June Seok Choi

Development of Nano-Carbon Bucky-Paper Membranes for Membrane Distillation

Membrane distillation (MD) is a special evaporation process to produce fresh water from seawater or contaminated water using membranes. MD has advantages over other evaporation technologies such as multi-stage flash vaporization (MSF) and multi-effect distillation (MED) due to its relatively low energy requirements, allowing the use of solar energy as its heat source. Nevertheless, lack of membrane materials for MD process hinders its practical implementation for desalination and water treatment. In this study, membranes made of carbon nanotube (CNT) are presented for MD. Flat sheet hydrophobic membranes made of polyvinylidene fluoride (PVDF) were selected as supports for bucky-paper membranes, allowing formation of CNT bucky-paper without chemical reactions. Laboratory-scale systems were used to evaluate their potential and performance in direct contact MD. Water permeability and salt rejection were analyzed for each case. D.I water and synthetic feed water were used for the lab-scale tests. It was demonstrated that the physical immobilization of CNT on a hydrophobic membrane changed led to an increase in vapor permeability while improving salt rejection.

Effect of Membrane Material Properties on Efficiency of Membrane Distillation

Membrane distillation (MD) integrates membrane technology with evaporation process to produce fresh water from seawater or contaminated water. In this study, we investigated the effect of membrane materials on the efficiency of membrane distillation process. Flat sheet hydrophobic membranes (PVDF, PTFE) with different characterizes were chosen as well as hollow fiber membranes (PE). Laboratory-scale systems were developed for initial screening of various membranes. The performance of the membrane was analyzed in terms of water permeability and salt rejection. Synthetic seawater (TDS = 35,000 mg/L) was used for the lab-scale tests. A simple model to analyze the transport of water through MD membranes was developed to interpret experimental results. In addition, long-term performances of the membranes were compared to examine the stability of membrane materials and fouling tendency using real seawater. Based on the lab-scale experiments, techniques to improve the performance of the membranes were examined by applying physical and chemical modification.

Development of Dynamically-Formed Membranes Using Colloidal Silica and Kaolin

Low pressure membranes such as microfiltration (MF) and ultrafiltration (UF) have been widely used for water and wastewater treatment. However, most MF and UF membranes are made of polymeric materials, leading to limited resistance to external streeses. Ceramic membranes are also used but they are more expensive than the polymeric membranes. In this study, novel inorganic membranes were developed for water treatment applications. Colloidal silica and kaolin were used to form dynamic membranes. Stainless steel filter was used as supports for the dynamic membranes. Laboratory-scale systems were used to evaluate their potential and performance. Water permeability and turbidity removal were monitored to confirm their initial efficiency and long-term stability.