Characterizing the Scouring Efficiency of Fluidized Granular Activated Carbon (GAC) Particles in Membrane Fouling Mitigation Via Wavelet Decomposition of Accelerometer Signals

Particle fluidization, a promising unsteady-state shear means of mitigating membrane fouling in order to lower energy requirement and prolong membrane lifespan [1, 2], has garnered increasing attention in membrane-based water treatment processes. In particular, the fluidized particles facilitate back-transport in the polarization layer [3] and also play the role of mechanical scouring agents [4], the latter of which is dominant for millimeter-sized particles. To date, the hydrodynamics of the liquid-solid fluidization of the millimeter-sized GAC particles is not understood, although the understanding of the physical behavior of the liquid and solid phases is key to the fouling mitigation phenomenon. Hence, the current effort aims at bridging the gap in the knowledgebase of the dynamics of the solid particles in effecting the scouring mechanism on membranes to mitigate fouling.

In this effort, an accelerometer was successfully used to reveal the liquid-dolid fluidization dynamics of three GAC particle diameters (namely, 1.20 mm, 1.85 mm, and 2.18 mm) [5]. Specifically, because both liquid and solid phases contribute to the accelerometer signal, wavelet decomposition was used to extract information in the frequency ranges corresponding only to the solid phase [6]. The energy contained in the accelerometer signal corresponding to the solid phase was consistent with the extent of fouling mitigation in the filtration tests. Results indicate that the smallest particle diameter of 1.20 mm conferred the least scouring efficiency, while both the larger particle diameters of 1.85 mm and 2.18 mm provided similar scouring efficiency. The impact of particle diameter is due to the balance between particle inertia, and the difference between superficial liquid velocity and minimum fluidization velocity. Calculations of energy requirement indicate that, the energy requirement of all three particle diameters (d_p) were similar at lower scouring efficiency, whereas the energy requirement of the smallest d_pof 1.20 mm was the greatest at higher scouring efficiency.

References

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