Characterization and coagulation-flocculation performance of a composite coagulant: poly-ferric-aluminum-silicate-sulfate

Composite coagulant has received widespread attention and research for its excellent coagulation performance in recent years. In this study, a new composite coagulant poly-ferric-aluminum-silicate-sulfate was synthesized using water glass, FeSO(4)7H(2)O, Al-2(SO4)(3)18H(2)O, and NaClO3, their structures and morphologies were characterized and compared by X-ray diffraction, infrared spectra, and scanning electron microscopy. In addition, to obtain the optimum synthetic conditions resulting in the maximum turbidity removal efficiency, single-factor method was used to examine the parameters such as Si/[Al+Fe], Al/Fe, and aging time by municipal wastewater treatment. The coagulation-flocculation process showed that chemical oxygen demand and turbidity removal efficiency could achieve 77 and 99.4%, respectively, when the optimum synthesis conditions were Si/[Al+Fe], Al/Fe, OH/[Al+Fe], aging time, and reaction temperature of 0.4:1, 3:7, 0.3, 24h, and 80 degrees C, respectively. In addition, when the Si/[Al+Fe] of coagulant was 0.2 and 0.4, the coagulant produced lower sludge volume. The result showed that PFASS exhibit superior flocculation effect, and the main mechanisms in reducing the surface charge of colloids are neutralization and adsorption/bridging coagulation-flocculation.