Effects of polymer dosage on alum sludge dewatering characteristics and physical properties

The proper use of polymers as conditioners is a critical aspect of dewatering processes. In this study, we investigate their physical properties, i.e. size, density and fractal dimension and correlate them with their dewatering characteristics (bound water content, CST and SRF) on alum sludge with cationic polymer conditioning. Using CST measurement to determine the optimum polymer dose may lead to an over-dosing for polymer conditioned sludge. Bound water depletion and interstitial water formation significantly affect the moisture content during polymer conditioning. Moreover, the magnitude of bound water content reflects net change in moisture content, which is decreased by bound water depletion and increased by water formation. Floc size and density measurement suggest poor dewatering performance and increased bound water content are attributable to enlargements in floc size and decreases in floc density. Experimental results indicate that increases in bound water and decreases in floc density are caused by variations of both floc size and aggregation configuration type, not degree of floc compactness.