Abstract

This study investigated water reclamation from an impaired-quality water using forward osmosis (FO) membrane functionalized by nano zero valent iron (nZVI) loaded polyelectrolyte multilayer films. Stormwater runoff was selected as the impaired-quality water, which served as a feed solution (FS) and a NaCl salt solution at a concentration representing reverse osmosis (RO) concentrate was used a draw solution (DS). RO concentrate is another impaired-quality water that is discharged to the environmental with little or no treatment. A commercial cellulose triacetate (CTA) FO membrane was modified using poly allylamine hydrochloride (PAH) (a polycation) and poly acrylic acid (PAA) (a polyanion) following a dip coating method. In-situ synthesis of nZVI within the PAA/PAH layers was conducted through sodium borohydride reduction. The efficiency of the nZVI-PAA/PAH functionalized FO membranes in removing selected stormwater derived contaminants was evaluated. The virgin CTA membrane had a rough surface and repeated applications of coatings were required to ensure uniform layers of PAA/PAH. Following 4, 8, 12, and 14 'bilayer' (BL) coatings, it was deduced that 14 BL coatings resulted in the most uniform layers with maximum surface overage. The scanning electron microscopy (SEM) images demonstrated that the membrane coverage and uniformity of coating improved as more BL coatings were applied. While the unmodified membrane initially had a high flux (16 L/m2.h) compared to the modified membranes, there was a sharp decline in flux (approximately 1.5 L/m2.h) within the first 2 to 3 h of operation, likely due to a rapid accumulation of foulants on the membrane surface. The modified membranes, on the other hand, showed markedly less initial flux (2 L/m2.h), but the flux was maintained throughout the experimental period with only a slight decline. The flux decline that may be anticipated owing to the additional layers on the membrane was probably offset by the hydrophilicity rendered by the PAA/PAH functional groups and less foulant accumulation. The nZVI-loaded PAA/PAH coatings did not have any adverse impact on reverse salt flux (RSF). Any reduction in RSF due to the coatings might have been counteracted by the PAA/PAH induced dilution of the DS. While both NO3- and PO43- removals were already very high ( > 97%) when using the unmodified membrane, a slight increase in the removal of NO3- with increased BL numbers (8 and 14 BLs) was observed. The removal of selected heavy metals (Cd, Pb, and Cu) by the unmodified and modified membranes ranged from approximately 87% for Pb to almost complete (~99%) removal for Cd. Mass balance and energy dispersive x-ray spectroscopy (EDX) analyses confirmed that a higher number of coating resulted in a higher retention of heavy metals by the functionalized FO membranes. This could be attributed to the complexation of metal ions with carboxylate and amine groups from the PAA/PAH bilayers. Furthermore, the unmodified CTA FO membrane exhibited very high removal ( > 97%) of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS). EDX mapping showed that the 14 BL-nZVI membrane adsorbed more PFOS/A compared to the virgin and the 8 BL-nZVI membrane.

Graduation Date

2020

Semester

Spring

Advisor

Sadmani, A H M Anwar

Degree

Master of Science in Environmental Engineering (M.S.Env.E.)

College

College of Engineering and Computer Science

Department

Civil, Environmental and Construction Engineering

Degree Program

Environmental Engineering

Format

application/pdf

Identifier

CFE0008416

Language

English

Release Date

November 2020

Length of Campus-only Access

None

Access Status

Masters Thesis (Open Access)

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