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My Research
Curriculum Vitae
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Fulin
Wang, Ph.D. student in Environmental Engineering
Advisor:
Dr. Volodymyr V. Tarabara I am currently looking for a R&D or application specialist position for membrane filtration processes, or a consulting position for water/wastewater treatment. My
Research
According to a
report in USA TODAY
[1],
severe fresh water shortages Pressure-driven membrane filtration processes, including microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO), are being increasingly used in water and wastewater treatment utilities. Low pressure membranes, MF and UF, are primarily used for removing turbidity, pathogens, and particles from fresh waters. They are stand-alone processes or serve as pretreatment for high pressure salt-rejecting membranes, NF and RO. NF or RO are usually used for softening, desalination, and removal of natural organic matter (NOM) and precursors of DBPs. The major obstacles of
a wider application of membrane filtration technology are membrane fouling
and disposal of concentrate. Membrane fouling occurs when the rejected
contaminants accumulate on the membrane surface and form a layer that
reduces permeate flux. Membrane fouling shortens membrane life, decreases
both product quantity and quality, and increases capital and operational
costs. Understanding membrane fouling is crucial to developing
low-fouling membranes, controlling membrane fouling, and ultimately
reducing operating costs. Depending on the properties of the contaminants being rejected by membrane, membrane fouling can be roughly categorized into four types: (1) colloidal fouling
(i.e. particulate fouling) from colloidal and particulate matter Key Words: water shortage, membrane technology, desalination, membrane fouling 2. Effect of concentration polarization and colloidal fouling on RO membrane performance (top) When a solute is rejected by a membrane, the concentration of the solute at the membrane surface will be higher than solute concentration in the bulk of the feed solution. This leads to the formation of a gradient of solute concentration toward the membrane surface. This phenomenon is known as concentration polarization.
When colloidal fouling is present, the fouling layer formed on the membrane surface increases the tortuosity of the solute pathway and hinders the back-diffusion of solutes in the layer, which increases the solute concentration at membrane surface. The hindrance effect is strongly dependent on the structure of the layer. We presented a novel approach to study the interplay between colloidal fouling and salt concentration polarization. The concentration of rejected salt at the membrane surface when colloidal particles were deposited on the membrane was determined experimentally based on measured salt permeability constant. Then the structure of the fouling layer was estimated in terms of effective porosity. This approach allowed for a clear identification of individual contributions of concentration polarization and colloidal fouling to the permeate flux decline. It was found that, at higher solution ionic strength, the effective porosity of the deposit layer was smaller and the effect of colloidal fouling on salt concentration polarization was more evident, as shown in the below figure.
Key Words: reverse osmosis, desalination, membrane fouling, concentration polarization 3. Effect of gypsum scaling and colloidal fouling on RO membrane performance (top) Scaling from sparingly
soluble salts, such as carbonate and sulfate, is a serious type fouling
for RO membrane. Scaling occurs when the solubility of the salts is
exceeded at a high recovery. Scales formed on membrane surface reduce
permeate flux, shorten membrane life and are difficult to be removed.
Carbonate scaling can be controlled by decreasing the pH of the feed
water. Calcium sulfate dihydrate (gypsum), however, is insensitive to pH,
and can not be controlled by adjusting pH. In practice, gypsum scaling usually occurs along with colloidal fouling in RO systems treating brackish surface water or seawater. Surprisingly, so far there has been no study available for the effect of the combined colloidal fouling and gypsum scaling on the performance of RO membrane. This study aimed at examining the interplay between the colloidal fouling and gypsum scaling in RO membrane systems. A significant synergistic effect was observed during the combined gypsum scaling and colloidal fouling. A significant synergistic effect was observed during the combined colloidal fouling and gypsum scaling. When gypsum scaling was dominated by surface crystallization, gypsum scaling enhanced colloidal deposition and the combined fouling resulted in a much faster permeate flux decline, which was larger than the sum of the flux decline from colloidal deposition and that from gypsum scaling alone.
Key Words: reverse osmosis, desalination, membrane fouling, gypsum scaling, colloidal fouling 4. Preparation of nano-composite polymer membrane (top) Development of
nanocomposite membranes filled with particles and/or fibers is an
increasingly hot topic. The incorporation of nanosized matter into the
membrane’s polymeric matrix is to improve the membrane’s mechanical
properties, enhance permselectivity, and increase biocidal activity. This
study aims at developing a theoretical model to predict the permeability
of the polymer membrane filled with silica particles or carbon nanofibers. Polysulfone polymer was dissolved in a mixture of dimethylformamide (DMF) and poly(ethylene glycol) (PEG). Polysulfone (PS) membrane was then cast using an automatic film application (right) in a relative humidity (RH) chamber (below). The membrane was prepared via vapor-induced phase separation (VIPS), during which the dope solution is exposed to a humid air to induce the removal of the solvent and formation of polymer membrane. By controlling the relative humidity and temperature the VIPS process can be used to obtain membranes with controlled morphologies. VIPS is a slow process which usually lasts up to several hours.
One PS membrane filled with carbon fibers in this study was shown below.
Another method, called phase inversion, leads a quick formation of polymer membrane by immersing the cast film into a non-solvent with respect to polysulfone (such as water). A carbon-filled PS membrane (courtesy of Julian Taurozzi) was shown below for comparison with that obtained using VIPS.
This project is in progress...... Last Updated @ April 2008 |
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affecting at least 400 million people today
will affect 4 billion people by 2050. 
