Comparing Aluminium Sulfate and Poly-Aluminium Chloride (PAC) Performance in Turbidity Removal from Synthetic Water

Abstract

Colloids are small suspended particles in water which cannot be settled or removed naturally due to their light weight and stability. These particles pose some degree of stability and cause water turbidity. There are some concerns regarding colloid removal efficiency in water treatment plants of Iran. In this study, the effectiveness of aluminium sulfate and poly-aluminum chloride was evaluated at different pH values and coagulant dosage in order to find optimal operational conditions for low to high turbidity waters. The influence of lime, as a coagulant aid, on coagulation process was also studied. A set of jar test experiments was conducted to find the optimal pH and coagulant dosage. Results demonstrated that coagulation process can assure turbidity removal from low to medium turbidity waters effectively using relatively low levels of aluminium sulfate and poly-aluminum chloride (10 to 20 mg/L). Turbidity removal efficiency still remained high when the initial turbidities of water were increased to 500 and 1000 NTU. Results showed that turbidity removal is dependent on pH, coagulant dosage, as well as initial turbidity of water for both used coagulants. The highest turbidity removal efficiency was within 82.9-99.0% for alum and 93.8-99.6% for poly-aluminum chloride over the applied range of turbidity. Both applied coagulants demonstrated promising performance in turbidity removal from water; however, poly-aluminum chloride showed better performance compared to aluminium sulfate. The results of the current study can be used as a baseline data for drinking water treatment facilities which uses these two types of coagulants.