Dong-Chan Choi

Enzyme-Immobilized Nanofiltration Membrane To Mitigate Biofouling Based on Quorum Quenching

Recently, enzymatic quorum quenching (in the form of a free enzyme or an immobilized form on a bead) was successfully applied to a submerged membrane bioreactor with a microfiltration membrane for wastewater treatment as a novel approach to control membrane biofouling. In this study, a quorum quenching enzyme (acylase) was directly immobilized onto a nanofiltration membrane to mitigate biofouling in a nanofiltration process. In a flow cell experiment, the acylase-immobilized membrane with quorum quenching activity prohibited the formation of mushroom-shaped mature biofilm due to the reduced secretion of extracellular polymeric substances (EPS). The acylase-immobilized membrane maintained more than 90% of its initial enzyme activity for more than 20 iterative cycles of reaction and washing procedure. In the lab-scale continuous crossflow nanofiltration system operated at a constant pressure of 2 bar, the flux with the acylase-immobilized nanofiltration (NF) membrane was maintained at more than 90% of its initial flux after a 38-h operation, whereas that with the raw NF membrane decreased to 60% accompanied with severe biofouling. The quorum quenching activity of the acylase-immobilized membrane was also confirmed by visualizing the spatial distribution of cells and polysaccharides on the surface of each membrane using confocal laser scanning microscopy (CLSM) image analysis technique.

Preparation and Application of Patterned Membranes for Wastewater Treatment

Membrane fouling remains a critical factor limiting the widespread use of membrane processes in water and wastewater treatment. To mitigate membrane fouling, we introduced a patterned morphology on the membrane surface using a lithographic method. A modified immersion precipitation method was developed to relieve the formation of dense layer at the solvent-nonsolvent interface, that is, the opposite side of the patterned surface. Diverse patterned membranes, such as pyramid-, prism-, and embossing-patterned membranes, were prepared and compared with a flat membrane in terms of morphology, permeability, and biofouling. Patterned membrane fidelity was largely dependent on the polymer concentration in cast solution. The patterned surface augmented the water flux in proportion to the roughness factor of the patterned membrane. However, the type of pattern did not affect substantially the mean pore size on the patterned surface. Deposition of microbial cells on the patterned membrane was significantly reduced compared to that on the flat membrane in the membrane bioreactor (MBR) for wastewater treatment. This was attributed to hydraulic resistance of the apex of the patterned surface, which induced local turbulence.

Characterization and theoretical analysis of isoporous cycloaliphatic polyurethane membrane for water treatment

AbstractA narrow pore size distribution is critical for most membrane separation processes even though it is difficult to achieve through conventional methods of membrane synthesis such as phase inversion. Although various technologies have been proposed for the preparation of isoporous membranes, few technologies are available for use in water treatment applications. In our previous works, we have prepared isoporous membranes using a novel technique based on soft lithography. A micro pattern of pyramid shape was applied to produce uniform pores. In this work, we aimed at the characterization of these isoporous membranes using both experimental and theoretical methods. The pore size distributions of the membranes were characterized by scanning electron microscopy image analysis. Using this image analysis technique, the pore size ranging from 2.2 to 21.4 μm could be identified. A simple theoretical model was developed to determine the pore size, porosity, and membrane resistance of the isoporous membranes....

Influence of the sublayer structure of thin-film composite reverse osmosis membranes on the overall water flux

We found that a support layer of a reverse osmosis (RO) membrane could have a significant effect on the membrane filtration efficiency. To be specific, we determined that the pressure drop occurring in the support layer during the RO operation can increase such that it affects the overall water flux, as a dense sponge-like structure and closed finger-like structure become predominant in the support layer. This considerable resistance was assumed to occur while more water passes through tortuous and segmented regions after being evenly discharged from the active layer. This hypothesis was supported by the estimated pressure drop using the Ergun equation and the tortuosity obtained from a forward osmosis test conducted to better reflect the influence of the sponge-like region. We attempted to factor in all of the parameters used in the Ergun equation in order to determine the main cause of the high pressure drop, and the tortuosity was found to be dominant. An interesting finding was that the tortuosity of the support layer can also significantly influence the overall water flux, even during the RO process. Moreover, the above phenomenon can become much more obvious when the active layer is highly permeable, suggesting that the support layer must be considered alongside the active layer when developing thin-film composite membranes with a highly permeable active layer. Overall, we concluded that the concentration of the polymer solution should be less than 20 wt% to ensure the best performance when preparing a support layer for brackish-water RO membranes.