Date of Award

Spring 2019

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Environmental Engineering - (Ph.D.)

Department

Civil and Environmental Engineering

First Advisor

Zhang, Wen

Second Advisor

Marhaba, Taha F.

Third Advisor

Hsieh, Hsin Neng

Fourth Advisor

Mitra, S.

Fifth Advisor

Yip, Ngai Yin

Abstract

Membrane filtration has been extensively used in water and wastewater treatment, desalination, dairy making, and biomass/water separation. However, membrane fouling, aging and insufficient removal efficiency for dissolved organic matters remain major challenges for wider industrial applications. In order to tackle these challenges, this doctoral dissertation investigates mechanisms of membrane fouling and development of antifouling membrane filtration technologies. Specifically, four major research areas are explored: (i) nanoscale physicochemical characterization of the chemically modified polymeric membranes; (ii) quantitative modelling between membrane properties and membrane fouling and defouling kinetics; (iii) development of quantitative structure-activity relationships for membranes that undergo thermal and chemical aging treatments; and (iv) design of microwave-assisted reactive and antifouling membrane filtration system.

The first research study focuses on the development and validation of atomic force microscope (AFM) and hybrid AFM-IR techniques to acquire surface topography, hydrophobicity and chemical distribution at nanoscale on polymeric membranes. AFM is used to obtain the topography images that show the pore size, porosity and also surface roughness of the polymeric membranes. Moreover, the chemical force mode of AFM is applied to probe nanoscale hydrophobicity on modified membranes. Furthermore, the AFM-IR technique offers accurate chemical identifications and distribution of additives on modified membranes at nanoscale, which is not achievable by conventional FTIR due to its low resolution or low sensitivity. The hybrid AFM techniques are believed to be critical for the nanoscale characterization for material properties in a wide spectrum of applications.

In the second work, predictive models for membrane fouling and defouling kinetics are developed. The models integrate membrane surface properties (i.e., hydrophobicity and surface charge) and filtration performances with protein, saccharides and natural organic matters (NOM) as model foulants. Positive correlations (R2=0.74-0.99) are obtained between the fouling rates and the foulant deposition rates on different membrane-foulant interaction systems. This correlation could be used for further developing predictive models of membrane fouling.

In the third work, the chemical and thermal stability of surface chemically modified polyether sulfone (PES) membranes are investigated. The membranes’ physical (i.e., pore size, roughness), mechanical (i.e., tensile strength) and chemical characteristics (i.e., IR spectrum, and hydrophobicity) are evaluated. The quantitative structure-activity relationships (QSAR) for membrane filtration after aging are developed.

Sustaining high flux and diversified pollutant rejection are two crucial benchmarks for membrane filtration. In the fourth work, a microwave-enhanced membrane filtration process that uses microwave (MW) to energize catalyst-coated ceramic membranes is designed. MW irradiation is selectively absorbed by catalysts and H2O2 to produce ‘‘hotpots” on membrane surface and promote generation of radicals and nanobubbles. The MW-Fenton-like reactions enhance chemical degradation of persistent organic pollutants (i.e., 1,4-dioxane) and significant mitigation of fouling. MW irradiation can effectively penetrate membrane modules and selectively promote surface reactions, which may open new avenues toward reactive and antifouling membrane filtration techniques.

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