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| Analysis of the shear stability of aerobic sludge flocs and anaerobic sludge granules. |
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Abstract The shear stability of some aerobic activated sludges and anaerobic sludge with determining the mass concentration changes of dispersed colloids eroded from some aerobic activated sludge flocs and anaerobic sludge granules were examined with standard shear test devices. Aerobic activated sludge in A2/O process possessed better shear stability, and the shear sensitivity (KSS) of their flocs was an order of magnitude less than the anaerobic sludge granules of ABR. Both the increase of total solid concentration (mT) of activated sludge and the increase of shear intensity (G) could result in increment in the dispersed mass concentrations of colloid particles at equilibrium (md,∞). Moreover, adhesion of small colloids on the aerobic flocs of sample 1 could be more prone to occur than that of sample 2, which could be testified by the higher adhesion–erosion equilibrium constant Km and more negative DG0adh/RT value of sample 1 estimated from the non-linear regression of md,∞versus mT with adhesion–erosion(AE)-model. With taking into account the effect of Brownian motion on colloid particle erosion dynamics, the modified AE-model could not only describe the concentration of small colloid particles in sludge solution without artificial shear, but also quantitatively model the shear data. Based on the regression results, the values for the equilibrium dispersed mass concentration of colloid particles prior to shear (m0) and DH/R could be determined. Modeling results indicated that more energy could be demanded for the deflocculation process with sample 1 than that with sample 2, but sample 2 was more remarkably affected by strengthened shear intensity. The discrepancy of shear stability between sample 1 and sample 2 of aerobic sludges implies some complex relations existed among shear stability, structure, properties of sludge and wastewater treatment effect in A2/O process.
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Received: 01 September 2008
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