Yonghyun Shin

Application of response surface methodology (RSM) in the optimization of dewetting conditions for flat sheet membrane distillation (MD) membranes

AbstractThis study focuses on the exploration of the optimum dewetting conditions to remove water in pores in membrane distillation (MD) process. Response surface methodology (RSM) was applied to build statistical models for the analysis of flux and liquid entry pressure (LEP) as a function of dewetting temperature and time. A set of MD experiments based on central composite design of experiments method are carried out. Using these experimental results, two response surface (RS) models were developed to predict flux and LEP. The RS models were further used to optimize the dewetting conditions for desired membrane properties. Moreover, the optimum dewetting condition derived from RSM was experimentally verified.

Economic Evaluation of a Hybrid Desalination System Combining Forward and Reverse Osmosis

This study seeks to evaluate the performance and economic feasibility of the forward osmosis (FO)–reverse osmosis (RO) hybrid process; to propose a guideline by which this hybrid process might be more price-competitive in the field. A solution-diffusion model modified with film theory was applied to analyze the effects of concentration polarization, water, and salt transport coefficient on flux, recovery, seawater concentration, and treated wastewater of the FO process of an FO-RO hybrid system. A simple cost model was applied to analyze the effects of flux; recovery of the FO process; energy; and membrane cost on the FO-RO hybrid process. The simulation results showed that the water transport coefficient and internal concentration polarization resistance are very important factors that affect performance in the FO process; however; the effect of the salt transport coefficient does not seem to be large. It was also found that the flux and recovery of the FO process, the FO membrane, and the electricity cost are very important factors that influence the water cost of an FO-RO hybrid system. This hybrid system can be price-competitive with RO systems when its recovery rate is very high, the flux and the membrane cost of the FO are similar to those of the RO, and the electricity cost is expensive. The most important thing in commercializing the FO process is enhancing performance (e.g.; flux and the recovery of FO membranes).

Comparison of fouling propensity and physical cleaning effect in forward osmosis, reverse osmosis, and membrane distillation

AbstractMembrane-based desalination technologies including reverse osmosis (RO), forward osmosis (FO), and membrane distillation (MD) hold promise as efficient methods to produce fresh water from saline water sources. However, the fouling properties of these membranes are quite different due to the difference in the driving forces among them. Accordingly, the objective of this study is to compare fouling behavior and physical cleaning efficiency for these three membranes under similar operating conditions. Colloidal silica and alginate were used as model foulants and NaCl was added to feed solutions. Laboratory-scale experiments were carried out to compare fouling rates and recovery of flux by physical cleaning. Results showed that fouling propensity was the highest in FO membrane and the lowest in MD membrane, which may be attributed to the effect of cake-enhanced concentration polarization. On the other hand, physical cleaning was more efficient to recover flux in FO and RO than in MD, suggesting that t...

Optimization of dewetting conditions for hollow fiber membranes in vacuum membrane distillation

AbstractMembrane distillation (MD) is a thermal separation process that uses a hydrophobic membrane as a barrier between a liquid phase and a gas phase. Accordingly, MD can only be applied under the conditions where the membrane is not wetted by the feed solution. In this study, a technique to remove water inside the pores of the wetted membranes, or “dewetting,” was developed to mitigate the problems of membrane wetting in MD process. High-temperature air was applied to the wetted membranes using a specially designed device. The dewetting efficiency was analyzed by measuring the liquid entry pressure, water flux, and salt rejection. The response surface methodology (RSM) was applied to explore the optimum conditions for dewetting of MD membranes. Results indicated that dewetting should be done under proper conditions. If the temperature and dewetting time were insufficient, the dewetting was incomplete. On the other hand, the membrane was partially deformed if the temperature was too high and the dewetti...

Hydrophobic surface modification of membrane distillation (MD) membranes using water-repelling polymer based on urethane rubber

AbstractMembrane distillation (MD) is a unit process that uses hydrophobic membranes to separate vapor from saline water. The performance of the MD process is largely affected by the properties of the membranes, which should be porous, hydrophobic, and stable under high temperature conditions. Accordingly, it is essential to develop highly efficient membranes for practical implementation of MD technology. In this study, we applied a water repellent chemical (WRC) made of urethane rubber onto hydrophilic membranes to develop a novel approach for MD membrane preparation. A spin coating method was adopted to introduce hydrophobic coating layers on polyamide membranes. Experiments were carried out in the direct contact membrane distillation mode. Contact angle and liquid entry pressure (LEP) were measured before and after the surface coating. In addition, scanning electronic microscope, FT-IR, and atomic force microscope analysis were conducted to confirm a coating layer of the membrane. The optimum condition...

Economic evaluation of the reverse osmosis and pressure retarded osmosis hybrid desalination process

AbstractThis paper presents a performance evaluation and economic analysis of a reverse osmosis (RO) and pressure retarded osmosis (PRO) hybrid process to propose guidelines for its economic competitiveness use in the field. A model to predict the performance of a hybrid process using RO and PRO was developed based on a solution-diffusion model modified with film theory. The effects of external and internal concentration polarization (ICP) on PRO efficiency were considered in the model. Moreover, a simple cost model was applied to analyze the effects of seawater TDS and feedwater for the PRO process, water and salt permeability of PRO membrane, and membrane and energy cost on the RO-PRO hybrid process. The results show that the water transport coefficient, ICP, and seawater and feedwater TDS are important factors affecting the performance of the PRO process. On the other hand, the effect of the salt transport coefficient is not substantial. The RO-PRO hybrid process can be economically competitive with th...

Comparison of Performances of Forward Osmosis and Membrane Distillation Processes for Shale Gas Plant Water Treatment

* Environmental & Plant Engineering Institute Korea Institute of Civil Engineering and Building Technology** Dept. of Civil and Environmental Engineering, Kookmin Univ. (Received January 23, 2014 ; Revised January 6, 2015 ; Accepted January 12, 2015)Key Words: Shale Gas(셰일가스), Water Treatment(수처리), Membrane Distillation(막증발법), Forward Osmosis(정삼투법), Plant(플랜트)초록: 전 세계적으로 셰일가스와 같은 비전통 석유자원이 널리 개발되고 있다. 이에 따라 셰일가스 채굴과정에서 발생하는 폐수의 적절한 처리가 중요해지고 있다. 그러나, 폐수 내의 오일 및 유기 물질, 유해성 화학물질, 무기 이온과 같은 물질이 고농도로 함유하고 있기 때문에 기존 처리 방법으로 많은 어려움을 격고 있다. 본 연구에서는 셰일가스 폐수에 대한 새로운 처리방법으로 정삼투 공정 및 막증발법에서의 가능성을 연구하였다. 실험실 규모의 정삼투 및 막증발법 장치를 제작하여 실험을 실시하였다. 그 결과, 합성 폐수를 처리하는데, 정삼투 공정에서 적용 가능하다고 판단되었다. 유도용액으로 5M의 염화나트륨수용액을 사용하였고, 낮은 범위의 폐수(66,000mg/L TDS)에서 약 6 L/m2-hr의 플럭스를 나타냈다. 그럼에도 불구하고, 높은 범위의 폐수(261,000mg/L TDS)에서 막증발법으로 처리하는 것이 더 효과적이었다.Abstract: As non-conventional oil resources such as shale gas have been widely developed, proper treatment of flowback and produced water is becoming important. However, application of conventional water treatment techniques is limited due to high concentration of pollutants such as oil and grease, organics, harmful chemicals, and inorganic ions. In this study, we examined the feasibility of using forward osmosis (FO) and air gap membrane distillation (AGMD) as novel treatment options for shale gas wastewater. Laboratory-scale FO and MD devices were fabricated and used for the experiments. Results showed that FO could be used to treat the synthetic wastewater. Using 5 M NaCl as the draw solution, the flux was approximately 6 L/m