Optimization of Coagulation Process Using Alum and Ferric Chloride for Surface Water Treatment

Water scarcity and increasing demand for various applications has led to more attention to the treatment and using potential resources. Surface water is one of water resources in the societies. In the present study, the performance of two coagulants, Alum and Ferric chloride, was considered to determine turbidity, color, COD, and microbial reduction in the surface waters in Tehran.
Sampling was carried out from two surface waters named Sorkhehesar and Salehabad, during summer, fall, and winter. After optimization of coagulant dosage and pH, jar test experiments were conducted, and turbidity, COD, color, and microbial changes were considered.
Turbidity range in Sorkhehesar and Salehabad was between 91 and 500 NTU, and 35 to 400 NTU, respectively. Optimized dose of alum for summer, fall, and winter was 45, 100, and 35 mg/L, respectively, while in case of ferric chloride the optimized dose for three studied seasons was 5, 70, and 10 mg/L. Optimized dose of alum and ferric chloride in Salehabad, was determined as 28, 115, 2 and 30, 65, and 5 mg/L. Turbidity removal efficiency using both coagulants was higher than 95 percent, and color was totally removed in all experimented conditions.
From the stand point of turbidity, color, and COD removal both alum and ferric chloride showed the same results, however, ferric chloride dose was lower than alum. In case of turbidity removal alum showed higher removal efficiency, while for COD reduction upon the conditions, e.g. seasonal variation, alum and ferric chloride performance was not the same and was varied accordingly.