Background: Coagulation process has a important place in water treatment. Currently, poly aluminum chloride is used in Kian-abad water treatment plant. The purpose of this study is to compare and investigate the efficiency of coagulants of poly ferric sulfate(PFS) against poly aluminum chloride (PAL) in removing turbidity and coliform bacteria in Ahwaz water treatment plant.

Methods: This study, was performed in lab scale and using of jartest apparatus in Ahwaz water treatment. Experiments was conducted in 35NTU turbidity in Ahwaz water treatment plant. The studied parameters included concentrations of coagulants, pH, turbidity, total coliform, fecal coliform and heterotrophic bacteria.

Results: The most optimal efficiency conditions of poly aluminum chloride were pH=8, rapid mixing of 120rpm and optimal dose of 5ppm which was 93.14% in pH=8 and 93.80% for optimal dose of 5ppm. The most optimal condition for poly ferric sulfate included pH=8, rapid mixing of 120 rpm and optimal dose of 8ppm.

In optimal condition of performance for poly aluminum chloride, efficiency of removing total coliform, fecal coliform and heterotrophic bacteria were 90.12, 83.70, 84.08% respectively. In optimal condition of poly ferric sulfate in dose of 8ppm efficiency removing total coliform, fecal coliform, and heterotrophic bacteria were 90.48, 84.83, and 84.69.

Conclusion: Finally, there was small difference between both PFS and PAC group about turbidity removal efficiency that was not significant statistically.