Hollow Fiber Ultrafiltration of Cottage Cheese Whey: Performance Study

Hollow Fiber Ultrafiltration of Cottage Cheese Whey: Performance Study

Hollow Fiber Ultrafiltration of Cottage Cheese Whey: Performance Study B A R R Y R. BRESLAU and B R I A N M. K I L C U L L E N Research and Developmen...

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Hollow Fiber Ultrafiltration of Cottage Cheese Whey: Performance Study B A R R Y R. BRESLAU and B R I A N M. K I L C U L L E N Research and Development Division Romicon, Inc. 100 Cummings Park Woburn, MA 01801

to each experiment the membranes were cleaned by recirculating a .5 to 1% caustic solution at 100 to 120 F. The cartridges then were backflushed with an ultrafiltered caustic solution produced from the initial caustic recirculation. The final step was sanitization with 100 to 200 p p m sodium hypochlorite at room temperature followed by a thorough rinsing. Centrifugal, positive displacement, and airoperated diaphragm pumps were used depending on the size of the cartridge in the particular study. Kjeldahl analyses were standard procedures for dairy products (1, 5).

ABSTRACT

The operation of hollow fiber ultrafiltration systems is discussed. Critical factors of fiber diameter, transmembrane pressure, pH, temperature, diafiltration, and cleanability are discussed for XM50 and PMIO hollow fiber ultrafiltration membranes in cottage cheese whey processing. While each membrane has its own particular characteristics, advantages and disadvantages, the 45 mil XMSO fiber, with 26.5 ft 2 of membrane area (43 in long fibers) is considered to be the optimal fiber for most cheese whey applications.

HOLLOW FIBER T E C H N O L O G Y

INTRODUCTION

Fiber Design

The potential capabilities of ultrafiltration in dairy applications has been generally accepted for many years (2, 3, 4). These capabilities include not only the fractionation of whey but also the concentration of milk, both skim and whole, for more efficient cheese making. In spite of these capabilities, ultrafiltration has y e t to make the dramatic impact on the dairy industry expected of it. This situation is largely the result of equipment manufacturers who have made a wide range of claims about the potential of ultrafiltration but have not provided data to support their claims. The purpose of this paper is not only to introduce a new form of technology to the dairy industry, that of hollow fiber uhrafiltration, but also to provide supporting data in the form of a performance study on the hollow fiber ultrafiltration of cottage cheese whey.

Hollow fiber membranes exist as single, coherent structures which can withstand pressures on either side of the active membrane surface without membrane rupture or separation from the support structure. Many different types of hollow fibers exist as illustrated in Fig. 1 which is a scaled drawing showing three of Romicon's ultrafihration fibers. These fibers are designed to allow flow to occur through the lumen, or inside of the fiber, with minimum prefihration, and each of these fibers has been used extensively on whey. The fiber is anisotropic with a tight thin skin on the inside surface which is supported by a sponge-like

TABLE 1. The effect of pressure drop on Reynolds number and linear velocity for 25 inch long 45 mil and 20 rail fibers. 20 mil fiber

E X P E R I M E N T A L PROCEDURE

All studies were with Romicon hollow fiber XMS0 and PM10 membrane cartridges and routine pressure and temperature control. Prior

Ap,

V,

psi

NRe

ft/s

NRe

ft/s

5 10 15 20

280 580 870 1150

1.9 3.7 5.6 7.6

1670 2620 3220 3570

4.3 6.4 7.6 8.8

Received July 9, 1976.

1977 J Dairy Sci 60:1379-1386

45 mil fiber

V,

1379

1380

BRESLAU AND KILCULLEN

3.f

HF 2 6 . 5 - 4 5 - X M 5 0 PH46 120*F

32

3O

26 24~ 22 2O 18

A

16

D

~

~B

14 12 I0

FIG. 1. Scaled drawing of the dimensions of three of Romicon's ultrafi/tration fibers used in whey processing.

outer structure. The active membrane, or skin, is only ",,.1 /~m thick and provides little resistance to flow. Furthermore, any species which passes through the skin readily passes through the outer structure. Any fouling which occurs, therefore, occurs solely on the skin and not in the sponge-like outer support. Such surface fouling readily can be removed by fluid flowing in the reverse direction, from the outside of the fiber to the inside. This backflushing technique is particularly effective in dairy applications in which there is a definite need periodically to remove calcium, protein, and lipid complexes which deposit on and subsequently foul the surface of the membrane. PERFORMANCE STUDIES-COTTAGE CHEESE W H E Y Effect of Concentration Factor on Ultrafiltration Flux

The flux of an ultrafiltration unit (permeate flow rate per unit of membrane area) usually will decrease as the material being processed is concentrated. This decrease typically follows a semilogarithmic relationship of the form: J =Kz-K2

lnCF

where J is the uhrafiltration flux (gallons/ft2/ day), CF is the concentration factor, and K 1 and K2 are experimental constants. The data of Fig. 2 show that the above equation is obeyed and that the constants K1 and K s tend to increase with increasing transmembrane presJournal of Dairy Science Vol. 60, No. 9, 1977

A

Z23

3,840

30.75

5 25

B

17.5

11,090

28.62

5.10

2D

3,0

4,0

CONCENTRATION

6.0

8D

I0

12 14 16 18

FACTOR

FIG. 2. Relationship of ultrafiltration flux with concentration factor as a function of transmembrane pressure.

sure drop. In this study, at a pH of 4.6 fluxes were maximized by running at a transmembrane pressure of 22.5 psi, which corresponded to a 25 psi inlet, 20 psi outlet pressure profile. This pressure profile results in only a 5 psi pressure drop across the cartridge which translates to low recirculation rates and low pumping costs. It is n o t necessary to operate at a high shear rate to get good fluxes on the 45 mii XM50 cartridge. The HF26.5-45-XM50 cartridge contains 43 inch long, 45 mil diameter XMS0 fibers and has a net membrane area of 26.5 ft 2. The functionality of the constants in Fig. 2 can be taken into account to consolidate the above equation as follows: J = 3.67 APT.12 In [17.2 APT-945/CF] where, APT = average transmembrane pressure drop calculated as the average of the inlet and outlet pressures z~PT = (Pintet + Poutlet)/2 CF = 1/(l-R) where R is the fractional recovery This equation is an empirical equation that describes the data of Fig. 2 as illustrated in Fig. 3. It should not, however, be used outside its domain of development.

COTTAGE CHEESE ULTRAFILTRATION

32

C_OTTAGE CHEESE WHEY HF26b-45-XMSO PH4,1~ " 120;F

30

COTT&GE CHEESE WHEY hlPl. 1 - 4 5 - XMSO

*

a

Z8

22

PH4.~

., i 2 0 " F

~" 20; x

24

IS

~sl

22 ~

1381

a0 FS

~-

iS!

E

14

EMPIRICAL RELATIONSHIP o IZ

- - 0~45

EMPIRICAL RELATIONSHIP

g

- - L20

E .... 1

ISS82 &P In ~ r

r 2 094

rZ o,9 I w

2

4

6

8

IO [~ 14 I~

I~ 20 ~2 ~4 26 ~

~0 32 ~4 EXPERIMENTAL

EXPERIMENTAL ULTRAPILTRATION FLUX ,GSFD

FIG. 3. Comparison of calculated vs. experimental ultrafiltration fluxes for the HF26.5-45-XMS0 car-

tridge.

In certain instances, depending on the quality or degree of clarification of the raw f e e d whey, the semilogarithmic relationship of Fig. 2 will cross showing that while it may be best to operate a high t r a n s m e m b r a n e pressure in the early stages of concentrating, it may be best to switch to a slightly higher recirculation rate (lower t r a n s m e m b r a n e pressure, APT, and subsequently higher shear rate, 4) as the material being c o n c e n t r a t e d b e c o m e s m o r e viscous. This is illustrated in Fig. 4. The penalty one pays for increased recirculation rate is, of course, increased pumping costs. It is definitely advantageous to run at as low a recirculation rate as possible, within the realm of reasonable fluxes.

ULTRAFILTRA¥10N

FLUX ,GSFO

FIG. 5. Comparison of calculated vs. experimental uhrafiltration fluxes for the HFl.l-45-XM50 cart'ridge.

The data of Fig. 4 and the f u n c t i o n a l i t y of the constants again can be consolidated as in Fig. 5. These e q u a t i o n s are empirical relationships which are used for systems design given a specific whe~¢. Figures 2 through 5 s h o w t h a t hollow fiber ultrafiltration of cottage cheese whey, at pH 4.6, follows relatively predictable patterns and that procedures are available for optimizing pressure and f l o w rate parameters. Effect of pH on Ultrafiltration F l u x

The effect of pH on flux is dramatic, and while this i n f o r m a t i o n has been k n o w n previ-

COTTAGE

CHEESE

WHEY

HFI.I-45-XM50 120=F

i

c

::iil

-

,..

50

X

,,

20 PHS 0 tS--"

~

CF=65

I0

i

"

,

a

.

*

~

,o ,z ,,,~,e2;

30

;o

6o

~; ,o~

¢ONC~NTRAT,O~ F~C'O~

FIG. 4. Relationship of ultrafiltration flux with concentration factor as a function of transmembrane pressure.

0

i

L

S AVERAGE

i

I0

i

i

i

IS

TRANSMEMBRANE

J

20

L

i

i

25

30

PRESSURE ,PSI

FIG. 6. Relationship of ultrafiltration flux with transmembrane pressure as a function of pH for a 45 nail XMSO cartridge. Journal of Dairy Science Vol. 60, No. 9, 1977

1382

BRESLAU AND KILCULLEN COTTAGE C H E E S E WHEY HF2.5-20-XM50 .X 120*F

2O u~

/'X--X f

PH i.5

/

PH 3 . 0

" 15

,..I tl.

5

~o

i

5

I0

AVERAGE

i

15

i

20

TRANSMEMBRANE

I

25 PRESSURE,PSI

FIG. 7. Relationship of ultrafiltration flux with transmembrane pressure as a function of pH for a 20 rail XMSO cartridge.

ously, it rarely has been taken advantage of because most ultrafiltration membranes could not withstand low pH environments for prolonged time. Romicon hollow fiber membranes, however, are noncellulosic and routinely can operate in pH environments of from 1.5 to 13.0. As in Fig. 6 through 8 the uhrafiltration fluxes of 45 mil XM50, 20 rail XMS0, and 20 mil PM10 fibers are increased significantly at all transmembrane pressures as the pH is reduced from 4.6. No exceptions exist. This increase in flux with reduced pH is related to the fact that cottage cheese whey is normally at its isoelectric point (pH %4.6) and that any adjustment of pH away from the isoclectric point, either above or below, tends to enhance stability. By adjusting to lower pH's, typically 3.0, the

added benefit of reduced microbial activity is attained. Data in Fig. 6 were collected at a concentration factor of both 6.3 and 1.3 while those of Fig. 7 and 8 were collected at a concentration factor of 1.3. A comparative study of the effect of pH on flux for 45 mil XMS0, 20 mil XMS0, and 20 mil PMIO fibers at a concentration factor of 1.3 is in Fig. 9 along with the effect of pH on the flux of the 45 mil XMS0 fiber at concentration factor 6.3. This figure appears to show that the increase in flux resulting from a decrease in pH is approximately equal for all of the fibers, but this conclusion is misleading. In Fig. 10 the data are replotted on a normalized basis, comparing the relative increase in flux obtained at pH's of 3.0 and 1.5 to that obtained a t a pH of 4.6. The relative effect of pH on the 20 rail fibers is significantly greater than that of the 45 mil fibers and that the 20 mil fibers, both PMIO and XM50, follow a single trend. Correspondingly, a single but reduced trend is followed by the 45 mil fiber at both 1.3 and 6.3 concentration factors. This effect is also in Table 2.

34 32 50

cFHFI'II=. - 4 5 " X M 5 0

28 26

,.a z4 ~ 22 _J u.

g

~

20

HF I.I- 4 5 - X M 30 -~,,~ CF'6

COTTAGE CHEESE WHEY HF/.8-20-PM I0 120"F _

E

_ _

_

~

PH I 5

/x,X

.

g 12

..J tl.

z 0

_

HFZ.5 -20-XMSO

I0

/X

~

^ ~.," PH 3 . 0

HFI.8 - 2 0 - P M I O

=PH 4 . 6 COTTAGE CHEESE WHEY I20"F ~ T " 2 0 . 0 PSI

J

5

AVERAGE

I0

15

20

TRANSMEMBRANE

25

PRESSURE,PSI

4,6

3.0

1,5

PH

FIG. 8. Relationship of ultrafiltration flux with transmembrane pressure as a function of pH for a 20 rail PM10 cartridge. Journal of Dairy Science Vol. 60, No. 9, 1977

FIG. 9. Effect of pH on ultrafiltration flux for 20 rail PMIO, 20 nail XMSO and 45 mil XMSO fibers.

C O T T A G E CHEESE U L T R A F I L T R A T I O N

13 8 3

34

COTTAGE 5.0

CHEESE

PT" 20 PSI

"#HEY

32

I20"F

COTTAGe CHEESE WHEy H~!S-4~-X,50 mO'F

"~

30

CF - 1.3

2e tS 24

HFI.8-20-PMIO H F 2.5 -20-XMSO 8 =18,240

1.8

HF1.8

-ZO- PMIO

H F 25

-20 - XM 50

z

1.5

~

m

~

m



o

~

"<-i:,; ........

~

~ ~ 0 o

I~T'175pSI

©

oo

u.

HFIA-45-XMSO

0 •~

o

~

sec -I

,/ a.o @ x

=

~= 9 , 1 7 0 s e c -~

SOLID DATA• pH 3 0 OPEN DATA =pH 4 6

1.3

3 4

8

8

IO 12 14 11~18~0

25 30

CONCENTRATION FACTOR

FIG. 11. Relationship o f ultrafiltration f l u x with c o n c e n t r a t i o n factor as a f u n c t i o n o f pH and transm e m b r a n e pressure. PH

FIG. 10. N o r m a l i z e d effect o f pH on ultrafiltration flux for the 2 0 mil PMIO, 2 0 mil X M 5 0 and 4 5 mil X M 5 0 fibers.

Effect of Concentration Factor on Ultrafiltration Flux at a pH of 3 . 0

By adjusting the pH to 3.0, approximately a 78% increase in flux was realized with the 20 rail fibers while an increase of approximately 33% was realized with the 45 mil fibers. All fibers in this study were operated in laminar flow, but the 20 rail fibers were operated at a much higher shear rate which is believed to be responsible for the increased flux by altering the rheology of the whey protein concentrate at low pH.

The relationship of uhrafihration flux with concentration factor at a pH of 3.0 as compared to that obtained at pH 4.6 is in Fig. 11 for the 45 rail XMS0 fibers. As illustrated, a semilogarithmic relationship is obtained, but at a significantly higher flux. Figure 11 also shows the effect of transmembrane pressure on flux at a pH of 3.0. In this case the optimum flux is at a transmembrane pressure of 20 psi (25 psi inlet pressure, 15 psi outlet pressure) which is at a slightly higher shear rate than that which occurs at a transmembrane pressure of 22.5 psi (25 psi

TABLE 2. Effect of pH o n ultrafiltration flux. F l u x at pH ( X ) / F l u x at pH 4 . 6 Fiber

.~a

cFb

4.6

3.0

1.5

20 mil XMSO 20 mil PMIO

18,240 18,240

1.3 1.3

1.00 1.00

1.77 1.79

2.38 2.40

4 5 mil X M 5 0 4 5 mil XMSO

9,170 9.170

1.3 6.3

1.00 1.00

1.33 1.34

1.51 ...

aShear rate, s-1 . b c o n c e n t r a t i o n factor. Journal o f Dairy Science Vol. 60, No. 9, 1977

1384

BRESLAU AND KILCULLEN COTTAGE

20

= ~ 3 , o 4 0 s e e "1

~ =Z417805ec -I

~

18

~

~

WHEY

HFIS-45-XMSO

49oc

IZO*F

--~PT • 2 2 . 5 PSI

30

°

28 x" 14

CHEESE

PH" 4.6

32

0 0

0

0 0

~

= 25,600 mee-q

26

4O*C ~? = 23,954 see-I

~ z4

=~ ,0 x

=,

22

20

"~0 "~0

0.......~~

COTTAGE CHEESE W~EY HF30-E0-XMS0

g,;2o

~X~

---J

I

2

4

8

t6

3Z

3

CONCENTRATION FACTOR

0

inlet pressure, 20 psi outlet pressure). A graphic demonstration of the effect of shear rate on ultrafiltration flux at pH 3.0 is in Fig. 12 which pertains to the 20 mil XM50 fibers. In this study, at both 40 C and 49 C, the ultrafiltration flux is relatively, independent of concentration factor to a concentration factor as high as 24×. This trend, which has been confirmed repeatedly, is believed due to the combined effect of relatively high shear operation and low transmembrane pressure (17.5 psi). Since this trend is only at pH 3.0, it also is believed to be associated with the rheology of the whey protein concentrate at pH 3.0. Effect of pH on Diafiltration Fluxes

It is often desirable to produce a high purity whey protein concentrate by selectively washing out low molecular weight species. This is accomplished by a diafiltration operation which consists of adding water to the whey protein concentrate and ultrafiltering until the net water added is removed as permeate. Since the membrane continues to retain the higher molecular weight proteins but allows the low molecular weight species to pass, the net effect of diafihration is increasing the protein content of the retained species on a dry solids basis. If the diafiltration operation is at pH 4.6, the fluxes will tend to decrease as in Fig. 13. This is due to the fact that diafiltering at pH 4.6 produces a slightly unstable concentrate, J o u r n a l o f D a i r y S c i e n c e Vol. 6 0 , N o . 9, 1 9 7 7

INITIAL FIRST

FIG. 12. Relationship of ultrafiltration flux with concentration factor as a function of temperature for the 20 rail XM50 fibers.

[] X

I0

CONCENTRATION

LEVEL

OF DtAFILTRATION

SECOND LEVEL

OF DIAFILTHATION

F I N A L CONCENTRATION ON DIAFILTERED WHEY

2,0

4.0

CONCENTRATION

OPERATION

6.0

8.0

IOD 12.0

FACTOR

FIG. 13. Relationship of ultrafihration flux with concentration factor as a function of diafiltration at pH 4.6.

and a lipid or protein complex (believed to be calcium associated) is formed which tends to come out of solution and coat the membrane surface. The fouling is reversible, but, nevertheless, it serves to reduce the operating flux. As in Fig. 14, if the diafiltration operation is at pH 3.0, no such fouling occurs and the rate of uhrafiltration actually increases. This increase is due to the reduced solids content of the whey protein concentrate. Supporting evidence of increased fouling at pH 4.6 can be obtained by comparing the rejection coefficients for the same membrane, 45 mil XM50, at a constant concentration factor (10×). The data of Table 3 show that the NPN species and lactose arc being retained much higher at pH 4.6 than at pH 3.0; this additional retention could be the result of secondary membrane building up on the surface of the active membrane. Effect of Temperature on Ultrafiltration Flux

The effect of temperature on ultrafiltration flux at a transmembrane pressure of 17.5 psi is

COTTAGE CHEESE ULTRAFILTRATION

56

26

54

COTTAGE HF26.5

Z4

PH4.6

DIAF~LTR ATION LEVEL

32

1 3 85

CHEESE

WHEY

-45-XM50 120=F

50

x

28

~ z6 2X c*.

24

0"

~x

•h.J

18

z

16

~ 2z ~

2o

ft.

16

"~ ~: .p.j ,T <[ ne Ia :D

CONCENTRATING OPERATION

g

O

OI AFILTERING

I0 8

OPERATION

6

IZ

10

0

DOWN

X

UP

SCALE

SCALE

4 COTTAGE CHEESE WHE_Y PH 3 . 0 HFI5-45-XMSO 1200F

2

~'PT = 22 5 PSI

0

• 80

1 90

I I00

I IlO

TEMPERATURE 0 0

i I0

I 2.0

40

6.0

CONCENTRATION

80

I0.0 12,0

FACTOR

FIG. 14. Effect of diafiltering at pH 3.0 on ultrafihration flux.

in Fig. 15. The study was during both heating and cooling and showed no hysteresis effect. Increased temperature resulted in increased fluxes with the increase averaging at .43 GSFD/C. Over a temperature range, the ultrafiltration flux increased 50%, or 3.0%/C. Obviously, to maximize fluxes high temperature operation is recommended wherever possible. High temperature operation has the added benefit of reducing microbial activity. SUMMARY This paper serves to review the performance

TABLE 3. Effect of pH on membrane rejections. Average membrane rejections

Protein (TCA, ppt) NPN a Lactose a

SFD • 0 , 2 4 - =F

- dT

12

.

.

pH = 4.6

pH = 3.0

.973 .310 .090

.979 .079 .000

I [20

*F

FIG. 15. Effect of temperature on ultrafiltration flux on a whey protein concentrate having a concentration factor of 2X.

of hollow fiber membranes on the uhrafihration of cottage cheese whey. The effect of a number of fiber parameters were discussed as well as a number of operating parameters. One performance criteria, aside from cleanability, is to determine the ratio of the flux of a given membrane to its recirculation rate normalized for membrane area. One would want to get as high a flux as possible with m i n i m u m recirculation (pumping costs) provided the recirculation was sufficient to keep the membrane free from fouling. The comparative performance of each hollow fiber on this basis is presented in Table 4. The 45 mil XMS0 fiber offers a distinct

T A B L E 4. P e r f o r m a n c e f a c t o r f o r c o t t a g e c h e e s e w h e y as a f u n c t i o n o f f i b e r d i a m e t e r , l e n g t h , a n d p H . P . F . = flux × 100/recirculation rate. pH = 4.6

pH = 3.0

20 mil XM50 (25") 20 mil PM10 (25")

1.87 2.50

... 4.30

4 5 rail X M 5 0 ( 2 5 " ) 4 5 mil X M 5 0 ( 4 3 " )

4.50 9.80

... 12.70

Nonprotein mtrogen. J o u r n a l o f D a i r y S c i e n c e Vol. 6 0 , N o . 9, 1 9 7 7

13 86

BRESLAU AND KILCULLEN

o p e r a t i n g a d v a n t a g e over t h e 2 0 mil fibers; also p H 3.0 o p e r a t i o n offers a n a d v a n t a g e o v e r p H 4.6 o p e r a t i o n in all cases. ACKNOWLEDGMENT

T h e assistance of Paul R. L a m b e r t , K e n n e t h J. L a m b e r t , a n d David F. P e n s e n s t a d l e r in a n a l y z i n g t h e d a t a is a p p r e c i a t e d greatly as is t h e assistance of D o n a l d A. V e n t u l l o , w h o did t h e g r a p h i c a l work.

Journal of Dairy Science Vol. 60, No. 9, 1977

REFERENCES

1 Bradstreet, R. B. 1965. The Kjeldahl method for organic nitrogen. Academic Press, Inc., New York. 2 McDonough, F. E. 1971. Membrane processing. Dairy Ind. 36:507. 3 Michaels, A. S. 1968. New separation technique for the CPI. Chem. Eng. Prog. 64:31. 4 Mort, C. V. 1976. Whey protein concentrates: an update. Food Tech. 00:18. 5 Standard methods for the examination of water and wastewater. 1971. 13th edition. Amer. Public Health Ass., Washington, DC.