The impact of concentration in electrolyte on ammonia removal in flow-electrode capacitive deionization system

Flow-electrode capacitive deionization (FCDI) technology has been demonstrated to be a promising approach for ammonia removal and recovery. The flow-electrode, where adsorption and desorption occur, is one of the most significant parts in FCDI cells. However, in previous studies, the influence of concentrations in the electrolyte was not well understood, which greatly influenced system performances. In this study, we initially evaluated FCDI performance by using electrolytes containing different amounts of activated carbon (AC), as well as initial ammonium concentrations. Results indicated that compared to concentration factors (CFs), the effect of AC contents on the deionization process was almost neglectable. To achieve efficient ammonia removal and enrichment, initial CF below 10 and refreshment of flow-electrode when CF exceeded 100 were recommended. Further experiments indicated that the poor system performance under high initial CF was caused by concentration polarization and ion back diffusion. The long-term experiment confirmed the above conclusion. Besides, a high concentration of 5600 mg.L-1 was gained for ammonia recovery. This study demonstrated that the concentration in the electrolyte needs to be considered carefully to maintain the system in an efficient and economic state.