Influence of two phase flow on cake layer resistance and flux
enhancement in spiral wound and submerged flat sheet
microfiltration membrane modules
a
T. M. Qaisrani*a, Aiman Fatima, W. M. Samhaberb
Department of Chemical Engineering, Pakistan Institute of Engineering & Applied Sciences,
P.O Nilore Islamabad, Pakistan
b
Institute of Process Engineering, Johannes Kepler University, Linz, Austria.
*
Corresponding author. Tel: +92-51-9248714: fax: +92-51-9248600: email: tmqaisrani@pieas.edu.pk
GRAPHICAL ABSTRACT
Abstract
Gas sparging has emerged as an effective technique for control of particle fouling in different
microfiltration membrane processes. However most of the research work carried out has been pertinent
to hollow fiber and tubular membrane geometries. A little attention has been paid to evaluate the
potentails of gas-liquid two-phase for control of particle fouling in spiral wound and submerged flat
sheet microfiltration membranes. This study focuses on control of particle fopuling by gas sparging in
open channel spiral wound and submerged flat sheet microfiltration membranes. Commercial yeast was
used as test suspension. The Effect of gas sparging on membrane fouling and permeate flux was studied
by analysing the cake layer characteristics like cake mass deposition, cake layer thickness and cake
porosity. The filtration flux and cake properties under various operating conditions, such as cross-flow
velocity, filtration pressure, particle concentration, and sparging intensity are analyzed based on
hydrodynamics. The results of this study show that gas sparging is very effective in control of particle
fouling for both membrane module geometries. It was found that gas bubbling reduced the deposition of
particles on the membrane surface due to which cake layer thickness decreases and resultantly permeate
flux increased substantially. The permeate flux increased with increase in gas sparging intensity. A
maximum flux enhancement of 170 % and 284 % were observed for spiral wound and flat sheet
membranes respectively when gas sparging was applied to the process.
Keywords:
1.
Microfiltration; Gas-liquid two-phase flow; spiral wound; submerged flat sheet;
Cake layer resistance; Flux enhancement
INTRODUCTION
The application of cross flow MF process is increasing rapidly throughout the world for separation of
fine solids from suspension which can not be separated by traditional separation techniques like settling,
sedimentation, centrifugation and filtration. Concentration, clarification and purification processes in
fruit juice, food, beverages & water processing industries involve suspensions with very fine particles.
Cross flow microfiltration and ultrafiltration are most suitable processes for the separation of fine solids
from the liquid. Fouling of the membranes induced by particulate deposition, surface adsorption and
pore blocking is the major limitation which not only hampers the membrane performance but also
reduces the membrane life due to excessive chemical cleaning. There are many proposed techniques
which have been found effective in controlling the deposition of particles on membrane surface. These
techniques are: turbulence promoters (Finnigan & Howel, 1995), rotating membranes (Kronev et al.
1987), Dean Vortices (Millward et al. 1995) along with unsteady flows, such as pulsating flows (Gupta
et al. 1992) and intermittent jets (Arroyo & Fonade, 1993). Although the efficiency of the microfiltration
process is improved by the above mentioned techniques, but the industrial application of such solutions
is limited by technological aspects. The pore blocking and the adsorption of solids can be only removed
either by back-flushing or by application of suitable chemical cleaning agent whereas the external
fouling, that is, formation of cake layer on membrane surface is influenced by hydrodynamic conditions
like flow velocity, applied pressure, particle size and particle concentration etc. The cake layer formed
by particle fouling can be removed either mechanically or by chemical treatment. Mechanical cleaning
is only possible in the tubular membranes whereas the main drawback of chemical cleaning is that it
reduces the membrane life due to aggressive nature of the chemicals against the membrane material
(Blanpain-Avet et al. 2009). This has stimulated an increased interest for use of hydrodynamic
techniques for control of cake layer formation on the membrane surface thereby reducing the use of
chemical cleaning agents in membrane processes. These techniques include back-flushing, pulsatile
flow, gas dispersion, etc. The use of gas dispersion in microfiltration process is getting more attention in
the present day research for its potential to control the fouling by increasing turbulences on the
membrane surface. The use of gas dispersion in hollow fiber was found to be effective in reducing the
fouling and enhancing the permeate flux in hollow fibre (Cabassud et al. 1997) and in tubular
membranes (Mercier et al. 1997 & Vera et al. 2000). As found in the work of M. Mercier-Bonin, et al
(1997), high wall shear stresses and low & uniform transmembrane pressure (TMP) have been found to
be good hydrodynamic conditions to improve the performances of microfiltration processes. Two phase
air-liquid flow generates a slug flow regime in these modules which has been found to be most effective
in controlling the fouling. Cui and Wright, 1994 showed up to a 175% increase in permeate flux in yeast
microfiltration with gas bubbling. Mercier et al. (1997) applied slug flow in tubular membranes to get a
significant increase in the permeate flux. In another study, Mercier et al. 1998 showed 3-time increase in
the permeate flux in ultrafiltration of bentonite and yeast suspension by air dispersion in tubular
membranes.
It is quite interesting to observe that most of the studies on gas-liquid two-phase flow have been
conducted for hollow fiber and tubular membrane modules with feed suspension flowing inside the
membrane module (Ndinisa, 2006). To date, more attention has been given to the application of gasliquid two-phase flow in submerged hollow fiber systems. There is only few published work on
application of gas sparging for fouling control in spiral wound and flat sheet membrane geometries.
Qaisrani and Samhaber (2008) were the first to report the influence of air dispersion on control of
fouling by air dispersion in microfiltration spiral wound membrane module. They used very final
colloidal suspension of starch and bacteria for their study and were able to increase the permeate flux up
to 60 %. In an unpublished work, Cui et al. (2003) found a flux enhancement of 25 % during their
ultrafiltration of dextran through a spiral wound membrane. In case of application of gas dispersion in
flat sheet membrane geometry, there is more published work as compared to that of spiral wound
membranes. Lee et al. (1993) were the first to apply gas bubbling in flat sheet membranes. They
reported that two phase flow enhanced flux for flat sheet ultrafiltration and microfiltration membranes
and then later Meircier-Bonin et al (2000a) also reported an enhancement in flux with air-liquid two
phase flow in ceramic flat sheet membrane during microfiltration of baker’s yeast suspension. Later on
Ducom et al (2002) observed benefits of injecting gas during nanofiltration of oil/water emulsion by a
flat sheet membrane. All these studies were external type applications where two-phase mixture was
pumped along the membrane surface. For submerged flat sheet membranes, the only studies reported are
for the membrane bioreactors (MBR) application for wastewater treatment (Ndinisa, 2006). Cheng &
Lee studied the effect of channel height and membrane inclination on flux enhancement in a flat plate
ultrafiltration membrane module in 2007. This study showed show that the permeate flux increased
significantly with increasing the gas addition in the narrow channel (2 mm height) no matter with the
membrane inclination. In the large channel (10 mm height), the introduction of gas enhanced the
permeate flux effectively as the membrane is installed at 90◦or 180◦inclination Yamanoi. I. & Kageyama
K. evaluated the effect of bubble flow properties between flat sheet membranes on shear stress for
optimizing the hydrodynamic parameters of a membrane bioreactor in 2010. They obtained the results
by using an apparatus consisting of a visible-channel, simulated-flat sheet MBR, in which the membrane
clearance and bubble diameter could be varied. The shear stress on the simulated membrane surface was
measured directly. They found that large bubbles with two-dimensional amorphous shapes between the
membranes could make the shear stress large in comparison to the case of bubbles smaller than the
membrane clearance. Youravong W. et al in 2010 studied the effect of gas sparging on membrane
performance during microfiltration of pineapple juice. They applied a ceramic tubular module for this
study. They found that a low gas injection factor could increase the permeate flux while higher gas
injection factor did not show any benefit on the permeate flux. Gas injection factor of 0.15 gave the best
improvement of permeate flux (up to 138%). Increasing gas injection factor tended to reduce reversible
fouling but not irreversible fouling. In addition, gas sparging also affected the fouling related to the
formation of cake layer onto membrane surface. The density of cake layer increased as the gas injection
factor increased
The spiral wound geometry with open channel spacers generates very high turbulence in the liquid
stream and is considered to be effective for control of fouling. The spacers in spiral wound assembly
create a feed-channel between facing membrane leaves & promote turbulent flow which reduces fouling
phenomena. Osmonics produced first spiral wound element made form Polypropylene in early 80’s with
open channel spacers with product code 52T-Y which are shown in figure 1.
Fig-1 Two views of the first ever spiral wound element with open channel spacers by
Osmonics (now GE Hydraulics and Water Technology, USA)
The spiral wound membrane geometries are considered to be effective against particle depositions as the
shape of the spacers help to generate high shear forces due to high level of turbulences in the feed
channels. These membranes are considered to be the workhorse in membrane world (Wagner, 2001) and
have been patented until recently in 2005. There is limited information available regarding the control of
fouling by gas sparging in spiral wound and flat sheet membrane geometries. According to W.G.J. van
der Meer, the contribution of research on application of two-phase flow in spiral wound geometries is
only 4.62 %. Therefore, the effectiveness of air-liquid two-phase for control of fouling in spiral wound
modules with different types of spacers needs to be studied in depth for finding the effectiveness of this
technique in reduction of membrane fouling and to optimize the hydrodynamic parameters like liquid
flow rate, gas flow rate, and TMP for enhancement of membrane process. Similarly, it is equally
important to investigate the control of particle fouling in submerged flat sheet modules due to their
increased applications in Membrane Bioreactors (MBRs) for wastewater treatment. This study therefore
focuses on control of particle fouling with the application of gas dispersion in spiral wound and
submerged flat sheet membrane geometries. In this study an effort has been made to find out how gas
bubbling influences different cake layer properties like cake mass deposition, cake layer thickness and
cake porosity. The comparison of performances of two membrane geometries can not be established due
to difference in membrane properties and different hydrodynamic conditions.
1.1
Mechanism of Particle Deposition on Membrane Surface
For devising an appropriate fouling control strategy, it is important to understand the mechanism of
particle deposition on membrane surface during filtration process. There are multiple forces which
influence the particle motion during the filtration process. Figure 2 shows such forces and their possible
direction of action on a single particle in a membrane system.
Figure – 2
Mechanism of particle fouling and influence various forces on particle
The adhesive forces which are causing the particle to move towards membrane surface are shown in
down and left-ward directed arrows whereas the forces shown with up and right-ward directed arrows
are lift forces which are forcing the particle to stay away from the membrane surface. The balance of
sum of these forces determines the condition of particle deposition on membrane surface. The particle
will deposit on the surface if the sum of adhesion forces is greater than the sum of lift forces otherwise it
will keep floating within the suspension. This implies that the deposition of particle on membrane
surface can be controlled by enhancing the lift forces in the membrane system. Gas bubbling has the
potential to generate high intensity shear forces along the membrane surface which eventually help to
minimize the particle deposition on the membrane surface.
2.
EXPERIMENTAL
2.1 Materials
Baker’s yeast suspension was used as test suspension. Yeast is composed of almost spherical particles
with a mean diameter of 4.5µm. Yeast was chosen as a model suspension due to its well-defined
granulometric properties. No previous washing of the yeast suspension was carried out in order to
evaluate the fouling capacity of both the yeast cells and the extra cellular macromolecules (mainly
proteins), which could cause more adhesive cake and severe fouling on the membrane surface.
2.1.1
Membrane module
A bench-mounted horizontal spiral wound module and a vertical flat sheet module were used for the
experimentation. For spiral wound geometry, PVDF microfiltration elements of type JX 2540 COS from
Desalination later named as Osmonics and now, GE Water Technology, USA, with an effective area of
1.01m2 were used for these tests. The open channel spacer used was of diamond & ladder shape. The
pore size of the membrane was 0.3µm. The flat sheet module was comprised of 0.016m2 membrane
from Microdyn-Nadir, Germany having a pore size of 0.2 µm. The flat sheet module was designed and
fabricated locally in the institute. The membranes were cleaned chemically with enzymatic membrane
cleaner before start of each experiment and each experiment was conducted at almost same initial pure
water flux for both the membrane systems.
2.1.2
Experimental apparatus and method
Fig-3(a) & 3(b) illustrates the experimental rigs for spiral wound and submerged flat sheet membrane
modules respectively for microfiltration of yeast suspension. The temperature of the feed tank was kept
constant during all the experiments. Positive displacement pumps (eccentric helical rotor pumps) were
used to circulate the feed flow. In spiral wound module, the air was injected at the inlet of membrane
module and at outlet of the pump in order to ensure complete dispersion of air in the liquid for
generating two-phase flow in both membrane modules. In case of flat sheet membrane, air was injected
at the bottom of membrane cell.
Permeate
FI
606
Drain
Retentate
Feed
Tape water
TI
612
Working
Vessel
15 L
Drain
M
PI
600
FI
606
Drain
Air
FI
610
Pump
16,8 m3/h
5-8 bar
Drain
Fig-3(a)
Schematic diagram of experimental set up for microfiltration with spiral
wound element
M
LS
PI
Retentate
Permeate
DI water
Storage tank
M
Filling
point
Air
FI
Pump
150 L/h
5 bar
Container
Balance
Fig-3(b)
Schematic diagram of experimental set up for microfiltration with
flat sheet element
In order to monitor any pressure drop due to air dispersion, a differential pressure
measuring pressure gauge was installed at the high-pressure side of the module. For
turbidity measurements, WTW-Turb 550 turbidity meter was used. Commercial yeast
was used to form the suspension for this study. The average particle size of yeast cell was
found to be 4.5µm and Atom Force Microscopy (AFM) was used to determine the size
and size distribution of the yeast cells. The experiments were conducted at high feed
concentrations of 30 g/L to 40 g/L. The particle size distribution for yeast suspension is
shown in the figure 4. The concentration of solids was calculated as function of turbidity.
The suspension system was passed through a 5-µm filter before processing through the
membrane. Yeast was chosen as a model suspension due to its well-defined
granulometric properties. No previous washing of the yeast suspension was carried out in
order to evaluate the fouling capacity of both the yeast cells and the extra cellular
macromolecules (mainly proteins) which could cause more adhesive cake and severe
fouling on the membrane surface. Pure water flux was measured and recorded before
starting the filtration of suspension. Pure water flux provides the reference to assess the
effectiveness of the membrane cleaning. All experiments were conducted in recirculation
mode. Both permeate and retentate were recirculated in the feed tank while the permeate
flow was measured volumetrically.
40
35
Percent (%)
30
25
20
15
10
5
0
1
2
3
4
5
6
7
8
9
Particle size (um)
Figure-4
Particle size distribution of yeast suspension obtained from AFM
It can be deduced from figure 3 that the mechanism of fouling will be cake formation as
the yeast particles are of the average size well above the membrane pore size. Membrane
cleaning was performed by using a commercially available enzymatic membrane
cleaning detergent Ultraperm-53 by Henkel, Germany. The feed concentration was
measured in terms of turbidity units. For this purpose, a WTW-Turb 550 turbidity meter
was used to measure the turbidity of feed and the permeate.
3.
RESULTS AND DISCUSSION
3.1
(a)
Effect of Feed Flow rate on Permeate Flux
Spiral wound module:
Microfiltration experiments with spiral wound element having open channel spacers were
conducted to check the effect of feed flow velocity on membrane performance. Figure 5
shows the results of these experiments. It was observed that the permeate flux increased
linearly with increase in feed velocity within the range of feed flow rate applied in this
study. Figure 5 also shows that the bulk feed concentration of solids increased with an
increase in cross flow velocity. The increased cross flow velocity caused increased shear
forces along membrane surface deterring the particles to deposit on membrane surface.
Permeate flux
1
2
200
180
160
140
120
100
80
60
40
20
0
Bulk feed concentration
3
4
Cb (NTU) x 20
Flux(L/m 2/h/b)
50
45
40
35
30
25
20
15
10
5
0
5
3
Feed flow rate (m /h)
Figure-5
Effect of feed flow rate on the permeate flux in spiral wound
membrane; ∆P=0.7 bar; C = 40 g/L;
The increased shear forces are due to turbulent flow regime in each capillary for all the
feed flow rates applied. Moreover, the bulk feed concentration in liquid also kept
increasing confirming the impact of shear forces on particles along membrane surface.
The increase in Reynolds No with flow rate is represented in figure 6. Therefore, the
permeate flux kept increasing with increase in cross flow velocity.
5000
4500
4000
3500
Re
3000
2500
2000
1500
1000
500
0
1,5
2
2,5
3
3,5
4
4,5
Liquid flow rate (m 3/h)
Figure-6
Relationship between Reynolds number and liquid flow rate for
spiral wound membrane
(b)
Flat sheet membrane module
In order to see the influence of cross flow velocity on membrane fouling in submerged
flat sheet membrane, experiments were conducted at varying cross flow velocities. The
35
3500
30
3000
25
2500
20
2000
15
1500
10
1000
Permeate flux
5
Cb (NTU) x 20
Permeate flux (l/m 2-h-bar)
typical results of these experiments are shown in figure 7.
500
Bulk feed concentration
0
0
0
0,5
1
1,5
2
2,5
Feed flow rate (l/min)
Figure-7
Effect of feed flow rate on the permeate flux in submerged flat
sheet membrane; ∆P=0.7 bar; C = 40 g/L;
The impact of cross flow velocity on permeate flux and on bilk feed concentration seems
to be similar to that in case of spiral wound element with open channel spacers. It has
been proved by many researchers that wall shear force increases as cross flow velocity is
increased. Hwang et al (1996) developed a predictive model for steady state flux in
which they correlated the steady state flux to be dependent on wall shear stress rate in
terms of cross flow velocity. In this study, they applied moment balance of hydrodynamic
and interparticle forces exerted on a single particle for development of their model. This
study showed that the permeate flux increased with increasing the cross flow velocity of
the liquid for all membrane pore sizes and particle sizes due to increase in wall shear
force. Similar results have been observed in figure 6 that as feed flow rate was increased;
it caused an increase in wall shear force due to which deposition of solids on membrane
surface decreases. Resultantly membrane performance was improved and permeate flux
increased with increase in feed flow rate.
3.2 Effect of Gas Bubbling on Particle Fouling
Experiments were conducted to investigate the influence of gas sparging on particle
fouling for both membrane modules at varying air flow rates. Flux enhancement factor φ
and cake resistance were considered as the indices for decrease in fouling. Flux
enhancement factor, φ is described as:
Flux air
Flux without .air
(% ) =
− 1.100
Whereas the cake resistance Rc was calculated from Darcy’s law as under:
J
=
P
(Rm + Rc )
Figure 8 shows the effect of air dispersion on flux enhancement and cake resistance for
spiral wound membrane whereas figure 9 shows the influence of air dispersion on cake
resistance and permeate flux for submerged flat sheet membrane.
Influence of air dispersion on flux enhancement and cake
resistance for spiral wound membrane at QL = 2 m3/h; ∆P = 0.7
bar; C = 40 g/l.
350
1,E+13
300
9,E+12
250
8,E+12
200
6,E+12
150
5,E+12
100
Rc (1/m)
φ (%)
Figure-8
3,E+12
Flux enhancement
50
2,E+12
Cake resistance
0
0,E+00
0
5
10
15
20
25
30
35
Air flow rate (l/h)
Figure-9
Influence of air dispersion on flux enhancement and cake
resistance for submerged flat sheet membrane at QL = Nil; ∆P =
0.7 bar; C = 40 g/l.
It can be seen from both the figures that injection of air reduced the cake layer deposition
on membrane surface resulting a decrease in cake layer resistance for both the membrane
geometries which caused an increase in the permeate flux as air flow rate was increased.
A maximum flux enhancement of 268% was achieved for flat sheet membrane module at
an air flow rate of 32 l/h whereas a maximum flux enhancement of 170% was attained for
spiral wound membrane module at an air flow rate of 50 l/h. Although the TMP and feed
concentrations were kept same for both modules, however due to varying hydrodynamic
conditions due to membrane geometries, the rise in flux can be compared.
It is also observed from figures 8 and 9 that this enhancement in permeate flux in both
membrane modules is due to decrease in cake-layer resistance associated to continuous
air bubbling during the filtration process. The air bubbles generate very high flow
instabilities and turbulences in the liquid stream which ultimately effect the cake
properties like cake-layer thickness, cake deposition on membrane surface and cake-layer
porosity in a way that the cake-layer resistance is decreased and membrane performance
is enhanced in terms of permeate flux. The influence of air bubbling on cake layer
properties and cake-layer resistance will be presented in some other paper.
4. Conclusions
The increase in cross flow velocity significantly reduced cake layer resistance by
reducing the quantity of deposited solids on membrane surface for both flat sheet and
spiral wound membrane modules. It was observed that the injection of air bubbling
improved the filtration process significantly for both membrane modules by reducing the
cake-layer resistance. A flux enhancement of 170% and 268% was obtained for spiral
wound and flat sheet membrane modules at an air flow rate of 32 l/h & 50 l/h
respectively. Air bubbling is more effective in improving membrane performance as
compared to increased cross flow velocity method in both membrane geometries. The
economic feasibility of air bubbling technique is yet to be established for different
membrane modules for same suspension system and with similar membrane effective
surface.
REFERΕNCES
1. Arroyo G., Fonade C., Use of intermittent jets to enhance flux in cross flow
filtration, J. Membr. Sci. 80 (1993) 117.
2. Blanpain-Avet, P., Migdal, J. F. & Benezech, T. (2009); Chemical cleaning of a
tubular ceramic microfiltration membrane fouled with a whey protein concentrate
suspension – Characterization of hydraulic and chemical cleanliness; J. Memb.
Sci. 337, 153-174.
3. Cabassud C., Laborie S. & Laine J. M., How slug flow can improve ultrafiltration
in organic hollow fibers, J. Membr. Sci. 128 (1997), 93-101.
4. Cui Z. F. & Wright K. I. T., Air sparging to enhance microfiltration in waste
water treatment, Engineering in Membrane processes II-Environmental
Applications II, Ciocco, Italy, (1994) April 26-28.
5. Cui, Z., F., Chang S., and Fane A. G., (2003), The use of gas bubbling to enhance
membrane processes;’ J. Memb. Sci. 221, 1-35.
6. Ducom, G., Puech, F.P. & Cabassud, C (2002); Air sparging with flat sheet
nanofiltration: a link between wall shear stresses and flux enhancement,
Desalination, 145, 97–102.
7. Finnigan S. M, Howel J. A., The effect of pulsatile flow on UF fluxes in a baffled
tubular membrane system, Desalination 79 (1990) 181.
8. Gupta B. B., Blanpin P., Jaffrin M. Y., Permeate flux enhancement by pressure &
flow pulsations in microfiltration with mineral membrane, J. Membr. Sci.70
(1992), 257.
9. Herron J., (2005), Open-channeled spiral wound membrane module, United States
Patent,’
Patent
No:
US
6,902,672
B2’,
http://www.freepatentsonline.com/6902672.pdf; 1-9.
10. Hwang, S-J., Chang, D-J., & Chen, C-H. (1996); Steady state permeate flux for
particle cross-flow filtration. The Chem. Eng. J. 61, pp171-178.
11. Kronev K. H., Nissinen V., Ziegler H., Improved dynamic filtration of microbial
suspension, Biotechnology 5 (1987), 921.
12. Lee, C., Chang, W. & Ju, Y., (1993); Air slugs’ entrapped cross-flow filtration of
bacteria suspension, Biotechnol. Bioeng. 41; 525–530.
13. Mercier-Bonin, M., Lagane, C. & Fonade, C. (2000a) Influence of a gas/liquid
two-phase flow on the ultrafiltration and microfiltration performances: case of a
ceramic flat sheet membrane, J. Memb. Sci. 180 (1) 93–102.
14. Mercier-Bonin M., Lagane C., Fonde C.,’ Influence of a gas/liquid two-phase
flow on ultrafiltration and microfiltration performances: case of a ceramic flat
sheet membrane, J. Membr. Sci. 180 (2000), 93-102.
15. Mercier M., Fonade C., Lafforgue-Delorme C., How slug flow can enhance the
ultrafiltration flux in mineral tubular membranes, J. Membr. Sci. 128 (1997), 103113.
16. Millward H. R., Bellhonse B. J., Sobey I. J. & Lewis R. W. H, Enhancement of
plasma filtration using the concept of the vortex wave, J. Membr. Sci. 100 (1995)
121-129.
17. Ndinisa, N. V. (2006); Experimental and CFD simulation investigations into
fouling reduction by gas-liquid two-phase flow for submerged flat sheet
membranes; Ph. D Thesis, University of New South Wales, Sydney, Australia.
18. Qaisrani, T., M. & Samhaber, W., M., (2008); Flux enhancement by air dispersion
in cross-flow microfiltration of a colloidal system through spiral wound module;
Global Nest Journal, 10, 461-469.
19. Vera L., Villarreal R., Delgado S. & Elmaleh S., (2000) Enhancing microfiltration
through an inorganic tubular membrane by gas sparging, J. Membr. Sci. 165 47.
20. Wagner, J. (2001); Membrane Filtration Handbook, 2nd Edition, Revision 2.
OSMONICS.
21. Y. Wibisono, E.R. Cornelissen, A.J.B. Kemperman, W.G.J. van der Meer, K.
Nijmeijer,’ (2014) Two-phase flow in membrane processes: A technology with a
future’, Journal of Membrane Science 453 566–602
22. Cheng T-W & Li L-N, (2007), ‘Gas-sparging cross-flow ultrafiltration in flatplate membrane module: Effects of channel height and membrane inclination’;
Separation and Purification Technology 55 (2007) 50–55
23. Yamanoi I. & Kagiyama K., (2010); ‘Evaluation of bubble flow properties
between flat sheet membranes in membrane bioreactor’; Journal of Membrane
Science Volume 360, Issues 1–2, 15 September 2010, Pages 102-108.
24.Youravong W., Li Z. & Laorko A., (2010); ‘Influence of gas sparging on
clarification of pineapple wine by microfiltration’; Journal of Food Engineering
96 (2010) 427–432.)