No change in pH was observed. According to the flocculation and sedimentation processes, the formation of flocs
after the addition of the chitosan was observed. They are bigger than those obtained with the chitosan used as
primary coagulant. They were of rounded shapes, glued one to the other, forming in the middle of the backer a big
ball. They settled well in less than 10 minutes. The final solution became very clear and very limpid. These results
are in agreement with those found by Guibal [20]. Indeed, according to Roussy et al. [14], the ionic sulfate
compounds have a significant effect on the chitosan's sorption, despite the fact that chitosan has a higher molecular
weight in the presence of sulfates [20]. Van Duin and Hermans [21] justified their hypothesis with the fact that
chitosan forms large aggregates which can easily precipitate in the presence of sulfate. They also reported that
taking into account the low dosage of chitosan in these experiments (less than 1 mgl-1), the amount of residual
organic carbon introduced to the system was low enough (less than 0,8 mgl-1) to make its contribution negligible for
the coagulation-flocculation performance. Thus, chitosan could be used as natural aid coagulant for drinking water
treatment with the lowest risks of organic release