Chemical cleaning of UF membranes fouled

DESALINATION
ELSEVIER

Desalination 179 (2005) 323-333

www.elsevier.com/locate/desal

Chemical cleaning of UF membranes fouled by BSA
Denis Kuzmenko*, Elizabeth Arkhangelsky, Sophia Belfer, Viatcheslav Freger,
Vitaly Gitis
Department of Biotechnology and Environmental Engineering, Ben Gurion University of the Negev,
PO Box 653, Beer-Sheva 84105, Israel
Tel. +972 (8) 647-9031; Fax: +972 (8) 647-2983; email: denisk@ bgumail.bgu.ac.il
Received 28 October 2004; accepted 22 November 2004

Abstract

Cleaning of MF and UF membranes is currently performed by a combination of water and air in either the forward
or backward direction. When the above-mentioned cleaning methods are not effective enough to restore the flux to an
acceptable level, it is necessary to clean the membranes chemically. During chemical cleaning, membranes are soaked
in a solution of strong acids and bases such as hydrogen chloride (HC1) or sodium hydroxide (NaOH), or disinfection

agents such as hypochlorous acid (HOC1). As a result of the effective chemical cleaning, the initial flux is restored and
the membrane deemed as amenable for further operation. The shadow side of the process is an alteration of the
membrane surface, which under some forced cleaning conditions results in formation of holes in the membrane skin
layer. Since such a chemical cleaning shortens membrane lifetime, the next logical step is to evaluate to what extent
chemical cleaning alters the membrane's surface. The parameters under investigation included various cleaning agents
and their concentration, time of clean-in-place treatment and frequency ofcleanings. As was found during the current
study, higher dosages of cleaning agents result in complete restoration of the initial flux at the first step, but lead to
more severe fouling, thus requiring faster clean-in-place operations in the long term. Another finding of the current
research was that the character of the bonding between the foulant and membrane surface changes between suspended
and adsorbed stages. Albeit the electrostatic character of BSA-PES surface interactions, the flux was not restored with
the application of NaOH at virtually any concentration.
Keywords: UF membranes; Flux; Chemical cleaning; Fouling

I. Introduction

One o f the main barriers in application o f the
UF membrane process for direct water treatment
*Corresponding author.

is the effect o f irreversible fouling. Membrane

fouling is referred to as the decline o f flux of a
membrane filter caused by the accumulation of
certain constituents in the feed water on the
surface o f the membrane or within the membrane

Presented at the conference on Membranes in Drinking and Industrial Water Production, L "Aquila, Italy, 15-17 November
2004. Organized by the European Desalination Society.
0011-9164/05/$- See front matter © 2005 Elsevier B.V. All rights reserved
doi: 10.1016/j.desal.2004.11.078

324

D. Kuzmenko et aL / Desalination 179 (2005) 323-333

matrix. According to origin of the foulant, the
membrane fouling is sub-divided into (a) inorganic fouling/scaling, (b) organic molecule
adsorption (organic fouling), (c) particulate deposition (colloidal fouling), and (d) microbial adhesion and growth (biofouling) [ 1]. Among these,
organic fouling (b) is believed [2] to be the most
significant factor contributing to flux decline for
source water with high organic content.

Organic fouling is governed by a complexity
of factors related to both the foulant and the
membrane surface such as structure and charge of
the foulant, composition, hydrophobicity and
surface potential of the membrane surface [3].
The structure of the foulant is mainly the function
of its size since larger molecules can have more
sites to make contact with a surface, expression of
hydrophilic/hydrophobic ligands in the outer
core, and structure stability since less stable
molecules can unfold to a greater extent and form
more contact points with the surface. Both
organic macromolecules and membranes are
usually charged; the same charge on both surfaces
will cause repulsion while the opposite charge
will issue attraction. The composition of the
membrane can be related to topography since
rough surface exposes more area for interaction,
expression of certain ligands causing covalent
binding [4], and heterogeneity since various surface domains might interact differently with

foulants. Hydrophobicity of the membrane surface promotes binding of organic macromolecules
to minimize contact between the hydrophobic
component and water molecules with a gain in
the system's entropy [5].
To minimize flux decline due to organic
fouling, membrane arrays are periodically depressurized and soaked in a solution of chemicals
in a so-called clean-in-place (CIP) operation.
Such an operation can last up to 3 h per 6-8 h of
production time, and it is performed daily in the
water treatment industry. Chemicals used to break
the bonds between the foulants and the membrane
surface will usually either enhance electrostatic

repulsion by a drastic change in the pH values, or
oxidaze the organic compounds into more hydrophilic residuals. The drastic change in the pH is
usually performed with the addition of caustic
soda, elevating pH values to 12-13. This causes
sufficient deprotonation of carboxylic and phenolic functional groups, thus increasing a negative charge of foulants. For some limited cases
such as polysaccharides and proteins, the introduction of NaOH might initiate the hydrolysis by
addition of extensive charge on few sites within

the macromolecule, resulting in strong electrostatic repulsion between the molecule's patches
[3]. Generally, however, to hydrolyze the foulants
an introduction of strong oxidants such as free
chlorine and hydrogen peroxide is necessary to
oxidize the organic compounds with ketones,
aldehydes and carboxylic acids as compound
residuals.
In terms of restoring the initial flux, breaking
the bonds between the foulants and the membrane
surface should result in effective membrane treatment with no side effects. Since membrane cleaning essentially occurs through chemical reactions
between cleaning chemicals and fouling materials, efficiency of cleaning will be highly influenced by concentration of cleaning agents and
length of cleaning periods. It implies, therefore,
that higher dosages of cleaning agents significantly contribute to diffusion of the chemicals to
near-membrane surface layers for faster and more
efficient CIP in a short period of time. Indeed,
introduction of high concentration gradients of
cleaning chemicals such as 0.1% NaOH and
100 ppm free chlorine [6] results in an almost
complete restoration of the initial flux [7-9].
The current research was initiated to assess the

adverse effect of intense chemical cleaning on
long-term applications of membrane treatment for
surface water. The study was performed on flatsheet membranes made of polyethersulphone
(PES) with a molecular weight curt-off (MWCO)
of 20 kDa. The initial suspension consisted of
bovine serum albumin (BSA) protein suspended

D. Kuzmenko et aL / Desalination 179 (2005) 323-333

in DI water (HPLC grade). As found during the
current study, higher dosages of cleaning agents
resulted in complete restoration of the initial flux
at the first step, but led to more severe fouling,
thus requiring faster CIP operations in the long
term. This was attributed to the effective oxidation in the first layer of adsorbed organic
macromolecules near the membrane surface. Such
oxidation resulted in formation of hydrophilic
hydrolyzates that covered the internal surface of
pores within the membrane matrix, resulting in
facilitated transport of water molecules accompanied with severe fouling upon introduction of

the initial suspension. Among the other findings
of the current research is that the character of the
bonding between the foulant and membrane surface changes between suspended and adsorbed
stages. Albeit the electrostatic character of BSAPES surface interactions, flux was not restored
with the application of NaOH at virtually any
concentration.

325

utator

.~rmeate
Fritted

Fig. 1. Membranecell set-up.
Table 1
Properties of the membranes
CE-20

PES-20

Spectrum
20
42/43
44

Sterlitech
20
55/60
50

2. Membranes and apparatus

Manufacturer
MWCO, kDa
Contact angle (0), ° in water
Permeability, L/m2-h-bar

Fig. 1 depicts a laboratory-scale, 500-ml
volume stirred cell used for the experiments. The

cell consisted of an acrylic glass cylinder containing raw solution stirred by a magnetic stirrer
at 400 rpm. The stirring rate may be varied. The
cell holds pressure up to 5 bars, has a backpressure controller for control of transmembrane
pressure (TMP) and provisions for 76-ram
diameter membranes. Round, flat membranes of
100 + 50 nm thickness were supported on a
Teflon support base. The system was framed by
stainless steel. The feed solution was pressured
by nitrogen at a constant pressure of 0.5 bar
throughout the testing of the various membranes
used. Pressure was set by Precision regulator
IR2000-FO2 equipped with a digital pressure
display ISE40 (both from SMC, Tokyo, Japan) in
a range between 0.1-2 bars to a 0.01 bar
accuracy. The precision regulator was integrated

downstream from a regular nitrogen pressure
regulator screwed into a cylinder outlet.
Two commercially available ultrafiltration
(UF) flat-sheet membranes made of cellulose

ether (CE-20) and polyethersulfone (PES-20)
were used in the study. The membranes are integrally skinned and asymmetric, usually prepared
by the phase inversion method. Table 1 gives the
characteristics of the membranes studied including manufacturer, material, and nominal MWCO.
The contact angle and permeability of pure
membranes were measured on site prior to the
experiments. Measurements of the contact angle
with a goniometer (Rame-Hart, CA) using the
sessile drop method were made to determine an
index of membrane hydrophobicity. In this test a
-20/xl drop of DI water was placed onto the dried
membrane surface using a microsyringe, and the

D. Kuzmenko et al. / Desalination 179 (2005) 323-333

326

air-water-surface contact angle was measured
within 10 s. Contact angle measurements were
made in triplicate using separate pieces of membrane. Contact angles greater than 90 ° indicate

that the membrane is hydrophobic, and extra
pressure should be applied to push the feed
through the membrane. Thus, in the current study
only hydrophilic membranes were used. The CE
membrane was more hydrophilic than the PES
one. Pure water permeability of the membranes
was obtained by filtration of DI water for 30 min
at 1 bar N 2 pressure after the membranes were
soaked in DI water at 30°C for 1 h to remove
glycerin.
Cold alcohol precipitated BSA was purchased
from Sigma-Aldrich Israel (Rehovot, Israel). A
0.15-g sample was dissolved in 500 ml deionized
water (RO quality) to form a 0.3 g/L protein solution. Ionic strength of the solution was changed
with the addition of KC1, and pH was adjusted in
a range between 2.9-10.1 with the addition of
HC1 or KOH (J.T. Baker Chemical, Philibsburg,
N J). All experiments were performed for 30 min,
a time sufficient for filtration of 50 ml of the feed
suspension. The experiments were performed at
a constant temperature of 204-I°C. The temperature and pH of the samples were measured and
recorded on site during each experiment. Flux
was measured by weighing samples of the permeate with semi-analytical weights collected over
fixed time intervals as

j__ Q_

,am

A pAtl

D2/4

(1)

60
where Am (g) is permeate weight difference; At
the frequency interval; D the active membrane
diameter, approximately 0.07 m for the current
setup; and P is the density of permeate filtrated
through the membrane, taken as 0.9982 g/ml for
DI water at 20°C. The flux J was normalized to
its initial value J0 obtained through 30 min

filtration of DI water before an experiment, and
plotted vs. time from the beginning of a filter run.
Permeate samples were analyzed for the presence
of BSA using the Loury method. After the experiments the membranes were cleaned by immersion
in aerated DI water for 1 h, and then the membranes were stored in 0.5% formaldehyde
solution at 4°C to prevent microbiological activity on the membrane surface.
Cleaning of the membranes was performed
with DI water, with 100,500, 1000 and 3000 ppm
NaOH solutions (Frutarom, Israel) with 100,
1000, 3000 and 5000 ppm free chlorine solutions
and with 100, 1000 and 3000 ppm hydrogen peroxide (Fluka, Switzerland). Free chlorine solutions were obtained from commercially available
bleach NaOC1 (aka Ekonomika, Unilever Best
Foods Israel, 15 g/L flee chlorine). The degree of
flux recovery was assessed by 30-rain filtration of
DI water after BSA membrane treatment and CIP
operation. The ratio of the specific flux (in
1/h-m2-bar) at 20°C of fouled/cleaned membrane
J to the initial flux of virgin membrane J0,

lux

,oo
DI water

was named the flux recovery criterion and used to
evaluate the recovery of the membrane flux.
Zeta potential and particle size of the BSA
was measured with ZetaPlus (Brookhaven Instruments, Holtsvitle, NY, USA), a zeta potential and
particle size analyzer equipped with a 30 mW
657 nm laser (Hamamatsu Photonics, Hamamatsu
City, Japan).
Visualization of protein patches on membrane
surfaces was performed with epifluorescent
microscope (Axioskop 2 plus, Carl Zeiss Jena,
Germany) equipped with a Nikon DXM 1200F
(Nikon, Japan) digital camera. Fluorescent staining of the BSA solution was performed in 0.1 M
sodium bicarbonate buffer at pH 8 with 62 g/l
BSA. Fluorescein was dissolved in dimethyl

327

D. Kuzmenko et al. / Desalination 179 (2005) 323-333

sulfoxide (DMSO, Sigma-Aldrich). The mixed
solution was stirred for 2 h; to get rid of free dye
residuals, the obtained conjugates were placed in
a 3500 Da MWCO dialysis membrane for a week
under stirring with DI water replaced daily.
The pore streaming potential was measured by
pumping a KC1 solution through the membrane
surface. For that the membrane cell was remodeled to include a salt bridge between retentate
and permeate via membrane in a set-up somewhat
similar to the one used by Pontie et al. [10]. The
measurements were performed with Ag/AgC1
reference electrodes (model 723/733, Metrohm,
Switzerland) and a high-impedance digital multimeter (EDM 2347, Escort, Taiwan). The asymmetry potential of the pair of electrodes was less
than 1 mV. Streaming potential values were
calculated from four measurements per value at
1 and 10 mM solutions of KC1 pumped at 0.5 and
I bar pressures using the Helmholtz-Smoluchowski equation [11 ]:

remove excess liquid, and then dried in air and in
a desiccator over P205 for 2 h. The samples were
then clamped to the ATR crystal.

3. Results and discussion

Fig. 2 presents values of the zeta potential of
BSA (upper chart) and the streaming potential of
PES membrane (lower chart) in a 10 mM KC1
solution. BSA is a protein with a 67 kDa MWCO
with a size ranging between 9 to 25 nm having a
point of zero charge in pH 4.2, in accordance
with earlier reported data [12]. The obtained
curve was divided into the regions of positive
charge (A), of zeta potential values closed to
electroneutrality (B), and of negative charge (C).
40
30
20

E

_ Ae rlk
A P e 0e

10

==
,m

0

(3)

-10
N

where AE is the potential difference across a
membrane, Ap the applied pressure, r I the dynamic viscosity of the electrolyte, k the conductivity, e the dielectric permittivity of water and e0
the permittivity of the vacuum.
Attenuated total reflection-Fourier transform
infrared (ATR-FTIR) spectra were recorded on a
Nicolet spectrometer (model 5PC, Thermo
Electron, Waltham, MA, US). The ATR accessory contained a ZnSe crystal (25 mm x 5 mm x
2 ram) at a nominal incident angle of 45 °, yielding about 12 internal reflections at the sample
surface. All spectra (100 scans at 4.0 cm -] resolution and rated to the appropriate background
spectra) were recorded at 25°C. The instrument
was purged with dry nitrogen to prevent the interference of atmospheric moisture with the spectra.
Samples taken from the membranes and stored in
water were blotted dry with clean filter paper to

-2Q
.30
-40
8

10

I Pzc=4"2 Ip.
10
5

E

I_:_

o-

o~ .10
.=
E
ca
.e -15

I

pzc=4.8

I

-20
-25

I
pH

Fig. 2. Zeta potential-pH dependence for BSA and
streamingpotential; pH dependence for PES membrane
in 10 mM KCI solution.

328

D. Kuzmenko et al. / Desalination 179 (2005) 323-333

The same division was performed for the pore
charges of PES membrane expressed in streaming
potential values. The streaming potential graph
exhibited a general similarity to the one reported
previously [ 10], although the point of zero charge
was somewhat higher (4.8 vs. 3.4) than that previously reported. To study how electrostatic
interactions affect flux and degree of fouling in
the BSA-PES system, the following experiments
were performed at various pH levels: 2.9, 5.3, 7.4
and 10.1. Here pH 2.9 corresponds to the A
region where both BSA and the membrane surface bear a positive charge; pH 5.3 accounts for
the B region to the point of zero charge for both
BSA and PES; and pH 7.4 and pH 10.1 are for
the region where both BSA and PES are negatively charged. The results are depicted in Fig. 3.
Flux decline was definitely, to some extent,
governed by the electrostatic interactions. At
pH 2.9 and 5.3, weakly charged membranes did
not interrupt accumulation of charged BSA on its
surface, but at pH 7.4 where both BSA and PES
membranes were negatively charged (-28 and

- 14 mV, respectively), the electrostatic repulsion
held part of BSA at some distance from the
membrane surface, thus minimizing the fouling
effect. The trend was even more pronounced for
a rather extreme pH of 10.1 with -32 mV and
-20 mV, respectively, where the effect of fouling
caused less than 10% flux reduction over a 30min filter run (as compared with 40% fouling for
pH 2.9 and 5.3).
The effect of ionic strength of the solution was
examined by measuring the flux decline with
experiments with 0.1, 1 and 10 mM KC1 addition
at pH 7.4 (data not shown). Once again, the
electrostatic considerations were revealed as a
useful tool since fluxes increased with decreasing
ionic strengths because screening of the charges
of the protein is reduced at lower ionic strengths.
Therefore, protein molecules strongly repel each
other, especially at the membrane surface where
the concentration of protein is high. This electrostatic repulsion increases mass transfer of protein
from the membrane surface back to the bulk.

85
--e-• o.
--'P--~ -

80
~7

\

75

.~
E

~.
X

=

70

pH
pH
pH
pH

~

V-- m

65

uV..-

~

2.9
5.3
7.4
10.1

, , 'r,7

~

60
\

0,.0

...... 0 .........

0

......

. .... 0 ....

55
........ O

50

¢

45

/
5

10

15

T i m e [min]

/

/

/
3O

Fig. 3. Flux decline as a function
ofpH.

D. Kuzmenko et al. /Desalination 179 (2005) 323-333
3.1. Flux recovery upon chemical cleaning

After each run the fouled membrane was
treated with various cleaning agents such as DI
water, caustic soda, free chlorine and hydrogen
peroxide at various concentrations. The degree of
cleaning was assessed by 30-rain filtration of DI
water before and after the experiments for each
membrane. The performances of various cleaning
agents are depicted in Fig. 4.
Cleaning with DI water was a very ineffective
treatment in terms of flux recovery, and resulted
in only a 5% gain in flux values as compared to
fouled membranes. This is probably due to some
degree of removal of loose foulants that form an
external cake layer. Alkaline washing with NaOH
raised pH of the cleaning solution to 11-13 but
had a very limited influence on the flux recovery
with 10% gain over fouled membrane flux. The
effect was not pronounced for various NaOH
concentrations such as 100, 500, 1000 and
3000 ppm. That finding is rather surprising considering the fact that electrostatic repulsion
obviously governed adsorption during the filtration run. The same mechanism was virtually
unfeasible during the stage of cleaning. Experiments with a strong oxidant such as hydrogen
peroxide (H202) unexpectedly resulted in an
actual loss of flux during cleaning. It was argued

140

329

that such a treatment might cause formation of
some viscous gel layer already on the external
side of the cake. The ultimate cleaning agent for
BSA from PES membranes was free chlorine
introduced at concentrations of 100, 1000, 3000
and 5000 ppm. Oxidation with hypochlorite ion
kept pH 6.8 practically neutral. No change in the
contact angle and streaming potential values upon
chemical cleaning with free chlorine was detected. The flux recovery rates varied between
95-136% with an average 104% recovery. The
5% average flux loss was suggested to be due to
the pore blocking in the membrane active layer.
That hypothesis was partially supported by the
ATR-FTIR studies.
BSA protein is a heteropolymer formed by a
chain of-50-500 amino acids, linked together by
peptide bonds. The protein is constructed from a
library of just 20 amino acids, which share a
common "backbone" but which are distinguished
by their chemically diverse side chains. Each
amino acid backbone contains polar amino (C-N
and N-H) and carbonyl (C=O) groups with defined 1570.1580 and 1630-1670 cm -1 bands of
FTIR spectra, respectively, that definitely indicate the presence of BSA protein on the membrane surface [13]. The spectrum of the initial
BSA solution is depicted in Fig. 5.

123

120

104

100
80

8.=

60

65

70
52

6O

X
--t

,-r

4O
20
0

--

virginby

BSA

DIW

NaOH

NaOCI

1-1202

NaOCI

fouled

treated

treated

treated

treated

Cleaning agent

Fig. 4. Recovery of membranepermeability
with different cleaning agents.

330

D. Kuzmenko et al. / Desalination 179 (2005) 323-333

1643 ~ M

0.14

/

0.12
0.10
0

~0.08
.D
~O.C~

/

/

f

J

/

i

\

/
J
,./

t

< 0.041725
°-°°:iJ V
1700

1600
W a v e n u m b e r s (crn-1)

There is a secondary peak at 1725 cm -t that
does not belong to the pure BSA solution spectra,
having no peak in this area [14]. It was argued
that the peak belongs to residuals of different
fatty acids, whose presence in BSA spectra is due
to an insufficient degree of purification. Of the
characteristic peaks the one at 1577 cm-~ overlaps
with one of the strong bands assigned to PES;
therefore, the amide II area (C-N and N-H bonds)
was not suitable for analyzing the presence or
absence of BSA. The second representative peak
at the 1640-1650 cm -~ wave band unexpectedly
appeared in the FTIR spectra of a virgin membrane as well (Fig. 6, spectrum 1). Since this peak
is absent in the IR spectrum of neat PES, its
presence in the spectrum of a pristine membrane
suggests that the membrane contains another
component, most probably polyvinylpyrolidone,
which is often added to PES during membrane
casting as a pore former and hydrophilizer and
also contains an amidic bond, hence an amide I
1650 cm -~ band in the IR spectrum. Still it is
possible to recognize qualitatively the presence or
absence of the protein on the membrane surface
by looking at the half width peak at the 1650 cmwaveband, which is widened for BSA due to the
presence of "shoulder" peaks.
The ATR-FTIR spectra of the virgin (I),
BSA-fouled (2), BSA-fouled and NaOH cleaned
(3) and BSA-fouled and NaOC1 treated (4) membranes are depicted in Fig. 6.

1500

Fig. 5. ATR-FTIR spectrum of
BSA protein used in the analysis,

It is clearly detectable that no BSA was found
in the virgin and BSA-fouled NaOCl-treated
membranes. As was already argued by analysis of
flux decline the BSA-fouled membrane was not
cleaned by NaOH, as can be seen from the
presence of the half-width peak 1650 cm -~ in
spectra 3. Thus, it was concluded that the introduction of free chlorine denatures protein and
results in effective cleaning of PES membranes
fouled by BSA.
The same effective cleaning with free chlorine
caused changes in the spatial arrangement of
adsorbing BSA on membrane surfaces. The
results presented in Fig. 7 demonstrate a fluorescent micrograph of virgin, fluorescein-BSA
fouled and NaOCl-pretreated fiuorescein-BSA
fouled membranes.
The obtained micrograph suggests that residuals of BSA after chlorine treatment can serve as
centers for further protein accumulation. Here the
white dots on the fluorescence micrograph of
NaOCl-pretreated BSA-fouled membrane
(Fig. 7C) are considered to be the patches of
protein on the membrane surface. That behavior
was strictly opposite to the unimodal distribution
mode obtained when a fluorescein-BSA solution
was filtrated by a virgin membrane (Fig. 7B). The
micrograph of a virgin membrane is depicted in
Fig. 7A for contrast comparison.
The concentration of cleaning agent was found
to be important in terms of future fouling. The

331

D. Kuzmenko et al. / Desalination 179 (2005) 323-333

3

E

I

1800

k

1600

1400

q

1200

Wavenumbers [cm"1]
Fig. 6. ATR-FTIR spectra of virgin (1), BSA-fouled (2), BSA-fouled and NaOH cleaned (3) and BSA-fouled and NaOC1
cleaned (4) PES membranes.

Fig. 7. Fluorescence micrographs of fluorescein-BSA fouled virgin (B) and NaOCl-pretreated (C) PES membranes. The
white dots on the right micrograph are believed to be dendrites of BSA. Here (A) is the fluorescence micrograph of a virgin
BSA membrane.
experiments were performed with various concentrations o f cleaning agent, and the results are
depicted in Fig. 8. Also the flux was recovered to
the initial levels of the virgin membrane; the
degree of fouling was greater as a more concentrated solution of NaOC1 was introduced. The

moderate fouling o f 10% for 1000 ppm free
chlorine was hardly comparable to 30% fouling
when the CIP was performed with 5000 ppm. It is
usually argued that effective chemical cleaning
increases hydrophilicity of the membrane, thus
allowing higher water flux for the same applied

332

D. Kuzmenko et al. / Desalination 179 (2005) 323-333
1.4

4. Conclusions
[ ---~- Ct = 5 glL-h ]

1,2

CIP

CIP

1.0

dCIP I +

1.2-

._=>

q=

1.01

"~

.,5.
6
1.4.

CIP

[

~

Ct = 24 g/L-h

Ct = 72 g/L-h i

1.2'
a=

10~

.=~
"~
n,,'

8.
.6
1.4.

.•

c,p

1.2-

l

As a result of this study, it was concluded that
the kinetics of flux recovery greatly depend upon
the exact cleaning procedure used. Effective
oxidation with free chlorine resulted in complete
restoration of the initial flux but caused a faster
fouling than the incomplete removal of the protein followed by the same degree of fouling each
consecutive time. It is argued that the probable
cause of this phenomenon is the alteration in
chemistry of the membrane surface other than
hydrophilicity and surface charge, as was concluded previously.
The other possible explanation of the observed
phenomena lies in the complexity of the protein
molecules. It was observed that the nature of
interactions between BSA in solution and the
membrane surface differs from the interactions of
the adsorbed protein and the membrane surface.
While in the former case the interactions are
mainly electrostatic, in the latter case the bonds
are probably covalent since the sharp increase in
pH values had no effect on protein removal.

.8.

20

413

60

80

Run time [min]

Fig. 8. Fouling of PES membranes cleaned by free
chlorine.
pressure or due to an increased negative charge
on the membrane after treatment at high pH conditions [15]. This study, however, suggests a
different mechanism of the pore blocking of the
active membrane layer with a fast uptake of the
water molecules but also with a more severe
fouling each consecutive time the membrane is
fouled by BSA and cleaned with OC1-. An
absence of BSA residuals on the membrane
surface suggests that part of the protein is actually
swelled by the membrane active layer and
actively contributes to the formation of a cake
layer upon each introduction of BSA solution.

Acknowledgements
This project is supported by a grant from the
The Stephen and Nancy Grand Water Research
Institute (GWRI).

References
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[2] J, Mallevialle, C. Anselme and O. Marsigny, Effects
of humic substances on membrane processes, in:
Advances in Chemistry, American Chemical Society,
Denver, Colorado, 1989.
[3] C.K.Dee, D.A. Puleo and R. Bizios, An Introduction
to Tissue-Biomaterial Interactions, Wiley-Liss, New
York, 2002.
[4] S.T. Kelly and A.L. Zydney, Effects of intermolecular thiol-disulfide interchange reactions on

D. Kuzmenko et al. / Desalination 179 (2005) 323-333

[5]

[6]

[7]

[8]

[9]

[10]

BSA fouling during microfiltration. Biotechnol.
Bioeng., 44(8) (1994) 972-982.
J. Lyklema, Fundamentals of interface and colloid
science, Vol. 2, Solid-Liquid interfaces, Academic
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