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Investigation of Fouling

Mechanisms Governing

Permeate Flux in the Crossflow

Microfiltration of Beer

P. Blanpain and M. Lalande

Laboratoire de GEnie des Pro&d& et Technologie Alimentaires (LGPTA),

lnstitut National de la Recherche Agronomique (INRA), 369 rue Jules Guesde, BP 39,

F-59651 Villeneuve dAscq, France

Based on a paper presented at the 7th World Filtration Congress, in Budapest,

Hungary in May 1996

The local phenomenology associated with membrane fouling has been investigated experimentally

at laboratory scale for the crossflow microfi ltration (CMF) of beer. Two downstream memb rane

processes were involved: clarification and sterilisatlon of beer. Fouling mechanisms were

interpreted and compared for two types of beer (clarified beer and rough beer), filtered through a

track-etched 0.2 pm polycarbonate membrane. Flux decay was analysed by using the combination of

the constant pressure blocking filtration laws with the measurement of membrane resistances

arranged in series. It was found that for both types of beer the permea te flux was governed by two

identical fouling mechanisms: an internal fouling of pores at the initial stages of filtration that

conforms to the standard blocking model, fo llowed by an external surface fouling conforming to the

cake filtration model. It was shown that the predominant membrane resistance arises from the build-

up of a loosely bound and reversible fouling layer over the membrane surface (representing more

than 80% of the total filtration resistance). Macrosolutes and colloids are likely to be involved both

in the progressive pore plugging and in the external fouling layer (in combination with the yeast

cells cake in the case of rough beer), because of their high tendency to interact with porous

material. Thus the relevance of using the so-called classical filtration laws for the investigation of

fouling mechanisms in terms of total resistance of the membrane in beer CMF has been

demonstrated.

C

ossflow microfiltration (CMF) has been evaluated as

an alternative method for beer processing in order to

obtain colloidal and microbial stabilisation.[-41

Research work has focused mainl y on two essential points

which are inherent in the application of membrane processes

in industry, namely:

J fouling mechanisms responsible for flux decay with

filtration time; and

0 the ability of membranes to be cleaned and regenerated

between two filtration cycles,

At the present time industrial membrane development for

beer filtration is limited both by low permeate flux and by

essential quality component retention. These two phenomena

arise from severe membrane fouling. Fouling in beer CMF

impli es several differen t mechanisms, such as:

0 Gel layer formationt3z 51 and concentration polarisation.t61

0 Cake layer formation.[7S *I

0 Pore blocking and in-depth adsorption/deposition.tg3 lo1

Relatively little work has been published on the local

phenomenology of membrane-solute interactions involved in

beer CMF, which may be because of the complexity of beer,

which contains a large variety of molecular and colloidal

fractions. This paper emphasises the key membrane fouling

mechanisms which are relevant to the crossflow microfiltra-

tion of beer with organic membranes.

THEORY

Blocking filtration laws

Constant pressure blocking filtrat ion laws, revised by Her-

mia,t] have been widely used in CMF for the analysis of

memb rane resistance increase in the course of filtrati on. They

have the advantage of a non-ambiguous interpretation of often

complicated phenomena which limit the filtration rate of a

complex solution like beer (including colloidal and particulate

fractions with a large particle size distribution). Blocking

filtration laws were derived from the dead-end filtration mode,

but they can also be applied in the crossflow filtration mode by

considerin g a constant solute back transport rate from the

membrane into the bulk stream at a stable crossflow velocity.

For constant-pressure filtrat ion, th e blocking filtration laws

can be written in a gener al characteristic form as follows :[l

where t is the filtration time (s), V the filtrate volume (m3), K

the fouling coefficient depending on the initial flow rate QO and

solution properties, and n is a parameter depending on

.filtration law.

In the present paper the convenient linearised form of the

blocking filtration laws has been chosen to fit experimental

data (see Table 1).

Resistances in series analysis

The group of filtration laws presented above is based on

Darcys Law, and expressions are develo ped in order to

model the change in overall hydraulic resistance. At any

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TABLE 1. CHARAC TERISTICS OF CONSTANT PRESSURE BLOCKING FILTRATION LAWS.

Coaespondlng Physical descrlptlon

(param& defined

l lnearlsedform

In Eqn.1)

Complete blocking

model (CBM)

Intermediate blocking

model (IBM)

2

Q = Qo - Kbv

1

1/Q = U/Qo) + Kit

Each particle reaching the membrane

blocks a pore (pore sea ling)

Each particle reaches the m embrane at any location

on the membrane.The proba bility of a particle

blocking a pore isevaluated

Standard blocldng

model (SBM)

Cakefiltration

model (CFM)

1.5

tlv =

U/&o)

+ W&-V

0

t/V = (l/Q01 +

(K/2)V

Porevolume decreases proportionally to filtrate volume

by particle deposition on pore walls

Particlesdepositonto themembranesurface

andafiltercakeforms

instant in the course of the fi l tration process, the permeate flux

J can be described as fol lows:

J2LP

S @t

(2)

where Q is the flow rate, S the membrane surface area, P the

transmembrane pressure, p the dynamic viscosity of the

filtrate and

Rt

the total filtration resistan ce.

The total f i l tration resistance & can be expressed by

adding up several resistan ces in series:

IJ An external foul ing re@tance, &f, located at the

membrane surface and w,hich can result from the concen-

tration polarisation and/or the build-up of a cake layer.

0 A fouled membrane resistance, &, comprising the virgin

mem brane resistanc e plus the internal fouling resistance.

Thus & is represented by & = R,f + &.

MATERIALS AND METHODS

Filtration experim ents for beer processing have been con-

ducted on a dead-end Sartorius filtration cell with a capa city of

200 ml. The schema tic diagram of the experimental f i l tration

unit with di fferent measuring instruments and detai ls has

been presented elsewhere. [W Two types of beer were used:

[7 A clarified (kieselguhr processe d) lager beer containing

less than one yeast cel l /ml, with haze below 1 EBC

(European Brew ery Conve ntion turbidity unit131).

0 A rough beer containing from 5 x lo5 to 1 x lo7 yeas t

cel ls/ml, with haze greater than 10 EBC.

The latter solution was, in fact, a reconsti tuted rough beer,

composed of the clar if ied beer with which a known am ount of

yeast cel ls was mixed. Yeast ceW size was evaluated using a

laser di ffraction technique (Mastersizer S, Malvern Instru-

ments Ltd, UK); yeast cei ls w ere found to have a diameter

ranging from 2 to 10 pm, with a mean diameter of 5 pm. This is

an order of magnitude larger than mem brane pores, which

ensured total rejection of yeast cells by the membrane. It

should be noted that neither solution contains the chill haze

that has to be removed in membrane beer processing.

Howeve r, they do contain the molecular compounds respon-

sible for chill haze, i.e. proteins and polyphenols, together

with dextr ins and ,@-glucans, whose concentration does not

exceed a few m g/l .

A track-etched Nuclepore membrane was used. It was a

polycarbonate membrane of 0.2 pm mean pore diameter, 10

pm thickness and 16% surface porosity. Such a membrane,

with regular cylindrical pores of uniform size and length, was

appropriate to this study. The transmembrane pressure P was

set either at 10 kPa or at 100 kPa. The stirring speed was

constant, and provided by a magnetic sti rring bar at 850 rev/

min. The fi l tration temperature was maintained at OC, as in

the brewing separation process.

The experimental procedure for measuring the resistances

in series was the same as has been reported elsewhere,r2, I41

namely:

0 R, +

R,f

from the value of the quasi-steady-state flux J,,

at the end of the filtration, i.e. (I$,, + R,f) = P/(pJ,,).

0 & from the water f lux J,, after gentle washing of the

membrane surface with Mil li -Q water, i .e. & =

P/(p&,).

This remo ves the reversible external fouling without

disturbing the @ternal mem brane fouling.

RESULTS

Blocking filtration laws analysis

Experimental data have been tested with the l inearised forms

of blocking fi ltration laws presented in Table 1. The minimum

m

E

-z

;

/ (4

Filtration time t (min)

J

(b) Filtrate volume v (ml)

I

Flgwo 1. SBM (a) and CFM (b) plots for rowk boar ml-a Ex-

slzh r

P =

100 kcI; 250 rovldm; 0% PC 0.2 F

s

7/25/2019 Investigation of Fouling Mechanisms Governing

3/5

F

E

z 150

2

.;

3

El00

50

o Experimental

- Calculated

0 20 40 60 80

100 12t

(a>

Filtration time t (min)

250

r

q

Experimental

- Calculated

Fi l trate volume v (ml)

I I

-0 2. SBN (a) l nd CFY (5) plol8 tw ekrl f lod b8w m lwofl thtlon.

hpUh88W dNl888: P = 100 It- 050 rov/mln; 0C; PC 0.2 pm

Nmkpore m8msr8 lw.

coefficie nt of linear regression R2 has been sought either on

the whole duration of the run or part of it.

It has been found tha t for all runs, experime ntal values

support SBM and CFM in the same manner for both clari f ied

beer and rough beer. Typical results of the data analysis are

presented in Figures la and lb for rough beer and in Figures

2a and 2b for clarified beer. F irst filtration confo rms to SBM

(for t imes ranging from 1 to 15 min), then CF M appl ies up to

the end of the run. As can be seen from the Figures, the end of

the SBM period corresponds to the beginning of the CFM

application (transition point A on the Figures).

In contra st with clarified beer, the rough beer experiments

som etime s exhibited a deviation from the linear relation

between

t/V

and

V

toward s the end of the run (point B in

Figure 1 b). This deviation, which occurs in the quasi-steady-

state filtration phase, is thought to be induced by the scouring

effect of the crossflow velocity, which tends to l imit the cake

layer build-up. It is also noted tha t the applicability of the

intermediate blocking law (IBM) cannot be rejected for rough

beer in the initial stag es of filtration (O-5 min).

Resistances in series ana/ysis

Measured resistances in the series &,

Ref

for both clarified

beer (at 100 kPa) and rough beer (at 10 and 100 kPa) are

summarised in Table 2. Measurements have only been

carr ied out for some runs, in contrast with the predicted

values presented in Table 3 , which have been carried out

using all of the runs. Figures 3a and 3b show the experimental

and calculated proportion of mem brane resistan ces for four

filtration runs at P = 100 kPa for clarified and rough b eer,

respectively. Experimental values are derived from the

experimen tal procedure described above, while the calcu-

lated ones are derived from the analysis of recorded filtration

data using the blocking filtration laws .

TABLE 2. EXPERIMENTAL RESISTANCES IN SERIES Ii& ,

Ref

AND MEMBRANE PORE DlAMmER DECREASE Ad.

Tvpe ol beer Ransmembrane Experimental pore Experimental

Experlmental

pressure P,

diameter decrease proportIonof&,

kPa Ad MI

properllon of R+

% %

Clar i f iedbeer 100 0.064

2

98

0122

a 92

0.064 2.9

97s

Roughbeer IO

0317 10.8

89.2

0115

10 90

0306 9 91

0319 11.5 88.5

Roughbeer 100

0161 5

94.6

0143

2 97.6

OS69

5.7 93.9

0371

1

98.6

TABLE 2. PREDICTED RESISTANCES IN SERIES &, & AND MEMBRANE PORE DIAMETER DECREASE Ad FROM BLOCKING

FlhATlON LAWS.

Type ol beer Ransmembrsne Calculated pore

Calculated

Calcolated

pressureP,

diameter decrease

proportlon of &,

kPa

Ad WI

propertlonof I?+

%

%

Clarif ied beer

100

0.085

7

93s

OS 11.6 88.4

0.062

3.7

96.3

0.065

4

96

OS1 17.3

82.7

Roughbeer 10 0.043

24.7

75.3

0.055 31.4 68.6

0.031

20.2

79.8

0.061 36 64

Roughbeer

100 0.081

63

93.9

0.054 33

96.9

0.085 6.9 93s

0.073 4.9

953

0.062

3.7

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3 m

$2 20

q

0

run 1 run2

run3

run4

q

% Rm (experimental) j % Rm (calculated)

(b)

q % Ref (experimental) q % Ref (calculated)

lgurr 3. Expuime ntal and calcuk tad proportlon of mem brans co-

slstan ces in srios l& Ref for okrifiad boor (a) and rough beor (b)

for four filtration runs. Exporlmo atal condltlons: P = 100 kPq 850

rev/mln; 0C; PC 0.2 pm Nucl iepore membrane.

It is clearly seen that, for the two types of beer, the larger

p$rt of the total filtration resistance is represented by a

reversible fouling resistance on the membrane surface (%R,f

> 88). The fouled microporous membrane R, is thus not

mainly responsible for the flux decline, and represents for all

runs a proportion less than 12%. It is noted from Table 2 that

for rough beer the proportio n of R, decreases perceptibly

with the transmembrane pressure

P.

Table 2 also includes the

reduction in the mean pore diameter (ad) derived from the

measured resistance I&. The mean pore diameter decrease

is calculated from

.,=,[,- (+y5]

where do = 0.2 pm, and RQ is the virgin membrane resistance

at the beginning of filtration. It is found that irreversible

membrane fouling leads to a constriction of the pore section

ranging from 10% to 73%. Moreover, at 100 kPa the pore

diameter decrease Ad for rough beer is significantly higher

than that for clarified beer.

Blocking filtration laws allowed us to determine the

predicted proportions of membrane fouling resistances from

the flux decline analysis, and to compare them with experi-

mental ones. The relative proportions of R, and &f are

derived from the value of the quasi-steady-state flux J,, at the

end of the filtration and from the calculated membrane

resistance Ii& at the end of the SBM period (corresponding

to point A in Figures 1 and 2). It is thus assumed in the

calculation that the totality of the external fouling layer

inducing CFM is reversible.

It appears (see Table 3) that the predicted external fouling

resistance I&f prevails for both types of beer (%& > 64 at

10 kPa and %&f

> 83 at 100 kPa). Experimental and

calculated values of Ad (ranging from 0.06 to 0.12 pm) are

close for clarified beer. Furthermore, the proportion of R, is

enhanced at low transmembrane pressure for rough beer, as

has been measured experimentally (Table 2).

Such results are in agreement with those obtained

experim entally from resistances in series analysis. However,

it is seen that for rough beer the calculated pore diameter

decrease Ad is systematically less than the experimental one

(about twice as much). Such a disagreement is believed to

result from several fouling phenomena which have not been

considered here in the SBM and CFM development:

0 A fraction of the external fouling layer R, f over the

memb rane surface is irreversible.

0 Pore sealing occurs at the membrane surface (responsible

for the IBM applicability).

0 Internal membrane fouling continues at the end of the SBM

period.

DISCUSSION

Based on the data presented in this paper, the following

conclusions may be drawn:

(a) For both clarifie d and rough beer, constant pressure

blocking filtration laws confirm the transition from an initial

internal blockage of the membrane (n = 3/2) to the formation

of an external cake layer (n = O), also c alled the secondary

dynamic membrane.

(b) The larger part of the total filtration resistance (on the

basis of the quasi-steady flux .I,, at the end of filtration) is

represented by a reversible fouli ng resistance over the

memb rane surface for both types of beer.

Such fouling phenomena (point a) have already been reported

for beer CMF at laboratory and pilot scale.fer Point (b) is

contrary to some results reported on rough beer CMF with

ceramic membranes,lO, K w for which in-depth pore

plugging was found to be the dominant factor. This may be

related to the specific nature of the track-etched polycarbo-

nate membrane used. Its low surface porosity as well as

smooth surface are favourable to the build-up of a polarised

layer or labile fouling layer on the membrane surface.

Blocking filtration laws have been analysed here in terms

of the total resistance of the membrane. This method allows a

better understanding of the actual phenomena involved in

membrane fouling, and the significance of both the internal

and the external fouling resistances.

The predicted relative proportions of internal and external

fouling resistances from model equations have been found to

be in a fairly good agreement with experimental ones derived

from water permeability measurements (Tables 2 and 3).

Nevertheless, a scattering effect arises from the definition of

the actual nature and reversibility of the surface fouling layer

responsible for CFM applicability. This is especially evident in

the presence of yeast cells, for which calculated and

measured Ad have been found to be quite different.

In particular, the existence of an irreversible fouling layer

at the membrane surface, induced by strong m embrane-

solute interactions, cannot be discarded in our case.t, I

Such a strongly bound surface fouling, composed of deposited

colloids and macrosolutes such as proteins and carbohy-

drates, is thought to lead to the extension of the SBM

application, a phenomenon which has been previously

suggested in the CMF of colloidal suspensions., *, 13 This

foul ing mechanism, which consists of a progressive constric-

tion of the efficient pore section at the surface of the

membrane, is not considered in the SBM development.

From these experiments, it has been shown that fouling

mechanisms have not been significantly modified in the

presence of yeast cells, which are known to have a strong

fouling effect in crossflow microfiltration. It is rather the

dissolved solutes, shared by the two types o f beer (i.e.

colloids and macromolecules) whose size is far lower than

that of membrane pores, which govern membrane fouling. It

results that, even though the first objective in CMF of beer is

the separation of suspended solids, the presence of colloids

makes the process more complex and more difficult to control

throughout one filtration cycle.

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ACKNOWLEDGMENTS

The authors.wish to thank the Terken brewery in Roubaix,

France for providing beer, and the Nord-Pas de Calais region

for financial support.

NO ME NCL A TURE

6 = in i t ia l pore d iameter of membrane, m

.J = permeate f lux, m/s

J,. = quasi-steady-state f lux at end of f i l tration, m/s

.J, = water f lux after washing of memb rane surface, m/s

K

= foul ing coef f icient depending on f i l t ra t ion law (Eqn. 1)

n

= parameter depending on f i l t ra t ion law (Eqn. 1)

P = transmembrane pressure, Pa

Q = fi l trate f low rate, m3/s

R. = init ia l memb rane resistance, mm

R,f = external fouling resistance, m-

R,,, = fouled memb rane resistance, rn-

Rt = total f i l tration resistance, m-

S = memb rane surface area, m2

t

= fi l tration t ime, s

V = fi ltrate volum e, m3

Ad = pore diamete r decrease, m

P

= dynamic v iscosity of f i l trate, Pa s

REFERENCES

1 Wagner, D., Donhauser, S. and Walla, G.: Cross-flow Mikrofi ltration

von Hefe und Bier. Filtration ohne Kieselgureinsatz . 21st Europe an

Brewery Conven tion Congress, Madrid, Spain , 1987, pp. 631-638.

2 Ryder, D .S., Davis, C.R., Anderson, D., Glancy, F.M. and Power, J.N.:

Brewin g experience with cross-flow fi l tration, MB AA Technical

Quarterly, 1988, 25, pp. 67-79.

3 Reed, R.: Advances in f i l tration, The Brewer, Septem ber 1989, 9, pp.

965-970.

4 Walla, G. and Donhauser, S.: Filtration of beer and residual beer

with crossflow microfi ltration. Proceedings of 5th World Filtration

Congress, Nice, France, 1990, Vol. 1, pp. 64-69.

5 Reed , R.J.R., Evans, S .P., Taylor, D.G. and Anderson, H.J.: Sing le

stage downstream processing of beer using pulsed crossflow fi l tration.

22nd Europe an Brewery Con vention Congress, Zurich, Switzerland,

1989, pp. 413-424.

6 OReil ly , S.M.G., Lumm is, D.J., Scott, J . and Molzahn, S.W.: The

applica tion of ceramic f i l tration for the recovery of beer from tank

bottoms and in beer f i l tration. 21st Europe an Brewery Conven tion

Congress , Madr id, Spain, 1987, pp. 639-646.

7 Leno el, M.: Beer recovery from yeast s lurr ies and tank bottoms from

pilot to industr ial results . European Brewery Conven tion, Monog raph

XVI : Separat ions Processes ; EBC Sympos ium, Leuven, Belg ium, 1990,

pp. 128-139.

8 Lenoel , M . , B lanpain, P. and Tay lor , J . : Rat ional des ign of a c leaning

procedure for microfi ltration memb ranes, MB AA Technical Quarterly,

1994,31, pp. 134-137.

9 Burreil, K.J. and Reed, R.J.R.: Crossflow microfi ltration of beer:

Laboratory-scale studies on the effect of pore s ize, Filtration &

Separa tion, June 1994, 31(4), pp. 399-405.

10 Gan, Q., Field, R.W., Bird, M.R., Engla nd, R., Howe ll, J .A.,

McKechnie, M.T. and OShaughnessy, C.L.: Beer c larif ication by

cross-flow microfi ltration: Fouling mechanisms and flux enhan cemen t,

Trans. IChem E, Part A, 1997, 75, pp. 3-8.

11 Hermia, J.: Constant pressure blocking fi l tration laws: Applica tion to

power-law non-New tonian fluids, Trans. Ind. Chem . Eng., 1982, 60, pp.

183-187.

12 B lanpain, P. , Herm ia, J . and Lenoel , M . : Mechanisms governing

permeate f lux and protein rejection in the microfi ltration of beer with a

Cyclopore memb rane, J. Membra ne Sci., 1993, 84, pp. 37-Y.

13 Analy t ica EBC, European Brewery Convent ion (Brauerei und

Getrlnke-Rundschau, Z&rich, Switzerland, 1987).

14 V isvanathan, C. and Ben-Aim, R. : S tudies on col lo idal membrane

fouling mechanisms in crossflow microfi ltration, J. Memb rane Sci.,

1989, 45, pp. 3-15.

15 McKechnie , M.T., Burrell, K.J., Gil l, C., Kotz ian, R. and OSull iva n,

P. : Ceramic membrane f i l t ra t ion of beer . Proceedings of IChemE Food

Process Engineer ing Conference, September 1994, Bath, UK.

16 Gan, Q., Howe ll, J ., Field, R.W. and Eng land, R.: Foulin g and backflush

in beer c larif ication using ceramic m embrane s. Proceedings of IChem E

Food Process E ngineer ing Conference, September 1994, Bath, UK.

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