MEMBRANES SEPARATION5 TECHNOLOGY FOR ...c Desalination, 56 (1985) 17-35 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands MEMBRANES SEPARATION5 TECHNOLOGY FOR

c

Desalination, 56 (1985) 17-35 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands

97 I I3 MEMBRANES SEPARATION5 TECHNOLOGY FOR INDUSTRIAL

By Peter S. C a r t w r i g h t , P . E . , C3 International, Roseville, M EFFLUENT TREATMENT - A REVIEW

INTROOUCTIMJ

Yhereas water p u r i f k e t i o n appl icat ions have been the dominant

markets f o r membrane separation technologies t o date, e f f l u e n t

treatment appl icat ions offar outstanding p o t e n t i a l f o r t h e future.

Today, opportuni t ies abound for e x i s t i n g membrane polymers and

conf igurat ions, but a very r e a l "knowledge gap" has prevented

greater use o f these technologies i n e f f l u e n t treatment appl ica-

t ions. Basica l ly , the end usor i s ignorant o f the p o t e n t i a l s

o f fered by these technologies end the membrane systems menufac-

t u r e r is equal ly uninformed about these applications.

Equally important, although the membrane element and systems

manufacturers are vary capable w i t h regard t o understanding mem-

brana performince or system design i n water p u r i f i c e t i a n applica-

t ions, they e x h i b i t an appal l ing leck o f confidence when confront-

ed w i th an e f f l u e n t treatment appl icat ion. This paper w i l l

attempt t o a l l a y these fears and provide a l e v e l o f confidence t o

enable t h e manufacturer t o take advantage o f t h e opportuni t ies

of fered by t h i s burgeoning market.

BACKGROUND

91Efflusnt11 can be defined a6 I waste component from a manufactur-

i n g o r processing a c t i v i t y .

The reasons f o r considering waste treatment are many and varied:

1) Government Regulation - The Federal Resource Conservation and Recovery Act [RCRA]

i d e n t i f i e s many water-borne contaminants which are con-

s idered t o be h&alth r i s k s , and regulates t h e i r discharge.

S ta te and l o c a l regulatory agencies must a t least m e e t the

Federal standards; however, many o f these egencies have

chosen t o impose even s t r i c t e r l i m i t s . Such diverse fac-

t o r s IS the indust ry involved, populat ion demographics end

f a c i l i t y i n t o which the eFfluent i s directed, e.g. p u b l i c l y

owned treatment works [POTW], stream, r i v e r , ocean, etc.

a f f e c t these decisions. Although many indust r ies have not

yet been regulated, i t is j us t a matter o f t i m e before sddi-

0011-9164/85/$03.30 Elsevier Science Publishers B.V.

18

21

31

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t i o n e l r e s t r i c t i v e regulat ions w i l l be promulgated. The

l i s t o f po l l u tan ts suspected o f causing cmcor , b i r t h ds-

fects o r other t o x i c react ions is g e t t i n g much longer and

w i l l continue t o grow.

Environmental Pressures - Powerful voices throughout t h e world arm being heard c la -

moring f o r even t i g h t e r and more r e s t r i c t i v e discharge reg-,

ulat'ions. Although many o f these concerns are no t founded

in fact , however, they represent a persuasive lobby and are

expected t o fur ther exacerbate the rush towards more t i g h t -

er discharge regulat ions.

Solute/Solvent Recovery - There are numerous cases o f economic bene f i t provided by

the recovery o f dissolved o r suspended mater ia ls from the

s f f luent stream, as we l l as the recovery o f the, solvent it-

self. W i t h t he increasing sca rc i t y o f raw materials, t he

concept of reuse o r recover ing and s e l l i n g t h e so lute

commands serious consideration. In addit ion, as h igh qual-

i t y water becomes increas ing ly scarce, i t w i l l become more

cos t l y t o purchase, thereby prov id ing incent ive f o r water

reuse also.

Technology Benefi ts - The membrane separation processes o f f e r t he fo l lowing ad-

vantages when compared t o other means o f separation:

- Low energy u t i l i z a t i o n - no phase o r temperature

i

\ change involved

- Continuous process- prov id ing t h e advantages of auto-

mation and uninterrupted operation

- Low maintenance w i t h a m i n i m u m o f moving pa r t s - t he

systems are easy t o operate and maintain

MEMBRANE TECHNOLOGY REVIEW

The four membrane separations technologies addressed in t h i s

peper - M i c r o f i l t r a t i o n

- U l t r a f i l t r a t i o n

- Reverse Osmosis

- E lec t rod ia l ys i s

Although they a l l accomplish separation o f l i q u i d borne contami-

nants from the l i q u i d , each u t i l i z e s a d i f f e r e n t separation mecha-

n i s m and each has spec i f i c advantages and disadvantages when com-

pared t o t h e others.

an attempt w i l l be made t o address these technologies i n terms o f

In s p i t e o f the d i f f i c u l t i e s i n general iz ing

t h e i r eFfectiveness i n trol l

spec i f io industr ies.

Figure 1 depict= t h e mechaii

m i c r o f i l t r a t i o n involves t t t

ranging i n s i z e from 0.1 ~ I I

'aostroms].

Microf iltr;

Figure 2 depic ts u l t r a f i l t r

mater ia le i n t h e .OOl t o O.,

Basical ly, u l t r a f i l t r a t i o n

whi le the suspended s o l i d s

* <e'* wate 1'.

r i

will be promulgated. The

causing cancer, birth de-

is getting much longer a d

world are being heard cla-

9 restrictive discharge reg-

3 0 concerns ere not founded

: a persuasive lobby and are

:he rush towards more tight-

iomic benefit provided by

rpended materials from the recovery of the solvent it-

: i t y o f raw materials, the

ind selling the solute

In addition, as high qual-

aarce, it will become more

iding incentive for water

9s offer the following ad-

means o f separation:

ihase or temperature

3 the advantages of auto-

-at ion

rm o f moving parts- the

and maintain

3ies addressed in this

1 o f liquid borne contami-

different separation mecha-

3nd disadvantages when com-

difficulties in generalizing

;e technologies in terms o f

19

their effectiveness in treating effluent streams f r o m a number of

specific industries.

Figure 1 depicts the mecheniem of microfiltration. microFiltration involves the removal of particulate materials

ranging in size from 0.1 to 10.0 microns [lo00 to ~OO,OOO ‘enstromsl.

Generally,

Microf iltration

macromolecules

4

Figure 2 depicts ultrefiltretion, which is used to separate materiels in the .001 to 0.1 micron ranga (10 to 1000 enstroms) . Basically, ultrefiltration is used to remove diesolved materials while the suspended solids are removed by microfiltration.

20

Figure 3 i l l u s t r a t e s reverse osmosis which t yp i ca l l y sepmrates

mater ia ls lese, than .001 micron (10 angstroms i n size]. Revorse

osmosis o f f e r s t h o added advantage o f r e j e c t i n g i o n i c mater ia ls

which ere normally small enough t o pass through the pores o f the'

membrane. A s w i t h u l t r a f i l t r a t i o n , reverse osmosis is used t o

remove dissolved materials.

Reverse Osmos

MEMBRANE - * . .".. ....

Figure 4 depicts e l e c t r o d i a l y s i s which u t i l i z e s permeable mem-

brane a m we l l as an anode and cathode t o e f f e c t separation. In-

stead o f d r i v i n g pure water through the membrane and leav ing contaminants behind, as i n thecsse o f t h e other membrane processes,

e lec t rod ia l ys i s u t i l i z e s membranes which se lec t i ve l y al low e i t h e r

the ca t i on i c or anionic so lute t o pass through i n response t o the

e l e c t r i c a l charges imposed by thyanode and cathode.

CATHODE d C

C A M ' X '

Cation Selective Membrane Anion Seleclive Membrane

Metal Catlons Anions

SYSTEM DESIGN CONSIOEAATIOM

In order t o t r e a t an eff lue

analyzed for t h e fo l lowing

To ta l s o l i d s contt

Suspended [TSS

Dissolved orgs

Dissolved inorr

Spec i f i c chemicall

Oxidiz ing chem

Organic so lver

PH Op e r a t i n g t emper E

Usually, t he goal i s t o "de

possible; t h a t is , t o remob

removal of t h e concentratec

the poss ib le reuse o f the F These two considerations a r

process and membrane davicc

Figure 5 depicts a general

of m i c r o f i l t r a t i o n , u l t r a f i i

these technologies, t h e i m p

process is described by the!

the permeate volume dividem

the percentage o f t h e feed

brane. Typica l ly , f o r e f F U

covery f i g u r e i s a t least E

crease concentrate volume1 ,, pended s o l i d s i n the concern

QF - F M C l o r r m t a

CF - Soluta o m o r r c r u l m Irr PP - P a r a o r r e C l w r r r a

CP - Solutr cmcutt r r r lm Im

PC - C a c m t r u a flor rmto

CC - Solu ta c o n c m o r a t l m Irr

t Figure 5. Membrane p r o c e s s l n i

i i c h t yp i ca l l y separates

getroms i n size]. Reverse

.e j a c t i n g i o n i c mater ia ls

i through the pores OF the '

' ipse osmosis is used to

4EMBRANE

u t i l i z e s permeable mem-

o e f f e c t separation. In-

membrane and leav ing con-

other membrane processes,

9 s e l e c t i v e l y al low e i t h e r

through i n response t o t h e

and cathode.

ODE C Cation Seleclwe Membrane

0 M+ MeIaI Cations A Anion Selective Membrane

X' Anions

SYSTEM DESIGN CONSXOERATIONS - order t o t r e a t an eFfluent stream, i t must be thoroughly

analyzed f o r t h e Fol lowing data:

Tota l s o l i d s content

Suspended CTSS)

Dissolved organic [TOC]

Dissolved inorganic (TDS)

Spec i f i c chemical const i tuents

\

Oxidiz ing chemicals

Organic solvents

PH Operating temperature

Usually, the goal is t o "dewater*' the feed stream as much es

possible; t h a t is, t o remove solvent t o f a c i l i t a t e e i t h e r reuse o r

removal o f t h e concentrated solute. O f secondary importance is

the possible reuse o f t h e pur iF ied so lvent- [usual ly water).

These two considerations are s ign iF icant i n determining both the

process and membrane device t o be usad.

Figure 5 depicts a general schematic For the membrme processes

OF m i c r o f i l t r a t i o n , u l t r a F i l t r a t i o n and reverse osmosis. In

these technologies, t h e imp l i ca t i bn OF increasing t h e dewatering

process is described by the term *'recovery,** which is def ined as

the permeate volume divided by t h e Feed volume, i n other words,

the percentage OF the Feed flow which i s pumped through the mem-

brane. Typica l ly , For eFFluent treatment appl icat ions, t he r e -

covery f i gu re i s e t least 90%. A s recovery i s increased [ t o de-

crease concentrate volume], t he concentrat ion OF so lute and sus-

pended s o l i d s i n the concentrate stream increases.

MEYIHANE ELEMENT LI

> PERMEATE STREAM \

-- \

-. ' F cF - \ QP CP

FEED STREAM

-- F& flom rlCr

S o l u t r o a c m r r + l a In frmd

P C I I L . flor m. bolut. cacmntrr+la In PCIIL-

C o M l m t r m t r f l a w r.tr

S o l u t r c o n e m t r r t l a In co11suitrmtr

Figure 5. Membrane processing schematic

RECOVERY = PP QF

( E x p r r m i r d m prrcmntl

22

For the processes o f ultrafiltration and reverse osmosis which

deal with dissolved materials, a property o f the solution known as

"osmotic pressure" becomes a limiting factor. Osmotic pressure ie

a characteristic of all solutions, and is loosely defined as the resistance of the solvent portion o f the solution to freely pass-

ing through the membrane. Osmotic pressure is e function o f both

the particular solute as well as its concentration.

The recovery of a system can be controlled by restricting the

quantity of flow in the concentrate stream, normally through the

use of a concentrate valve. As recovery is increased, with the resulting decrease in concentrate flow, the concentration o f

solute in the concentrate stream increases, which results in an

increased osmotic presure.

No membrane is perfect in that it rejects 100% o f the solute on

the feed side; this solute leakage is known as q'passage.t* Ex- pressed as "percent passage, ,' the actual quantity o f solute which passes through the membrane is a Function o f the concentration OF

solute on the feed side. Under high recovery conditions, the con-

centration of solute on the feed side is increased and therefore the actual quantity o f solute passing through the membrane also increases. Because most effluent applications demand that, in

addition to a minimum concentrate volume,'the permeate quality be

high enough to allow reuse or to meet discharge regulations, the

"Catch-22" predicament o f permeate quality decreasing as recovery

is increased can impose design limitations. A,dditionally, the

increased osmotic pressure resulting as recovery is increased also imposes a design limit. Generally, pumping pressures in excess

o f 1000 psi are impractical for most applications.

Electrodialysis systems separate ionic species from water and

other dissolved materials by attracting the salts through the

membrane. Because pumping energy is not used to effect the sepa-

ration, osmotic pressure is not a factor; however, the conductiv- ity o f the solution is important and becomes a factor limiting the

degree o f purification that can be accomplished. The maximum con-

centration that can be obtained is generally limited by practical

considerations o f membrane surface area required and equipment

costs. When comparing alektrodialysis to reverse osmosio,the

Former process can generally produce concentrate streams ten times

the concentration o f reverse osmosis; however, non-ionic soluta

cannot be concentrated and the permeate is not as pure in dis-

solved ionic concentration a!! With regard to membrane eletncc

important physical character..

device configurations avail all

Element Conf iquration Spiral wound H

Tubular L I 1

L I1 Plate and frame Hollow fine fiber H

Electrodialysis stack L I 1

*Membrane area per unit volutl

Because o f the propensity O F

to settle w t on the metnbranci

turbulent flow conditions muif

excess o f 2000). For high r f l

quires recycling a significaii

to the feed side OF the pump

stream into the feed solutiou

sol ids c oncentr at ion f urt her

TESTING CONSIDERATIONS

A l l o f these factors: recovri lity, recycle, etc., serve ti

specific waste stream as tho11

effluent streams often vary

is important that either a c

be obtained f o r test purpose!!

or more of the following1

when evaluating membrane tectl

stream.

Cell Test - Utilizing small 1 1

Of sheet membrane mounted in1 to the test solution using ttl is effective For quick evalui membrane polymmre to determiti

Advantegecr: Fast

Inexpensi

Only smat requi,

id reverse osmosis which

' t y of t h e s o l u t i o n known as

actor. Osmotic pressure is

i s loosely defined as the

e s o l u t i o n t o f r e e l y pass-

sure i s a func t i on o f both

ncentrat ion.

l ed by r e s t r i c t i n g the

em, normally through the

y i s increased, w i t h the

the concentrat ion o f

5es1 which r e s u l t s i n an

ts 100% of t he so lu te on

i o w n as @ypassage.l@ Ex-

1 quan t i t y of so lu te which

in of t h e concentrat ion o f

:overy condi t ions, t he con-

s increased and therefore

irough t h e membrane a l so

at ions demand t h a t , i n

I, the permeate q u a l i t y be

scharge regulat ions, t he

t y decreasing as recovery

ns. A,dditionslly, the

recovery is increased a l so

i n g pressures i n excess

l i c a t i o n s .

pecies from water and

the s a l t s through the

used t o ef fect the sepa-

; however, the conductiv-

omes a factor l i m i t i n g the

Dlished. The maximum con-

s l l y l i m i t e d by p r a c t i c a l

'equired and equipment

J reverse osmosis,the

:entrate streams ten t imes

uever , non-ionic so lu te

is n o t as pure i n d i s -

23

i o n i c concentrat ion as tha t produced by reverse osmosis.

w i t h regard t o membrane element c o n f i ~ r a t i o n , Table 1 l i s t s the

important phys ica l character is t ics of t he various membramelement

device conf igurat ions avai lable today:

TABLE 1

E 1 cment Packing Suspended Sol ids Confiquration Oensity* To1 erance

S p i r a l wound High F a i r

Tubular Low High

p l a t e and frame Low High

~ ~ l l o w f i n e f i b e r Highest Poor

E lec t rod ia l ys i s stack Low High

*Membrane area per unit volume

Because o f t he propensity of suspended or p r e c i p i t a t e d mater ie ls

t o s e t t l e out on t h e membrane surface and p lug the membrane pores,

turbulent Flow condi t ions must be maintained [Reynolds numbers i n

excess of 20001. For high recovery systems, t h i s usua l l y r a -

quires recyc l i ng a s ign i f i can t percentage o f t he concentrate back

t o the Feed s ide of t he pump. The add i t i on o f t h i s concentrate

stream i n t o t h e Feed so lut ion obviously increases t h e dissolved

so l i ds concentrat ion fur ther increasing osmotic pressure.

TESTING CONSIDERATIONS

A l l OF these factors: recovery, osmotic pressure, permeate qua-

l i t y , recycle, etc., serve t o underscore the value o f t e s t i n g the

spec i f i c waste stream as thoroughly as possible. Because

e f f l uen t streams often vary i n analysis ffi a funct ion OF time, i t

i s important t h a t e i t h e r a composite or a "worst case" sample

be obtained f o r t e s t purposas.

One or more o f t h e fol lowing t e s t procedures s h w l d be u t i l i z e d

when evaluat ing membrane technology w i t h a p a r t i c u l a r e f f l u e n t

stream.

C e l l Test - U t i l i z i n g small [approximately 15 inches 3 cut pieces

of sheet membrme mounted i n a *@cell1@ t h a t axposes t h e membrane

t o t h e t e s t s o l u t i o n using the cross-Flow mrchanism. This t e s t

is eFfact ive For quick evaluation of a number o f d i f f e r e n t

membrene polymers t o determina degree o f oeparation.

2

Advantages: Fast

Inexpensive equipment involved

Only small qwant i t ies OF t e s t so lu t i on

required

24

Disadvantages: Cannot i n d i c a t e long-term chemical e f fec ts o f

so lu t ion on polymer

Ooes not provide engineering scale-up data

Gives no i n d i c a t i o n o f optimum membrane

element conf igurat ion

Does not provide data on f o u l i n g e f f r c t s o f

t e s t s o l u t i o n

Appl icat ions Test - Typica l ly involves the evaluat ion of a 30-50

gal lon sample o f so lu t i on on a production-sized membrane element.

The element i s mounted i n a t e s t machine w i t h t he engineering

features o f production systems.

be completed w i t h i n 1-2 hours. Figure 6 d e t a i l s t h e appl icat ions

For a given element, t he t e s t can

syetem design.

Advantages:

Oisadvantages:

Fast

Provides scale-up data [Flow, element e f f i c i -

ency, osmotic pressure as a funct ion o f re -

covery, pressure requirements, etc.]

Can provide an i nd i ca t i on of membrane s t a b i l i t y

00- not i nd i ca te long-term chemical e f f e c t

Ooes not provide data on fw l ing r f f e c t s o f

the t e s t s o l u t i o n

membram

Expens Xi

requi.

0 i sadvant ages :

APPLICATIONS

Metal F in i sh inq

1) Electroplat ing so lu te r r l

osmosis recovery o f plii

r e t u r n of the concentrii

t he l a s t r inse. [Figun

BATH TREATED

Nickel

Acid Copper

Acid Z i n c

Copper Cyanide

Hexavalent Chrom

Feed TDS: 2-3000 ppm

Typical feed rate: 2-10 gal

Present market po ten t i a l : !!

Projected growth rate: lo%,,

I 1 - - -

MEMBRANE ELEKNT

I 1 I I

s n i m RECVCLC

Figure 6. Applications test schematic

PERYATE

l s m

P i l o t T e s t - Usual ly i nvo l v rs p l a c i n g a t e s t machine [such as t h a t

used for t h e eppl icat ions t e s t ] i n t h e process operat ing an a

"oidr-etrermw f o r a minimum o f 30 days.

Advantragee: Accomplishes e l 1 o f t h e funct ions o f t he

appl icat ion= t e s t plum provides long-term

Figure 7. "Zero ((

E lec t rod ia l ys i s recovery OF

stagnant r i n s e t m k s precedill

[Figure el Number o f ewisii

Feed TDS: 4-!!

.

ig-term chemical e f f e c t s

ier

Qineer ing scale-up data

o f optimum membrane

t i o n

o f

t a on f o u l i n g e f fec ts OF

the evaluat ion of a 30-50

ion-sized membrane element.

ne w i th the engineering

given element, t h e t e s t can

6 d e t a i l s t h e appl icat ions

vta [ f low, element e f f i c i -

;sure es a f unc t i on o f r e -

'equirements , etc. 1 :at ion o f mambrane s t a b i l i t y

ng-term chemical e f f e c t

.e on f w l i n g e f f a c t s o f

I

1 I I

. - - - - - - ELEMENT

5t schematic

s t e s t machine [such as t h a t

process operat ing on e

I funct ions o f t he

provides 1 ong-term

25

membrane fou l ing and s t a b i l i t y data

Expensive i n terms OF monitor ing and t ime Disadvantages:

requirements

APPLICATIONS

Metal F i n i s h i n q

1) Electroplat ing Solute recovery ["zero dischargevi) reverse

osmosis recovery of p l a t i n g s a l t s from e l e c t r o p l a t i n g r inses;

r e t u r n of t he concentrate t o the p l a t i n g bath and permeate t o

the l a s t r inse. [Figure 7 )

BATH TREATEO

N icke l

Acid Copper

Acid Zinc

NUMBER OF E X I S T I N G SYSTEMS

150

12

1

Copper Cyanide

Hexavalent Chrome

Feed TOS: 2-3000 ppm

Typical feed rate: 2-10 gal/min

Present market potent ia l : $5-10 MM/yr

Projected growth rate: 10X/yr

1

1

WORK FLOW * - - - - - - -

l Y

a- - )4 4. 2nd 3rd 1.t PLA 1 I N G

TANK R l n m m Rincr R i n s e

PERMEATE J

OSMOS IS

Figure 7. "Zero discharge" with reverse osmosis

Elec t rod ia l ys i s recovery o f p l a t i n g s a l t s from "drag-outv' o r

stagnant r i n s e tanks preceding f lowing counter-current r inses.

[Figure e] Number OF e x i s t i n g systems: 35

Fred TOS: 4-5000 ppm

26

B. Y l x i d R l m m r

C U n t r r m C m d l

Typical feed rate: 5-20 g p m


Projected growth rate: 30-40X/yr

4 . 1 . . Raeyslad to 90-952 . . : Prcls~Bo . . . L

b) Reverse osmosis on clan

metals compliance. C F Y

P L A T I N G TANK

- *'DRAG (LIT

R I N S E \i .

ELECTR001AL7S IS

RINSE

Figure 8. E l e c t r o d i a l y s i s recovery o f p l a t i n g salts

21 "End o f Pipe" E f f l u e n t Treatment - the use o f membrane tech-

nology t o dewater mixed p l a t i n g r i n s e streams:

a) Reverse osmosis p r i o r t o chemical p r e c i p i t a t i o n / c l a r i f i- c a t i o n t o reduce hydraul ic loading t o t h e c l a r i f i e r

(Figure 91

To convmtional C h o m l s o l Trorrmmt

Figure 9. "End of pipe" e f f l u e n t t reatment

r', c1 N I f Ird

Eff 1 ""e

F r o m C onv en+ i on mi Chmmicml l r r a t m - t i I

Figure I O . "Encc

c) M i c r o f i l t r a t i o n on tot :

p r e c i p i t a t i o n step to

press. [Figure 1 1 3 . Feed TOS - 1000-10,0000

Toxic metals COncentrE

Number o f e x i s t i n g s y c

Present market potent l l

Projected growth ra te=

F igu re I I . "E

3m

61-2 MM/yr

10X/yr

i b) Reverse osmosis on c l a r i f i e d a f f l u e n t t o ensure t o x i c

metals compliance. [Figuro 101

recovery of p l a t l n g s a l t s

the use OF membrane tsch-

)sa streams:

:a1 p r e c i p i t a t i o n / c l a r i f i -

l ing t o t h e c l m r i f i e r

R-cycled to Proces.

’ f I uent t reatment

i

R r v r r r r O r m a i m

Recyc led t o Procrss

c1 or 1 f Ird . From Conventi oni l C h r m i c i l Trratment

5-10% 1 Figure IO. “End o f p ipe” e f f l u e n t trea-$nent

c ] M i c r o f i l t r a t i o n on t o t a l eFf luent immediately fo l l ow ing

p r e c i p i t a t i o n step t o pre-dewater sludge p r i o r t o f i l t e r

press. (Figure 111. Feed TOS - 1000-10,000 ppm

Toxic metals concentration: 1-100 ppm

Number OF e x i s t i n g systems: 10-20

Present market p o t e n t i a l : $7-15 MM/yr


Figure I I . “End o f p ipe” e f f l u e n t treatment

28

Dissolved or emulsi f ied o i l s can be separated from water through

t h e use o f u l t r a f i l t r a t i o n . Typica l ly , t he o i l - r i c h concentrate

i s recycled t o the feed tank u n t i l t h e o i l concentrat ion i s h igh

enough t o al low i t t o be i nc ine ra ted f o r the BTU value~60-70X~.

PULP U L T M F l L T R A T I M U N I T

TO OISP06AL

m I N C I N C E M T ~ ~

Figure 12. Oily waste t reatment

3) O i l y waste treatment o f can forming r i n s e waters - u l t r a -

f i l t r a t i o n t o remove drawing and forming o i l s From one-piece

can cleaning r i n s e waters.

Permeate can be recycled as r i n s e water; concentrate hauled

or incinerated

Typical feed stream COO: 2000-5000 ppm

Approximately f i v e systems present ly operat ing

Typical Feed rata: 10-20 gpm

Present market po ten t i a l : $3 MM/yr

Projected growth rate: 10-20X/year

O i l y waste treatment o f c o i l coat ing r i n s e waters - use of

u l t r a f i l t r a t i o n to remove r o l l i n g o i l s from aluminum and s t e e l

c o i l c leaning r i n s e waters.

tergent i s recovered and t h e permeate i s reused; concentrate

4)

In some cases t h e valuable de-

i s hauled or incinerated.

Typical feed stream COO:

Approximately f i v e systems

Typical feed rate: 10-211

Present market po ten t i a l :

Pro jectsd ,growth rate: lo!! 51 O i l waste treatment o f rinr,

c leaning - use OF u l t r a f i l -

gent c leaning r i n s e waters,

t r a t e hauled o r incineretoel

Typical feed COD: 2-10,OIi

Approximately 15 systems pi1

Typical feed rate: 20-501

Present market potent ia l :

Projected growth rate: 211

61 Electrodeposi t i o n pa in t bar

stream" u l t r a f i l t r a t i o n of:

remove water and contaminaa

t h e bath; permeate i s usedl

[Figure 131.

T h i s i s a mature market (i.

on t h e automotive and appl.

W O W FLW - - - - - - -

I P I I N T TANK

U U

F igu re 13. E l e c t r a

--

parated from water through

, the oil-rich concentrate oil concentration is high

f o r the BTU valueC60-70%].

YOVAL

1 PERMEATE TO OISCWRGE m REUSE

U L l R A F l L T R A T l M U N I T

eatment

ig rinse waters - ultra- 'orming oils from one-piece

water ; concentrate hauled

IO0 ppm

.ly operating

I

'YP ! ar

ng rinse waters - use o f

oils from aluminum and steel

me cases the valuable de- late is reused ; concentrate

is hauled o r _icineratsd.

Typical feed stream COD: IO-20-ppm

Approximately five systems presently operating

Typical feed rate: 10-20 gpm

Present market potential: $2 MM/yr

Projectad ,growth rate: 10%/yr

5) Oil waste treatment o f rinses from automotive end aircraft

cleaning - use of ultrafiltration to remove oil from deter- gent cleaning rinse waters; permeate can be recycled, concen-

trate hauled or incinerated.

Typical feed COO: 2-10,000 ppm

Approximately 15 systems presently operating

Typical feed rate: 20-50 gpm Present market potential : $5-10 MM/yr

Projected growth rate: 20-30% /yr

6) Electrodeposit ion paint bath dewatering - continuous "side stream" ultrafiltration o f electrodeposition paint bath to

remove water and contaminarrts. Concentrate is returned to the bath; permeate is used es first rinse or discharged.

[Figure 13).

This is a mature market [if not saturated] end is dependent on the automotive and appliance markets.

S P M V RINSES - W O R K FLW

AAA

ULTnAFILTRIITIDI uw I T

Figure 13. Electrodeposition paint dewatering

30

FOOO PROCESSING

Membrane technology o f f e r s p o t e n t i a l i n many diverse food pro-

cessing appl icat ions such as those requ i r i ng separation a t

ambient temperatures, continuous operation, f ract ionat ion, etc.

In general, w i t h t he exception o f cheese whey appl icat ions, these

are just now being invest igated end there are only p i l o t i n s t a l l a

t f ons i n operation.

11

21

31

Cheese whey dewatering o r f rac t i ona t ion - reverse osmosis t o

concentrate whole whey p r i o r t o spray drying, u l t r a f i l t r a t i o n

t o f ract ionate whey t o recover lactalbumin p ro te in and elec-

t r o d i a l y s i s t o de-ash u l t r a f i l t r a t i o n permeate.

Approximately f o r t y systems i n s t a l l e d i n the United States

s ince 1981.

To ta l sales t o date: $22 MM

Equipment requires USOA 3A Oairy construct ion and FOA

approved membrane elements.

Market p o t e n t i a l depends upon federal government decisions

regarding "standards of ident i ty.**

a p o t e n t i a l ex i s t s of $10-12 MM/yr; if not, p o t e n t i a l i s

I f changes are mandated,

$1-2 MM/yr.

D i s t i l l e r y " s t i l l age" dewatering - u t i 1 i z a t i o n o f membrene

technology t o concentrate organic mater ia l l e f t over a f te r

t h e alcohol d i s t i l l a t i o n process i n the production of e t h y l

alcohol. The concentrate i s used as animal feed and permeate

can be used as b o i l e r feed.

Typical feed stream character is t ics :

TOS: 30-40 ppm

Suspended sol ids: 5000 ppm

BOO: 20,000 ppm

Present market po ten t i a l : $1-2 MM/yr


Brewery waste treatment - use o f membrane technology to:

a] Recover valuable enzymes such as isohumulone

b] Remove co lor a d enhance f l a v o r

c] Concentrate hops for reuse

d] Provide llend-of-pipeq* e f f l u e n t dewatering

Typical feed stream charac te r i s t i cs :

TOS: 30-40 ppm

Suspended sol ids: 500 ppm

\

4) Wine processing - use

to:

11 Remove bacter ia cc:

23 Improve color, enhi

Typica l feed stream chi

TOS: 50-60,000 ppm

Suspended so l ids: 5011

BOO: 12,000 ppm

Present market potent i

Projected growth rate:

5 ) Meat processing - use

a] P ro te in recovery fii

b] Blood plasma f r a c t .

c] Gelat in recovery/pii

d] Pork p i c k l i n g [cur,

Typical feed stream chi8

TOS: 3-5 ppm

Suspended s o l ids: 24:

BOD: 2-3000 ppm

COO: 5000 ppm

20% Sodium Chloride Coil

Prote in molecular weig(l

61 Grain seed o i l process

from ex t rac t i ng solvenii

Typical feed stream Chi i

Molecular weight 011

Typical feed rate: 3 1

Present market potent iii


71 Sugar processing - memtt l i q u i d sucrose:

Typical feed stream c h r r

Typical feed rate: !E

Present market potentizi


81 F r u i t j u i c e c l a r i f i o a t a

t i o n t o remove co l l o id i i

Approximately 15-20 sys

31

n many diverse food pro-

l u i r i ng separat ion a t

I t ion, f rac t i ona t ion , etc.

ise whey appl icat ions, these

#ere are only p i l o t i n s t a l l a

a t i o n - reverse osmosis t o

ray drying, u l t r a f i l t r a t i o n

talbumin p r o t e i n and elac-

i o n permeate.

l e d i n t h e United States

onst ruct ion and FDA

re1 government decis ions

I f changes are mandated,

; i f not, p o t e n t i a l is

u t i l i z a t i o n o f membrane

n e t e r i a l l e f t over a f t e r

7 t h e product ion o f e t h y l

ES animal feed and permeate

3:

smbraoe technology to :

BS isohumulone - dewatering

3:

Wine processing - us8 Of m i c r o f i l t r a t i o n and u l t r a f i l t r a t i o n

to: 1 3 Remove bacter ia [co ld s t e r i l f z e t i o n )

2) Improve co lor , enhance f l a v o r

Typical fged stream character is t ics :

70s: 50-60,000 ppm

Suspended so l ids: 500 ppm

BOO: 12,000 ppm

present market potent ia l : $1-2 HM/yr

Projected growth rate: 5-1OX/yr

Meat processing - use o f membrane technology fo r :

a) Pro te in recovery from t o t a l e f f l u e n t

b] B l o o d plasma f rac t i ona t ion

e) Gelat in recovery/pur i f icat ion

d) Pork p i c k l i n g [curing) b r i n e recovery

Typical Feed stream charac te r i s t i cs :

TOS: 3-5 ppm

Suspended so l ids: 2-3000 ppm

BOO: 2-3000 ppm

COO: 5000 ppm

20% Sodium Chloride Concentration

P ro te in molecular weight about 5000

Grain seed o i l processing - u l t r a f i l t r a t i o n t o separate o i l

From ex t rac t i ng solvents:

Typical feed straem character is t ics :

Molecular weight of o i l : 1-2000 dal tons

Typical faed ra te : 50-100 gpm


Projected growth rate; 10-20%/yr

Sugar processing - membrane technology t o remove co lor from l i q u i d sucrose:

Typical feed stream character is t ics : Temp. o f 70 deg. C

Typical feed r a t e : 50-200 gpm


Projected growth rete: 10-2O%/yr

F r u i t j u i ce c l s r i f i o a t i o n - m i c r o f i l t r a t i o n and u l t r a f i l t r a -

t i o n t o remove c o l l o i d a l contaminants:

Approximately 15-20 systems operat ing worldwide

I

32

Typical feed rater 10-300 gpm


Projected growth rate: 10-20%/yr

9) Juice processing - u l t r a f i l t r a t i o n and reverse osmosis to :

a) Preconcentrate [dewater) tomato, orange, apple, beet,

lemon, etc. p r i o r t o evaporation

b) Fract ionate f ru i t Juices t o remove pect ins


High suspended s o l i d s [pulp) which m u s t remain




10) Corn sweetener concentrat ion - u l t r a f i l t r a t i o n t o concen-

t r a t e dextrose from 4-6% to 25-302


Molecular weight o f dextrose - 180 daltons

Temperature o f feed - 80 dag. C



Projected growth rata: 20-30%/yr

PHARMACEUT ICAL/BIO TECHNOLOGY APPLICATIONS

The use o f membrane technology i n these indust r ies o f f e r s much

promise. Such c r i t i c a l and d iverse requirements as l o w tempera-

t u r e concentration, so lu te f r a c t i o n a t i o n and continuous process-

i n g provide outstanding oppor tun i t ies f o r a l l four membrane

eep aret i on techno 1 og i os.

Other than t h e p u r i f i c a t i o n o f water f o r product r i n s i n g O r

medication preparation, these technologies have bean used sparing-

l y t o date; however, t he r a p i d

dustry w i l l requ i re s i g n i f i c a n t u t i l i z a t i o n o f a l l membrane tech-

nologiera as large-scale manufacturing processee evolve from t h e

preeent laboratory preparat ion procedurecr.

Possible appl icat ions include:

growth o f the biotechnology in-

Continuouo bio-reactor

Product concentration/dewatering

Fract ionat ion/pur i f i c a t i on

Cold s t et- i 1 iz a t i on

Solvent reuse I

1990, the membrane techii

$100-150 MM/yr, w i t h a p ro

BRINE WATER TREATMENT

Reverse osmosis o r electrotc

brought t o the surface i n 1 1

Typical feed strati

TOS : 50-350,000

Typical feed r a t e l

BOILER/COOLING TOWER BLOWDil

Reverse osmosis t o dewater'

towers.

Blowdown may contain chromt

Typical feed ratet

TANNERY WASTE TREATMENT

Reverse wmosie t o dewaterb

operations.

Typical feed stret

pH: approximatet

BOO: 14,000 ppm

COO8 30,000 ppm

P ossi b l e tr i ve l em

TEXTILE WASTE TREATMENT

11 Oye recovery - use OF t o r e t u r n to the dye vat;

Typical feed e t re i

TOS: 2-15,000

Suspended s o l i d s :

BOO: 300 ppm

COD: 1500 ppm

pH: approximetet

Typical feed ra te l

Present market PO)

Projected growth

21 S iz ing recovery - ul t r .

acetate compounds fromi

recovered f o r r ins ing.

'7

I and reverse osmosis t o :

0 , orange, apple, beet,

on

move pect ins

:s :

lhich m u s t remain

, MM/yr

'r

r a f i l t r a t i on t o concen-

s:

180 dal tons

ONS - indus t r i es o f f e r s much

uirements es low tempera-

n end continuous process-

or e l l four membrane

r product r i n s i n g o r

i es have been used sparing-

o f t h e biotechnology in-

t i o n o f e l l membrane tech-

rocesses evolve from t h e

m.

33

1990, the membrane technology market i s expected t o t o t a l

$100-150 MM/yr, w i th e projected growth r a t e o f GOX/yr.

BRINE WATER TREATMENT

Reverse osmosis or e lec t rod ia l ys i s t o dewater h igh TOS waters

brought t o the surFace i n o i l and gas d r i l l i n g operations.

I

Typica l feed stream character is t ics :

TOS: 50-350,000 ppm

Typical feed rete: 10-50 g p m

BoILER/COOLING TOWER BLOWOOWN

Reverse osmosis t o dewater blowdown from bo i l e r6

towers.

Blowdown may conta in chromates [ t o x i c waste]


TANNERY WASTE TREATMENT

Reverse osmosis t o dewater e f f l u e n t from leather

operations.

Typica l feed stream character is t ics :

pH: approximately 12

BOD: 14,000 ppm

COO: 30,000 ppm

Possible t r i v a l e n t chrome present

TEXTILE WASTE TREATMENT

11 Dye recovery - use o f membrane technology t o

and coo l i ng

tanning

concentrate dye

t o r e t u r n t o t h e dye vat; permeate reused f o r r i ns ing .

21

Typical feed stream charac te r i s t i cs :

TOS: 2-15,000 ppm


BOD: 300 ppm

COO: 1500 ppm

pH: approximately 12

Typica l feed rata: 50-300 gpm

Present market p o t e n t i a l : $ 5 4 HM/yr

Pro jected growth rate: 20-30X/yr

S i r i n g recovery - u l t r a f i l t r a t i o n t o recover p o l y v i n y l

acetate compounds from r inses for reuse. Permeate can be

recovered For r ins ing,

34


TOS: 10-20,000 ppm


COO: 30,000 ppm

pH: approximately 6



Projected growth ra te : 20-3O%/yr

PULP AND PAPER WASTE TREATMENT

U l t r a f i l t r a t i o n recovery o f l ignosul fonates f r o m spent s u l f i t e

l iquor .


TOS: SO-120,000 ppm

Wood sugar: 20-40,000 ppm

Lignosulfonates: 40-80,000 ppm

Suspended so l ids: 1-8,000 ppm

pH: 3-4

Typical feed 'rate: 100-1000 gpm

Present market p o t e n t i a l :

Projected growth rete: l - S % / p

$6-10 MM/yr

OEWATERING PHOTOGRAPHIC RINSES

Uoo o f reversw osmosis t o concentrate ferrocyanide, t h i o s u l f a t e

md s i l v e r s i l t s i n photo processing r i n s e water. Concentrated

e i lvmr can be wasi ly recovered e l e c t r o l y t i c a l l y and th iosul fa tes

oxidized w i t h otonw t o f a c i l i t a t e discharge.


aoo: 1200 ppm

coo: 2000 ppm

S i l v e r 30 PPm

15 systems cu r ren t l y i n s t a l l e d i n Uni ted States

Typical feed rate: 5-20 g p m

Present market po ten t i a l : $1.5-2 MM/yr

Projected growth ra te : lO%/yr

SUMMARY

T h i s prpmr has mttempted to i d e n t i f y some o f t he oppor tun i t ies

oFfmrod by membrane processes i n e f f l u e n t treatment appl icat ions,

but there are no easy answers

so lu t i on f o r a l l problems.

Certainly, t he requirement F OII

enough; however, f o r those ap((

can be e f fec t i ve l y t reated wi- provide outstanding performance

Some experts p red ic t t ha t , w i "

along w i t h food and chemical 11

of t he t o t a l membrane process..

The t ime has come - opportuni"

charac te r i s t i cs :

1000 p p m

6

50-300 gpm

, t i e l : $5-8 MWyr

e: 20-30%/yr

ates from spent s u l f i t e

cha rac te r i s t i cs :

P m

000 ppm

0-00,000 ppm

-8,000 ppm

100-1000 gpm

t i a l : $6-10 MM/yr

e: l - S % / y r

srrocyanide, t h i o s u l f a t e

-me water. Concentrated

y t i c a l l y and t h i o s u l f a t e s

srge.

:harecter ist ics:

i n s t a l l e d i n United States

5-20 Qpm

t i e l : $1.5-2 MM/yr

B: 10%/yr

ne o f t he oppor tun i t ies

q t treatment appl icat ions,

35

but there are no easy answers; no s ing le technology i s t h e

so lu t i on f o r e l l problems.

Certainly, t h e requirement for t e s t i n g cannot be emphasized

&tough; however, for those eppl icat ions which t e s t i n g ind icates

can be e f f e c t i v e l y t reated w i t h membrane technologies, they can

provide outstanding performance.

Some experts predic t that , w i t h i n 10-20 years, e f f l u e n t treat'mmnt,

along w i th food and chemical processing, w i l l represent go-go% OF the t o t a l membrane processing market.

The t ime has come - opportunity awaits!

N W TBCmOLa3Y I# THE HETAL FINISHINC INDUSTRY

PAT WERScrmLZ &mica1 And Related Life Technologies, Inc. Qrltech Associates, 1%. 6 Carnrerce Drive Suite 2 W Cranford, Neu Jersey 97916

INTROWCTION

%is paper reviews the state of developnent of membrane technology and its application to metal finishing wastewater treatment. electroplating rinses, can contain toxic heavy metals such as cacfniun, chraniun and lead. The two ca”n treatments used are precipitation and ion exchange. The former, by precipitating the metal ions, produces a sludge that has to be disposed of in a secure landfill. In addition to the sludge, there are problens with chelating agents present in the rinse water that inhibit precipitation. Flocculants are sometimes added to aid in filtration. sludge. be regenerated with strong acids or bases. solution then must be handled for reprocessing or disposal. technology is anerging that makes zero sludge, zero discharge, and xecycling of metal possible.

Metal finishing wastewaters, particularly those from

These significantly increase the bulk of the

The regenerating Ion exchange resins, while not producing a sludge, must

New

It has been estimated that the metal finishing industry utilizes more than one hundred surface finishing and fabricating processes that require aqueous application and removal of various metals to and from metallic and plastic parts (1). Possible contaminants in rinse waters are listed in Table I. Included are the various cationic metals and their associated

as in the manufacture of automobiles, printed wire boards, and other industrial metal finishing. In most electroplating operations, various organic additives, including chelating agents, are used to clean and brighten the metal.

Sane of the more well known additives used in these processes include EDTA, formaldehyde and saccharin (2 ) .

i

anions that are involved in various types of electroplating such 5

Q I C 1

Unfortunately the identities of these compounds are considered proprietary.

TABLE I

POSSIBLE CONSTITUENTS OF METAL FINISHING RINSE WATERS

CATIONS ORGANICS ANIONS

cu+l, +2

Brightners

Cleaners

-2 Cr 2’7 cro4-2

Ni+2 +3 Chelating agents CN-I

Sn+2, +4

Au+l + 3

Ag+l

zn+2

Detergents so4-2

BF4-1

s20s-2

c1-1

P ~ o ~ - ~

NH4+l

a + 2

The major problem with the hazardous wastes fran metal

Often the baths are heated to high

finishing is the chemical and physical envirownt these species are found in. ranging from 0 to 14. temperatures. Mixing of wastes occurs in the rinse phase. The organics sometimes react and form unknown polpric ccmpounds in this harsh environment (2).

There are three inherent problem areas in membrane separations that a treatment system designer must consider: low flux, fouling and chemicalfiiological resistance. a Murphy’s law in membrane separations that the greater the selectivity, the lower the permeability. ored to exclude smaller and smaller species, the flux becgnes smaller and a high throughput rate is needed to treat the amount of wastewater produced, resulting in a large costly treatment plant. Related to the flux rate is the fouling problem. Particles or molecules sometimes enter the pores and adhere to the sides, or they cling to the surface of the membrane. Both of these situations lower the flux rate and sometimes change the selectivity. membrane to withstand chemical and biological attack. manbrane lifetimes are to be measured in years and not days, the canponent materials must tolerate high or low pH conditions, strong oxidizers and be sterilizable.

Metal finishing uses extremes of pH with values

There seg~ls to a be

As a system is tail-

The third area of concern is the ability of the If

446

REVERSE OSMOSIS

Reverse osmosis is a process in which an applied pressure is used to reverse the normal osmotic flaw of water across a semipermeable “brane (3) . In noma1 osmosis, pure or dilute solvent flows across the menbrane to the more concentrated side. Flow fran the concentrated side back to the dilute side is prevented by the osnotic pressure of the concentrated solution. Osrrotic pressure is a coligative property of the solution. For water to flow in the reverse direction, pressure greater than the osmotic pressure must be exerted on the solution. reverse osnosis, solvent crosses fran the concentrated solution to the dilute, producing a very concentrated solution and a purified solvent.

In

Reverse 0snosi.s is not a filtration technique like ultrafiltration 01 microfiltration, but a true membrane process. The pore size ranges from 1 to 10 angstrans and will exclude any molecule larger than a molecular weight of about 300. Historically, the first and largest application was in desalination of water. In 1960, Loeb and Sourirajan produced the first thin cellulose acetate membrane in a tubular design which had a sufficient flux rate to make desalination practical ( 4 ) . Shortly afterwards, Dupont produced a hollow fiber configuration using a membrane made of aromatic polyamide. The spiral wound configuration was developed by Westmoreland (and later Bray) for a more efficient design. At the same time, a new more chemically resistant membrane, called a thin film composite membrane, made of cellulose esters and polysulfones was developed.

Essentially, there are three membrane materials being used: cellulose acetate (a), aromatic polyamides (PA) and thin film composites (TFC). There are three types of configurations available: tubular, hollow fiber and spiral wound. Cellulose acetate is known to degrade with time. to biological attack and cannot tolerate a pH of higher than 7.5. as a problem (5). pH range in both basic and acidic media, cannot tolerate chlorinated water. Fouling also has been a problem (5).

Fouling can affect all types of membranes under different conditions, particularly in the treatment of wastewater. example, rejection of Cr(V1) is good under basic conditions, but if any aluminum hydride is present it will precipitate and foul the membrane (5).

It is subject

Belfort also reports leakage of certain feed constituents The polyamide, while operating over a wider

For

Available data indicate that reverse osnosis is a proven technique for treating electroplating wastewater. currently being used to recover brass, hexavalent chranium, cop~r, nickel and zinc. to have zero discharge, with pure water and concentrate being

is I

The ultimate goal of these systm is

447

recycled in the process ( 6 ) . sufficiently concentrate the solution to bath strength. Rinses after Watts nickel, bright nickel, and nickel sulfamate all can be treated successfully in a zero discharge system; however duplex nickel, a semi-bright nickel, cannot ( 6 ) . A l l three types of membranes have been applied under various conditions. No one menbrane can handle all types of electroplating wastes. The two configurations used have been hollow fiber and spiral wound. Table I1 shows a surmary of installations. Most installations require pretreatment, usually a 5 micron ultrafilter (7). Cartwright, an expert in the area of applications of manbrane technology to metal finishing, also sees applications of RO to tin/lead fluoroborate rinse waters. He does not believe reverse osmosis can successfully treat zinc cyanide rinse waters on a cannercia1 scale. He claims the osmotic pressure of the zinc cyanide solution is too high to undergo RO. cyanide but there has been no reported carmercial plating operation currently using reverse osmosis for zinc cyanide.

Naporators may be needed to

Preliminary work had been done by Abcor (8) on zinc

TABLE I1

CURRENT RO INSTALLATIONS IN THE ELECTROPLATING INDUSTRY(7)

TYPE OF BATH

Bright nickel Nickel sulfamate Watts nickel

Copper sulfate

Zinc sulfate

Brass cyanide

Copper cyanide

Hexavalent chromium

TYPE OF MEMBRANE AND CONE’IGURATION

Cellulose acetate Spiral wound

Polyamide Cellulose triacetate Thin-film composite Hollow-f iber Spiral wound

Thin-film cqosite Spiral wound

polyamide Cellulose triacetate Hollow-fiber

Polyamide Hollow-fiber

Thin-f ilm composite Spiral wound

NUMBER OF

ZERO DISCHARGE INSTALLATIONS/

l50/yes

12/no

1/90% recovery

5/90% recovery

2/90% recovery

Under investigation

448

ULTRAFILTRATION

ultrafiltration is in the middle of the continuun of exclusion meubrane separation techniques that ranges fran reverse osmosis through microfiltration. Ultrafiltration menbranes are generally not defined by their pore si-, which ranges fran 10 angstrans up to 10 microns, but by the size of particle excluded. These “branes cannot be considered to have pores of just one size but rather have a spectrum of pore sizes. The cutoff that divides ultrafiltration fran microfiltration has been variously reported to be 100,000 to 500,000 molecular weight units. This report will use tonsdale‘s definition (4) that UF “branes retain species in the molecular weight range Of 300 to 300,000.

The first major advance in UF membranes came at the same time as for RO with the beb-Sourirajan cellulose acetate menbrane. The final step in the formation of the Loeb-Sourirajan RO membrane is to anneal the manbrane in water at 80 degrees Celsius. The unannealed reverse osmosis membrane turned out t o be a good ultrafiltration membrane (4) .

ultrafiltration membranes are made fran a wider selection of polymers than RO membranes. Chemical and biological resistance is better because of greater selection of materials for various applications. polycarbonate, polyvinyl chloride, polysulfone, polvinylidene fluoride, copolymers of acrylonitrile and vinylchloride, polyacetal, polyacrylates, polyelectrolyte canplexes, and crosslinked polyvinyl alcohol are used. There are four basic module configurations used today: tubular thin channel, hollow fiber and spiral wound

those used in RO, but the hollow fiber configuration is completely different. In ultrafiltration, the membrane skin is formed on the inside diameter of the hollow fiber. passes through the bore and product water permeates out through the outer support structure. In reverse osmosis, the membrane skin is on the outer diameter and the product water flows into the fiber bore (10).

concentration polarization, the major problem in ultrafiltration. Two things occur when filtering solutions with large macromolecules. Macranolecules adhere to the walls of the menbrane pores and reduce the pore diamter (fouling). or macramolecules deposit on the surface of the manbrane, sometimes forming a gel, causing resistance to flow (concentration polarization).

the “ n e surface to minimize concentration polarization.

Besides cellulose acetate and polyamide,

flat-plate thin channel, (9).

The uF spiral wound and tubular configurations are similar to

Feedwater

Flux rates are normally high except when there is fouling or

All module configurations must maintain high shear rates at

449

mnping must be used to maintain the high shear rates. solutes with molecular weight less than 300 readily permeate the membrane, there is no great oaaotic pressure difference between the feed water and the product water. As a result, processing is carried out at relatively low pressures (1-5 atmospheres).

Ultrafiltration is a proven technology in the electroplating industry and in the overall waste treatment field. electroplating industry, 5 micron ultrafilters are used as pre- filters for units (7). (xle system has k e n designed for “end of pipe” mixed wastewaters, to remove the chemically precipitated heavy metals without flocculation and gravity sedimentation. are used in such diverse chemical and biological envirorrnents that one could extrapolate their use to many separations.

Leeper et al. (9) reports work is being done on alloy membranes, membranes made of blends of two or more materials. Developnent has begun on membranes that incorporate specific canpounds into the barrier layer to enhance selectivity.

Since

In the

Ultrafiltration marubranes are so versatile and

ELECTRODIALYSIS AM> ION EXCHANGE MEMBRANES

Electrodialysis, as its name implies, is a dialytic process, in which an applied electric field is used to draw ions across a membrane. cormrercial applications are generally more recent. The usual cannercial configuration is the stack, consisting of pairs of cation/anion exchange membranes with separators and an anode at one end and a cathode at the other. Anions flow toward the anode until they are stopped by cation-selective membrane (and vice versa). alternate concentration or depletion of ionic species. Membranes are made of copolymers of divinylbenzene-styrene with an ion exchange group attached to the benzene ring. The cation exchange “brane generally has sulfonate groups attached and the anion exchange membrane generally has quaternary m n i u m groups attached as the ion exchangers, much like ion exchange resins (4 ) .

of anion-exchange membranes by organic and inorganic materials. This fouling is apparently created by the local pH shift that occurs on the concentrate side of the mexbrane. This fouling leads to an increased voltage drop across the stack, which leads to a greater expenditure of energy (4) .

mentioned above has been ameliorated by reversing the polarization of the stack. diluting coYnpartments and vice versa. applications in the electroplating field and one c m n y alone

This process dates back to the 1930’s although

The result is a series of cells where there is

Electrodialysis has a major problem with fouling, Grticularly

The problem of fouling and concentration polarization

Concentrating canpartments become There have been many

450

0

has over forty installations. reverse osmosis and ultrafiltration in its proven installations in electroplating wastewater treatment.

Electrodialysis ranks behind

One system that is about to be introduced into the market uses a membrane like an ion exchange resin. radiation grafted polypropylene felts that allow water to penmate, but do not allow ionic species to pass. opposite of Donnan dialysis, where ionic species transverse the manbrane. stripped later by a rotating cathode. tested successfully in electroplating operations (11) , particularly in goldplating, where the gold metal is recovered as a strip of metal foil.

Rrese manbranes are

This is the

Instead ions are captured onto the mgnbrane to be This system has been

Another system developed in conjunction with an electrode is the COPS or Chraniun Oxidation and Purification System. Unlike electrodialysis, only a perfluorosulfonic acid cation exchange membrane is used between an anode and a cathode. Metalic impurities such as copper, zinc and cadmiun pass through to the cathode, but trivalent chraniun does not. It is oxidized to hexavalent chrmiun by the ancde and is restored to the process tank for reuse (12).

LIQUID MEMBRANES

Liquid mgnbranes, developed in 1968 by Norman L i , are the newest type of marubrane. liquid film which acts as a diffusional barrier between the phase containing the species to be removed and the stripping phase (13). The species to be removed, and not the solvent, permeates the membrane, the opposite of exclusion membranes. Liquid membranes are either supported or unsupported. liquid is imnobilized onto a solid support, it is known as an imnobilized liquid membrane. membrane is usually enhanced by a chemical reagent which reacts or interacts with the species to be ranoved. tramport is coupled transport. exchange agent is imnobilized onto a hollow fiber and is held in the pores of the support by capillarity. place on one side of this manbrane by the organic molecule picking up a metal cation out of the feed solution. In order to maintain conservation of charge, a positive hydrogen ion mst be released by the “brane into the feed stream for every positive charge on the metal ion. dissolved in the organic liquid and migrates to the other side of the membrane where there is an abundance of positive hydrogen ions in an aqueous product solution. The organic canpound picks up the positive hydrogen ion and releases the metal cation into

Liquid menbrane systarrs have a thin

When the

Transport through the liquid

Cme type of A water-imniscible liquid ion

Ion exchange takes

The metal ion caqlex is then

45 1

the product stream. metal cation and positive hydrogen ion is why it is referred to as coupled transport. hydrogen ion concentration just as in cationic Donnan dialysis. As long as the pH of the product stream is two pH units lower than the feed stream, regardless of the metal cation concentration, ion transport will occur in the desired direction (14). Choosing the organic ion exchanger phase allows you to select the metal cation@) transported.

available. Consep, a &nd Research affiliate will probably be the first in the market. configurations: hollow fiber, sheets, and beads. Developnent and field testing for the last eight years has been done quite heavily in the metals recovery area, in electroplating and other industries, with success especially in the recovery of copper and chrcnniun.

The shltaneous uptake and release of

The driving force is the positive

mbilized liquid membranes are close to being cannercially

There are three proposed

OTHER INNOVATIONS

In conjuction with the work done on imnobilized liquid membranes J3end Research has developed a fouling-resistant, inside-skinned, large hollow fiber RO "brane. is used as a support for the liquid membrane, holding the liquid membrane in its porous walls. by Consep for wastewater treatment and many other applications (15).

This membrane

It is currently being introduced

S m Y

There are three goals in treatmnt systems for metal finishing: discharged or recycled in the process, to recycle the metal, and, if possible, reduce or eliminate sludge. carmercially available membrane systens-reverse osmosis, ultrafiltration and electrcdialysis-can achieve those goals. There are over 200 installations in this country that prove that.

to improve water quality so that it can either be

Three

Membrane systenrj are sometimes included as part of larger treatment/recycling systems. Occassionally when membranes alone are insufficient to dewater the metal ion concentrate so that it can be recycled into the plating bath, evaporators are incorporated into the system. Problems occur when waste streams are mixed so that an "end-of-pip" treatment is required before discharging or recycling the water. One canpany has designed a canbined precipitation and ultrafiltration system that is installed in many electroplating operations.

Copper anl nickel are the easiest types of electroplating rinsewaters to treat and chranim is the most difficult becaw, in the anionic state, it is such a powerful oxidizer.

Generalizations about the economics of membrane system are difficult to make. The cost of a menbrane systen is dependent on three factors: type of stream to be treated, amount of water to be treated and the amount of pretreatment required prior to the "brane process. Membrane systems can save money in four ways: in the value of recycled metals, in th re-use of treated water elsewhere in the process, in the elimination or reduction of sewer charges, and in the elimination or reduction of sludge removal and disposal. Payback of system vary, but all of the canpnies report a ROI (Return on Investment) of less than two years, some one year.

~ e w menbrane technology will be introduced in the next few years. ion exchange rrembranes.

The new types will be Wbilized liquid d r a n e s and

Nonnan Li, the inventor of liquid membranes, has been quoted "The future of separations is in the selected as stating (16):

use of chemistry to form weak bonds to selectively separate species." menbranes, new polymeric alloys, and novel ion exchange membrane systems point in the direction of increased selectivity. future of separations science, not just membrane technology, lay in this direction.

new membrane technologies such as liquid

The

REFERENCES

1.

2.

3.

4.

5.

6. 7.

8.

Craig, A.B.,Jr., and Cushnie, G.C.,Jr., Treatment Program, in Schumacher, H.,Jr. et al., Third

EPA's Centralized

Conference 0" Advanced Pollution Control for the Meta Finishing Industry EPA 600/2-8 1 - 0 ~ r ~ r y 7 9 ~ Heller et al., Identification of a Mmbrane Foulant in Electrodialytic Recovery of Nickel, Analytical amistry, VOlUne 55, p. 555lA, 1983 Strathnan, H., Membrane Separation Processes, JOUKM~ of Membrane Science, 9:121, 1981. Lonsdale, H.K., The Growth of Membrane Technology, JOUKM~ of Membrane Science, 10:81, 1982. Belfort, G., Pressure-Driven Membrane Processes and

--

- Wastewater Renovation, Water Renovation and Reuse, kadenic Press, Inc., New York, 1977. Cartwright, P., Cartwright, P., An Update on Ro for Metal Finishing, Plating -- and Surface Finishi-, April 1984. MCNulty et al., Damnstration of Zinc cyanide Recovery Using Reverse Osmosis and Evaporation, EPA-600/S2-81-132, September, 1981.

Today's RO, Product Finishi?, May 1984

452 453

9. Leeper, S.A., et al., Membrane "ethnology and Applications: An Assessment, DOE No. DE-AC07-76lDO1570, February, 1984,

10. Applegate, L., Membrane Separation Processes, chanical Engineeriy V o l m 64, June 11, 1984, p. 64.

11. RAI Researc Corporation, Product Literature and Specifications, Hauppauge, New York, July, 1984.

12. DuPont Canpany, Polymer Products Department, NAFION Case History, Wilmington, Deleware.

13. Bungee, D.L. and Noble, R.D., Organic and Heavy Metal Extraction Using Rnulsion Liquid Membranes, proposal sutmitted to the Enviromntal Protection Agency.

14. Babcock, W.C. et al., Sludge Reclamation Using Coupled- Transport Manbranes, EPA Contract No. 68-02-4042, April, 1984.

15. Warren, Doris, ed., Membrane and Separation Technology News, February, 1985. p.12.

16. Funk, E, W., presented at the Carltech Membrane/Ion Technology Information Exchange, Colunbia, Maryland, Sptenber 20-21, 1984.

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Documents

MEMBRANES SEPARATION5 TECHNOLOGY FOR ...c Desalination, 56 (1985) 17-35 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands MEMBRANES SEPARATION5 TECHNOLOGY FOR