Advantageous and detrimental effects of air sparging in membrane filtration: Bubble movement, exerted shear and particle classification

Membrane fouling in membrane bioreactors—Characterisation, contradictions, cause and cures

“…This particle segregation becomes more pronounced as crossflow velocity is increased. The effect was confirmed in the fractionation of milk [176], or in flux-stepping experiments with MBR mixed liquor [167] and by sensitivity analysis of a rigorous MBR filtration model [50]. It is in agreement with findings by Le-Clech et al [2] who reported that cakes formed under crossflow conditions had higher specific resistances and that increasing shear stress only reduced the amount of reversible fouling while the irreversible part remained constant.…”

Impact of Aeration on Mixed Liquor in Submerged‐Membrane Bioreactors for Wastewater Treatment

“…5), in CFD simulations, the mean velocity of a 2-cm bubble was 0.23 m s -1 in mixed liquor and 0.27 m s -1 in water, i.e., the velocity was 15 % lower in mixed liquor than in water. This corresponds to the trend observed experimentally for slug flow and found by Drews et al [39] for single bubbles, with rather good agreement. It confirms, firstly, that the viscosity has an important effect on this flow and, secondly, that modeling mixed liquor with a fluid corresponding to the Carreau model rheology is a suitable assumption.…”

“…A study of two-phase flow hydrodynamics in mixed liquor (8-10 g L -1 , the same MLSS range as in the present study) reported on bubble velocities being 15-20 % lower than in water [39]. Although the velocities found in this study are not directly comparable to those of Drews et al [39] because of the difference of configuration, namely, hollow fiber versus flat sheet, and the fact that different cases are considered, i.e., slug flow versus isolated bubble, a similar trend is observed, with mean velocity values being 18-26 % lower in mixed liquor. This trend has its importance as it validates the CFD simulation in mixed liquor and its good modeling of rheological behavior.…”

“…The non-Newtonian nature of activated sludge flows [38] is not considered in these cases. The works [13], [17], and [39] should be mentioned as exceptions as they simulate two-phase flows in SMBRs with mixed liquor as a non-Newtonian fluid, using a Bingham [13] and Ostwald-de Waele/power law equation [17,39]. Following this trend, rheological tests were carried out to determine the best model available in Fluent that matched the mixed-liquor behavior and the parameters required as input for this model.…”

CFD simulation and optimization of membrane scouring and nitrogen removal for an airlift external circulation membrane bioreactor

“…However, uneven distribution of shear stresses were often observed whenever the aeration diffuser was perpendicular (Ndinisa et al, 2006) or parallel (Liu et al, 2010) to the membrane surfaces. To get even shear stresses distribution on different membrane sheets, many approaches were studied including optimization of parameters in configurations (Kang et al, 2008) and in operation (Drews et al, 2010). One of the most effective approaches in our previous findings was to elevate the height of gas-liquid dispersion h m (Zhang et al, 2013).…”