WATER POLLUTION CONTROL RESEARCH SERIES • 17O4O—O5/7O
        RENOVATION OF
      MUNICIPAL WASTEWATER
          BY REVERSE OSMOSIS
ENVIRONMENTAL PROTECTION AGENCY • WATER QUALITY OFFICE

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          WATER POLLUTION CONTROL RESEARCH SERIES

The Water Pollution Control Research Series describes the
results and progress in the control and abatement of pollu-
tion of our Nation's waters.  They provide a central source
of information on the research, development, and demon-
stration activities of the Water Quality Office, Environ-
mental Protection Agency, through inhouse research and grants
and contracts with Federal, State, and local agencies, re-
search institutions, and industrial organizations.
                                              j

Inquiries pertaining to the Water Pollution Control Research
Reports should be directed to the Head, Project Reports
System, Office of Research and Development, Water Quality
Office, Environmental Protection Agency, Washington, D.C. 20242,

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RENOVATION  OF MUNICIPAL WASTEWATER BY REVERSE OSMOSIS
                          By
                                              *
        Mr.  John M. Smith,  Sanitary Engineer
        Mr.  Arthur N. Masse,  Chief*
        Mr.  Robert P. Miele,  Sanitary Engineer
           MUNICIPAL TREATMENT RESEARCH PROGRAM
       ADVANCED WASTE TREATMENT RESEARCH  LABORATORY
                   Water Quality Office
              ENVIRONMENTAL  PROTECTION AGENCY
                     CINCINNATI, OHIO
      **
       LOS ANGELES COUNTY SANITATION DISTRICT
                LOS ANGELES, CALIFORNIA

                       MAY 1970
          For sale by the Superintendent ot Documents, U.S. Government Printing Olnce
                    Washington, D.C., 20402 - Price 65 cents

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                             ABSTRACT
     The increasing demand for clean water makes clear the need for
improved treatment of municipal wastewater.  Deliberate reuse of
wastewater requires efficient removal of "residual" organic and inor-
ganic solutes.  A common and effective approach has been to supplement
biological processes with chemical and physical processes that, together,
are capable of achieving water quality consistent with reuse requirements,
A more direct approach is to use a single process such as reverse osmosis
which exhibits a potential to separate a broad spectrum of contaminants
from primary and secondary effluents.

     The pilot plant studies reported herein were addressed toward
defining the problems associated with the reverse osmosis processing
of variously treated wastewaters.  The effects of feed water quality
on membrane performance were evaluated, as were methods to control
membrane fouling.  A comparison of three configurations; flat plate,
spiral-wound, and tubular was made to determine their relative merit
in treating wastewater.  Finally, a cursory examination of costs
was made.
                                 ii

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                             CONTENTS



                                                          Page

TITLE PAGE                                                 i

ABSTRACT                                                   ii

CONTENTS                                                   ill

INTRODUCTION                                               iv

HISTORY OF REVERSE OSMOSIS DEVELOPMENT                     1

PILOT PLANT INVESTIGATIONS                                 4
     Pomona, California                                    4
        Spiral-Wound Configuration                         4
        Tubular Configuration                              16

     Lebanon, Ohio                                         27
        Flat-Plate Configuration                           27

DISCUSSION AND INTERPRETATION OF PILOT PLANT RESULTS       51

CONTRACT AND RELATED INVESTIGATIONS                        53

RELATIVE POSITION AND FUTURE ROLE OF REVERSE OSMOSIS
     IN RENOVATING WASTEWATER                              55

REFERENCES                                                 59
                                 iii

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                           INTRODUCTION
     Since the fresh water resources of the world are limited, it is
axiomatic  that our ever-increasing water needs will demand more
efficient use of our present water supplies.

     One way of improving this efficiency is through multiple use of
available surface water.  This,of course,requires treatment technology
capable of achieving water quality consistent with the planned future
uses of the water.  In many cases,, present-day treatment techniques will
not be adequate, and must be supplemented or replaced with advanced
processes that can effect a high removal of undesirable contaminants.
Of primary concern is the removal of nutrients, dissolved mineral
salts, oxygen-demanding organics and undesirable bacteria and viruses
presently being discharged as a result of inadequate wastewater
treatment.

     Advanced waste treatment of primary or secondary municipal effluents
is currently accomplished by a series of unit processes, each capable of
selectively removing a particular fraction of the residual waste load.
This approach has been successful but could be enhanced through the
development and utilization of a single process exhibiting removal
efficiencies of the combined unit processes.

     Reverse osmosis is a process with the demonstrated capacity to
separate dissolved organics and inorganics as well as the larger
organic species from aqueous solution, and is therefore worthy of
evaluation as a potential advanced waste treatment process.
                                iv

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               HISTORY OF REVERSE OSMOSIS DEVELOPMENT
     The early work of Reid and co-workers at the University of Florida
first demonstrated the effectiveness of cellulose acetate as a desali-
nation membrane  (1).  Further investigation by Loeb and Sourirajan
(1959-1960) at the University of California, using aqueous magnesium
perchlorate as a swelling agent in the casting solution for cellulose
acetate membranes, resulted in a membrane that exhibited much higher
water permeation rates while still maintaining the solute rejection
characteristics of the earlier membranes.  The original Loeb-Sourirajan
film formulation, identified as batch No. 25, is shown in Table 1
(2) (3) (4).
                              TABLE 1
               CASTING SOLUTION	BATCH NO. 25

           COMPONENT                              (WT %)

        Cellulose Acetate                         22.2
     (acetyl content 39.8%)

            Acetone                               66.7

        Magnesium Perchlorate                      1.1

            Water                                 10.0
                         TOTAL                   100.0
     This formulation established the practicality of reverse osmosis
as a desalination process, and has been reported extensively in the
literature.  Innumerable modifications of the early Loeb formulation
have been made since 1960 in an effort to improve the initial flux
and solute rejection characteristics of the membranes.  These modifi-
cations have included basic changes in the casting formulation as well
as improvements in the casting and curing techniques.  The basic cellu-
lose acetate designated by Eastman Kodak as E-398-3 is now used in
combination with additives and other cellulosic derivatives to produce
optimum membranes for the conversion of brackish and sea water.  Much
of the membrane development work to date has been sponsored by the
U. S. Department of the Interior's Office of Saline Water.
                               - 1 -

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      As  the  development  of membranes  progressed , the need  for  a practical
module configuration  became  apparent  and  the need was met  by the design and
testing  of three  principal configurations;  the plate and frame, the
spiral-wound,  and the tubular modules.  Extensive pilot plant  evalu-
ation of these modules on  brackish water  illuminated the problems of
concentration  polarization and  scaling  that could be expected  with
these feedso   The effect of  concentration polarization was minimized
by maintaining turbulent flow conditions  within  the brine  channels
while the precipitation  of sparingly  soluble salts was controlled by
depressing the feed stream pH to  a value  of 6.0 or less.

      The application  of  reverse osmosis in  treating municipal  wastes
was  first considered  late  in 1962 when preliminary investigation by
Aerojet-General Corporation  at Azusa, California indicated that the
cellulose acetate membranes  were  an effective barrier for  both organic
and  inorganic  solutes.   Following preliminary testing, a contract was
awarded  to Aerojet by the  Public Health Service's Advanced Waste
Treatment Program (now FWQA) to conduct an  in-depth bench-scale study
to evaluate the potential of reverse osmosis for renovation of muni-
cipal wastes.

      This study was conducted on  filtered municipal secondary  effluent
using 3-inch diameter  flat-plate test cells operated at pressures of
750  and  1500 PSIG.  The  feed stream was recirculated during the tests
and  a 5-10 fold increase in  feed concentration was produced.   The pH
of the feed stream was maintained at 5.5 by the addition of sulfuric
acid.  Three types of  cellulose acetate membranes were used for these
tests with nominal flux rates that varied from 10 to 60 gallons per
square foot per day (GFD).  Results of this study demonstrated that
high quality water could be produced by this process from  secondary
effluent.  Results of  two tests are shown in Table 2 and indicate
greater  than 95% removal of  total dissolved solids (TDS) and chemical
oxygen demand  (COD)(5).

     It was also  found that high flux (30-60 GFD) membranes were
unstable and, after a  few hours of operation, exhibited flux rates
as low as the lower flux (10-20 GFD) membranes.  Generally, the flux
rates were considered  too low to be practical.  Several possible
causes of the high flux rates were proposed, including the possibility
of organic fouling, poor hydrodynamic conditions and excessive concen-
tration of organic solutes.  There was also some question  regarding
the resistance of the membranes to biological attack.

     This initial bench-scale evaluation using the flat-plate  test
cells was followed in  early  1965 by a series of experiments conducted
at the Pomona Pilot Plant located adjacent to the Pomona Water Renovation
Plant in Pomona, California.  This study was a cooperative effort
between the County Sanitation Districts of Los Angeles County  and the
                               - 2 -

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                               TABLE 2
                       WATER MINERAL ANALYSIS

INITIAL
BENCH SCALE STUDY

AEROJET-GENERAL . CORPORATION
TDS
ABS
COD
PH
Cations
Na+
K++
NH+
Ca^
M ++
Mg
Fa**-
Anions
Cl"
N0~
HC03
C°3
so;
Si°3
PO; (total)
Feed Water
(Typical)
ppm
550
4.5
95
51
85
40
25
125
50
N.D.
65
2
260
0
200
30
25
Product
(Test 18)
ppm
15
0.1
2
6.3
4.6
4.9
0
0
0.7
0
20.3
0
8.1
0
1.7
2.9
0
Product
(Test 28)
ppm
28
0.1
6.0
5.5
6.1
2.7
3.9
2.6
0
0
22.1
0
3.5
0
3.3
2.9
0
N.D. - not determined




1 - pH adjusted during test.
                                - 3 -

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General Atomic Division of  the General Dynamics  Corporation  (b). The
experiments were  conducted  at a pressure of 200  PSIG at 5% recovery
using  the  spiral-wound modules developed by General Atomic.  The feed
to  the test loop  was diatomaceous earth-filtered secondary effluent.

     Results of these tests again demonstrated the high organic and
inorganic  solute  rejection  seen in  the earlier tests.  Also noted
during these tests was a  significant decrease in membrane flux with
time.  This was attributed  to fouling of the membranes by deposition
of  organic material present in filtered secondary effluent.  This
deposit could be  partially  removed  by increasing local turbulence
at  the membrane surface and by establishing a backward flow potential
through the membrane.

     These preliminary results, while promising, clearly indicated
the need for continuing the investigation of reverse osmosis at the
pilot plant scale to further evaluate the fouling potential of various
treated waste streams, to determine optimum operating conditions, to
examine different module configurations, and to determine the required
pretreatment for  sustained  operation.
                    PILOT PLANT INVESTIGATIONS

                        (Pomona, California)

Spiral-Wound Configuration

     The first pilot plant investigation of reverse osmosis was con-
ducted at the Pomona Water Renovation Plant under a joint FWQA-LACSD
contract in 1966.  This study was conducted using a 5000 GPD unit
employing the spiral-wound module shown in Figure 1.  The module
consists of 3/8" PVC pipe to which is attached a permeate flow channel
enclosed on each side by a cellulose acetate membrane.  The membrane
is glued around the edge to form an envelope through which the per-
meate flows to the center collection pipe.  The feed enters the
module axially and is distributed through the module by a polyethy-
lene vexar brine-side spacer.  This spacer is rolled up between the
membranes to form a cylindrical module which is then placed into the
pressure vessel.  A completed module is shown in Figure 2.  The
arrangement of the individual modules within a pressure vessel is
shown in Figure 3, and Figure 4 is a flow diagram of the entire unit.

     The first 11 months of operation of the spiral-wound module on
secondary effluent were plagued by problems of module construction
and mechanical failures.  The major problems were excessive module
leaking, brine seal failures, and telescoping of modules.  These
problems were compounded by a faulty pH control system and frequent
pump failures.
                               - 4 -

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                   ROLL TO
                   ASSEMBLE
FEED  SIDE
SPACER
                                                                              FEED FLOW
                                                PERMEATE FLOW
                                                (AFTER PASSAGE
                                                THROUGH MEMBRANE)
PERMEATE OUT
          PERMEATE SIDE BACKING
          MATERIAL WITH MEMBRANE ON
          EACH SIDE AND GLUED AROUND
          EDGES AND TO CENTER TUBE
                        FIGURE 1.   REVERSE OSMOSIS MODULE ASSEMBLY

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                                                              SEE DETAIL A
                                               BACKING MATERIAL
MESH SPACER
                   MEMBRANE
                                                                        PERMEATE TUBE
                                                                GLUE  LINE
                                   DETAIL A
                        FIGURE  2.   MODULE FABRICATION

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       FEED
VICTAULIC
COUPLING
                       ANTI-CORROSION
                       PLASTIC COATING
                                                             PRESSURE TUBE
                                                    MODULE
                                                         INTERCONNECTOR
                                                                                                                 PURGE VALVE


                                                                                                                     PURIFIED
                                                                                                                 T,  WATER
                                                                                                                     TUBE
                                                                                             END CAP-
                                                                                                    CONCENTRATE
                                                                                                    OUTLET TUBE
                             FIGURE  3.  ARRANGEMENT  OF SPIRAL-WOUND MODULES IN A
                                         MULTIMODULE  PRESSURE VESSEL

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  CARBON
  TREATED
  SECONDARY
  EFFLUENT
    !  i
                                             innir
                                             PUMP
                                          pH CONTROL
                                            SYSTEM
                                     I   I  MCl
                                     I	I SUPPLY
 MIXING
CHAMBER
MOYNO
PUMP
             SPIRAL-WOUND MODULES
                             \
                               PRESSURIZED
                               FEED
      u
      J.-I
     I  I
     .L.l-1
                                             PRESSURE REGULATING VALVE
f PRODUCT WATER
                        BRINE
                           FIGURE 4

           FLOW  DIAGRAM OF GULF  GENERAL ATOMIC

     REVERSE OSMOSIS  TEST FACILITY, POMONA,  CALIFORNIA

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     Notwithstanding these early difficulties, it was concluded that
the spiral-wound modules could process secondary effluent with high
organic and inorganic rejection, but that some form of pretreatment
was necessary to prevent excessive clogging of the brine-side spacers
from suspended solids present in secondary effluent.

     Bearing this in mind, and considering the possible fouling poten-
tial of soluble organic species, it was decided to pretreat the reverse
osmosis feed by passage through a granular carbon adsorption process.

     Two runs were conducted on the carbon-treated secondary effluent.
Objectives of these two runs are shown below:

     1.  To determine the water-flux-time relationship for the
         system when operating on an effluent from an activated
         carbon plant.

     2.  To monitor the water quality produced by the membranes and
         note any change in water quality with time.

     3.  To achieve a high rate of water recovery from the system
         and to determine, if possible, any adverse effects on the
         system as a result of high-water recovery.

     4.  To test the structural integrity of spiral-wound modules
         being subjected to a long-term test under normal environ-
         mental conditions.

     5.  To determine the materials responsible for any membrane
         fouling which might occur.

     6.  To investigate procedures for minimizing or preventing
         membrane fouling, along with methods for cleaning fouled
         membranes.

     A summary of the operating conditions for the  two experimental
runs are shown in Table 3.  It should be noted that for Run #1 the
diameter of modules within the seven series pipes are progressively
decreased to provide a relatively constant brine velocity, while Run
#2 was conducted at a higher initial, but gradually decreasing, brine
velocity since all of the modules are 4-inches in diameter.
                                -  9  -

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                               TABLE 3
               SUMMARY OF CONDITIONS FOR EXPERIMENTAL
          RUN IN GULF GENERAL ATOMIC REVERSE OSMOSIS UNITS
 No.  of Modules in Unit

 Module Diameter

 Total  Membrane Area

 Feed Water Source

 Feed Pressure

 Initial Feed Flow

 Initial Brine  Flow

 Initial Water  Recovery

 pH Control

 Chlorination
         Run #1

           85

   45t4",  20-3",  20-2"

         550 ft2

     Carbon Effluent

        400 psi

   2.8 gpm (4040 gpd)

   0.56 gpm (805 gpd)

           807c

   to 5.0  using HC1

   5.0 mg/1 dosage
     using NaOCl
4.8 gpm (6910 gpd)
1.0 gpm (1440 gpd)
5.0 mg/1 dosage
  using NaOCl
     A summary of the data from each experiment is shown in Figures 5
and 6.  These figures show the time dependent variation of flux and
salt rejection throughout the run.  Salt rejection was calculated  for
these runs by use of the formula:
   Salt rejection
Average feed conductivity - Product conductivity
            Average feed conductivity
   where,

   Average feed conductivity
           Feed conductivity + brine conductivity
                             2
     All data was obtained from readings taken daily and then averaged
over 100-hour intervals.

     The flux decline curve for Run #1 can be divided into 3 segments -
0 - 600 hours, 700 - 1600 hours, 1700 - 2500 hours.  The abrupt
increase in flux rate between 600 and 700 hours is due principally
                             - 10 -

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8
o 7
Sl'
z
x 5
£ 4
3

2
1
n

^ 	 % SALT REJECTION
"*""'"'x.-.x— x.x»x.^-N
•XB
\ • • —
-
FLUX (GFD)
r'x^,. ^^^
.-•— «x._^.-.
-
RUN -#1
FEED -CARBON TREATED
SECONDARY EFFLUENT
PRESSURE • 400 PSIG
i i i
1UU 5
0
95 S
ac
90 5
85 ^?









                       TIME IN HOURS

                           FIGURE 5
     FLUX AND SALT REJECTION PERFORMANCE FOR GULF GENERAL
ATOMIC SPIRAL-WOUND REVERSE OSMOSIS  MODULE,  POMONA,  CALIFORNIA

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  10
=: 4
                          % SALT REJECTION                                10°
                                  FLUX |GFD)


                                  "*~"*^»»«.»*      m'*   '***
                                        "-•-•^.s      ^,
                                           RUN •# 2
                                           FEED -CARBON TREATED
                                                 SECONDARY EFFLUENT
                                           PRESSURE-400 PSIG
                     100055005500
                                TIME IN HOURS

                                   FIGURE 6
             FLUX AND SALT REJECTION PERFORMANCE FOR  GULF GENERAL
         ATOMIC SPIRAL-WOUND REVERSE OSMOSIS MODULE,  POMONA,  CALIFORNIA
95 2

90

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to a replacement of six modules in the unit and partially to slight
leakage of feed water through the membrane which developed during
that period.  The increase in flux rate between 1600 and 1700 hours
resulted from an increased leakage of feed water through the membranes
which is also reflected in the salt rejection curve of Figure 5.

     The only abnormality in the flux vs. time curve for Run #2
occurs between 2300 and 2600 hours.  This is a result of two factors,
(1) the replacement of six modules in the unit; and (2) a one-week
depressurized flushing of the unit with tap water.

     A summary of the feed and product water quality data for Runs #1
and #2 is shown in Table 4.  The data for Run #1 is divided into two
time periods:  0 - 1600 hours, when all of the modules were functioning
properly, and 1600 -' 2500 hours, when several of the modules had
developed leaks.  The differences in the relative level of N03-N and
NH3-N between the two time periods shown in Table 4 resulted from  tha
method of operation of the Pomona secondary treatment plant.  All  of
the data shown in the two tables is based on average values of 24-hour
composite samples taken throughout the time period involved.  Samples
were collected for analyses twice weekly.

     As the product-water flow decreased throughout each run, the
water recovery also decreased.  However, since the final brine flow
rather than  the feed flow was being held constant, the decline in
water recovery did not accurately reflect the declining product water
flow.   Thus, the decline in water recovery from the beginning to
the end of Run #1 was from 80% to 78%.  Comparable values for Run  ''2
were from 80% to 647o.

     Attempts were made throughout both experiments to control the
flux decline in the membranes or to restore flux after decline had
occurred.  Previous experiments at Pomona had  indicated that a daily
15-minute air-tap water flush with the system  in a depressurized
condition was successful in controlling excessive pressure drops
across the brine side of the modules.  The excessive pressure drops
resulted from clogging of the brine passageways by suspended material
in the feed water.  This procedure was followed throughout both
experiments, and while it was again successful in controlling head-
loss, it did not appear to have any significant effect on restoring
flux rates.

     Along with the air-tap water  flushing, two other methods of
cleaning the membranes were investigated.  One procedure, which has
been successful in cleaning Gulf General Atomic modules fouled when
in use on a  brackish water, was a  citric acid  recirculation  through
the system.  The other cleaning attempt was a  procedure employing  an
anionic detergent solution  flush.  Neither of  these procedures were
successful in restoring membrane flux.
                               -  13  -

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                               TABLE 4
                   FEED AND PRODUCT WATER QUALITY
DATA FOR EXPERIMENTAL RUNS NO. 1 & 2
IN GULF GENERAL ATOMIC REVERSE OSMOSIS
Run No.l
TIME 0 - 1600 HRS Feed
COD (mg/1) 10.8
NH3-N (mg/1) 9.2
NO,-N (mg/1) 2.4
J
P04-P (mg/1) 10.1
TDS (mg/1) 623
Product
1.7
1.7
0.8
0.2
73
Brine
43.8
49.0
7.5
57.7
3402
UNIT
7, Rejection
93.8
94.2
84.0
99.4
96.4
    TIME  1600 -  2500 HRS
      COD (mg/1)          12.2      1.9       37.2        92.3
      NH3-N  (mg/1)        5.3        1.5       25.1        90.1
      N03-N  (mg/1)        12.2      6.0       34.9        74.6
      P04-P  (mg/1)        9.0        1.4       43.2        94.6
      TDS  (mg/1)          543        145       2738        91.2

Run No. 2
COD (mg/1)
NH--N (mg/1)
j
NO--N (mg/1)
j
PO. -P (mg/1)
b
TDS (mg/1)
11.4
17.1
2.1
9.7
552
0.7
2.9
0.8
0.07
51
37.4
59.9
8.9
39.8
2576
97.1
92.5
85.5
99.7
96.7
Notes:  (1) All analyses run on 24-hour composite samples
        (2) 7o Rejection calculated using average feed where,
                    Average feed =  feed + brine
        (3) Figures shown are  average values.
                              - 14 -

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     Each run was interrupted because of a mechanical problem with
the Moyno feed pump.  In each instance, the unit was inoperative for
3 to 4 weeks while the pump was being repaired.  During this time,
tap water was run through the unit at line pressure.  When the pump
was repaired and the unit was returned to normal operation, most of
the modules had developed excessive leaks and were producing water of
unacceptable quality.  The modules remained in operation for several
weeks after the run was resumed to see if the leaks would seal them-
selves; but, to the contrary, the product water quality continued to
deteriorate until the end of each run.  Investigation of the membranes
indicated that the leakage was caused by a combination of membrane
deterioration, and failure of glue and seals in the modules.  No
satisfactory explanation has yet been advanced for the cause of the
membrane deterioration.

     The difference in initial flux rate between Run #1 and Run #2 is
due mainly to improvements in membrane casting and module fabrication
techniques made by Gulf General Atomic in the interim period between
the start of each run.  However, some of the difference may be due to
the higher brine flows used during Run #2.  While these higher brine
flows did not increase the brine velocity in the downstream modules
because of the constant diameter modules used during that run, they
did result in an increased brine velocity in the upstream modules.
This increased brine velocity may have decreased the boundary layer
enough to result in higher flux.

     In only one instance during the  two runs was the  effect  of
high water recovery on the system evident.  At  the  start  of Run  #2,
the pH of the feed water was maintained at  5.5  rather  than 5.0  as had
been the case in all previous runs.   After  200  hours  of operation,
the  flux of  the  last set of  modules  on stream had  shown a significant-
ly greater decline  than the  other modules  in  the system.  A  one-hour
acid flush of these modules  returned  the  flux to a  level  consistent
with the remaining modules.  Calculation  of solubility levels,  along
with consideration  of boundary  layer  factors,  indicated that  a  form
of calcium phosphate was possibly precipitating on  the membrane  surface,
After acid flushing, the pH  was maintained  at 5.0  and  no  further evi-
dence of excessive  flux decline was  observed  in the last  set  of modules,


     Results of these two experimental runs support the following
observations:

     1.  The extent of flux  decline  in the  spiral-wound reverse
         osmosis system operating on  activated  carbon  effluent  is
         far greater than would be tolerable  in a practical system.

     2.  The quality of the  water produced  by the reverse osmosis
         process is excellent.
                               -  15  -

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     3.  An air-tap water-flushing procedure was successful  in
         controlling headless  through  the  system.

     4.  All attempts to clean  fouled  membranes were unsuccessful.

     5.  The high-water recovery obtained  in these experiments had
         no adverse effect on  the downstream modules at a pH of 5.0.

     6.  The cause of the apparent membrane deterioration during pro-
         longed tap-water flushing has not been determined.

Tubular Configuration -

     The second configuration  to be evaluated at the Pomona  Water
Renovation Plant was of tubular design, manufactured and furnished
by the Havens Company.*  The module configuration for this unit is
shown in Figure 7.  A module consists  of seven, 8-foot  long,
1/2-inch inside diameter fiberglass tubes  coated on the inside with
a cellulose acetate membrane.   The individual tubes are arranged in
series and are enclosed in a PVC shroud to collect the product water
that permeates from the feed stream side (inside) to the outside of
each tube.  The complete unit  included 48  modules, a high pressure
pump, acid addition equipment  and the  necessary piping, valves and
controls.

     Six separate experiments were conducted during this phase of
the investigation utilizing three membrane types (designated  as Type 3A,
4A, and 5A) on two waste streams, secondary effluent and granular
carbon-treated secondary effluent.  Types  3A, 4A and 5A refer to the
relative "tightness" of the membranes.  The operating conditions for
each of the six experiments are summarized in Table 5.  The  quality
of the feed and product water  for both feed streams is tabulated and
shown in Table 6.  The membrane flux for both clean and fouled modules
is compared to the "rated" value in Table  7.  A normalized flux decline
pattern for both feed streams  is shown in  Figure 8.

     These results demonstrated greater than 92% removal of  both
organic and inorganic solutes with the exception of NH-j-N and N03~N,
which were poorly rejected at pH 5.0.  Examination of Table 7 illus-
trates that the "clean module  flux" values are much lower than the
"rated flux" for the two higher flux modules, and that the flux
decline was more severe for the higher flux module, i.e. 35% for the
3A module rated at 27.0 GFD and 10% for the 5A module rated  at 10 GFD.
Comparison of the flux decline slopes  shown in Figure 8 for  each feed
indicates a two-week flux decline of 137<> for the carbon-treated second-
ary effluent and a 17% decline  for the secondary effluent feed. While
this difference is not large, it may be attributed to higher COD and
turbidity of the secondary effluent.
* Havens Industries, San Diego, California.  Mention of products  by
  name does not constitute endorsement by  the  Federal Water  Quality
  Administration.
                              - 16 -

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                          FIGURE 7
                   SCHEMATIC OF  HAVENS
                  REVERSE OSMOSIS  MODULE
                                          OUT
1] FIBERGLASS TUBE
2) OSMOTIC MEMBRANE
3) END FITTING
4) PVC SHROUD
  to  collect  product water
5) PRODUCT WATER
6) FEED SOLUTION
7) EFFLUENT
                           5
                        3
                                              1
                    6

-------
                                             TABLE 5
                      SUMMARY OF EXPERIMENTS ON HAVENS REVERSE OSMOSIS UNIT
Experi-
ment Feed
I Secondary
Effluent

II Secondary
Effluent
i
i— Ill Secondary
00 Effluent
i
IV Activated
Carbon
Effluent
V Activated
Carbon
Effluent
VI Activated
Carbon
Effluent
Feed
Pressure
(psi)
800

800
700
800

850

800

Feed
Flow
(gpm)
2.5

2.5
3.0
3.2

3.8

3.7

Type
Module
4A,5A

4A.5A
3A,4A,
5A
4A,5A

4A,5A

4 A, 5 A

Additive
To
Influent
50 mg/1
Sodium
Sulfite
5 mg/1
Calgon
CL-77
(See Note 1)
(See Note 1)

(See Note 1)

(See Note 1)

Duration
(hrs)
20

25
325
140

170

460

Initial
Recovery
(?.)
78

75
58
50

78

69

Final
Recovery
<%)
48

45
47
50

78

59

Reason
For
Termination
Rapid Flux
Decline

Rapid Flux
Decline
Pump
Failure
Pump
Failure

Excessive
Module
Breakage
Excessive
Module
Breakage
Notes:   (1) 87» Sulfuric acid added  to control product water  pH at  5.0 *
         (2) No acid addition during first 40 hours.

-------
                               TABLE 6





         WATER QUALITY DATA FOR HAVENS REVERSE  OSMOSIS  UNIT
Secondary Number
Effluent of
as Feed Samples
COD (mg/1)
Turbidity (JTU)
TDS (mg/1)
P04 (mg/1)
NH--N (mg/1)
J
Activated Carbon
Effluent As Feed
COD (mg/1)
TDS (mg/1)
PO^ (mg/1)
NH--N (mg/1)
j
NOQ-N (mg/1)
J
Cl (mg/1)
8
6
4
6
4

7
5
6
3
4
2
Feed
45.3
12.8
607
30.5
11.4

8.9
536
26.3
10.9
3.9
121
Product
1.9
0.1
26
0.15
1.5

0.6
40
0.25
1.4
1.2
10
% Rejection
95.8
99.4
95.7
99.5
86.8

93.4
92.5
99.0
87.0
69.4
91.9
Note:  All analyses run on grab samples.
                               - 19 -

-------
                                TABLE  7
                        COMPARISON OF MODULE FLUX
Module
Type
3A
4A
5A
Rated
Flux 2
(gpd/fO
27
18
10
"Clean" Modules
Flux (gpd/ft2)
Ave . Range
17.5
12.4
10.8
14.0-2C.8
11.3-14.0
8.6-12.0
"Fouled" Modules
Flux (gpd/ft2)
Ave . Range
11.4
9.7
9.5
9.1-14.0
8.0-12.4
8.2-11.5
% Decline
From Clean
State
35
22
10
Notes:

1.  Rated flux obtained using 5,000 mg/1 sodium chloride solution at
    600 psi, 25°C, flow rate of 1.5 gpm.  Values as reported in Havens
    Industries literature.

2.  "Clean" and "Fouled" fluxes obtained at 800 psi, influent flow
    rate of 2.5 gpm and influent IDS of 600 mg/1.

3.  "Clean" modules flux represents values taken shortly after
    experiment was begun.

4.  "Fouled" modules flux represents values taken after recovery
    had fallen to 45% - 50%.

5.  "Clean" and "Fouled" modules flux represent readings from fourteen
    Type 3A modules, seven Type 4A modules and ten Type 5A modules.
                               - 20 -

-------

12
4 Jfe
10
8
6
4
2
PRODUCT WATER CONDUCTIVITY
^<— • •
\ . A
-w\/\ ]
A
	 /-/ V\..--.. /s_
>. FLUX (GFD) N
v . ^/\
\''' "^X,.-^^ 	 ^..^. xx- — ^
H^
EXPERIMENTS -#3 & #6
"" SECONDARY EFFLUENT FEED*AS SHOWN
— 	 tARBUN IKtAltU
SECONDARY EFFLUENT
1 1 1 I ! 1 1 1 1 1 I 1
^ ° § s
ER C8HOUCTIVITY ( MHI
p"
40 5
Cd
ca
^

0   SO   100  150  200  250  300  350  400  450  500
                         TIME IN HOUtS
                             FIGURE  8
           FLUX AND PRODUCT WATER CONDUCTIVITY FOR HAVENS
         TUBULAR REVERSE OSMOSIS UNIT, POMONA ,  CALIFORNIA

-------
      These early results,  employing the tubular configuration,  were
 sufficiently encouraging to warrant continuing the investigation.   A
 Universal  Water Corporation reverse osmosis unit was used for this
 second-stage effort.   This system utilized a 1/2-inch plastic perfor-
 ated  tube  approximately 50 inches long, into which is fitted a preformed
 tubular membrane sealed at each end with 0-rings.  Eighteen of these
 elements were connected in series and placed within a 4-inch diameter
 PVC pipe to form a single  module that contains 7 sq ft of membrane
 surface.  The complete experimental unit was comprised of thirty-two
 of  these modules arranged  in banks of four modules each and plumbed
 originally in a 5-3 array  as shown in Figure 9.  This arrangement
 was modified after Run #1  to increase the initial system recovery
 from  40% to 73%.  Two  experimental runs have been completed to  date
 with  this  unit using granular carbon-treated secondary effluent as
 feed.

    Run #1 was conducted at  a feed pressure of 600 PSIG with the feed
 acidified  to pH 5.0 using  sulfuric acid.   A brine flow of 4.90  GPM
 was maintained with a  feed  flow of 8.10 GPM and product water flow
 of  3.20 GPM.   The  total headloss  across the system increased from  an
 original value of  90 PSIG  to a  final  value of 110 PSIG.  The flux
 decline and salt rejection  for  Run #1 are shown as a function of
 time  in Figure 10,  and  the  feed  and product water quality are pre-
 sented  in  Table  8.  Run #1 was  terminated after 1000 hours in order
 to  replumb the unit in  a 3-2-2-1  array in order to achieve higher
 overall  recovery.   Following the  shutdown,  the modules were flushed
 for one  hour with  a 0.75% bioenzyme solution* that had proven effec-
 tive  in restoring  the  flux decline in a Gulf General Atomic reverse
 osmosis  unit also  being tested  at  Pomona.   This technique increased
 the flux from  18.0  GFD  to 20.6  GFD, compared to an original flux of
 23.9 GFD.

     Run #2 was  conducted under  the same  conditions  as Run #1 except
 for the  recovery ratio, which was  increased from 40% to 73%.  This
 caused  the  exit  brine  flow to decrease from 4.9 GPM, which for  a
 1/2-inch diameter  tube  is equivalent  to a bulk velocity of 2.0  ft/sec,
 to  1.0  GPM which corresponds  to  a  bulk velocity of 0.4 ft/sec.   The
 effect  of  the  decreased velocity  and  higher recovery can be seen by
 comparing  the  flux  decline for Run #2 shown in Figure 11,  to  that
 exhibited  by Run #1 shown in Figure 10.   Flux decline for Run #1 was
 11% during the  first 300 hours  compared  to 41% during the first 300
 hours of the high  recovery run.   The  flux decline was observed  to
 be  more  pronounced  for  the downstream modules,  confirming the detri-
mental effects of  the poor hydrodynamic  conditions  experienced  by
 these modules.   This condition was  probably aggrevated by the in-
creased  brine  concentration  in  the later  modules.   Following  the
 first 300 hours  of operation, the  unit was  depressurized  to accom-
modate regeneration of the granular carbon  columns.   This  caused a
significant, but temporary,  increase  in membrane  flux as  did an
enzyme detergent flush at 450 hours.
                              - 22 -

-------
PRESSURE
REGULATING
VALVE
   BRINE
1 SECONDARY
TREATMENT


CARBON
ADSORPTION
COLUMNS
                                                  STORAGE
                                                   TANK
                                             CHLORINE
            PRODUCT WATER
                                            	PRESSURE
HIGH
IESSI
PUMP
                                 i  i  i  i
                                   i  i  i
                                             ACID
                                            PUMP
      pH  CONTROL
        SYSTEM
                                         SULFURIC
                                          ACID
                                FIGURE 9
             FLOW DIAGRAM, UNIVERSAL WATER  CORPORATION
          TUBULAR  REVERSE OSMOSIS UNIT, POMONA, CALIFORNIA

-------
                                              TABLE 8

                         SUMMARY OF FEED AND PRODUCT WATER QUALITY FOR UNIVERSAL
                                         WATER CORPORATION UNIT
                                         EXPERIMENTAL RUN NO. 1
Chemical
Analysis
Total COD
Dissolved COD
N03-N
NH3-N
i
to 4
** TDS
Ca
Mg
K
Na
S°4
Cl
No. of
Tests
10
9
9
10
8

10
4
3
4
4
3
3
Feed
Ave . Range
9.4 7.2 - 12.7
8.3 6.3 - 12.0
3.6 0.1 - 12.0
11.7 2.5 - 18.1
10.1 8.8 - 11.7

6.9 5.4 - 711
39.6
24.5
12.1
111
227
85
Product
Ave . Range
0.3 0.0 - 1.0
-
0.7 0.0 - 2.2
0.7 0.2 - 1.4
0.12 0.0 - 0.4

39 20 - 72
>1
2.0
0.8
7.6
0
8
Brine Percent
Ave. Range Rejection
14.6
12.7
5.5
18.9
15.5

1018
55.4
39.3
17.9
156
383
153
11.1 - 19.0 96.8
9.7 - 18.6
0.1 - 19.0 80.6
3.5 - 36.5 94.0
12.9 - 18.9 98.8

633 - 1859 93.7
>97.5
91.8
93.4
92.8
100.0
90.6
Notes:   (1) All analyses run on grab samples.
         (2) Feed samples taken after acidification with H-SO,; hence values of SO, shown in table
            include sulfate contributed by acid addition.
         (3) All values shown are in mg/1.

-------
  20


O 16
ik
O

z

X  '
D
i  4


   0
                                                      jioo 2
            % SALT REJECTION

                                                          
-------






o
5
z
X
u.









24

20
16

12

8
4
O
% SALT REJECTION

'•^—- ~>^i-^-.^. s 	 \ .-••;
^•'~ " V
•••
mt»

FLUX (GFD)
\ A T^. /N-- s T*
X' \/x— >.. 'x«x\/ ^'' ^'
RUN - #2
FEED - CARBON TREATED,
SECONDARY EFFLUENT
PRESSURE - 600 PSIG
i i i i i i i i i i i i
100 o
u
95 %
Ul
90 £
to

*







100 200 300 400  500 600 700 800  900 1000
                  TIME IN  HOURS

                       FIGURE 11
   FLUX AND SALT REJECTION PERFORMANCE OF UNIVERSAL WATER
       CORPORATION TUBULAR UNIT, POMONA  , CALIFORNIA

-------
                           (Lebanon, Ohio)

Flat Plate Configuration

     Experimental investigation of reverse osmosis at the Lebanon, Ohio
Pilot Plant has involved the performance evaluation of a 100 sq ft
(2000 GPD) flat-plate reverse osmosis unit on waste streams that
represent varying degrees of pretreatment.  Principal objectives of
this study were to demonstrate the efficacy of treating wastewater
with a flat-plate configuration and to evaluate the performance
characteristics of the experimental unit as a function of feed water
quality.

     The five waste streams evaluated during the course of this
investigation are shown in Figure 12.  The modular arrangement of
the reverse osmosis cell and a flow diagram of the entire system are
shown in Figures 13 and 14, respectively.

     The membrane plates are arranged in eight vertical modules within
the pressure vessel.  The  feed stream enters the uppermost module,
and passes in series through each succeeding module leaving the
eighth module as the reject stream.  The product water flows from
each module through separate channels within a central collection
tube to allow individual product water quality monitoring from each
module.  The plates are 14-inches in diameter and consist of two
molded phenolic half plates bonded together to form a completed plate
which encloses a product water channel.  The enclosed channel conducts
the product water to the central collection tube.  The support sub-
strates and cellulose acetate membranes are mounted on the outside of
a completed plate.  Adjacent plates are then separated by a poly-
styrene spiral-flow-baffle that directs the feed stream across the
surface of the membrane.   Construction of the half plates and the
spiral-flow baffle are shown in Figures 15 and 16, respectively.  Each
successive module within the pressure vessel contains fewer plates
in order to maintain a relative constant brine velocity as the product
water is withdrawn from the feed stream.

     Referring to Figure 14, each of the five waste streams evaluated
enters an equalization tank containing a thermostatically-controlled
immersion heater that acts as a heat exchanger to maintain the feed
temperature between 22 and 25°C.  After leaving this tank, the pH of
the feed is automatically  controlled at 5.0 "t 0.2 units by the auto-
matic addition of sulfuric acid.  The five micron filters preceding
the high pressure pump were used as a precautionary measure during
Runs #1 and #2, but were removed for the remaining three runs.  The
operating pressure was held within the range 450 to 485 PSIG through-
out the entire study.
                               -  27  -

-------
 RAW
SEWAGE
         PRIMARY
       TREATMENT
   SECONDARY     LIME     DUAL MEDIA
   TREATMENT  CLARIFICATION FILTRATION
   RUN NUMBER
1
3
              GRANULAR
               CARBON
             ADSORPTION
                                             TREATED
                                             EFH.UENT
                                                             5
                              FIGURE 12

              SCHEMATIC DIAGRAM  OF WASTE STREAMS
                           LEBANON, OHIO

-------
            FEED
          MODULE 1
          MODULE 2
          MODULE 3
          MODULE 4
           MODULE 5
           MODULE 6
           MODULE 7
           MODULE 8
            REJECT
                           PRODUCT FLOW
                          OF TOTAL PRODUCT
                                  16.2C
                              13 5 /;
                             13 4°/=
                          1O 7
                     -   85
                       73
              FIGURE  13
MODULAR ARRANGEMENT  OF  AEROJET GENERAL
       FLAT PLATE CONFIGURATION

-------
FLUSHING SOLUTION
AND RECYCLE TANK
FEEDS -1-2-3-4-5
                           EQUALIZATION
                           AND
                           TEMPERATURE
                           CONTROL TANK
                                       HIGH
                                     PRESSURE
                                       PUMP
                         LOW
                       PRESSURE
                         PUMP
                  ACHI
                  PUMP
                   i
                   I—
              i
             5 MICRON
             FILTERS
     pH CONTROL
      SYSTEM
REVERSE
OSMOSIS
  CELL
8 SERIES
MODULES
                                    REJECT
       PRODUCT WATER
                       FLOW MEASURING
                        AND RECORDING
                    pH
                 TEMPERATURE
                 CONDUCTIVITY
                                         EIGHT SEPARATE
                                         PRODUCT WATER
                                         STREAMS     -
                              FIGURE 14
                 FLOW DIAGRAM, AEROJET GENERAL
       PLATE & FRAME REVERSE OSMOSIS UNIT,  LEBANON .OHIO

-------

                       FIGURE 15
              TWO PHENOLIC HALF PLATES
14-INCH DIAMETER AEROJET-GENERAL PLAT AND FRAME UNIT

-------

                                                .

                 FIGURE 16
PHENOLIC HALF PLATE AHD SPIRAL FLOW BAFFEL
14-INCH DIAMETER AEROJET-GENERAL PLATE AND
                FRAME UNIT

-------
     The feed flow rate to the cell was controlled at 1.8 GPM by a
variable speed positive displacement pump.  This flow rate resulted
in an initial volumetric recovery of 52% , which ultimately declined
during the course of the investigation to 35% due to the irreversible
membrane fouling that occurred.

     The reverse osmosis unit was operated continuously during each
run unless interrupted by mechanical difficulties (which were infre-
quent after the first week of Run #1) .  The desalination cell was
depressurized and stored in a 0.25% formaldehyde solution between runs,
or for periods of storage greater than two weeks.

     The first experimental run was conducted on lime-clarified,
dual-media filtered, and carbon-treated secondary effluent.  The flux
decline pattern and salt rejection performance for this run are
presented in Figure 17 and the rejection efficiency is tabulated
and shown in Table 9.
                              TABLE 9

                 FEED AND PRODUCT WATER QUALITY DATA
                              (Run #1)
               Lime-Clarified, Filtered, Carbon-Treated
                           Secondary Effluent

PC>4 as P
NO -N
N03-N
NH3-N
Organic-N
TOC
Turbidity (JTU)
Feed
mg/1
0.60
0.90
3.0
< 0.1
< 0.2
1.0
< 0.5
Product
mg/1
< o.i
0.60
1.1
< 0.1
< 0.1
0.5
< 0.1
Results based on average of  10 determinations.

     As can be  seen  from the  above  table,  the  feed  concentration  of
the parameters  of  interest are too  low  to  allow meaningful  interpre-
tation of the rejection performance of  the membranes.   The  TDS  rejec-
tion averaged 90.1%  during the run  as determined  by feed  and  product
water conductivity measurements.  The rejection performance of  each
                               -  33  -

-------





16

14
Q
i^
0 10
z
X 8
3
ML 6
4
2
0
% SALT REJECTION
^^ •

"*"

<-B
FLUX (GFD)

x- 	 .
_
RUN - #1
FEED - CARBON TREATED LIME
CLARIFIED, FILTERED
SECONDARY EFFLUENT
PRESSURE - 470 PSIG
-
i i i i i i i i i i i i i t i
z
0
^^M
on ^*
90 V
Ml
UJ
80 5
<
lie









  02  4   6   8  TO  12  14  16 18 20 22 24  26  28 30
                   TIME IN DAYS
                   FIGURE 17
FLUX AND SALT REJECTION PERFORMANCE  OF AEROJET
      GENERAL FLAT PLATE CELL, LEBANON, OHIO

-------
module was examined independently during the first run to determine the
effect of the increasing brine and organic solute concentration on
rejection performance.  The results indicated that both the salt and
water permeation rates were constant over the entire length of the
cell.

     The pressure drop across the brine side of the cell was 17 PSIG
and remained constant for this run with a feed flow of 1.8 GPM.

     The second run was made under the same conditions as Run #1
except that the granular carbon adsorption columns were omitted from
the pretreatment train.  This run was interrupted on seven separate
occasions due to operating schedules, and was finally terminated after
127 days.  The flux decline pattern and salt rejection performance
are shown in Figure 18, while the feed and product water quality data
are shown in Table 10.

                             TABLE 10

                  FEED AND PRODUCT WATER QUALITY
                               (Run #2)

             Lime-Clarified, Filtered Secondary Effluent
               Average Values
               First  72 days
                             **
                                                                  ***
  Average Values
72nd to 127th day

P04
NO--N
N02-N
NH3-N
ORG-N
TOC
Feed
1.0
1.5
1.9
9.6
1.8
10.6
Product
0.1
0.5
1.7
1.1
0.5
1.0
% Rejection
90
67
11
88.5
72
90.5
Feed
-
2.9
*
9.5
2.6
13.3
Product
-
1.2
*
1.0
0.4
1.7
% Re lection
-
58
*
89
84.5
95
 Total  Bacteria
 Count  x ID** Per
100 ml 7.3
Turbidity
JTU 1 . 3
0.8 99 -
< 0.1 - 2.2 < 0.1
 Results in mg/1 unless noted.
 *   Feed and product NO -N less than 0.1 mg/1.
 **  Average values based on 28 determinations from samples withdrawn
     at regular intervals during the run.
 *** Average values based on 8 determinations from samples withdrawn at
     regular intervals during the run.
                               - 35 -

-------
      Comparison  of the  flux decline pattern for the  first 8  days  of
 Run  #2  to  that exhibited  by Run #1  demonstrates the  effect of the
 higher  organic load as  a  principal  contributor to the  increased  flux
 decline.   Several  efforts to recover this  flux decline were  made,
 including  daily  air and water flushing cycles  combined with  periodic
 cell depressurizations  as well as attempts to  create a "back diffusion
 potential" to reverse the permeate  flow through the  membrane. These
 methods were only  marginally successful as shown by  Figure 18.

      The most promising flux restoration was achieved  by flushing
 the  cell for one hour using a 0.7%  bioenzyme (BIZ) solution.   This
 procedure  resulted in recovery of 63% of the total flux  decline
 experienced during the  run.   Several attempts  to further improve
 the  cleaning efficiency during the  flushing cycles were  made following
 this initial su'ccess.   The most efficient  procedure  evaluated was to
 fill the desalination cell with a 0.35% bioenzyme solution at pH  9.7
 at a temperature of 25  to 30°C and  allow the cell to "soak"  for a
 period  of  45 minutes followed by a  15-to 30-minute high  velocity  flush
 at an average cell pressure of 50 PSIG.  The brine was recirculated
 without filtration during the flushing cycle which was conducted  at
 twice the  normal operating velocity.  The  TOC  and organic nitrogen
 removals accompanying the first five flushing  cycles are given in
 Table 11.

                              TABLE  11
                   REMOVAL OF TOC AND ORGANIC NITROGEN
                          FROM MEMBRANE  SURFACE
                  USING A BIOENZYME FLUSHING SOLUTION
Flushing
 Cycle
Initial Flushing
    Solution
0.35% Bioenzyme
In Product Water
     Reject Stream
After Completion of 45 min.
 Soak and 15 min. Flushing
          Cycle

1
2
3
4
5
TOC (Total) mg/1
62
44
67
69
93
ORG-N mg/l
1.1
0.4
1.1
2.1
4.0
TOC (Total) mjs/1
500
450
480
435
650
ORG-N mjj/1
80
71
25
44
94
     The appearance of the flushing stream changes from a light blue
color before flushing to a light brown turbid solution following the
flushing cycle.  Each flushing requires 20 gallons of water, ten of
which are contained in the cell, with the remainder used to fill the
                              - 36 -

-------
12
                      SALT REJECTION
                    FLUX (GFD)
   h
                                    CO
 8

 6

 4

 2

 0



                         I
    DP. • INDICATES CELL
        WAS DEPRESSURIZED
               32
                     48     M     80
                        TIME IN DAYS
     ir> co
                                                      -1100 =
                                                         90
                                                        80
                                                            UJ
                                                           CO
96
112    128
                         FIGURE 18
FLUX AND SALT REJECTION  PERFORMANCE OF AEROJET
        GENERAL FLAT PLATE CELL,  LEBANON, OHIO

-------
recirculating lines, pump and mixing tank.  The TOC and organic nitro-
gen levels shown in Table 11 are representative of the increase that
occurs during each cleaning cycle and illustrate the organic nature
of the membrane deposit.

     The TDS rejection capacity of the membranes remained relatively
constant at 92.1% during the run.  The repeated exposures of the
membranes to a pH of 9.5 during the cleaning procedures have shown
no adverse effect on membrane performance thus far.  Similarly, there
has been no evidence of biological degradation of the membranes.

     The third run with the Aerojet-General reverse osmosis unit was
conducted on lime-clarified secondary effluent.  System operating
pressure was maintained at 470 PSIG, with feed stream pH controlled
at 5.0 "t 0.2 units by the addition of sulfuric acid.  The feed and
product water quality data for this run are shown in Table 12.

                             TABLE 12
FEED AND PRODUCT
WATER QUALITY
(RUN #3)
Lime-Clarified Secondary Effluent


PO, as P
4
NCyN
N03-N
NH3-N
ORG-N
TOC
Turbidity
(JTU)
Feed

2.0
< 0.2
0.2
mo
3.0
20.8

7.5

High
0.1
0.4
0.4
1.7
1.6
9.0


Produc t
Average
0.1
< 0.2
0.1
1.1
0.7
2.8

< 0.1

Low
0.1
< 0.1
< 0.1
0.6
0.1
0.8



Ave.% Rejection
95
*
*
90
86
87

99
Results in mg/1 unless noted.
* Feed concentrations of NO«-N and NO--N are too low for meaningful
  rejection data.
     Membrane performance was satisfactory throughout this run with
TDS and TOC rejection averaging 92% and 87%, respectively.  The TDS
rejection and flux decline pattern are shown in Figure 19.

                              - 38 -

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  •
10
9
8
7
6
S
4

3
2
1
0
                 SALT REJECTION
FLUX (GFD)
         RAW ENZYME AND
         ENZYME DETERGENT
         COMBINATIONS
      7  8 9 10
   1 1 I  I 1 I
_l J_ 1 1 i
         2,2,3,32
          1 1  1 1
                                   RUN  -#3
                                   FEED-LIME CLARIFIED
                                       SECONDARY EFFLUENT
                                   PRESSURE-470 PSIG
                       1 1  1 1  1
1  1 1
0123
141511  1818202122232425
              353837383840414243444548
                          TIME IN DAYS
                         FIGURE 19
       FLUX AND SALT  REJECTION  OF AEROJET
     GENERAL FLAT PLATE CELL, LEBANON, OHIO
                                            100  *

                                                Cd
                                                LU
                                             90  =
                                                                 CO
                                                              80 >,o

-------
      Several  standardized  flushing  cycles were  employed during  this
 run  using  BIZ,  as well  as  a number  of raw enzyme  detergent  combinations.
 The  raw  enzymes used were  the protease-amylase  enzymes manufactured
 specifically  for the detergent  industry.  A  comparison of the relative
 effectiveness of these  enzymes  is presented  in  Table  13.  Although
 results  of these flushing  procedures  are not quantitative,  some  gene-
 ralities concerning the effectiveness of the enzymes  can be seen.

      The raw  enzymes appear to  be more effective  when used  with  a
 detergent.  Enzyme concentrations less than  35  mg/1 and detergent
 concentrations  less than 3500 mg/1  tend to limit  the  cleaning effec-
 tiveness for  a  service  interval of  24 hours.  The three enzymes
 evaluated  seem  to be equally effective in removing the organic  fouling
 layer.   An  enzyme/detergent ratio of  1 to 100 appears to be the  most
 effective  combination evaluated.  This ratio approximates the reported
 concentration of enzyme contained in  the BIZ  formulation.   The effect
 of pH has  not been well defined by  the evaluation but information from
 enzyme suppliers indicates that the optimum  pH  for the detergent
 enzymes  is  between 7.5  and 9.5.

      The percent flux increase  associated with  each flushing cycle is
 highly variable, depending on the amount and nature of the  organic material
 deposited during the previous service cycle.  A portion of  this  fouling
 layer seems relatively  easy to  remove as evidenced by the flux increase
 (6.3  to  7.4 GFD) resulting from the flush with  a  detergent  solution on
 March 3, 1969.  Following  completion  of this flushing cycle, a  BIZ
 solution resulted in an additional  flux recovery  (from 7.4  to 8.7 GFD).

      The average flux during this run was 7.6 GFD compared  to 8.7 GFD
 for Run  #2.   This decrease was  apparently due to  both the higher
 organic  and suspended solids load of  the feed and the less  efficient
 flushing cycles employed while  comparing the  raw  enzymes.

      The pressure drop  across the brine side  of the membrane increased
 from  an  average value of 20 PSIG for  Run #2  to  28 PSIG for  the present
 run.  This  increased pressure drop is  a result  of the higher suspended
 solids concentration of the feed stream which tends to accumulate in
 the feed channels.  Continued accumulation of these solids  is easily
 controlled, however, by the higher velocities associated with the
 flushing cycles.

      The fourth run with the Aerojet-General  flat-plate configuration
was conducted on secondary effluent.   This run, lasting 22  days, was
 interrupted after the llth day  for a  period of  60 days and  was then
resumed  for an additional eleven days.  The  system pressure  averaged
485 PSIG with the feed  stream pH controlled at  5.0 T  0.2 units during
 the run.  The desalination cell was stored in a 0.25% formaldehyde
solution during the 60-day shutdown to prevent  possible biological
hydrolysis  of the membranes.
                              - 40 -

-------
               TABLE 13
EVALUATION OF ENZYME FLUSHING SOLUTIONS



Date
2/11/69
2/13/69
2/14/69
2/18/69
2/20/69
2/25/69
2/26/69

2/27/69

2/28/69

3/1/69

3/2/69

3/3/69
3/3/69
3/4/69
3/5/69



Flushing
Solution
BIZ
BIZ
BIZ
HT-Proteolytic
HT-Proteolytic
HT-Proteolytic
HT-Proteolytic
with TIDE
HT-Proteolytic
with TIDE
Milezyme
with TIDE
Milezyme
with TIDE
Milezyme

TIDE
BIZ
BIZ
WT-2
with TIDE

Service
Preceding
Flush in HRS.
24
48
24
24
48
24
24

24

24

24

24

24
0
24
24
24
Concentration
of Flushing
Solution in
PPM
3500
3500
3500
3.5
10
10
35
10
35
3500
35

35
500
10
500
3500
3500
3500
35
3500

pH of
Flushing
Solution
9.5
9.5
9.4
5.2
5.2
9.4
7.0
_
8.8
-
8.8

8.6

8.6

8.8
9.4
9.5
8.8



Flux in


GFD
Before-After
7.6 -
6.5 -
7.8 -
7.4 -
6.8 -
6.8 -
6.8 -

6.0 -

6.8 -

6.8 -

6.5 -

6.3 -
7.4 -
6.6 -
6.8 -

9.6
9.1
9.1
8.4
8.3
8.2
8.0

8.4

8.4

8.4

7.6

7.4
8.7
8.9
8.3



% Flux
Increase
26.3
42.0
16.3
13.5
22.0
20.6
17.5

40.0

23.6

23.6

17.0

17.5
17.5
35.0
22.0


Membrane
Rejection
Performance
Good
Good
Good
Good
Good
Good



Good
Good

Good

Good

Good
Good
Good
Good


-------
      The rejection  performance  of the  cell  is  shown in Table  14  for
 both the period  preceding and  following the shutdown.   In general,
 rejection of the divalent ions  was greater  than 94% while the rejec-
 tion of the  monovalent  ions  was varied from 80 to  90%.

      The effect  of  the  60-day  storage  on membrane  performance is
 somewhat anomalous.   The  TDS rejection declined from 91.5% before
 storage to 86% after  storage,  a drop of 5.5% as measured  directly
 (by evaporation  of  composited  feed and product water samples).
 Conductivity measurements show  this decline to be  9.3%,  from  90.3%
 before  storage,  to  81%  after storage.   This apparent discrepancy can
 be  resolved  by considering the  increasing percent  rejection that
 occurred following  the  storage  period  as shown by  Figure  20,  and by
 noting  that  the  TDS samples  were composited during the 20th and  23rd
 day.  Conductivity measurements on the product water from the indi-
 vidual  modules indicated  the decrease  in membrane  performance was a
 result  of a  generalized condition, exhibited by all eight modules
 rather  than  a localized condition. The increase in rejection per-
 formance with time may  result  from the "healing" of imperfections
 present in the membrane.   This  rationale presumes  that previously
 deposited organic materials  were leached out during the  storage  period,
 thereby causing  the increase in salt permeation.

      Organic rejection, as measured by TOC,  increased  slightly from
 89% to  94% during the storage period.   No particular significance can
 be  attached  to this increase, however,  in view of  the  relatively low
 TOC levels involved.

      The flux decline characteristics  for this run are shown  in
 Figure  20, and indicate that a  moderate flux decline can  be maintained
 by  employing a one-hour daily enzyme flush.

      It  should be noted that the  quality  of  the  secondary effluent
was  exceptionally good during this  run  with  TOC  averaging 14.9 mg/1
 for  the  first 11 days and  8.3 mg/1  for  the remaining 11 days.  Feed
 turbidity  similarly decreased from an  average  of 6.1 JTU  during  the
 first half of the run to  2.4 JTU  during the  last half  of  the  run.

      The  fifth run was made  on  primary  effluent.   This run was con-
ducted  at  an  average operating  pressure of 480 PSIG  with  a  feed
stream  pH  of  5.0 1" 0.2 units.   The  flux decline characteristics  and
rejection performance for  this  run  are  shown in Figure 21.  The  flux
declined  from a daily average of  5.4 GFD  on  the  third  day of  operation to
3.8 GFD on the 12th day.   This  represents a  30% decline in  flux  that
occurred  in nine days with daily  bioenzyme  flushing.   The  5.4 GFD
 is  significantly lower  than  the daily  average  of 7.8 GFD  that was main-
tained during the run on  secondary  effluent.   The  feed and product
water quality data for this run are presented  in Table 15.  The  TDS
rejection decreased from  a high of  90%  to a  low of 84% during this
run.  This decline in rejection is not  surprising  in view of  the
lower flux and poor distribution  of the  feed caused  by plugging of
the feed channels.

                                - 42 -

-------
.p-
oo
                                                       TABLE 14


                                           FEED AND PRODUCT WATER QUALITY

                                                      (Run #4)

                                                  Secondary Effluent



                                    Before 60-day Shutdown                After 60-day  Shutdown
Constituent

Calcium (Ca)
Magnesium (Mg)
Sodium (Na)
Potassium (K)
Iron (Fe)
Manganese (Mn)
Phosphate (PO.asP)
Sulfate(SO.)
Chloride (Cl)
Silica (SiO.)
Nitrite (NOp
Nitrate (NCp
NH_-N
Organic-N
Total Alk. (CaCO_)
TDS (Conductivity
TDS (Evaporation)
TOC (Unfiltered)
Turbidity (JTU)
Cone.
Feed
104
30.5
95.5
8.5
<0.3
<0.1
6.6
113
133
12.4
<0.2
<0.2
8.7
2.1
332
-
726
14.9
6.1
in mg/1*
Product
5.2
0.4
15.0
1.5
<0.3
<0.1
0.4
14
26
4.1
<0.2
<0.2
1.7
0.3
39
-
66
1.7
<0.1
7o Rejection

95
99
84
82
-
-
94 (1)
88C1)
81
67
-
-
80
86
88
90.3
91.5
89
-
Cone.
Feed
110
28.6
91.0
8.2
0.3
-
6.8
107
131
13.8
-
8.6
1.0
0.9
326
-
644
8.3
2.4
in mg/1*
Product
2
.5
14.0
1.3
0.1
-
0.6
7
26
3.4
-
4.7
0.3
0.1
40
-
88
0.5
<0.1
% Rejection

98
98
85
84
-
-
91
93
80
75
-
45
-
89
88
81
86
94
"•
% Change

+3
-1
+1
+2
-
-
-3
+5
-1
+8
-
-
-
+3
0
-9.3
-5.5
+5
~
       *  Average of two 24-hour composite  samples .


       (1) Feed water sample taken before addition of  H-SO, .

-------
       	.	•-"—-*_   SALT REJECTION
  10

O 8
ik

2*
X 4
D
£ 2
  0
FLUX (GFD)
     KjANNSTv
                                RUN - #4
                                FEED - SECONDARY
                                     EFFLUENT
                                PRESSURE - 485
                                          PSIG
BEFORE 60 DAY
SHUTDOWN
       AFTER 60 DAY
       SHUTDOWN
                                                  90
                                                        80
                                                        70
                                            V)

                                            fc?
    0  2
       6  8  10  12  14  16  18 20 22  24  26 28 30 32
                   TIME IN DAYS
                    FIGURE 20
          FLUX AND SALT REJECTION PERFORMANCE
     OF AEROJET GENEUl FLAT PLATE CELL. LEBANON, OHIO

-------
  9

  8

  7

0 6
u.
® 5
Z
X
2 3
Ik
  2
  1h
      \
SALT REJECTION
_.—-^
 FLUX IN (GFD)
                    RUN -#5
                    FEED - PRIMARY
                          EFFLUENT
                    PRESSURE - 480 PSIG
                                12
                     14
16
               Z
            90 2
               
18
'024     6    8    10
                 TIME IN DAYS
                      FIGURE 21
    FLUX AND  SALT REJECTION  PERFORMANCE OF
AEROJET GENERAL FLAT PLATE  CELL, LEBANON, OHIO

-------
                             TABLE  15


                    FEED &  PRODUCT  WATER QUALITY
                              (Run #5)
                          Primary Effluent

Constituent                         Concentration mg/1

Calcium (Ca)
Magnesium (Mg)
Sodium (Na)
Potassium (K)
Iron (Fe)
Manganese (MN)
Phosphate (PO^as P)
Sulfate (S04)
Chloride (Cl)
Silica (Si02)
Nitrate (NO )
Nitrite (N03)
NH3-N
Organic-N
Total Alkalinity (as CaCCO
TDS (Conductivity)
TDS (Evaporation)
TOG (Unfiltered)
TOC (Filtered)
Turbidity (JTU)
Feed
mg/1
138
30.7
141
11.0
1.5
*
9.7
173
168
26.7
*
*
12.5
6.4
395
-
917
97
35.0
52.0
Product
mg/1
2.0
0.4
24.7
2.6
0.1
*
0.4
5
47
6.0
*
*
2.1
0.6
23
-
128
13.4
12.0
< 0.1
% Rejection
99
99
82
76
93
-
96
97(D
72
80
-
-
83
91
94
86
86
89
66
-
*  Concentration < 0.1 mg/1.
(1) Feed water sample taken before addition of H.SO,.

(2) Feed filtered through glass-fiber  filter paper, Type  1106  BH,
    Mine Safety Appliances  Company, Pittsburgh,  Pennsylvania.
                              - 46 -

-------
     The most notable change in operating conditions during this run
was the more pronounced pressure drop that was experienced across the
desalination cell.  This drop ranged from a low of 40 PSIG after the
daily flushing to over 80 PSIG near the end of the daily service cycle.
In many cases it was necessary to decrease the velocity of the feed
stream to maintain the pressure drop across the cell to values less
than 100 PSIG.  This lower brine velocity may have significantly
affected the flux decline rate resulting in a distorted comparison
to the performance characteristics exhibited by the previous feed
streams.

     A comparison of the rejection of principal constituents for the
five runs conducted at Lebanon is shown in Table  16.  These results
indicate that the rejection performance was similar for the waste
streams evaluated.

                             TABLE 16
                 SUMMARY OF REJECTION PERFORMANCE
                               FOR
                      LEBANON WASTE STREAMS
Constituent     Run #1    Run #2    Run #3    Run #4    Run #5
P04 as P
NCyN
NH3-N
Organic-N
TOC
TDS
Turbidity(JTU)
*
*
*
*
*
90
*
91
68
88
89
85
92
99
90
63
89
78
89
92
99
93
*
80
87
94
91**
99
96
*
83
91
89
90
99
*  Feed concentration too low  for meaningful  rejection  data.
** TDS rejection before 60-day storage period.
     Experience has shown that  the  time-dependent  flux  decline
pattern of a membrane system operated on  a  feed  containing  both
organic and inorganic solutes at constant pressures  can be  linearized
by plotting log flux vs  log time; the slope of  the resulting  straight
line of best fit  is commonly referred to  as the  "flux decline slope"
and is used to quantitatively describe  the  change  in flux with  time.
                               -  47  -

-------
     The flux decline slopes for Runs #1 and #2 are compared in
Figure 22.  The differences in the flux decline slopes for these
two runs indicate the effect of carbon adsorbable material on flux
decline.  It should be remembered that the feed for both Runs #1
and #2 was passed through a 5 micron cartridge filter prior to en-
tering the desalination cell.  This, combined with the increased
feed TOC exhibited by Run #2, supports a positive role for soluble
and colloidal organic carbon in causing flux decline.

     A similar comparison of flux decline slopes for Runs #3, #4,
and #5 is presented in Figure 23.  These runs were made after removal
of the 5 micron filters and reflect the effect of the particulate
material in the respective waste streams.  It is encouraging to note
that, by employing a one-hour bi-daily cleaning schedule for Run #3 -
lime-clarified effluent, and a daily cleaning schedule for Run #4 -
secondary effluent, respective flux decline slopes of -0.03 and
-0.04 could be maintained.  These slopes are less than the slope of
-0.05 experienced when operating on carbon column effluent, a much
higher quality water.  These data support the concept of controlling
membrane fouling by employing periodic cleaning procedures as an
alternate to pretreating the feed to prevent fouling.

     The importance of maintaining a reasonable flux decline slope
and membrane lifetime can be seen from an examination of Table 17.
                             TABLE 17
     FLUX DECLINE SLOPE                   ACCUMULATIVE 7. LOSS OF
    LOG FLUX VS LOG TIME                 ORIGINAL FLUX AFTER YEARS

-0.01
-0.05
-0.10
(1)
5
25
44
(2)
5.5
28
47
(3)
6
30
51
     The flux decline characteristics shown above indicate that the
first-year flux decline represents well over 80% of the decline that
may be expected for any reasonable membrane lifetime and that the
one-year flux value would provide a rational design figure.
                              - 48 -

-------
    2.6
     2-
0
o
z
X
 10-
 9
 8
 7

 6 -

 5


 4-



 3-

2.5-


 2-


1.5-
             RUN •  #1    LIME CLARIFIED, FILTERED, CARBON TREATED
                        SECONDARY EFFLUENT, FLUX DECLINE SLOPE = -0.05
TURBIDITY
   JTU

TOC mg/l
          MEMBRANE
          CLEANING
                                       RUN - #2 LIME CLARIFIED, FILTERED SECONDARY
                                                EFFLUENT FLUX DECLINE SLOPED -0.14
               FEED CONDITIONS
RUN #1
  0.5


  1.0

 NONE
RUN #2
  1.3

 10.6

 NONE
       1     10   22.63   4   S678910     10   2263    4  66789 1O
                                     TIME IN  DAYS
                                      FIGURE  22
                COMPARISON OF FLUX DECLINE SLOPES FOR EXPERIMENTAL
       RUNS #1 AND #2, USING AEROJET GENERAL FLAT PLATE CELL, LEBANON,  OHIO

-------
2.5.

2 •


1.5-
       SUMMARY OF OPERATING CONDITIONS
        TURBIDITY    TOG   FLUX DECLINE
          JTU
                SLOPE
            FLUSHING
            INTERVAL
RUN #3    7.4
RUN #4    6.1
RUN #5   52
       20.8
       14.9
       97
-0.3
-0.04
-0.19
48 HRS.
24 HRS.
24 HRS.
                                                 RUN #5
                                                              RUN #3
                                                            RUN #4
                             i  tiii
                                   J	I
        1J5
 2.5 3
507891O     15   2
      TIME IN DAYS
        2.5 3
        6 7 8 9 10
                                 FIGURE 23
  COMPARISON OF FLUX  DECLINE SLOPES FOR EXPERIMENTAL  RUNS 3, 4 &  5
        USING AEROJET GENERAL FLAT PLATE CELL, LEBANON, OHIO

-------
       DISCUSSION AND INTERPRETATION OF PILOT PLANT RESULTS
     The foregoing experiences in operating small reverse osmosis
modules on variously treated waste streams have demonstrated, in
all cases, that excellent separation of the contaminants of major
concern can be achieved.

     In general, the membranes were found capable of rejecting 93 to
95% of the total dissolved solids, 95 to 99% of the phosphate, 80 to
90% of the ammonia nitrogen, 60 to 70% of the nitrate nitrogen, 99
to 100% of the particulate matter, 90 to 95% of the total organic
carbon and greater than 907<> of the COD.  The rejection performances
exhibited by the three types of modules evaluated were similar, with
the small observed differences being attributed to intrinsic differ-
ences in the membranes evaluated.

     In many cases, the studies were conducted with prototype units
which resulted in an initially high incidence of mechanical failures.
Many of the earlier malfunctions have been eliminated by design
changes resulting in much improved equipment.

     All of the experiments were conducted with modules equipped with
membranes designed for the conversion of "brackish water," which is
characteristically low in organic content and much higher in IDS
than the normal municipal wastewater streams of  interest.

     Work conducted early in  the program showed  that  pH  control  of the  feed
was necessary to control the precipitation of calcium carbonate, even
at moderate recovery ratios.  Possible precipitation  of  a complex
calcium phosphate at 80% recovery was noted once during  the investi-
gation, and was controlled by reducing the pH of the  brine to 5.0
from an original value of 5.5.  No further instance of inorganic
fouling was observed during the investigation.

     Organic fouling of the membranes was experienced in all  of  the
experimental runs and can be  cited as the principal cause of  the  flux
declines that occurred.  There is considerable interest  and some
controversy at  the present  time regarding the principal  cause of
organic fouling.  The major argument centers around  the  correct
identification  of the class of material responsible  for  flux  decline
due to  fouling.  Most investigators  agree that the material is organic
in nature but dispute the particle size and  size distribution respon-
sible  for the observed declines.  Experimental evidence,  including
data reported herein, can be  cited that supports equally well both
sides  of  the issue  in question.   The argument  is partially academic
when one  realizes the diverse nature of raw  and  treated  wastewaters
which  are candidate  feeds  for treatment by reverse  osmosis._,These „
streams encompass a particle  size range  that varies  from 10    to 10
microns with molecular weights  that  range  from less  than one  hundred
                               - 51 -

-------
 to  several million.  Attempts to characterize these waste streams as
 the  first step  in understanding the interfacial phenomena and
 fouling mechanism that occur at the membrane surface have not been
 successful,  largely because of the complex nature of the waste.  It
 is becoming  increasingly clear, however, that soluble, colloidal,
 and  suspended species are all fundamentally involved in the fouling
 that takes place at the membrane surface.  Figure 22 shows that even a
 water  free of gross particulate matter  (turbidity of 1.3 JTU) exhibits
 a fouling potential sufficiently high to prohibit economic treatment
 by a membrane separation process unless some provision is made to
 control deposition of the fouling material, which can range from mole-
 cularly disperse systems through the colloidal range to the larger
 suspended particles.

     The most successful approach in controlling the organic fouling
 of reverse osmosis membranes employed to date is to routinely depres-
 surize the unit and to flush the brine sides of the membranes using
 the enzyme detergent flushing solution previously described.  Success
 of the method may be due to protein hydrolysis of a slime layer that
 is physically deposited during operation coupled with the dispersing
 and cleaning action of the accompanying detergent.  This concept is
 supported by investigations conducted at the Pomona Pilot Plant by
 Gulf General Atomic under FWQA Contract No. 14-12-181.

     Although very little investigation of the hydrodynamic factors
 affecting fouling was conducted under this program, limited experi-
 ences with superficial velocity increases during the cleaning opera-
 tions on the flat plate unit at Lebanon indicate some promise for
 this approach.  Experimental investigations conducted at the Oak
 Ridge National Laboratory on filtered and unfiltared lake water indi-
 cate that substantially lower flux decline rates can be achieved by
 increasing the axial velocity in a 1/2" diameter tube.  Additional
 studies employing turbulence promoters have shown promise of improving
 the efficiency of water transport through a cellulose acetate membrane (7)

     A fundamental question in utilizing either increased velocity or
 turbulence promoters is whether these approaches will offer an econo-
mic advantage when the greater pumping cost is balanced against the
 increased productivity.  Perhaps the greatest advantage will be
 realized in periodically increasing the velocity during a flushing
 operation.  The question of membrane attrition must be dealt with
 and may prevent the continued use of axial velocities greater than
 3-5 ft/sec (6).  Preliminary investigation of fouled modules taken
 from the Universal Water Corporation unit operating on carbon-treated
 secondary effluent at Pomona, California showed some evidence of
physical attrition of the membrane near the end of the module.  The
 severity of this type of problem has not been fully assessed at this
 time and will require further investigation (8).
                              - 52 -

-------
                CONTRACT AND RELATED INVESTIGATIONS
     In addition to the above-mentioned pilot-plant investigations,
the FWQA has supported, in cooperation with other government agencies,
a great deal of contract research in reverse osmosis.

     This research has been directed toward three goals; the develop-
ment of improved high-flux membranes tailored specifically for waste-
water renovation, investigation of new methods to control flux decline
due to organic fouling of the membranes, and improvements in modular
design and contacting systems.

     Improved cellulose acetate membranes for wastewater renovation
have been developed in the laboratory by two investigators.  North
Star Research and Development Institute, under Contract No. 14-12-587,
investigated the application of ultrathin membranes  (200-2000 A) for
the renovation of municipal effluents.  These ultrathin membranes
were prepared on polysulfone supports and demonstrated 600 PSI fluxes
of 58 to 91 OFD with salt rejections of 76 to 86% when tested in the
laboratory against a 0.1% sodium chloride solution.  These membranes
were tested with filtered secondary effluent and demonstrated average
fluxes of 17 to 38 GFD, depending on the pore size of the filter used
to pretreat the feed.  Evidence indicated that particles smaller than
1 micron were responsible for nearly 80% of the observed flux decline.
It was also demonstrated that about one quarter of this decline could
be eliminated by chemical clarification of the feed  followed by
passage through a 1 micron filter.

     Another contractor, Aerojet-General Corporation, working with
assymetric  cellulose  acetate  films  under Contract  No.  14-12-553,
developed three classes of membranes  suitable  for  wastewater  renova-
tion.  One membrane,  a crosslinkable  cellulose acetate  methacrylate
 (CAM) membrane, synthesized by methacrylation  of Eastman Type E-360-60
cellulose acetate having a degree of  substitution  (d.s.)  of  2.09  to
2.12  to a  total d.s. of 2.34 to 2.39,  produced  700  PSI fluxes  of  70
to  90 GFD with a TDS  rejection of 80  to 90% when tested in  the  labora-
tory in flat sheet  form against  a synthetic  feed solution.

     Another membrane formulation using Eastman  E-383-40 cellulose
acetate as  the base polymer with a  d.s. of 2.28  produced 600  PSI fluxes
of  64 to 105 GFD with a sodium chloride rejection  of 61  to  67% when
tested in flat sheet  form against a 0.1% sodium chloride solution.

     The third class  of membranes,  a  blend of  diacetate and triacetate,
produced 600 PSI  fluxes of 60 to 70 GFD with  a sodium chloride  rejec-
tion of 70  to 80%.
                               -  53 -

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     These  three classes of membranes were all tested on secondary
 effluent and demonstrated satisfactory rejection of both organic
 and inorganic species of interest.  The flux of these membranes was
 sharply reduced by organic fouling when tested without cleaning.
 It was demonstrated, however, that average fluxes as high as 50 GFD
 could be sustained when processing secondary effluent by periodically
 cleaning the membrane with an enzyme solution.

     The above results are encouraging and indicate that, by
 sacrificing a small amount of salt rejection, the intrinsic flux of
 reverse osmosis membranes can be substantially increased.  It was
 also shown  that as the membrane flux increases the fouling problem
 becomes more severe.

     The problem of membrane fouling has received attention from
 several investigators.  Aerojet-General, under Contract No. 14-12-184,
 conducted an extensive investigation of pretreatment procedures as
 a means of controlling flux decline due to fouling.  This study
 involved over ninety controlled experiments to evaluate the effects
 of feed quality and pretreatment on flux decline.  Several classes
 of feed additives such as chelating agents, dispersants, and floccu-
 lating agents were evaluated on a number of waste streams including
 primary effluent, secondary effluent, and carbon-treated secondary
 effluent.  In general, the flocculating agents were found to be the
 most successful cleaning agents, especially when followed by rapid
 sand filtration as a pretreatment for reverse osmosis.

     Another approach taken by Gulf General Atomic, under Contract
 No. 14-12-181, was the examination of flushing procedures that can
 be periodically employed during operation to limit flux decline to
 acceptable levels.  Gulf General Atomic first used the enzyme presoak
 formulations as membrane cleaning agents to aid in the removal of
 organic slimes.  This has proven to be the most successful method
 presently available to maintain reasonable fluxes when treating
 wastewater.

     Other methods of controlling membrane fouling under considera-
 tion are the periodic or sustained use of higher brine velocities,
 the use of integral and detached turbulence promoters, gas bubble
 generation at the membrane surface, generation of electric current
 at the membrane surface, charged membranes, and membranes containing
 attached enzymes.  Of these methods, turbulence promoters, charged
membranes, and periodic velocity increases appear most promising.

     In addition to the development of high-flux membranes and
 fouling control techniques, there is some interest in developing
more efficient modules and module configurations in an effort to
 lower the capital cost of reverse osmosis systems.
                              - 54 -

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     Developments in this area include studies of in-situ membrane
replacement, cast-in-place membranes, membrane regeneration techniques,
and replaceable membranes for the popular configurations.  Also under
study is the development of new module configurations that employ
hollow fibers spun from cellulose acetate.  These promise a substan-
tial increase in module productivity, but are just entering the
deve1opment stage.
RELATIVE POSITION AND FUTURE ROLE OF REVERSE OSMOSIS IN RENOVATING
                            WASTEWATER

     At the present time, the role of reverse osmosis in the
reclamation of wastewater is not clear.  Factors that will affect
the utility of this process are three-fold; first - the need to
demineralize wastewater for reuse applications; second - the economic
attractiveness of reverse osmosis when compared to competing proc-
esses such as ion exchange, electrodialysis, distillation for the
demineralization of wastewater on an equitable basis;  and finally
the potential of using reverse osmosis as a pollution control device
with discharge to a receiving stream.

     Since each domestic use of a water supply adds 300 to 400 mg/1
of IDS it is clear that continued reuse of a single supply will
require demineralization.  The amount of demineralization required
to maintain drinking water quality standards of 500 mg/1 TDS will
depend upon the TDS concentration of the source and the consumptive
use ratio of the particular community.  A recent study sponsored by
the Office of Saline Water (9) indicates that, of the  approximately
20,000 communities in the United States, about one-half are served
by public water supply systems.  The study further estimates that
the water distributed through over 98% of these community water
systems has a total dissolved solids content below the USPHS standard
of 500 mg/1.  Municipal water use figures in the United States
indicate that the consumptive use averages about 13%  (10).  Wide
variation in this figure occurs with as high as 50% comsumption
recorded in some arid or semi-arid regions.  At the latter locations,
demineralization of wastewater for reuse at 907,, volumetric recovery
will require about 25% make-up water and a demineralization effi-
ciency of 60% except for nitrogen.

     There have been several cost estimates made for  the competing
processes under consideration for the demineralization of waste-
water.  These include ion exchange, electrodialysis,  distillation
and reverse osmosis.  Of these, ion exchange and reverse osmosis
appear to offer an economic advantage over electrodialysis and
distillation.  A recent cost study made by the County Sanitation
 Districts  of Los Angeles County compared the cost, exclusive of brine
 disposal,  of electrodialysis,  ion exchange and reverse osmosis for the
                               -  55  -

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demineralization of 1000 mg/1 IDS water to 667 mg/1 IDS  (11).  In
this study, the feed to each demineralization process was carbon-
treated secondary effluent.  The total flow from the carbon adsorption
columns was treated by the electrodialysis unit for a total cost of
26.9C/1000 gallons including the cost of the carbon pretreatment.  The
cost for ion exchange and reverse osmosis was based on demineralizing
377o of the carbon column effluent and blending the product water with
carbon column effluent to achieve a blended product quality of 667 mg/1
IDS.  The total cost of the blended product for these two processes
including carbon pretreatment was 19.5c/1000 gallons for ion exchange
and 24.8c for reverse osmosis.  This study indicates an advantage for
ion exchange for the demineralization of carbon-treated secondary
effluent.  The cost for reverse osmosis used in this study was based
on an average flux of 10 GFD for a membrane lifetime of two years.
Using the same assumptions, but increasing the flux to 15 GFD (a
demonstrated flux rate for carbon-treated secondary effluent) decreases
the cost for reverse osmosis to 20.Sc/1000 gallons.  In general, the
cost of reverse osmosis is quite sensitive to flux rate, membrane life-
time and membrane cost.  Another consideration is that, depending on
the intended reuse of the demineralized water, the carbon adsorption
pretreatment could be replaced with mixed-media filtration as pre-
treatment for reverse osmosis for an additional savings of 5c/1000
gallons.

     Consideration of the successive elimination of required pretreat-
ments poses the question, can reverse osmosis be considered a potentially
useful AWT process if demineralization for reuse is not the principal
objective?  It has generally been accepted that treatment of municipal
wastes by reverse osmosis with discharge of product to a receiving
stream is not practical.  A little reflection, however, can demonstrate
a potential in this area.  The total costs for a conventional biologi-
cal treatment system followed by tertiary processes for nutrient and
residual organic removal are given below for a 10 MGD plant (12).
               Treatment                       Total Cost
                 Step                          c/1000 gal.

               Primary                             6.2
               Activated Sludge                    4.8
               Lime Clarification                  7.8
               with Recalcination
               Ammonia Stripping                   3.6

               Filtration Through Sand or
               Graded Media 4 gpm/sq ft            2.8

               Activated Carbon Adsorption        10.2
                          TOTAL                   35.4

                              - 56 -

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     Examination of the treatment sequence and associated costs  suggest
several possible treatment schemes incorporating reverse osmosis.
Several possible combinations and the corresponding competitive costs
for reverse osmosis are presented in the following table.

Pretreatment and          Cost for Reverse Osmosis             Total
Associated Cost         to be Competitive c/1000 gal           Cost

Primary           6.2              29.2                        35.4

Primary and
Sand Filtration   9.0              26.4                        35.4

Primary and
Activated Sludge 11.0              24.4                        35.4

Primary and
Activated Sludge
and Sand
Filtration       13.8              21.6                        35.4
     This comparison clearly indicates that  for  reverse  osmosis  to
become competitive, it should be employed near the primary end of a
treatment train.  For the situation outlined above, the application of
reverse osmosis to primary or filtered primary effluent at a cost of
29.2 and 26.4 cents per thousand gallons of treated water appears
competitive with present-day technology for achieving similar water
quality.

     The cost of brine disposal must be included in the cost of
reverse osmosis treatment, and, in many cases, may prove to be a
limiting factor in inland areas.  A recent investigation of the dis-
posal of brines produced in the renovation of municipal wastewater
was conducted by Burns and Roe, Inc. under FWQA Contract No. 14-12-492.
This study indicated that brine disposal cost varies from $0.052/1000
gallons to SO.76/1000 gallons for solar evaporation of a Colorado River
water source near Denver.  Brine disposal  at  Tucson, Arizona is  esti-
mated at $0.13/1000 gallons by  deep-well injection.  Another study of
deep well disposal of desalination brine waste was conducted by  Dow
Chemical Company under OSW Contract No. 14-01-0001-1691  and reported
in Research and Development Program Report No. 456.  This study
estimates the cost of deep-well injection  to  vary  from 2.5C/1000
gallons at Arkansas City, Kansas to 35C/1000  gallons for Morgan,
Colorado.  The  cost of inland brine disposal, whether by deep-well
injection or by solar evaporation, is highly  variable depending  on
local geologic  and climatic conditions  as  well as  on current land uses
and value.  In particular, disposal of  reverse osmosis brines will
undoubtedly require some  form of pretreatment to remove  the organics,
especially if applied to wastewater streams  such as primary or filtered
primary effluents.

                              - 57 -

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     The reverse osmosis process, barely ten years old, developed
primarily as a demineralization process is now competitive for that
purpose.  Present day costs of this process are prohibitively high
for water renovation, unless a high premium is placed on the need
to demineralize wastewater for reuse.  Recent emphasis by FWQA in
supporting development of membranes and membrane systems specifically
designed for wastewater treatment, the progress being made in control-
ling organic fouling, and technological improvements being made by
the industry itself should substantially improve the posture of
reverse osmosis in the foreseeable future.  Widespread use of this
process will ultimately depend, of course, on the economic advantage
that will be demonstrated over competing processes in any particular
treatment scheme.
                              -  58  -

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                            REFERENCES
1.  Reid, C.E. and Breton, E.J., Applied Polymer Science, 1, 133,
     (1959).

2.  Loeb, S.J. and Sourirajon, S., "Sea Water Demineralization by
    Means of a Semipermeable Membrane," Department of Engineering,
    University of California, Los Angeles, Report No. 60-60  (1961).

3.  Loeb, S. and Sourirajon, S., Advanced Chemistry Series.  38,
    117  (1963).

4.  Loeb, S., Sourirajon, S., and Weaver, D.E., U. S. Patent No.
    3,133,137  (May 12,  1964).

5.   "Reverse Osmosis  as  a Treatment  for Wastewater," - A final
    report  to U. S. Public Health Service, Contract No. 86-63-227,
    Report  No. 2962  (January 1965).

6.  Bray, D.T. and Merten, U., "Reverse Osmosis for Water Reclamation,"
    General Atomic Division, General Dynamics Corporation, Augustas,
    Max,  County  Sanitation Districts of Los Angeles County.

7.   Sheppard, J.D. and  Thomas, D.G., "A Study of  a Hydrodynamic  Aspect
     of Reverse Osmosis," (Hyperfiltration) Monthly Reports,  July 15,
     1968  to March  15, 1970, OSW  Contract No, 14-01-0001-534.

8.   Personal Communication from  James  Gratteau, Project  Engineer,
    Research and Development, Los Angeles County  Sanitation  District,
     Los Angeles, California.

9.   Office  of  Saline  Water Research  and Development Report  462,
     "Communities of  Over 1000 Population with Water Containing in
     Excess  of  1000 PPM of Total  Dissolved Solids."

10.   Senate  Select  Committee on National Water Resources, Water Resource
     Activities  in  the U. S. Water  Supply  and Demand,  Committee Print
     No. 32, (1960).

11.   Carry,  C.W., "Demineralization  of  Wastewater  by  Electrodialysis,
     Ion Exchange,  and Reverse  Osmosis,"  Presented at  the 42nd Annual
     Conference of  the Water  Pollution  Control  Federation,  Dallas,
     Texas,  October,  1969, Session  No.  9.

12.   Middleton,  P.M.,  "Advanced  Treatment  of Municipal Wastewaters in
     the United States of America," Presented  at the  Biennial Conference
     of the South African Branch of the Institute  of Water  Pollution
     Control,  Capetown, South  Africa (March  19,  1970).
                               - 59 -

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1
Accession Number
w
5
2

Organization Environmental
Federal Water
Subject Field &
05D
Protection
Oualitv Adi
Group
SELECTED WATER RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
Agency
ninistration



              Municipal Treatment Research Program
              Advanced Waste Treatment Research Laboratory,  Cincinnati,  Ohio
    Title
              RENOVATION OF MUNICIPAL WASTEWATER BY REVERSE OSMOSIS
 10
    Authors)
          Smith, John M.
          Masse, Arthur N.
          Miele, Robert P.
                                 16
Project Designation
         ORD-17040---05/70
                                 21
                                    Note
 22
     Citation
 23
 Descriptors (Starred First)
 *Reverse osmosis, *Desalination processes,  *Membranes,  *Demineralization, *Semi-
  permeable membranes, osmosis, separation  techniques, pressure, membrane processes,
  water reuse, water renovation, wastewater treatment, fouling, organic fouling
 25
 Identifiers (Starred First)
 *Ultrafiltration, *Cellulose acetate membranes,  *reverse osmosis modules, Hyper-
  filtration, Water conversion, Reverse  osmosis modules tubular, Reverse osmosis
  modules spiral wound, Flux, Flux  decline
IT
 Abstract
      The increasing demand  for clean water  makes clear the need for improved treat-
ment of municipal wastewater.  Deliberate reuse of wastewater requires efficient
removal of "residual" organic and  inorganic  solutes.  A common and effective approach
has been to supplement biological  processes  with chemical and physical processes
that, together, are capable  of achieving water quality consistent with reuse require-
ments.  A more direct approach is  to use a single process such as reverse osmosis which
exhibits a potential to  separate a broad spectrum of contaminants from primary and
secondary effluents.
      The pilot plant studies reported  herein were addressed toward defining the
problems associated with the reverse osmosis processing of variously treated waste-
waters.  The effects of  feed water quality on membrane performance were evaluated,
as were methods to control membrane fouling.  A comparison of three configurations;
flat plate, spiral-wound, and tubular was made to determine their relative merit in
treating wastewater.  Finally, a cursory examination of costs was made.

                                                    (Smith-FWQA)
AbstTotin M. Smith
                           Institution
                                   Federal Water Quality Administration
  WR:'02 (REV. JULY 1969)
  WRSIC
                         SEND. WITH COPY OF DOCUMENT. TO: WATER RESOURCES SCIENTIFIC INFORMATION CENTER
                                                   U.S. DEPARTMENT OF THE INTERIOR
                                                   WASHINGTON. D. C. 20240
                                                                               * GPO: 1970-389-930

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