Sludge rheology

Sludge rheology may play an important role in CFD modelling of the MBR process as it determines the hydraulics and transport phenomena near the membranes (Rios et al, 2007a). It has been found that activated sludge behaves as a non-Newtonian fluid and therefore the relationship between the shear stress (x) and the shear rate (7) exhibits a power-law (Table 15.3) rather than a linear relationship (Rosenberger et al, 2002 Rios et al, 2007a). 

Tixier, N., Guibaud, G., and Baudn, M. 2003. Effect of pH and ionic environment changes on interparticle interactions affecting activated sludge floes A rheological approach. Environ. Technol. 24 971-978. 

Moeller G, Torres LG. Rheological characterization of primary and secondary sludges treated by both aerobic and anaerobic digestion. Bioresour Technol 1997 61(3) 207-11. 

Dick, R. I., and B. B. Ewing. 1967. Rheology of activated sludge. Journal of Water Pollution Control Federation, 39, 543. 

Rios et al, (2007a) investigated the rheology of activated sludge from the aerobic zone of a lab-scale side-stream MBR with MLSS concentration of 8 g/L.The sludge was concentrated or diluted to obtain 11 different concentrations and correlated with shear rate-stress. The Herschel-Buckley rheology model with Papanastasiou s (H-B-P) adaption was found to exhibit the best fit to the experimental data for MLSS concentrations between 6 and 16 g/L and shear rates between 0.05 and 1600 s h... 

Buetehom et aL, (2008) evaluated the rheology of solutions of carboxym-ethyl cellulose (CMC), glycerol and xanthan gum containing different concentrations of silica particles and found that both CMC and glycerol solutions show Newtonian characteristics for shear rates between 0 and 1000 1/s while xanthan -gum could well mimic the properties of sludge for MLSS concentrations between 10 and 16 g/L. Therefore, xanthan-gum solution could be used for validation purposes. 

A rotational rheometer has been commonly used to measure the rheology of activated sludge (Rosenberger et al, 2002 Rios et aL, 2007a Brannock et al, 2010b). Rheograms can then be developed based on the measurement... 

Rios, N, Nopens, I, de Schepper, V, Jiang, T, Verstraete, W and Vanrolleghem, P (2007a). A rheological model for activated sludge in a side-stream MBR . TWA 4th International Membrane Conference, 15-17 May 2007, Harrogate, UK, IWA. 

Rosenberger, S, Kubin, K and Kraume, M (2002), Rheology of activated sludge in membrane bioreactors . Engineering in life sciences, 2(9) 269-275. 

Inclusion of Herschel-Buddey with Papanastasiou s adaption to model the rheology of wastewater sludge in the water phase... 

Measurement of sludge Rios et al. rheology to calibrate (2007b) viscosity values in the model... 

Inclusion of Power-law function to describe the rheology of wastewater sludge... 

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