Integrated Struvite Precipitation and Fenton Oxidation for Nutrient Recovery and Refractory Organic Removal in Palm Oil Mill Effluent

Anaerobically treated palm oil mill effluent (AnT-POME), containing a high concentration of ammoniacal-nitrogen (NH4+-N) and soluble chemical oxygen demand (sCOD) was subjected to sequential processes of struvite precipitation to recover NH4+-N and Fenton oxidation for sCOD removal. The optimization of treatment was conducted through response surface methodology (RSM). Under optimized struvite precipitation conditions (Mg2+/NH4+, PO43-/NH4+ molar ratios: 1; pH 8.2 +/- 0.1), NH4+-N concentration decreased to 41 +/- 7.1 mg L-1 from an initial 298 +/- 41 mg L-1 (78.8 +/- 1.6 % removal). Field emission scanning electron microscopy (FESEM) coupled with energy-dispersive X-ray spectroscopy (EDX) confirmed NH4+-N was recovered as struvite. Subsequent Fenton oxidation under the optimized conditions (H2O2 dosage: 2680 mg L-1; molar ratio of Fe2+/H2O2: 0.8; reaction time: 56 min) reduced sCOD concentration to 308 +/- 46 mg L-1 from an initial 1350 +/- 336 mg L-1 (76.0 +/- 1.0 % removal). The transparent appearance of treated AnT-POME validated the removal of sCOD responsible for the initial brownish appearance. Models derived from RSM demonstrated significance, with high coefficients of determination (R-2 = 0.99). Overall, integrated struvite precipitation and Fenton oxidation effectively removed NH4+-N and sCOD from AnT-POME, contributing to nutrient recovery and environmental sustainability.