Seawater desalination is a rapidly growing coastal industry that is
increasingly threatened by algal blooms. Depending on the severity
of algal blooms, desalination systems may be forced to shut down
because of clogging and/or poor feed water quality. To maintain
stable operation and provide good feed water quality to seawater
reverse osmosis (SWRO) systems, ultrafiltration (UF) pre-treatment
is proposed. This research focused on assessing the ability of UF
and other pre-treatment technologies to reduce biofouling in SWRO
systems. An improved method to measure bacterial regrowth potential
(BRP) was developed and applied at laboratory, pilot and full scale
to assess the ability of conventional UF (150 kDa) and tight UF (10
kDa) alone and in combination with a phosphate adsorbent to reduce
regrowth potential and delay the onset of biofouling in SWRO. The
improved bacterial regrowth potential method employs a natural
consortium of marine bacteria as inoculum and flow cytometry. The
limit of detection of the BRP method was lowered to 43,000 +/-
12,000 cells/mL, which is equivalent to 9.3 +/- 2.6 g-Cglucose/L.
The reduction in bacterial regrowth potential after tight UF (10
kDa) was 3 to 4 times higher than with conventional UF (150 kDa).
It was further reduced after the application of a phosphate
adsorbent, independent of pore size of the UF membrane. Pilot
studies demonstrated that the application of tight UF (10 kDa)
coupled with a phosphate adsorbent consistently lowered the
bacterial regrowth potential and no feed channel pressure drop
increase was observed in membrane fouling simulators (MFS) over a
period of 21 days. The study also showed that non-backwashable
fouling of UF membranes varied strongly with the type of algal
species and the algal organic matter (AOM) they release. The
presence of polysaccharide (stretching -OH) and sugar ester groups
(stretching S=O) was the main cause of non-backwashable fouling. In
conclusion, this study showed that an improved BRP method is
suitable for the assessment of SWRO pre-treatment systems and it
can be a useful tool to develop potential strategies to mitigate
biofouling and improve the sustainability of SWRO systems.
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