Effect of organic polyelectrolyte characteristics on floc strength

Polyelectrolyte properties are known to have a large effect on floc strength. Very high molecular weight polyelectrolytes have been shown to produce stronger flocs than lower molecular weight polyelectrolytes. This paper examined the effect of polyelectrolyte charge density on sewage floc strength for very high molecular weight, cationic polyelectrolytes. Polyelectrolytes of low to medium charge density (0.18–1.42 mequiv./g) were shown to produce the strongest flocs. It was considered that very low charge densities resulted in poor polyelectrolyte adsorption on the floc and weak flocs, while for high charge density polyelectrolytes electrostatic patch flocculation rather than bridging flocculation was thought to occur, and therefore weaker flocs resulted.