recovery in the scope of domestic wastewater treatment. The electrochemical behavior and structural parameters of AC electrodes were investigated as a part of this work. CDI electrodes were fabricated from microporous activated carbon, and the specific surface area of the electrode material was 210 m²/g. The negative effect of polymeric binder on the AC electrodes performance was observed as well. The specific capacitance of the fabricated AC electrodes at 40 mV/s scan rate was 0.5 F/g and 19 F/g for 1 and 1000 mM electrolyte (NH₄NO₃), respectively. The CDI performance was examined as a function of flow rate (2, 4, 9, 14 mL/min), applied voltage (0.6, 0.8, 1.0, 1.2 V), and initial nitrate concentration (10, 25, 50, 70 mg/L) in single-pass (SP) mode. Regeneration performance and recovery efficiency of the CDI cell were observed during 5 subsequent operational cycles. The recovery efficiency of nitrate ions from low salinity water was 21%, while the electrosorption capacity of 5.5 mg/g and removal efficiency of 48% was achieved. Presence of the competitive ions in the tested solution resulted in a slight decrease (~10%) of nitrate removal efficiency.