Removal of Escherichia coli from synthetic turbid water using titanium tetrachloride and zirconium tetrachloride as coagulants

Performances of titanium tetrachloride (TiCl4) and zirconium tetrachloride (ZrCl4) for removal of Escherichia coli from synthetic turbid water were studied. Jar test experiments were conducted at various coagulant doses (10 to 60 mg L–1), pH values (6–8.5) and effect of inorganic ions (Na+, Ca+2 and Mg+2) to determine the optimum conditions based on removal efficiencies of turbidity, E. coli and zeta potential. With increase of the coagulant dosages, the coagulation performances increased while the coagulants showed greater capacity for turbidity and E. coli removal at near their isoelectric points (40 and 50 mg L–1), where turbidity and E. coli removal ware 96.96% and 4.69 logs, respectively for TiCl4 and 92.5% and 3.97 logs, respectively, for ZrCl4. The pH had different effect on the removal performances, where the best results were in pH = 8.5 for TiCl4 and pH = 6.5 for ZrCl4, in which E. coli reductions were 4.85 logs and 4.35 logs, respectively, for TiCl4 and ZrCl4. Increase in the dose of ions improved coagulation performances, where decrease in the zeta potential revealed that compression of the double layer was the main mechanism for both coagulations. In summary, these results indicate that both TiCl4 and ZrCl4 enable adequate removal of E. coli from turbid water.