Prevention of Colloidal Fouling in Crossflow Membrane Filtration: Searching for Optimal Operation Conditions Year 2

Prevention of Colloidal Fouling in Crossflow Membrane Filtration: Searching for Optimal Operation Conditions Year 2

U.S. Geological Survey

03/01/03 - 02/28/05


Crossflow membrane filtration processes involving reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF), and microfiltration (MF) have steadily gained importance in environmental engineering separations over the past decade. Numerous improvements in the technology have spurred widespread adaptation of this process in environmental, chemical, pharmaceutical, and biomedical applications. Microfiltration is used in a wide variety of industrial applications where particles of a size greater than 0.1 µm, have to be retained from a liquid. Applications include the sterilization and clarification of all kinds of beverages and pharmaceuticals, and in particular pre-treatment for subsequent finer membrane filtrations, especially in water and wastewater treatment. Ultrafiltration and nanofiltration, in particular, are important processes for the removal of solutes, macromolecules (such as natural organic matter), pathogenic viruses, and small colloidal materials in water and wastewater treatment. The production of potable water from seawater or brackish water by reverse osmosis has become increasingly important, especially in Hawaii and other Pacific and Asian island areas.

There are, however, several aspects of this evolving membrane technology that had not yet been addressed conclusively and still posed formidable obstacles toward its wide adoption. One important issue was membrane fouling due to concentration polarization and cake formation of particulate materials. Concentration polarization is a phenomenon wherein there is a concentration of particles in a thin layer adjacent to the membrane which has the effect of reducing flow through the membrane. Cake formation is the accumulation of particulate matter on the membrane surface. It also reduces the flow.

Project Description:
The objectives of Dr. Kim's research were (1) developing a fundamental statistical mechanical approach to identify the transition point from a liquid-like to a solid-like structure of colloidal dispersions due to several physico-chemical and operational conditions in membrane filtration, (2) making a simulation-based empirical correlation that can be used by engineers for determining optimum operation conditions in pilot and/or real membrane systems, and (3) deciding the critical permeate flux under which only concentration polarization is a dominant cause of the flux decline before the cake layer forms.

Therefore, this research provided answers to the following important questions: (i) How do the inter-particle interactions and dispersion microstructure govern the nature and extent of concentration polarization, the transition to cake formation, and the resulting permeate flux decline behavior?; (ii) What is the particle concentration at which a colloidal dispersion undergoes a transition from a liquid-like disordered state (pure concentration polarization) to a solid-like state (cake/gel layer) during membrane filtration processes?; and (iii) How can the membrane fouling by the cake formation be prevented and/or reduced by changing physico-chemical and operating conditions of the membrane filtration with a given particle suspension? Based on the results, this research has enhanced our understanding of fouling problem, and thus has helped develop solutions to prevent and treat membrane fouling.

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