Jaewuk Koo

Pressure assisted forward osmosis for shale gas wastewater treatment

AbstractThis study investigated the feasibility of using pressure assisted forward osmosis (PAFO) for shale gas wastewater treatment. PAFO combines osmotic gradient across a membrane with external pressure together, which was expected to obtain higher flux than forward osmosis (FO). Experiments were performed in a laboratory-scale PAFO system, which allows the application of external pressure up to 10 bar on the feed solution side. Deionized water and three kind of synthetic shale gas wastewater, including low range, medium range, and high range wastewaters, were used as feed solutions and NaCl was used as a draw solution. The water flux was improved up to 10–15% by applying external pressure to FO when low range and medium range wastewaters were treated. However, the effect of the external pressure was significantly reduced when the high-range wastewater was treated. After FO treatment, air gap membrane distillation was successfully applied to re-concentrate the draw solutes.

Experimental comparison of direct contact membrane distillation (DCMD) with vacuum membrane distillation (VMD)

Abstract Membrane distillation (MD) is a thermally driven membrane process using porous hydrophobic membranes. MD has been investigated as an alternative desalination technology due to its advantages over multi-stage flash (MSF) and reverse osmosis (RO). Nevertheless, it is difficult to design and optimize the MD systems under various conditions, because both thermal and hydrodynamic effects play an important role. Therefore, this study focused on performance analysis of MD systems in different configurations. Direct contact MD (DCMD) and vacuum MD (VMD) were experimentally compared using laboratory-scale systems. A simple model was also applied to analyze the difference between two configurations theoretically. Experimental results indicated that permeate flux in DCMD and VMD were sensitive to the operating conditions. Using same membranes, two MD systems showed different flux behaviors. The influences of operating parameters for DCMD and VMD on overall efficiency were also investigated. The model result...

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...

Evaluation of economic feasibility of reverse osmosis and membrane distillation hybrid system for desalination

AbstractThis study seeks to evaluate the economic feasibility of membrane distillation (MD) and reverse osmosis (RO)-MD hybrid system for seawater desalination. A theoretical cost model was applied to analyze the effects of flux, recovery, membrane properties, and energy price on RO, MD, and RO-MD hybrid system. The simulation results showed that MD stand-alone system and RO-MD hybrid system can be cost-competitive compared with RO systems when the recovery and flux of MD system are higher than those of RO system and the steam cost is relatively cheap. It is also revealed that the water costs of RO-MD hybrid system and RO system are same under similar operating conditions, but the water cost of MD stand-alone system is higher. The effect of thermal energy cost on water cost for MD and RO-MD systems was also analyzed. Based on these results, guidelines for an analysis of economic feasibility of MD and RO-MD were suggested.

Theoretical analysis of different membrane distillation modules

AbstractMembrane distillation (MD) is a thermally driven separation process that uses hydrophobic membranes. Although MD has been considered as an alternative desalination technology, relatively little information is available on the design and optimization of MD modules. Accordingly, this study focused on the comparison of various MD modules and the optimization of their operation conditions. Direct contact MD, air gap MD, and vacuum MD were experimentally compared using laboratory-scale systems. Then, the results were theoretically analyzed using a simple transport model. Different mass transfer mechanisms inside the membrane were considered in the model, including molecular diffusion, the Knudsen diffusion, and viscous flow. Experimental results showed that the temperature dependences of MD modules were different. This suggests that the optimum feed temperature should be different for each MD module. The dominant mass transfer mechanisms were also identified using the theoretical model for better under...

Organic fouling and osmotic backwashing in PRO

AbstractThe pressure-retarded osmosis process is the next generation seawater desalination technology and is considered as eco-friendly and economic renewable energy. As such, there are active studies of means of efficient cleaning to restore the membrane performance degraded due to the reversible membrane fouling that inevitably occurs after prolonged operation. This study evaluated the fouling rate by organic alginate, humic, and BSA (bovine serum albumin). Also, we focused on the comparison of cleaning methods which are physical flushing and osmotic backwashing (OB). For the comparison of the cleaning efficiency, we used alginate compound as a model substances representative of natural organic matter. Physical cleaning (PC) is the flushing method by flowing the distilled water on the membrane active and support layer in high velocity to remove the accumulated foulants on the membrane surface. OB is the method of backflow generated by osmosis to remove the accumulated foulants on/in the membrane active ...

Integration of forward osmosis with membrane distillation: effect of operating conditions

Abstract Hybrid desalination systems combining both thermal and membrane desalination processes are currently considered a viable alternative to conventional desalination plants. Recently, an incorporation of forward osmosis (FO) with membrane distillation (MD) has been considered as a new hybrid desalination technology. Nevertheless, few works have been done to design and optimize these types of new hybrid systems. The focus of this study was to investigate FO–MD hybrid process in which MD is being used to recover draw solutes in product water from FO. Laboratory-scale systems for FO and MD were developed to examine the effect of key operating conditions (draw solute concentration, operation time, temperature, etc.) on flux and solute transport. The results indicated that the efficiency of FO–MD hybrid is affected by the selectivity of draw solute transport through the MD membrane. As decreasing the temperature difference between the feed and distillate in MD, the rate of separation decreases but the sel...

Optimization of hybrid system consisting of forward osmosis and reverse osmosis: a Monte Carlo simulation approach

Abstract Forward osmosis (FO) is a membrane process that has been studied as novel technology for treatment of a wide variety of aqueous solutions. FO uses a semi-permeable membrane to extract cleaning water from impaired water by an osmotic pressure gradient but it also needs to have a posttreatment so-called “draw solute recovery.” The focus of the current study was to investigate a FO–reverse osmosis (RO) hybrid process in which RO is being used to recover draw solutes in product water from FO. A Monte Carlo method was applied to optimize the system. The key parameters affecting the energy efficiency of the hybrid system were also identified. The results indicated that the FO–RO hybrid system has advantages over RO-only system under high fouling conditions. It was found to be essential to minimize the internal concentration polarization to ensure high-energy efficiency and smaller requirements of membrane surface area.

Theoretical and experimental investigation of boron rejection by forward osmosis membrane

AbstractThis study focused on the investigation of the boron rejection from model solutions using a forward osmosis (FO) membrane. A laboratory-scale plate-and-frame membrane module and stirred cell device were used for the experiments. The boron rejection were examined in both reverse osmosis and FO operating modes. A theoretical model based on the film theory was applied for the analysis of boron rejection. Experimental results indicated that the boron rejection by FO membranes was improved by raising pH, suggesting that the removal of boron is done either by charge repulsion or by size exclusion. FO treatment of feedwater containing a high proportion of boric acid led to relatively high concentration of boron in the permeate water. This implies that FO membrane may require another process to attain sufficient rejection to boron. The model calculation was also compared with the experimental data for better understanding of boron rejection in FO membrane systems.

Comparison of hollow fiber membranes in direct contact and air gap membrane distillation (MD)

AbstractHollow fiber microporous membranes was used for seawater desalination in direct contact membrane distillation (DCMD) and air gap membrane distillation (AGMD) configurations. The efficiencies of hollow fiber membranes with different membrane materials and pore size were compared in a laboratory-scale DCMD system. The water flux and salt rejection were shown to be different depending on the membrane properties. The apparent permeabilities for water vapor and NaCl ion were estimated to determine the optimum membrane distillation (MD) membranes. A novel AGMD membrane module utilizing hollow fiber membranes was designed, and its prototype was fabricated using a 3D printer. Using this AGMD module, the performance of the hollow fiber membrane was examined and compared with the results from DCMD experiments. The water flux in AGMD configuration was less than 40% of that in DCMD configuration due to high mass transfer resistance and insufficient cooling plate area. However, it holds promise for practical a...