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Warkiani M.E.,Nanyang Technological University | Gong H.Q.,Nanyang Technological University | Fane A.G.,Nanyang Technological University | Wicaksana F.,Singapore Membrane Technology Center
Technical Proceedings of the 2011 NSTI Nanotechnology Conference and Expo, NSTI-Nanotech 2011 | Year: 2011

The effects of the membrane pore geometry on the fouling mechanism of high-flux polymeric micro-fabricated membranes were studied using latex particles with different sizes and concentrations. The micro-fabricated membranes are made of a thin layer SU-8 photoresist with smooth surface and well defined slotted (or circular) pores using dissolving mold technique. For particles larger than the membrane pore size, the fouling mechanism was pore blockage followed by cake filtration while pore narrowing was the dominant mechanism when the particles were smaller than the membrane pore size. Filtration with slotted membrane offers some interesting advantages over conventional filtration with circular pores. The initial rate of flux decline was slower for the membrane with slotted pores compared to the membrane with circular pores since the initial particle deposition only covered a small fraction of the slits. The flow resistance is also much lower for the slotted membrane compare to the circular membrane. Source


Warkiani M.E.,University of New South Wales | Wicaksana F.,Singapore Membrane Technology Center | Wicaksana F.,University of Auckland | Fane A.G.,Singapore Membrane Technology Center | And 2 more authors.
Microfluidics and Nanofluidics | Year: 2015

Investigations of membrane fouling at the pore-scale have long been of limited interest due to microstructural defects of the commercial membranes that prevent any quantitative analysis of the experimental results. In this paper, we employed novel microengineered membranes with regular pore size to investigate the effect of the membrane pore geometry on the fouling mechanisms during filtration of micron-sized particles. For particles larger than the membrane pore size, the fouling mechanism was pore blockage followed by the cake filtration, while pore narrowing was the dominant mechanism when particles were smaller than the membrane pore size. Filtration with the slotted pore membrane offers some interesting advantages comparing to the filtration with circular pores. The rate of flux decline was slower for the membrane with slotted pores compared with the membrane with circular pores since the initial particle deposition only covered a small fraction of the pores. It was also found that the flow resistance of the slotted pore membrane is much lower than the circular one because a slotted pore has a smaller perimeter than several circular pores with the same total surface area. We can conclude that by proper selection of membrane pore geometry, flux decline can be hindered while maintaining a high selectivity during microfiltration. These findings can be useful also for researchers who are using microfluidic platforms with integrated isopore filters for various applications such as stem cell enrichment, cancer cell isolation, blood fractionation and pathogen removal. © 2014, Springer-Verlag Berlin Heidelberg. Source


Zhang Y.P.,Nanyang Technological University | Law A.W.K.,Singapore Membrane Technology Center | Law A.W.K.,Nanyang Technological University | Fane A.G.,Singapore Membrane Technology Center
Journal of Membrane Science | Year: 2010

An improved method combining mass balance and image analysis was developed in this study to determine the critical flux during crossflow microfiltration. The proposed method gave a better representation of the physical deposition processes on the membrane surface, and the results obtained were more accurate than the previous methods based on the observation technique alone. In addition, by studying the fractional deposition of the membrane surface when the operating flux is above the critical flux, it was found that not all the particles convected toward the membrane would eventually deposit onto the membrane surface when the operating flux was above the critical flux. The fractional deposition also varied under different operating conditions of the crossflow microfiltration. © 2010 Elsevier B.V. Source


Zhang Y.P.,Nanyang Technological University | Fane A.G.,Singapore Membrane Technology Center | Fane A.G.,Nanyang Technological University | Law A.W.K.,Singapore Membrane Technology Center | Law A.W.K.,Nanyang Technological University
Journal of Membrane Science | Year: 2010

The critical flux and particle deposition of fractal flocs during crossflow microfiltration were investigated experimentally in this study. Flocculated hematite flocs were used as the model flocs. The critical flux was determined based on the observation of floc deposition using the Direct Observation Through Membrane (DOTM) technique. The experimental results showed that in addition to the particle size distribution, the fractal structure of the flocculated flocs also exerted a strong influence on the fouling mechanisms. Larger flocs typically yielded higher critical fluxes as in monodisperse suspensions, and the effect of particle size was less pronounced for the more porous flocs. The critical flux was also found to increase with the fractal dimension, especially for the larger flocs. © 2010 Elsevier B.V. Source


Xia L.,Singapore Membrane Technology Center | Xia L.,Nanyang Technological University | Law A.W.K.,Singapore Membrane Technology Center | Law A.W.K.,Nanyang Technological University | And 2 more authors.
Water Research | Year: 2013

Air sparging is now a standard approach to reduce concentration polarization and fouling of membrane modules in membrane bioreactors (MBRs). The hydrodynamic shear stresses, bubble-induced turbulence and cross flows scour the membrane surfaces and help reduce the deposit of foulants onto the membrane surface. However, the detailed quantitative knowledge on the effect of air sparging remains lacking in the literature due to the complex hydrodynamics generated by the gas-liquid flows. To date, there is no valid model that describes the relationship between the membrane fouling performance and the flow hydrodynamics. The present study aims to examine the impact of hydrodynamics induced by air sparging on the membrane fouling mitigation in a quantitative manner. A modelled hollow fiber module was placed in a cylindrical bubble column reactor at different axial heights with the trans-membrane pressure (TMP) monitored under constant flux conditions. The configuration of bubble column without the membrane module immersed was identical to that studied by Gan etal. (2011) using Phase Doppler Anemometry (PDA), to ensure a good quantitative understanding of turbulent flow conditions along the column height. The experimental results showed that the meandering flow regime which exhibits high flow instability at the 0.3m is more beneficial to fouling alleviation compared with the steady flow circulation regime at the 0.6m. The filtration tests also confirmed the existence of an optimal superficial air velocity beyond which a further increase is of no significant benefit on the membrane fouling reduction. In addition, the alternate aeration provided by two air stones mounted at the opposite end of the diameter of the bubble column was also studied to investigate the associated flow dynamics and its influence on the membrane filtration performance. It was found that with a proper switching interval and membrane module orientation, the membrane fouling can be effectively controlled with even smaller superficial air velocity than the optimal value provided by a single air stone. Finally, the testing results with both inorganic and organic feeds showed that the solid particle composition and particle size distribution all contribute to the cake formation in a membrane filtration system. © 2013 Elsevier Ltd. Source

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