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Abstract Introduction: There are many colloidal and suspended solids in surface water for which coagulants should be used in process of water treatment. Plyaluminum chloride (PACl) is one of the newest coagulants . In this research, PACl has been used to coagulate water samples token from Arvandrood and Bahmanshir rivers as the main water suppliers of Abadan City. Materials and Methods: A necessary number of water samples were taken during normal conditions from water sources of Abadan. The turbidity of a few samples was intentionally increased by addiny clayey soil because the turbidity of Abadan Rivers increases considerably in rainy seasons. The optimum coagulant doses and coagulation condition were then determined by standard Jar tests. Besides, residual Al and COD concentrations in finished water samples have been determined along with routine analyses of water. Results: The results show that turbidity removal rate from sample waters in Jar tests were 90 to 98 % and Al residual concentrations were about 0.41 mg/L. For samples with high turbidity, the removal rates were 98 to 99 %, but the Al residuals were about 0.06 mg/L. Conclution: Since the concentration of all pollutants decreased to less than their MCL values after the treatment of water with PACl , it can be concluded that using this new chemical dose not produce any adverse health effect. Considering the various advantages vis a vis conventional coagulation, PACl can be recommended to be used in trwating water in the Abadan plant. ***

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Introduction: The development of health and protection of environment is depended on the provision of safe and clean water. The turbidity of water comes from the suspended and colloidal matters contained in it. The purpose of the present investigation was to compare the efficiency of natural coagulant chitosan with poly aluminum chloride (PACl) in the removal of water turbidity. Chitosan is a cationic biopolymer with high molecular weight that is produced from the crust of crustaceans like shrimp and crab. Materials & Methods: This investigation was performed, in the laboratory scale, on water samples containing synthetic water turbidity by applying kaolin in high, middle, and low turbidities. The first phase of tests aimed to determine the optimum concentration of the coagulants chitosan and poly aluminum chloride and the efficiency of turbidity removing. The second stage of experiments aimed to determine the optimum pH and the effect of coagulant on the water pH. Findings: Optimum dosages of chitosan for removing the turbidities 1000, 500, 50 and 10 NTU were 10, 6.5, 1.5 and 1 mg/L, respectively and the optimum PH values were also 8, 8, 7.5, and 8, respectively. Optimum dosages of PACl in the respected turbidities were 28, 18, 15 and 12 mg/L, respectively and the optimum PH values were also 8, 7.5, 7.5, and 8, correspondingly. Discussion & Conclusion: The results showed that only in the turbidity 10 NTU, the efficiency of poly aluminum chloride was better than the efficiency of chitosan. In other turbidities, chitosan showed better performance. Chitosan had a lower effect on the water PH, while PACl had a noticeable effect on the water PH. The optimum dosage of chitosan was less than that of PACl in all turbidities. At different levels of turbidity, the optimum concentration of chitosan was significantly lower in comparison with poly aluminum chloride. Coagulant dose reduction decreases the cost of water treatment. This subject is one of the advantages of the bioorganic polymer, chitosan, to the inorganic coagulant, poly aluminum chloride, in the refinement of water with considering the economic aspects. Chitosan, in contrast to poly aluminum chloride, had little effect on the water pH.