Seung-Hyeon Moon

Removal of chromium from water and wastewater by ion exchange resins.

Removal of chromium from water and wastewater is obligatory in order to avoid water pollution. Batch shaking adsorption experiments were carried out to evaluate the performance of IRN77 and SKN1 cation exchange resins in the removal of chromium from aqueous solutions. The percentage removal of chromium was examined by varying experimental conditions viz., dosage of adsorbent, pH of the solution and contact time. It was found that more than 95% removal was achieved under optimal conditions. The adsorption capacity (k) for chromium calculated from the Freundlich adsorption isotherm was found to be 35.38 and 46.34 mg/g for IRN77 and SKN1 resins, respectively. The adsorption of chromium on these cation exchange resins follows the first-order reversible kinetics. The ion exchange resins investigated in this study showed reversible uptake of chromium and, thus, have good application potential for the removal/recovery of chromium from aqueous solutions.

Kinetics of adsorption of Co(II) removal from water and wastewater by ion exchange resins.

The capacity of ion exchange resins, IRN77 and SKN1, for removal of cobalt from aqueous solution has been investigated under different conditions namely initial solution pH, initial metal-ion concentration, and contact time. The equilibrium data obtained in this study have been found to fit both the Langmuir and Freundlich adsorption isotherms. The adsorption of Co(II) on these resins follows first-order reversible kinetics. The film diffusion of Co(II) in these ion exchange resins was shown to be the main rate limiting step. The studies showed that these cation exchange resins can be used as efficient adsorbent material for the removal of Co(II) from aqueous solutions.

Investigation on removal of hardness ions by capacitive deionization (CDI) for water softening applications.

Capacitive deionization (CDI) for removal of water hardness was investigated for water softening applications. In order to examine the wettability and pore structure of the activated carbon cloth and composites electrodes, surface morphological and electrochemical characteristics were observed. The highly wettable electrode surface exhibited faster adsorption/desorption of ions in a continuous treatment system. In addition, the stack as well as unit cell operations were performed to investigate preferential removal of the hardness ions, showing higher selectivity of divalent ions rather than that of the monovalent ion. Interestingly, competitive substitution was observed in which the adsorbed Na ions were replaced by more strongly adsorptive Ca and Mg ions. The preferential removal of divalent ions was explained in terms of ion selectivity and pore characteristics in electrodes. Finally, optimal pore size and structure of carbon electrodes for efficient removal of divalent ions were extensively discussed.

Lactic acid recovery using two-stage electrodialysis and its modelling

An experimental study was carried out on a two-stage process for lactic acid recovery, which consisted of desalting electrodialysis and water-splitting electrodialysis. Limiting current densities were measured at various lactate concentrations in the feed solution for the determination of the condition for switching from constant-current mode to constant-voltage mode in the desalting electrodialysis. The relationship between the electrical resistance of membrane stack and the lactate concentration was identified. The amount of water transferred due to electroosmosis which caused volume change in the feed and permeate solution was also experimentally determined. Based on the experimental results, mathematical models were developed, in which time changes in the feed and permeate volumes and the electrical resistance were considered. Model predictions of lactate concentration, volume changes, switching time and energy consumption were in good agreement with the experimental data. The prediction of total operating time for desalting electrodialysis showed some errors. However, it was considered to be due to the difficulties involved in determining the termination time in actual operation.

Designing of an electrodialysis desalination plant

The design and operation of an electrodialysis desalination process are based on a set of fixed and variable parameters such as stack construction, feed and product concentration, membrane properties, flow velocities, current density, recovery rates, etc. These parameters are interrelated and may be rather different for different applications. For an efficient operation of an electrodialysis desalination plant, the process has to be optimized in terms of overall costs considering component properties and operating parameters. In this study the design and optimization of an electrodialysis plant to be used for brackish water desalination has been treated. The required equations were derived or, as in the case of the limiting current density, were experimentally determined. As an example, an electrodialysis plant with a sheet-flow stack construction and given feed solution composition was designed and optimized in terms of overall costs and the sensitivities of the different parameters are analyzed.

CLEANING STRATEGIES FOR FLUX RECOVERY OF AN ULTRAFILTRATION MEMBRANE FOULED BY NATURAL ORGANIC MATTER

One of the most common problems encountered in water treatment applications of membranes is fouling. Natural organic matter (NOM) represents a particularly problematic foulant. Membranes may be fouled by relatively hydrophilic and/or hydrophobic NOM components, depending on NOM characteristics, membrane properties, and operating conditions. To maximize flux recovery for an NOM-fouled ultrafiltration membrane (NTR 7410), chemical cleaning and hydraulic rinsing with a relatively high cross-flow velocity were investigated as cleaning strategies. The modification of the membrane surface with either an anionic or a cationic surfactant was also evaluated to minimize membrane fouling and to enhance NOM rejection. Foulants from a hydrophobic NOM source (Orange County ground water (OC-GW)) were cleaned more effectively in terms of permeate flux by acid and caustic cleanings than foulants from a relatively hydrophilic NOM source (Horsetooth surface water (HT-SW)). An anionic surfactant (sodium dodecyl sulfate (SDS)) was not effective as a cleaning agent for foulants from either hydrophobic or hydrophilic NOM sources. High ionic strength cleaning with 0.1 M NaCl was comparatively effective in providing flux recovery for NOM-fouled membranes compared to other chemical cleaning agents. Increased cross-flow velocity and longer cleaning time influenced the efficiency of caustic cleaning, but not high ionic strength cleaning. The membrane was successfully modified only with the cationic surfactant; however, enhanced NOM rejection was accompanied by a significant flux reduction.

Removal of phenol from aqueous solution and resin manufacturing industry wastewater using an agricultural waste: rubber seed coat

Activated carbon prepared from rubber seed coat (RSCC), an agricultural waste by-product, has been used for the adsorption of phenol from aqueous solution. In this work, adsorption of phenol on rubber seed coat activated carbon has been studied by using batch and column studies. The equilibrium adsorption level was determined to be a function of the solution pH, adsorbent dosage and contact time. The equilibrium adsorption capacity of rubber seed coat activated carbon for phenol removal was obtained by using linear Freundlich isotherm. The adsorption of phenol on rubber seed coat activated carbon follows first order reversible kinetics. The suitability of RSCC for treating phenol based resin manufacturing industry wastewater was also tested. A comparative study with a commercial activated carbon (CAC) showed that RSCC is 2.25 times more efficient compared to CAC based on column adsorption study for phenolic wastewater treatment.

Studies on adsorptive removal of Co(II), Cr(III) and Ni(II) by IRN77 cation-exchange resin

The adsorption of cobalt, chromium and nickel from aqueous solutions on IRN77 cation-exchange resin has been studied comparatively. The percentage removal of cobalt, chromium and nickel was examined by varying experimental conditions, viz. dosage of adsorbent, pH of the solution and contact time. It was found that more than 95% removal was achieved under optimal conditions. The adsorption capacity (k) for cobalt, chromium and nickel were calculated from the Freundlich adsorption isotherm. The adsorption of cobalt, chromium and nickel on this cation-exchange resin followed the Lagergren kinetic model. Also the competitive adsorption of multi-metals onto the IRN77 resin was studied. The studies showed that this cation-exchange resin can be used as an efficient adsorbent material for the removal of cobalt, chromium and nickel from water and nuclear power plant coolant water.

A review of current developments in non-aqueous redox flow batteries: characterization of their membranes for design perspective

The non-aqueous redox flow battery (RFB) is one of the emerging large-scale energy storage systems that may overcome the low energy density limited by breakdown of water at a high voltage in aqueous RFBs. Yet development of the non-aqueous RFB is at an early stage, so its components are not thoroughly understood. As a key component of non-aqueous RFBs, the role of the membrane is to suppress cross-contamination between the anolyte and catholyte confined in two separate compartments, and to transport the charge carrier ions selectively for the completion of the circuit during cell operation. In this review, recent studies on non-aqueous redox flow systems are summarized including redox couples, electrolytes, and systems including membranes. A focus is placed on comparison of battery performance in terms of the current and power density through membranes. In addition, we introduce syntheses and characterization of membranes used for non-aqueous RFBs.

Effects of metal ions on diffusion dialysis of inorganic acids

Abstract Diffusion dialysis has been studied to investigate the effects of metal species on its performance for recovery of inorganic acids. It was observed that metal–acid complex formation affected the selectivity and flux of the diffusion dialysis operations due to the existence of negatively-charged complexes. In the limited concentration ranges, nearly 90% of HCl, HNO 3 , and H 2 SO 4 were recovered. Of five metal species investigated, Fe, Ni, Cr, and Cu in the feed solutions were rejected reasonably by the dialysis membrane, while Zn in the HCl solution leaked through the membrane significantly. Moreover, the high Zn content decreased the mobility of the acid in the membrane. Proton release from formation of Fe–F complexes in a HF–HNO 3 acid mixture gave the unusual result of a nitric acid recovery exceeding 100%.