Revisiting of coagulation-flocculation processes in the production of potable water

Water Treatment Plants treat "flushy" raw waters and the majority use electrolytes and polyelectrolytes for the removal of the solid and organic impurities included in surface waters. The dose of the used reagents depend strongly on the nature of the incoming surface water and its turbidity. Turbidity is due to the suspended particles in the source water and up to date is main criterion for the appropriate choice of the electrolyte and polyelectrolyte nature and dosage. One of the main findings of the present work is that the selection of the appropriate dose of coagulants and flocculants as a linear function of turbidity is not right, especially for the large values of turbidity. The most common electrolytes Aluminum sulfate and PolyAluminiumChloride together with the polyelectrolyte PolyAcrylaMide, are tested for their effectiveness in the removal of suspended particles and their results discussed based on the particle’s ζ-potential and size distribution. These common reagents have raised public health concerns due to the residual aluminium and acrylamide which remain in treated water and at produced sludge. Thus, the present work examined and suggests the use of polymers as the natural Chitosan and CMInulin and the synthetic PolyDiallylDiMethylAmmoniumChloride, as alternative, environmentally friendly coagulants, for their performance on the treatment of potable water. The new reagents proved to reduce the turbidity of the surface water up to 96%.