Forward osmosis (FO) is a natural process in which a solution with high
concentration of solutes is diluted when being in contact, through a semipermeable
membrane, with a low concentration solution. This osmotic process has been
demonstrated to be efficient to recover wastewater effluents while diluting a saline
draw solution. Nevertheless, the study of the removal of micropollutants by FO is
barely described in the literature. This research focuses on the removal of these
substances spiked in a secondary wastewater effluent, while diluting water from the
Red Sea, generating feed water that can be desalinated with a low pressure reverse
osmosis (LPRO) system. Another goal of this work is to characterize the fouling of
the FO membrane, and its effect on micropollutants rejection, as well as the
membrane cleaning efficiency of different methods. When considering only FO with
a clean membrane, the rejection of the hydrophilic neutral compounds was between
48.6% and 84.7%, for the hydrophobic neutrals the rejection ranged from 40.0% to
87.5%, and for the ionic compounds the rejections were between 92.9% and 96.5%.
With a fouled membrane, the rejections were between 44.6% to 95.2%, 48.7% to
91.5% and 96.9% to 98.6%, respectively. These results suggest that, except for the
hydrophilic neutral compounds, the rejection of the micropollutants is increased by
the fouling layer, possibly due to the higher hydrophilicity of the FO fouled membrane compared to the clean one, the increased adsorption capacity and
reduced mass transport capacity, membrane swelling, and the higher negative
charge of the surface, related to the foulants. However, when coupled with low
pressure reverse osmosis, the rejections for both, the clean and fouled membrane,
increased above 98%. The fouling layer, after characterizing the wastewater effluent
and the concentrated wastewater after the FO process, proved to be composed of
biopolymers, which can be removed with air scouring during short periods of time,
reaching a flux recovery of more than 90%, proving that this cleaning method is
very effective; chemical cleaning was effective against transparent exopolymer
particles (TEP) attached to the support layer of the membrane.
| Date of Award | Jul 2011 |
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| Original language | English (US) |
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| Awarding Institution | - Biological, Environmental Sciences and Engineering
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| Supervisor | Gary Amy (Supervisor) & Peng Wang (Supervisor) |
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