WATER POLLUTION CONTROL RESEARCH SERIES • 17O2ODUDO9/7O
        NEW TECHNOLOGY
        FOR  TREATMENT  OF
  WASTEWATER BY REVERSE OSMOSIS
ENVIRONMENTAL PROTECTION AGENCY • WATER QUALITY OFFICE

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               WATER POLLUTION CONTROL RESEARCH SERIES

The Water Pollution Control Research Reports describe the results
and progress in the control and abatement of pollution in our
Nation's waters.  They provide a central source of information on
the research, development, and demonstration activities in the
Water Quality Office, in the Environmental Protection Agency,
through inhouse research and grants and contracts with Federal,
State, and local agencies, research institutions, and industrial
organizations.

Inquiries pertaining to Water Pollution Control Research Reports
should be directed to the Head, Project Reports System, Planning
and Resources Office, Office of Research and Development, Environ-
mental Protection Agency, Water Quality Office, Room 1108, Wash-
ington, D. C.  20242.
    This report was purchased from funds
    supplied by ES-00159-07

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NEW TECHNOLOGY FOR TREATMENT OF WASTEWATER BY REVERSE O^OSIS
                              by
                    ENVIROGENICS COMPANY
                       A Division of
                 Aerojet-General Corporation
                 El Monte,  California   9173^4
                           for the

                   WATER QUALITY OFFICE

             ENVIRONMENTAL PROTECTION AGENCY
                      Program # 17020 DUD
                      Contract #1*1-12-553
              WQO Project Officer, J. M. Staith
       Advanced Waste Treatment Research Laboratory
                      Cincinnati, Ohio
                       September, 1970
         For sale by the Superintendent of Documents, U.S. Government Printing Office
                   Washington, B.C., 20*02 - Price 70 cents

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            WQO Review Notice

This report has been reviewed by the Water
Quality Office and approved for publication.
Approval does not signify that the contents
necessarily reflect the views and policies
of the Water Quality Office, nor does mention
of trade names or commercial products con-
stitute endorsement or recommendation for use.
                    ii

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                             ABSTRACT
Stable, high-flux membranes were sought for use in the renovation of
wastewater by reverse osmosis.  Cellulose ester membranes were  formu-
lated to produce fluxes greater than 60 gal/ft2-day which would not
decrease by more than 20% after the first year of operation,  and re-
ject at least 60$ of sodium chloride and 95$ of sodium sulfate  when
tested at 600 psi with 1000 ppm feed solutions.

The target osmotic performance was achieved with each of three  mem-
brane types:  A cellulose diacetate of moderately-low acetyl content,
a cellulose triacetate-diacetate blend, and crosslinked cellulose
acetate methacrylate.  The intrinsic flux stabilities of these  mem-
branes extrapolated to flux losses of only 12 to 18$ after the  first
year of operation.

The fluxes of these high-performance membranes declined rapidly in
bench-scale tests with secondary sewage effluent but were restored
to within 80 to 90$ of the initial values after cleaning with an en-
zymatic laundry presoak (Biz).  Daily cleaning by this technique main-
tained the fluxes at a nearly constant level over a 5-day test period.
The rejection of sewage components by the high-flux membranes was ex-
cellent, the best of them rejecting 90 to 97$ of TDS, 70 to 100$ of
COD, 86 to 96$ of ammonium ion, 72 to 99$ of nitrate ion and 97 to 99$
of total phosphate.

Techniques were explored for attachment of proteolytic enzymes to cel-
lulose acetate membranes to render them resistant to colloid fouling.
The proteolytic enzyme trypsin was chemically attached to the active
layer surface of a membrane prepared from the N-hydroxysuccinimide
ester of cellulose acetate hydrogen succinate.  The resulting enzymatic
membrane displayed hydrolytic activity toward an ester substrate of
low molecular weight.  The enzyme-polymer compound (in bulk rather than
membrane form) also hydrolyzed casein, a model for proteinaceous col-
loids present in sewage.

This report was submitted in fulfillment of Contract No. lU-12-553,
Program No. 17020 DUD, between the Federal Water Quality Administration
and Aerojet-General Corporation, and covers the period June 1969 to
July 1970.
                                 iii

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                             CONTENTS

                                                                     fege


I.    CONCLUSIONS	       1
II.   RECOMMENDATION^


III.  INTRODUCTION
IV.   STABLE, HIGH-FLUX MEMBRANES	       7

      Membranes from Cellulose Diacetate	       7

      Cellulose Triacetate-Diacetate Blend Membranes	      11

      Cellulose Acetate Methacrylate Membranes	      l6

V.    TESTING OF HIGH-FLUX MEMBRANES WITH SEWAGE	      27

VI.   MEMBRANES RESISTANT TO COLLOID FOULING	      53

      Methods of Attachment of Enzymes to Celluloslc
      Membranes	      53

      Attachment pf Enzymes to Bulk Polymeric Supports	      55

      Preparation of Enzyme-Coupled Membranes	      57

      Membranes from Cellulose Acetate Hydrogen Succinate	      58


REFERENCES	      60

APPENDIX               		      62
                                iv

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                            FIGURES
Figure
1
2
3

Void Structure of CAM-360 Mambranes
Flux Decline of £-383-^0 Membranes During
Test No. 2
Flux Decline of B-Series £-383-^0 Membranes
with Different Effluents
£S
23
32
38
          Effect of Periodic Biz Cleaning on Performance
            of B-Series E-383-^0 Membranes with
            Secondary Effluent
          Effect of Membrane Initial Flux on Flux
            Decline During Test No. k with Pomona
            Secondary Effluent
6         Flux Decline of DS 2.55 Blend Membranes
            During Test No. 5
7         Flux Decline of the Three Membrane Types
            During Test No. 6

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                               TABLES
Table                                                              Page

 1          Osmotic Properties of £-383-^0 Cellulose
              Acetate Membranes  _      9

 2          Long-Term Osmotic Properties of E-383-UO
              Cellulose Acetate Membranes _     10

 3          Osmotic Properties of Unannealed DS 2.63
              Blend Membrane _     13

 U          Osmotic Properties of DS 2.55 Blend Membranes _     15

 5          Osmotic Properties of Crosslinked CAM-360
              Membranes Cast at -10°C _     18

 6          Reformulation of CAM-360 Membranes for
              Room-Temperature Casting _     19

 7          Effect of Annealing Temperature on Osmotic
              Properties of CAM-360 Membranes Cast at
              Room Temperature _     21

 8          Long-Term Osmotic Properties of Crosslinked
              CAM-360 Membranes Cast at Room Temperature _     25

 9          Testing of E-383-kO Cellulose Acetate Membranes
              with Pomona Secondary Effluent - Test Number 1 _     28

 10         Testing of E-383-lfO Cellulose Acetate Membranes
              with Pomona Secondary Effluent - Test Number 2 _     29

 11         Composition of Sewage Feeds in Test Numbers 1
              and 2 _ ___ _     30

 12         Cleaning of Fouled Membranes from Test Number 2
              with Biz                                              3l*
 13         Testing of E-383-40 Cellulose Acetate Membranes
              with Pomona Carbon-Treated Secondary Effluent -
              Test Number 3 _     35

 1^         Peed Composition - Test Number 3 with Pomona Carbon-
              Treated Secondary Effluent _ _ __     3°

 15A        Testing of £-383-^0 Membranes with Sewage Utilizing
              Periodic Biz Cleaning - Test Number k -
              Membrane A                            _     39
                                 vi

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                       TABLES (Continued)
Table                                                              Page

 15B        Testing of E-383-^ Membranes with Sewage
              Utilizing Periodic Biz Cleaning - Test
              Number 4 - Membrane B                                  ^O
 16         Composition of Primary and Secondary
              Effluent Feeds in Test Number 4 _      hi

 IT         Testing of DS 2.55 Blend Membranes with
              Pomona Secondary Effluent - Test Number  5              ^7
 18         Comparative Test of Three Membrane Types
              with Pomona Secondary Effluent  - Test
              Number 6   __        50
                                vii

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                          I.  CONCLUSIONS
The work carried out during this program has shown that flat-sheet mem-
branes with greatly improved fluxes and excellent flux stability can be
fabricated from cellulose esters.  At the same time, rejection of or-
ganic and ionic constituents adequate for renovation of municipal waste-
water by reverse-osmosis was achieved.  The best of the high-flux mem-
branes rejected 90 to 91% of TDS, 70 to 100# of COD, 86 to 96% of
ammonium ion (at pH 5.00 £ 0.25), 72 to 99% of nitrate ion, and 97 to
99$ of total phosphate from secondary effluent at initial fluxes of 50
to 100 gal/ft2-day (gfd).

The new membranes exhibited flux decline slopes of -0.011 to -0.021 with
initial fluxes of 50 to 70 gfd in 200-hr reverse-osmosis tests conducted
at 600 psi with 1000 mg/6 sodium chloride solution.  Flux losses of only
9 to 18% are projected from these flux decline rates after the first
year of operation at 600 psi.  On the basis of their demonstrated intrin-
sic flux and flux stability, and excluding the effects of fouling, these
membranes are calculated to produce 16,500 to 21,000 gal/ft2 of product
water during the first year of reverse-osmosis operation at 600 psi.
These values compare with first-year total water productivity (TWP) of
7000 to 9000 gal/ft2 calculated for state-of-the-art cellulose diacetate
brackish-water membranes produced in these and other laboratories.

Certain of the new membranes exhibited osmotic performance suitable for
low-pressure reverse-osmosis operation, which may offer economic advan-
tages over operation at higher pressure.  A crosslinked cellulose ace-
tate methacrylate membrane produced a flux of 36 gfd at 200 psi, with no
appreciable flux decline, along with 70$ salt rejection in a 200-hr test
with 1000 mg/4 sodium chloride solution.  The total water productivity
calculated for this membrane over the first year of operation at this
pressure is 13,000 gal/ft2.

Although the new high-flux membranes exhibited excellent flux stability
with salt solutions, tests on various sewage effluents demonstrated that
membrane fouling is the single most important factor responsible for re-
duced membrane productivity in the treatment of wastewater.  The rate
and extent of flux decline appears to depend on the quality of the efflu-
ent used, the initial membrane flux, and to a lesser extent, the type of
polymer used to fabricate the membrane.

Periodic cleaning with the enzymatic presoak, Biz,  during bench-scale
reverse-osmosis operation on secondary sewage effluent was shown to be
an effective means of maintaining the high flux of  the new membranes.
For example, in a test conducted at 600 psi with secondary effluent, the
fluxes of specially formulated cellulose diacetate  membranes were main-
tained at k-0 to 70 gfd over a 6-day period during which the membranes
were cleaned every 2U to k8 hrs with Biz solution.

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Three membrane types exhibited the excellent performance desired for
wastewater treatment.  These were Eastman Type E-383-UO cellulose
diacetate; a blend of commercial cellulose triacetate (Eastman Type
A-432-130B) and diacetate (Eastman Type E-398-3) having an average
degree of substitution of 2.55; and a crosslinked cellulose acetate
methacrylate.

Chemical attachment of proteolytic enzymes to cellulose ester membranes
was investigated as a novel technique for making them resistant to foul-
ing by sewage components.  Methods were developed which allow the prepa-
ration of membranes from a cellulose acetate containing a reactive func-
tional group capable of surviving the casting and annealing process; and
subsequently binding an enzyme covalently.  Membranes prepared from the
N-hydroxysuccinimide ester of cellulose acetate hydrogen succinate (CAHS-
NHS), then treated with trypsin, exhibited 2 to 3$ of the esterolytic
activity of the native (unattached) enzyme.  This degree of activity may
be greater than is apparent since the exposed area of the membrane is
very small compared with that of the finely divided bulk material.  A
bulk fibrous preparation of CAHS-trypsin displayed 13 to 17$ of the es-
terolytic activity of the native enzyme and 3$ of the activity of the
native enzyme toward hydrolysis of casein, a model proteinaceous colloid.
This indicated that the enzymatic membranes should display similar ac-
tivity in catalyzing the breakdown of proteinaceous colloids present in
sewage.

The results obtained in a reverse-osmosis test of CARS membranes with
secondary effluent were indicative of an antifouling effect resulting
from the negative charge on the CAHS polymer.  These results, while pre-
liminary in nature, indicate that membranes carrying a suitable negative
surface charge may be resistant to colloid fouling.

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                        II.  RECOMMENDATIONS
Excellent results were obtained during this program in the develop-
ment of new membranes in flat-sheet configuration.  The fabrication
of high-flux membrane types in tubular form was beyond the scope of
the program.  A tubular membrane configuration offers advantages for
scaled-up operation as well as for flow characteristics.  It is
therefore recommended that the highly promising membranes based on
E-383-^0 cellulose acetate and the ds 2.55 blend be developed into
high-flux tubes for evaluation against various sewage effluents.

The development of crosslinkable cellulose acetate methacrylate (CAM)
membranes in flat-sheet form should be continued, with emphasis on
casting these on porous substrates of the type used to line the inside
of tubular  supports.  CAM prepared from the commercially  available
£-383-^0 cellulose acetate should be investigated as  a membrane polymer
to determine whether membranes fabricated from it will duplicate the
outstanding performance of CAM made from a special lot of cellulose di-
acetate (Type E-360-60).

Further work should be  conducted with enzymatic membranes to  demonstrate
their  antifouling properties with sewage effluents.   Simple and inex-
pensive techniques for  attachment of enzymes  to membranes should also
be sought.

Weakly-charged membranes  prepared from acidic or  basic polymers, or
blends of these with  cellulose acetate, should be examined for their
antifouling properties  in tests with sewage effluents.

Some measures to  control  the effects of fouling,  if  not  the process it-
self,  must  be taken in  order to realize even  a healthy fraction of the
high intrinsic water  productivity obtainable  with suitably formulated
cellulose ester membranes.   It is therefore recommended that  novel methods
for the characterization  and removal of colloids  from wastewater be in-
vestigated  and that such  studies, as well  as  the  use of more  conventional
techniques  such as membrane  cleaning and feed pretreatment, be coupled
with the testing  of high-flux  tubular membranes with sewage.

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                        III.  INTRODUCTION
The overall objective of this program was to develop improved mem-
branes for renovation of municipal wastevater by reverse osmosis.   A
major effort was placed on the fabrication of membranes having very
high flux with high flux stability and sufficient rejection of sewage
components to produce acceptable product water.  The goals of osmotic
performance were a flux of at least 60 gal/ft2-day (gfd) with a flux
decline of less than 20% (as projected from absolute values of meas-
ured flux decline slopes of less than 0.02U) in the first year of op-
eration at 600 psi along with moderate rejection of sodium chloride.
A secondary objective was to develop membranes inherently resistant to
colloid fouling, the factor which appears to be most responsible for
flux decline during operation of reverse osmosis units with sewage ef-
fluent.  Such a high flux and flux stability are needed for economical
treatment of wastewater.

Until recently, attainment of fluxes in the desired range was relatively
easy, but maintaining them at acceptably high levels over long test
periods had not been achieved.  Earlier efforts to produce high-flux
membranes for desalination of brackish water consisted of reducing the
annealing temperatures used in the preparation of cellulose diacetate
membranes formulated for the very high salt retention (99$ + ) necessary
for single-pass desalination of seawater.  The flux stability of these
seawater membranes, however, was dependent on high annealing tempera-
tures (e.g., 90 to 95°C).  While the fluxes of such membranes could in-
deed be increased by lowering the annealing temperature, their flux
stability suffered greatly.  The high fluxes produced initially by this
approach were only transitory and after very short periods of testing
declined to values comparable to those of the membranes annealed at
higher temperatures.

More recently, a program was undertaken in these laboratories under
sponsorship of the Office of Saline Water to investigate more effective
ways of attaining stable, high-flux brackish-water membranes.1 Two very
promising approaches to stabilization of the high flux potentially
attainable with asymmetric cellulose ester membranes were found as a
result of these efforts, and these approaches were applied very success-
fully during this program to the fabrication of high-flux membranes
suitable for wastewater treatment.

The first of these approaches was to attain stable high fluxes through
modification of the casting formulation.  This method entailed the use
of larger amounts of, or more powerful, swelling agents in the formula-
tion than were employed in the case of the older cellulose diacetate sea-
water membranes.  This is believed to effect a higher degree of swelling
during the gelation step, and the resulting membranes, due to their high
intrinsic water permeability, still produce high fluxes after annealing at
high temperatures.  An improvement in the flux stability of cellulose di-
acetate brackish-water membranes was obtained with this fabrication pro-
cedure with an attendant increase in long-term total water productivity.

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In the second approach, flux stabilization of membranes was achieved
by chemical crosslinking.  It vas felt that crosslinking would serve
to lock the polymer chains into position and thus reduce the tendency
of the membrane to compact under pressure during reverse-osmosis op-
eration.  Such membrane compaction, due to both reversible elastic
compression and irreversible plastic creep, was believed to be respon-
sible for most of the flux decline observed with reverse-osmosis mem-
branes during operation under pressure.^3  Crosslinking of membranes
prepared from cellulose acetate methacrylate (CAM), a mixed cellulose
ester containing pendant unsaturation in its chemical structure, was
shown to result in a more stable flux.1  The initial fluxes of the
crosslinked CAM membranes, moreover, were higher than those of the
corresponding uncrosslinked CAM membranes indicating that resistance
to the rapid compaction which occurs immediately on pressurization was
increased by crosslinking*

The aim in the development of improved high-flux membranes for waste-
water treatment was to achieve maximum flux consistent with both high
flux stability and, consequently, high total water productivity over
long periods of operation, along with acceptable sewage solute rejec-
tion.  Membrane productivity was evaluated on the basis of intrinsic
membrane flux stability  independent of other factors, such as membrane
fouling and degradation, which affect flux.  The requirements for mem-
brane rejection were felt to be less stringent  in general than those
for flux and flux  stability, because of the low total dissolved solids
(TB6) content of domestic sewage,  such as  sulfate, phosphate, and higher
molecular weight organic compounds, which  are efficiently rejected  by
cellulose ester membranes.  It was recognized,  however, that  although
moderate TDB rejection is acceptable, the  requirements  for removal  of
certain constituents,  such as nitrate, ammonia, and  soluble COD (which
Includes lower molecular weight organics)  are more demanding.  The
target rejection properties  chosen as criteria  for the  rapid  screening
of candidate membranes were  6O% rejection  of  sodium  chloride  and 95$
rejection of  sodium sulfate  from 1000 mg/2 feed solutions.  These goals
appeared reasonable in view  of  the high  sulfate-to-chloride rejection
ratio usually  obtained with  cellulose acetate membranes,  and  permitted
considerable flexibility in  both formulation  and choice of polymer  dur-
ing membrane development.

High-flux membranes meeting  all of the  osmotic  performance goals were
prepared from each of three  polymer types  during the program.  The
choice  of these polymer  types was  based on certain desirable  character-
istics  shown by each,  as well as promising results obtained with  them
in other programs  to develop brackish-water desalination membranes.
Eastman Type E-383-UO cellulose acetate was an attractive candidate be-
 cause  of  the high flux potentially available  by virtue of its moderately-
low degree  of substitution (ds of 2.28 compared with 2Al for the more
 commonly  used Type E-398-3 cellulose  diacetate), and its commercial
 availability.   Blends of cellulose triacetate and diacetate are also
based on  commercially available polymers (Eastman Type A-U32-130B tri-
 acetate and E-398-3 diacetate)  and membranes produced from them have

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exhibited generally higher flux stability and salt rejection than those
prepared from cellulose diacetate alone.*•>*  Membranes prepared from
cellulose acetate methacrylate (CAM) were of particular interest, not
only because they could be crosslinked, but because of their very desir-
able flux and rejection properties.  The CAM polymers, prepared by methac-
rylation of various cellulose acetates, are not now available in commer-
cial quantities but are readily synthesized by established techniques.1*^

Covalent attachment of proteolytic enzymes to the surfaces of cellulose
acetate membranes was investigated as a novel approach to making them re-
sistant to fouling by colloidal deposits during operation with sewage ef-
fluents.  It was expected that the attached enzymes could minimize the
buildup of flux-depressing deposits by catalyzing the hydrolytic break-
down of colloidal particles present in wastewater when these contacted the
membrane surface, or by otherwise interfering with the process of adhesion
of the particles to the surface.  Since the concentration of colloids in
wastewater is on the order of 5 nig/jt, the amount and activity of enzymes
needed to minimize deposition may be very small.5  The aim was to develop
techniques for the chemical attachment of the enzymes to cellulose ace-
tate without undue loss of enzymatic activity.  For this purpose, modi-
fied cellulose acetate polymers containing reactive groups capable of
binding the enzymes were synthesized and these coupled with the enzymes.

The sensitive chemical nature of most enzymes imposes certain restrictions
on the methods used for preparing enzyme-coupled membranes.  Most enzymes
are readily denatured by heat, although enzymes covalently attached to an
insoluble support often show increased heat stability."  It therefore
seemed unadvisable to attach enzymes to membranes by a scheme which re-
quires the enzyme to undergo the membrane annealing process.  Enzymes are
also denatured readily on contact with solvents such as alcohols and
acetone.7  The membrane casting procedure would thus be expected to affect
adversely the activity of an enzyme coupled to the membrane material.

To avoid the deleterious effects of heat and solvents, two alternatives
were considered.  In the first of these, the polymer (a modified cellulose
acetate) would be prepared with reactive functional groups capable of sur-
viving the casting and annealing temperatures.  The reactive membrane would
then be treated with an enzyme under mild, aqueous conditions to produce
the enzyme-coupled membrane.  In the second alternative, a cellulose
acetate membrane (or substituted cellulose acetate) would be prepared in
the usual way, treated with an "activating" reagent or bifunctional cou-
pling agent, and then coupled with the enzyme.  Bifunctional coupling
agents pose the problem of crosslinking the cellulosic polymer or the en-
zyme, while the "activating" reagents, such as cyanogen bromide, may pro-
duce a coupling reaction which has not been completely characterized."
It appeared particularly important to avoid the uncertainties present in
the latter methods since the literature at the outset of this program re-
vealed only one report of an enzyme-coupled membrane, which was prepared
by crosslinking papain adsorbed in a collodion membrane.9  Accordingly,
the more complex but better characterized scheme involving a reactive
polymer was adopted in the initial exploration.

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                  IV.  STABLE, HIGH-FLUX MEMBRANES
Although membranes were fabricated and tested in flat-sheet form
throughout the program, fabrication conditions applicable to tube
preparation were used where possible with the flat-sheet membranes
in anticipation of later development of the most promising formula-
tions into tubes.  In the process for producing tubular membranes,10
used in these laboratories, the membrane is formed by extruding the
casting solution onto the inside of a fabric or paper tube at room
temperature and gelling the wet film in cold water before any appreci-
able drying of it occurs.  The flat-sheet membranes, accordingly, were
cast at room temperature and gelled in water at 1°C within several
seconds of casting.  The casting and gelation were carried out on 6-in.-
wide aluminized Mylar film in a laboratory-scale casting machine.  The
membranes were cast at a thickness of 10 mils and gelled for a period
of 10 man.  Annealing (heat-treating) was conducted by immersing the
membranes for a period of 3 min in a water bath thermostatted at the
specified annealing temperature.  After annealing, the membranes were
stored in a refrigerator under water in sealed containers until ready
for testing.

Reverse-osmosis testing of the flat-sheet membranes was conducted in
3-in. diameter flat-plate test cells* over the 200 to 700 psi pressure
range.  The test cells and ancillary equipment used has been described
in previous reports.1*A!  Three specimens of each membrane were evalu-
ated in all of the tests carried out with salt solutions and sewage,
and test data reported are the averages of the individual test specimens.

MEMBRANES FROM CELLULOSE DIACETATE

Eastman Type E-383-40 cellulose acetate was an attractive candidate
polymer for development of high-flux membranes because of its moder-
ately low degree of acetyl substitution (ds); its ds value is 2.28 in
comparison with a ds of about 2.1*5 for the cellulose diacetate used in
state-of-the-art membranes.  Since the intrinsic water permeability of
homogeneous films of cellulose acetate of comparable density has been
shown to increase with decreasing acetyl ds of the polymer,•"• it was of
interest to exploit the high flux potential of this material in membrane
development.  Cellulose acetate Type E-383-UO has the lowest ds of any
of the commercially available cellulose acetate polymers and no previous
reports of its use in reverse-osmosis membranes have been found.
 The  cells provide a  channel height of 0.007 in. over a 2.7-in. diameter
 section of exposed membrane.  The minimum flow velocity which occurs at
 the  center of the circular flat plate is calculated to be I.h ft/sec at
 5 GFH  circulation rate and 2.8 ft/sec at 10 GPH circulation rate.

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A formulation study was carried out with E-383-1K) cellulose acetate
using acetamide as the swelling agent; acetamide had been found to
be very effective in promoting high flux with cellulose triacetate-
diacetate blend membranes.1  In this study, the amounts of acetone
and acetamide in the casting solution were varied, and the membranes
annealed at temperatures ranging from 80 to 90 C.  The reverse-osmosis
properties of the membranes prepared from the most promising of these
formulations are given in Table 1.  The tests were conducted with 1000
mg/l solutions of sodium chloride and sodium sulfate, respectively, at
300 and 600 psi.

The short-term (2-hr) osmotic properties of the membranes cast from
formulation 33A and annealed at 80 to 90°C, and those cast from for-
mulation 33B and annealed at 80 to 85°C, were well within the target
performance range of the program, with fluxes of 6h to 105 gfd, sodium
chloride rejections of 6l to 67% and sodium sulfate rejections of 95
to 98$ determined at 600 psi.  The membranes annealed at 80°C showed
potential for low-pressure (200 to 300 psi) operation producing at 300
psi, fluxes of k2 to U8 gfd with 60 to 66% rejection of sodium chloride.
The relatively low sodium sulfate rejections obtained with the high-flux
membranes cast from formulation 33C indicated that they contained de-
fects possibly due to overswelling at the higher level of acetamide and
lower level of solvent.  No further work was done with this formulation.

The intrinsic flux stability of the experimental membranes was assessed
by comparison of the flux decline slope, m, defined by the equation
log J = log J  + m log t, where J  is the flux after 1 hr of testing and

J is the flux at time t.  A least means squares analysis of the flux
data measured during a nominal 200-hr reverse-osmosis test is used to
calculate the value of the slope.  In the absence of fouling or membrane
degradation the flux decline behavior of membranes appears to obey the
linear relationship given by the above equation, on the basis of many
long-term tests conducted in these and other laboratories.  Integration
of the logarithmic equation leads to the following expression for the
total water production (TWP) in gallons/ft2 expected during time t, where
t is expressed in hours.
                           TWP »


It should be noted that because of the exponential form of both
equations, the predicted decline in flux or productivity during the
second and subsequent years is very small.  For example, a flux decline
slope of -0.02U corresponds to a flux loss of 20% during the first year
of operation but less than 2% additional loss during the second year.

Long-term (170-hr) tests were conducted at 600 psi with the most promis-
ing E-383-4o cellulose acetate membranes to determine their rates of
flux decline.  The results of these tests, summarized in Table 2, indi-
cate excellent flux stability for these membranes.  On the basis of


                                 8

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                                                            TABLE 1
vo
OSMOTIC PROPERTIES OF E-383-UO CELLULOSE ACETATE MEMBRANES
Casting Solution Formulation (parts by weight)
Annealing
Temp., °C
80

85

90
E-383-40
Acetone
Acetamide
Water
Pyridine
Test
Pressure,
psi
300
600
300
600
600

33A
10
Uo
11
3
h
Formulation 33A
Flux,
gfd
14-2.2
105
38.3
85.3
6U.3
NaCl Na2S°U
66.3
63.0 96. k
72.8
66.7 98.2
97.2
33B
10
35
11
3
1^
o
Osmotic Properties
Formulation 33B
Flux,
gfd
Vf.7
98.0
32.3
&.7
32.0
NaCl S2 k
60.5
60.8 96.3
70.5
65.9 9^-5
99-0
33C
10
32.5
12
3
U
Formulation 330
Flux,
gfd
^5.0
81.3
37.3
66.3
29.3
NaCl
59-9
60.5
59.0
65.1

Na2S04
_
85.9
-
85.3
99-0
              Tested for 2 hrs against 1000 mg/X feed solutions.

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                                                           TABLE  2
                             LONG-TERM OSMDTIC  FROIERTIES OF E-383-UO CELLULOSE  ACETATE MEMBRANES
                 Casting
              Formulation
                   33A
                Annealing
                Temp.j °C
                    85
One Hour Flux
       ,b,c
63.07 + 0.78
                                                                  Flux
                                                                 Decline
                  Slope, m
                          b,c
                                  First Year
                                  Total Water
                                  Production
                                  gal/sq.  ft.
                   -0.017 +  .003     20,000
Salt Rejection, j6
2 hr        170 hr
H
o
                   33A
                   33B
                    90
                    85
  .50 + 0.36      -0.016 + .002     13,^00
66.92 + o.f
                  -0.021 + .003     20,700
66.8

78 A
                                                                                                            72.
            79-3
               Formulations  given in Table  1.
               Determined  at 600 psi with 1000 mg/i  sodium chloride solution.   Duration of test  was  170 hrs.
               Given by the  equation:   log  J = log J +  m log t,  where J = flux at time t (hrs)  and  J  is the flux
               after 1  hr.                           X
Calculated from the equation:  TWP =
pH of feed was maintained at 5.2 + 0.2.
                                                       1""
                                                          /2h (mfl).

-------
measured flux decline slopes of -0.016 to -0.021, flux losses due to
membrane "compaction" expected during the first year of operation are
13 to l8#.  Values of 20,000 to 21,000 gal/ft2/yr were calculated for
the expected total water production (TWP) during the first year of
reverse-osmosis operation with the 85°C membranes.  These are greatly
superior to the productivity values of 7000 to 9000 gal/ft2/yr calcu-
lated for state-of-the-art cellulose diacetate brackish-water membranes
from data obtained at 800 psi with 5000 mg/Z sodium chloride solution.

A number of test specimens of the 33A and 33B membranes were fabricated
and heat-treated at 85°C for testing against sewage effluents.  The re-
sults of these tests are presented and discussed in a later section en-
titled "Testing of High-Flux Membranes with Sewage."

CELLULOSE TRIACETATE-DIACETATE BLEND MEMBRANES

The development of high-flux membranes from blends of cellulose tri-
acetate (Eastman Type A-U32-130B) and diacetate  (Eastman Type E-398-3)
was of interest because of the superior flux stability and salt rejec-
tion which has been shown by blend membranes formulated for desalination
of brackish water in comparison-to that of brackish-water membranes pre-
pared from the diacetate alone.   Work in this program was directed
toward realization of the maximum flux of blend  membranes through both
modification  of the  casting formulation and variation of the triacetate-
diacetate ratio (and accordingly  the average ds), while retaining the
intrinsically high flux stability and good rejection properties.

Membranes were  cast  from the formulation of a 1:1  (by weight) blend  of
triacetate and  diacetate (average ds = 2.63) shown below.

              Component            Amount (parts  by weight)

            A-432-130B                      10

            E-398-3                         10
            1,4-Dioxane                     55

            Acetone                         35

            Methanol                         9

            Maleic Acid                      3

The  casting and gelling procedure employed was  the same as that de-
 scribed at the  beginning  of this section except that the membranes
were  gelled after a  30-sec drying period.   Testing was conducted with
 a 1000 mg/£  TDS mixed feed solution of ionic  composition characteristic
 of that of a typical wastewater.  This was done to establish a baseline
 for further development of blend membranes for wastewater treatment.
The membranes were evaluated in the unannealed state to obtain maximum
 flow.
                                  11

-------
Both the feed composition and test results are shown in Table 3»  The
test was conducted for 2-hr periods successively at 200 psi, TOO psi
and again at 200 psi.  Considerable compaction of this membrane oc-
curred at TOO psi as evidenced by the very small increase in flux pro-
duced at this pressure over that produced initially at 200 psi, and by
comparison of the initial and final fluxes at 200 psi (before and after
testing at TOO psi, respectively).  The unannealed blend membrane would
best be suited for low pressure operation, where it produces high flux
with low chloride rejection but moderate overall rejection.  This for-
mulation was not an optimum one for producing stable, high-flux mem-
branes because a low annealing temperature was necessary to obtain the
high flux.

Efforts to reformulate the 1:1 blend (ds 2.63) to achieve high flux
with high annealing temperature through use of a more potent swelling
agent than maleic acid were not successful.  Membranes were cast at
room temperature from the formulations shown below, gelled in ice water
within 1 sec of casting, annealed at 85°C and tested for 2-hr periods
at 200 and 600 psi against a mixed feed containing 300 mg/i of sodium
chloride and TOO mg/i of sodium sulfate»

             Component             Amount (parts by weight)

            A-U32-130B                       10

            E-398-3                          10
            1,^-Dioxane                      lf-5

            Acetone                          35

            Jfethanol                       0, 5, 10
            Propionamide                   8, 10, 12

Most of the membranes appeared overswollen, producing excessive flux
with little or no rejection of either solute.  The membranes prepared
from the formulations containing no methanol and 8 or 10 parts of
propionamide produced mediocre flux (T to 28 gfd at 200 psi and 13 to
53 gfd at 600 psi) and low rejection (9 to k2 of sodium chloride and
36 to T8$ of sodium sulfate).  The low sodium sulfate rejection was in-
dicative of flaws in these latter membranes.  In view of these results,
no further work with the 1:1 (ds 2.63) blend was carried out.

Considerably better results were obtained with a blend of 3 parts of
cellulose triacetate and T parts of cellulose diacetate having an aver-
age ds of 2.55.  It was theorized that the ds 2.55 blend, by virtue of
its lower ds should have higher flux potential and still exhibit the
excellent flux stability and rejection behavior characteristic of 1 to
1 blends.  This contention was borne out by results obtained with the ds
2.55 blend during the course of the program.

Two formulations of the ds 2.55 blend were examined using a combination
of maleic acid and acetamide or propionamide as swelling agents.  A


                                 12

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                                               TABLE 3




                       OSMDTIC PROPERTIES OF UNANNEALED DS 2.63 BLEND MEMBRANES
                                Feed
Pressure,
psi
200
(initial)
700
200
(final)
J£-
8.0
7.6
8.9
Cl"
Cone . ,
ppm
178
180
180
Conductance,
// mho cm
1180
1250
1150
Flux,
gfd
38.6
39.2
27.0

Cl"
50.0
60.0
56.2
Rejection, %
Electrical
Conductivity
73.1
77.U
77.2
Nominal feed composition (mg/X):  Na+, 180; Ca++, 80; Mg^, 33; Cl", 17^; HCO ~,  1^00; S0^~,  133-
 Determined after 2-hr test periods at designated pressures.

-------
series of membranes vas cast from these formulations and annealed
over the temperature range of Ik to 85°C utilizing the casting and
gelling procedure described at the beginning of this section.  The
reverse-osmosis properties of these membranes tested vith 1000 mg/jfc
solutions of sodium chloride and sodium sulfate at 300 and 600 psi
were sufficiently close to the target values for the program to war-
rant further work with this blend.  The formulations used and test
results obtained are summarized in Table k.  Fluxes of 52 to 72 gfd
with 62 to 66% rejection of sodium chloride produced at 600 psi were
within the target range, but the somewhat low sodium sulfate rejec-
tions of 89 to 91$ were indicative of membrane imperfections.  The
relatively low rejections, particularly of sodium sulfate, exhibited
by this first series of ds 2.55 blend membranes were apparently due
to the presence of rather large (approximately 100 y,m diameter) voids
or bubbles which could rupture under pressure producing pinholes.
Such holes provide the leakage paths for salt solution which lowers
the salt rejection of the membrane.  Sodium sulfate rejection of less
than 99$ is usually an indication of membrane imperfections, since
the intrinsic permeability of cellulose acetate membranes toward this
solute is very low.

The number and size of the voids in the ds 2.55 blend membranes were
reduced considerably by more careful drying of casting solution in-
gredients, particularly the cellulose triacetate, before preparing
the solution.  A membrane prepared from a solution of carefully dried
ingredients contained very few voids, which were 20 to 30 urn in
diameter.  This membrane, cast from the 35A formulation, annealed at
85°C and tested with 1000 mg/4 salt solutions at 600 psi, produced
lower flux (36 gfd) but much higher salt rejection (95# of sodium
chloride and 98$ of sodium sulfate) than did previous membranes fabri-
cated and tested under the same conditions, but cast from solutions
of less carefully dried ingredients.

The flux stability of the ds 2.55 blend membranes fabricated from both
of the casting formulations described in Table k and annealed at 85°C
determined in a long-term (172-hr) reverse-osmosis test conducted at
600 psi with 1000 rag/I sodium chloride solution was outstandingly high.

  Casting         One-Hour          Flux Decline      Salt Rejection,  %
Formulation       Flux,  gfd            Slope	      2 hr      172 hr

    35A          59.Ik + 0.60      -0.013 + 0.003      69.5       73.1

    35C          1*9.39 1 0.58      -0.011 + 0.003      7^.5       79.7

The total water production for the first year of operation calculated
from this data was 18,500 gal/ft2 for the 35A membrane and 16,500 gal/
ft2 for the 35C membrane.  The results of tests conducted with the ds
2.55 blend membranes on secondary sewage effluent are described later
in the section entitled "Testing of High-Flux Membranes with Sewage."

-------
                               TABLE  k
OSMOTIC PROPERTIES OF DS
Casting
2.55 BLEND MEMBRANES
Formulation (parts by wt)
A-U32-130B Cellulose Triacetate
35A
6

E-398-3 Cellulose Diacetate Ik
Dioxane
Acetone
Maleic Acid
Acetamide
Propionamide





^5
ko
6
10
-





6
Ik
k5
ko
6
-
Ik
p
Osmotic Properties
Formulation 35A
Annealing
Temp., °C
Determined with
Ik 300 psi
600 psi
80 300 psi
600 psi
85 300 psi
600 psi
Determined with
80 300 psi
600 psi
Flux,
gfd
1000 mg/4
57.7
101
1^0.5
77.0
25.2
52.3
1000 mg/e
38.0
73.0
Re,}.,
Sodium Chloride
k6.8
57.7
50.1
55.^
65.6
65.7
Sodium Sulfate
87.2
89.0
Formulation
Flux,
gfd
Solution
56.2
92.7
UU.2
72.0
31.8
5^.3
Solution
30.0
55.0
35C
Rej.,
56.0
1*7.6
61.9
56A
65.8
90.5
90.7
aDetermined after 1- to 2-hr test periods.
                                  15

-------
CELLULOSE ACETATE METHACRYLATE MEMBRANES

One of the approaches to flux stabilization of membranes investigated
in this program was crosslinking.  A considerable effort was devoted
to fabrication of high-flux membranes from cellulose acetate methacry-
late (CAM), a mixed cellulose ester containing unsaturated groups in
its chemical structure which serve as crosslink sites.  The CAM polymer
used for membrane fabrication during the program was synthesized by
methacrylation of Eastman Type E-36b-6o cellulose acetate (ds 2.09 to
2.12) by an established procedure.1  This polymer, designated herein as
CAM-360, was synthesized in 1000-g batches which had total ds ranging
between 2.3^ to 2.39 and methacrylyl ds ranging between 0.2 to 0.3.  A
methacrylate ds in this range is considered sufficiently high to permit
adequate crosslinking.  This particular CAM polymer was chosen because
of its relatively low total ds, compared with the CAM polymers derived
from higher ds cellulose acetates such as E-383-UO (da 2.28) and E-398-3
(ds 2.Ul), and because of the excellent osmotic properties exhibited by
brackish water membranes prepared from it on another program.

As in the case of the blend membranes, CAM-360 membranes formulated for
brackish water desalination were tested using the 1000 mg/JL six-ion
mixed feed described in Table 3, as a starting point in the wastewater
membrane development effort.  Unlike the cellulose diacetate and blend
membranes described in this report, these membranes were cast at -10°C
on glass plates and allowed to dry in air for 3 min at this temperature
before gelling in water at 1°C.  The following casting solution formula-
tion was employed:

            Component              Amount (parts by weight)

            CAM-360                          10

            Acetone                          40

            Water                            10

            Maleic Acid                      lk
The membranes were annealed at 80C and 83C for 3 min then crosslinked
to 93$ acetone insolubility by immersion for 3 min at 90°C in a solution
containing 0.035 M of potassium persulfate and 0.0^0 M of sodium bisulfite
using a previously described procedure.^  The degree of acetone insolu-
bility of a crosslinked CAM membrane is an indication of how completely
the crosslinking reaction has taken place since crosslinking of a polymer
insolubilizes it.  The acetone insolubility of a membrane is determined
by measuring the loss in weight occurring after it is stored for several
hours at room temperature in the solvent.

Short-term reverse osmosis tests were conducted on the CAM-360 membranes
at 200 and 700 psi with a 1000 rag/Ji mixed feed solution similar to that
used with the unannealed blend membrane described previously (see Table
3) .  The osmotic properties of these crosslinked CAM membranes as shown
                                 16

-------
by the data in Table 5 were characterized by very high flux (70 to 90
gfd at TOO psi) with relatively high chloride rejection (80 to 90$)
and somewhat higher total dissolved solids (TDS) rejection as measured
by electrical conductivity.  The nearly proportionate increase in flux
produced by the membranes with increased test pressure was indicative
of high resistance to compaction, particularly so with the membrane an-
nealed at 83°C.

It was of interest to determine the maximum flow obtainable with the
crosslinked CAM-360 membranes while maintaining salt rejection and flux
stability within an acceptable range.  Such information would also estab-
lish the potential for development of very high flux CAM membranes suit-
able for low pressure operation.  For this purpose, additional specimens
of membranes cast at -10°C from the formulation described above were
annealed at lower temperature, ?U and T7°C, respectively, crosslinked
to 85 to 90$ acetone insolubility by the same procedure used with the
membranes annealed at 80°C and 83°C, and tested for 200 hrs at 200 psi
against a feed  containing 292 mg// of sodium chloride and 708 mg/4 of
sodium sulfate.  The test results, summarized below, indicate that very
high fluxes can be obtained at low pressures, together with suitable salt
retention.


      Annealing     One-Hour       Incline        Rejection,  ft
       Temp.,  °C      Flux,  gfd       Slope        Nad
           Jk            61.7        -0.015       67.2       96.0

           77            ^9-0        -0.015       76.5       95.5

 Although exhibiting excellent osmotic properties for wastewater treat-
 ment,  these CAM membranes were fabricated under conditions (cast at -10°C,
 with long drying time before gelation) unsuitable for development of
 tubular membranes.   Consequently, CAM-360 was reformulated for room tem-
 perature casting and gelling within several seconds of casting, the con-
 ditions which prevail in the extrusion of tubular membranes.  Two basic
 formulations were examined, one based on maleic acid/water as the swell-
 ing agent/non-solvent combination (similar to the formulation used in
 preparation of the CAM membranes described above) and the other utilizing
 acetamide /water for this purpose.  A series of membranes was prepared
 from each basic formulation in which the amount of acetone was varied.
 The solvent level (i.e., polymer concentration) in the casting solution
 sometimes has a marked effect on the properties of the resulting mem-
 branes.  The membranes were all annealed at 7l4-°C and tested without
 crosslinking at 300 psi and 600 psi against 1000 mg/J sodium chloride
 solution.  The formulations and test results are summarized in Table 6.
 The most notable observation with these results was the difference in
 flux and rejection behavior with increased pressure between the maleic
 acid and acetamide formulations.  The membranes cast from the maleic acid
 formulations (flos. 32A through 32D, Table 6) exhibited a marked drop in
 salt rejection when the test pressure was increased with a flux increase
 proportionately higher then the pressure increase, particularly at the


                                  17

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                                                          TABLE 5
                            OSMDTIC PROPERTIES OF CROSSLIUKED CAM-360 MMBRABES CAST AT -10°C
                                                           Peed                    	osmotic Properties
                                                        Cl        _                               Rejection, %
            Annealing        Pressure,                 Cone.,       n UC B^f     Flux,         _       Electrical
            __      f\ _             .              __                  „ _ *   _. •         	a a       **^ ^       ««	a___j__»	*j	
                                                                                                 ^
            Heap.,  °C           psi            pH       ppm        Mnho cm          gfd       Cl"       Conductivity
                80               200           8.3       180           1190          32.7     85.2           88.5

                80               700           7.U       200           1180          91.3     81.1           8^.1
)-•
°°               83               200           8.3       180           1190          22.2     89.5           93.0

                83               700           j.k       200           1180          70.0     88.0           91.8
            Nominal feed composition(mg/4): Na+, 180;  Ca++,  80;  Mg**,  33;  Cl",  17^;  HC»3",  ^00; SO^, 133-
            ^Determined after 2-hr test periods at designated pressures.

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                                               TABLE 6
REFORMULATION OF CAM-360 MEMBRANES FOR ROOM-TEMIERATURE CASTING


CAM-360
Acetone
Maleic Acid
Acetamide
Water

32A
10
40
14
-
10
Casting
32B
10
35
14
-
10
Solution
32C
10
32.5
14
-
10
Formulation
32D
10
30
14
-
10
(parts
32E
10
40
-
8
5
by wt.)a
32F
10
35
-
8
5

32G
10
32.5
-
8
5
Osmotic Properties
300 psi Flux, gfd
Rej., %
600 psi Flux, gfd
Rej., %
23.5
85.9
57.8
69.4
25.5
87. 8
55-3
78.7
21.0
89.0
131
32.1
22.7
87.6
79-0
56.0
23.5
78.5
53-3
83.3
33.7
27.8
55-7
35.9
53.5
8.9
74.7
11.4
Membranes cast at room temperature, gelled at 1°C within 1 sec of casting and annealed at 74°C.
Membranes were not crosslinked.

Determined after 2 hrs test time at the designated pressures with 1000 mg/jt  sodium  chloride  solution.

-------
lower  solvent levels.  This is  indicative of the rupture of voids at
the higher pressure.  Formulation  32B, however, yielded a membrane
which  decreased only moderately in salt rejection on high pressure op-
eration.  In contrast, the salt rejection of all the acetamide mem-
branes (formulations 32E through 32G, Table 6) increased with pressure
and their fluxes increased with pressure in a more normal behavior for
reverse-osmosis membranes.  Promising results were obtained with the
acetamide formulation at an acetone level of kO parts per 10 parts of
polymer.  The low rejections obtained with the membranes cast from solu-
tions  containing less solvent were apparently due to pinhole defects
which  formed during their fabrication rather than during operation since
the rejections were low even at the low pressure.

Additional CAM-360 membranes were  cast from the maleic acid and acetamide-
based  formulations 32B and 32E,  respectively, to determine the range of
flux and salt rejection obtainable with uncrosslinked membranes fabri-
cated  under these conditions.   In  contrast to the first series, these
membranes were cast at room temperature, dried for a few seconds, and
annealed at low temperatures (50 to T0°c).  This second series of mem-
branes exhibited very desirable osmotic properties as shown by the re-
sults  of short-term tests conducted at 300 psi and 600 psi with 1000
mg/£ sodium chloride and sodium sulfate solutions, summarized in Table 7.
Fluxes of 71 and 88 gfd with sodium chloride rejections of 75 and 65$
produced at 600 psi by the membranes annealed at 60°C and 50 C were well
within the program performance  goals.  The 60°C membranes when tested
against sodium sulfate solutions gave high (90 to 97$) rejection of this
solute.  These membranes were cast from the same batch of casting solu-
tion used to prepare the 60°C membranes tested with sodium chloride solu-
tion but were annealed and tested  separately from the latter.  The higher
fluxes produced with the sodium sulfate feed may have been due to random
variations in annealing temperature and test pressure.  The 50°C membrane
showed potential for low pressure  operation, producing 56 gfd flux with
66% sodium chloride rejection at 300 psi.

Contrasting behavior of flux and salt rejection with increasing test
pressure was again exhibited by the two formulations - the maleic acid
formulation showing a decrease  in  salt rejection while the acetamide
formulation showed a slight increase in rejection.  This difference in
behavior is attributed to differences in the void structures of the two
types  of membranes.  Voids, as  described in the previous section on blend
membranes,  are bubbles or cavities present in the microporous membrane
substructure which are large in size compared to the thickness of the
dense active layer of the membrane, and which form during the gelation or
desolvation step in membrane fabrication.  They occur very commonly in
asymmetric reverse-osmosis membranes and can impair membrane performance
by rupturing when the membrane  is pressurized.  The microporous substruc-
ture provides ample mechanical  support for the active layer at the pres-
sures  commonly employed in reverse-osmosis operation.  The presence of
large voids very close to the active layer surface, however, causes weak
spots  in that surface.  Failure  at these weak points usually occurs under
pressure to produce holes or breaks in the active layer which leak salt
solution,  and subsequently, reduces salt rejection.
                                 20

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                              TABLE 7

  EFFECT OF ANNEALING TEMPERATURE ON OSMOTIC PROPERTIES OF CAM-360
                 MEMBRANES CAST AT ROOM TEMPERATURE
                                                           o
                                         Osmotic Properties
Annealing
Temp., °C
^

70

60

50


Test
Pressure, psi
Determined with 1000 mg/jfc
300
600
300
600
300
600
300
600
Determined with 1000 mg/l
32Bb
Flux, Re,).,
Sodium Chloride
25.5 87.8
55.3 78.7
27.8 81*. 5
53.3 82.1
1*1.0 78.0
70.7 7^.6
56.3 65.6
88.2 61*. 9
Sodium Sulfate
32Eb
Flux,
gfd
Solution
28.5
53.3
21.8
U3.3
1*5.0
71.3
-
-
c
Solution

Rej.,
-JL-
78.5
83-3
86.6
89.6
6»*.0
68.9
-
-

    60                300           55.3    97.3        52.0     93.8
                      600           98.7    90.0        81*.0     96.3


aDetermined after 2 hrs of testing at the pressures and with the feeds
 designated.
 Formulation given in Table 6.  Membranes cast at room temperature and
 gelled within 1 sec of casting.  Membranes were not crosslinked.
cMembranes were annealed separately from those tested with sodium chloride
 solution.
                                 21

-------
The CAM-360 membranes prepared from either formulation contained numer-
ous small (1 to 10 micrometer diameter) and large (20 to 30 micrometer
diameter) voids, as shown in Figure 1 by the scanning electron micro-
graphs of the maleic acid (formulation 32B) and acetamide (formulation
32E) membranes.  In the former membranes, large voids are seen to be
situated very close to the active layer (top) surface.  These membranes
exhibited a drop in salt rejection and disproportionately large increase
in flux with increased pressure, which behavior is indicative of void
rupturing.  In contrast, the voids, particularly the larger ones, in the
acetamide membrane were located further beneath the active layer surface,
and these membranes showed no evidence of void rupturing at the higher
test pressure (see data of Tables 6 and 7).  These differences are
brought out particularly well by the data obtained with the 1000 mg/A
sodium sulfate feed and shown in Table 7.  The rejection of this solute
decreased from 97 to 90% with the 32B membrane while increasing from 914.
to 96$ for the 32E membrane when the test pressure was increased from
300 to 600 psi.

Although the mechanism of void formation is not yet well understood., it
has been established from work accomplished under other programs,Ij^ASAS
that void frequency, size, shape and location in a membrane are greatly
dependent upon a number of factors, such as formulation, fabrication con-
ditions and polymer type.  Much progress has been made in the control of
void formation through modifications in membrane formulation and fabrica-
tion conditions and the problem does not appear to be a limiting one in
the development of membranes for wastewater treatment.  A detailed study
of this phenomenon was beyond the scope of this program, but its impor-
tance to membrane performance is borne out by the observations described
above for the CAM-360 membranes, and in the previous section for the ds
2.55 blend membranes.

Crosslinking of the CAM-360 membranes cast at room temperature from the
32B (maleic acid-based) and 32E (acetamide-based) formulation described
above (see Tables 6 and 7) and annealed at 60°C was attempted using the
procedure employed previously with the membranes cast at -10°C and an-
nealed at higher temperature.  This procedure was unsatisfactory for
treatment of the reformulated membranes because of excessive shrinkage
and deformation which occurred.  Treatment of the membranes for h to 12-
hr periods at room temperature in the crosslinking solution rather than
90°C was also unsatisfactory because of apparent membrane degradation,
evidenced by excessive flux and low salt rejection (e.g., 50$ rejection
of sodium sulfate).

Acceptable crosslinking was finally achieved by Immersion of the membranes
in the per sulfate-bisulfite bath at the temperature at which the membranes
had been annealed for periods of 5 to 20 min, depending upon the tempera-
ture.  The results of 1-hr reverse-osmosis tests conducted at 300 and 600
psi with 1000 ng/Jt sodium sulfate solution with uncrosslinked and cross-
linked CAM-360 membranes cast from the 32E formulation (at room tempera-
ture with short drying time before gelation) and annealed at 60°C are
summarized below.  The membranes were crosslinked to 60$ acetone insolu-
bility by immersion for 15 min at 60 C in the persulfate-bisulfite bath.
                                 22

-------
            32B (Maleic Acid) Formulation
              32E (Acetamide)  Formulation
50 micrometer
LO micrometer
    Figure 1.   Void Structure  of CAM-360  Membranes

-------
^                    m    „**                 NaoSO), Rejection, %
Pressure,    	     Flux, gfd	    	2  k       .
   psi       Uncrosslinked   Crosslinked    Uncros slinked   Crosslinked

   300            52.0           78.0            93.8          98.5

   600            Qk.O          lH.0            96.3          98.3

Excellent osmotic properties were also obtained with similar membranes
annealed at ?0°C and crosslinked to 60$ acetone insolubility by treat-
ment in the bath for 10 min at TO°C.  The results of 1-hr tests con-
ducted with these latter CAM-360 membranes both uncrosslinked and
crosslinked at 600 psi with 1000 mg/4 sodium chloride are given below.

              Flux, gfd                 	NaCl Rejection, %	
    Uncrosslinked      Crosslinked      Uncrosslinked     Crosslinked

         ^3.3             73-3               89.6             91.7

The short-term osmotic properties of the crosslinked CAM-360 membranes
described above were extremely promising, particularly in view of the
high salt rejections obtained at high flux levels.  The crosslinked 60°C
membranes appeared ideal for low-pressure (e.g., 200 psi) operation.
Crosslinking of these membranes is seen to have greatly increased their
fluxes (72% increase for the 60°C membrane and 69$ increase for the 70°C
membrane at 600 psi) with a slight increase in salt rejection.  This be-
havior is attributed to an increase in the compaction resistance of the
membranes as a result of crosslinking.  The relatively low degree of
acetone insolubility (approximately 60$ compared with 85 to 93$ obtained
earlier with CAM-360 membranes crosslinked at 90°C) found for these mem-
branes after crosslinking indicated that the crosslinking procedure war-
rants further improvement.  The degree of crosslinking achieved, however,
evidently provided adequate flux stabilization, as shown by the results
of long-term tests described below.

The osmotic properties of the crosslinked CAM-360 membranes fabricated
by casting at room temperature and gelled within seconds of casting
compared very favorably with those of the earlier membranes cast at -10°C
and gelled after relatively long drying times.  Lower annealing tempera-
tures were required with the former than with the latter membranes to
achieve the same flux.  The crosslinked CAM-360 membranes, in general,
exhibited higher salt rejection at a given flux level than did the
E-383-^0 cellulose acetate and ds 2.55 blend membranes.

The flux stability of the crosslinked CAM-360 membranes fabricated at
room-temperature, under short drying time conditions was determined in
long-term (nominal 200-hr) tests conducted at 200 and 600 psi with 1000
mg/4 sodium chloride solution.  The 32B and 32E membranes annealed and
crosslinked at 70°C were tested at 600 psi and a 32E membrane processed
at 60 C was tested at 200 psi. The results are summarized in Table 8. The

-------
ro
VJl
                                                         TABLE 8


                 LONG-TERM OSMOTIC PROPERTIES OF CROSSLINKED CAM-360 MEMBRANES CAST AT ROOM TEMPERATURE



                                                                 TTon-r                    First Year
                                      Percent    -Test                           ne      Total Water      Salt
              Casting     Annealing   Acetone   Pressure,         ^'        ^cxine      Production,  Rejection, %
            Formulation   Temp.,  C  Insoluble     psi         gfd           Slope       gal/sq.. ft.  2 hr  175 hr


                32E           60C       58         200     35.52 + 0.51  -0.001 ± 0.004    12,800     70.1   68.8


                32E           70d       65         600     63.19 + 0.72  -0.020 + 0.003    19,700     87.2   87.0


                32B           70d       29         600     73.36+1.19  -0.05^+0.004    17,400     7^-7   75-5
            Formulations given in Table  6
           b
            Determined with 1000 mg// sodium  chloride  solution.  Duration of test was  175 hrs.

            Membrane crosslinked by immersion for 15 min at  60°C in a  solution of K0S-,0Q (0.035 M)  and NaHS00
            (O.OkO M).                                                              2  2  t3        -           3

            Membranes crosslinked as in  c except for 10  min  at 70°C.   Both  membranes  treated simultaneously in
            same bath.

-------
membranes prepared from formulation 32E (based on acetamide) showed ex-
cellent flux stability, under the test conditions employed, veil within
the program performance goal (absolute value of flux decline slope less
than 0.02k}.  The 60°C membrane, when tested at 200 psi, showed, for all
practical purposes, no flux decline, and the value of 13,000 gal/ft2 for
the first year's total water productivity, calculated for this membrane
compares very favorably with values at 800 psi of 7000 to 11,000 gal/ft2
calculated for current cellulose diacetate and 1:1 blend brackish-water
membranes operating on 5000 mg/jK sodium chloride.  The performance of
the crosslinked 32E membrane (70°c) at 600 psi was outstanding in terms
of combined high water productivity and high salt rejection.

The difference in flux stability observed between the crosslinked 70°C
membranes prepared from the 32B formulation (based on maleic acid) and
the 32E formulation (based on acetamide) was evidently due to the differ-
ence in their extent of crosslinking.  The 32B membrane was the less
stable of the two, with a flux decline of -0.05^ compared with a slope
of -0.020 for the 32E membrane.  The former had an acetone-insoluble
fraction of only 29$ compared with 65% insolubility of the latter mem-
brane.  These differences and their interrelationships were quite clear-
cut in view of the fact that both membranes were crosslinked under
identical conditions in the same bath.  A possible explanation of the
inferior results with the 32B membrane is that chemical degradation took
place either due to residual maleic acid or during the crosslinking
treatment through acid-catalyzed hydrolysis of the methacrylate groups.
Such degradation of CAM-360 has been observed with solutions of the 32B
formulation after storage at room temperature for periods of a week or
more.

The results obtained with both crosslinked and uncrosslinked CAM-360
membranes point up the superiority of the acetamide-based formulation
over the maleic acid-based formulation in terms of osmotic properties
and ease of crosslinking of flat-sheet membranes, fabricated under con-
ditions applicable to extrusion of tubular membranes.  The outstanding
performance obtained with the membranes prepared from this formulation
was very encouraging and indicated high potential for development of
practical CAM membranes for wastewater treatment.  The results of tests
conducted with CAM-360 membranes against secondary sewage effluent are
discussed in the next section.
                                 26

-------
         V.  TESTING OF HIGH-FLUX MEMBRANES WITH SEWAGE
The best flat-sheet membranes developed from each of the three polymer
types examined during the program were evaluated against sewage effluents
obtained from the Pomona Water Reclamation Plant, Pomona, California.
The tests were conducted at 600 psi for periods of 5 to IT days in 3-in.
flat-plate test cells, constantly recirculating the feed from a 5-6&1
reservoir.  Except for two cases where primary and carbon-treated
secondary effluents were employed as feeds, all of the tests were con-
ducted with untreated secondary effluent.  The pH of the sewage feeds was
maintained at 5.00 + 0.25 by the addition of dilute sulfuric acid.  Five
milliliters per gallon of 5$ sodium hypochlorite solution was also added
to each feed batch as a routine measure.  Each batch of sewage effluent
used at the start of the tests and to replenish the feed during the tests
was obtained from the water reclamation plant the morning of the same day
that it was used.  Variation of the feed composition during tests in which
the feed was replaced periodically with fresh effluent, then, reflected
day-to-day variations in effluent quality originating at the reclamation
plant.  In each test, the feed and product were analyzed for electrical
conductivity, chloride ion, TDS (by residue on evaporation), GOD  (total
and "soluble1), nitrate ion, ammonium ion  (as NHo) and total phosphate.
The electrical conductivity and chloride ion concentrations were measured
twice daily and the concentrations of the  other  constituents  determined
in most cases daily.  "Soluble" COD in the  feed was  determined on the
filtrate after passage of the feed through a 0.^5 micrometer  (p,m) MiHipore
filter.  The reverse-osmosis test loop employed  contained six test  cells.
Three specimens of each membrane were tested in  each case  (except in Test
No. 6 where two test  specimens were used for each membrane evaluated)  and
the results reported  were the averages of  each set  of three test  circles.
Prior to testing with sewage, the membranes were tested (at 600 psi) with
1000 mg/J&  sodium chloride  solution, and  in several  cases with 1000  mg/4
sodium  sulfate solution, to  determine their intrinsic flux and rejection
properties.  These values provided a reference point for judging  rejec-
tion behavior and  rate and extent of  flux  declines  with the sewage  feeds.

Preliminary tests  with  Pomona  secondary  effluent were  conducted for 5 to
6-day periods using  E-383-^0 cellulose acetate membranes cast from two
promising formulations  (those  designated 33A and 33B in Table l)  and
annealed at 85 C.   Specimens of these membranes  had previously exhibited
excellent osmotic  properties and flux  stability  when tested with 1000
mg/4  sodium chloride solution,  as shown by the  data in Table  2.  The pur-
pose  of these  first  tests  with secondary effluent  was to observe  the rate
and extent of flux decline due to fouling and the  rejection of organic
and inorganic  sewage components.   The results  of these  tests, designated
Test  Nos.  1 and 2  are summarized in Tables 9 and 10.  The composition of
 the sewage feeds,  determined during each day of the tests (except for the
weekends), are given in Table  H.   In Test No.  1,  the sewage feed was
 recirculated through the test cells at a rate of 5 GPH and allowed to
 concentrate  over the duration of the test to the point at which its
 electrical conductivity had increased to approximately twice the original
 value.   In Test No.  2 and all subsequent tests,  the feed was recirculated
                                 27

-------
                                                                            TABLE 9
                                        TESTING OF E-383-^0 CELLULOSE ACETATE MEMBRANES WITH POMONA SECONDARY EFFLUENT
                                                                         TEST NUMBER 1
ro
oo
Test
Time,
Days
Membrane A -
Start (2 hrs)
1
2
5
6
Membrane B -
Start (2 hrs)
1
2
5
6

Flux,0
Initial Osmotic
19
31
26— ~
12
9
Initial Osmotic
W
31
29 —
13
10

Electrical
Conductivity
Properties6: 73 gfd
87
89
29f 89
80
79
Properties6: 57 gfd
89
92
32f 91
86
83
Rejection, %
, a
TDS Cl"
flux, 6I*# rejection
.
93 75
91 70
^7
-
flux, 72$ rejection
.
9!* 78
93 75
60


CODb'C

_
98
>99
91
81

_
98
>99
77
86

b b
N\+ N03"

-
91 33
77 55
62 62
77 B8

.
92 33
85 55
70 kO
80 8g

Total
Phosphate13

.
97
98
95
9^

_
99
99
97
96
                Determined at 600 psi with 5 GPH feed circulation velocity.  Values reported are the averages of morning and afternoon samplings.
                One sampling per day carried out.  TDS determined as residue on evaporation.
               °Based on feed filtered through 0.8 f/m Millipore filter.
                Formulations were those of 33A (Membrane A) and 33B (Membrane B) given in Table 1.  Both membranes annealed at 85 C.
                Determined at 600 psi with 1000 mg/A sodlmn chloride solution after 1 hr of testing.
               f
                Flux increased to this value when feed circulation velocity was increased to 10 GPH for 1 hr.
                    values probably due to faulty analytical results.

-------
                                                                                TABLE 10
ro
VO
TESTING OF E-383-^0 CELLULOSE ACETATE MEMBRANES WITH POMONA SECONDARY EFFLUENT
TEST NUMBER 2
Test
Time,
Days a
Membrane A -
Start (1 hr)
1
2
k
5
Membrane B
Start (1 hr)
1
2
k
5

Flux,
gfd°
Initial Osmotic
57
28
18
15
15
Initial Osmotic
1*5
27
19
17
Ik

Electrical ,
Conductivity
Properties*: 83 gfd
92
92
90
88
90
Properties1" : 57 gfd
95
9k
93
93
93

TDSC
flux, 70%
_
89
-
73
93
flux, Q2%
-
91
-
86
95
Rejection, %
Cl~ CODC'd "V
rejection
77 - -
7k 83 88
-
73 -100 77
66 83 91
rejection
85
81 80 85
.
75 93 89
73 79 &

NO ~° Total
3 Phosphate13

_
31 99
-
50 95
35 97

-
75 99
-
57 87
56 99
                    Feed replaced with fresh secondary effluent each day except over weekend.
                   b
                    Determined at 600 psi with 10 GPH feed circulation velocity.  Values reported are the averages of morning and afternoon samplings.
                    One sampling per day carried out.  TDS determined by residue on evaporation.
                    Based on feed filtered through OA5 p,m MUllpore filter.
                    Formulations were those of 33A (Membrane A) and 33B (Membrane B) given in Table 1.  Both membranes annealed at 85 C.
                    Determined at 600 psi with 10OO mg/Jt sodium chloride solution after 1 hr of testing.

-------
                                                              TABLE 11
U)
O
Test
Time,
Days
Test No. lc
Start (2 hrs)
1
2
5
6
Test No. 2d
Start (1 hr)
1
2
k
5
COMPOSI
Electrical
Conductivity,
/imhos cm"*
1200
1500
1825
2200
2700
1230
1530
1770
1555
1150
TION OF SEWAGE FEEDS IN TEST NUMBERS 1 AND 2
Concentration, mg/jf
TDS Cl" CODb mk N03

1041 165 52 (61*) 12 3.0
1131* 190 k2 (50) 15 k.9
220 50 13 5.8
66 26 k.8
8k - -
1265 138 81 (98) 12 7.1
_ _
190 35 (53) 13 2k
897 100 52 (69) 33 28

Total
Phosphate
20
50
53
51

36
-
35
38
                   Average of morning and afternoon readings.
                  filtered (unfiltered).
                  CSee Table 9.
                  dSee Table 10.

-------
at the rate of 10 GFH and replaced periodically with fresh effluent to
keep the feed concentration relatively constant.

The membrane fluxes decreased rapidly during both tests with secondary
effluent.  After only 1 to 2 hrs on the sewage feed, the fluxes had
declined to 67 to 8^ of the initial values produced with the sodium
chloride solution; after 1 day they had fallen to 5^ to 34# and after
5 days to 30 to 12$ of the initial values.  The rate of flux decline was
greater with the higher-flux A-series membranes in both tests, as seen
by comparing the data for each membrane in Tables 9 and 10, and the plots
of log flux versus log time for the A and B-series membranes in Test No.
2 shown in Figure 2.  The increase in flux decline rate which appeared to
occur after the first 20 hrs of Test No. 2, shown in Figure 2, cannot be
adequately explained because of insufficient data at times less than 20
hrs.  This behavior, observed in  subsequent tests to varying degrees, is
suggestive of more than one type  of fouling or  a change in the fouling
process taking place during the test.  Similar  abrupt  increases in  flux
decline rate have been observed in long-term tests with salt solutions
and have been attributed to iron  deposits.  It  is entirely possible that
inorganic  deposits formed from heavy metal compounds present in the sewage
effluent or  introduced externally during  the test were responsible  for
this behavior.   Evidence for this hypothesis was obtained in a later  test
and is  discussed later in this section.

 The rejection behavior of the high-flux £-383-^ membranes observed in
 Test Nos.  1 and 2 was excellent.  With the  exception of a few erratic
 analytical results,  the  rejection of various  components achieved during
 the two tests is summarized as  follows:   electrical conductivity, 80  to
 95#; TDS,  89 to 95&  chloride,  60 to 85#; "soluble" COD,  80 to „ lOOfo
 ammonium ion,  77 to 94$;  nitrate ion,  31 to 75$J  and total phosphate, 95
 to 99%.   The B-series membranes,  with higher initial rejection of sodium
 chloride,  showed higher rejection of sewage components than did the A-
 series membranes.  The  drop in rejection seen at the end of Test No.  1
 and not observed in Test No.  2 was expected and is attributed to boundary
 layer effects due to the deposit built up on the membrane as well as the
 increased TDS concentration of the feed and decreased flux due to foul-
 ing.  The lower feed circulation velocity employed in the first test as
 well as the increase in TDS concentration during this test (see Table ll)
 are factors which could have been responsible  for an increased boundary
 layer.

 The nitrate rejections were quite variable, and similar behavior has been
 observed in a previous program.^  The value of 8$ nitrate rejection
 obtained with both membranes during the  last day of Test No. 1 appears
 excessively low and is attributed to faulty analytical results.  Cellu-
 lose acetate membranes reject nitrate ion to a somewhat lesser degree
 than chloride ion but the difference is  exaggerated when nitrate ion is
 present in low concentration.  Such behavior is attributed to a mixed
 ion effect, which has been observed to be quite marked in tests  conducted
 with mixed  feeds containing sodium chloride and sodium sulfate,  in which
 the chloride ion rejection was reduced in the  presence of sulfate.   The
 magnitude of the effect depends  both upon the  sulfate-to-chloride  ratio
                                  31

-------
I
100
 90

 80
 70

 60

 50


 ko


 30
    20
                                                             Test Conditions

                                                             600 psi
                                                             25°C
                                                             10 GPH Feed Circulation Rate
                                                             Pomona Secondary Effluent
                                      Membrane A
    10
                                 J	1	I   I  I  I
                                                                      J	'   '   '  '
                                                  10

                                              Test Time,  Hrs

                              Figure  2.  Flux Decline of E-383-^0 Membranes
                                             During Test  No. 2
                                                                                      100
200

-------
in the feed and the membrane annealing temperature.   The results of a
study of this phenomenon are presented and discussed in the Appendix.

With the exception of the suspect analyses, the nitrate rejections ranged
between 33 and 62%.  This is catiofactory for the feeds employed in this
program which rarely contained greater than 20 rag/A  of nitrate.  Higher
nitrate rejections (60 to 99$) were obtained, however, in subsequent
tests (Nos. 3 through 5) conducted with sewage effluents using similar
E-383-40 cellulose acetate membranes as well as ds 2.55 blend membranes,
as is discussed later in this section.

The high rates of flux decline observed in these first tests conducted
with secondary effluent point up the seriousness of the fouling problem.
That the flux decline was due mainly to fouling was indicated not only
by the low flux decline slopes found previously for these membranes in
tests with salt solutions, but more directly in the substantial restora-
tion of the fluxes of the fouled membranes of Test No. 2 by cleaning.
At the end of the test, a 2000 mg/Ji aqueous solution  of Procter and
Gamble's enzymatic laundry presoak, Biz (pH 9.3), was circulated at
ambient pressure and 50 to 6o°C through the test cells for 15 min at a
velocity of 10 GPH.  Deionized water was then pumped  through the cells
at 600 psi and room temperature for an additional 15  min and the mem-
branes tested at 600 psi with 1000 mg/4 sodium chloride solution.  As
seen by the data summarized  in Table 12, the fluxes were restored to
within 70 to 84^ of the original values, with no  decrease  in rejection
from that originally observed (except for  one circle  of membrane B which
apparently was damaged).  The membranes appeared  visually  clean after
removal from the test cells.  By contrast, the membranes at the end of
Test No. 1, where  no cleaning was employed, were  covered with  a substan-
tial yellow-brown  gelatinous deposit.  The use of Biz in cleaning  membranes
has also been investigated by others and reported by  Aerojet under another
program.

Additional  specimens of the  A and B-series E-383-^0 cellulose  acetate
membranes were tested for a period  of 8 days with carbon-treated secon-
dary effluent from the  Pomona Water Reclamation  Plant to observe  flux  and
rejection behavior with this higher-quality  effluent.  In  this test (Test
No. 3,  see  Table 13), the  sewage  feed was  replaced  daily with  fresh efflu-
ent to maintain feed composition relatively  constant  throughout the test.
The feed compositions are  given in  Table  Ik.   During the first 20 to 30
hrs of  Test No. 3  the rate  of flux  decline was less than that  observed in
the test conducted under similar conditions  with untreated secondary efflu-
ent  (Test  No. 2).   The  rate and extent  of flux decline observed after 5
days  of testing in each case,  however,  was similar  as shown by the percent
of initial flux after various test  times  tabulated below for the B-series
membranes  with  each effluent.
                                 33

-------
                                                           TABLE 12
U)
CLEANING OP TOULED MEMBRANES PROM TEST NUMBER
Membrane
Number
A - 1
A - 2
A - 3
(Average)
B - 1
B - 2
B - 3
( Average )
Initial8
Flux,
gfd
86
80
8k
(83)
52
60
60
(57)
NaCl
ReJ.. %
71
71
68
(70)
8k
82
82
(83)
Immediately
Before Cleaning0
Flux,
gfd
Ik
17
ik
(15)
22
10
11
(Ik)
Cl"
Rej., H,
58
66
60
(61)
75
66
63
(68)
                                                                                                After Biz
                                                                                                 Cleaning
 NaCl
Rej..
  78
  76
  73
 (76)
  8k
  82
  77
 (81)
               Determined after 1 hr of testing at 600 psi with 1000 mg/i  sodium chloride  solution before testing
               with secondary sewage effluent.
               Data obtained at end of fifth day of Test No. 2 with secondary sewage effluent, and immediately be-
               fore cleaning with Biz.
              c
               Determined after testing 1 hr at 600 psi with 1000 mg/4  sodium chloride solution.  Cleaning was carried
               out by circulating for 15 min at 50 to 60°C, 10 GPH and ambient pressure,  a 20OO mg/X solution of Biz
               through the test cells, followed by a 15-min wash at 600 psi with deionized water.
               Data given for each individual membrane circle.
Flux,
 gfd
 66
 60
 68
(65)

 k8
 55

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                                                                                               TABU 13

                                                     TESTING OF E-363-tO CELLULOSE ACETATE MEMBRANES HITH POMONA CARBON-TREATED SECONDARY EFFLUENT

                                                                                             TEST NUMBER 3
OJ

Test
Tine,1
Days


* Flux, Electrical .
gfd= Conductivity
Membrane Ae - Initial Osmotic Properti
Start
1
3
k
5
6
7
8


{1 hr) 62
U5
30
25
23
19
17
17
Cleaned with Bii8 and tested at
16% rejection (107* of initial).
esf : 68 gfd
90
91
91
92
91
90
90
90
600 p»i with

Membrane Be - Initial Osmotic Properties : 68 gfd
Start
1
3
U
5
6
7
8


(1 hr) 65
52
35
27
25
20
19
19
Cleaned with Biz and tested at
83* rejection (109* or initial).
92
93
93
9U
92
92
90
91
600 psi with


TDSC
flux, TL%
-
95
-
91
95
92
93
-
1000 mg/i

flux, 76*
-
97
-
91
96
93
9U
-
1000 ing/*

Rejection, £
b
Cl"
rejection
ft
67
62
58
58
60
66
65
sodium chloride:

rejection
67
70
68
62
58
66
66
69
sodium chloride:


CODC'd

-
80
&
57
51
81
60
70
57 gfd flux


-
ks
53
72-
kk
80
67
57
62 g* a flux


"V

-
85
87
83
88
89
83
88
(8H Initial),


-
91
95
91*
-
91
88
91
(91* of initial)


c
NO,"

-
>75
>75
>75
-
k9
50
59



-
>75
>75
>75
-
63
55
63
t


Total
Phosphate

-
99
98
97
98
98
98
98



-
98
95
99
99
99
99
98


                                   "Feed replaced dally with fresh effluent.
                                   ^Deternlned at 600 psl with 10 OPH feed circulation velocity;  3 circles of each membrane  tested and averaged.
                                    are the averages of morning ana afternoon samplings.   Sewage  feed pH maintained at  5.00  +^ 0.25.
                                   C0ne sampling per day carried out.  IDS determined as  residue  on evaporation.
                                   dBased on feed filtered through O.Ujjim Millipore filter.
                                   eFon«ulations vere those of 33A and 33B given in Table 1.   Both membranes annealed at 85  C.
                                   fretermlned at 600 psi with 1OOO ng/X sodium chloride  solution after 1 hr of testing.
                                   8Thirty-minute wash with 2000 vtjt Biz solution (pH 9-3 to 9.5) at room temperature, 600  pel,  12 OFH.
Values reported

-------
                                                         TABLE
CO
FEED COMPOSITION - TEST NU
Test Electrical Q
Time, Conductivity,
Days n mho cm
Start (1 hr)
1
3
4
5
6
7
8
1025
1175
1430
1300
1175
1350
1250
1400
fMBER 3 WITH POMDNA CARBON-TREATED SECONDARY EFFLUENT
Concentration, mg/£
a +
TDS Cl" COD 4 N03
9k -
808 91 21 (21) 2k oA
103 31 (32) 19 oA
838 86 33 (33) 2 oA
813 74 ^7 (56) 25 oA
820 87 31 (31) 20 3.5
864 118 31 (35) 21 17
115 28 (31) 21 23
Total
Phosphate

32
42
50
38
38
36
36
              Average of morning and afternoon samples.
              Filtered (unfiltered).

-------
                       Flux Retention  (% of Initial Flux)
                                              Carbon-Treated
    Test Time       Secondary  Effluent      Secondary Effluent
   vith Sewage         (Test No.  2)             (Test No. 3)

      Start                81                     96

      1 hr                 79                     96
      5 days               25                     37
      8 days                 -                     28

This similarity is also seen  by comparison of the log flux-log time plots
given in Figure 3.  An increase in the rate of flux decline was observed
after about 30 hrs in Test No. 3 with carbon-treated secondary effluent
at least as marked at that seen during Test No. 2 with untreated secon-
dary effluent.  This behavior with carbon-treated effluent was rather
surprising, in view of its higher quality compared with untreated secon-
dary effluent.  These results together with results obtained in tests
conducted with carbon-treated secondary effluent under a previous program,
are highly suggestive of extraneous matter, such as airborne dust, in the
feed.

The rejection behavior of the membranes observed during the test with
carbon-treated secondary effluent (Test No. 3) was similar to that ob-
served with  untreated secondary  effluent (Test No. 2) except for the lower
"soluble"  OOD rejection (generally 50  to 8o#  vs. 80 to 100$ as shown in
Tables 10  and 13).  This difference is illustrated by the fact that higher
product  COD  values  were obtained in Test No.  3 than in Test Nos. 1 and 2.
The lower  "soluble" COD rejection may  have resulted from the presence  of a
highly permeable  organic or oxidizable inorganic component present in  the
carbon-treated secondary effluent.

Cleaning of the fouled membranes at the end of Test No. 3 was  conducted
by circulating a  2000 mg/A solution of Biz through the test cells  for  30
min at 600 psi and room temperature at a  flow rate of 12 GPH.  The mem-
brane fluxes were restored to Qk%  (membrane A) and 91$  (membrane  B)  of
their initial values  with  increases in salt rejection over that  originally
observed for each membrane (see Table  13).

In view of the effectiveness  of Biz cleaning  in  restoring  the  flux of
fouled membranes, observed after Test  Nos. 2  and 3 with  secondary and
 carbon-treated secondary  effluents,  respectively,  a  test was  carried out
with more frequent cleaning.   Specimens of Membranes A and B,  annealed
 at 85°C, were again employed and the  test (Test  No.  4)  was conducted at
 600 psi with Pomona secondary sewage  effluent.  The  cells  were cleaned
 intermittently by treatment  at 600 psi and 12 GEH circulation rate for
 30 min with a 2000 mg/A solution of Biz at room temperature.   The highly
 promising results of this test are summarized in Tables 15A and 15B, for
 membranes A and B, respectively.  The composition of the sewage feeds
 used are summarized in Table 16.  During the first 9^ hours of the test,
 when the Biz cleaning was carried out every 2^ hours,  the flux of Membrane
                                  37

-------
 100
  90
  80

  70

  60

  50


  UO
i
2
<- 30
        -Initial Fluxes on 1000 mg/j2 Nad Solution
                                                   Carbon-treated Secondary Effluent
                                                     (Test No.  3)
  20
                                              Secondary Effluent
                                                (Test No. 2)
Test Conditions

600 psi
25°C
10 GPH Peed Circulation Rate
  10
                     J_
                 I     i    i   i  i  i t  1
                                                  I	I
i    I   I   I  I  i  I
                                                  10

                                                  Test Time, Hrs

                Figure 3.  Flux Decline of  B-Series E-383-lt-O Membranes with Different Effluents
                                                                             100         200

-------
                                                    TABLE 15A


                    TESTING OF E-383-l*0 MEMBRANES WITH SEWAGE UTILIZING PERIODIC BIZ CLEANING

                                           TEST NUMBER U - MEMBRANE A



                                               Rejection,

Date
3/17/70
3/17/70

3/17/70
3/17/70
3/18/70
3/18/70
3/18/70
3/18/70

3/19/70
3/19/70
3/19/70

3/19/70
3/20/70
3/20/70
3/20/70
3/21/70

3/22/70
3/23/70
3/23/70
3/23/70

3/23/70
3/23/70
3/2U/70
3/2U/70
3/2l*/70
3/2U/70
3/2U/70
3/25/70
3/25/70

Time
1100
1200

1300
1600
0900
1130
1330
1600

0900
1000
1200

1600
0900
1200
1600
1000

1000
0900
1100
1200

16OO
2200
09OO
1200
1300
1600
2200
0900
1200
Flux,'
gfd
Electrical
Conductivity
- h
Cl COD
9l* gfd flux, 72* rejection
73

68
6U
56
73
61*
71*

51
68
65

56
51
66
67
1*8

"*3
1*2
61
58

31
21
13

U9
33
21
17

.

92
93
93
89
91
91

90
89
90

89
92
90
91
91

90
90
87
89

90
88
88
6l gfd flux, 79*
88
88
86
86
1*0 gfd flux, 85*
.

68
67
66 100
63 73
-
76

69 96
91*
73

73
61* 83
-
-
82

-
81
-
79

-
-
61
rejection
-
-
-
59
rejection
NH+ NO" Total
NHlt 3 Phosphate

_

-
-
92 80 97
86 79 97
-
.„

90 91 98
87 76 97
.

-
93 *72 98
-
-
96 81* 98

-
90 95 98
.
87 "*5 99

.
.
88 67 >99

-
-
.
85 67 98


Comments
1000 ng/-4 W*01
Start vith
secondary effluent



Biz Cleaning0

Add fresh secondary
effluent

Biz Cleaning
Add fresh secondary
effluent


Biz Cleaning0

Add fresh secondary
effluent


Biz Cleaning0
Start vith primary
effluent



Biz vashd, then
1000 vg/i Bad
Add trash primary effluent



Biz wash8, then
1000 mg/J Had
^Determined at 6OO pal vith 10 OPH feed circulation velocity.  Values reported
 are the averages of 3 test circles.  Sevage feed pH maintained at 5-00 + 0.25.

bBased on feed filtered through 0.1*5 urn Milllpore filter.

C20OO mg/Jt aqueous solution of Biz circulated at 12 OPH, room temperature and 600 pal
 for 30 min, then svitch to previous feed.

Stashed for 30 min as in C above, then reduced pressure to ambient for 1 Bin and
 continue vith 15 min vash at 600 psi as before.

"Washed as in d above except for only 15 Bin before pressure cycling.
                                                         39

-------
                        TESTING OF E-383-kO WWHUWES WITH SEWAGE UTILIZIHO FERIOnEC HZ CLEAHIHO

                                               TEST NUMBER k - tCMBUUIE B
                                                        Rejection. <*

Date
3/17/70
3/17/70

3/17/TO
3/17/70
3/18/70
3/18/70
3/18/70
3/18/70

3/19/70
3/19/70
3/19/70

3/19/70
3/20/70
3/20/70
3/20/70
3/21/70

3/22/70
3/23/70
3/23/70
3/23/70

3/23/70
3/23/70
3/2k/70
3/2k/70
3/2k/70
3/2k/70
3/2U/70
3/25/70
3/25/70


Time
1100
1200

1300
1600
0900
1130
1330
1600

0900
1000
1200

1600
09OO
1200
1600
1000

1000
0900
1100
1200

1600
2200
0900
1200
1300
1600
2200
0900
12OO

Flux,
gfd

50

M
*8
kk
51
50
51

U2
51
k9

k;
lie
k6
k7
in

38
37
k6
kk

30
20
Ik

kk
30
18
Ik


Electrical
Conductivity
62 gfd flux, 87*
.

9*
95
96
9k
95
95

95
9k
9k

9k
96
95
96
96

95
95
9k
95

95
95
9k
k6 gfd flux, 92*
9k
9*
9k
93
35 gfd flux, 93*

• V
O. ODD
rejection
.

T9
8k
79 97
68 82
-
86

8k 95
81
8k

78
73 89
-
-
88

.
85
-
82

.
.
66
rejection
_ ^
-
.
61
rejection

nn+ _-- Total
""k ^J Phosphate

.

.
.
92 >98 99
93 >98 99
.
.

90 >96 99
91 >95 99
. .

.
96 91 99
.
.
93 >97 99

- - .
91 95 >99
-
86 *2 >99

-
-
91 85 >99

-
-
- . .
92 75 >99



Comments
looo mg/t mci
Start vlth
secondary effluent



Biz Cleaning0

Add fresh secondary
effluent

Bit Cleaning0
Add fresh secondary
effluent


Biz Cleaning0

Add fresh secondary
effluent


Biz Cleaning0
Start vlth primary
effluent



d
Bit wash , then
1000 Bg/Jl Had
Add fr«ih primary
effluent


Biz vash", then
1000 Bg/4 fcCl
 Deternined at 6OO pal with 10 GPH feed circulation velocity.   Value*  reported are the
 averages of 3 teat circles.  Sevage feed pR Maintained at  5.00 +  0.25.

b£aaed on feed filtered through O.l»5 u* MlUlpora  filter.

C2000 ng/i aqueous solution of Biz circulated at 12 QPH, room  temperature and 600 psl for 30 Bin,
 then svltch to previous feed.

 washed for 30 Bin as in c above,  then reduced pressure to  aaiblent for 1 Bin and continue vlth
 15 Bin vaah at 600 pal aa before.

ewashed as in d above except for only 15 Bin before pressure cycling.

-------
                                                                             TAME 16
H
COMPOSITION OF PRIMARY AND SECONDARY EFFLUENT FEEDS IN TEST NUMBER 4
Feed
Secondary Effluent
Secondary Effluent
Secondary Effluent
Secondary Effluent
Secondary Effluent
Secondary Effluent
Secondary Effluent
Secondary Effluent
Secondary Effluent
Secondary Effluent
Secondary Effluent
Secondary Effluent
Secondary Effluent
Primary Effluent
Primary Effluent
Primary Effluent
Primary Effluent
Date
3/17/70
3/17/70
3/18/70
3/18/70
3/18/70
3/19/70
3/19/70
3/19/70
3/20/70
3/21/70
3/22/70
3/23/70
3/23/70
3/23/70
3/24/70
3/24/70
3/25/70
Time
1200
1600
0900
1130
1600
0900
1000
1600
0900
1000
1000
0900
1100
1200
0900
1600
0900
Electrical
Conductivity,
U mho cm"
1360
1380
l44o
1625
1350
1460
1200
1300
1500
1400
1630
1700
1500
1350
1550
1550
1800
Concentration, me/I
Cl~ CODa
80
85
100 41 (53)
160 65 (69)
110
145 43
100 37
90
42
51
-
37 (45)
-
64 (149)
46 (114)
-
70 (135)
K
-
-
21
24
-
14
16
-
19
20
-
18
-
20
31
-
19
NO"
-
4.4
6.2
-
9.8
7.5
-
7.8
12
-
18
-
3.6
2.7
-
11
Total
Phosphate
-
50
50
-
35
36
-
40
42
-
50
-
38
36
-
37
                aFiltered  (unfiltered).

-------
A was maintained at 48 to 73 gfd (66 to 100$ of the initial flux on secon-
dary effluent) and that of Membrane B at 4l to 51 gfd (82 to 102$ of the
initial flux on the sewage).  Of equal note was the low rate of flux
decline observed with the secondary effluent between Biz washings, this
being comparable or lower than that observed in the test with carbon-
treated secondary effluent (see Table 13).  Between each of the first
three Biz cleanings the flux of the A membrane decreased by 23 to 30$ and
that of the B membrane by 11 to 18$, compared with 26$ and 20$ decreases
in flux of the A and B membranes, respectively, during the first 24 hours
of testing with carbon-treated effluent.  During the 4th and 5th day of
the test, when no Biz cleaning was employed, the fluxes of the A and B
membranes decreased by only 12 and 10$, respectively, compared with
decreases of 33$ observed with each membrane during a corresponding
48-hour period in Test No. 3 with carbon-treated effluent.  The effective-
ness of the periodic cleaning in maintaining high flux levels with secon-
dary effluent is illustrated graphically in Figure 4 by log flux-log time
plots for the B-series membranes in Test Nos. 2 and 4.  Several plausible,
but speculative, explanations can be offered for the relatively low rates
of flux decline between Biz cleanings in Test No. 4.  First, it is possi-
ble that the Biz treatment imparted some antifouling properties to the
membrane through adsorption of enzymes on its surface.  Second, the quality
of the secondary effluent used during this test was unusually high.  Third,
contamination of the feed by extraneous matter, such as airborne dust from
the laboratory ventilation system, which may have contributed to the flux
decline in the previous tests, may have been less in Test No. 4.

Although the rejection behavior of both membranes during Test No. 4 with
secondary effluent was excellent, Membrane B was again superior.  The
B-series membranes, which gave initially lower flux and higher rejection
of sodium chloride than the A-series membranes, consistently exhibited
better rejection behavior as well as lower flux decline when tested against
sewage effluents.  The rates of flux decline of the A and B-series mem-
branes in Test No. 4 during the first 24 hours of the test, between clean-
ings and over the duration of the test with secondary effluent are com-
pared graphically in Figure 5-  Again, as in the previous tests, the rate
of flux decline was greater with the membrane producing higher initial
flux.  Slopes of -0.081 for the A-membrane (initial flux on sodium chloride
of 94 gfd} and -0.054 for the B-membrane  (initial flux on sodium chloride
of 62 gfd) on Pomona secondary effluent are obtained for the lines defined
by the initial flux values on sodium chloride for each membrane and the
flux values obtained on the secondary effluent immediately after each
cleaning.  These slopes yield extrapolated year-end post-cleaning flux
values of 44 and 38 gfd, respectively, for the A and B-membranes.  Still
more favorable flux decline slopes of -0.071 and -0.033, respectively,
were calculated for the A and B-membranes using all of the points shown
in Figure 5.  Even these results, however, do not reflect the full poten-
tial of these membranes, since similar membranes exhibited intrinsic flux
decline slopes of only -0.04 and -0.02, respectively, in long-term tests
with salt solution.  Therefore, still greater productivity might be real-
ized by further improvement of the cleaning procedure, feed pretreatment,
etc.
                                 42

-------
I

I
100

 90

 80

 70

 60


 50


 ko



 30
                                                                    30-min Bis Wash
Test No. 2
       Test Conditions
          600 psi
          25°C
          10 GPH Peed Circulation Rate
          Pomona Secondary Effluent
    10
                 Figure
                                                10
                                         Test Time, Hrs

                        Effect  of Periodic  Biz  Cleaning on Performance  of B-Series
                           E-383-40 Membranes with Secondary Effluent
                                                                                          100
                                                                                                   200

-------
                                                                          30-min Biz Wash
I

I
100
 90

 80

 70

 60

 50


 ko


 30
          Test Conditions
                                    \_
                                        Membrane B
       6OO psi
       25°C
       10 GPH Peed Circulation Rate
       Pomona Secondary Effluent
    20
    10
                                      I   I  I  I  I  I
                                                 10
                                            Test Time, Hrs

                   Figure 5.  Effect of Membrane Initial Flux on Flux Decline  During
                             Test Number k with Pomona Secondary Effluent
                                                                                      100
2OO

-------
During the last 2 days of Test No.  4,  Pomona primary sewage effluent was
used as feed to observe membrane performance and the efficacy of Biz
cleaning with this lower quality effluent.  The data obtained in this
experiment are shown in Tables 15A and 15B.   As expected,  the rate of
flux decline was considerably greater with the primary effluent than
that observed with secondary effluent (72 to 79$ decline for Membrane
A and 70$ decline for Membrane B in 21 hrs between cleanings as compared
with 23 to 30$ and 11 to 18$ declines, respectively, during corresponding
2^-hr periods with secondary effluent); and the cleaning procedure was
less effective with the primary than with the secondary effluent.  In the
first cleaning cycle with primary effluent,  fluxes were not restored
appreciably when circulating the Biz solution under pressure but were
restored immediately after reducing the pressure to ambient for several
minutes.  The fluxes were not completely restored to the original peak
values after the second cleaning attempt.  At this point the test was
terminated and the membranes removed for examination.  All of the membrane
circles were found to contain an opaque bluish-white surface deposit, the
color apparently caused by the bluing agent present in Biz.  The amount
of the deposit appeared by inspection to vary inversely with the final
flux produced by each circle.  Of equal significance was the observation
of the residue of a second type of deposit,  more characteristic of the
organic matter deposited from sewage.   This transparent, gelatinous,
yellow-brown material was present in small quantity on top of the bluish-
white surface deposit on one or two of the membranes.  The presence of
this second type of deposit did not relate to final membrane flux and
since it was present in small quantity on only certain membranes it
appears to be readily removable by the Biz cleaning treatment.

A sample of the bluish-white deposit was collected, dried, pyrolyzed in
a furnace at 1000 F and the residue submitted for flame emission analysis
to determine major metallic constituents.  The results of the analysis
are summarized below.

                    Element          $, Based on Oxides

                       Fe                    3.7

                       Al                   36.3
                       Mg                    1.5

                       Si                    2.3
                       Na                   25.6

No phosphorus was detected in the flame emission spectrum, and a quali-
tative test for sulfate was negative,  eliminating the possibility that
the deposit had been comprised substantially of phosphates or calcium
sulfate.  Precipitation of polyvalent metal phosphates during the Biz
treatment had been suspected, in particular, since the phosphate content
of Biz is 18.7$ based on elemental phosphorus.

On the basis of the above analyses, and its relatively dense physical
form, the original blue-white membrane deposit appears to have been

-------
inorganic  in nature, and comprised of a refractory metal oxide mixture.
Its origin appears to have been extraneous having been introduced into
the primary effluent in the form of airborne dust either at the Pomona
Water Reclamation Plant or in the laboratory during the test.  The
latter alternative seems to be a good possibility, the prime suspect
being fine particles of insulation material (e.g., mineral wool) from
the air ducts of the laboratory ventilation system entering the
uncovered  feed tanks.  Such contamination may also have been responsi-
ble for the increased flux decline with time in Test Nos. 1, 2, and 3.
Accordingly, the feed tanks were kept covered during the remaining tests
with sewage described below.

The results obtained in the tests of the £-383-^0 cellulose acetate mem-
branes with various sewage effluents were very encouraging with respect
to rejection behavior and the utility of membrane cleaning in moderating
the flux decline due to fouling.  At the same time, they were instructive
as to the  extent of the fouling problem in reducing the productivity of
membranes  having high intrinsic flux and flux stability.  It was there-
fore of interest to evaluate and compare the performance of the other two
membrane types, namely the ds 2.55 blend and crosslinked CAM-360, in
similar tests with sewage effluent.  The two remaining tests, Nos. 5 and
6 described below, were conducted for this purpose, using untreated secon-
dary effluent as the feed.

Specimens  of ds 2.55 blend membranes cast from the formulations designated
35A and 35C in Table h and annealed at 85°C were tested for a period of
17 days at J)00 psi with Pomona secondary effluent.  The results obtained
in this test,  designated Test No.  5,  are summarized in Table IT.   The
feed compositions are given below.
                 Electrical
        ,
    Days         n mho cm       Soluble   Total     k     3   Phosphate
Start (1 hr)        1^60           ko       40    19    1?        33
     6              1^50           36       5^    1A-    29        36
    12              1690           35       5^    16    kh        38
    IT              1^00           -        -

The test data indicate relatively low rates of flux decline (for secon-
dary effluent) throughout much of the test period, as well as generally
very high rejection of all components analyzed.  The low COD rejections
obtained on the 6th and 12th days of the test were inconsistent with the
high rejections of other components observed on those days as well as
the high COD rejections obtained at the beginning of the test.  This
discrepancy could have been caused by faulty analyses, sample contamina-
tion or the presence of highly permeable oxidizable components in the
feeds used on those days.
                                  1*6

-------
                                                          TABU! IT

                              TESTING OF DS  2.55  BLEND MEMBRANES WITH FOMOKA SECONDARY EFTLUBlfT


                                                       TEST NUMBER 5
                                                                    Rejection. <*
Test
Tine,
Days
Membrane 35AC
Start (1 hr)
1
2
5°
6
12
l4e
17

Membrane 35°°
Start (1 hr)
1
2
5°
6
12
l4e
17

f»*
- Initial
51
53
45
43
4o
38
37
32
After
Electrical
Conductivity
Osmotic ft-opertles*'4:
94
95
94
95
95
94
95
95
cleaning vlth Blsf: 57
- Initial Osmotic Bropertles*' d:
46
42
36
33
28
26
24
21
After
90
96
95
95
95
94
95
92
cleaning vlth Biz': 47
COD
Soluble1* Total
68 gfd flux. 77* rejection
100 100
-
-
-
51 68
56 72
-
-
gfd flux, 89* sodium chloride rejectla
57 gfd flux. 6oi rejection
100 100
-
-
-
47 65
48 66
-
-
gfd flux, 840 sodium chloride rejectlo
<
96
-
.
-
91
87
-
-
Is)
93
-
-
-
91
92
-
-
n.-«d
- Total
3 ftoaphate
99 99
-
.
-
99 99
99 99
-
-

99 99
.
>
.
99 99
99 99
.
-

'Determined at 600 pal.   Data reported are averages of 3 teat ipeclMni.

bBuwd on feed filtered  through 0.45  |tm Ntlllpore filter.

cFonnlatlon 35A (parts  by vt) - cellulose triacetate A-432-130B, 6} cellulose acetate B-398-3, lU| dlozane, 45
 acetone, UO; n»l«io acid, 6; acetanlde,  10.   Tonmlation  35C - saae except used lU parts proplonavlde Instead
 of acetavLde.  Hnibranes annealed at 85°C.
            vlth 1000 ug/* sodlua chloride solution at 600 pel after 1-hr test period.

eps«d replaced vlth fresh effluent.

 Carried out at end of test by circulating a 2000 mg/t aqueous solution of Bit at roo» tesiperature. 600 pal and
 10 GPH.

-------
Cleaning of the membranes with Biz at the end of Test No. 5 increased
the fluxes to more than 80$ of their initial values determined with
1000 mg/4 sodium chloride solution and revealed an improvement in salt
rejection.  The flux decline behavior of the membranes during the test
is shown graphically by log flux-log time plots in Figure 6.  The rate
of flux decline on the secondary effluent was similar for the two mem-
branes, and was approximately linear after the first 2k hours of oper-
ation.  Slopes of -0.030 to -0.032 of the lines drawn between the flux
values determined with 1000 mg/^ sodium chloride solution at the
beginning of the test and at the end of the test after Biz cleaning
are even better than the corresponding value of -0.05^ obtained in Test
No. k for an E-383-^0 cellulose acetate membrane of comparable initial
flux (B-membrane).  These values correspond to less than 25% loss in
flux after the first year of operation.  As in the case of the E-383-^0
membranes, the intrinsic flux decline slopes of these membranes (-0.011
to -0.013J with salt solution indicate that improved control of fouling
will yield still greater flux stability in the treatment of sewage.

A final test (Test No. 6) was conducted with the best examples of each
of the three promising high-flux membrane types examined in the program
in the same test apparatus using a common "secondary effluent feed, to
obtain a more direct comparison of their performance on sewage.  The
test was conducted with 2 circles of each membrane type at 600 psi for
a period of 6 days and yielded the results summarized in. Table 18 and
presented graphically in Figure 7«  For the CAM membrane, formulation
32E in Table 6 was cast at room temperature, annealed at 70°C and cross-
linked at that temperature for 10 rain as previously described.  The
£-383-^0 membrane was cast from the formulation designated 33A in Table
1 and annealed at 85°C; and the blend membrane was cast from the formu-
lation designated 35A in Table 4 and annealed at 85°C.  Each of the mem-
branes was tested for 1 hr with both sodium chloride and sodium sulfate
before testing with the sewage feed.  The sewage feed was replaced every
other day with fresh effluent and the flux and electrical conductivity
of the feed and product were measured twice daily.

All three membranes at the beginning of Test No. 6 gave high sodium
sulfate rejections (97 to 99$).  The CAM membrane exhibited the best
rejection characteristics of the three - 92$ of sodium chloride, 99$ of
sodium sulfate and 95 to 97$ of TDS in sewage.  Its initial flux on
secondary effluent was 57 gfd falling to 29 gfd after 6  days on the
sewage.  The E-383-40 membrane exhibited the highest initial flux (85
gfd) on salt solution but the greatest flux decline on secondary efflu-
ent of the three (see Figure 7) producing after 6 days on the sewage
only 22 gfd flux.  Although its rejection performance was greater than
the minimum requirement, the E-383-^0 membrane, giving the lowest rejec-
tions of sodium chloride (70$) and sodium sulfate (97$), also gave the
lowest rejection of TDS (87 to 92$) with the sewage.  The blend membrane
produced the lowest initial flux (50 gfd) on salt solutions and exhibited
a flux decline rate on the sewage comparable to that of  the crosslinked
CAM membrane, giving after 6 days a flux of 20 gfd.  The blend membrane
ranked intermediate in rejection performance among the three membranes

-------
vo

100
  90
  80
  TO

  60

  50


  1*0


  30
                                                                                                30-min Biz Wash
                                                                   Membrane 35A
                 20
            Test Conditions

            600 psi
            25°C
            10 GPH Feed Circulation Rate
            Pomona Secondary Effluent
                                                               z:
                                                                   Membrane  35C
                 10
                                            J    I    I   I  I  I  I  I
                                                             I       I
                                                                            I
                                                                                                           I     I
                                                                                                       100
                                                10
                                               Test Time,  Hrs

                   Figure 6,  Flux Decline of DS 2.55 Blend Membranes During Test Number 5
200    300  UOO

-------
CrosBllnked
CAM-360a




Flux,
_g«_
TDS
BeJ.. %
Initial Osmotic
Properties*'6
1000 mg/4
1000 Vi/t

Secondary

Test
Tine,
Hrs
1
3
20
27
44
51
116
123
l4o
Had
*£aou
H -f
Kffluenta'r
Electrical
Conductivity
of Feed,
hfc mho ctn
1525
1525
1600
1700
1700
1550
1700
1500
1500
69
66






57
56
42
44
38
41
34
32
29
92
99






95
96
97
97
97
97
97
96
97
Cleaned with Blz,g
Tested with 1000 mg/i »Cld
43 gfd
95* Re
                                        OOMPARATrVE TEST OF THREE MEMBRANE TYPES
                                             WITH KSCHA SECOHDAK EFFLUENT
                                                      TEST IUHBEB 6
                                                                      E-383-40
                                                                  Celluloae Acetate
                                                                 Flux,IBS
                                                                  gfd         BeJ.. I
                                                                  85
                                                                  83
TO
97
                                                                  Tl
                                                                  66
                                                                  43
                                                                  43
                                                                  36
                                                                  36
                                                                  25
                                                                  24
                                                                  22

                                                                  32 gfd
8T
88
90
90
89
92
91
90
92

85* Sej.
                    1 2.55 Blend
               Flux,
                gfd
47
51
                             TDS
41
4o
33
34
30
31
23
22
20

28 gfd
91
92
9!*
94
94
95
96
94
96

93% BeJ.
aCast from 32E formulation (Table 6),  annealed and crossllnked at 70°C.
 Cast from 33A formulation (Table 1),  annealed at 85°C.
CCast from 35A formulation (Table 4),  annealed at 85°C.
^Testing conducted at 6OO pal vlth 10  GFH reclrculatlon  velocity.  Two circles  of each membrane tested and results averaged.
 Determined after 1-hr test periods.
 Sevage feed pH maintained at 5.00 + 0.2 and replaced every other day with fresh effluent.
gAqueous solution of Hz (2000 mg/< circulated for 30 Bin at room temperature,  600 psl  and 10 GFH).
                                                        50

-------
   100

    90

    80

    70

    60


    50


    ItO
S
»   30

I
   10
 7
                DS 2.55 BLEND
Teat Conditiona

600 pai
25°C
10 GPE Teed Circulation Rate
Pomona Secondary Effluent
                       J	   I
                             I   I   I  I  I  I
I     I    I   I   I  I  I I
                                                   10                                     100
                                                    Teat  Tine,  Hra

                         Figure 7.  Flux Decline of the Three Meaferane Typea During Teat Number 6
                                                                                            200

-------
with 91 to 96$ IDS rejection on the sewage.

Cleaning of the three membranes at the end of Test No. 6 with Biz was
not as effective as in previous tests with secondary effluent, as shown
by the data in Table 18.  The fluxes were restored to only 38 to 62% of
the initial values on salt solution, and the membranes still contained
a gelatinous deposit.  The CAM and blend membranes were cleaned to a
greater degree, and the deposit seemed, on inspection, to adhere less
strongly to them than the E-383-40 membrane.  The reasons for the incom-
plete cleaning achieved in this test with the Biz treatment are not
clear, but the nature of the deposit formed from the secondary effluent
used appears to have been the root of the problem.  More frequent clean-
ing during this test would probably have been more effective.

The crosslinked CAM-360 membrane gave the best performance, in every
respect, of the three membrane types evaluated in Test No. 6.  CAM mem-
branes appear to be very attractive candidates for further development
in the renovation of wastewater.  The greater rate of fouling and lesser
ease of cleaning observed with the £-383-^ cellulose acetate membranes
could be attributed to both their lower ds and higher initial flux,
compared with the CAM and blend membranes".  Clarification of these points
will require further work.

-------
           VI.  MEMBRANES RESISTANT TO COLLOID FOULING
METHODS OF ATTACHMENT OF ENZYMES TO CELLULOSIC MEMBRANES

Several coupling reactions were available for attaching enzymes to
reactive polymers.  Two types of reactive polymers which offered ver-
satile intermediates were investigated, namely, carboxyl- substituted
and arylamine-substituted cellulose acetates.  The carboxyl groups
could be converted to an activated ester and coupled with enzyme amino
groups, while arylamino groups could be converted either to reactive
isothiocyanates or diazonium salts, which would couple with enzyme amino
or phenolic groups, respectively.

An activated ester group which appeared to fit the requirements of water-
stability and mild reaction conditions was reported by Anderson and co-
workers, 5 who utilized N-hydroxysuccinimide esters of amino acids for
peptide synthesis.  Amide formation between an amine and the activated
ester occurs in aqueous solution at pH 8.0, conditions which are ideal
for enzyme attachment.  Accordingly, cellulose acetate hydrogen succinate
(CAHS) was prepared by treating 212 g of cellulose acetate (Eastman Type
E-400-25, acetyl  ds 2.38) with 2k g of succinic anhydride in UL of pyri-
dine.  The product was purified by precipitation from 24 of acetone in 74
of 50$ aqueous methanol; the succinate ds values determined for two batches
were 0.17 and 0.15.  The CAHS was converted to its N-hydroxysucciniraide
ester  (CAHS-NHS)  by treatment of a stirred solution of 10 g of CAHS  (6.5
meq of COOH) in 250 ml of acetone with 0,75 g  (6.5 raraole) of N-hydroxy-
succinimide and 1.5 g (7-^ mmole) of dicyclohexylcarbodiimide  at  room tem-
perature for 16 hours.  The NHS content was estimated by reaction of the
polymer with tryptamine.  An ultraviolet absorption spectrum of the
product indicated that complete esterification of the hydrogen succinate
groups had occurred.  The reaction scheme for  the preparation  of  this
reactive support  polymer is outlined below.
         Cell
         rwnx
         uea.ji
             N.
                                  pyridine
                OH
OAc
                              dicy c lohexy Ic arbo di imi de
                                      acetone
                                 53

-------
Aminoaryl-subctituted support polymers were prepared by acylation of cel-
lulose acetate with a nitroaryl acid chloride and reduction of the nitro
group to an amine.  Sixty grams of cellulose acetate [type E-400-25 was
acylated with 18 g of p-nitrobenzoyl chloride in 500 ml of dioxane and
25 ml of pyridine at 100° for 5 hours.  The p-nitrobenzoyl (PNB) ds of
the resulting polymer, found by ultraviolet spectrophototnetry, was 0.28.
An earlier batch, prepared using an impure sample of p-nitrobenzoyl
chloride, had a PUB ds of 0.08.

Reduction of 10 g of the lower ds material with 2 g of sodium hydrosulfite
in 150 ml of water at 25 C produced cellulose acetate p-aminobenzoate
(CAPAB) with a FAB ds of 0.05.  The product from a similar reduction of
the higher ds material was not sufficiently soluble in dioxane (or other
suitable solvents) to permit determination of the PAB ds by ultraviolet
spectrophototnetry.  Acylation of 60 g of E-^00-25 cellulose acetate with
22 g of U-(V-nltrophenyl)butyryl chloride in 500 ml of dioxane and 25 ml
of pyridine produced cellulose acetate 1<— (4f -nitrophenyl)butyrate (CAPNPB)
with a ENPB ds of 0.22, measured by ultraviolet spectrophotometry.  Ten
grams of this polymer was reduced with 10 g of sodium hydrosulfite in 150
ml of 67$ aqueous ethanol at 75°C.  The only solvent found for the product
was dimethyl sulfoxide; the (p-aminophenyl)butyryl (PAPB) ds was found by
ultraviolet spectrophotometry to be O.l8.  The reaction scheme for the
preparation of aminoaryl support polymers is summarized below:
                  ^OAC            /——y        ||         .
             Cell"^      +   0 NWYVWCH } fl-Cl   Pyridine
             ceil         +   OgN-Y^^CHg^C-Cl   'dioxane >

                  ^OH
                                        (n

-------
ATTACHMENT OF ENZYMES TO BULK POLYMERIC SUPPORTS

Before preparing membranes having attached enzymes, the methods of attach-
ment were investigated by coupling of the enzymes with the bulk support
polymers.  It has been generally noted, in studies of insoluble enzymes,
that a greater reduction in activity (compared with the native enzyme)    ,
is observed with macromolecular substrates than with monomeric substrates.
This effect is generally ascribed to steric hindrance by the polymeric
support.  During investigation of methods of attachment, the resulting
insoluble enzymes were assayed by kinetic procedures utilizing a monomeric
substrate; this allowed a rapid evaluation of the efficacy of the attach-
ment procedures.

After samples of native trypsin, chyrnotrypsin, and papain were assayed
for activity against monomeric substrates, it appeared that trypsin could
be assayed most conveniently and with the greatest sensitivity.  Trypsin
was therefore used in the majority of insoluble enzyme preparations, and
the activity was measured by ultraviolet spectroscopic determination of
the rate of hydrolysis of benzoyl arglnine ethyl ester (BAEE).1^  The
protein content of the insoluble enzyme preparations was determined by a
modification of Habeeb1s 2,^,6-trinitrobenzenesulfonic acid (TUBS) method
for monitoring protein hydrolysis.1!  The insoluble enzymes were hydrolyzed
in 6 N hydrochloric acid, and an aliquot was neutralized and treated with
TNBS at pH 9.0.  After acidification, the concentration of the colored
reaction product was determined spectrophotometrically.  Calibration
curves for this analytical method were prepared using known concentrations
of each enzyme.

When 50 mg of trypsin was stirred with 500 mg of CAHS-NHS in 10 ml of 1$
aqueous sodium bicarbonate solution at 25°C for k hours, an insoluble
enzyme containing 3.2$ protein was obtained.  The activity of this mate-
rial, as measured by BAEE assay, was 6 of the activity of a like amount
of native trypsin.  When the reaction temperature was reduced to 0 to k°C
the protein content was almost the same, 2.8$ but the activity of the
insoluble enzyme was 13-17$ of that of native trypsin.

Since a proteolytic enzyme such as trypsin loses activity in solution due
to self-digestion, it was thought that even greater retention of enzymatic
activity might be obtained by inhibiting the enzyme during the attachment
reaction.  When attachment was carried out at 0 to k°Q in the presence
of 0.1 M benzoylarginine, which inhibits BAEE hydrolysis by trypsin, the
apparent protein content of the insoluble enzyme was 4.0$.  Based on the
observed 4.0$ protein content, the enzymatic activity measured by BAEE
was 7$ of that of native trypsin.  (The TNBS reagent used to determine
protein content measures the concentration of free amino groups.  If
benzoyl arginine reacted with the CAHS-NHS, arginlne would be liberated
upon acid hydrolysis, and an erroneously high apparent protein content
would be observed.)  Because of these poor results, no further investi-
gation of the use of inhibitors during attachment was carried out.

The preparation of insolubillzed chymotrypsin and papain was carried out
by reaction of the native enzymes at room temperature with bulk CAHS-NHS.
                                55

-------
These preparations were attempted before the discovery,  with trypsin,
that lower reaction temperatures (i.e., 0 to ^°C) resulted in greater
retention of enzymatic activity after attachment.  The insoluble CAHS-
chymotrypsin obtained was found to contain k.5% protein; its activity
was 2.8% of the activity of the native enzyme, as measured by hydrolysis
of tyrosine ethyl ester. 1^  ihe sample of native papain used was found to
contain only 2^$ protein, and the sample of insoluble CAHS-papain obtained
contained only 0.8$ protein.  In view of the low purity and activity toward
BAEE hydrolysis of the native papain, no attempt was made to assay the
activity of the insoluble enzyme.  Although a purified native papain would
probably give improved results, further efforts in the preparation of  an
enzymatic membrane were limited to trypsin, as described below.

Although the lack of solubility of the amlnoaryl derivatives of cellulose
acetate in the usual membrane casting solvents may present some difficulty
in preparing membranes from these polymers, an insoluble enzyme was pre-
pared by diazonium coupling of CAPAPB to trypsin.  The protein content
of this material was 2.1$; the activity, compared with native trypsin,
was nil (probably less than 0.05$).  TM-S lack of activity may have
resulted from the inactivation of trypsin by the polymeric diazonium
salt, a low enzymatic activity having been reported for insoluble trypsin
prepared by coupling with a dlazotized copol^oner of p-amino-DL-phenyl-
alanine and L-leucine.°  Diazonium coupling, therefore,  is apparently  not
a feasible method for preparing trypsin membranes.

Attachment of an enzyme to an insoluble carrier frequently results in a
shift in the pH optimum (the pH at which maximal activity occurs).  The
shift may be to either more positive or more negative values, depending
on the electrostatic charge on the carrier.  Since hydrolysis of N-hydroxy-
succlnimide ester groups which were not involved in binding the enzyme
would result in a negative charge on the carrier, it was of interest to
determine whether a shift in optimum pH had occurred.  The variation with
pH in activity of the insoluble trypsin, relative to native trypsin at
pH 8.0, is shown by the following data.

                         pH             Activity

                         7.0                7%

                         8.0

                         9.0
The optimum pH for insoluble CABS- trypsin is apparently between 7 and 9,
not significantly different from that of the native enzyme.1"

To provide a measure of the effectiveness of insoluble trypsin in hydroliz-
ing proteinaceous colloids, a sample of the insoluble enzyme (CAHS- trypsin)
was assayed with casein as substrate, using the TUBS procedure of Habeeb.M
The sample of insoluble trypsin which had shown an activity toward BAEE
hydrolysis of 13 to 17$ of that of the native trypsin was 2.9$ as active
as the native enzyme when assayed with casein.  This lower activity toward
a macromolecular substrate is in agreement with literature reports on other

-------
insoluble enzyme preparations.

PREPARATION OF ENZYME-COUPLED MEMBRANES

A membrane intended for enzyme coupling was prepared by machine  casting
at room temperature from a solution containing (by weight)  CAHS-NHS,  10
parts; propionamide, 7 parts; maleic acid,  3 parts; dioxane,  20  parts;
acetone, 20 parts.  This membrane was gelled at 0°C after less than 5
sec drying time and stored under methanol at 5°C until ready  for use.
Reaction of a sample of the CAHS-NHS membrane with tryptamine in the
same manner described previously for the bulk polymer indicated  that
7^$ of the NHS groups remained intact after casting.  A second portion
of the membrane was annealed in water for 3 min at 74°C; tryptamine
analysis of this sample indicated that ^3$ of the NHS groups  originally
present in the polymer remained after both casting and annealing.  These
experiments, together with the successful attempts at enzyme  coupling
described below, demonstrated that although the very reactive CAHS-NHS
polymer was susceptible to hydrolysis, membranes could be fabricated from
it under normal conditions which contained sufficient reactive sites for
enzyme attachment.

An enzyme-coupled membrane was prepared by immersing a 27.5 cm2  specimen
of the unannealed CAHS-NHS membrane in a solution of 50 mg of trypsin in
5 ml of 2$ aqueous sodium bicarbonate for 70 hrs at k°C.  Following this
treatment, the membrane was thoroughly washed, in succession, with 0.001
N hydrochloric acid, 0.01 M borate buffer (pH 9.0) and water.  The result-
ing membrane was found to contain 1.1$ protein.  A portion of the mem-
brane which had been left in contact with the trypsin solution for 10
days before washing was found to have a protein content of 1.4$, indi-
cating that most of the enzyme attachment was complete after 70 hrs.

A sample of the enzymatic membrane prepared by reaction with trypsin for
70 hrs was cut into 1 to 2-mm squares, and its enzymatic activity assayed
with BAEE.  The activity of enzyme attached to the membrane toward BAEE
hydrolysis was found to be 2.5$ of that of the native trypsin.  After k
days in aqueous suspension (pH ca. 6, 25°C) at room temperature, the
enzymatic activity was 1.7$ compared to native trypsin (68$ of its ini-
tial activity).  Bar-Eli and Katchalski1" have examined the stability
of trypsin solutions as a function of pH.  They found that a solution of
trypsin containing 25  g enzyme per ml lost 60$ of its activity in 25
hours at pH 6 and 25°C.  Their result indicates that native trypsin would
retain only 2 to 3$ of its activity under conditions where the enzyme
membrane retained 68$ of its initial activity.  It is clear from this
experiment that attachment to the CAHS-NHS membrane stabilized the trypsin
toward loss of activity, which presumably occurs by self-catalyzed hydrol-
ysis.  Such a stabilizing effect has been observed for other insoluble
enzyme preparations, including other trypsin derivatives."  These results
indicate that enzymes having greater stability than trypsin should be
investigated for attachment to membranes, in order to insure maximum
retention of activity of enzymatic membranes during long periods of
reverse-osmosis operation.
                                57

-------
The trypsin membrane described above was prepared with both sides of the
membrane exposed to the trypsin solution.  For prevention of colloid
fouling, only enzymes on the active layer side will be effective.  Fur-
thermore, the substructure of the enzyme is mvch more porous than the
active layer, and enzymes could possibly have penetrated and become
attached within the substructure.  Interior enzymes would contribute to
the observed protein content, but might be less reactive than surface
enzymes since the substrate would have to diffuse into the membrane and
products would have to diffuse out.  To examine an enzyme membrane with
essentially only surface enzymes a portion of membrane was masked with
Mylar film and waterproof tape to allow only the active layer to contact
the trypsin solution.  The resulting membrane contained 0.22$ protein;
its activity relative to native trypsin was 1.8$, slightly less than the
membrane with trypsin on both sides.  The lower activity of the membrane-
bound enzyme relative to the enzyme attached to bulk polymer under the
same conditions can probably be ascribed to the effect of surface area.
Manecke has reportedl-9 that increasing the surface area of synthetic poly-
mers used as enzyme carriers increases the amount of enzyme bound, and
also Increases the reaction rate of the insoluble enzyme with its sub-
strate.  Thus, trypsin attached to the membrane, especially on the active
layer side with its smaller surface area, is somewhat less reactive than
trypsin attached to the fibrous bulk polymer.

Verification that trypsin had become attached to both sides of the earlier
membrane and only one Bide of the latter one, was obtained by staining
both membranes with Pink RL dye, a protein-specific stain.  Excess dye
was removed with ethanol and sections of the two membranes were examined
at 1+20X magnification under reflected light.  The pink dye was concentrated
at both surfaces of the first membrane, with only a faint color in the
interior.  In the second membrane (active layer side only), however, the
dye was concentrated at the active layer surface, with essentially no
color at the other surface and very little color in the interior.

A demonstration of hydrolysis by the enzyme-coupled membrane of a colloidal
protein, such as casein, was not practical.  Based on the BAEE activity of
the enzymatic membranes and the bulk enzymes, hydrolysis of casein by either
membrane would not be measurable by the assay procedures available.  It has
been demonstrated (vide supra) that bulk CAHS-trypsin is capable of effect-
ing hydrolysis of a model proteinaceous colloid, namely casein.  Moreover,
the trypsin membranes have been shown to possess enzymatic activity by
hydrolysis of BAEE.  The colloid concentrations to be found in secondary
effluent probably do not exceed 5 rag/A, 5 a concentration which is one or
two orders of magnitude below the sensitivity of the methods used to assay
casein hydrolysis.  While the enzymatic activity on the active layer is
small, a small activity may well be sufficient to prevent fouling by waste-
water colloids at these low concentrations.  Tests of the enzymatic mem-
brane with sewage are required to answer this question.

MEMBRANES FROM CELLULOSE ACETATE HTDROGEN SUCCINATE

Prior to preparing enzyme membranes, preliminary membrane formulation

-------
studies were conducted with cellulose acetate hydrogen succinate (CAHS).
These were not extensive enough to optimize the formulation,  but did
provide a formulation adequate for the highly swollen membranes used in
preparing trypsin membranes.  Some reverse osmosis data were also
obtained on these membranes which may indicate another method of prevent-
ing fouling by colloids.

The best reverse osmosis performance with GABS membranes was attained
with a formulation containing (by weight):  CAHS, 20 parts; propionamide,
Hk parts; maleic acid, 6 parts; dioxane, ^5 parts; and acetone, Ho parts.
Membranes were cast from this solution at room temperature with less than
5 sec drying time and gelled at 0°C.  After annealing at jk°G this mem-
brane exhibited a flux of 13 gfd with 8<# rejection when tested at 600
psi with 1000 mg/jfc sodium chloride feed solution.  After two hours on
secondary effluent the flux was 46 gfd with f2% conductivity rejection.
This increase in flux was accompanied by a change in the reclrculating
feed from an initial pH of 7.0 to pH 8.2.  After 3 hours the pH was
adjusted with 6 N sulfurlc acid to pH 4.9.  During the next 18 hours the
pH rose to 6.8, with a flux of 27 ef& at 78$ rejection.  After 2^ hours
the membrane was subjected to a Biz wash.  After the Biz wash the flux
was increased only to 32 gfd with 32$ rejection, declining to 18 gfd and
21$ rejection over a period of three days.  Visual examination after the
test showed very little of the slimy deposits generally accumulated in
that length of time.

The large changes in flux and rejection observed during the above test
can probably be ascribed to the effect of the CAHS carboxyl groups.  The
charge density on the membrane would be expected to Increase with increas-
ing pH in the pH range encountered above, which would alter the permeabil-
ity to water and ionic species.  The increase In pH which occurred during
the test is also probably due to the presence of carboxyl groups.

The highly alkaline conditions of the Biz wash apparently resulted in
degradative damage to the active layer, as evidenced by the large decrease
in conductivity rejection.

To ascertain whether the negatively charged CABS membrane might have inher-
ent antifoullng characteristics another membrane  from a similar formulation
(using 10 parts of acetaoide Instead of propionamide) was tested for 16
days on Pomona secondary effluent, maintaining the feed pH at  U.7 to 5.5
by periodic addition of dilute sulfuric acid.  Initially the flux was 15.5
gfd, with 80$ conductivity  rejection.  After 6 days the flux was unchanged,
and the rejection was 87$.  The flux dropped to  13.5 gfd after 8 days and
to 6 gfd after 16 days.  The complete absence of flux  decline  over the
first 6 days, however,  suggests that the  CAHS membrane may  have inherent
fouling resistance.  The colloids  involved in fouling may be negatively
charged at  the pH maintained during this  test, and would thus  be repelled
by a membrane of like charge.  This possibility  should be  pursued further.
                                59

-------
                           REFERENCES
 1.   D. L. Hoernschemeyer, ejt al., Research and Development of Nev and
      Improved Cellulose Ester Membranes,  Aerojet-General Corporation,
      Report No. 1319-F, a final report  to the  Office of Saline Water,
      USDI, Contract No. 14-01-0001-2205,  January 1970.

 2.   C. W. Saltonstall, Jr., et al.,  A  Study of Membranes^ for Desalina-
      tion by Reverse Osmosis, Aerojet-General  Corporation,  Report No.
      3292, a final report to the Office of Saline Water, USDI, Contract
      No. 14-01-0001-338, October 1966;  Office  of Saline Water Research
      and Development Progress Report  No.  232.

 3.   U. Merten, et_ altj> Reverse Osmosis Membrane Research,  General Atomic
      Division of General Dynamics, Report No.  GACD 7192, a quarterly
      report to the Office of Saline Water,  USDI,  Contract No. 14-01-
      0001-767, May 1967.

 4.   P. A. Cantor, et al.. Research and -Development of  Nev and Improved
      Cellulose Ester Membranes, Aerojet-General Corporation, Report No.
      3343-F, a final report to the Office of Saline Water,  USDI,  Contract
      No. 14-01-0001-1732, January 1969; Office of Saline Water Research
      and Development Progress Report  No.  434.

 5.   R. B. Dean, et al.. Environ. Sci.  Tech.,  1,  147 (1967).

 6.   I. H. Silmn and E. Katchalski,  Ann.  Rev.  Biochem., 35, 873  (1966).

 7.   A. White, P. Handler, E. L. Smith, and D.  Stetten,  Jr., "Principles
      of Biochemistry," 2nd Ed., McGraw-Hill, New York,  1959, P« 152.

 8.   R. Axen, J. Porath, and S. Ernback,  Nature,  214, 1302 (1967).

 9.   R. Goldman, et al., Biochemistry,  If
10.   Development of Technology for Continuous  Production of Low-Cost
      Reverse-Osmosis Modules, Aerojet-General  Corporation,  Report No.
      F1301-01, a final report to the  Office  of Saline Water, USDI,
      Contract No. DI 14-01-0001-2146,  November 1969.

11.   Reverse Osmosis as a Treatment of Wastewater,  Aerojet-General
      Corporation, Report No. 2962, a  final report to  the U. S.  Public
      Health Service, Contract No. 86-63-227, January  1965.

12.   P. A. Cantor, et_ al»^ Development and Scale-up of New and Improved
      Cellulose Ester Membranes, Aerojet-General Corporation, Report No.
      ^bbtf-Ol-F, a final report to the Office of Saline Water, USDI,
      Contract No. 14-01-0001-1767, May 1969.
                                60

-------
13.   W. M. King, e_t al., High Retention Tubular Membranes for Reverse
      Osmosis, Aerojet-General Corporation,  Report No.  1372-8, a monthly
      report to the Office of Saline Water,  USDI, Contract No. 14-01-
      0001-2224, February 1970.

I1*.   Reverse Osmosis Renovation of Municipal Wastevater. Aerojet-General
      Corporation, a final report to the Federal Water Pollution Control
      Administration, USDI, Contract No. 14-12-184, December 1969.

15.   G. W. Anderson, J. E. Zimmerman,  and F. M. Callahan, J. Am. Chem.
      Soc., 86, 1839 (1964).

16.   W. Rick, in H. Bergmeyer,  Ed., "Methods of Enzymatic Analysis,"
      Academic Press, Nev York,  1962, pp. 800-823.

IT.   A.F.S.A. Habeeb, Arch. Biochem. Biophys.,  119, 264 (1967).

18.   A. Bar-Eli and E. Katchalski, J.  Biol. Chem., 238, 1960 (1963).

19.   G. Manecke, Biochem. J., 107, 2 P (1968).
                                  61

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                             APPENDIX

              EFFECT OF SULFATE ON CHLORIDE REJECTION
                           IN MIXED FEEDS
                             CONTENTS

Table

 A-l    EFFECT OF FEED COMPOSITION ON REJECTION BEHAVIOR"
          OF CAM MEMBRANE                                         64

 A-2    EFFECT OF ANNEALING TEMPERATURE ON REJECTION
          CHARACTERISTICS OF BLEND MEMBRANES                      65
                                62

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                             APPENDIX
EFFECT OF SULFATE ON CHLORIDE REJECTION IN MIXED FEEDS

In brackish-water tests carried out several years ago, abnormally low
nitrate rejection was observed in feed waters containing sodium nitrate
in the presence of a large excess of calcium sulfate.  It was considered
of practical interest, during this program, to determine the extent to
which this effect applied to sodium chloride rejection in mixed feeds
containing sodium chloride and sodium sulfate since such feeds were used
in evaluation of membranes in the program.

A crosslinked CAM-360 membrane, cast at -10 C, and annealed at 80 C, was
tested at 200 psi against a series of feeds, all of which had the same
osmotic pressure, in which the ratio of sodium sulfate to sodium chloride
was varied.  Included in the series were feed solutions containing either
solute alone.  The results, summarized in Table A-l,  indicate a strong
effect of sulfate on chloride rejection, the chloride rejection decreasing
with increased sulfate-to-chloride ratio in the feed. The chloride rejec-
tion was observed to decrease from a value of 85$ with the feed containing
sodium chloride alone to 56$ with the feed containing the highest ratio
of sulfate to chloride.  The aulfate rejection also was affected by varia-
tion in feed composition, increasing with  increased  sulfate-to-chloride
ratio.

A second series of tests was carried out to determine to what extent  the
mixed ion rejection effect was a function  of membrane annealing tempera-
ture.  To this end, membranes were  cast from a 1:1 blend  (ds 2.63)  for-
mulation, annealed at various temperatures and tested at  150 psi succes-
sively against the following feed  solutions:

      Peed No. 1  -   250 mg/J NaCl, 750 mg/4 NagSO^
      Peed No. 2  -   1000 mg/4 NaCl

      Peed No. 3  -   1000 mg/A NBgSO^

The  results  of these  tests,  summarized in Table A-2, indicate  that the
extent to which  sodium chloride  rejection decreases  in the presence of
 sodium sulfate is greater  the lower the annealing temperature  for a
 given membrane formulation.   With the unannealed membrane, sodium
 chloride rejection  fell from a value  of 5256 with pure sodium chloride
 solution (feed No.  2) to 11# with the mixed feed (feed No. l),  a decrease
 of 78$.  The percentage decrease fell consistently as the annealing tem-
 perature was increased, so that with the 70°C membrane, sodium chloride
 rejection was reduced from 93# with the sodium chloride feed to 85# with
 the mixed feed,  a drop of only

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                             TABLE A-l

             EFFECT OF FEED COMPOSITION ON REJECTION
                    BEHAVIOR OF CAM MEMBRANE
Feed Composition,
  0
1500

2500

3500
                       Flux,
                       32.7

                       36.8

                       39.7

                       38.U

                       35-8
   Nad
Rejection,
    #

  85.2

  7^.0

  70.0

  55.7
Rejection,




   90.6



   97.3

   96.1
 Measured at 200 psi after 2-hour test period using membrane annealed
 at 8o°C.  The casting formulation vas as follows (amounts of ingredi-
 ents in parts by weight):  CAM-360, 10; acetone, li-O; maleic acid, lU;
 water, 10.  Crosslinking was carried out after annealing by immersion
 of the membranes for 3 min at 90°C in a solution containing 0.037 M
 of potassium persulfate and 0.038 M of sodium bisulfite.

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                                                                         TABLE A-2


                                                       EFFECT OF ANNEALING TEMPERATURE ON REJECTION
                                                            CHARACTERISTICS OF BLEND MEMBRANES
vn
a
Annealing
Temp., °C
25
(unannealed)

50


60

70



Feedb
1
2
3
1
2
3
1
2
3
1
2
3

Flux,0
35.8
36A
36.2
22.3
23.2
22.5
14.2
13 A
13.7
8.7
8.1
8.3
NaCl
Rejection,0
I
11.3
52.0
-
38A
68.8
-
68.1
8k.k
-
83.8
93.1

Ha2 L
Rejection,0
99-9
98.1
99.7

98.6
99-9
98.3
99-7

98.0
f> Keauction of
NaCl Rejection
by NagSOi
78.3
-
UU.2

-
19-3
-
10.0
—
-
                ''Membrane formulation (parts by vt) - E-398-3, 10; A-1*32-130B, 10; dioxane, 55; acetone, 35;
                 methanol, 9; maleic acid, 3.


                 Feed No. 1 - 250 mg/X sodium chloride, 750 mg/4 sodium sulfate
                 Feed No. 2 - 1000 mg/1 sodium chloride
                 Feed No. 3 - 1000 mg/£ sodium sulfate


                cDetermined at 150 psi after 2-hour test periods.

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The reduction of chloride and nitrate ion rejections in the presence
of other ions, such as sulfate, does not appear to be of serious con-
sequence in the treatment of wastewater by reverse osmosis because
the rejections obtained are still high enough to produce product water
vith acceptably low concentrations of these ions.  The rejection of
organic components, furthermore, should not be affected by the presence
of ionic components, since the former are, in almost all cases, non-
ionic in nature.
                                66

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1

5

Afcrxxioii Number
2

.Sub/erf Ftt*/d & Croup
05D
SELECTED WATER RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
Ortf«ni>«fiofl
Envirogenics Company, a division of Aerojet-General Corporation,
El Monte, California
  6 |r""
NEW TECHNOLOGY FOE TREATMENT OP WASTEWATER BY REVERSE OSMOSIS
 ]Q f
         Fisher,  B.  S.
         Lowell,  J.  R.,  Jr.
                         16 I p""'ec' »«'*«•'•<>•'FWJA Program # 17020 DUD.
                        I	'                Contract # lU-12-553
                         211*""
    Citmlion
    Descriptor* (St*tn4 Fittl)
     *Reverse osmosis,  *Semipermeable membranes,  ^Sewage treatment, *Wastewater treatment,
     *Tertiary treatment,  Demineralization,  Membranes,  Membrane processes, Sewage
     effluents, Water purification,  Water treatment,  Desalination processes
                       *Membrane fouling, *Proteolytic enzymes, *Enzymatic membranes,
     *Wastewater renovation, Enzymes, Membrane cleaning, Enzymatic detergent.
 271 **••'•"'  Stable,  high-flux membranes were sought for use in the renovation of wastewater
——' by reverse osmosis.   Cellulose ester membranes were formulated to produce fluxes
   greater than 60 gal/ft -day which would not decrease by more than 20$ after the first
   year of operation,  and reject at least 60$ of sodium chloride and 95$ of sodium sulfate
   when tested at 600 psi with 1000 ppm feed solutions.  The target osmotic performance was
   achieved with each of  three membrane types:  A cellulose diacetate of moderately-low
   acetyl content, a cellulose triacetate-diacetate blend, and crosslinked cellulose ace-
   tate methacrylate.   The intrinsic flux stabilities of these membranes extrapolated to
   flux losses of only 12 to 18$ after the first year of operation.  The fluxes of these
   high-performance  membranes declined rapidly in bench-scale tests with secondary sewage
   effluent but were restored to within 80 to 90$ of the initial values after cleaning with
   an enzymatic laundry presoak (Biz).  Daily cleaning by this technique maintained the
   fluxes at a nearly constant level over a 5-day test period.  The rejection of sewage com-
   ponents by the high-flux membranes was excellent.  Techniques were explored for attach-
   ment of proteolytic enzymes to cellulose acetate membranes to render them resistant to
   colloid fouling.   The  proteolytic enzyme trypsin was chemically attached to the active
   layer surface of a membrane prepared from the N-hydroxysuccinimide ester of cellulose
   acetate hydrogen succinate.  The resulting enzymatic membrane displayed hydrolytic
   activity.
Aba
ractor
B.
S.
Fisher
Inftttfufion
Envirogenics Cot
Aero.let-Oeneral
roan
tor
y, a division
pbration
of

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