Características de agregados resultantes de floculação com tanino comercial em água sintética com cor aparente elevada

Abstract

Tannin is a coagulant of natural origin, extracted from many different trees and is regarded as an alternative to synthetic coagulants used in Water Treatment Stations (WTS). Many researches showed it has good turbidity and color removal, is easy to use and generates a higher biodegradability sludge in comparison with other synthetic coagulants. The present work aims to create the coagulation diagram for Tannin in color removal of synthetic water with high apparent color (107 uH), morphologically evaluating flocs formed during coagulation/flocculation process verifying their behavior under 4 different slow stir mean velocity gradients (Mvg) (20, 30, 40 and 60 s-1) besides two different breakage situations (Mvg) of 120 and 500 s-1). Results showed maximum color removal efficiency of 94% and low floc-breakage influence in removal efficiency. It was verified that for Mvg of 20 and 30 s-1 flocculation occurred incompletely, with the presence of many non-developed flocs due to lesser chock opportunities. Breakage under Mvg of 120 s-1 didn’t show much impact, with lowest strength factor of 79% and no floc recovery on Mvg of 40 and 60 s-1 whereas for Mvg of 500 s-1, strength factors as low as 55%, with average recovery of 15% for Mvg of 40 s-1 and 5,7% for 60 s-1 were obtained. Statistical analysis were used to verify behavior similarities between the different slow stir Mvg used. Mvg of 20 s-1 resulted in the lowest fractal dimensions, indicating that there is a higher floc chain formation for this lower agitation degree, while higher slow stir Mvg were enough to prevent big ramifications due to superficial erosion, leading to higher fractal dimensions.