Trang Thi Cam Truong, Phuc Tuong Ngo Hoang, Ha Manh Bui
Abstract The recovery of nitrogen and phosphorus from nutrient‐rich wastewater is essential for sustainable agriculture and circular resource management. Fish‐blood wastewater from aquaculture contains high organic and nutrient loads but is rarely explored for nutrient recovery. This study developed a hybrid coagulation–electrocoagulation system combining calcium oxide (CaO) with magnesium electrodes to simultaneously reduce chemical oxygen demand (COD) and recover nutrients as struvite. The effects of CaO dosage, current density, pH and reaction time were optimized. Under optimal conditions, COD reduction reached 84.20% at pH 10.5, while NH 4 + –N and PO 4 3− –P conversion into solid precipitates reached 76.03% and 90.46%, respectively, at pH 9.5. Box–Behnken Design showed excellent predictive accuracy (R 2 > 0.97) and principal component analysis (PCA) confirmed that CaO mainly controlled COD reduction, whereas current density governed struvite formation. COD reduction followed second‐order and Behnajady–Modir‐Shahla–Ghanbary models and X‐ray diffraction (XRD), scanning electron microscope (SEM) and Fourier‐transform infrared spectroscopy (FTIR) verified crystalline struvite (MgNH 4 PO 4 ·6H 2 O). These performances were achieved with an overall energy demand of ~5.4 kWh/m 3 , demonstrating the feasibility of integrating treatment and nutrient recovery in a single electrochemical process.