Young-Nam Kwon

Preparation and applications of poly vinyl alcohol (PVA) modified cellulose acetate (CA) membranes for forward osmosis (FO) processes

AbstractPolyvinyl alcohol (PVA)-coated cellulose acetate (CA)-based flat-sheet membranes have been fabricated and tested in the forward osmosis (FO) process. PVA was used as a surface modifying agent. CA membranes prepared by conventional immersion precipitation were treated in an aqueous solution of PVA and tested water flux and salt rejection. The effects of PVA concentration, treatment time on the hydrophilicity of membrane surface, water permeability, and salt retention property of the membrane were estimated. The modified membrane was characterized by X-ray photoelectron spectroscopy and contact angle measurement. A hydrophilicity of membrane surface was observed in longer modification times and the higher PVA solution concentration accounted for a attaching of the PVA chains by glutaraldehyde as cross-linking agent. The best condition of salt rejection and permeability performance was obtained by using 1 wt% PVA solution and treatment time of 2 min. In the FO process, modified CA membrane exhibited ...

Effect of chlorination condition and permeability of chlorine species on the chlorination of a polyamide membrane.

Most studies on membrane chlorination have been investigated in an unpressurized chlorination mode, even if the polyamide membrane was continuously exposed to chlorine under high operating pressure in real water/wastewater treatment plants. In this study, performance changes due to polyamide membrane chlorination were investigated in both pressurized and unpressurized chlorination modes. Chlorination in an unpressurized mode showed a flux increase at high pH and a flux decline at low pH due to the compaction and swelling of the polyamide chains, respectively. On the other hand, chlorination performed in a pressurized mode decreased the water flux in both acidic and alkaline conditions, showing that compaction is overwhelming compared to swelling. The permeability of HOCl, a dominant species at low pH, through the polyamide membrane was pH independent and almost similar to the system recovery, but the permeability of OCl(-), which is dominant at high pH, was maxima at a neutral pH. The different performance behaviors of membranes chlorinated at various pH conditions in the presence or absence of applied pressure could be explained by the permeability of chlorine species and compaction/swelling of polymer chains after chlorination. The effect of membrane chlorination on the chemical property changes at the two different modes was confirmed using attenuated total reflection Fourier transform infrared analysis, and a conceptual model of performance change was proposed to explain the performance discrepancy between the two chlorination modes.

Protocol for development of various plants leaves extract in single-pot synthesis of metal nanoparticles

This article is aimed to extend a simple protocol for preparation of various plant leaves extract and their application to green synthesis of the metallic nanoparticles. Five plant leaves extract showed mild reduction and stabilization ability for silver and gold nanoparticles (AgNPs and AuNPs) at room temperature. The particle size range varied from 25 to 42 nm and 21 to 47 nm for AgNPs and AuNPs, respectively. Plant leaves extract-mediated nanoparticles were characterized to confirm the shape, size, crystallinity, and content using different spectroscopic investigations. Differences in stability of nanoparticles at different pH were also measured by zeta potential.

Assessing the effects of bacterial predation on membrane biofouling.

Membrane biofouling is one of the major obstacles limiting membrane applications in water treatment. In this study, Bdellovibrio bacteriovorus HD 100, a Gram-negative predatory bacterium, was evaluated as a novel way to mitigate membrane biofouling and its subsequent performance decline. Dead-end microfiltration (MF) tests were carried out on Escherichia coli DH5α and B. bacteriovorus HD 100 co-culture feed solutions. Predation of E. coli was performed at either a low or high multiplicity of infection (MOI), which is defined as the predator to prey cell ratio. The MOIs tested were 2 and 200, and the viability of both the E. coli prey and the predator was monitored over 48 h. The higher MOI (high predator, HP) culture showed a nearly 6-log loss in E. coli number after 24 h when compared to both the control and low MOI (low predator, LP) cultures, whereas the E. coli population within both predated cultures (HP and LP) became nearly identical at 48 h and 4-log lower than that of the control. The unpredated cultures led to significant loss in water flux at 12, 24, and 48 h of culture, but the HP and LP membranes showed less loss of flux by comparison. Analysis of the total membrane resistance showed a similar trend as the flux decline pattern; however, irreversible resistance of the membrane was much higher for the 48 h LP culture compared to the unpredated and HP cultures at 48 h. This increase in irreversible resistance was attributed mainly to E. coli debris, which accumulated in the medium after the predator lysed the prey cells. These results show that pretreatment of wastewater using a suitable concentration of predatory bacteria such as B. bacteriovorus can enhance membrane performance.

Single-step green synthesis of imine-functionalized carbon spheres and their application in uranium removal from aqueous solution

Carbon spheres (CSs) have become a recent focus of attention in environmental remediation techniques. In this study, imine-functionalized CSs were synthesized from plant extract (peCSs) for the first time and effectively used in U(VI) removal from contaminated water. Plant extracts of Sorbaria sorbifolia were utilized for the synthesis of peCSs via a single-step hydrothermal carbonization, and the physico-chemical properties of the synthesized peCSs were characterized by spectroscopic analysis. The peCSs showed high nitrogen content (∼7.49%) due to the presence of naturally occurring cyanogenic glycosides and mesoporosity (8.31 nm). The plant extract concentration played an important role in determining the size of the peCSs, which ranged from 0.5 to 3.0 μm. The adsorption capacity (Qm) of peCSs for U(VI) (Qm ≈ 113 mg g−1) was higher than that of the glucose-derived CSs (Qm ≈ 57 mg g−1) and commercial powdered activated carbon (Qm ≈ 44 mg g−1). A plausible mechanism for the higher adsorption efficacy of peCSs was proposed via sorbate–sorbent interactions. The ionic strength (0.01 M to 1 M NaCl) showed the weakest effect on the U(VI) adsorption. The multiple adsorption–desorption cycling test revealed that the efficacy of peCSs does not significantly decrease after repetitive use.

Cellulose acetate graft-(glycidylmethacrylate-g-PEG) for modification of AMC ultrafiltration membranes to mitigate organic fouling

A hydrophilic cellulose acetate-graft-(glycidylmethacrylate-g-polyethylene glycol) (CA-g-(GMA-g-PEG)) was synthesized and incorporated into acetylated methyl cellulose (AMC) to prepare antifouling ultrafiltration membranes. The successful synthesis of CA-g-(GMA-g-PEG) was confirmed by 1H-NMR and X-ray photoelectron spectroscopy studies. The AMC blend membranes were characterized by X-ray diffraction (XRD), thermo gravimetric analysis (TGA), scanning electron microscopy (SEM), atomic force microscopy (AFM), confocal laser scanning microscopy (CLSM) and contact angle analysis to investigate the effect of CA-g-(GMA-g-PEG) on the properties of the membrane surface. The increase of CA-g-(GMA-g-PEG) content in the AMC matrix reduced the macrovoids and transformed to a sponge-like structure in the entire membrane cross section. Furthermore, the increase in the graft moiety enhanced the performance of the membranes. Surface free energy parameters calculated from the contact angle measurements indicate that the interfacial free energy of the blend membranes were lower than those of the pure AMC membranes. The modified membrane surface became more hydrophilic and more wettable because of the preferential orientation of these polar groups towards the membrane surface. The efficiency of these membranes in the separation of singlet foulants and multi foulants increased significantly, thus increasing the fouling resistance. These membranes would be useful for organic fouling prevention during water and wastewater treatment.

Preparation of newly synthesized forward osmosis membrane

Abstract Forward osmosis (FO) membrane was fabricated with a newly synthesized acetylated methyl cellulose (AMC) membrane. The FO membrane performance was compared with a commercially available reverse osmosis (RO) membrane for seawater desalination. Interfacial polymerization was done on the AMC support membrane for FO membrane preparation. Polyamide layer was successfully formed. The membranes were characterized by scanning electron microscopy and atomic force microscopy analysis. The surface of two membranes shows similar ridge-and-valley structure. However, the support layer of two membranes was completely different. The polyamide membrane based on the AMC support layer shows much better FO and RO performance than the RO membrane due to difference at the membrane cross-section between two membranes. The big macrovoids of the AMC support layer make flux much higher. In contrast, the RO membrane shows sponge-like structure at the membrane cross-section.

Distinctive green recovery of silver species from modified cellulose: Mechanism and spectroscopic studies

The present study aimed to recover precious silver in order to identify the adsorption coupled reduction pathways that determine this process. A combination technique of adsorption and nanocrystallization was used to investigate the recovery of silver species from taurine-cellulose (T-DAC) samples. The non-synthetic route of nanocrystallization yielded spherical zero-valent silver sized ∼ 18 nm. Rate-controlling steps were modeled by adsorption parameters by the best fit of Langmuir capacity (55 mg/g), pseudo-second order curves, and exothermic chemical reactions. The T-DAC was an excellent sorbing phase for the treatment of silver-polluted waters over a broad range of pH (2.1-10.1) and varying ionic strengths (8.5-850 mM, as NaCl), which are the conditions often encountered in industrial and mining effluents. A good recovery of silver (40-65%) was also obtained in the presence of Cd(II), Co(II), Cr(VI), Ni(II), and As(V) at lower or equivalent concentrations with Ag(I), either from individually added metals or from all metal ions mixed together. Desorption was compared with a series of five eluents including complexing agents. In these experiments acidified thiourea yielded 86% desorption of Ag(I). Aqueous silver reduced to metallic silver on the surface of the T-DAC samples, which was confirmed by X-ray photo electron spectroscopy.

Application of a FO/MD-combined system for the desalination of saline solution

AbstractThe objective of this study was to systematically investigate the effects of draw solution (DS) chemistry on the performance of a forward osmosis (FO)/membrane distillation (MD)-combined system, and to apply the integrated system to the desalination of a saline solution. Extraction of pure water from saline water was conducted by the FO process, and subsequent production of fresh water and recovery of draw solutes from the DS diluted by the FO process were achieved by MD. Experiments at various temperatures, concentrations, and types of DS showed that the diffusion coefficient of the draw solutes and interaction of the salt ions with water molecules caused severe effects on the performance of the integral system, along with the temperature and concentration of the DS. This study suggests that optimum operating conditions and selection of proper draw solutes with higher diffusion coefficients and lower hydrophilicities can make the FO/MD-combined process a promising candidate for the desalination o...

Pretreatment with alum or powdered activated carbon reduces bacterial predation-associated irreversible fouling of membranes.

This study evaluated the co-application of bacterial predation by Bdellovibrio bacteriovorus and either alum coagulation or powdered activated carbon adsorption to reduce fouling caused by Escherichia coli rich feed solutions in dead-end microfiltration tests. The flux increased when the samples were predated upon or treated with 100 ppm alum or PAC, but co-treatment with alum and predation gave the best flux results. The total membrane resistance caused by the predated sample was reduced six-fold when treated with 100 ppm PAC, from 11.8 to 1.98 × 1011 m−1, while irreversible fouling (Rp) was 2.7-fold lower. Treatment with 100 ppm alum reduced the total resistance 14.9-fold (11.8 to 0.79 × 1011 m−1) while the Rp decreased 4.25-fold. SEM imaging confirmed this, with less obvious fouling of the membrane after the combined process. This study illustrates that the combination of bacterial predation and the subsequent removal of debris using coagulation or adsorption mitigates membrane biofouling and improves membrane performance.