Phosphate removal from industrial wastewater through in-situ Fe2+ oxidation induced homogenous precipitation: Different oxidation approaches at wide-ranged pH

Abstract

Phosphate removal through in-situ Fe2+ oxidation induced homogenous phosphate precipitation has shown its advantages in municipal wastewater treatment. Its feasibility and suitability for phosphate removal in industrial wastewater with wide-range pH variation like electro-plating wastewater were investigated in bench scale experiments using synthetic wastewater and continuous experiment using real wastewater. Bench scale experiments showed that different Fe2+ oxidation approaches worked well for phosphate removal at varied pH conditions. Sole dosing Fe2+ salt with aeration achieved sound phosphate removal at alkaline condition (pH ≥ 8). At neutral pH (6 < pH < 8), transition metallic ions catalytic oxidation is a suitable alternative. Cu2+ exhibited superior catalytic Fe2+ oxidization over Mn2+, Zn2+, and Ni2+. At acid pH (3.0 ＜ pH ≤ 6.0), Fenton reaction oxidation (H2O2 = 5 mg/L) showed its efficiency. At their corresponding optimal pH conditions and with Fe2+/P ratio of 1.8, dosing sole Fe2+ salt, Cu2+ catalyzed Fe2+ oxidation, and Fe2+/H2O2 treatments can achieve the TP discharge limit of 0.5 mg/L. In a 30-day continuous experiment using real electro-plating wastewater (pH 4.9–5.5), in both direct Fe2+/H2O2 treatment and Cu2+ catalyzed Fe2+ oxidation treatment after wastewater pH being adjusted to 7 effluent TP met China's discharge requirement 0.5 mg/L.