Jae-Hyuk Kim

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.

Engineering Light: Advances in Wavelength Conversion Materials for Energy and Environmental Technologies

Upconversion photoluminescence (UC) occurs in optical materials that are capable of absorbing low energy photons and emitting photons of higher energy and shorter wavelength, while downconversion (DC) materials may absorb one high energy photon and emit two of lower energy for quantum yields exceeding unity. These wavelength conversion processes allow us to transform electromagnetic radiation so it may be more effectively utilized by light-capturing devices and materials. Progress in designing more efficient organic and inorganic photochemical conversion systems has initiated a recent surge in attempts to apply these processes for practical uses, including enhancement of many energy and environmental technologies. In this review, we introduce important concepts in UC and DC materials and discuss the current status and challenges toward the application of wavelength conversion to solar cells, photocatalysis, and antimicrobial surfaces.

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.

Effect of disintegrated sludge recycling on membrane permeability in a membrane bioreactor combined with a turbulent jet flow ozone contactor.

We have combined a turbulent jet flow ozone contactor (TJC) with a membrane bioreactor (MBR) to establish a zero-discharge system in terms of excess sludge in the MBR. The TJC-MBR system was compared with the conventional MBR (Control-MBR) with respect to i) the size and zeta potential of the sludge particles, ii) the loosely bound extra-cellular polymeric substances (EPSs) and tightly bound EPS of the microbial flocs, iii) the porosity and biovolume of the bio-cake accumulated on the membrane, and iv) the membrane permeability. The TJC system generated the ozonated sludge with a negligible amount of loosely bound EPS and a positive zeta potential. As a result, when such ozonated sludge was recycled, the average size of the sludge particles (e.g., microbial flocs) increased in the TJC-MBR. Consequently the bio-cake formed in the TJC-MBR had greater porosity than that in the Control-MBR, giving rise to higher membrane permeability in the TJC-MBR.

Control of Organic Micropollutants Using Dual Functional Adsorbent/Catalyst System

This study focuses on the development of novel catalysts for simultaneous adsorption and oxidation of micropollutants in aqueous phase. Molecular catalysts were physically immobilized on the surface or pore of amberlite IRA-400 or powdered activated carbon (PAC). Comparison of different combinations of catalysts and adsorbents showed that the Fe(III)-TsPc combined with amberlite had the highest removal efficiency for target compounds. Although the catalyst was immobilized by electrical attraction, no dissociation of catalyst from adsorbent occurred during the tests. Amberlite-supported Fe(III)-TsPc shows more than 98% removal efficiency in 40 min. In homogenous system (suspension of Fe(III)-TsPc in aqueous solution), the oxidation reaction occurred only in acidic conditions (pH ~ 4.5) and the catalyst deactivation rate was fast. On the contrary, the reaction was fast in neutral pH and catalytic deactivation was negligible using the amberlite-supported Fe(III)-TsPc.