Evolução do diâmetro fractal de agregados formados a partir de água com baixa turbidez

Abstract

Coagulation and flocculation are important processes in the treatment of drinking water, with direct impact on operational reliability, cost and quality of water treatment plants. In this work, high resolution images were used in order to monitor and compare the evolution of flocs’ fractal dimension in the flocculation process for low-turbidity waters (6,5 NTU) using three coagulants in a laboratory-scale (jar test): polyaluminum chloride, aluminum sulfate and ferric chloride, under six shear rates (20, 40, 60, 80, 100, 120 s-1). With this technique is possible to obtain direct images of flocs while the process is underway. As a result of a combination of camera control and image analysis softwares, it was possible to obtain data for determination of the fractal dimension. The results demonstrate that the fractal dimension development is not sensitive to the change of the shear rates for low turbidity waters. The flocs formed under these conditions showed Df values between 1.73 and 1.86. The use of Ferric Chloride and PAC in flocculation ensures the formation of flocs with similar fractal diameter at the same shear rate and time, while those generated by the use of polyaluminum chloride are slightly lower than other coagulants.