Correlating the hydrodynamics of fluidized media with the extent of membrane fouling mitigation: Effect of bidisperse GAC mixtures

The anaerobic fluidized-bed membrane bioreactor (AnFMBR) makes use of fluidized granular activated carbon (GAC) to mechanically scour the membrane to mitigate fouling. The question addressed in the current study is whether fluidizing bidisperse mixtures (i.e., particles of two different sizes) can improve the energy-efficiency in mitigating membrane fouling. The hydrodynamic parameters (including particle velocity, particle concentration, particle momentum and extent of segregation) of the fluidized media numerically obtained via a Two-Fluid Model (TFM) were correlated with the fouling rate experimentally obtained. Three bidisperse mixtures with the same mean particle diameter (namely, 1 mm) but different particle diameter ratios (namely, dp2/dp1 = 1.22 - 1.86) were studied over a range of superficial liquid velocities. The key highlights are that (i) the fouling rate decreased (i.e., fouling mitigation was more effective) as the particle diameter ratio increased, which indicates the benefits of fluidizing multi-sized particle mixtures over monodisperse ones, (ii) the fouling rate (dTMP/dt) was positively correlated to the mixing index (M), which implies that segregated systems were more effective at mitigating membrane fouling, and (iii) the effect of bidispersity was more significant at the lower power input, which suggests that the advantages of fluidizing such bidisperse mixtures should only be harnessed at moderate power but not higher ones.