Removal of turbidity from water by dissolved air flotation and conventional sedimentation systems using poly aluminum chloride as coagulant

Flotation is a method in which particles in liquid phase are transported to the surface by air bubbles. In this experimental study, a comparison has been made between conventional sedimentation and dissolved air flotation (DAF) systems to remove turbidity from water. Initially, optimal operational conditions for each system utilized using water artificially turbid with Kaolin. For each system, samples were taken at 20-min interval after the system reached its optimal operational conditions. Parameters, such as turbidity, alkalinity, temperature, pH, and total suspended solids, were measured. For 20, 30–50 and 90–110 NTU, turbidity average removal efficiencies in DAF system were 14.7, 11.1 and 10.9%, respectively, larger than the conventional sedimentation system. The effect of coagulant dose indicated that DAF system with lower dosage of coagulant have higher removal efficiency. On the other hand, the results showed that due to increased efficiency of DAF system, solid concentration of sludge produced in this system was more than the sedimentation system (p < 0.01). However, operation of DAF system needs accurate control devices and experienced technical staff to operate the system.