Transformation between flocs and aggregates in the conditioned sludge suspensions during a rotational test using a torque rheometer

Floccky tester is a typical torque rheometer used to study flocculants and flocculation characteristics of wastewater sludges. This study presents the variations in rheological, geometric characteristics of conditioned anaerobic digested sludge (ADS) to analyze the transformation between flocs and aggregates during a rotational test with a floccky rheometer. The results revealed that the network strength and resistance to shear reach their maximum values at the optimum dose of polymer zetag7557 on the basis of the area under torque-time curves of ADS. Large aggregates, even big sludge lumps, were observed as soon as the optimum polymer dose was injected into the ADS suspensions, and they continued to grow in average size as the shear duration was prolonged. Afterwards, these aggregates broke into smaller ones or were directly transformed into smaller and smaller flocs with the extension of shear application. The corresponding torque values in the torque-time curve showed similar behavior to the above variations. During the above process, the strongest network formed in conditioned ADS suspensions in which large aggregates were generated, while the ADS suspension with the largest single aggregate or the highest average size of aggregates/flocs did not assure the strongest network. The climax of fractal dimensions for conditioned ADS flocs were not coincident with that of the peak height in the torque-time curves for these ADS suspensions. (C) 2011 Elsevier B.V. All rights reserved.