hien tuong fouling trong dd co protein

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Mebrane Fouling duringMicroltration of rotein

Soutions

Thesis submitted

for the degree of Doctor of Philosophy

at Massey University

New Zealand

by

Veera Venkata Satyanarayana Chiukuri


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Abstract

Membrane ouling during croow microlraion (CFMF o proein i complex

depending upon eed properie operaing condi ion and membrane properie Four

dieren proein oluion (reconiued whey proein BSA lacoerrin and erriin

wih a range o phyicochemical properie were inveigaed a a varey o permeae

uxe under dieren oluion condiion o elucidae ouling mechanim durng

conan ux CFMF

MF ouling uually occur in hree age i adorpion ii pore ouling (pore plugging

or depoiion near he pore enrance and iii ormaion o a urace layer. The

imporance o ep (ii depend upon wheher a proein i compleely or pariallypermeable hrough he membrane.

BSA probably oued ineally r by pore plugging ollowed by ormaion o a

urace layer once all he pore were plugged. Prelraion and he preence o SDS

reduced ouling bu did no preven i uggeing ha aggregae preen in he iniial

eed a well a hoe ormed during MF conribue o pore plugging and o lead o

evere ouling.

Fouling reiance curve or lacoerrn indicae an iniial phae o low ouling by

plugging or depoiion o aggregae. Mahemaical modelling uggeed ha ouling

wa paricularly evere a he pore enrance. A ux wa increaed lacoerrin ormed a

concenraioninduced urace layer.

Ferriin ormed a concenraioninduced gel layer even a relaively low uxe (91

m.h) when he wall concenraion oproein reached he "gel concenraion. The gel

layer wa highly reverible o change in hydrodynamic condiion uch a croow

velociy and ranmembrane preure. Fouling wa more evere wih reconiued

whey han wih reh whey due o he preence o proein aggregae in he reconiued

whey.

The role o he phyicochemical properie o proein in aggregaion and probable

ouling mechanim during CFMF are dicued. Proeinproein ineracion under he

inuence o hear paricularly a higher uxe lead o aggregaion and ubequen

ouling.


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11

Acknowledgemens

Fry I would ke o hank my che upervor Peer Munro or h encouragemen

gudance and hep all hrough h proec. My mmene graude o Alen Marhall

or h drecon eng me o hare h MF expere help n provdng me all he

acle durng my expermen n he plo pan parcuarly howng me how o

run MF rg h help durng preraon run. I am grael o Hander Sngh or

h proen chemry expere and upervon durng proen anay. I have

alway enoyed workng wh my PhD upervory eam.

I am hghy grael o New Zealand Vce-Chanceor Commee or awardng mecommonwealh cholarhp I hank Roya Socey o New Zealand or granng me a

ravel award o aend my r neaonal conerence n Sydney. The nanca

aance by New Zealand Dary Reearch Inue and Maey Unvery o aend

he conerence hghly apprecaed. The nancal aance by New Zeaand Dary

Board oward he preparaon o he he acknowledged

There are o many people who have helped encouraged movaed durng he

proec. I have ganed a new perpecve whch que deren rom wha I ea

durng my prevou undergraduae and pograduae ude. I hank New Zeaand

Dary Reearch Inue or gvng me he opporunty o conduc he expermen

ung conan ux MF rg n her plo plan. I alo hank Maey Unvery or

provdng me al he compung and laboraory acle I hank Taua Co-operave

Dary Company d and New Zealand Phanaceucal or gvng proen powderor he udy.

I am hankl o a o Proen Technology plo plan Mke Bruce Ian Bal

Gordon Alan Shane or her help and conderaon durng my expermen. I

exend my hank o Proen Technology a parcularly Mark Vay Ne Dedre

and Anne or reang me ncely. A Maey Unvery numerou people have

helped me Owen McCarhy Ovaldo Rod Benne Byron Mckllop June Mark

Dorey Seve Glagove and my ellow uden Taa Heavea Ram hank you a.


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111

I wih to acknowledge ta at Indutrial Reearch Ltd, Max, John, Monwar, Andrew

Roberton, Zaid and many other or encouraging me to complete my thei. To all

thoe who have helped in the proect, Tim Winter Tatua, Loui Buchanan NZP

or their ource o inormation on protein literare, Andrew Fletcher NZDRI orhi help duing gain modication to permeate controller and Skelte Anema NZDRI

during ome paticle izing experiment thank you

I thank my riend and their amilie both in Palmerton North and Wellington,

Viay, Bolan, Satya Paumathy, PK Samal, Ranan, Pramod, Khannan Joghee, Raiv

Raman, Vihnu, Venkat Serie Karla, Ananthula, Cherukuri, Rameh and many

other My appreciation to tudent riend and variou inteational club preident

at Maey Univerity Student Aociation, cholarhip ocer, Mr Margaret ilbet

or all their help and riendhip I am gratel to my parent who nourihed me and

made me what I am today and alo relative and riend in ndia or encouraging me

to go overea to do a degree I highly appreciate moral uppot and encouragement

o ta at the college o Agricultural Engineering, ANR Agricultural Univerity,

India

Finally, would like to thank my wie Prauna, daughter Keethy and on Aun or

their patience, love, caring and upport during my tay in New Zealand


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Tabe of Contents

Astract

Acnowledgements 1Tale of Contents

. ntroduction 1

2 Literature review: fouling y protens during microltration 4

2 Inducin 4

2 2 Pein adpin 10

2 3 Cncenain plaiain 1 2

24 Fain a dynamic membane/uace aye 14

2 5 Pe uing pein depiin 1 5

2 5 Fuing wihin he membane uctue 1 5

252 Fuing a he pe enance 1 5

26 Eec eed ppeie 6

26 1 Pein ize 6

262 Aggegain ae he pein 6

263 Secnday aggegain 1 7

264 pH and Inic engh 1 9

26 5 Cncenain 2

2 6 6 Peain 22

2.6 7 Peence mineal and uacan 2227 Eec membane ppeie 23

27 1 Pe ize 23

27 2 Pe mphgy 24

2. 7 3. Miccpy tudie n uing 26

2 Eec peaing vaiable 27

2. . Peeae ux/Tanmembane peue 27

2 2 Shea 302 3 Cw velciy 32


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29. Foulng mechanim 33

2 0 Summary of lieraure review 4 1

2 . Need for rher ude 42

3 Theoretical and quantitative aspects of memrane processes 47

3 1 . nroducon 47

3 2 Polariaion in lraion 47

3 3 . CP model 49

3.4 Membrane foulng model 50

3 4 1 . Foulng reiance model 50

3 .4 2 Cake layer model 5 1

3 .4 3 Pore rericon model 52

344 Proein depoion model 52

35 Proein ranmion calculaion 53

3 .6 Pore blockng law 53

3 6. Pore narrowng model (andard blockng law 54

362 Pore plugging model (complee blockng law 54

3 .6 3 nermedae law 55

3 7. Micellaneou calculaon 55

4 Materials and methods 57

4 1 Membrane rg and preparaion 57

42 Feed preparaon 60

42 1 . Whey proen oluon60

422 Freh cheee whey 6

42 3 . Pure proein oluion 6

4 3 Plan operaion 62

43 Whey proen oluon and reh cheee whey 62

4 3. 2 Pure proein oluon 62

44. Meauremen and analy 63

v


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5. Microltration fouling y reconstituted whey protein solutions 64

5 Introduction 5 2 Results 65

5 2 Overvew o experiments 6552.2. Eect othe permeate ux 65

5 2 3 Eect o onic strength 69

52.4 Naure o the eed material 7

5 2 5 Eect o the membrane pore size 72

526 Reversble versus irreversble ouling resistance 73

5 2 7 Relatonshp beween protein transmssion and 74

oulng resistance

5 3 Dscussion 75

5 3 Foulng on the 00 and 00 nm membranes 75

5 3 Inuence o permeate ux 75

5 3 2. Impact o onc strength 75

5 3 2. Probable oulng mechansms 77

5 3 2 Foulng on the 20 nm membrane 77

5 322 Foulng on the 00 nm membrane 7

5 3 2 3 Fouling on the 00 nm membrane 0

5 3 2 4 Comparson o ouling by resh whey

and reconstituted whey

5 3 2 5 Comparison o oulng behaviour on

00 and 00 membranes

5 4. Conclusions 2

. Microltration fouling y ovine serum alumin solutions 3

6. Inroduction 3

62 Results 4

62. Eect o the permeate ux 4

62 2 Eect o calcium addton 90

623 Eect opreltration and SDS additon 9262.4 Eect o sulphydryl b locking agent 9

6 2 5 Eect o cysteinyl blocked BSA 9

VI


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62.6. Foulng reance veru proen ranmon 1 0

6 2 7. Effec o he membrane pore e 03

63 Dcuon 106

6 3 1 Effec of he permeae ux 06632 Role of calcum n proenproen neracon 07

6.3 3 Effec of hear and proenproen neracon 1 1 0

633 Dulde neracon 1 1

6332 Hydrophobc neracon 1 3

6.3.4 Propoed oulng mechanm 14

6.4 . Concluon 2 1

7 Microltration fouling by bovine lactoferrin solutions 123

7 1 Inroducon 123

72 Reul 123

7 2 1 Effec of he permeae ux 124

72. 2. Effec of calcum 127

72 3 . Effec of ux on rreverble and reverble 12

foulng reance

724. Effec o SDS on oulng 129

7.2 .5 Efec of foulng reance on proen 134

ranmon

726 Efec o he croow veocy 1 3 5

73 Dcuon 139

73 1 . Probable oulng mechanm 3973 . . Proen adorpon 39

732 Proen depoon 40

73 3 Marhall model 144

7314 Surace layer 45

732 Efec o permeae ux and concenraon 146

nduced foulng by aggregae

7 3 3 . SDSProen neracon 1477.3 4 . Summary of he propoed foulng mechanm 149

74 Concluon 150

v


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8. Microltration fouling y ovine ferritin solutions

Inroducon

2 Reu

2 1 Effec of he permeae ux 22 Effec of SDS

2 3 Effec of cacum

24 Effec of foung reance on proen

ranmon

1 5

1 5

52

52155

5

60

2 5 Effec of permeae ux on he reverby 6

of foung reance

26 Effec of cro-ow veocy and ranmembrane 162preure on he reverby of he foung ayer

3 Dcuon

3 1 Probabe foung mechanm

3 1 Adorpon

3 1 2 Ge ayer formaon

3 2 Appcaon of ge mode o predc

permeae ux

167

67

167

6

169

3 3 Effec of ouon envronmen on 174

foung mechanm

34 Summary of foung behavour by ferrn 176

4 Concuon 76

MF Fouling y dierent protein solutions a general discussion 177

9 1 Inroducon 177

9 2 Comparave reu 79

93 Dcuon 6

93 1 Roe of phycochemca propere of proen 6

n aggregaon and foung

9 32 Foung behavour of BSA acoferrn ferrn 190

and whey proen ouon

V


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93 3 Eec o ouling on eady ae proein

ranmiion

93.4 Comparaive ouling mechanim

93 5 Eec o oluion environmen on heouling behaviour o proein

9.4 Concluion

0 Recommendatons for further research

0 1 MF ouling by proein oluion

02 . General

Nomenclature

2 References

1 9 1

192

95

95

97

97

9

99

201

X


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1. Introduction

Membrane eparaton procee have found a wde range of applcaton n the food

and botechnologcal ndutrie. Ultraltraton (U extenvely employed to

concentrate mlk whey proten clar uce wne and proce antbotc. Recent

progre n croow mcrolraton (CFMF ha opened up new poble

applcaton uch a eparaton of ndvdual proten caen tandardaton of

cheee mlk defattng and clarcaton of whey n the producton of hgh qualty

whey proten concentrate (WPC cell recovery from fermentaton broth and terle

ltraton of heat lable proten oluton etc.

Membrane foulng a maor problem retardng rher applcaton of CFMF.

Membrane foulng ha been extenvely uded. Mot of thee tude are pertnent

to foulng of polymerc and mcro ltraton (MF membrane n trreduntrredbatch cell ung contant preure operaton. In foulng occur predomnantlyon the membrane urface where the dynamc membrane control membrane

behavour. In MF evere pore pluggng by proten occur n pte of the pore beng

an order of magntude larger than the proten. In both the above procee foul ng

reult n a declne n ux wth tme and change n electvty of the membrane. The

ncreae n retenton an advantage n U applcaton but a dadvantage n ome

MF applcaton that requre hgh proten tranmon Croow devce are

generally preferred due to reducton n concentraton polaraton and urface foulng

compared to deadend devce

There growng nteret n the ue of ceramc membrane for MF There are three

maor advantage of ung ceramc membrane 1 they are retant to chemcal

cleanng 2 they can be team terlzed and backuhed and 3 they have long

membrane lfe. Wth the advent of ceramc membrane and ther applcaton n the

ndutry there a need to tudy mcroltraton foulng on ceramc membrane. A

membrane materal nuence the foulng proce t not reaonable to apply the

reult obtaned for polymerc membrane to ceramc membrane It uggeted nthe lterature that MF operaton at contant ux better than operaton at contant

preure becaue the former avod hgh permeate uxe n the rt few mnute.


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2

Vey few sudies hae een conduced in cossow mode unde consan pemeae

u coniions usin ceamic memanes

Recen ndamena sudies indicaed ha foulin of MF memanes is inuenced y1 memane popeies 2 opeain condiions and 3 popeies of feed maeia

Seee memane fouin has een epoed in micoaion epeimens wih

oine seum aumin (BSA een when he poe size was much lae han he

poein (Bowen & Huhes 1990 Fanken et al., 1 990 Bowen & Gan 1 99 1 onssonet al 1992a Kelly et aI, 1993 Key & Zydney 1994 1995 acey & Dais 1994onsson et al. 1 996 Muee & Dais 1 996 Heeo et aI, 1 997 The eason fo he

seee fouin appeas o e he pesence of poein aeaes in he feed HoweeHaacek and Bouche (1993 showed ha peeed BSA soluions can si fou he

memane

Key and Zydney (1995 showed ha iniial fouin was caused y he conecie

deposiion of poein aeaes on o he memane suface onsson et al. (1996and Heeo et al (1997 hae poposed wo consequen seps in fouin sufacelockin and cake fomaion duin BSA laion In amos all hese cases foulin

occus pedominany on he memane suface y poein aeaes On he ohe

hand Fanken et al (1990 Bowen and Gan (1991 1992 and onsson et al (1992ahae suesed ha shea wihin he memane poes causes he poein o deposi

acey & Dais (1994 and Muelle & Dais (1996 duin foulin sudies usin

BSA on 02 m MF memane hypohesised ha poein molecues o aeaes

deposi a he poe walls o mouhs. Bowen and Gan ( 1 993 and Masha et al.(1997 hae suesed ha fouin duin MF of poein souions is mos ikey due

o he ineacion of poein wih he poe eomey a he poe enance Thee is

consideale deae whehe foulin is iniiaed on he memane suface o wihin

he poes o a he poe enance

Alhouh he aoe sudies ae some undesandin of he possile mechanisms of

poein foulin hee ae sill conicin iews aou he undeyin pinciples ha

oe poein fouin duin MF


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3

he pesen sudy was undeaken as an eension of Masha (994 P hesis

wok which invesiaed wo aspecs of MF fouin, one in which he feed conained

poeins considealy lae han he memane poes (casein miceles) and he ohe,

in which he poein (lacoouin) was much smae han he poes wasdemonsaed ha a casein "e aye fomed on he memane suface caus

sevee fouin duin MF of skim mik on a 0 m poysufone memane (Mashal

et aI 1 996 Duin MF of -lacoouin on 50 and 00 nm ziconium oide

memanes a hih ues, poein-poein ineacions a o nea he poe led o poe

naowin and he evenual eenion of he poein y he memane (Masha et aI

1 997 he wok sessed he impoance of feed popeies on fouin and

ecommended he wok usin a ane of poeins of diffeen molecua weihs o

invesiae he effec of physicochemical popeies of poeins on foulin

mechanisms

he oecive of he pesen wok was o invesiae he fouin ehaviou of poein

soluions conainin whey poeins o ovine seum aumin o ovine lacofein o

ovine feiin on ceamic memanes duin CFMF unde consan pemeae u

condiions he effecs of poein size in soluion and peeamens such as

peion, aiion of calcium an addiion of a poein dissociain aen (sodium

doecyl su fae, SDS) on foulin mechanisms wee invesiaed In paicua he

effec of pemeae u and poein soluion envionmen on fouin ehaviou wee

invesiaed


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2. Literature review: fouing by proteins during microtration

2 Introducton

Mcroltraton membrane foulng has been a maor problem n the process ndustry

Even though the pore szes n MF membranes are generaly over an order of

magntude larger than the characterstc sze of the proten there s consderable

expermental evdence that severe foulng occurs and protens play a crtcal roe n

MF foulng. A number of foung mechansms may arse dependng upon operatonal

varables, feed and membrane properes. embrane foulng n genera has been

extensvely studed and has been revewed by Fane and Fel (1987), Nlsson (990)

Marsha et (993) and Belfor et (1994). However there s currently ttle

nformaton avalable on the foulng behavour of protens on ceramc mcroltraton

membranes under constant ux and cross-ow condtons rotens are compex

molecules and a greater understandng of ther conformaton, stabty and nteractons

n dfferent membrane envronments and under condtons of shear s cruca to

understand and control foulng n these processes. The present lteraure revew

buds on the revew of arshal et (1993) and focuses on more recent work

manly related to membrane foulng durng F of proten soutons.

It s common to nd varous terms n the foulng lterature use erent authors

dependng on ther background, as there s no unversaly accepted termnology.

Foung s the deposton of solute partces both on the membrane surface and/or n

ts pores leadng to a change n the membrane performance (Gekas, 1988). For the

purpose of ths revew, a broad categorsaton s made under the terms adsorpton

deposton aggregaton and pore foulng (whch ncudes pore pluggng and pore

narrowng). The term adsorpton s rreversble atachment of a macromolecule due

to nterfaca forces an s lmted to a monoayer thckess Ths s dfferent from

deposton whch s aso rreversble but occurs by a varey of mechansms n

addton to adsorpton. Proten deposton ncludes the proten adsorbed under statc

condtons plus addtonal proten strongly assocated wth the membrane durng

ltraton Aggregaton s a term used to refer to a varety of protenproten

nteractons. The term pore puggng s the physca attachment of a macromoecue

at the pore openng or wthn the pore and s consdered synonymous wth pore

blockng /sealng /bndng /cloggng However the term pore brdgng means that


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5

he pore is plugged by more hn one molecule by some sor of ggregion or

colescence of proein Pore nrrowing or pore consricion is process by which

inel pores of he membrne will hve reduced pore dimeer due o iniil

dsorpion nd subsequen deposiion of proein on he pore wll

Bowen nd Huges 1990) invesiged he deposiion of BSA on luminium oxide

MF membrnes They suggesed h deposiion occurred in wo phses The rs

phse of rpid deposiion ws he resul of monolyer dsorpion on o he membrne

surfce nd he BSA ws very srongly bound The second less rpid phse ws he

building up of relively wekly bound mulilyers of proein They concluded h

he level of proein deposied incresed if permee ux incresed possibly due o

incresed collisions wihin he pores resuling in greer inercion Clrk et l

1991) during consn pressure lrion of BSA on 100 nm lumin membrne

hypohesised h he fouling ws due o dsorpion reled pore plugging bu did no

differenie fouling by dsorpion nd pore plugging Proein deposis hve lso

been idenied wihin he mebrne srucure in MF Ai et l 1991 b) showed

h csein boh formed lyer on he surfce of he membrne nd penered he

membrne srucure o deposi wihin he pores during MF using 08 m membrnes

In mos MF processes rnspor of proein hrough he membrne is reuired Bowen

& n 1993) Inercions of proeins wih he inel pore srucure of he

membrne cn hve subsnil inuence on he effeciveness of such seprions

I hs been shown h effeciveness of selecive proein lrion cn be drmiclly

lered by ppropriely conrolling elecrosic inercions hrough chnges in pH

nd ionic srengh Sksen & Zydney 1994)

Belfor et l 1994) presened differen possibiliies of fouling mechnisms in MF

Fig 21) depending on he proein o pore size rio They dened pricle dimeer

d nd pore dimeer o illusre possible fouling mechnisms When d hepricles could ener os pores nd could conceivbly close smller pores hereby

reducing he open crosssecionl re for ow


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FNG A

CSB: PORELUGGINGI

d-p

d CASC: GUAKE LAYERFMlO

d Dn =na

TBUON

.L.t.

s r pvw i r A

(,) :"') Vw "0. :

POz Sf

6

Figure 21 . Possible fouling mechanisms during membrane ltration Belfort

. 1994)

This is shown schemticlly s oss of poes om the poe size distibution nd

decese in the slope of the ux. A simi effect occus when d nd some poese ost becuse of poe plugging. Fo the cse when d the ptices e unbeto ente most poes nd hence deposit on the fce of the membne esuting in

cke/ge build up Assuming the poe size distibution of the membne emins the

sme s fo clen membne the shpe of the poe size distbution of the ge/ckewil most likely chnge with time nd tnsmembne pessue (TMP Compction,

engement nd deposition of smle pticles in the poes of the gel/cke coud

expin this In this cse, the slope of the ux vesus TMP cuve will decese with

incesing pessue. This is oen obseved expeimentlly nd hs been ttibuted to

incesed deposit thickness (Btt et a 1970 nd o osmotic effects (Jonsson

984.

Muele nd Dvis (1996 pesented dt tht showed occuence of inte nd

exte fouing duing MF of BSA unde constnt pessue conditions (Fig 2.2

They epesented fouing by totl esistnce which they clcuted using R

P/.J The slope of the esistnce cuves ws used to intepet whethe fouling ws

intel o extel.


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501

WZ 30+12


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z

>

0

08

0

0.4

02

05

Prateln

o BA

e Obi 6 aobin

P e 6-ln

Fro Tm ()

90 12

Figure 23. Permeae ux loss (o anel) and rae of ux decline (boom anel)during MF of BSA, ovalbumin and lacoglobulin hrough 0.22 m PFmembrane a a consan ressure o 14 Pa and 00 rm. Solid lines are modellines (Key & ydney 7

Ty prpsd a mdl a nsidrd surfa arg inrains and drag fr du

nviv ux In is as fuling urs prdminanly in frm f a surfa

layr

Rnly Marsall et a (199) av usd rlainsip bwn fuling rsisan

and prin ransmissin luida fuling baviur f laglbulin (Fig 24)

Ty pld fuling rsisan daa frm all xprimns prfrmd a diffrn

nsan prma uxs agains rrspnding prin ransmissin valus Ty all

fall ls a singl urv a rprsns a dras in prin ransmissin

ninuusly wi an inras in fuling rsisan Ty dvlpd a mamaial

mdl wi swd a prin dpsiin urs prdminanly nar pr

nran

8


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9

8

\+

6 + D.

.

,

.

40 60 70 O 0 100F U x )

Figure 2.4. Proein ransmission versus fouling resisance for a 0 nmmembrane during MF of acoglobulin. The line is a model redicion, deailsof which are given in he ex (Marsh all . 997

Fouling whih esults in deline in peete ux nd poo seletivity is due to

viety o mehnisms The ux deline is used by sevel phenomen in o ne

the membne In genel, the ux deline is used by deesed diving oe

n/o n inesed esistne. The esistne duing lttion poess n be

gouped into , R p R nd the esistne o the membne itsel Fig 25)Poes n beome plugged by the solute Rp nd dsoption o the solute on to the

wlls o the poes nd o the membne sue ) p is used by phenomenon

known s 'onenttion polistionP) whih is umultion o etined

moleules ne the membne sue Thee hs been howeve onsideble

debte ove how P edues the peete ux One gument is tht the

onentted lye ne the membne oes esistne to peete ow nd the

othe gument is tht the osmoti pessue II) indued by the umultion o

momoleul solutes t the membne sue eetively deeses the

tnsmembne pessue nd hene the peete ux


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R

R R

m

R

0

0 0 T

R

R : 0

: aza

igure 2 Possible resistnces to permete ux in membrne ltrtion nden Berg, 988

Wen te concentraton at te membrane nterface reaces a certan eve dependng

on te tpe of feed te concentrated soton ma cange nto a ge aer" wt a

resstance R n ts revew epermenta evdence on eac penomenon casng

decne w be presented separate and ten te most mportant factors tat

nence MF fong b protens w be dscssed

. Proten dsorton

Adsorpton s a termodnamca spontaneos process and s probab te rst step

n te fong process t s we known tat protens adsorb at qdsod nterfaces

and te amont of proten adsorbed depends on te membrane srface caracterstcs

(dropobc dropc and srface carge) te proten tpe and te soton

propertes (pH onc strengt and concentraton) n statc stdes Mattasson

(1983) on pomerc membranes and Cark et (199) on an amna membrane

ave fond tat BSA adsorpton ncrease to a satraton vae wt ncreasng

soton concentraton and te adsorpton was mc greater near te proten

soeectrc pont of pH 49. Bowen and Gan (991) drng MF of BSA sng 0 m

capar pore amnm ode membranes fond tat proten adsorpton

corresponded to appromate a monoaer However te oss of permeabt de

to adsorpton was sbstanta ess tan te decrease n te rate of permeaton drng

te traton of proten soton Bowen and Gan (1993) sng posfone MF

membranes nder dnamc condtons fond tat te membranes adsorbed on 3/4

0


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11

of a monoayer of he enzyme yeas alohol dehydrogenase YADH) The obsered

derease in permeaion rae was de neiher o onentraion polarisaion nor o

proein adsorpion alone. Howeer i was anied sing he sandard bloking

raion law whih desribes a derease in pore ome de o deposiion of proein

in he inerior srre of he membrane Persson et al. 993a) sing laogobin

on for differen poymer MF membranes also fond ha proein adsorpion

orresponded o a monoayer on and in he pores of he membrane.

Proein adsorpion was fond o be sighly reded on hydrophili membranes sing

BSA (Bowen & Gan, 1991) and laoglobin Persson et al 1993a) Akhar et al(1995) reaed PVDF and CA membranes wih a srfae graing of

meharyoyoxyehyl phosphoryholine They showed ha membranes wih his

oaing ha inhibied proein binding improed he iniia x in boh he membranes

inesigaed, b proed o be more effeie for PVDF membranes in reding an

86% x deine o 10% han for he CA membrane in reding a 48% x deine o

17% dring MF of BSA. This improemen in membrane performane was

onomian wih a redion in proein foing on he srfae and wihin he marixof he oaed membranes as assessed by ransmission eeron mirosopy For a

typial MF membrane (wih a pore diameer of 0.2.0 m), he x redion ased

by monoayer adsorpion of a proein sh as BSA is ony 212 % Befor et al

1994) Howeer, a larger peren redion in x wod be expeed o or pon

adsorpion of ery arge maromoeles or aggregaes

A eas in MF, de o reaiey larger pores, x deine de o foing an be

aribed in a smal par o proein adsorpion of a monolayer, b he major

onribion is from proein deposiion nder dynami ondiions. Howeer

adsorpion of proeins on he membrane pays an imporan par in he iniia sages of

foling pariarly in he ase of inea foling whih is a more dominan form of

foling wih MF membranes.


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To coclude pote adsopto at the pote-membae teface s almost

evtable ad s ueced by a umbe of paametes. oweve t ca be mmsed

by sutable membae suface modcato techques o choosg membaes that

ae vey low adsobes-maly used pocessg of hgh value potes. At least MF though adsopto aloe may ot affect ux substatally but t ca play a

mpotat ole the subsequet foulg.

2.3. Concentrtion olristion

2

The covectve taspot of solute towads a membae U ad evese osmoss

(RO) causes t to accumulate at the membae suface a cocetated boudaylaye leadg to a loweg of ux elatve to that of pue solvet U & R,

cocetato polasato bulds up quckly (Chudacek & Fae, 984 Fae 986;

Ama et a 99) ad s a cto of the hydodyamcs the membae system.

t s depedet of the popetes of the membae f eteto s 00%. t s

mpotat to dstgush betwee cocetato polasato ad foulg Foulg s

the couplg of deposted mateal to the membae though the temedate step of

C whch st causes a accumulato o cease cocetato o the membaesuface (Mashall et a 993). The loss of ux due to C s evesble i.e. upo

ushg of the membae wth wate the poto of the ux loss ue to C s estoed

ad whee foulg s sgcat the ux etus to ts ogal value (Mashall &

Dau 995) O the othe had loss of ux due to foulg s geeally evesble

i e upo ushg wth wate the poto of ux loss due to foulg s ot estoed

utl afte the membae has bee chemcally cleaed

The cotbuto of C to foulg s domat UF wheeas ts effect s elatvely

less MF stuatos whee thee s eteto of macomolecules ethe tally o

late the pocess due to poe foulg C ca play a mpotat ole eve MF,

cotollg ux ad pote tasmsso.


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13

Bot of tese effects sould be eggble fo te ltato of pote soutos

toug te cea M membaes sce tese age poe membaes ae essetay

o etete to most potes Howee tese peomea ca be mpotat fo

fouled membaes due to pote deposts (pog & Zydey 99; Moczuk &Zydey 992) smotc pessue may become mpotat fo a foued membae

ee M

Te accumulato of soute ea te membae suface s geeally descbed by te

m model Te lm model assumes tat te cocetato bouday laye esdes

wt a t lama lm at te membae suface ad tat all mass tasfe takes

pace by cka dfso pepedcula to te membae Te m s dyamc

atue Some estgatos (fo eg Nakao et al 979 saacso et al 980

Josso 984) ae used te osmotc mode to expla te ux decle Te osmotc

model assumes tat esstace to ow esdes wt te solute accumulated ad s

caused by osmotc pessue Ufotuately tese models we apped to M of

collod patcles udepedct te ux obseed Te easo fo ts ux paadox"

(Romeo & Das 988 990) at least fo collods appeas to be due to ceased

back-taspot caused by ydodyamc effects ke ) sea duced dfso ad 2)

lateal mgato due to etal l (See efeeces Belfot et al (994) fo moe

detas) addto to dfso Alteate models suc as sea duced dfso

ad ateal mgato models ae bee poposed to descbe te taspot of patces

away fom te membae Romeo ad Das (988 990) cosde ts ssue

moe detal Romao & Das (988) ad Lojke et a! (992) eewed te aous

modes tat ae bee poposed to expla ts beaou Recety a ued model

combg gel ad osmotc models as bee poposed to pedct ux (Battacaee et al 996). Howee appcato of tese modes to

macomoecula solutos s questoabe as ux decle M s pedomaty due

to tea foulg


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24. ormtion of dynmic membrne/surfce lyer

Several researchers have reported foation of a dynmic layer by proteins dring

R and UF Lim et al. 971; Glover & Brooker, 974; Lee & Merson, 975, 976a;

Kim et al 1992; Marshall et aI 1996). This is generally expected as the protein sieis larger than the pore sie of the membranes sed in their stdies Srprisingly, a

dynamic layer was reported even dring MF for example, sing skim milk on a 02

m membrane Attia et al 991a) Casein micelles foed a srface layer as they

are of similar sie to the membrane pores. Srface layer foation was observed

even dring MF of proteins which are mch smaller than the pore sie mainly dring

the later stages of the processing de to complete loss of inteal pore area Jonsson et

aI 996; Marshall et aI 1997). Generally in MF once a srface layer has foned, it

redces the protein transmissions to a level that wold be deteined by the porosity

of the deposited srface layer.

Interestingly in some cases sing nonprotein feed streams, a dynamic membrane had

a positive inence on the membrane perfoance, for example, Cakl and Miklek

1995) dring MF of latex particles of broad sie distribtion sing almina

membranes showed that an adeqate secondary membrane can improve x by

rotectin the membrane from ore lgging and therefore contribtes to a higher and

more stable x also see section 2.9). AMalack and Anderson 1996) showed that

the dynamic membrane foed on the rimary membrane can be sed as an anti

foling techniqe They foed a dynamic membrane sing potassim peanganate

KMn) with particle sies less than the pore sie of the primary membrane. Pore

narrowing pore bridging by the particle and precipitation on the membrane srce

were reported to be the mechanisms of dynamic membrane foation. Improved x

and trbidity were obsered with increased concentration of KMn when this

dynamic membrane was sed to treat a secondary eent from waste water.

Kberkar and Davis 1998) reported that a secondary membrane foed by yeast and

BSA mixtre improved BSA transmission compared to when BSA alone was

microltered on a 0.07 m celllose acetate membrane

4


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25 Pore ouling or protein deposition

25 ouling within the membrne structure

usch and Wach 982) showed eecton micoaphs of the top suface of a 3 m

Nucepoe memane ae ltation of atexstyene paticles Even thouh the

paticles wee ony onetenth of the poe diamete, they inteacted with the poe wals

of the memane, thus fomin aomeates that nally locked the poes. A

nume of investiatos have found potein adsoption within the memane poes

(Nakao et al 1988 Dejmek & Nisson 989 Hanemaaije et al 1989 Bowen &

Gan, 99) Matsumoto et al 988) compaed esistance due to inteal and suface

laye fouin with ovalumin 44 kDa) on ceamic memanes With low veocities

(amina) and with the 02 m and to a lesse extent the 08 m memane, suface

aye fouin dominated With lae poe sizes 5 3 m) poe pluin appeaed

to e the pedominant foulin mechanism With hih velocities, fo al fou

memanes, poe pluin was pedominant Bowen and Gan 993) used a thin m

composite polysulfone memane duin MF of YADH. hey suested that

deposition of macomolecules inside the poe stuctue was an impotant mechanism

fo ux oss. To conclude, thee is expeimental evidence that potein deposits withinthe memane poes as well as on the suface

252 oul ing t the pore entrnce

Visvanathan and Ben Am 989) suested that in the ealy staes of tation,

cooids can deposit on the memane suface in etween the poes and thus

accumuate ate, aeates of cooids can fom ides ove the poe openins,

esultin in patial lockin of the poes A smae poe stuctue is then availae

fo susequent cooids to deposit This idin of aeated colloids leads to the

eventual fomation of a lm of colloids on the memane suface Bowen and Gan

199) poposed that potein deposition occus in the immediate vicinity of the poe

entance due to the hih shea caused y the local pemeate ows. Tacey and Davis

1994) duin MF of BA solutions usin tacketched poycaonate memanes

found that the poe adii deceased on the feed side ut not on the pemeate side,

indicatin that the foulin laye is not evenly distiuted thouhout the poes, ut

instead concentated nea the poe entances. Masha et al 1997) duin MF of

lactoloulin showed that fouin occued ove a smal pat of the memane

15


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6

pobably at the poe entance Km et al 1997) have also epoted BSA oulng data

that suppots poten deposton at the poe entance also see secton 27.3)

To summase, a numbe o studes have hypothessed that poten deposton occus

nea the entance o the membane poe

2.6. Effect of feed properties

2.6. . Protein sie

Pdanos et al 996) lteed 5 deent potens pepsn, BSA, lpase, globuln

and nvetase) wth molecula weghts o 36, 67, 80, 150 and 270 kDa on 002 m

patally etentve Anopoe membanes They ound that as the molecula weght

nceased, thee was a declne n u. Howeve, nvetase showed a stange

behavou; t was the bggest poten, but ts u declne cuve was between those o

lpase 80 kDa) and BSA 67 kDa) Ths behavou was attbuted to the ato o

molecula and mean poe szes whch s >1 o nvetase and also t s the only poten

studed that s totally etaned by the membane wheeas othes gave etentons below

70% Unde the same condtons o ltaton, nvetase appeaed to have blockedvey ew poes educng the u only a small amount wheeas lpase and -globuln

could block a lot moe poes and conseuenty educe the pemeate u substantally

Gell and Davs 996) ound that BSA and lysozyme dsplayed only nteal

membane oulng on 0.2 m PS and PC membanes wheeas ovalbumn hghe

molecula weght) ehbted an ntal phase n whch nteal oulng domnated

ollowed by a suace laye on the same membanes ndcatng the eect o poten

sze on oulng behavou

2.6 .2. Aggregtion or stte of the protein

Poulot et al 1994) dung MF o whey potens usng alumna membanes ound

that oulng was stongly dependent upon the state o the potens n the eed They

concluded that pH and onc stength ae the mpotant soluton popetes that

nuence aggegaton o the poten theeby aectng poten oulng Bowen and

Hall 1995) obseed that the ate o taton and tansmsson o YADH though an

MF membane depend on the molecula state degee o aggegaton o the enzyme n

soluton) Kelly et al 1993) showed that BSA oulng was assocated wth the


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7

deposton of trae quanttes of aggregated anor denatured BSA wt tese foulng

spees servng as ntaton stes for foulng durng strred ell traton troug 0

m membranes e foulng tendeny of dfferent BSA preparatons was gly

orrelated wt te onentraton of BSA dmers and oter g moleular wegt

spees present n tese BSA solutons Gsan et al 993 found tat durng MF of

pretreated wey usng arbosep M4 membranes protens and alum pospate

aggregates were responsble for foulng w nreased aordng to te omplete

blokng" ltraton law Maa and Hsu 99a reported tat wen zn ons were

added to ndue aggregates te foulng tendeny of reombnant uman growt

ormone rGH solutons nreased wt nreasng amount and sze of te

aggregates ndatng tat te aggregates present before ltraton mgt be

responsble for membrane foulng n summary tere s onsderable expermental

evdene tat proten aggregates are responsble for severe foulng durng MF

2.6.3. Secondry ggregton

Suk et al 984 ypotessed tat aggregaton of proten BSA s possble at g

MP due to onvetve ow leadng to supersaturaton of membrane surfae wtproten ey proposed tat aumulaton of solute provdes a reseror of moleules

on te membrae tu raall x ro moue due to aeaton and

oulaton on te memrane surfae Later Suk et al 98 attempted to model

UF foulng by assumng tat proten aggregated n te onentrated laer next to te

membrane based on oulaton teory Usng data avalable for BSA te ux was

alulated as te aggregated layers bult up Inreased ux delne at ger feed

onentratons was predted by te model However te model does ot allow for

dfferenes n te membrane propertes

Mereles et al 990 usng lgt satterng analyss and turbdty measuremets

sowed tat BSA fomed aggregates of large sze durng UF at 22 ey sowed

tat at a temperature of 1 te ger te gear pump speed te eaver te

deaturaton w tey nterpreted usg trbdty measurements In a later

publaton Mereles et al 99a reported tat te rate of proten denaturaton

nreased wt temperature rossow veloty FV and tme of proessng ey

suggested tat under g onentraton polarsaton denaturaton an our n te


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odary layer if the wa cocetratio exceeds 40% hey attrited BSA foig

to partial deatratio eadig to aggregatio XJiag et al (1995) drig dead ed

MF sig two eraes i series hypothesised that at roo teperatre (22C) ad

with a pisto pp givig high shear coditios, BSA is ssceptie to deatratio

casig a rapid rise i pressre drop drig costat rate ltratio. hey attrited

the pressre drop to adsorptio aloe eglectig pressre drop de to pore plggig

y aggregates. Blapai et al (1993) drig MF of eer reported foratio of loca

aggregates of acro sotes over the pore opeigs eadig to foig

Ki et al (1992) coclded that aggregate foratio drig is exacerated ycoditios like erae srface roghess ad high covective ows cose to the

erae srface hey fod foratio of aggregates with higher iitial x eraes, t ot o the ower x eraes. hey attrited aggregatio to

coforatioa chages i the BSA olecles associated with the high shear rates

that exist ear the erae srface. hey hypothesised that these cofoatioal

chages exposed hydrophoic regios o the BSA oeces which the iteracted to

for arge protei aggregates at the erae srface.

Maa ad Hs (1996a) sggested that folig was ore attrited to the aggregatio

takig place i the lter pores drig ltratio (secodary aggregatio) tha to the

aggregates preset efore tratio. Foratio of BSA aggegates drig acta

stirred cell ltratio was hypothesised y Kelly ad Zydey (1995). Josso et al

(1996) hypothesised isitu geeratio of BSA aggregates drig ppig. It wassggested that high deatratio de to ppig eads to foratio of aggregates that

caot peetrate ito pores t for a cake

he effect of operatig coditios o protei aggregatio drig UF was ivestigated

y Ki et al (1993a) They hypothesised that high shear rate coied with high

protei cocetratio ehaced protei aggregatio. Havacek ad Bochet (1993)

deostrated that protei sotios iitially free of aggregates ca ipair a MF

process, if deatratio ad aggegatio coditios are preset i the syste. Protei

aggregates ca for y a variety of echaiss. Persso ad Gekas (1994) i their

18


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reew, sggested that aggregation of macromoleces IS de to their exible

secondary and tertiary strctre

In concsion, protein aggregates in the feed or those generated dring processing

appear to pay an important role in the severe foling observed with MF membranes

264 pH nd ionic strength

he inence of p and ionic strength on protein foing in UF was reported by Fane

et al. 983) and Ski et al. 984) hey showed that deposition was highest at theisoeectric p IEP) of the protein BSA and reatively low at p away from the IEP

Addition of sat NaC) generally increased deposition he expanation given is as

follows: BSA molecles at the IEP no sat) are in their most compact state and carry

no net charge giving the least permeabe deposit layers Away om the IEP and in

the absence of salt, the molecles expand and have sigicant net charge giving

relatively permeabe layers Addition of salt at these p extremes will shied charges

casing moleclar contraction At the IEP, the effect wold be different since the

addition of salt cases anion binding, enlargement of the molecle and acqisition of

char with an xpected increas in permeability

einemann et al. 988) stdied the effect of salt on foing and protein transmissiondring MF of whey protein soltion throgh a 02 m hydrophiic membrane hey

fond that addition of 00 mM NaC decreased x of protein sotions, the x

decrease being independent of p owever steady state protein transmission was

30-35% higher and the degree of loss of transmission was less at p vales away

from the IEP Protein transmission of the sat-free soltion was at a maximm arond

the IEP, whereas in the presence of salt, the steady state transmission was at a

minimm hey considered interaction of charged moeces with the charges on the

membrane srface to expain the reslts Addition of sat seems to have redced

eectrokinetic interaction between protein and membrane leading to a compressed

dobe ayer, less interaction and increased protein transmission owever redced

size of the protein apparenty cased pore pgging and denser deposits redcing x

hey proposed that at the IEP, in the presence of sat, the salting ot" effect

9


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20

enhances aggregaon an he bul up of enser eposs resung n reuce ux

an proen ransmsson

Palecek et al 993) nvesgae he effec of onc envronmen on he hyrauc

permeably of he eposs urng F of BSA usng a 0 6 m Poyehersufone

PES) membrane They foun ha permeabl of epose ayers of BSA was a

mnmum a he proen soelecrc pH an ecrease wh ncreasng souon onc

srengh IS) a pH boh above an beow he IEP They aso foun ha ux was a

ncon of he eecrole composon wh he ux for BSA n NaC approxmaey

40% greaer han ha for BSA n a CaC soluon of he same IS Ths epenency

on IS an on vaency was arbue o porosy n he epos whch was eermne

prmary by he baance beween he compressve pressure assocae wh he rae

ux an he elecrosac repuson beween he charge proens whn he epos.

Palecek an Zyney (1994a) foun ha seaysae permeably for albumn,

lysoyme rbonucease A haemogobn an mmunoglobun eposs was a

mnmum a he proen soelecrc pH an ecrease wh ncreasng saconcenraon a pH values boh above an beow he IEP In a aer pubcaon

Paecek an Zyney (1994b) suggese ha ux eclne urng proen lraon

hrough even large pore F embranes s ue o he formaon of a proen epos

on he membrane wh he epose proen layer provng a arge aona

hyrauc ressance o he lrae ow The seay sae ux hrough he fferen

proen eposs was a mnmum a he proen soelecrc pon an appeare o

ncrease amos lnearly wh he proen surface charge ensy. Poulo et al (994)

have aso foun sgncany hgher foung a he proen IEP ue o ncrease

eposon an hyraulc ressance.

Baakrshnan an Agarwal 1996) use a vorex ow er o suy ux an

ransmsson behavour of ysoyme (14 kD, pI 106) ovalbumn (44 kD, pI: 46)

an myogobn 17 pI 68) usng a 100 kD cuoff hyrophc polyacronre

membrane For a hese proens he ux ncrease nearly wh ncreasng TP up

o 30 kPa an rher ncrease n TP resue n a margnal nonlnear ncrease n

ux The foung was mnmal for ovalbun bu ysoyme an myogobn showe a


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2

sall reducon (7 & 35%) n ux durng proen raon. The ranssson

however vared arkedly for hese hree proens Whe ovabun and yogobn

exhbed proen ransssons n he range of 25-50 & 75-95% respecvey

lysozye exhbed an unexpecedy hgh ranssson up o 20% pyng

concenraon of proen n he pereae srea They arbued hs o he presence

of aracve proen-ebrane elecrosac neracons under he condons used

The dfference n proen ranssson was arbued o he pH condons of he

soluons The experens were conduced a pH 68 whch was below he pI of

ysozye Consequenly lysozye was posvely charged a hs pH and

experenced overall aracon owards he hydrophc ebrane apparenly leadng

o a hgh proen ranssson of abou 20% On he oher hand ovalbun (I 6)

whch s negavely charged a hs pH was repelled by he ebrane surface and

dspayed ranssson arkedly below 00% (25-55%) Mygobn whch s a

zweron a pH 68 foowed a prole sar o ha of ovalbun bu wh uch

hgher ransssons (75-95%) Ths was appareny because onc neracons

beween he neura yogobn olecules and he ebrane surface were na

causng he yoglobn ranspor o occur any by olecuar sevng

o suars foun s svere a proen I and becoes ess severe boh above

and below I Addon of sa generally ncreases severy of foulng a pH away

fro I however a I decreases foulng

2.6.5. Concntrton

Concenraon of he feed sees o deerne he ype of foulng echans Tracey

and Davs (199) found ha foung by 00% BSA soluons was ore severe han

wh 0% soluons on 02 poycarbonae ebranes I was hypohessed ha

proen aggregaes ha fored a 01 % concenraon are larger han aggregaes

fored a 00 % causng exeal foung leadng o foraon of a porous cake

whereas saer aggregaes a low concenraon are sucen o ener he pores and

cause nea foung reducng proen ranssson below ha obaned wh

exea foung On he oher hand Ge and Davs (996) usng a 02

ebrane repored ha ovabun aggregaes ha fored a hgh concenraon

ncreased ux declne by pore puggng Bowen and Ha (995) usng e anayss of


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22

ltration data obtained fro MF of YADH showed that the fouing echanis

changed o inpore deposition to surface deposition as concentration was increased

In suary concentration of protein which is inked to aggregate foration can

affect fouing by plugging the pores or foring a surface layer depending upon

aggregate size The porosity of the deposited layer of aggregates affects the ux and

protein transission

266 Preltrton

Kelly et al (993) deonstrated that preltration of BSA solutions prior to MF

substantially reduced their fouling tendency with the degree of iproveent

increasing as the preltration was perfored through saler olecuar weight cut

off ebranes Maa and Hsu (996a) also observed reduction in fouing when

recobinant huan growth horone (rhGH) was pretered On the other hand

Hlavacek and Bouchet (993) found that preltered BSA solutions sti fouled during

MF Jonsson et al (996) observed a signicant deay in cake foration when BSA

was preltered In suary pretration sees to reduce the severity of fouling butdoes not eliinate it copletely especially when secondary aggregation occurs

267 Presence of mnerls nd surfctnts

Vetier et al (988) during MF of ik on auina ebranes found that caciu and

phosphorous sats increased fouing probably by aowing better adsorption of casein

icees on the aluina and by acting as inteicear bonds in the deposit. The

seru ilk proteins were retained by the porous icear deposit under both static

and dynaic conditions resulting in progressive fouing of the dynaic icear

ebrane enabing ilk to be processed with a inera MF ebrane Scanning

electron icroscopy (SEM) studies revealed that fouing occurred in dynaic

ltration which was siiar to that described for static conditions except that the layer

was uch thinner with a iniu of 5 (thicknesses 50 ties greater were

observed in static experients) The ost iportant role of the caciu and

phosphorous sats present in the soluble phase of ilk is to act as a ceent between

icelles and aluina in fouling and between the iceles theselves It was

suggested that fouing was initiated by adsorption of a thin of casein and sats on


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23

whch wee then deposted othe mcelles whch may be connected by phosphocalcc

bonds

Maa and Hs (1996b obseved mpoved taton by the addton o sodm dodecyl

sate (SDS a sactant Ezo et al (1996 ond that the pesence o tton

a nononc sactant cased weake adheson oces between glass patcles and a

model membane consstng o a ceose dacetate m They ond easy emoval

o patces om the sace de to the pesence o sactant The edcton n

adheson enegy de to the pesence o sctant s expaned by a nmbe o actos

The hydophobc tas o the tton ae adsobed on patcle saces and the

membane sace s ths exposed to the hydophlc head gop o the sactant

The pesence o tton ndced stec eects between saces and a sbstanta

decease n adheson between patces and the membane sace was obseved

2.7 Effect f membrne prperties

27 Pre size

Hghe pemeate xes ae expected wth MF becase o the elatvey lage poesze Bt Atta et al (1991 b whe pocessng skm mlk on almnm oxde MF

memaes on e emeate xes wth a 02 m membae than a 08 m

membane Spsngy seveal nvestgatos have shown that thogh xes

nceased wth nceasng poe sze x declne was geate as the poe sze

nceased Pot et al (1984 consdeed the peomance o Nclepoe membanes

(001 003 005 008 01 m wth cheese whey n an Amcon Ce Fxes

nceased ntl the 008 m membanes ae whch the x declned In addton

they ond that etenton was owest o the 005 m membane nceasng as the

poe sze both deceased and nceased Meeles et al ( 1991 b) consdeed the

peomance o a ange o poyslone membanes wth BSA ovalbmn and

lactabmn Ae 1 mnte the poten etentons o BSA wee 100 85 and 20% o

10 40 and 100 MWCO membanes espectvely Howeve poten etentons o

the thee membanes at steady state wee 100 100 and 98% Changes n poten

etenton by olng ae moe sevee as the membane poe sze nceases n a

nmbe o cases an optmm poe sze wth espect to pemeate x has been

dented below whch the esstance o the membane tsel and the omaton o a


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surface fouling layer reduce the permeate ux and above which the increased rate of

membrane fouling due to deposition within the pores causes ower long te uxes.

Jonsson et al (996 studied the effect of pore size on fouing. t was observed that

surface bocking rate decreased with an increase in mean pore radii and a decrease in

porosity whereas the cake formation step decreased with an increase in mean pore

radii. Kim et a. (992 comparing the different membranes used in their studyfound that there is a general relationship for the membranes between the amountof protein deposited and the ux decine This observation was ess apparent with the

Nucepore and Anopore MF membranes Whist the Anopore membrane had a lower

ux decline in spite of its greater protein deposition the Nuclepore membrane

showed a tremendous ux oss (>90% for a relativey sma amount of protein

deposition The explanation advanced was the lower porosity of the Nuclepore

membrane (0% compared to the Anopore membrane (50%) Comparing 02 m

and 005 m polycarbonate membranes during ltration of BSA solutions Tracey &

Davis (994 hypothesised that the 02 m membrane initiay fouls inteally as no

signicant protein reection is occurring and yet the resistance is increasing; once the

pores are constrcted fouling becomes exteal. However on the 005 m membranecake ayer build up occurs immediately on the surface of the membrane

2.7.2. Pore morpholo

Use of membranes with the matrix side facing the feed soution (YADH gave much

slower decreases in ltration ux showing the importance of pore morphology in the

optimisation of ltration rates (Bowen & an 993 However the resut was not

repeated when ltering industrial ferentation broth. The results were attributed to

pressureinduced pore broadening of the polymeric membrane whereas with

fermentation broth the high suspended solids present blocked the exposed matrix

Persson et al (993b used liquid displacement porosity (DP to characterse four

polymeric MF membranes. DP showed a clear pore size distribution for al

membranes analysed with 0% of the pores having at east 90% of the permeabiity

Mueller and Davis (996 investigated effects of varying membrane morphoogy and

surface chemistry on protein fouling mechanisms of MF membranes. A 02 m

tracketched polycarbonate (PC membrane foued inteally with exteal fouing


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becomin the dominant means of foulin only at later times. A 02 m cellulose

acetate CA) membrane showed only inteal foulin, while 0.2 m polysulfone PS)

and polyvinylidene uoride PVDF) membranes showed only exteal foulin It is

hypothesised that the low surface porosities and lare thickness of the PS and PVDF

membranes reduced permeate ux and allowed protein areates to uickly plu the

few pores, leadin to almost immediate exteal foulin surface layer), while the

hiher surface porosities and small thickness of the PC and CA membranes yielded

hiher uxes and caused extensive inteal foulin before exteal foulin took over

They reported sinicant loss of protein transmission durin exteal foulin In part

11 of the study, on the effects of various surface modications, results show thatsurfacemodied polyethlene and polypropylene membranes have lower initial

uxes than the unmodied membranes However, the hydrophilic modied

membranes demonstrated comparable nal uxes and lower percent ux declines

than the unmodied membranes The azlactone modied membranes showed very

low lon-term uxes and lare decreases in permeate protein concentration due to

ecient protein bindin Aain, protein transmission remained constant or only

slihtlydecreased durin inteal foulin, while a sinicant loss of protein

transmission was observed durin exteal foulin J onsson et al (99) suested

that membrane morholo rather than surface chemistr is more important in MF

foulin as the primary cause of the ux decline is the deposition of protein areates

affected by morpholoy) rather than adsorption of protein molecules affected by

surface chemisr) Gell and Davis ( 996) found that lower surface porosity

membranes exhibited more rapid exteal foulin probably due to pluin of the few

pores that contrbute to the larer permeate ows

In summar, pore foulin appears to have a sinicant inuence on subseuent MF

foulin Membranes with lare inteal area may have increased interactions between

proteins and membranes These interactions sometimes lead to formation of protein

areates and pluin of lare pores resultin in dramatically lower uxes even

thouh initial uxes are hih


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27.3. Microscopy studies on ouling

Drec observaton of foed membranes sng SEM Atomc Force Mcroscopy

(AFM) and Fed Emsson Scannng Eecron Mcroscopy (FESEM) ave been

performed by severa nvesgators o ecdate te fong mecansms Km et al(1992) sng FESEM observed srface deposon even on membranes ta pass

sbstana amons of proens. Tere was no FESEM observabe proen wn te

pores. Two dfferen ypes of foant deposs were observed on te membrane

srface fong by mayer (cake) coang and fong by aggregaes of proens.

Tey sowed at proen aggregaes were formed on a poysfone membrane

mmedatey ( 1 mn) . Grow of aggregaed proen wt tme drng UF of 0 1%

BSA on poysfone membranes was demonstrated Havacek and Bocet ( 1 993)

sng SEM sowed at e fong drng consant x MF of BSA on a 02 m

M pore membrane s mosty a srface depos made p of proten aggregaes. Key

and Zydney (199 ave aso sowed a fong was predomnany by aggregates

on te srface ayer. Tracey and Davs ( 1 99) sng SEM reveaed a pore rad and

pore densy bo decreased w raon me Bowen and Ha ( 1 995) sng AFM

fond arge amons of Y ADH deposed on a Cycopore membrane srface w onya few pores vsbe ncovered by deposs. Maa and Hs ( 1 996a) sng SEM anayss

sowed a .2 m membranes wen sed o er rGH sotons nder 035 bar

TM were pgged o a grea exen.

Km et al (1997 measred sreamng poentas of vrgn and foed membranes to

sdy fong. Tey sed sets of poycarbonate rack etced membranes of two pore

sze ranges smaer pore sze (001 0.03 .05 m) and arger pore sze (0.1 and 0.2

m) o er BSA. Comparson of apparen zea poentas (cacaed based on

sreamng potena measrements of vrgn and foed membranes sggesed tat te

measred poenas are deermned by e proen propertes. I appears at te

proen adsorpon compeey moded e srface carge of e orgna membranes

Tey sed forer ransform nfrared (FTIR) specroscopy o ook a e exen of

proten deposton F or e membranes w sma pores e B SA peak dd notappear n e specra b te BSA peaks were seen ceary w bgger pore sze

membranes Te amon of proen adsorbed on te smaer pore sze membrane may

be nder te deecon m of te nsrmen de to er ow porosty and sma pore


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ze Fo the membanes with lage poes howeve, the BSA peaks inceased with

inceasing poe size due to the geate volume of BSA solution passed Analysis of

the FTIR specta of the potein fouled 02 m membane pefomed on both sides of

the membane indicated that the feed side gave moe intense BSA peaks than the

pemeate side suggesting that the adsoption is pedominantly on the feed suce

The depthpoling of the fouled membane also suggests that potein adsoption was

mainly on the suface o nea the poe enties athe than thoughout the membane

poe Suface poperties ofthe fouled membanes mio popeties of the deposited

potein. Thee is a lack of poe size effect on the zeta potentials of the potein fouled

membane suggesting again pedominantly suface laye, which was conmed by

Electron micoscopy To simulate BSA fouling they lteed silve colloids of size 8

nm using a 02 m membane. FESEM pictues showed gadual poe bidging and

evenual coveage by the silve colloids They poposed that a simila mechanism is

expected with BSA even though BSA molecules ae quite diffeent fom silve

colloids.

To summaise, all the above diect observations of MF membanes obtained aepotein ltation indicate that fouling did not occu thoughout the membane

strucue but pedominantly on the suface o nea the poe entrance

2.8 . Effect of operating variables

2.8.1 . Permeate uxTransmembrane pressure (TMP)

Piot et al. (1986) obtained esults when pocessing whole milk on a 8 m ceamic

membane The ate of ux decline deceased and the aveage pemeate ates

inceased as the TMP was educed fom 1 0 to 0.8 to 065 ba These esults show that

thee is possibly an optimum TMP at which ux ate is a maximumfo the given poe

size . Optimum TMP deceased as the poe size inceased Inceasing the TMP also

esulted in lowe wate ux ecovey ae wate ushing suggesting that moe sevee

fouling had occurred (Pesson et al., 1 993a) Van de Host and Piesma ( 988)

duing CFMF of skim milk found that fo both 04 and 07 m membanes the ux

deceased with inceasing TMP and deceasing coss-ow velocity Bowen and Gan

( 1 99 ) when pocessing BSA with 02 m Anopoe capil lay membanes found that

inceasing the TMP (0 14 , 034, 0 .69 and 1 .3 8 ba) inceased the initial pemeate ux


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b also increased e rae of x declne Te nal permeae xes were fairly

simlar Tey sggesed a e reason for connos declne in x was sear

ndced deposon of proen molecles Jonsson et al 992b) obseved x decline

dng MF of BSA solions Tey sggesed a e x declne cold be relaed odenaraion of e BSA molecles a e pore enries becase of e ig sear

forces Bowen and Gan 992) fond a x declne was more severe wen

operaed a ger TM Tey demonsraed a decreased aciviy of YADH was

becase of enzyme ineracons resling om a sear indced deformaion of e

enzyme srcre Dan and Merin 1995) repored qoing io et al 986) and

Malmberg and Holm 988) work a e TM s a mos crcal parameer

nencing x decline in MF of milk I was sown a increasing TM by 0 1 5

bar dobled e x b wen TM exceeded 0 bar or 065 bar foling occrred

mc faser Frenander and Jnsson 1996) glged a crical TM o minimse

foling dring consan x operaon

Te imporance of consan x operaon as been sressed o redce foling in MF

Seean et al 988) sed permeae ow conrol n preference o permeae pressreconrol and e average x was fond o ncrease by a facor of 25 dring e

recover of an exracel llar baceral proease Te repored a n order o redce

e folng rae i s imporan o keep TM as low as possble wle mainainng

recrclaion rae as g as possible Marsall et al 996) dring MF of skim mlk

sng 0 1 m polyslfone membrane demonsraed a severe foling cold be

prevened by carel sar p procedres and b conrol of permeae x However i

was fond a ere was no bene of sng consan x operaon drng UF vanRes et al 997) wile separang IgGBSA and BSA monomerolgomer mxres

sggesed a operaion n e pressre dependen regme of e lrae x cve

and carel conrol of id damc sar p condiions will minmse foling and

increase selecivy

Meller and Davis 1996) sowed a increased ransmembrane pressre resled nmore severe folng of e polyslfone and VDF membranes erssonet a 993a)

sing for dfferen polmeric MF membranes fond a increased TM resled in

an ncreased foling layer for e wey proein Irreversible foling increased wi


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ncreasng TMP leadng to poor x recovery Tey sggested tat ncreased folng

was a combnaton of pore narrowng pore pggng and cake layer bd p

coverng a te possbe optons).

Blanpan et al 1 993 ) ave reported ncrease n adsorpton at ger TMPs Increase

n TMP seems to ncrease drvng force to te membrane enancng proten

concentraton at te srface of te membrane and ts ncreasng te adsorpton

Marsa et al 1 997) ave reported severe folng at ger permeate xes Tey

proposed tat as te x s ncreased te sear sress n te pore s ncreased casng

an ncrease n te proten nfoldng deposton and fong drng MF of

lactoglobln

Boyaval et al. 1 996) sded te effect of TMP on permeate x drng MF of actc

acd bactera on a 02 m membrane In ts case te ce s were totay rejected by

te membrane de to ter sze compared to te argest pores of te membrane

Folng was predomnanty de to te formaton of a reversble cake of mcroba

partces on te srface. At ower pressres an ncrease n TMP from 0 1 to 03 bar)ndced a sarp ncrease of x wc reaced 120 Lm for a TMP of 03 bar At

TMP above ts vale x reaced almost a stable vale At constant TMP beow

ts vale x was constant wt tme Ts beavor s smlar to te cassca

pressre verss x relatonsp observed n UF Ts ype of beavor s generay

observed wen tere s predomnantly a srface layer on te MF membrane Tey

also stded te effect of transent operaton condtons on fong Tey fond tat

fast ncrease of TMP 5 mn) reslted n severe folng compared to ncrease of TMP

over a perod of 30 mn Tey sggested tat n a fast transent regme te

convectve forces are stronger and partces ave less tme and space to organse Te

depost composed of a ess dense strcre wod ten be capabe of entrapment of

medm molecles wereas te slow transent regme ndced a more organsed

depost

A dfferent observaton was made by Cakl and Mkek 1995) we terng PVC

latex Tey sowed tat ncreasng TMP dd not aways ncrease te x Tey

reported tat TMP ncreased x nearly f te partcles were bgger tan te pores


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I was fond a e x nceased lneay w TM a ow vaes p o a cca

vae en e ae of ncease deceased and nay x become neay ndependen

of TM a g vales. I seems ee s an opmm TM below wc e dvng

foce s oo ow and above wc nceased fong cases a edcon n x Ts sabed o e fomaon of a le cake w ge essance once e deposed

pacles ndego compacon nde ge TMs

Mc Donog et al 1995) sed a ado soope ecnqe and eecon dode aay

mcoscope EDAM) o sdy C dng UF and MF of BSA and dexan ble 2000

) solons on 001 m poe polysfone and 05 and 08 m poe ceose

aceae membanes. Te aon cel was paced beween e wo enses of e

EDAM sc a e egon exendng om e membane sface no e ow

cannel was vewed paalel o e membane sface and pependca o e

decon of coss-ow. Tey sowed a ncease n TM nceased e soe

concenaon nea e membane and also nceased e exen o sze of e

polased aye e egon wee e concenaon s ge an e blk Te nea

wall concenaon of dexan meased a a dsance of 20 m fom e membanewa de o e eqpmen consan) nceased fom abo 20 gl fo e case of 05

ba o 1 1 5 g / a 1 ba and o 1 0 g/ a 1 .5 ba.

In smmay appeas a opeaon on e low TM sde of e maxmm n e

pesse dependen egon s bee fo edcng fong emeae xes ae

genealy obseved o s ncease w nceasng TM and afe a cean cca

vae ey wold decease w e ncease n TM. TM s vey cca o

peven sevee folng n MF pocesses. Te TM wee e maxmm x occs

seems o decease as e membane poe sze nceases fo e gven ype of feed

Low and nfom TM appeas o be ccal o mnmse folng dng MF.

2..2. Sher

Nelson and Gaz 1985) epoed a nde d sea condons aggegaonnvoves e followng seps. Inay aggegaon occs by coll sons ndced by

e Bownan moon of e poens. Ts esls n e fomaon of pmay

aggegaes . Aggegaon connes by s mecansm nl e aggegaes become


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large enog for id moion o promoe collisions a wic poin rer

aggregaion is goveed by sear indced coll isions Aggregaion does no conine

indeniely insead as e aggregaes ge bigger eir growt rae decreases and

evenally ey reac a limiing size wic depends on e inensity of e sear eldJonsson et al 996) aribed foling of membranes o a slig denaraion of

proeins de o e ig sear sresses presen inside e pmp Comparaive foling

sdies by em wi and wio pmping indicaed less severe foling in e no

pmping case sggesing no aggregae formaion in e absence of pmping. Maa

and Hs 996b) repored some canges in proein conformaion wen recombinan

man growt ormone rGH) was sbeced o ig sear raes (> 0 ) in a

omogeniser. Maiorella et al 99 ) repored a sear damages nearly 30 of

animal cells by a lobe pmp a a ow velocity of 3 5 m/s. Tog ere is no direc

experimenal evidence of proein denaraion by sear i is ypoesised a sear

a e membrane pore cases aggregaion of proein leading o sbseqen foling in

MF Candavarkar 990 Meireles et al 99 a) On e oer and a os of oer

invesigaors Franen et a 990 Bowen & Gan 99 992 993 Jonsson et al

992a Marsall et a 997) ypoesised a sear a e membrane pore enrance

cased proeins o deposi dring MF. One ing is clear in MF as e ineal

membrane area is signicanly larger an a of membranes ineracion ofproein wi e membrane geomery can play an imporan role especially nder ig

sear given a proein and membrane are bo srface acive

Hig sear sress a e membrane wall is generally elpl in sweeping away any

deposis on e membrane srface. A criical raio of x and sear sress J/) adeermines e balance beween convecive ow owards e membrane e

angenial erosion Aber et al 993) and sear indced difsion Davis &

Leigon 987 Belfor et a, 99) was proposed o minimise foling in siaions

were foling is predominanly by formaion of a srface layer or cake Boyaval et

al 996) dring MF of lacic acid baceria fond a foling was faser and more

severe wen J was greaer an a criical vale of 5 m a Le Berre andDan 994) previosly repoed a similar concep and presened a criical vale of

L ma for MF of skim milk and prereaed wey Gsan et al 995) is

no known wy e vale is so close wi ese wo feeds esed.


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To smmaise shea can case poein o deposi a he poe enance o enhance

aggegaion of poein leading o sevee foling in mos cases

2.83. Crossow veloci

Sheehan et al (1988) obseved ha inceasing eciclaion ae om 60 o 00

liesmine (coesponding o linea velociies of 06 o 10 ms ) podced a

oghly 50 incease in x pefomance fo he same TM pole ding cell

sepaaion Howeve Meieles et al ( 1 990) epoed ha incease in eenae velociy

inceased poein aggegaion and sbseqen foling ding BSA laion on

polymeic membanes Bowen and Gan ( 99 ) sdied he effec of siing ding

U and MF of BSA solions They sowed ha siing (500 pm) had lile effecon pemeae x when leing sing a 02 m Anopoe membane wheeas sing a

UF membane (MW c-off of 10 kDa) in he same cell nde compaable condiions

siing gave a dobling in he pemeaion ae In he case of he UF membane bo

C and deposiion on he on face of he membane appeaed o be impoan

Siing had lile effec in MF as ee is no appaen accmlaion of poein

deposis on he fon face of he membane. On he ohe hand Cakl and Mklek(995) ding laion of acylic copolyme laex paicles on a 0 m membane

showed a inceasing CFV did no always incease he x In is case he

membane foled ineally Tey fond a powe law elaionship beween x and

feed velociy in he case of VC laex paicles on a 02 m membane In his case

foling was in he fom of a cake Mackley and Sheman ( 993) ding laion of a

polyehylene sspension fond ha inceased CFV deceased lae x Inceased

CFV appaenly fomed an ecienly packed le cake leading o low poosiy

Taleon and Wakeman (993) ciing Fische et al (986) leing calcim cabonae

slies epoed ha e size of he paicles in he cake laye deceased as he CFV

inceased leading o a edcion of he pemeae x even hogh he cake hickness

was deceased. Li et al ( 996) epoed MF ofEColi sing a ceamic membane E

Coli fomed a sface cake as i is signicanly lage han e membane poe size

(02 m) Inceasing CFV inceased pemeae x

In conclsion CFV appeas o affec foling in siaions whee sface laye

fomaion is he dominan mechanism of foling Howeve is effec was minimal


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wen foung was predomnanly by an nea pore foulng mecansm excep n

cases were ncreased CFV reduced parce se ncreasng e possby of

puggng

2.9. ouling mechnisms

Te mecansms by wc foung may occur are several Tese depend on: )

weer e gven proen s smaller or arger an e average pore se of e

membrane; 2) e ype of proenproen neracons; and 3) e proen-membrane

neracons nvolved A sngle ype of mecansm appears o be rare as ere s

usualy a se dsrbuon n bo e membrane pores and e macromoecueslered. Smuaneous occurrence of more an one mecansm s mos kely

dcang ux and seecvy n MF. As a resul e use of exsng foulng modes s

med o e analyss of expermenal daa w quanave predcons of ux under

specc condons raer an provdng an undersandng of e foulng

penomenon A beer undersandng of e foung mecansms s essena f CFMF

s o be exploed fuy by mnmsng foulng.

Frs foung mecansms durng lraon of non-proen feeds are consdered

followed by foulng mecansms nvolvng proens. Ten e reevance of non

proen foulng o proen foulng wll be dscussed

ore brdgng by collods was repored by Vsvanaan and Ben Am (989) we

erng coods of average dameer 12 nm roug a 200 nm pore se membrane

Tey found a foulng a ow appled pressure was manly due o a combnaon of

e brdgng of coods over e pore openngs and a concenraon poarsaon ayer

wc ed o exeal membrane foulng wereas neal foulng of e membrane

played a reavely nsgncan role Te brdgng was presumaby by collodal

aggregaes a were formed on e membrane surface appareny due o deposon

and cuserng. roens n smar suaons woud probaby gve more severe

foulng as proen-membrane and proenproen neracons are expeced o be far

more sgncan


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Tarleton and Wakeman 1993) sggested tat folng by partclates appears to be

cased by two ndependent mecansms wc occr smltaneosly Te rst

acconts for ntal sarp declne n permeate x and s rreversble for all practcal

prposes and s de to te rapd deposton and captre of ner parcles omsspenson and ter sbseqent penetraton nto te pores of te membrane Te

second mecansm s largely reversble and cases rter partclate layers) to form

above te membrane srface n te form of a cake

Km et al 1 993b) sded te effect of collod sze on te membrane pore sze drng

ltraton of dlte slver collods of sze 8326 nm sng 30 1 00 300 k and 022

m membranes Slver partcles formed a cake on te small pore sze 30 k

membrane Wt te 00 and 300 k membranes wose pore sze was larger tan te

sze of te folant severe folng occrred de to folng wtn te membrane pores

However wt te 022 m membrane te retenton of slver collods was low and

te small ncrease n resstance was peraps de to te deposton of slver partcles

on te pore walls

Cakl and Mklek 1995) dented two pases of x declne drng constant

pressre MF of syntetc collods Acrylc copolymer AC) latex & poly vnyl

clorde VC) latex partcles of average szes 0 1 m and 1 0 m respectvely were

processed on 0. 1 and 02 m almna based ceramc membranes respectvely Frst

reversble concentraton polarsaton blt p wtn te rst mnte Ten x

contned to declne for p to several ors de to polymer collod deposton on te

front srface of te membrane or wtn te membrane pores Tey conclded tat

cake formaton prevals f te parcles are larger tan te pores VC latex)

Increasng feed velocty generally ncreased permeate x A dfferent folng

beavor occrred f te actve layer pore sze was very close to te dameter of te

partcles ltered AC latex parcles). Increasng te feed velocty ad a lmted

effect If te parcles are sfcently exble tey can enter te pores and reman

nsde probably de to some nteracton wt te membrane materal Wen te feedvelocty was scently low s) te perod of pore l lng was sor Te pores

may be only slgtly entered by partcles wc ten begn nstantly to brdge over te

pore and form a very tn l ter cake Ts depost can be taken as a secondary


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membrane wc proecs e MF membrane agans pggng by parcles and

erefore conbes o a ger and more sabe x A ger veoces (> s)

smaler parces can block e pores redcng x

Boyaval et al ( 996) drng MF ofactobacillus helveticus (rods of -5m n eng

and 05 1 m n dameer) sng 02 m almna membranes fond a fong was

de o a reasonably consan rreversble ayer formaon and o a domnan reversbe

ce cake nder varos permeae xes nvesgaed Domnan reversble cake was

de o e oal rejecon of e ce s by e membrane Ts work sggess a wen

mcrobal ces of sze mc bgger an e membrane pore sze are ered a

consan amon of rreversble folng predomnanly by adsorpon and a domnan

reversble srface ayer or cake occrs

Te effec of pore sze on e ype of fong mecansm was repored by Da-Cn et

al ( 996) Tey fond a membrane folng was e res of varyng combnaons

of adsorpon pore pggng and concenraon polarsaon or gel ayer formaon

drng UF of a plp m een conanng parces of a broad sze range 0 o 37m sng membranes of molecar weg coff (MWCO) range 300 Da o >500

kDa. Tey ypoessed a srace asorpon was key for ower MWCO

membranes and a e adsorbed layer was conrong membrane performance

wereas adsorpon seemed o ave cased pore narrowng w ger MWCO

membranes

To smmarse fong by non proen maerals folng wn e membrane or as a

cake layer occrs dependng pon weer e parce sze s larger or smaer an

e pore sze Cooda aggregaes may form brdges over pore openngs eadng o

pore consrcon and formaon of a cake In some cases formaon of a srface ayer

(secondary membrane) can proec agans pore plggng W sver collods e

fong mecansm canges from deposon wn e membrane pores o foaon

of a cake as e pore sze s decreased I appears a fong by less neracve nonproen feeds s domnaed by deposon and cake formaon wereas w proens

addona facors ke er neracons w e membrane and emseves pay a

major roe A leas n eory more severe folng s expeced w proens


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compared o ess ineracive non-proein eeds Nevereess knowedge o non

proein oing cod o a basis or ndersanding proein oing Te aggegaion

endency o proeins is an imporan aspec a ms be considered wi proein

oing

Meireles et al 1 990) sggesed a in genera membrane oing by proeins can be

de o a combinaion o naive proein adsorpion and o aggregae deposiion, e

aer being sensiive o operaing condiions e ormer dependen on e

concenraion o e proein.

Adsorpion and pore plgging played a signican roe on 35 and 100 nm pore size

almina membranes o orm a gel layer ding raion o BSA nder consan

pressre condiions Cark et a 1991) Tey aibed gel ayer omaion o

proeinproein ineracions van Reis et al 1991) wile separaing proeins om

mammalian cels sing a 0.2 m polypropylene membrane ypoesised e

olowing x decine mecanisms: 1) adsorpion 2) denaraion de o proein

membrane ineracion or e generaion o airiqid inerces; and 3) reenion bymoeclar sieving de o aggregaes in e eed or aggregaes prodced dring

lraion isel

Severe oing by BSA on a range o membranes o varios pore sizes was repoed

by onsson et al 992a). Adsorpion o BSA ad a major role on a 20 k

polyslone membrane However wi 02 and 1 m pore size membranes wen

exposed o BSA nder saic condiions adsorpion alone cased a vey sma drop in

x However nder low pressre lraion 0 1 05 bar) very severe oing

occrred sowing a pore pgging dominaed oing wi ese membranes

Using SEM ey ave demonsraed a oing occred on e ron ace o e

membrane. I is ineresing o noe is beavior wi BSA as severe oing as

been obseved wi a range o pore sizes. Is oing beavior nder consan

pressre operaion as been repoed as a wo sep process onsson et a 1996) Ioled ineally rs and laer a srace ayer omed Tey sggesed a BSA

ineracs wi e membrane srcre and nally orms a srace layer I is no cear

weer is beavior is specic o BSA Is oling beavior nder consan x


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37

condons w be ineresng o invesgae as ow inia TMs mg avoid TM

nduced proen-membrane neracons and subsequen fouing

Larger aggregaes can actuay reduce e foung effec f ey are bigger an epore sze as repored by Tracey and Davis ( 994) . Tey used e umped erms

"exea fouing and "nea foing drng MF Exea fouing refers o

foung due o e accmuaon of proein aggregaes a do no ener e pores

wereas inea fouing refers o foing wiin e inea pore srcure of e

membrane de o adsorpion and deposiion Tey ypoessed a drng MF of

very diue BSA soions (001 using a 02 m poycarbonae membrane fouing

occurred a e mous of e pores, sowy cosng off pore entrance we aowng

compee ransmission of proen for a period of me. Evenuay, e pores became

so constrced a proen ransmssion decreased and a ayer of rejeced proen

formed on e exea membrane surface However w 0 souons of BSA on

e same membrane, foing aowed for neary compee ransmssion of proens for

e enre eng of e expermens I was ypoessed a proein aggregaes a

form a 0 1 concenraion are arger an aggregaes formed a 0.0 concentraionTe arger aggregaes did no pass roug e membrane and so e foung was

exea Te rejeced ayer of arger proein aggregaes was appareny packed

oosey enoug o aow proein monomers o pass roug For due proen

souons i s proposed a aggregaes are sufceny sma o ener e pore mou

and cause inea fouing evenuay pugging e pores redcing proein

ransmission.

Simiar resus sowng a arger aggregaes can mnmize foung nder certain

condiions were aso repored by Gsan et al ( 995) Tey demonsraed e benes

of a modied prereamen meod o mnmse fouing for carng wey by MF

Longer MF operaion and better wey carcaon due o arger cacum pospae

parices and ower cacim and pospae conen in e aqueous pase were

aceved as a res of modied prereamen Loosey srcured deposis caused by

arger compex-pd-cacum pospae parices on e membrane srface, ncreased

e permeaon rae of deposs enancing MF uxes


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Initiation o f fouling by aggregates present i n the feed seems to be the key factor in

determining the fouing mecanism (Kely & Zydney, 99 , 997) Te fouling

behaviour of BSA, cysteinyated BSA, ovabumin, ysoyme, pepsin, myglobin,

actalbumin & actoglobuin on a 022 m pore sie PVDF membrane under

constant pressure conditions was studied (Kelly & Zydney, 997) Fouing was

severe wit -actogobulin and ovalbumin and ighter with lysoyme while other

proteins behaved in the intermediate range Lysoyme was smallest of a in

moecular weigt They reported two distinct mechanisms ) deposition of arge

protein aggregates and 2) chemical attachment of native proteins to the growing

deposit The chemica attacment was found to occur via the formation of

intermoecuar disulde inkages invoving a ee suphydryl group in the native

protein Among the proteins investigated, actogobuin fouled severely athoug it

has ony one ee suphydry group They aributed the fouing to the reactivity of

the sulphydry groups rather than the number of groups Ovabumin aso foued

severely even though it does not have any free sulphydr group They attributed the

fouling behaviour of ovalbumin to aggregation by other mechanisms such as

hydropobic interactions

Daun and erin ( ) atriuted ouing during o pretreated whe at constant

ux to pore blocking This phenomenon exhibited itsef as a slow increase of fouling

resistance (R) with time, in which pores were progressively blocked until a point

when the remaining active ltering layer must compensate for bocked pores by

tering larger volumes The inevitable consequence was a fast fouing which was

expressed in a sharp increase of R unti l the limiting value As a consequence, a fast

decrease in protein transmission was also observed The fouing mechanism

hien tuong fouling trong dd co protein

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