• Journal of Korean Society of Water and Wastewater
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• v.23 no.2
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• pp.207-214
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• 2009

This study examines the optimum filtration conditions in pretreatment of seawater desalination by reverse osmosis. For this purpose, Masan bay seawater is treated through a gravity filter column while $FeCl_3$ is added as coagulant. The conditions of coagulantd osage, media depth, filtration rate, and backwash time are evaluated. The study results show that the filtrate quality improved with increasing coagulant dosage, but head loss rapidly increased. After 4mg/L, the unit filter run volume reduced to less than $200m^3/m^2$. Considering the head loss development, 4mg/L is determined as the optimum dosage. The better filtrate qualities are obtained with depth of 100cm than that of 80cm. The two stage filtration, which outperformed the single stage filtration, is suggested for treatment of Masan bay. The filtration rate of 5m/h is decided as the optimum condition considering the head loss development. At 10m/h, the filtrate quality deteriorated even though the extent was minimal, and head loss increased rapidly. The backwash time of 10 min is decided appropriate.

• Membrane Journal
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• v.28 no.1
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• pp.75-82
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• 2018

Forward osmosis (FO) desalination system has been highlighted to improve the energy efficiency and drive down the carbon footprint of current reverse osmosis (RO) desalination technology. To improve the trade-off between water flux and salt rejection of thin film composite (TFC) desalination membrane, thin film nanocomposite membranes (TFN), in which nanomaterials as a filler are embeded within a polymeric matrix, are being explored to tailor the separation performance and add new functionality to membranes for water purification applications. The objective of this article is to develop a graphene nanocomposite membrane with high performance of water selective permeability (high water flux, high salt rejection, and low reverse solute diffusion) as a next-generation FO desalination membrane. For advances in fabrication of graphene oxide (GO) membranes, layer-by-layer (LBL) technique was used to control the desirable structure, alignment, and chemical functionality that can lead to ultrahigh-permeability membranes due to highly selective transport of water molecules. In this study, the GO nanocomposite membrane fabricated by LBL dip coating method showed high water flux ($J_w/{\Delta}{\pi}=2.51LMH/bar$), water selectivity ($J_w/J_s=8.3L/g$), and salt rejection (99.5%) as well as high stability in aqueous solution and under FO operation condition.

• Membrane Journal
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• v.31 no.1
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• pp.16-34
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• 2021

Water supplies are decreasing in comparison to increasing clean water demands. Using nanofiltration is one of the most effective and economical methods to meet the need for clean water. Common methods for desalination are reverse osmosis and nanofiltration. However, pristine membranes lack the essential features which are, stability, economic efficiency, antibacterial and antifouling performances. To enhance the properties of the pristine membranes, graphene oxide (GO) is a promising and widely researched material for thin film composites (TFC) membrane due to their characteristics that help improve the hydrophilicity and anti-fouling properties. Modification of the membrane can be done on different layers. The thin film composite membranes are composed of three different layers, the top filtering active thin polyamide (PA) layer, supporting porous layer, and supporting fabric. Forward osmosis (FO) process is yet another energy efficient desalination process, but its efficiency is affected due to biofouling. Incorporation of GO enhance antibacterial properties leading to reduction of biofilm formation on the membrane surface. Pressure retarded osmosis (PRO) is an excellent process to generate clean energy from sea water and the biofouling of membrane is reduced by introduction of GO into the active layer of the TFC membrane. Different modifications on the membranes are being researched, each modification with its own advantages and disadvantages. In this review, modifications of nanofiltration membranes and their composites, characterization, and performances are discussed.

• Journal of Korean Society of Environmental Engineers
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• v.33 no.9
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• pp.677-685
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• 2011

The reverse osmosis membrane processes have several operational problems. Fouling by inorganic scale occurs on membrane surface due to increases in concentrations over solubility by retaining ions on feed side of the membrane. Inorganic scales could be controlled by antiscalants or acid addition. In this study, three antiscalants having different characteristics were selected and evaluated on efficiency of $CaCO_3$ scale control. The $CaCO_3$ scale was inhibited by the antiscalants : 0.4 mg/L for SHMP, 0.6 mg/L for Spectra Guard, and 3 mg/L for Flocon 150 N. Increasing concentration factors of simulated sea water resulted in increases in antiscalant doses for the scale control. The increases in doses were positively proportional to the concentrate factors used in this study. Spectra Guard, one of the polyacrylate type antiscalants, was the most effective to control $CaCO_3$ scale. The antiscalants with the different scale inhibition time and doses implied the different control mechanisms.

• Journal of Korea Water Resources Association
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• v.54 no.spc1
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• pp.1023-1035
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• 2021

The electricity cost of a desalination facility was also predicted and reviewed, which allowed the proposed model to be incorporated into the future design of such facilities. Input data from 2003 to 2014 of the Korea Hydrographic and Oceanographic Agency (KHOA) were used, and the structure of the model was determined using the trial and error method to analyze as well as hyperparameters such as salinity and seawater temperature. The future seawater quality was estimated by optimizing the prediction model based on machine learning. Results indicated that the seawater temperature would be similar to the existing pattern, and salinity showed a gradual decrease in the maximum value from the past measurement data. Therefore, it was reviewed that the electricity cost for seawater desalination decreased by approximately 0.80% and a process configuration was determined to be necessary. This study aimed at establishing a machine-learning-based prediction model to predict future water quality changes, reviewed the impact on the scale of seawater desalination facilities, and suggested alternatives.

• Journal of Korean Society of Water and Wastewater
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• v.23 no.2
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• pp.215-222
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• 2009

This study compares the performance of the filters with various media in pretreatment of seawater desalination by reverse osmosis. For this purpose, Masan bay seawater is used as raw water. The filter performance is evaluated by the filtrate quality and the head loss development. Five media is selected in this study: anthracite, $Filtralite^{(R)}$, sand, Pumice, $AFM^{(R)}$. These media are used in combination for dual media filter and alone for mono media filter. The comparison results show that NC0.8-1.6 is the best $Filtralite^{(R)}$. The dual media filter of NC0.8-1.6 and sand outperformed other filters in particle removal. The dual media filter of anthracite and sand showed good performance in organic removal. The mono media filter of Pumice produced the similar filtrate quality as the mono media filter of sand although the effective size of Pumice is considerably greater than that of sand. Due to big size, head loss development is maintained slow in the filtration of Pumice.

• Membrane Journal
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• v.32 no.4
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• pp.235-252
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• 2022

Forward osmotic pressure-free reverse osmosis (Δ𝜋=0 RO) was invented in 2013. The first patent (US 9,950,297 B2) was registered on April 18, 2018. The "Osmotic Pressure of Concentrated Solutions" in JACS (1908) by G.N. Lewis of MIT was used for the estimation. The Chang's RO system differs from conventional RO (C-RO) in that two-chamber system of osmotic pressure equalizer and a low-pressure RO system while C-RO is based on a single chamber. Chang claimed that all aqueous solutions, including salt water, regardless of its osmotic pressure can be separated into water and salt. The second patent (US 10.953.367B2, March 23, 2021) showed that a low-pressure reverse osmosis is possible for 3.0% input at Δ𝜋 of 10 to 12 bar. Singularity ZERO reverse osmosis from his third patent (Korea patent 10-22322755, US-PCT/KR202003595) for a 3.0% NaCl input, 50% more water recovery, use of 1/3 RO membrane area, and 1/5th of theoretical energy. These numbers come from Chang's laboratory experiments and theoretical analysis. Relative residence time (RRT) of feed and OE chambers makes Δ𝜋 to zero or negative by recycling enriched feed flow. The construction cost by S-ZERO was estimated to be around 50~60% of the current RO system.

• Membrane Journal
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• v.27 no.4
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• pp.291-312
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• 2017

Seawater desalination is currently considered to be one of the primary technologies to resolve the global water scarcity problem. A basic understanding of membrane filtration phenomena is significant not only for further technological development but also for integrated design, optimal control, and long-term maintenance. In this vein, the present work reviews the major transport and filtration models, specifically related to reverse osmosis phenomena, provides theoretical insights based on statistical mechanics, and discusses model-based physical meanings as related to their practical implications.

• Journal of the Korean Society for Marine Environment & Energy
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• v.17 no.1
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• pp.13-19
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• 2014

The feed temperature has an effect on the performance during desalination of seawater by membrane separation. When the permeate flux intends to increase using the waste heat, it is necessary to analyze the effect of feed temperature precisely on the membrane performance. The experiments were carried out to investigate the performance of membranes by varying the seawater temperature from $10^{\circ}C$ to $60^{\circ}C$. The increase of permeate flux with increase of feed temperature was interpreted as the change of water viscosity and the membrane itself. While the increase of permeate flux could be predicted by the viscosity change in case of nanoflitration membrane, there exists 30% difference between the experiment data and the prediction by the viscosity change in case of reverse osmosis (RO) membrane, which seems to be due to 8% decrease of the pore size in 60caused by the contraction of membrane with the increase of temperature. Therefore, the desalination of seawater should be carried out within the range that the elevation of temperature does not cause the alteration of membrane itself even for the purpose of increasing the permeate flux.