Phosphate removal from industrial wastewater through in-situ Fe~(2+) oxidation induced homogenous precipitation: Different oxidation approaches at wide-ranged pH

摘要

Phosphate removal through in-situ Fe~(2+) 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 Fe~(2+) oxidation approaches worked well for phosphate removal at varied pH conditions. Sole dosing Fe~(2+) 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 Mn~(2+), Zn~(2+), and Ni~(2+). At acid pH (3.0 < pH < 6.0), Fenton reaction oxidation (H_2O_2 = 5 mg/L) showed its efficiency. At their corresponding optimal pH conditions and with Fe2_/P ratio of 1.8, dosing sole Fe~(2+) salt, Cu~(2+) catalyzed Fe~(2+) oxidation, and Fe~(2+)/H_2O_2 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 Fe~(2+)/H_2O_2 treatment and Cu~(2+) catalyzed Fe~(2+) oxidation treatment after wastewater pH being adjusted to 7 effluent TP met China's discharge requirement 0.5 mg/L.