Fouling Behavior of Microstructured Hollow Fiber Membranes in Dead-End Filtrations: Critical Flux Determination and NMR Imaging of Particle Deposition

Abstract

The fouling behavior of microstructured hollow fibers was investigated in constant flux filtrations of colloidal silica and sodium alginate. It was observed that the fouling resistance increases faster with structured fibers than with round fibers. Reversibility of structured fibers' fouling was similar during silica filtrations and better in sodium alginate filtrations when compared with round fibers. The deposition of two different silica sols on the membranes was observed by NMR imaging. The sols had different particle size and solution ionic strength and showed different deposition behaviors. For the smaller particle-sized sol in deionized solution (Ludox-TMA), there was more deposition within the grooves of the structured fibers and much less on the fins. For the alkali-stabilized sol Bindzil 9950, which had larger particles, the deposition was homogeneous across the surface of the structured fiber, and the thickness of the deposit was similar to that on the round fiber. This difference between the deposition behavior of the two sols is explained by differences in the back diffusion, which creates concentration polarization layers with different resistances. The Ludox sol formed a thick polarization layer with very low resistance. The Bindzil sol formed a slightly thinner polarization layer; however, its resistance was much higher, of similar magnitude as the intrinsic membrane resistance. This high resistance of the polarization layer during the Bindzil sol filtration is considered to lead to quick flow regulation toward equalizing the resistance along the fiber surface. The Ludox particles were trapped at the bottom of the grooves as a result of reduced back diffusion. The fouling behavior in sodium alginate filtrations was explained by considering the size-dependent deposition within the broad alginate size distribution. The better reversibility of fouling in the structured fibers is thought to be the result of a looser deposit within the grooves, which is more easily removed than a compressed deposit on the round fibers.

Estimation of the structure dependent performance of 3-D rapid prototyped membranes

“…Innovative fabrication techniques afford non-circular hollow-fiber membranes with topological features on the in-and outside of the membrane. [28][29][30][31][32][33] Tubular or irregular hollow-fibers can be combined into non-parallel bundles to shape the flow-profile and improve mass transport. [34][35][36][37] These studies indicate that the macroscopic membrane geometry and their arrangement is a key factor to improve mass transport and reduce fouling to boost membrane performance.…”

“…The smoothness results from a local area minimization principle, which causes the disappearance of mean curvature and Young-Laplace pressure [40]. This local smoothness should also prevents topology induced fouling [29,31,33].…”

Particle deposition on the patterned membrane surface: Simulation and experiments

“…Recently, the patterned membrane technology whose surface has micro-sized patterns was developed by combining hydrodynamic methods with the surface modification technology. Çulfaz et al fabricated hollow fiber ultrafiltration (UF) patterned membrane and they found that the fouling resistance was increased with micro-sized surface patterns [7,8]. Won et al modified the immersion precipitation method and successfully prepared patterned membranes with various surface patterns [9].…”

Identification of key factors affecting the organic fouling on low-pressure ultrafiltration membranes

“…Because of a broad size distribution, SA has both small molecules with high diffusivities and large molecules with low diffusivities. Therefore, they would be fractionated in the deposited cake with larger molecules closer to the membrane and smaller ones in the bulk [9].…”