Pyung-Kyu Park

Effect of the removal of DOMs on the performance of a coagulation-UF membrane system for drinking water production

Coagulation with only rapid mixing in a separate tank (ordinary coagulation) and coagulation with no mixing tank (in-line coagulation) were applied prior to ultrafiltration with an inside-out type hollow fiber membrane. In result the filterability at the former conditions was superior in both the crossflow and dead-end modes. Thus the relative importance of the removal rate of DOMs was investigated. Precoating the surface of the membranes with metal hydroxide particles of coagulants was also examined. This method of utilizing coagulants resulted in a smaller consumption of coagulant in the coagulation-UF system.

Analysis of filtration characteristics in submerged microfiltration for drinking water treatment.

Hollow fiber membranes have been widely employed for water and wastewater treatments. Nevertheless, understanding the filtration characteristics of hollow fiber membranes is complicated by the axial distributions of transmembrane pressure (TMP) and flux, which are key factors for both fouling control and module design. In this study, model equations to account for different fouling mechanisms were derived to analyze the performance of submerged hollow fiber systems with different conditions in terms of feed water characteristics and membrane material. A series of experiments with synthetic feed and raw water were carried out using hydrophilic and hydrophobic membrane modules. The model successfully fits the experimental results for synthetic feed as well as raw water. The major fouling mechanisms for filtration of raw water using hydrophilic and hydrophobic membranes are identified as cake formation and standard blocking, respectively. The model calculations indicate that the distributions of flux and cake (fouling) resistance are sensitive to the fiber length of the membrane.

A facile route to enhance the water flux of a thin-film composite reverse osmosis membrane: incorporating thickness-controlled graphene oxide into a highly porous support layer

In this study, we demonstrated that a reduction in solely the concentration of the polymer solution for preparation of the support layer effectively enhances the water flux of a thin-film composite (TFC) reverse osmosis (RO) membrane. However, a decrease in the polymer concentration caused the sub-surface structure of the support layer to become too porous, which unavoidably weakened the mechanical strength of the support layer. To overcome the problem, we prepared a highly porous support layer with improved mechanical strength by incorporating graphene oxide (GO) platelets. The thickness of the GO platelets was controlled by adjusting the mechanical energy input per volume of the precursor solution. We confirmed that well-exfoliated GO platelets (mean thickness: about 1.5 nm) are more effective in enhancing the mechanical properties of the support layer. The TFC RO membrane made of the GO composite support layer had almost 1.6 to 4 times higher water flux with comparable salt rejection compared to both the current upper bounds of the RO membranes prepared by modification of the active layer and commercial RO membranes.

More Efficient Media Design for Enhanced Biofouling Control in a Membrane Bioreactor: Quorum Quenching Bacteria Entrapping Hollow Cylinder

Recently, membrane bioreactors (MBRs) with quorum quenching (QQ) bacteria entrapping beads have been reported as a new paradigm in biofouling control because, unlike conventional post-biofilm control methods, bacterial QQ can inhibit biofilm formation through its combined effects of physical scouring of the membrane and inhibition of quorum sensing (QS). In this study, using a special reporter strain (Escherichia coli JB525), the interaction between QS signal molecules and quorum quenching bacteria entrapping beads (QQ-beads) was elucidated through visualization of the QS signal molecules within a QQ-bead using a fluorescence microscope. As a result, under the conditions considered in this study, the surface area of QQ-media was likely to be a dominant parameter in enhancing QQ activity over total mass of entrapped QQ bacteria because QQ bacteria located near the core of a QQ-bead were unable to display their QQ activities. On the basis of this information, a more efficient QQ-medium, a QQ hollow cylinder (QQ-HC), was designed and prepared. In batch experiments, QQ-HCs showed greater QQ activity than QQ-beads as a result of their higher surface area and enhanced physical washing effect because of their larger impact area against the membrane surface. Furthermore, it was shown that such advantages of QQ-HCs resulted in more effective mitigation of membrane fouling than from QQ-beads in lab-scale continuous MBRs.

Effect of the Shape and Size of Quorum Quenching Media on Biofouling Control in Membrane Bioreactors for Wastewater Treatment.

Recently, spherical beads entrapping quorum quenching (QQ) bacteria have been reported as effective moving QQ-media for biofouling control in MBRs for wastewater treatment owing to their combined effects of biological (i.e., quorum quenching) and physical washing. Taking into account both the mass transfer of signal molecules through the QQ-medium and collision efficiencies of the QQ-medium against the filtration membranes in a bioreactor, a cylindrical medium (QQ-cylinder) was developed as a new shape of moving QQ-medium. The QQ-cylinders were compared with previous QQ-beads in terms of the QQ activity and the physical washing effect under identical loading volumes of each medium in batch tests. It was found that the QQ activity of a QQ-medium was highly dependent on its specific surface area, regardless of the shape of the medium. In contrast, the physical washing effect of a QQ-medium was greatly affected by its geometric structure. The enhanced anti-biofouling property of the QQ-cylinders relative to QQ-beads was confirmed in a continuous laboratory-scale MBR with a flat-sheet membrane module.

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.

Immobilization of hydrous iron oxides in porous alginate beads for arsenic removal from water

For removal of arsenic in the aqueous phase, hydrous iron oxides (HIOs) were immobilized in alginate beads with enhanced porosity (designated as HIO-P-alginate beads). The HIO-P-alginate beads had macropores, observed by SEM, as well as mesopores and featured a higher BET surface area than previously developed adsorbent beads. Thus, the adsorption of As(III) and As(V) by the HIO-P-alginate beads was more rapid than that of previously reported HIO-alginate adsorbents. The kinetics of adsorption were well described by a pseudo-second-order model, indicating that chemisorption mainly governed the As(III) and As(V) adsorption. We confirmed a chemisorption mechanism for the As(III) and As(V) adsorption, through isotherm studies using the Dubinin–Radushkevich isotherm model. The application of an intraparticle diffusion model to the kinetic data suggested that the As(V) adsorption onto the HIO-P-alginate beads was controlled entirely by intraparticle diffusion whereas the As(III) adsorption was governed by intraparticle diffusion only at short contact times. As(III) adsorption was highest at neutral pH; however, As(V) adsorption was highest at low pH. Both As(III) and As(V) adsorption did not compete with nitrate adsorption, and the As adsorption improved with increasing ionic strength. The HIO-P-alginate beads could be regenerated several times with a NaOH solution and were successfully reused for arsenic removal.

Basic Principles of Simulating Boron Removal in Reverse Osmosis Processes

Removing boron to meet increasingly stringent water quality regulations has been challenging for sea water reverse osmosis (SWRO) membrane plants. The rejection of boron follows a mechanism different from those of other ionic solutes such that it cannot be readily correlated with the rejection of other ionic species. Therein, computer simulations have been proven to be an effective tool to predict and optimize boron removal by full-scale SWRO processes. This chapter summarizes fundamentals of a mechanistic predictive model based on an irreversible thermodynamic model coupled with a film theory. The model takes account of boron speciation as a function of pH which significantly affects the overall boron removal. The finite element analysis approach to simulate spiral wound elements and mass balance approach for pilot- and full-scale RO (reverse osmosis) processes are further discussed. Finally, an example on how the model can be utilized to predict the boron rejection in pilot- and full-scale plants under various design and operation scenarios is presented.