Hyeongrak Cho

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...

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 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...