Treatment by dissolved air flotation of water with high coloured and low turbidity

In this study, the performance of laboratory scale batch flotation equipment for treating a coloured and low turbidity raw water (synthetic water) has been investigated with results of experimental researches. Experiments were performaned by varing the aluminium sulfate dosage range from 10-50 mg/L and pH value range from 4-7. It was determined effect of cationic polyelectrolit addition on coagulant dosage and turbidity. Turbidity efficiencies were obtained according to batch flotation velocities (Vf) 4 m/h, 8 m/h, 19 m/h, 40 m/h. In addition optimal saturation pressure, floculation time and recyle ratio were determined. The most proper laboratory scale batch operation conditions were obtained pH value 6.3, recyle ratio %8, flocculations times of 10 minutes and Vf velocity of 8 m/h for treatment of water coagulated with alum dosage of 30 mg/L and polyelectrolit dosage of 0.20 mg/L. At these conditions, very good removal efficiencies of turbidity and naturally organic matter has been respectively % 95 (residual of 0.56 NTU), % 85 (residual of 0.58 mg/L) for batch flotation equipment. In addition, though DAF unit could be operated at very high such as Vf = 19- 40 m/h, good results was obtained. Thus, suitability of DAF process for removal of colour and turbidity has been proved with obtained high yields. Keywords: Dissolved air flotation, high rate flotation, humic acid, water treatment, coagulation, flocculation IX