Study on transformation between flocs and aggregates in conditioned anaerobic digested sludge(ADS) suspensions during a shear test

Key words: 
• anaerobic digested sludge(ADS) /
• conditioning /
• flocs/aggregates /
• torque-time rheogram /
• fractal /
• transformation

Abstract: This study presented the variations in rheological, geometric and physical 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 both elastic network strength and resistance to shear reached their maximum values at the optimum dosage of polymer zetag7557 on the basis of the area under torquetime rheograms of ADS. Large aggregates were observed as soon as the optimum polymer dosage was injected into the ADS suspensions, and they continued to grow 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 imposed shear. During the above process,the corresponding torque values in the rheogram also showed similar behavior to the variations of conditioned ADS biosolids. The strongest elastic 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 elastic network. The climax of fractal dimensions for conditioned ADS flocs were not coincident with that of the peak height in the rheograms for these ADS suspensions. In addition, residual polymers after absorption onto the surface of ADS biosolids could neutralize some of the negative surface in these biosolids exposed by shear application in the Floccky test.