Reverse osmosis successfully proves to remove more than 99% of solute in
seawater, providing fresh water supply with satisfied quality. Due to some
operational constraints, however, some trace contaminants removal, such as boron,
cannot be achieved in one pass system. The stringent criterion for boron from
World Health Organization (WHO) and Saudi Arabia local standard (0.5 mg/l) is
hardly fulfilled by single pass sea water reverse osmosis (SWRO) plants. Some
design processes have been proposed to deal with boron removal, but they are not
economically efficient due to high energy and chemical consumption. The objective
of this study was to study boron removal by different reverse osmosis membranes
in two pH conditions, with and without antiscalant addition. Thus, it was expected
to observe the possibility of operating single pass system and necessity to operate
two pass system using low energy membrane. Five membrane samples were
obtained from two different manufacturers. Three types of feed water pH were
used, pH 8, pH 10, and pH 10 with antiscalant addition. Experiment was conducted
in parallel to compare membrane performance from two manufacturers. Filtration
was run with fully recycle mode for three days. Sample of permeate and feed were
taken every 12 hours, and analyzed for their boron and TDS concentration.
Membrane samples were also tested for their surface charge. The results showed that boron rejection increases as the feed pH increases. This was caused by
dissociation of boric acid to negatively charged borate ion and more negatively
charged membrane surface at elevated pH which enhance boron rejection. This
study found that single pass reverse osmosis system, with and without elevating the
pH, may not be possible to be applied because of two reasons. First, permeate
quality in term of boron, does not fulfill WHO and local Saudi Arabia regulations.
Second, severe scaling occurs due to operation in alkaline condition, since Ca and Mg
concentration are still high to cause precipitation. Using low energy membrane at
pH 10 may be considered, since it gives comparable performance to ordinary
brackish water membranes in term of boron and TDS rejections, but consume less
energy.
Date of Award | Jul 2011 |
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Original language | English (US) |
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Awarding Institution | - Physical Sciences and Engineering
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Supervisor | NorEddine Ghaffour (Supervisor) |
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