Synthesis and coagulation performance of composite poly-aluminum-ferric-silicate-chloride coagulants in water and wastewater treatment and their potentially use to alleviate the membrane fouling in MBRs

The aim of this work was the study of the combination of an inorganic pre-polymerized coagulant (PACl) with ferric species and polysilicic acid in various mixing order, Al/Fe/Si and OH/Al molar ratios, and two polymerization techniques for the production of a unique reagent representing a coagulant, more efficient than commercial PACl-18 and laboratory prepared PACllab for water or wastewater treatment A number of coagulants were prepared and were examined by jar tests for the treatment of simulated water; pH, turbidity and UV254nm absorbance were measured in the treated water. PSiFAC1.5:10:15 prepared by co-polymerization was found to be the most efficient coagulant from all the tested compounds; in addition, no flocculant aid (polyelectrolyte) was required with this product. Low coagulant doses, about 1.5-2 mg/L were required for the reduction of turbidity values to lower than 1 NTU; furthermore, PSiFAC1.5:10:15 resulted in very low residual aluminum concentration of about 140μg Al/L. The most effective coagulants obtained were also used for the treatment of tannery wastewater to evaluate their performance and it was observed that high turbidity removal (~99%) was obtained at doses of about 100 mg/L. The most effective coagulants are under study for their potential use to alleviate membrane fouling in MBRs.