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

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. Cu ²⁺ exhibited superior catalytic Fe ²⁺ oxidization over Mn ²⁺ , Zn ²⁺ , and Ni ²⁺ . At acid pH (3.0 ＜ pH ≤ 6.0), Fenton reaction oxidation (H ₂ O ₂  = 5 mg/L) showed its efficiency. At their corresponding optimal pH conditions and with Fe ²⁺ /P ratio of 1.8, dosing sole Fe ²⁺ salt, Cu ²⁺ catalyzed Fe ²⁺ oxidation, and Fe ²⁺ /H ₂ O 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 ₂ O 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.
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