Effects of polymer flocculation upon sludge dewatering in potable water treatment

This study quantifies the effect of polymer flocculation (at the head of the plant) upon the dewatering of sludges generated in conventional drinking water treatment. A rigorous theoretical framework was used to extract two dewatering parameters that fully characterise basic operations from clarification and thickening to centrifugation and filtration. Coagulation and flocculation were carried out under various conditions representative of full-scale operation. Two high-molecular-mass polymers were used: one weakly cationic, the other weakly anionic. The results indicate that flocculation has little effect on the equilibrium parameter, 'compressive yield stress', suggesting the internal aggregate structure was unchanged. Moreover, flocculation typically led to a twofold improvement in the dynamics, represented by the 'hindered settling function'. As industrial processes tend to be rate-limited, the latter enhancement is expected to translate directly into commensurate increases in throughput.