Application of backwashing with demineralized water
for UF fouling control in UF-RO desalination
Sheng Li, S. G. J. Heijman and J. C. van Dijk
ABSTRACT
The effectiveness of demineralized water backwash on ultrafiltration (UF) fouling control of seawater
is investigated in this study. Fouling experiments for two different backwashes (UF permeate and
demineralized water) were conducted at three fluxes: 120, 180 and 240 L/(h m
2
) to compare their
fouling control efficiency on UF membranes. Results show that backwashing with demineralized
water improved the fouling control of UF membranes. When the UF membranes were backwashed
with demineralized water, probably because more foulants were flushed away from the UF
membrane than UF permeate backwashes, the increase in trans membrane pressure (TMP) for
backwashing with demineralized water was less than that with UF permeate. Furthermore, the
fluxes of experiments also played a role on the fouling control. When the flux was 120 L/(h m
2
), the
difference between two different backwashes was small. However, at the flux of 240 L/(h m
2
), the
TMP for backwashing with UF permeate increased faster than that with demineralized water,
although the TMP for backwashing with demineralized water increased as well.
Sheng Li (corresponding author)
S. G. J. Heijman
J. C. van Dijk
Delft University of Technology,
P.O. Box 5048,
2600 GA Delft,
The Netherlands
E-mail: s.li@tudelft.nl
Key words | ultrafiltration, backwash, demineralized water, desalination
INTRODUCTION
Ultrafiltration as an pretreatment of desalination
Ultrafiltration (UF) has been applied for water treatments
for two decades due to its good removal on the particles
and microorganisms (Laine et al. ). With the develop-
ment of membrane technology, the cost of low pressure
membranes (microfiltration and UF) decreases to an accep-
table level for application. That is the reason why the use of
low pressure membranes for water purification has substan-
tially grown in the past decades. Not only in the drinking
water treatment, but also in the desalination field, UF as a
pretreatment for the reverse osmosis (RO) currently
appeared.
Several studies have investigated using hollow fiber UF
membranes as a pretreatment for desalination with reverse
osmosis (SWRO). Ahmad & Aleem () showed that
comparing to conventional pretreatments, the inside-out
hollow fiber UF process is an easy-to-use and robust
alternative. Hoof et al.() carried out a pilot test in
Addur using X-Flow hollow fiber UF membranes as a pre-
treatment for six months, and results showed that the UF
permeate had a stable SDI as low as 1.5. Merrilee &
James () successfully supplied a UF–SWRO system to
the government of the United Arab Emirates that treats
about 11.4 million litres (3 million gallons) of seawater a
day with UF to supply 3.8 million litres (1 million gallons)
to the SWRO system.
Application of the DEMIFLUSH concept
Same as the UF in drinking water treatment, the main chal-
lenge of UF in the seawater treatment is still fouling. Since
all industrial plants produce water at a constant flux, the
trans membrane pressure (TMP) has to be increased to over-
come the increased resistance caused by fouling. In order to
control fouling, normally the membrane is hydraulically
backwashed to recover the membrane permeability. The
part of TMP reduced after a hydraulic backwash is related
364 © IWA Publishing 2011 Water Science & Technology: Water Supply | 11.3 | 2011
doi: 10.2166/ws.2011.033
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