The aim of this study was to evaluate the influence of both sludge characteristics and operational parameters on polymer selection and optimal dose requirements to improve the dewatering characteristics of aerobically digested sludges of a contact stabilization activated sludge plant in Jeddah, Saudi Arabia. In order to determine the dewatering characteristics of the sludge samples, capillary suction time (CST) and specific resistance to filtration (SRF) were measured.

Cationic conditioning polymers were found more effective than the anionic types. The optimum polymer dose was equal to 4.2 kg of polymer/ton of dry matter for three of the cationic polymers used in this study namely Zeetag 57, Superfloc C420, and Zeetag 92.

The optimum dose requirements are increased substantially with increasing pH values. A linear relationship was found between the optimal polymer dose in mg/l and the sludge solids concentration. The optimum total mixing time was found to be 2 min: 30 sec of rapid mixing at 100 rpm and 90 sec of slow mixing at 40 rpm. The sludge temperature variations were found to have a slight effect on polymer dose requirements.

A linear relationship was obtained between the CST and SRF with a correlation coefficient of 0.99.

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