A Systematic Investigation on Fouling of NF and RO Membranes by Complex Suspensions Containing Colloids and Dissolved Organic Macromolecules

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ABSTRACTA Systematic Investigation on Fouling of NF and RO Membranes by Complex Suspensions Containing Colloids and Dissolved Organic MacromoleculesThe world-wide water shortage has made drinking water production from non-traditional sourcesusing nanofiltration (NF) and reverse osmosis (RO) an attractive option of potable water supplies.However, current applications of NF and RO for this purpose are economically inefficient, largely attributed to the fouling of membrane materials. Improvement requires elucidation of fouling mechanisms and predictive models for membrane performance. Although considerable research has been done on membrane fouling, almost all mechanistic studies have focused on a single foulant type. Results from these studies are not applicable to water and wastewater applications because fouling in these systems is always caused by both colloidal materials and dissolved organic macromolecules, the interactions between which can significantly alter the behavior of each other. Therefore, a systematic investigation on the behavior of complex suspensions containing colloids and dissolved organic macromolecules in NF and RO systems is imperative to further development of these technologies for water and wastewater applications.The overall project objective is to determine and quantitatively describe the effects of colloid-macromolecule interactions on fouling of NF and RO membranes by complex suspensions containing colloids and dissolved organic macromolecules. The research plan is based on three hypotheses: 1) The interactions between colloids and macromolecules hinder the back transport of each other in the concentration polarization layer; 2) The presence of dissolved organic macromolecules changes the surface properties of the colloids, leading to changes in colloidal interactions and consequently fouling layer properties; 3) The particle transport and fouling layer formation are governed by two coupled physical chemical processes: concentration polarization and particle adhesion. This project will take systematic theoretical and experimental approaches to quantify the effects of important foulant-foulant and foulant-membrane interactions on three key aspects of membrane fouling: 1) foulant back transport; 2) foulant deposition on the membrane surface; and 3) morphology and hydraulic resistance of the fouling layer. These interactions will be measured at nanoscale with atomic force microscopy under various solution conditions. New theories will be developed to determine the back diffusion coefficient and deposition rate of interacting foulants based on the measured interaction potentials, and to quantitatively incorporate these interactions into a foulant transport model and a membrane flux model.The proposed research aims at improving current technologies for sustainable water supply, which has profound broader impacts on global water resource issues. It has a strong educational component. Two graduate students and a number of undergraduate students will obtain research training through the project. Student presentations will be made at national scientific meetings. The membrane filtration experimental system will be incorporated into the laboratory sessions of a graduate level course. To reach a larger population, the research will be introduced to high school students, freshman undergraduate students, and the local community through the Summer Science Academy Program, the freshman orientation class, and a public seminar series on Nanotechnology and Sustainability.