Preparation of a composite coagulant from fly ash and its application in domestic wastewater treatment

Fly ash was investigated as a raw material for the preparation of a composite coagulant with sulfuric acid. Types of acid solution, H₂So₄ concentration, ratio of H₂SO₄ to fly ash and stirring time were respectively examined as factors that influenced the efficiency of converting the iron and aluminum components into a composite coagulant and coagulation performance on domestic wastewater. The coagulant was attained at the condition of H₂SO₄-fly ash ratio of 5 mL/g, H₂SO₄ of 2 mol/L, stirring time of 4h and stabling time of 30 min, and contained Fe ³⁺ of 0.010 8 mol/L with conversion efficiency of 11.4% and Al³⁺ of 0.0354 mol/L with conversion efficiency of 4.3%. Removal efficiencies of COD and SS by this type of coagulant reached 70.4% and 91.9% respectively when treating domestic wastewater. This study provides a promising means to utilize fly ash for coagulation, which possibly makes wastewater treatment more economical and more sustainable.