Optimized sustainable development for phosphorus separation with electricity generation in a novel aluminum-air reverse electrodialysis

Abstract

A new electrochemical system is proposed for simultaneous electricity production and phosphorus removal using an aluminum- air reverse electrodialysis (RED) cell combined with an air cathode and a metal anode. This study aims to evaluate the electricity production along with the nutrient (PO4-P) removal. The cell with a novel flow design contains low and high concentration (LC and HC) NaCl feed solutions, which are directed serially into each stack cell. Anolyte (2.12 mM KH2PO4, 111 mM NH4Cl, 10 mM NaCl) and catholyte (10 mM NaCl and 598 mM NaCl) was used for three different configurations: without recirculation (WR-10), recirculation (R-0) and without recirculation (WR-598) to optimize the operation technique. The cells produced a peak power density of 698–1449 mW/m2 over 8-hour operation time. In addition, 90.66 % phosphorus removal was achieved. Both conventional electrocoagulation and this new system share a common mechanism for phosphorus removal, involving the formation of AlPO4 precipitates with an aluminum anode. However, our system had other possibility for phosphorus removal except for AlPO4 formation, which was phosphorus loss through membrane. Therefore, to assess phosphorus removal and monitor phosphorus movement, the phosphorus ion concentration in the feed solution was measured, and then no detectable phosphorus ion concentration was found in the feed solution. This indicate that major removal mechanism of phosphorus was AlPO4 formation. Additionally, the formation of AlPO4 precipitates on the metal anode surface in the recirculation (R-0) configuration was confirmed through Fourier transform infrared spectroscopy, scanning electron microscopy with energy-dispersive spectroscopy, and X-ray diffraction. Since the aluminum removal reaction occurred at the interface between the aluminum anode and water, AlPO4 formed on the surface of the aluminum anode. Some of this AlPO4 then detached and dispersed into the bulk solution as white precipitates. These findings demonstrate effective electricity production and phosphorus removal using this innovative aluminum-air RED technology.