Efficient Removal and Recovery of Phosphate and Ammonium from Wastewater by Redox Flow Deionization Cell

Abstract

Wastewater stemming from both residential and industrial sources commonly contains notable quantities of ammonium (N) and phosphate (P). Elevated levels of N and P within wastewater can give rise to significant challenges for aquatic ecosystems and wildlife. Meanwhile, it is crucial to recognize that N and P are valuable resources with diverse applications. This dual role of N and P, both as potential environmental pollutants and indispensable resources, underscores the need for efficient and sustainable approaches to manage and recover these nutrients from wastewater. The initial facet of this study delves into the utilization of the redox flow deionization cell (RFDC) as a new alternative approach for the elimination of N and P from wastewater. RFDC boasts commendable attributes, including heightened energy efficiency, continuous operational capabilities, and concurrent deionization within the ion’s removal channel, coupled with ion concentration within the concentrated channel. The investigation of RFDC performance was conducted, taking into consideration the influence of wastewater concentration and applied cell voltage. This encompassed an appraisal of parameters such as the average salt removal rate, ion removal efficiency, and electrical energy consumption, including both N and P removal experiments. Additionally, the impact of coexisting ions, namely sodium cations (Na+) and chloride anions (Cl-), on N and P removal efficacy was subject to examination. The findings of this study underscore the expeditious removal of N and P within the ion’s removal channel, coinciding with the concurrent concentration of ions within the concentrated channel. Intriguingly, it emerges that N exhibits a heightened selectivity in contrast to the coexisting cation (Na+), while P exhibits considerably diminished selectivity when juxtaposed with the coexisting anion (Cl-). This observation manifests in augmented electrical energy consumption attributable to the concomitant removal of coexisting ions. Consequently, the subsequent facet of the study was embarked upon with the overarching objective of refining the removal selectivity and retrieval efficiency of P. This was actualized through the introduction of pretreated anion exchange resins into the RFDC system, representing a novel methodological innovation. Varied categories of anion resins were subjected to pretreatment and subsequently evaluated within the RFDC system. Furthermore, the study scrutinized the effects of wastewater concentration ratios pertaining to P and Cl- ions, alongside the influence of applied cell voltage on RFDC performance. An array of pivotal performance metrics was computed, encompassing P selectivity, average P removal rate, P removal efficiency, and electrical energy consumption, collectively serving to gauge the efficacy of the process. The discerned outcomes underscore the effectiveness of pretreated anion exchange resins in conjunction with RFDC as a discerning and resourceful modality for the extraction and recuperation of P. Importantly, these findings proffer compelling evidence attesting to the viability of this pioneering technology for integration within the domain of wastewater treatment.