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Chemical cleaning of reverse osmosis membrane fouled by sugar solution.

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ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING
Asia-Pac. J. Chem. Eng. 2010; 5: 691–700
Published online 10 September 2009 in Wiley Online Library
(wileyonlinelibrary.com) DOI:10.1002/apj.387
Research Article
Chemical cleaning of reverse osmosis membrane fouled
by sugar solution
S. S. Madaeni,* A. Sasanihoma and S. Zereshki
Membrane Research Center, Department of Chemical Engineering, Razi University, Kermanshah, Iran
Received 30 November 2008; Revised 2 July 2009; Accepted 6 July 2009
ABSTRACT: Membrane fouling is a complex phenomenon and typically results from several reasons. Chemical
cleaning is a strategy for regeneration of the fouled membranes. In this work, BW30 reverse osmosis membranes were
fouled with sugar solution. The effect of different cleaning agents on the revival of the fouled membrane was studied.
The role of chemical and physical interactions on chemical cleaning of organic-fouled RO membranes using a wide
variety of cleaning agents including acids (HCl and HNO3 ), bases (NH3 and NaOH), complexing agents [ethylene
diamine tetra acetic acid (EDTA)], surfactants [cetyle three methyl ammonium bromide (CTAB) and sodium dodecyl
sulfate (SDS)], and water have been systematically investigated. Resistance removal (RR) and flux recovery (FR) were
used for demonstration of the cleaning efficiency. Membrane fouling is customarily indicated and measured by permeate
decline at constant operating conditions. It has been shown that the cleaning efficiency changes with increasing the
concentration of the cleaning agent. NH3 was the best cleaning agent for removing sucrose from membrane surface.
EDTA and SDS were quite effective in reacting with organic foulants in the fouling layer. Moreover, pure water was
used as cleaning agent with acceptable results. Water is safe, cheap, and broadly available in most plants and could be
considered as a good recommendation.  2009 Curtin University of Technology and John Wiley & Sons, Ltd.
KEYWORDS: membrane; reverse osmosis; sugar; sucrose; fouling; cleaning
INTRODUCTION
Food industry is one of the major applications of reverse
osmosis membranes. Concentrating a solution containing sucrose is a feasible application of membrane in the
sugar industry.[1] Permeation of carbohydrates through
a membrane depends on the morphology of the membrane and operating conditions, such as pH and velocity
of the fluid.[2] Reverse osmosis may be employed for
the concentration of other syrups, such as corn syrup.[3]
The benefits of membrane application compared with
evaporation are lower energy consumption and higher
quality of the product. A two-stage process is proposed
for concentrating the sugar syrup using BW30 reverse
osmosis membrane by Madaeni et al .[4] A moderate
transmembrane pressure (TMP) (around 20 bars) was
recommended for this purpose.
On the basis of the terminology introduced by
IUPAC, fouling is ‘a process resulting in loss of performance of a membrane due to the deposition of suspended or dissolved substances on its external surfaces,
at its pore openings or within its pores’.[5] Fouling not
*Correspondence to: S. S. Madaeni, Membrane Research Center,
Department of Chemical Engineering, Razi University, Kermanshah, Iran. E-mail: smadaeni@yahoo.com
 2009 Curtin University of Technology and John Wiley & Sons, Ltd.
only reduces the flux but also changes the retention.
Numerous researches are carried out around the world
for fouling reduction and cleaning of the fouled membranes.
Flux as a measure for membrane performance is
controlled by two phenomena, concentration polarization and fouling. However, it is unlikely to completely eliminate fouling, control of fouling is of utmost
importance. Techniques involved are pre-treatment of
feed which reduces the particulate density, changing operating conditions, e.g. applying moderate pressure, cross flow, and backwashing, and membrane
regeneration.
An important technique for membrane regeneration
is chemical cleaning of fouled membrane. Cleaning is
defined as ‘a process where material is relieved of a substance which is not an integral part of the material’.[6]
Many substances mostly chemicals and different procedures are used for cleaning of membranes. Choosing
the best materials depends on feed composition and precipitated layers on the membrane surface, and in most
cases is performed by trial and error.[7] The selected
materials should be chemically stable, safe, cheap, and
washable with water.[8]
Chemical cleaning means removing impurities by
means of chemical agents. Up to now there are some
692
S. S. MADAENI, A. SASANIHOMA AND S. ZERESHKI
Asia-Pacific Journal of Chemical Engineering
problems associated with membrane cleaning. Cleaning
consumes time and money. Cleaning procedures need
long time operation,[9] consume chemicals,[10] degrade
some membranes,[11] and may cause corrosion in the
system.[12] In general, around 5–20% of the operating
cost is the cost of cleaning.[13] This shows the importance of the continuous research in this field. The investigation of fouling and cleaning mechanisms leads to
better understanding of cleaning process and provides a
basis for tailor-made chemicals and procedures. It seems
that cleaning agent diffuses into the deposited cake layer
on the membrane surface. Diffusion rate depends on different factors including turbulancy. A chemical reaction
may occur between cleaning agent and the substances
on the cake layer. Depending on their type, the reaction may be hydrolysis, dissolution, or dispersion. This
results in removal of fouling materials from the membrane surface.
The aim of this research was evaluating the best
chemical cleaning agent and optimum conditions for
cleaning of BW30 reverse osmosis membrane fouled
by sugar solution. The fouled membranes were washed
with chemical agents such as acids, bases, and surfactants. The effects of the type of chemical agents and
process conditions on cleaning efficiency as well as
cleaning mechanism are discussed.
MATERIALS AND METHODS
Apparatus
A bench-scale cross-flow batch concentration apparatus
(Fig. 1) was used for all experiments. Permeate was
concentrate
by-pass
9
3
5
6
4
4
10
taken out of the loop, and concentrate was returned
to the tank. The characteristics of the high-pressure
pump were QMax = 480 l/h, PMax = 80 bar, TMax =
50 ◦ C. Excluding some parts of the line that were of
stainless steel, other parts were high-pressure hoses.
The system consisted of a valve to control the applied
pressure and a bypass valve. These valves control the
flow and the pressure. The membrane cell consisted
of two cubic parts which are made by a specific
alloy. The membrane with the active area of 0.002 m2
was sandwiched between two parts and settled on
a resistant compact foam layer, to protect it against
deformation and displacement. There were two oil
pressure gauges (0–60 bar) on the flow line to show
the pressure of the concentrated phase before and after
the cell.
Prior to the cleaning, membrane was fouled by
filtration of sugar solution for 70 min at 22 bars.
The fouled membranes were cleaned according to the
protocol suggested by Fane and colleagues.[7]
Before and after fouling, the water flux of the
membrane was measured by passing distilled water
through the membrane (initial water flux = Jwi , water
flux after fouling = Jwf ). The fouled membrane was
washed with distilled water for 10 min to remove
unbound substances from the membrane surface. The
water flux was measured after washing (Jww ). This was
followed by washing the membrane with a cleaning
agent for a specific time (10 min) without applying
pressure. The water flux after chemical cleaning was
determined (Jwc ). Fouling can be quantified by the
resistance appearing during the filtration, and cleaning
can be specified by the removal of this resistance. The
resistance is due to the formation of a cake or gel layer
on the membrane surface. The flux (J ) through the
cake and the membrane may be described by Darcy’s
law:
1
V
P
(1)
J = ≡ ×
A
t
µ
R
3
permeate
1
where P is the TMP (driving force), µ the viscosity
of the fluid, R the sum of the resistances, A the
membrane surface, V the permeated volume, and t the
required time for permeation of V .
Membrane resistance (Rm ) can be estimated from the
initial water flux:
7
2
8
1 Feed tank
2 Pump
3 Valve
4 Pressure gauge
5 Crossflow cell
6 Membrane
7 Permeate
8 Balance
9 Concentrate
10 By-pass
Figure 1. Schematic of reverse osmosis experimental
setup.
 2009 Curtin University of Technology and John Wiley & Sons, Ltd.
Rm =
P
µJwi
(2)
The resistance which appears after fouling (Rf ) can
be calculated from the water flux after washing with
water:
P
(3)
− Rm
Rf =
µJww
Asia-Pac. J. Chem. Eng. 2010; 5: 691–700
DOI: 10.1002/apj
Asia-Pacific Journal of Chemical Engineering
CHEMICAL CLEANING OF REVERSE OSMOSIS MEMBRANE
The resistance which remains after cleaning (Rc )
can be calculated from the water flux after chemical
cleaning:
P
(4)
− Rm
Rc =
µJwc
ammonium bromide (CTAB), sodium dodecyl sulfate
(SDS), all supplied by Merck, and ethylene diamine
tetra acetic acid (EDTA) supplied by Panreac Company.
The concentration of all the cleaning solutions was 1%
(w/v).
Resistance removal (RR) which is a criterion for
cleaning quantification can be calculated from:
(Rf − Rc )
× 100
(5)
RR(%) =
Rf
Fouling and cleaning procedure
Flux recovery (FR) is another method for quantification of cleaning efficiency:
(Jwc − Jww )
× 100
(6)
FR(%) =
(Jww − Jwi )
Both parameters, i.e. resistance removal and flux
recovery, have been used for demonstrating the cleaning
efficiency.[14,15]
Membrane
Thin-film composite polyamide reverse osmosis membrane, BW30 (Filmtec Company, USA) was used during
this study. The active area of the membrane used in the
apparatus was 0.002 m[2] . The characterizations of this
membrane are as follows:[16]
Thickness
Maximum operating temperature
Maximum operating pressure
pH range, continuous operation
pH range, short-term cleaning
Free chlorine tolerance
150 µm
45 ◦ C
41 bar
2–11
1–12
<0.1 ppm
For obtaining the flux for each step, the feed (distilled
water or sugar syrup) was passed through the membrane. The flux was measured gravimetrically by continuously weighting permeate. By dividing the permeate
weight to the time and membrane surface area, flux was
calculated.
The permeation flux of distilled water, Jwi , was
measured at 38 ± 3 ◦ C and 22 bars in 10 min intervals
for 70 min as required time for complete fouling
(Fig. 2). Feed was passed continuously through the
membrane surface with a linear cross-flow velocity of
1 m/s. The flux of this step was introduced as Jwi in
the next step. After feed filtration, distilled water was
used to wash some loose materials from the membrane
surface.[17] Then the permeation flux of distilled water,
Jww , was measured.
Fouled membrane was washed by cleaning agents at
25 ◦ C, applying no pressure for 10 min, and then the
final flux of distilled water, Jwc , was measured. Fouling was evaluated after determining resistance removal
(RR) and flux recovery (FR).[17] The effectiveness of
different chemicals with different concentrations and
operating conditions could be compared by using these
two parameters (RR and FR).
30
25
In all experiments, sugar (sucrose) solution with total
soluble solid (TSS) = 20◦ Brix and pH = 7.1 was
used as feed. Thus, foulant component was pure
sugar or sucrose solely. Temperature of the feed
was 38 ± 3 ◦ C, and TMP was kept constant at 22
bars.
Flux (lit/m2 h)
Feed
20
15
10
5
0
0
Cleaning agents
Chemical substances used as cleaning agents were
sodium hydroxide (NaOH), hydrochloric acid (HCl),
nitric acid (HNO3 ), ammonia (NH3 ), cetyle three methyl
 2009 Curtin University of Technology and John Wiley & Sons, Ltd.
20
40
60
80
Time (min)
Figure 2. Flux behavior for filtration of sugar solution
using the BW30 RO membrane (22 bars, 38 ◦ C, 0.5 m/s,
and feed Brix = 20◦ ). This figure is available in colour
online at www.apjChemEng.com.
Asia-Pac. J. Chem. Eng. 2010; 5: 691–700
DOI: 10.1002/apj
693
S. S. MADAENI, A. SASANIHOMA AND S. ZERESHKI
Asia-Pacific Journal of Chemical Engineering
RESULTS AND DISCUSSION
Comparison of cleaning agents
Cleaning efficiency of fouled membrane is affected by
the type of cleaning agent. The efficacies of various
chemicals are represented in Fig. 3. Ammonia showed
high performance around or more than 90%, followed
by EDTA and SDS. In contrast, HCl and CTAB showed
very low effect on flux recovery.
NH3 has pyramidal molecular spatial configuration
with loan pair of electron on nitrogen. It leads to
high electro negativity difference between nitrogen and
hydrogen so makes stronger hydrogen bonding with
foulant (sugar) and finally removes it completely from
membrane surface in comparison with NaOH linear
configuration.
SDS and CTAB are anionic and cationic surfactants, respectively. The repulse of CTAB positive head
and the positive oxygen of sugar as fouling material decreases its cleaning efficiency with respect to
SDS. SDS decreases the surface tension of adjacent
molecules. Therefore, it is expected to have acceptable
results as a cleaning chemical.
Surfactants are components that could have both
hydrophilic and hydrophobic structures. They can form
micelles with fat, oil, and proteins in water and help to
clean the membranes fouled by these materials. Some
surfactants may also interfere hydrophobic interactions
between bacteria and membranes.[18] In addition, surfactants can disrupt functions of bacteria cell walls.
Therefore, surfactants affect fouling dominated by the
formation of bio-films.
It is proposed that an efficient cleaning agent and
favorable cleaning conditions could 7be selected by
110
RR
100
FR
90
80
Recovery (%)
694
70
60
50
40
considering two important mechanisms: chemical reaction between cleaning agents and foulants in the fouling
layer, and mass transfer of chemical agents (from the
bulk phase to the fouling layer) and foulants (from the
fouling layer to the bulk phase). Efficiency of a cleaning
solution at fixed physical conditions was mainly governed by the chemical reaction of the cleaning agent
with the foulants in the fouling layer. A more favorable
chemical reaction would lead to a lower foulant–foulant
adhesion force and hence higher cleaning efficiency.
Therefore, it seems that cleaning agents which form
hydrogen bonds, electrostatic attraction, chemical reaction, or their combinations could be more effective.
Using bases in the majority of cleaning agents is
recommended for sugar as the major foulant which is
an organic material.[15]
The polymeric active layer of BW30 RO membrane
is polyamide.[16] Double bonds between carbon and
oxygen molecules in polyamide molecular structure
make it a fixed and flat structure. Incidentally, electro negativity difference between oxygen and hydrogen
molecules originates a partial negative charge on oxygen molecules of the active layer. The electrostatic
attraction between sucrose hydrogen molecules with
positive charge and polyamide active layer with negative charge causes sucrose molecules to adsorb on the
membrane.
To compare the cleaning agents, similar membranes
were fouled with the same feed in the same conditions,
and the fouled membranes were cleaned with different
chemicals.
On the basis of the previous results, it has been shown
that chemical reaction of the cleaning agent with the
foulants in the fouling layer plays a critical role in determining the overall cleaning efficiency. Determining the
intermolecular adhesion forces between foulants in the
fouling layer in the presence or absence of cleaning
solution enables us to predict the capability of chemical reaction between cleaning agent and the foulants. A
more favorable (or reactive) cleaning agent will result
in less intermolecular adhesion force between foulants
in the fouling layer.
Following this prediction, the selected favorable
cleaning solution can be used for cleaning experiments
to determine the optimal physical cleaning conditions
in terms of both cleaning efficiency and operating cost.
30
20
Operational parameters affecting cleaning
10
0
HN
O3
(1
%
)
N
aO
H
(1
%
)
H
(
Cl
1%
)
TA
(1
%
)
H3
(1
%
)
AB
N
CT
ED
Cleaning agents (%w/v)
(1
%
)
S
DS
(1
%
)
Figure 3. Effect of different cleaning agents on cleaning
of RO membranes fouled by sucrose solution. This figure is
available in colour online at www.apjChemEng.com.
 2009 Curtin University of Technology and John Wiley & Sons, Ltd.
Effect of concentration
The first part of Fig. 4 shows increasing ammonia concentration up to 1.5% (w/v) increases the cleaning
efficiency. In contrast, the second part of the chart
expresses decreasing efficiency with increasing concentration. This effect can be explained due to the
permeability of the cake layer. In general, cleaning
Asia-Pac. J. Chem. Eng. 2010; 5: 691–700
DOI: 10.1002/apj
CHEMICAL CLEANING OF REVERSE OSMOSIS MEMBRANE
100
90
RR
FR
80
Recovery (%)
70
60
50
40
30
20
10
0
0.25
0.9
1
1.5
2
2.5
NH3 Concentration (%w/v)
Figure 4. Effect of ammonia concentration on cleaning
efficiency (pH = 11). This figure is available in colour online
at www.apjChemEng.com.
may remove the deposit layer or alter its permeability. Increasing the concentration of cleaning agent to
the optimum concentration provides maximum voidance and highest cleaning efficiency. The cake porosity
may decrease with a further increase in chemical concentration, which results in lower cleaning efficiency.
The appropriate chemicals are able to dissolve a part
of the cake layer formed on the membrane surface.
Another possibility is increasing the cake porosity, i.e.
the chemicals dissolve a part of deposited species in
the cake leading to higher voidage and less porosity.
However, the capability of the chemicals for both phenomena is somewhat limited. At higher concentration,
the chemicals may remain on the membrane surface
or in the voidage of the porous cake. The latter may
result in lower porosity due to the filling of the voidage
by remaining materials. This lowers the cleaning efficiency. Obviously, the limitations of the available apparatus are an obstacle for proving these phenomena via
experiments.
At high concentrations, acids or alkalis may destroy
part of these molecules. This breakage expels some
agents which may increase the fouling. One of the
cleaning limitations is the effect on membrane integrity.
The chemicals are able to affect the membrane structure
beyond a specific concentration. This may destroy the
membrane or results in membrane swelling. The first
one is easily recognized by the passage of feed species
through the membrane. However, the second one is not
observable. Swelling compresses the cake formed on
the membrane surface leading to lower cake porosity
and reduces the cleaning efficiency.
Chemical agents can also attack the membrane during
the cleaning process, causing swelling. Both phenomena
result in less cleaning efficiency.
 2009 Curtin University of Technology and John Wiley & Sons, Ltd.
Ammonia has two different cleaning functionalities:
(1) hydrolysis and (2) solubilization. There are a number of organic materials including polysaccharides and
proteins which could be hydrolyzed at high pH. During the cleaning procedure using ammonia, pH of the
cleaning solution can be as high as 11. At this pH,
even the weakest phenolic groups would dissociate
by 50%. As a result, the negative charges on organic
molecules increase to a great extent, so does their solubility. Phenolic groups are typically associated with
the most hydrophilic portion of natural organic matter
(NOM) and likely to have strong adhesion to membranes. Hydrophilizing this portion of organic matter
undoubtedly weakens the bond between membrane and
those fouling materials. In addition, the molecules of
NOM are likely to have stretched, linear configuration
due to the repulsion between negatively charged functional groups.[19] This change in molecule configuration
creates a loose fouling layer that allows an easier access
for chemicals to penetrate the inner portion of fouling
layer, therefore facilitates mass transfer, and enhances
the efficiency of cleaning.
The results for EDTA as cleaning agent are presented
in Fig. 5. Cleaning efficiency was increased proportionally with EDTA concentration up to 1% and then
decreased. Figure 6 shows that SDS concentration has
considerable effect on the flux recovery. With increasing
the concentration up to 1%, the efficiency was increased
and then decreased.
Cleaning efficiency depends on the type of the
cleaning agent and its concentration. The concentration
that provides the highest cleaning efficiency can be
considered as the optimum concentration. Concentration
of cleaning chemicals can affect both the equilibrium
and the rate of reaction. Unlike reactions occurred in
liquid phase and reactions between cleaning chemicals
and fouling materials occur in the interface of liquid
100
RR
FR
90
80
Recovery (%)
Asia-Pacific Journal of Chemical Engineering
70
60
50
40
30
20
10
0
0.8
1
1.5
2
EDTA concentration (%w/v)
Effect of EDTA concentrations on cleaning
efficiency (pH = 5). This figure is available in colour
online at www.apjChemEng.com.
Figure 5.
Asia-Pac. J. Chem. Eng. 2010; 5: 691–700
DOI: 10.1002/apj
695
S. S. MADAENI, A. SASANIHOMA AND S. ZERESHKI
90
100
RR
90
FR
70
80
60
70
Recovery (%)
Recovery (%)
Asia-Pacific Journal of Chemical Engineering
RR
80
50
40
30
FR
60
50
40
30
20
20
10
10
0
1
2
3
4
0
8.5
SDS concentration (%W/V)
10
11.8
pH
Effect of SDS concentrations on cleaning
efficiency (pH = 8.5). This figure is available in colour
online at www.apjChemEng.com.
Figure 6.
and a solid fouling layer. The concentration profile of
cleaning chemicals within the fouling layer is a function
of the concentration of cleaning chemicals in the bulk
liquid phase; therefore, the concentration of cleaning
chemicals not only needs to maintain the reasonable
reaction rate (kinetics need) but also needs to overcome
mass transfer barriers imposed by the fouling layer.
In practice, the concentrations of cleaning chemicals
are usually high enough to satisfy the kinetics need. It
is mass transfer that sets the lower boundary for the
concentration of cleaning chemicals.
Effect of pH
Figures 7 and 8 show that cleaning efficiency is quite
sensitive to the pH of EDTA and SDS solutions.
100
RR
90
FR
80
70
Recovery (%)
696
60
50
40
30
20
10
0
5
8
11
pH
Figure 7. Effect of the pH of EDTA solution (1% w/v)
on cleaning efficiency. This figure is available in colour
online at www.apjChemEng.com.
 2009 Curtin University of Technology and John Wiley & Sons, Ltd.
Figure 8. Effect of the pH of SDS solution (1% w/v) on
cleaning efficiency. This figure is available in colour online at
www.apjChemEng.com.
The highest membrane recovery, approximately 100%,
obtained at pH = 11 and 11.8 for EDTA and SDS,
respectively.
At pH = 11, all the carboxylic functional groups of
EDTA are deprotonated (pKa values are 1.99, 2.67, 6.16,
and 10.26).[20,21] The increase in the chelating ability
of EDTA at this pH results in a more effective reaction
between EDTA and sucrose within the gel layer. The
chelating ability of EDTA to remove fouling through a
ligand-exchange reaction increases at higher pH where
more carboxylic groups of EDTA are deprotonated. At
higher pH, the gel layer is easily broken down compared with lower pH which results in a higher cleaning
efficiency. The results imply that the pH of cleaning
solution is a governing factor affecting chemical reaction between EDTA and deposited foulants.
Increasing charge density and polarity of solutes,
and pH will increase electrostatic repulsion between
the membrane and solutes, which reduces the adhesion
between membrane and fouling materials and enhances
the cleaning efficiency.
Because ionization of a functional group depends on
pH, surface charge of a particular membrane is also
pH-dependent. Surface charge of membrane media is
the result of ionization of particular functional groups
existed on the membrane surface (e.g. carboxyl and
amine). In pH range of typical NOMs, most membranes
appear to have a neutral to negative net surface charge.
On the other hand, colloids, particles, and dissolved
organic matters typically carry negative charges and
there is a tendency of electrostatic repulsion between
membranes and those constituents.
One interesting but less clear aspect is how surfactants affect membranes fouling dominated by sucrose.
For the sake of simplicity, let us consider the interaction
Asia-Pac. J. Chem. Eng. 2010; 5: 691–700
DOI: 10.1002/apj
Asia-Pacific Journal of Chemical Engineering
CHEMICAL CLEANING OF REVERSE OSMOSIS MEMBRANE
of a hydrophobic membrane and a nonionic surfactant
with a linear configuration, i.e. a hydrophilic head and
a hydrophobic tail. Because the surfactant is nonionic,
the interaction between the membrane and the surfactant is dominated by hydrophilic/hydrophobic reaction.
Since the membrane is hydrophobic, hydrophobic tail
of the surfactant is preferably adhered to the membrane surface and hydrophilic head is orientated toward
aquatic phase. This arrangement is similar to have the
membrane a hydrophilic ‘coating’, resulting in a more
hydrophilic membrane.
the chemical reaction between the cleaning agent and
deposited foulants has weakened the structural integrity
of the fouling layer.
Physical aspects of cleaning
The physical parameters affecting the cleaning are
cross-flow velocity, temperature, and cleaning time.
Cleaning is carried out in a specific time called ‘cleaning
time’. This is considered as the time required for
membranes performance to exceed 90%. The cross-flow
velocity is the speed of the fluid (chemical solution)
moving on the membrane surface. The temperature
of the chemical agent is another affecting parameter.
These values were constant for previous experiments
considering the chemical cleaning. The cleaning time
was fixed to 1 h, cross-flow velocity to 1 m/s, and
temperature as 38 ◦ C.
Effect of velocity
As shown in Fig. 9, recovery is increased with increasing cross-flow velocity. It is obvious that cross-flow
velocity plays a critical role as one of the operating
conditions for an effective mass transfer. Cross-flow
velocity in the membrane cell mainly controls the mass
transfer. During cleaning, mass transfer of foulants from
the fouling layer to the bulk solution takes place after
Effect of temperature
Figure 10 shows that cleaning efficiency is dramatically increased with increasing the temperature of cleaning solution from 12 to 38 ◦ C. There is no significant difference between cleaning efficiency at 38 and
48 ◦ C.
Both the rate of chemical reaction of cleaning agent
with the deposited foulant (sucrose) and the diffusive transport of foulants from the fouling layer to
the bulk solution is proportional to temperature. At
higher temperature, the swelling of the gel layer
might also have contributed to weaken its structural
stability.[18 – 22]
Temperature can affect both equilibrium and kinetics of a reaction. An indirect effect of temperature
on reaction equilibrium and reaction rate is that elevated temperature generally increases the solubility of
chemical species with a few exceptions (e.g. calcium
and magnesium carbonates). Therefore, temperature can
affect membrane cleaning by changing the equilibrium
of the chemical reaction, changing the reaction kinetics,
and changing the solubility of fouling materials and/or
reaction products during the cleaning. Generally, an elevated temperature promotes better membrane cleaning.
Again, one should check the compatibility of membrane
and other filter components regarding temperature during cleaning.
Growth of microorganisms is very low at high temperatures; therefore, processing at optimized higher
temperatures in the case of microorganism foulants is
recommended. In the studied case with sugar as the
Effect of cleaning temperature on flux
recovery and resistance removal using NH3 solution
(1% w/v). This figure is available in colour online at
www.apjChemEng.com.
Figure 10.
Effect of the cross-flow velocity on cleaning
efficiency. This figure is available in colour online at
www.apjChemEng.com.
Figure 9.
 2009 Curtin University of Technology and John Wiley & Sons, Ltd.
Asia-Pac. J. Chem. Eng. 2010; 5: 691–700
DOI: 10.1002/apj
697
S. S. MADAENI, A. SASANIHOMA AND S. ZERESHKI
Asia-Pacific Journal of Chemical Engineering
◦
100
RR
90
FR
80
70
Recovery (%)
main foulant, 38 C could be suggested for economical
consideration.
Minimizing chemical consumption and using chemicals in a safer manner is one of the important goals
in the membrane industry. Figure 11 shows that using
water as the cleaning agent tends to a cleaning efficiency of near 90% at 48 ◦ C. Water is safe, cheap, and
broadly available and could be considered as a good
recommendation. One of the interesting conclusions of
the current study is the nearly perfect effect of pure
water for removing the cake layer on the membrane surface, especially at higher temperature. Although water
is not considered as a chemical but definitely is a
cleaning agent. The mechanism is simple. The remaining sugar on the membrane surface is dissolved in
water and removed, leading to superior cleaning efficiency.
60
50
40
30
20
10
0
10
20
30
40
50
60
Washing duration (min)
Effect of cleaning duration on resistance
removal and flux recovery using distilled water as a
cleaning agent (pH = 11.8). This figure is available in
colour online at www.apjChemEng.com.
Figure 12.
Effect of cleaning time
Figure 12 shows the effect of cleaning time on cleaning
efficiency using water as a cleaning agent. As shown,
FR and RR have been almost completed within 60 min
using distilled water at 40 ◦ C, but longer cleaning time
has no effect.
The rate and extent of solute transport are functions
of cleaning time and temperature. It is important to note
that cleaning time also affect chemical reaction between
cleaning agent and foulants since contact time (between
cleaning agent and fouling layer) influences the extent
and rate of reaction.
In chemical cleaning, chemicals need enough time
to react with the precipitated materials; therefore, it
is expected that a longer cleaning time will increase
flux recovery. An optimum cleaning time reduces operational cost.
100
90
RR
FR
80
70
Recovery (%)
698
60
50
40
30
20
10
0
20
30
48
Temprature (°C)
Figure 11. Effect of cleaning temperature on cleaning effi-
ciency using distilled water as a cleaning agent. This figure
is available in colour online at www.apjChemEng.com.
 2009 Curtin University of Technology and John Wiley & Sons, Ltd.
Cleaning mechanism
The blocking filtration law for the analysis of filtration behavior in filtration process was developed
by Hermia.[23] Blocking filtration laws formulated for
unstirred no back diffusion and constant concentration,
constant pressure filtration with complete retention of
particles. They provide a procedure on the basis of filtration time (t) and permeate volume (V ) for ascertaining
the dominant filtration mechanism which may change
during the filtration period.[15] For a mechanism of pore
blocking, the plot of exp(t) vs V should be linear. For
cake (gel) deposition, t/V vs V is linear and for internal
pore-closure t/V vs t is linear. The linearity of the plots
is the criterion for interpretation of filtration behavior.
Figures 13–15 depict the blocking laws for the data
of the current experiments. Although all graphs are linear, there are two procedures to justify the dominant
filtration mechanism. First, the coefficient of determination (R 2 ) may be assessed. Greater number for this
coefficient indicates higher linearity of the graph. The
coefficients are 0.9553 for t/V vs V , 0.9430 for t/V
vs t, and 0.9401 for ln(t) vs volume. The numbers
clearly suggest the cake formation as the filtration mechanism. The second procedure for confirmation of filtration mechanism is investigating the membrane surface
using electron microscopy.
Scanning electron microscopy (SEM) can be used
to support the above conclusions. After filtration of
sugar solution, some of the materials in the feed are
absorbed on the membrane surface. SEM micrographs
show that foulants cover the membrane surface (Fig. 16
vs Fig. 17). This clearly shows the enclosure of the
membrane pores. Cleaning must remove at least some
parts of the foulants. Figure 18 represents membrane
Asia-Pac. J. Chem. Eng. 2010; 5: 691–700
DOI: 10.1002/apj
Asia-Pacific Journal of Chemical Engineering
CHEMICAL CLEANING OF REVERSE OSMOSIS MEMBRANE
1.4
Time/volume (min/ml)
1.2
1
0.8
y = 0.0045x + 0.9806
R2 = 0.9553
0.6
0.4
0.2
0
0
10
20
30
40
50
60
70
Volume (ml)
Mechanism determination for filtration of
sugar solution using BW30 reverse osmosis membrane
(t/V vs V). This figure is available in colour online at
www.apjChemEng.com.
Figure 13.
Figure 16. SEM micrograph of BW30 membrane surface fouled by sugar solution.
1.4
Time/volume (min/ml)
1.2
1
0.8
y = 0.0035x + 0.9943
R2 = 0.943
0.6
0.4
0.2
0
0
10
20
30
40
50
60
70
80
Time (min)
Mechanism determination for filtration of
sugar solution using BW30 reverse osmosis membrane
(t/V vs t). This figure is available in colour online at
www.apjChemEng.com.
Figure 14.
5
Figure 17. SEM micrograph of virgin BW30
membrane surface.
4.5
4
3.5
Ln(t)
3
surface after cleaning with NH3 . Removal of most of
the deposited materials from the membrane surface is
clearly observed.
Cleaning dissolves and removes sugar and other
constituents which remain in the membrane matrix or
on the membrane surface. Opened pores are clearly seen
in the micrograph.
y = 0.0391x + 2.179
R2 = 0.9401
2.5
2
1.5
1
0.5
0
0
10
20
30
40
50
60
70
Volume (ml)
Mechanism determination for filtration of
sugar solution using BW30 reverse osmosis membrane
(ln(t) vs V). This figure is available in colour online at
www.apjChemEng.com.
Figure 15.
 2009 Curtin University of Technology and John Wiley & Sons, Ltd.
CONCLUSION
Membrane fouling during food processing is a complex
phenomenon. Membrane cleaning involves both chemical and physical interactions. The chemical reaction
is greatly influenced by the type and dose of cleaning
Asia-Pac. J. Chem. Eng. 2010; 5: 691–700
DOI: 10.1002/apj
699
700
S. S. MADAENI, A. SASANIHOMA AND S. ZERESHKI
Asia-Pacific Journal of Chemical Engineering
Jww Fouled membrane permeation flux (l/m2 h)
Jwc Cleaned membrane permeation flux (l/m2 h)
Rm Membrane resistance (1/m)
Rf Fouled membrane resistance (1/m)
Rc Cleaned membrane resistance (1/m)
RR Resistance removal
P Pressure difference (Pa)
REFERENCES
Figure 18. SEM micrograph of BW30 membrane
surface after cleaning with 1% w/v NH3 solution
(1 h, 38 ◦ C, and 1 m/s).
agent as well as the pH of cleaning solution. In addition,
the fouling layer composition influences the reactivity
of a cleaning agent with foulants in the fouling layer.
Chemical cleaning was employed for cleaning of
BW30 membrane fouled by sugar. NH3 , EDTA, and
SDS showed the best performance for removing sucrose
from the membrane surface. Pure water, with superior
performance, is recommended due to its safety, availability, and cheapness.
NOMENCLATURE
FR Flux recovery
J Permeation flux through membrane (l/m2 h)
Jwi Membrane permeation flux (l/m2 h)
 2009 Curtin University of Technology and John Wiley & Sons, Ltd.
[1] M. Kallioinen, M. Pekkarinen, M. Mänttäri, J. NuortilaJokinen, M. Nyström. J. Memb. Sci., 2007; 294, 93–102.
[2] D.W. Chung, Sh. Higuchi, M. Maeda, Sh. Inoue. J. Am.
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[3] C.T. Egger, G.B. Pfundstein, D.L. Gillenwater. 1970; US
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[10] J. Lindau, A.S. Jdnsson. J. Memb. Sci., 1994; 87, 71–78.
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125–134.
[12] H.F. Bohner, R.L. Bradley. J. Dairy Sci., 1992; 75, 718–724.
[13] A.G. Fane. Proceeding of Symposium on Characterization of
Polymers with Surface, Lappeenranta, Finland, 1997; p. 51.
[14] M. Bartlett, M.R. Bird, J.A. Howell. J. Memb. Sci., 1995; 105,
147–157.
[15] http://www.pall.com/pdf/mtcpaper.pdf.
[16] http://www.lenntech.com/Replacement/Filmtec-BW30-4040.
htm.
[17] A.H. Clark, S.B. Ross-Murphy. Adv. Polym. Sci., 1987; 83,
57–192.
[18] S.T. Moe, K.I. Draget, G. Skjak-Bræk, O. Smidsrød. Carbohydr. Polym., 1992; 19, 279–284.
[19] S. Hong, M. Elimelech. J. Memb. Sci., 1997; 132, 159–181.
[20] J.A. Dean. Handbook of Organic Chemistry, McGraw-Hill
Book Company: New York, 1987.
[21] A. Seidel, M. Elimelech. J. Memb. Sci., 2002; 203, 245–255.
[22] S.S. Madaeni, T. Mohammadi, M.K. Moghadam. Desalination, 2001; 134, 77–82.
[23] J. Hermia. Trans. Inst. Chem. Eng., 1982; 60, 183–187.
Asia-Pac. J. Chem. Eng. 2010; 5: 691–700
DOI: 10.1002/apj
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