Performance of fluorine removal using flow electrode capacitive deionization (FCDI): validation and optimization

This study demonstrates the efficacy of a symmetrically designed flow-electrode capacitive deionization (FCDI) system for the electrochemical defluorination of photovoltaic (PV) wastewater, with a systematic investigation conducted to optimize operational parameters and analyze key factors influencing system performance, offering valuable insights into enhancing FCDI efficiency. The results revealed that an optimal applied voltage of 1.2 V yielded a fluoride removal efficiency of 92.9% with an energy consumption of 6.49 kWh/mol. Increasing the electrode content to 0.75 wt% enhanced the removal efficiency to 98.3%; however, further increases in electrode content led to higher energy consumption due to elevated viscosity. Optimizing the flow rate to 45 mL/min resulted in a removal efficiency of 98.6%, accompanied by improved adsorption rates and reduced energy consumption. Adding 1 g/L of electrolyte substantially enhanced system performance, achieving a fluoride removal efficiency of 92.9%. In mixed-ion wastewater, competitive adsorption between <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mi>NO</mml:mi></mml:mrow><mml:mn>3</mml:mn><mml:mo>-</mml:mo></mml:msubsup></mml:math> and F⁻ was observed. Doubling the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mi>NO</mml:mi></mml:mrow><mml:mn>3</mml:mn><mml:mo>-</mml:mo></mml:msubsup></mml:math> concentration relative to F⁻ decreased the F⁻ removal efficiency from 96.2% to 87.3%. Nonetheless, the FCDI system demonstrated robust fluoride removal performance under high ion concentrations and complex matrix conditions, offering an efficient and sustainable approach for industrial wastewater treatment.