Date of Award

1-1-2013

Document Type

Open Access Dissertation

Department

Civil and Environmental Engineering

First Advisor

Yeomin Yoon

Abstract

This overall theme of this dissertation is to investigate the potential engineered application of low pressure membranes incorporated with single-walled carbon nanotubes (SWNTs) and forward osmosis (FO) membrane systems for the removal of synthetic organic compounds (SOCs) and natural organic matter (NOM) from drinking water sources. The focus is on the use of SWNTs-ultrafiltration (UF) and FO membrane systems to facilitate the removal of these compounds and potential applications of these membrane system designs for reducing the energy demands and membrane fouling in environmental water filtration process and seawater desalination. The SWNTs-UF results indicate that SOCs transport is influenced by NOM, which fouls the membrane through pore blockage and cake/gel formation. A strong linear correlation between the retention and adsorption of SOCs was observed, indicating that retention by the SWNTs-UF membranes is mainly due to the adsorption of SOCs onto the membrane, the SWNTs, and/or NOM. The performance of SWNTs-UF was also evaluated on the basis of a resistance-in-series model, filtration laws, and NOM transportation mechanisms. The addition of SWNTs to the UF process did not significantly exacerbate the permeate flux decline and total membrane resistances. Further, it appeared that the effect of SWNTs on membrane fouling is a function of hydrodynamic and operational conditions. The results suggest that the NOM transportation in SWNTs-UF systems depends, to a significant extent, on the concentration polarization and cake/gel layer formation at the membrane boundary. In the application for artificial seawater in SWNTs-UF, the presence of SWNTs shows 20% increase in membrane flux and a strong linear correlation between retention and adsorption of SOCs was obtained. In FO membrane systems, the cellulose triacetate based FO membrane exhibited the better separation properties than that of polyamide based reverse osmosis (RO) membrane. And, in active layer (AL)-facing-feed solution (FS) configuration in FO mode, the RO membrane exhibited higher removal efficiency at the expense of severe internal concentration polarization (ICP) and flux reduction. Under higher cross-flow velocity operations in FO mode, both reduced external concentration polarization and retarded SOC diffusion from the reverse flux of sodium chloride contributed to the improved SOC removal performance. The FO membrane removal behavior was principally related to size exclusion, while the RO membrane removal behavior was related to interactions between hydrophobicity, size, and electrostatic repulsion. The results significantly confirmed the dominant role of ICP, and the trade-off between flux and removal efficiency depends on the porous supporting layer in AL-facing-FS configurations in the FO process.

Rights

© 2013, Jiyong Heo

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