Removal of phosphate from secondary effluent with Fe 2+ enhanced by H 2O 2 at nature pH/neutral pH

Abstract

Removal of phosphate in secondary effluents was investigated in presence of Fe 2+/H 2O 2. The effect of H 2O 2-dose, Fe-dose and initial phosphate concentration were assessed. The results indicated that Fe 2+/H 2O 2 could greatly increase the removal of phosphate compared with those achieved by Fe 2+ alone. For initial phosphate concentration of 0.97–3.75 mg P/L, phosphate removal rates of 50–60% were observed at 1:1 molar addition of Fe(II). However, a 125% excess of Fe-dose was necessary for complete phosphate removal. The experimental data demonstrated that removal of phosphate with Fe 2+/H 2O 2 was higher than that observed with ferric coagulation alone. This fact suggested that in situ formed Fe(III) having much affinity for ligand phosphate. Chemical co-precipitation was considered as the dominant mechanism about phosphate removal in presence of Fe 2+/H 2O 2. The electron paramagnetic resonance (EPR) spectra tests in secondary effluents showed that Fe 2+/H 2O 2 could produce an increasing hydroxyl radical concentration with a decrease in both H 2O 2 dosage and phosphate concentration. Fe 2+/H 2O 2 had the potential to be utilized for removal of phosphate due to the lower cost and the higher phosphate removal capability.