Synchrotron based Micro Tomography (SR-μCT), Experimental, and Computational Studies to Investigate the Influences of Cross Flow Air Injection in Ultrafiltration Process

Abstract

The goal of the present study is to gain an in depth understanding of the influences of air injected concurrently and counter currently on membrane fouling and permeate flux for homogeneous Polycarbonate (PC) and heterogeneous Polysulfone (PS) membranes in the cross-flow ultrafiltration (UF). The Synchrotron-based X-ray microtomography (SR-μCT) technique, available at the biomedical imaging and therapy (BMIT) beamlines at the Canadian Light Source (CLS), answered the key research questions related to quantitative analysis and the visualization of particle depositions, layer by layer, in heterogeneous membrane matrices that would otherwise be opaque to optical access. In particular, high photon flux to achieve high resolution is infeasible, using lab-based radiography systems. SR-μCT was used to assess the influence of air injection on membrane fouling in each membrane layer of PS membrane matrices. A multiphase cross-flow filtration and the hydrodynamics was simulated, in the rectangular filtration channel, using computational fluid dynamics (CFD) at different air velocities. Furthermore, the scanning electron microscope (SEM) and confocal microscope imaging were used at different positions of the membranes to examine the influences of the velocity profiles on membrane fouling. SR-μCT innovative techniques proved that counter current air flow resulted in the elimination of membrane fouling at the top layers, but severe fouling between intermediate and lower layers of the investigated region inside the PS membrane matrices using counter-current air injection compared to concurrent air injection. These results indicate more particle deposited and trapped inside membrane matrices when air was injected counter-currently, which led to more turbulences and a reduction of the permeate flux. On the other hand, top layer indices depict strongly fouling on the bare PS without air injection. CFD analyses supported the experimental results, where the concurrently injected air was more effective in increasing the shear rate and reducing the concentration polarization while reducing turbulences and vortexes, as compared to the counter currently injected air. This innovative study is the first to report the SR-μCT for investigating membrane fouling in UF process for water and wastewater treatment.