Efficient Phosphate Recovery via Membrane-Free Electrochemical Separation Coupled with Fluidized Bed Crystallization:...

Traditional electrochemical processes for phosphate (P) removal and recovery typically rely on membrane materials within the electrochemical modules or recovery stages to achieve a high phosphate removal efficiency. Moreover, cathode failure during prolonged operation remains a significant challenge. To overcome these limitations, this study introduces a membrane-free electrochemical separation (MFES) and fluidized bed crystallization (FB) process. The MFES unit employs cathode boundary-layer pumping to rapidly separate cathodically generated OH^- from bulk solution, achieving >96.0% phosphate removal without membranes. This system effectively treats phosphate (5-60 mg·L^-1) and Ca²⁺ (10-100 mg·L^-1) across varying concentrations and demonstrates robust tolerance to interfering ions (Mg²⁺, HCO₃^-, and NH₄⁺). Using a 15 mm × 10 mm pore stainless-steel cathode, the process maintained >80.0% P removal during continuous 700 h operation without operational interruptions (e.g., backflushing). The MFES effluent feeds directly into the FB system, where fluidization accelerates amorphous calcium phosphate (ACP) adsorption and crystallization onto seeds, enabling rapid product recovery. The MFES-FB process achieves (1) 73.8% overall P recovery and (2) energy consumption of 55.3 kWh·kg P^-1 while eliminating membrane materials throughout the entire process. This study not only achieves long-term stable operation, demonstrating strong practicality and scalability, but more importantly reveals a "spatiotemporal decoupling" synergistic mechanism. This insight may help stimulate fresh perspectives for the future development of novel electrochemical resource recovery systems.