AWWA JAW17256

Polyelectrolytes, most commonly used as flocculant aids or as primary flocculants, have received increased attention in the water industry in recent years. Their benefits include stronger, larger, and better-settling flocs; less sludge; and lower chemical dosages. Despite the advantages of using polyelectrolytes, no method on which to base their selection currently exists. This study examined the interrelationships between polymer molecular weight, charge density, polymer dosage, mixing intensity, and the flocculated particle-size distribution in an effort to aid in the development of a scientific method of polymer selection. A series of twelve experiments with commercially available polymers showed that in most cases dosage was independent of molecular weight, that a strong correlation appears to exist between the number of charges a molecule carries and its optimum flocculation dosage, and that the size and strength of a floc may be controlled to some extent by proper selection of polymer molecular weight. Includes 25 references, tables, figures.