Efficient phosphorus removal from ultra-low concentration wastewater by flow-electrode capacitive deionization

• The Lotus leaf-based biochar was synthesized by the hydrothermal carbonization . • FCDI was efficient for phosphorus removal from ultra-low concentration wastewater. • Optimal operating conditions were systematically investigated. • The SEC of flow electrodes modules dominated the total SEC. • The phosphorus removal mechanism was complex. During the 14th Five-Year period, the stringent phosphorus emission standard puts forward higher requirements for the phosphorus removal. In this study, lotus leaf-based biochars were prepared by hydrothermal carbonization method and used as low-cost FCDI electrode materials to remove ultra-low concentration phosphorus in wastewater at the first time. The governing factors and optimal adsorption conditions were systematically investigated as 1.2 V applied voltage, 24 s HRT, 10 wt% content of biochars. The maximum removal efficiency reached 98.55 % under 20 mg/L initial phosphorus concentration, which ensured that the phosphorus concentration of the effluent could meet discharge standard (0.3 mg/L) of WWTPs. Furthermore, the microscopic and spectroscopic characterization revealed that phorphorus removal mechanism included physical adsorption, electrosorption, ion exchange, precipitation and ligand exchange, which may take place simultaneously or supplementing each other. Using in situ potential measurement method, the potential gradient and energy consumption contribution of each FCDI component were described. The results showed that total specific energy consumption was very low and the flow electrodes modules dominated (more than 50 %) in all FCDI components. The findings opened up a promising way for managing biowastes and confimed the application of engineering biochar in environmental pollution treatment field.