3.1 Microfiltration (MF) and ultrafiltration (UF ...shodhganga.inflibnet.ac.in/bitstream/10603/6274/9/09_chapter 3.pdf3.2 MF/UF of sugarcane juice 3.2.1 History and current status

Literature review

TERI University Ph.D. Thesis, 2007 9

Literature review

3.1 Microfiltration (MF) and ultrafiltration (UF) applications in juice processing

MF and UF are pressure driven membrane processes for the selective separation

of two or more components from a fluid stream (Cheryan, 1998). The separation

is primarily based on size differences with the retention of macromolecules and

particles larger than 0.001-0.02μm for UF and 0.1-5µm for MF. The process

involves continuous molecular separation without phase transfer; also under

ideal conditions, it does not involve the addition of heat or chemicals.

Clarification of fruit juice by UF was commercialized in the late 1970‘s (Jönsson

and Trägårdh, 1990). Since then, maximum number of UF plants have been

established for apple juice clarification; however others like grape, pear,

pineapple, cranberry and citrus juices have also been processed.

Freshly squeezed apple juice is cloudy due to the presence of protein and

tannins, which remain in suspension because of the polysaccharide pectin

(Mondor and Brodeur, 2002). Thus large quantities of pectinase and gelatin

have to be added to induce clarification. UF not only improves the quality of

juice but also increases juice yield by up to 8%. Juice flux can be further

enhanced 2-3 fold by appropriate pretreatment with enzymes (Alvarez et al.,

1998) and filter aids like bentonite and gelatin (Gökmen and Çetinkaya, 2007).

In another recent work with a plate and frame UF system using 50 kD PES

membranes, pasteurization alone was reported to result in higher and more

stable juice flux over a 20h full scale operation when compared to a full scale

tubular UF system with 200 kD membrane (He et al., 2007). The opposite effect

was observed with juice heating prior to UF of orange juice using inorganic

membranes (Merin and Shomer, 1999). The flux was reduced after heat

treatment, possibly due to the interaction of the coagulated pectins and proteins

with the membrane-filtering layer.

In apple juice clarified by UF, haze formation is a problem because of the

polymerization of phenols and its interaction with other components, e.g.

proteins (Siebert et al., 1996). In particular, UF through higher molecular weight

cut off (MWCO) membranes displayed increased turbidity with time as well as at

higher storage temperature (Girard and Fukumoto, 1999). Also, UF with

PES/PVP (polyvinylpyrrolidone) membranes exhibited better removal of

3

Literature review


yellowish brown color and polyphenols compared to commercial cellulose

membrane (Borneman et al., 1997).

To obtain high permeate flux at low membrane fouling, pretreatment prior to

UF is usually followed with most juice streams. For instance, a combination of

enzymatic treatment followed by adsorption using bentonite resulted in the

maximum permeate flux with mosambi (Citrus sinensis (L.) Osbeck) juice

ultrafiltered in a continuous stirred filtration cell using 50 kD thin film

composite polyamide membrane (Rai et al., 2007). Enzymatic pretreatment

alone has been employed in several instances. Flux increase was reported with

pectinase pretreatment prior to cross flow UF of West Indian cherry (Malpighia

glabra L.) and pineapple (Ananas comosus (L.) Meer) juice clarification using

100 kD PS hollow fiber and 0.01μm ceramic tubular membranes (De Barros et

al., 2004). In the UF of depectinized kiwi juice, flux was higher with a modified

polyetherether ketone (PEEK) hollow fiber membrane (MWCO>69 kD) when

compared to that obtained with commercial 10-50 kD tubular (PVDF) and

hollow fiber membranes (Tasselli et al., 2007). Enzymatic pretreatment has also

been successful in improving flux during the filtration of pulpy feeds such as in

the MF of pasteurized, diluted umbu (Spondias tuberosa Arr. Cam.) pulp in a

pilot unit equipped with 0.2 m polypropylene tubular membrane (Ushikobo et

al., 2007).

Apart from apple juice, UF has been applied effectively for pear juice

clarification (Kirk et al., 1983) and the process is employed commercially

(www.unipektin.com). These successes have encouraged trials on dark colored

fruit juices such as blackberries, redcurrants, raspberries, sour cherries,

strawberries and elderberries. Here, the permeate must retain its color while

being free from turbidity. In a pilot study on dark colored juices (cherry,

raspberry and redcurrant) with polymeric (PS, PVDF) and ceramic tubular

membranes, ceramic membranes reportedly reduced turbidity without affecting

the color (Bolduan and Lartz, 2002). Further, the permeate from UF ceramic

membranes showed good stability even after hot/cold tests. In another

investigation, blood orange juice was clarified by UF using tubular PVDF

membranes (Cassano et al., 2007a). West Indian cherry juice clarified using a

0.14 m tubular ceramic MF membrane retained a high concentration of the

ascorbic acid but the color became lighter (Wang et al. 2005). Unlike apple juice,

enzyme pretreatment for removal of phenolic compounds resulting in haze and

sediment formation is not necessarily recommended with dark juices. In trials

on pomegranate juice with laccasse treatment prior to UF, there was a loss of

http://www.unipektin.com/

Literature review


natural red color and unwanted dark brownish color formation in the treated

juice (Alper and Acar, 2004).

More recently, integrated membrane processes like UF followed by osmotic

distillation have gained attention for temperature sensitive juice processing. For

instance, extended thermal treatment practiced with cactus pear juice to protect

it from microbial invasion also degrades juice taste and alters the juice color and

flavor. UF followed by osmotic distillation preserved the organoleptic,

nutritional and sensorial characteristics of the fresh juice (Cassano et al.,

2007b). A similar sequence has been successfully tested for clarification and

concentration of kiwi fruit juice (Cassano et al., 2004) and melon juice (Vaillant

et al., 2005). In addition to retaining its natural characteristics, the melon juice

retentate was enriched in provitamin A. In another study, UF followed by

reverse osmosis (RO) and then osmotic distillation has been successfully pilot

tested for clarification and concentration of red orange and carrot juices

(Cassano et al., 2003). Osmotic distillation, preceded by a combination of MF

and reverse osmosis has also been used for dewatering grape juice to an extent

that it achieved a high sugar content and could be preserved without cooling

(Rektor et al., 2006)

3.2 MF/UF of sugarcane juice

3.2.1 History and current status

The De Danske Sukkerfabrikker (DDS) was the first to investigate the possibility

of membrane filtration application in the sugar industry. The company was

initially involved in developing the process for beet sugar. In 1972, DDS

conducted tests in Tanganyika Planting Company (Tanzania) on UF of

sugarcane juice. The results were promising but could not meet industrial

requirements (Madsen, 1973; Nielsen et al., 1982). Subsequently, Madsen (1973)

carried out detailed laboratory investigations on sugarcane juice purification by

UF, followed by concentration using cellulose acetate based reverse osmosis

membranes. UF was conducted at 30°C, between pH 3-8, using plate and frame

unit. Filtrate of the cold-limed juice was reportedly satisfactory for direct white

sugar production. However, UF of clarified juice was not recommended due to

the deposition of waxy material on the membrane surface.

Literature review


The development of polysulfone membranes in the mid-seventies successfully

addressed the pH and temperature limitation associated with cellulose acetate

membranes. This provided the impetus for further laboratory trials on

sugarcane juice clarification using MF/UF (Table 3.1). Further, application of

membrane filtration for direct production of white sugar (Monclin, 1995; Saska,

2000; Reisig et al., 2001) as well as for preparing ready-to-drink shelf-stable

sugarcane juice beverages (Singh et al., 2004) have also been described.

The first reported factory trial was conducted in PakSap sugar mill, Laos

(Batstone, 1990). Using sixty 6˝ diameter X 37˝ length polymeric spiral-wound

modules with 1.4mm non-mesh spacer, the mill was able to produce 10,000L/h

of sparkling clear juice. Near white sugar could be made in a single

crystallization step. Subsequently, several on-site demonstrations in sugar mills

have been reported as summarized in Table 3.2.

In all the studies, UF resulted in juice quality improvement. With polymeric

membranes with MWCO value of 20 kD or less, color removal was significant

(Kishihara et al., 1981; Balakrishnan et al., 2000; Ghosh and Balakrishnan.,

2003) but sucrose rejection was also high. The purity of the ultrafiltered juice

was found to be higher than that of the juice obtained by conventional

clarification (Kishihara et al., 1981; Ghosh et al., 2000). Verma et al. (1996)

reported almost 100% turbidity removal using 20 kD polysulfone membrane. To

improve the final product quality and to reduce sucrose loss, UF has also been

combined with other decolorization/purification techniques. Saska et al. (1999)

reported 99% sucrose recovery by UF followed by diafiltration of the retentate.

This was in addition to 100% dextran (polysaccharides) and suspended solids

removal. Over 98% removal of color, turbidity, ash and dextran from raw

sugarcane juice was attained using UF in combination with adsorption on

macroporous styrene divinylbenzene structure having anionic functionality

(Willet, 1997). The product obtained directly by evaporation and crystallization

of the permeate after adsorption treatment was of refined sugar standards. UF

alone could not reduce the color of the juice but the syrup obtained by

concentrating the ultrafiltrate was much less colored than that obtained from

conventionally clarified juice. This could be due to the removal of the color

forming precursors from the juice, which produce color during the boiling

process (Willet, 1997). Hamachi et al. (2003) reported a maximum of 59% color

removal from cane sugar solution by 1 kD mineral membrane with a steady-state

permeate flux of 29 L/m2h. They suggested further processing of the permeate

Literature review


on adsorbents or ion-exchange resins for complete decolorization. To improve

the permeate flux without compromising the extent of decolorization, feed

pretreatment followed by MF or UF with higher MWCO membrane appears to

be more acceptable. Color removal similar to that reported by Hamachi et al.

(2003) (50-58%) was obtained with flocculation of raw cane sugar solution with

cationic polymer before MF/UF with 0.2µm, 300 kD and 15 kD Kerasep mineral

membranes (Cartier et al., 1997). Also, turbidity removal was above 90%.

In view of the enhanced purity of the ultrafiltered sugarcane juice, direct

production of refined quality white sugar has also been explored. The process

can involve traditional juice clarification followed by UF (Steindl, 2001);

alternatively, raw juice can be passed through a fine screen before UF (Willet,

1997). The ultrafiltered juice can then be softened using ion-exchange resins

(Kwok, 1996; Fechter et al., 2001; Kochergin et al., 2001) to remove calcium and

magnesium ions thereby reducing evaporator scaling. This, in turn, would add to

the evaporator capacity and would also reduce the maintenance and downtime

accruing from frequent evaporator cleaning. The soft juice can be additionally

decolorized by chromatography (Kochergin, 1999a). Juice purification by

removal of non-sugars to the maximum extent before evaporation and

crystallization leads to higher crystal growth rate and thus higher production.

Even without the additional softening step, UF alone or with a single

decolorization treatment can produce juice resulting in refined quality sugar

(Chou et al., 2002). Thus, the refining operations can either be reduced or even

completely eliminated thereby improving the overall process economics of

refined sugar production.

In addition to MF/UF, other membrane based processes have also been

investigated. To reduce the energy consumption in thermal concentration,

nanofiltration (NF) and RO of sugar syrup has been examined (Madaeni et al.,

2004). The RO membrane BW30 alone led to 60% sugar rejection and a 2-step

filtration process resulted in a maximum of 88% sugar recovery. Membrane

distillation using polypropylene membrane has also been reported for the

concentration of raw cane sugar syrup and microfiltered sugarcane juice (Nene

et al., 2002).

Literature review


Table 3.1 Laboratory scale trials on MF/UF of sugarcane juice and sugar melt

Membrane details Module

Flux

(Lm-2h-1) Details Reference

10 and 20 kD Spectra Por

(Spectrum Medical

Industries, U.S.A), 15 kD

(Hydranautics, India)

Flat sheet

(Stirred

cell)

16-21 Limed raw juice at

ambient temperature

Bhattacharya et

al., 2001

20 kD PES, 50 kD PS

(Permionics, India); 10 kD

PES, 30 kD and 50 kD

Acrylic (TechSep France)

Cross-

flow

22-30 On site trials in a

sugar mill on raw,

mixed and clarified

juice at 45°C

Balakrishnan et

al., 2000, 2001

20 kD PES (Permionics,

India) and modified PS

(Cellpore, Switzerland)

Spiral

wound

21-40 On-site trials in a

sugar mill on raw and

clarified juice at

50-53°C

Ghosh et al., 2000

50 kD-0.45µm TiO2/α-Al2O3 or

ZiO2 coated ceramic

CarbosepTM40 (TechSep,

France)

Tubular 40-450 Limed mixed juice at

90°C

Nene et al., 2000

Literature review


Table 3.1 Contd.


Flux


5-100 kD PES (Pall, France) Stirred 7-50 Raw sugar solution at

80°C

Karode et al.,

2000

15-50 kD Carbosep mineral

membrane (TechSep, France)

Tubular Up to 50 Raw sugar solution at

70-80°C, Cross flow

velocity 2.5m/s

Karode et al.,

2000

20 kD PS (Ion Exchange,

India)

Hollow

fiber

0.043-

0.168

Limed juice at 30-

60°C

Verma et al., 1996

Ceramic (TDK Corporation,

Japan)

Tubular 24-105 Trials at 60°C with

raw limed, vacuum-

filtered juice with

both hand-milled and

factory sample

Kishihara et al.,

1989

5 kD, 10 kD, 30 kD YM and

10 kD, 3 kD PM series

(Amicon, U.S.A.)

Flat sheet

(Stirred

cell)

>60 Raw and limed juice

at 85°C

Tako and Nakamura,

1986

Literature review


Table 3.1 Contd.


Flux


10 kD PM series (Amicon,

U.S.A)

Flat sheet

(Stirred

cell)

~50 Raw and limed juice

at 60°C

Kishihara et al.,

1983

10 kD PM and 300 kD XM

(Amicon, U.S.A., 5 kD G-05T

(BioEngineering, Japan),

200 kD, UK 200 (Toyo Roshi,

Japan)

Flat sheet

(Stirred

cell)

18-97

Raw and limed juice

at 60°C

Kishihara et al.,

1981

Literature review


Table 3.2 Pilot trials on MF/UF of sugarcane juice and sugar melt


Flux

(Lm-2h-1) Details

Trial

location Reference

20 kD PES,

Permionics (India)

Spiral

wound

7 Clarified juice at

60°C and > 90°C;

10m3/h system

India Ghosh and

Balakrishnan, 2003

200Å -1.4µm ceramic

Carbosep (TechSep,

France) and 0.1µm

stainless steel

(Graver

Technologies, U.S.A)

Tubular Not

available

Pilot trial on

clarified juice using

Applexion Process

South

Africa

Fechter et al.,

2001

Not available Spiral

wound

Not

available

Hot prefiltered

sugarcane juice; 4

m3/h system

Indonesia Martoyo et al.,

2000;

50 kD PVDF (Koch,

U.S.A)

Spiral

wound

40-60 12m3/h field trials

with clarified juice

at 95°C

U.S.A Saska et al.,

1999; Eringis and

Jaferey, 2001

Literature review


Table 3.2 Contd.


Flux

(Lm-2h-1) Details

Trial

location Reference

0.2µm, 0.1µm, 15 kD

and 300 kD Kerasep

mineral membranes

(TechSep, France)

Tubular 65 Pilot trials with

flocculated raw cane

sugar solution at

85°C

France Cartier et al.,

1997

0.1-0.2 µm

SELECTFLOTM (Dow,

U.S.A.)

Hollow

fiber

Not

available

Field trials with

mixed juice, Honiron

A.B.C. Process

U.S.A.,

Mexico,

Colombia

Willet, 1997

0.02 µm ZrO2 coated

ceramic Kerasep

mineral membrane

(TechSep, France)

Tubular 210-330 Pilot and Field

trials with clarified

juice at 98°C over

24-48h

U.S.A. Cartier et al.,

1996; Kwok,1996

Literature review

TERI University-Ph.D. Thesis, 2007 19

3.2.2 Challenges

In spite of the advantages, UF/MF for sugarcane juice clarification has not found

commercial acceptance due to the following key processing challenges

(Kochergin, 1999b).

Variation in feed composition: The system should be capable of handling

seasonal and even daily variation in sugarcane juice composition in terms of

varying suspended solids and non-sugars (polysaccharide, gums etc.)

content. These variations originate both from the cane properties (e.g.

differences in cane varieties, soil and agro-climactic conditions, post-harvest

injuries to the cane etc.) as well as mill operation conditions (e.g. changes in

clarification parameters, cane crush rate and milling parameters etc.)

(Ghosh and Balakrishnan, 2003).

Large-scale, high temperature (60-100 C) operation with minimum

processing time: The juice volumes are typically very large. For instance, the

smallest size Indian sugar mill crushing 2500 tons cane/d (TCD) processes

100m3/h of juice. Thus, high flux (flow rate per unit membrane area, L/m2h)

is essential; further, this has to be coupled with high concentration factors

(ratio of the feed volume to the concentrate volume) to minimize sugar loss

in the reject stream. The processing time should also be as short as possible

since sugar solutions are prone to degradation and color formation with

storage. Furthermore, high temperature operation is preferred. This avoids

microbial contamination, reduces feed viscosity (making pumping easier)

and also improves the filtration (e.g. in UF, juice flux at 60 C is double that

at 30 C) (Kishihara et al., 1981).

Membrane durability: The membrane should be mechanically stable to

withstand continuous operation for the sugar-manufacturing season lasting

6-10 months. During this period, the membrane should maintain its

performance in terms of high flux and adequate separation. In addition, it

should be resistant to small amounts of abrasive materials (grit, sand etc.),

which concentrate in the recirculation loop and may thereby result in

membrane surface abrasion. This requirement is essential while processing

mixed/raw juice streams without rigorous pretreatment. Further, the

membrane should be amenable to rapid and easy cleaning.

Literature review


Membrane fouling: A major operational limitation in sugarcane juice UF is the

high membrane fouling (Madsen, 1973; Kishihara et al., 1989, 1983, 1981;

Verma et al., 1996; Balakrishnan et al., 2000; Ghosh et al., 2000). Chemical

cleaning is required to recover the flux; however, frequent cleaning increases

downtime, reduces the membrane life span and affects selectivity. These, in

turn, adversely impact the process economics since membrane replacement cost

can be up to 20-50% of the initial capital investment (Kochergin, 1998).

Furthermore, though the manufacturer warranty may cover membrane

replacement cost, it typically does not cover the expenses related to reduced

plant capacity or downtime.

3.2.3 Membrane foulants

Vercellotti et al. (1999) attempted to identify juice components that interfere

with membrane filtration by filtering centrifuged final C molasses through o.2

μm (1000 kD) filter and studying the molecular weight composition of the

retentate and permeate by size exclusion chromatography (SEC). The SEC

results suggested association of molecules several times smaller than 1000 kD,

thereby forming aggregates that could be probable membrane foulants. Nuclear

Magnetic Resonance (NMR) studies of the different molecular weight fractions

of the retentate indicated a predominant presence of polysaccharides and other

carbohydrates. Polysaccharides and other carbohydrates have been established

as membrane foulants in other similar feed streams like fruit juice (Chiang and

Yu, 1987), beer (Taylor et al., 2001) and wine (Belleville et al., 1990, 1991;

Vernhet et al., 1999; Vernhet and Moutounet, 2002). Vidal et al. (2003)

fractionated the total polysaccharides present in ethanol insoluble part of red

wine using a combination of anion-exchange, size exclusion and affinity

chromatography. Based on the glycosyl-residue composition, mannoprotein

(MP), arabinogalactan-proteins (AGP), rhamnogalacturonans (RG) I and II were

found to be the main polysaccharides. In membrane fouling experiments with

polyphenol enriched fraction of wine, specific deposition of AGP was noticed

along with MPs (Vernhet et al., 1999; Vernhet and Moutounet, 2002).

Polysaccharides have a detrimental effect on filterability of wine in MF

(Belleville et al., 1990, 1991). Further, a linear arabinan isolated from red wine

was found to cause haze and was also probably associated with membrane

fouling (Belleville et al., 1993).

Literature review


In fruit juice clarification by UF, the polysaccharide pectin characterized by high

molecular weight (10-1000×103) and arabinogalactan type II structure was

responsible for fouling layers on the membrane surface (Will and Dietrich,

1994). Sugarcane juice contains several polysaccharides but no pectin (Clarke,

1993). Cuddihy et al. (2001) have described the different polysaccharides

present in sugarcane juice. These include (Figure 3.1):

Starch (consists of amylose and amylopectin), hemicellulose and pentosans,

which are the products of the metabolic activity of the sugarcane plant

Dextran and levan, which are produced by bacterial activity before or during

the sugar manufacturing process.

Other polysaccharides, such as sarkaran that are formed after harvest by the

activity of enzymes present in juice.

These polysaccharides have an adverse impact during juice processing. The

presence of polysaccharides has been found to be detrimental to the uniform size

and shape of the crystals (Chen, 1993a). In particular, dextrans and raffinose in

sugar syrup result in elongation of sugar crystal. Polysaccharides also retard

crystal growth by increasing the viscosity of the sugar syrup (Kaur et al., 2004).

Roberts et al. (1976) has identified soluble polysaccharides (indigenous

sugarcane polysaccharides, ISP) in cane juice and raw sugar. ISP contributes

most abundantly to the overall concentration of polysaccharide found in cane

process streams and is responsible for several problems (Moore et al., 2002).

Since ISP is associated with phenolics, it contributes to significant color in the

juice and has a tendency to transfer to the sugar crystal. Further, it has been

implicated in acid beverage floc formation and turbidity in refined sugar and

contributes to the high level of viscosity in cane molasses. Unlike starch and

dextran, there are no specific enzymes available for ISP degradation.

Sugarcane juice primarily contains simple carbohydrates (sucrose 70-88%,

glucose 2-4%, fructose 2-4% of soluble solids) with the other components (3.5-

5.1%) being salts of organic and inorganic acids, starch, gums, waxes, fats and

phosphatides (Clarke, 1993). Furthermore, a small amount of protein (0.5-0.6%

of soluble solids) is also present in the juice (Clarke, 1993) and appears to be

primarily in the form of a high molecular weight glycoprotein (Legaz et al., 1995)

or glucan (Godshall, 1999). Proteins are well-established membrane foulants

(Chan and Chen 2004); however, their role in membrane fouling with sugarcane

juice has not been investigated.

Literature review


Amylo

se

Dextr

an

Amylopec

tin

Leva

n

Figure 3.1 Structure of different polysaccharides in sugarcane (source: www.chem.qmul.ac.uk/iubmb/enzyme/reaction/polysac/levan.html

www.scientificpsychi.com/fitness/carbohydrates1.html )

http://www.chem.qmul.ac.uk/iubmb/enzyme/reaction/polysac/levan.html

http://www.scientificpsychi.com/fitness/carbohydrates1.html

Literature review


In addition to the juice organic components, the lime defecation method

universally applied in sugarcane juice clarification enhances the calcium

concentration. This can be an additional source of membrane fouling (Cheryan,

1998). Calcium ions can precipitate on the membrane surface as phosphate salt.

The presence of calcium ions can lead to increased adsorption by electrostatic

charge shielding, complexation and/or bridging effects. It has been observed to

increase interactions between polysaccharide (alginate) molecules (Jermann et

al., 2007)

The conventional sugarcane juice clarification process results in almost

complete removal of irreversible colloids and waxy materials but only partial

removal of soluble gums and reversible colloids (Chen, 1993b). These

components, in turn, are carried through to the raw sugar. The clarification step

removes around 50% of the polysaccharides but the color components, which

are mainly plant pigments associated with polysaccharides, remain unaffected

(Godshall et al., 2002). Furthermore, a very high molecular weight

polysaccharide component of ~1000 kD was isolated during cane sugar refining

(Godshall, 1999). This polysaccharide, which was pale yellow with a turbid

appearance and had a tendency to be occluded in the sugar crystal, was believed

to be responsible for most of the color in white sugar.

Jacob and Jaffrin (2000) investigated membrane fouling in UF of brown cane

sugar solutions with 15 kD ceramic membranes. Using different models for

fouling at constant transmembrane pressure (TMP) (Hermia, 1982), they

observed that a single model was unable to explain the fouling for the entire

duration of filtration. Pore narrowing was dominant in the initial hour whereas

cake filtration model dominated subsequently. De Barros et al. (2003) adopted a

similar approach while studying UF fouling mechanism with depectinized

pineapple juice. Susanto and Ulbricht (2005) studied dextran-membrane

interaction in an attempt to better understand the nature of polysaccharide

fouling. The analysis indicated formation of a monolayer of dextran on the

membrane surface and there was very little dextran-dextran interaction.

3.2.4 Fouling mitigation strategies

In general, fouling control involves one or a combination of the following

strategies viz. adjusting the feed properties, optimizing the operation conditions

and modification of the membrane surface properties.

Literature review


3.2.5 Feed properties

UF of cane juice at high temperature (70-90°C) and neutral pH (around 7.5)

resulted in better clarification and relatively high permeate flux (Kishihara et al.,

1981; Verma et al., 1996; Saska et al., 1999; Balakrishnan et al., 2000, Ghosh et

al., 2000). The juice type (mixed or clarified) has a significant influence on

membrane flux and fouling. In experiments with 20 kD PES and modified PS

membranes, fouling was considerably higher with mixed juice (Ghosh et al.,

2000) in comparison to clarified juice (Balakrishnan et al., 2001). This was

attributed to higher content of non-sugar impurities in the mixed juice fraction,

which was precipitated out upon treatment with lime in the clarification step.

The effect of suspended solids on juice flux is unclear. Bagacillo present in the

feed stream after initial screening reduced the permeate flux in a cross-flow

system (Ghosh et al., 2000, Balakrishnan, 2000). This was contradictory to an

earlier observation wherein the flux reportedly improved in a stirred cell,

possibly due to scouring effect of the suspended bagasse particles (Kishihara et

al., 1983). Of the different feed pretreatment strategies viz. juice liming, liming

combined with boiling, α-amylase treatment, flocculation of limed and

untreated juice and centrifugation that have been investigated to improve the

juice permeability, liming alone is established to be an effective method of flux

enhancement (Kishihara et al., 1981; Balakrishnan, 2001).

3.2.5.1 Operation parameters

Operation parameters like temperature, trans-membrane pressure (TMP) and

cross-flow velocity (CFV) have a significant impact on fouling.

An increase in temperature from 30 to 60° C almost doubled the sugarcane juice

flux probably due to the decrease in viscosity (Kishihara et al., 1983) At higher

temperature the microbial activity is also reduced Therefore sugarcane juice

filtration was suggested to carry out at maximum possible temperature within

the tolerable range of Browning effect.

In feeds containing suspended particles, the effect of cross-flow velocity on

permeate flux depends upon the particle size distribution (Wakeman and

Tarleton, 1991). With fine suspension, the shear force generated at higher CFV

causes fewer particles to accumulate near the membrane surface and thus

results in lesser fouling. In contrast, larger particles are carried away at higher

CFV and the finer particles settle down onto the membrane surface to cause

Literature review


fouling resulting in reduced filtration rate. This behavior was observed in the

UF of mixed sugarcane juice using 20 kD PES and 50 kD PS membranes in a

cross-flow unit (Balakrishnan et al., 2000). As the CFV was increased, the

permeate flux decreased with increasing TMP. The membrane surface was

visibly covered with a brownish-green layer, attributed to the suspended solids

(bagacillo), which formed a secondary layer on the membrane surface. A

decrease in juice permeate flux upon an increase in TMP was attributed to the

increasing compactness of the fouling layer on the membrane surface. Kishihara

et al. (1981) reported a similar behavior in the UF of limed sugarcane juice in a

stirred cell with 5-200 kD PES and 300 kD cellulose ester membranes. Similarly

in raw sugar melt filtration, membrane fouling was prominent under conditions

of low CFV and high TMP (Dornier et al., 1994). In an investigation on the start-

up procedure of cross-flow MF, a progressive increase in TMP and cross-flow

velocity was observed to result in higher and consistent permeate flux (Dornier

et al., 1995).

3.2.5.2 Membrane surface characteristics

Most of the investigations on sugarcane juice MF/UF have been conducted on

commercial membranes, without any modification in the surface properties. The

effect of surface hydrophilization on sugarcane juice UF was studied by the

adsorption of 0.1% polyvinyl alcohol (PVA) on 20 kD PES membranes

(Balakrishnan et al., 2001). There was a perceptible reduction in fouling with the

PVA adsorbed membrane and the flux decline with time was less than with the

corresponding unmodified membrane. Moreover, the increase in permeate

purity (expressed as a percentage of polarizing substances in the total dissolved

solids) was significantly higher with the modified membrane, indicating a higher

rejection of non-sugar components. More recently, PEGMA (poly (ethylene

glycol) methacrylate) photo grafting on PES membrane surface was reported to

reduce fouling resistance in UF of sugarcane juice polysaccharide fraction

(Susanto et al., 2007); furthermore, the modified membrane also displayed

higher retention of high molecular weight components.

3.3 Membrane cleaning

Membrane fouling, due to deposition of the rejected material on the surface and

within the pores, results in both flux decline and change in membrane

Literature review


selectivity. Strategies like feed-pretreatment, adjusting the operation parameters

and membrane surface modification can minimize fouling but cannot completely

eliminate it. Thus, cleaning is an integral part of membrane applications.

Membrane cleaning can involve one or a combination of the following methods.

physical e.g. ultrasound (Muthukumaron et al., 2004), sponge balls

(Maartens et al., 2002 ), back pulsing (Mores and Davis, 2002)

biological e.g. enzymatic treatment (te Poele and Graaf, 2005) and

chemical using acids, alkalis, disinfectants, detergents (Lee et al., 2001;

Liikanen et al., 2002; Maartens et al., 2002; Kuzmenko et al., 2005;

Strugholtz et al., 2005).

For food processing applications like UF of milk, whey and juices, chemical cleaning is most common (Sayed Razavi et al., 1996; Gan et al., 1999; Rabiller-Baudry et al., 2006a; Kazemimoghadam and Mohammadi, 2007; Cassano et al., 2007c).

The efficiency of chemical cleaning is governed by the choice of the cleaning

agent(s) as well as the cleaning conditions. These include pH, ionic strength,

duration and temperature as well as the cross-flow velocity. Further, if multiple

cleaners are being employed, the sequence is also important. Appropriate

chemicals usage causes less damage to membrane surface thereby extending its

lifetime and reducing the frequency of membrane replacement. Thus,

developing an optimal membrane-cleaning strategy for a given application is

essential since it has a direct impact on the process economics.

For most chemical cleaners, 30-60 minutes is generally required for complete

action (Cheryan, 1998); in fact, prolonged chemical cleaning beyond optimal

time may actually refoul the membrane. Thus, there have been several reports

on short chemical cleaning cycles (up to 30 minutes) for membranes fouled by

various multi-component feed streams viz. food streams like passion fruit juice

(Chiang and Yu, 1987), aqueous extract of soy flour (Sayed Razavi et al., 1996),

apple juice (Borneman et al., 1997), milk (Kazemimoghadam and Mohammadi,

2007), effluents like oily wastewater (Lindau and Jonsson, 1994), spent sulfite

liquor (Weis et al., 2003; 2005), palm oil mill effluent (Ahmed et al., 2005) etc.

Literature review


Various chemicals have been employed for membrane cleaning in food

processing applications. These include sodium hydroxide (NaOH), acids like

hydrochloric acid (HCl), nitric acid (HNO3) and citric acid (C6H8O7.H2O),

oxidizing agents like hydrogen peroxide (H2O2), sodium hypochlorite (NaOCl).

Commercial membrane cleaning detergents and surfactants like Terg-a-zyme

(Alconox Inc.) (Sayed Razavi et al., 1996), Tween 20(Henkel), Ultrasil (Henkel-

Ecolab), Ultraclean II (Koch) (Lindau and Jonsson, 1994; Weis et al., 2005;

Rabiller-Baudry et al., 2006a, 2006b) etc. are also employed extensively.

NaOH is a common cleaner for organic fouling (protein, polysaccharides) and

acts by hydrolysis and solubilization of the organic macromolecules (Liu et al.,

2001). It also helps in loosening the foulant layer by imparting conformational

changes. If hypochlorite is used in combination with NaOH, the cleaning action

is enhanced by the oxidative action of free chlorine, which increases the number

of oxygen containing functional groups and thus increases the membrane

hydrophilicity. Acids are used primarily for removing the scales and metal

oxides from fouling layers. Chelating agents like EDTA

(ethylenediaminetetraacetate) are primarily active against divalent cations.

Surfactants help to clean membranes fouled by fat, oil, and proteins in water by

forming micelles. Therefore, foulant nature determines the choice of the

cleaning agent(s). For example, for milk-fouled membrane in the dairy industry,

Kazemimoghadam and Mohammadi (2007) reported 40% water flux recovery

with NaOCl but acids (HCl, HNO3) or alkali (NaOH) alone resulted in a

maximum of 10% recovery. A combination of EDTA with sodium dodecyl sulfate

(SDS) surfactant and NaOH almost completely restored the water flux. Also,

when employing sequential cleaning, alkaline cleaners should be used prior to

acid cleaners (Mohammadi et al., 2003). This allows the protein and fats in the

cake layer to be dissolved before the acid acts on the mineral component. Initial

application of acid can result in compression of the cake layer thereby increasing

its resistance and aggravating the fouling.

NaOH is an effective cleaner for polymeric membranes fouled with fruit juice.

Borneman et al. (1997) reported complete water flux recovery of apple juice

fouled PES/PVP membranes cleaned with 0.1 M NaOH solution for 30 minutes.

In tubular membranes fouled with passion fruit juice, a 30 minutes water rinse

followed by two 5 minutes cleaning cycles with 0.1% NaOH resulted in full

recovery of the initial water flux (Chiang and Yu, 1987). For PES membranes

fouled with sugarcane juice, around 75% water flux was recovered with 0.1%

Literature review


NaOH at 60°C for 15 minutes cleaning duration (Ghosh et al., 2000). The water

flux recovery could be enhanced to 90% by 30-90 minutes cleaning with 0.1-

0.3% enzymatic detergent at 40°C (Balakrishnan et al., 2001).

Membrane cleaning in successive steps is often more promising than single step

cleaning. For example, in the cleaning of membranes fouled with aqueous soy

flour extract using different cleaning agents viz., NaOH (0.5wt%, pH 12.5),

NaOCl (150 ppm), HCl (0.5wt%, pH 1.5) and protease detergent (0.75wt% Terg-

a-zyme), a maximum water flux recovery of 42% was obtained with the protease

detergent over 30 minutes cleaning at 50°C (Sayed Razavi et al., 1996). For the

same membrane, almost complete recovery was reported when the same

cleaning chemicals were used in successive steps viz. NaOH, followed by

protease and then NaOCl.

In recent years, cleaning of protein-fouled membranes has been investigated

extensively (Argüello et al., 2005; Tran-Ha et al., 2005; Kuzmenko et al., 2005;

Bansal et al., 2006; Mourouzidis-Mourouzis and Karabelas, 2006; Chen et al.,

2006; Platt and Nyström, 2007). Polysaccharides are common membrane

foulants in juices as well as in wastewater streams (Mänttäri et al., 2000;

Hatziantoniou and Howell, 2002; Jarusutthirak et al., 2002; Vernhet and

Moutounet, 2002; Kimura et al., 2004); however, there are limited studies on

cleaning of polysaccharide-fouled membranes. Strugholtz et al. (2005) evaluated

the performance of different chemicals and their combinations as well as the

effect of temperature in the cleaning of 0.1µm PES MF membranes fouled in

water treatment. The analysis of cleaning solutions using Liquid

Chromatography–Organic Carbon Detector (LC-OCD) revealed the maximum

removal of polysaccharides by 50ppm NaOCl solution at 20°C. In another study

with surface water fouled PES hollow fiber membranes, Batsch et al. (2005)

reported enhanced polysaccharide removal efficiency at longer cleaning duration

(24h) using NaOH at pH 12. In a recent report (Sakinah et al., 2007), alkaline

cleaning (0.1N NaOH) was found to be more effective in restoring water flux for

cyclodextrin (oligosaccharides with 6-8 glucose residues) fouled PES membrane

than acid cleaning (0.1N HCl). The starch and protein removed by the alkali was

double the amount removed by the acid.

Literature review


3.4 Membrane surface modification for fouling control

Surface hydrophilization by introducing large number of hydrophilic groups

(like –OH) results in reduced membrane fouling by aqueous feed stream

components (Cheryan, 1998; Mulder, 2000). Consequently, several researchers

have examined altering UF membrane surface (Figure 3.2) properties using

various methods. These include UV induced graft polymerization (Yamagishi et

al., 1995a, b; Ulbricht et al., 1996a, b, 1998; Kilduff et al., 2000; Kaeselev et al.,

2001, 2002; Kim et al., 2002a; Taniguchi et al., 2003, 2004; Hilal 2003, 2005;

Susanto et al., 2007), surfactant treatment (Grebenyuk et al., 1998), coating with

oriented monolayer using Langmuir-Blodgett methods (Kim et al., 1989),

chemical modification involving introduction of side chains by aromatic

substitution and their subsequent modification (Nabe et al., 1997; Kukovičič et

al., 2000), redox initiated grafting (Belfer et al., 2001, 2004; Gilron et al., 2001;

Good et al., 2002), plasma modification (Ulbricht and Belfort, 1995, 1996; Kim

et al., 2002b; Wavhal and Fisher, 2005; Zhao et al., 2005; Tyszler et al., 2006),

and ion-beam irradiation (Chennamsetty et al., 2006). Kato et al. (2003) have

presented a comprehensive review of polymer surface modification.

Of these various approaches, photochemical surface modification has distinct

advantages. It can be performed at mild reaction conditions and low

temperature, high selectivity is possible by choosing suitable reactive groups /

chromophores and respective excitation wavelengths (Ulbricht et al., 1996b), it

is simple, low cost and has a wide range of applications (Taniguchi et al., 2003;

Pieracci et al., 1999). In addition, this method mainly impacts the membrane

surface and thus does not affect the properties of the bulk polymer (Chan, 1994).

Commonly used monomers for photochemical modification include

polyethylene-glycol ester of methacrylic acid (PEGMA), methacrylic acid (MA),

2-hydroxyethyl methacrylate (HEMA), sulfopropyl methacrylate (SPM),

dimethyl-amino ethyl methacrylate (DMAEM), 2-acrylamido-2-methyl

propanesulfonic acid (AMPS), N-vinyl-2-pyrrolidone (NVP), 2-

acrylamidoglycolicacid monohydrate (AAG), 2-acrylamido-1-methyl-1-

propanesulfonic acid (AAP). Figure 3.3 shows the chemical structure of different

monomers.

Literature review


In most of the studies, performance of the modified membranes has been tested

using model macromolecules, especially proteins. Increased hydrophilicity after

surface modification resulted in decreased protein fouling especially due to

lower adsorption; besides the membrane performance improved in terms of

higher permeate flux and retention (Yamagishi et al., 1995b). PES membranes,

surface modified by pre-adsorption of poly (sodium 4- styrene sulfone) (PSS)

have shown better antifouling properties with dextran and polyethylene glycol

(Reddy et al., 2003). In another study, Kaeselev et al. (2002) modified the

surface of 50 kD PES membranes by UV grafting of different monomers viz.

NVP, AAG and AAP. NVP modified membranes exhibited higher dextran

retention when compared to membranes modified by AAG and AAP. This was

ascribed to a strong cross-linking of the grafted NVP chain. Similarly modified

PS and PES membranes also showed low protein fouling even at low degree of

grafting; also, they displayed excellent cleaning characteristics (Kaeselev et al.,

2001).

Membrane surface modification can also reduce the potential of biofouling

(Hilal, 2003). Quaternary 2-dimethyaminoethylmethacrylate (qDMAEMA)

grafted on commercial PES MF membranes displayed much less affinity towards

biofouling compared to the unmodified membrane when tested with Escherichia

coli suspension.

In another study, modification of NF membranes by graft polymerization of

hydrophilic monomers viz., PEGMA, MA, SPM, DMAEM resulted in reduced

adsorption of the model polysaccharide karaya gum (Belfer et al., 2004). FTIR

spectra of the fouled membranes showed minimum adsorption of karaya gum on

the PEGMA grafted membrane surface. Further, SPM and PEGMA grafted

membranes exhibited lower initial flux decline in the NF of karaya gum; also, the

water flux was readily recovered after washing the membrane with water.

O

O

OH

O

OH

O

Figure 3.2 Monomer grafted on a membrane surface

Literature review


Figure 3.3 Different monomers used for membrane surface modification and grafting on

membrane surface

CH2 NH C

CH

3

OH CH C CH

2

O O

AAP

CH

3 S

O

O

(CH2-CH2-

O)n

H O

CH

3

C H2C

C

PEGMA

AMPS

NH

O CH2 C

HSO3CH2(CH3)2C

C

H

N O

NVP

SPM

O

O CH2 C

K+ -

SO3(CH2)3

C

CH

3

(CH3)2-N-

CH2-CH2

DMAEMA

O

O CH2 C C

CH

3

CH2 NH CH

OH

OH CH C C

O O

AAG O

CH2-CH2-O H O

CH

3

C H2C

C

HEMA

Documents

3.1 Microfiltration (MF) and ultrafiltration (UF ...shodhganga.inflibnet.ac.in/bitstream/10603/6274/9/09_chapter 3.pdf3.2 MF/UF of sugarcane juice 3.2.1 History and current status