Efficient and economical removal and recovery of phosphorus via a novel dual-electrode electrochemically induced crystallization process: Performance and crystallization mechanisms

Abstract

Electrochemically induced crystallization is a promising method for removing and recovering P from wastewater but may be hindered by intrinsic limitations, e.g., high energy consumption and cost. To overcome such limitations, a dual-electrode electrochemically induced crystallization process (DEIC) was proposed using an electrochemical reactor equipped with an iron anode and a stainless-steel cathode. Results showed that > 95% P removal was achieved in 20 hours at the experimental conditions of current density = 0.2 mA/cm2, pH = 6.5, Ca2+ = 5.4 mM, and P concentration = 6.5 mM. The specific energy consumption was calculated as 0.82 kWh/kg P, which is much lower than the reported results (7 – 65 kWh/kg P). According to the XRD and SEM-EDS analysis, P removal was achieved in the form of vivianite (Fe3(PO4)2.8 H2O) and CaP crystallization, induced by the releases of Fe2+ and OH– at the anode and cathode, respectively. Vivianite was found to be deposited at the anode with high purity and a regular plane structure. The DFT calculation confirmed that the control of vivianite growth in a plane shape is thermodynamically feasible. Lastly, the economic analysis showed that the operational cost of DEIC (1.07 USD/kg P) was lower than that of conventional chemical precipitation (1.3 – 1.8 USD/kg P), suggesting that the DEIC process could be a viable method to achieve P removal and recovery.