Highly efficient and selective extraction of phosphorous from wastewater as vivianite in a strategically operated four-chamber flow electrode capacitive deionization

Phosphorus (P) is not only one of the main contaminants in wastewater but also an essential nutrient for all living organisms. In this study, we demonstrate a highly efficient and selective process for extraction of P from wastewater in the form of solid vivianite using a strategically operated four-chamber flow electrode capacitive deionization (FC-FCDI). The separated diluate and concentrate chambers in FC-FCDI enables continuous production of dephosphorylated water and P-rich brine, realizing P removal rate (0.22 mu mol/(cm(2).min)) and enrichment efficiency (concentration factor of 17.2) much higher than previous studies. The spontaneously enriched competing ions in the concentrate mitigate their further migration due to concentration countering effect, realizing to date the highest selectivity for P over SO42- (4.4) in CDI systems. Most importantly, the precipitated vivianite has high P content (12.4 %) and much smaller volume compared with the P-recovered solution in previous studies. The recovery of P in the solid state prevents the production of brine wastes, requires no water input for concentrate replenishment, and is conducive to transport, storage, and direct usage for various purposes. This work suggests a novel method for highly selective and efficient extraction of P from wastewater using tailor-designed and strategically-operated FC-FCDIs.