Ammonia recovery from concentrated solution by designing novel stacked FCDI cell

Abstract

Ammonia recovery from wastewater gained increasing attention worldwide with the growing world population. However, subsequent treatment of the recovered ammonia was still complex and challenging. Therefore, a proof of concept approach by designing a novel stacked flow electrode capacitive deionization (FCDI) cell was presented in this study, to achieve ammonia recovery and generation of value-added products. Ammonium sulfate was generated successfully in the product chamber with K2SO4 worked as an additive. To avoid the influence of the co-existing ions, the effect of a monovalent cation-selective exchange membrane (M-CEM) was emphasized in the stacked FCDI cell. Compared with the standard cation exchange membrane (S-CEM), the product purity increased from around 50% to 85%, while the ratio of NH4+ towards co-existing cations increased almost 2 times by using M-CEM. To illustrate the reasons for the enhanced ion selectivity, the characterizations of both membranes were conducted by Electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), Fourier transform infrared spectrometry (FTIR) and X-ray diffractometry (XRD). Therefore, this study indicated that the novel design and efficient operation of the stacked FCDI reactor is an alternative way for ammonia recovery and generation as value-added products, as well as a possible approach to scaling up.