Optimization of struvite crystallization protocol for pretreating the swine wastewater and its impact on subsequent anaerobic biodegradation of pollutants

► Wastewater pre-treatment by precipitation of MAP (struvite) reduced pollutants load. ► MAP protocol: pH 10, stir 10 min (400 rpm) +30 min (160 rpm) and P:Mg:N (1:1:1.2). ► Reduced NH4 and increased C:N ratio in MAP supernatant augment anaerobic treatment. ► Follow-up anaerobic biodegradation of MAP supernatant further decreased pollutants. ► Anaerobic treatment via MAP crystallization was effective and yielded higher biogas.