Removal of phosphate from secondary effluent with Fe2+ enhanced by H2O2 at nature pH/neutral pH.

Removal of phosphate in secondary effluents was investigated in presence of Fe(2+)/H(2)O(2). The effect of H(2)O(2)-dose, Fe-dose and initial phosphate concentration were assessed. The results indicated that Fe(2+)/H(2)O(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(2)O(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(2)O(2). The electron paramagnetic resonance (EPR) spectra tests in secondary effluents showed that Fe(2+)/H(2)O(2) could produce an increasing hydroxyl radical concentration with a decrease in both H(2)O(2) dosage and phosphate concentration. Fe(2+)/H(2)O(2) had the potential to be utilized for removal of phosphate due to the lower cost and the higher phosphate removal capability.