Enhanced phosphate removal and recovery through flow electrode capacitive deionization: The role of MgO-modified biochar derived from orange peels

Phosphate contamination in water bodies poses significant threats to aquatic ecosystems, while also highlighting the need to recover this vital nutrient from waste streams, given its scarcity and the environmental impact of its disposal. To address this challenge, a flow electrode material derived from orange peel waste was synthesized via a two-step process involving carbonization followed by MgO modification through co-precipitation and subsequently employed for phosphate removal in a flow-electrode capacitive deionization (FCDI) system. The MgO-modified biochar electrode achieved a remarkable phosphate removal efficiency of 97.2% with minimal energy consumption of 0.537 kWh kg -1 at 1.2 V, 2.5 wt% carbon content, 10 mL min -1 flow rate, and 120 min charging time, recovering 27.4 mg of phosphate at pH 5. Furthermore, the successful recovery of phosphate as struvite directly from the flow electrode filtrate demonstrates the efficacy of this integrated approach, where MgO-modified biochar facilitates both electrosorption and subsequent nutrient precipitation. This work represents a notable advancement in phosphate recovery methodologies, combining a simplified electrode preparation process with seamless integration of FCDI and struvite precipitation, thereby offering a sustainable pathway for phosphate management from waste streams.