EPA-670/2-73-076
SEPTEMBER 1973
                        Environmental Protection Technology Series
  Selective Nutrient  Removal

  From Secondary Effluent
I
55
o
\
                                                 LU
                                                 O
                                  Office of Research and Development

                                  U.S. Environmental Protection Agency

                                  Washington, D.C. 20460

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                    RESEARCH REPORTING SERIES
Research, reports of the Office of Research and Development,
Environmental Protection Agency, have been grouped into five
series.  These five broad categories were established to facili-
tate further development and application of environmental
technology.  Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in
related fields.  The five series are:

     1.  Environmental Health Effects Research
     2.  Environmental Protection Technology
     3.  Ecological Research
     4.  Environmental Monitoring
     5.  Socioeconomic Environmental Studies

This report has been assigned to the ENVIRONMENTAL PROTECTION
TECHNOLOGY series.  This series describes research performed to
develop and demonstrate instrumentation, equipment and methodology
to repair or prevent environmental degradation from point and
non-point sources of pollution.  This work provides the new or
improved technology required for the control and treatment of
pollution sources to meet environmental quality standards.

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                                                 EPA-670/2-73-076
                                                 September 1973
SELECTIVE  NUTRIENT REMOVAL FROM SECONDARY EFFLUENT
                         by

                  John L. Eisenmann
                  J. Douglas Smith
               Contract No. 14-12-179
               Project No. 17010  FBJ
               Program Element  1B2043
                   Project Officer

                 Dr. Carl A. Brunner
       U.S. Environmental Protection Agency
      National  Environmental Research Center
              Cincinnati, Ohio 45268
                    Prepared for

        OFFICE  OF RESEARCH AND DEVELOPMENT
       U.S. ENVIRONMENTAL PROTECTION AGENCY
              WASHINGTON, D. C.  20460
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 - Price $1.75

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              EPA Review Notice
This report has bee^, reviewed by the Office of
Research and Development and approved for publi-
cation.  Approval does not signify that the
contents necessarily reflect the views and
policies of the Environmental Protection Agency,
nor does mention of trade names or commercial
products constitute endorsement or recommenda-
tion for use.
                      11

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                            ABSTRACT
An examination of the potentialities of a novel separation technique,
the Exchange-Diffusion  (EXD) Process, has been made.  In this
process, anions or cations in a feed stream are exchanged across
an ion-exchange membrane for similarly charged ions carried in a
regenerate or receiving stream.  Due to Donnan equilibrium constraints
the exchangeable ionic species in the feed stream can be concentrated
in the regenerate stream to several orders of magnitude over their
feed concentration.

Application of EXD to the removal and concentration of nitrate,
phosphate and ammonium ions from secondary effluents has been
demonstrated on laboratory and pilot scale.  The economic feasibility
of atmmonium removal appears promising.  A combined nitrate-phosphate
removal system is probably too costly to be competitive with other
methods in its present state of development.  Improvements in cell
configuration and membranes are possible and could substantially
improve cost figures.  Further development work and a field demon-
stration unit appear to be warranted.

This report was submitted in fulfillment of Project Number 17010 FBJ,
Contract Number 14-12-179, by Process Research, Inc., under the
sponsorship of the Environmental Protection Agency
                                111

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                        CONTENTS

Section                                                 Page

   1       Conclusions and Recommendations                1

   2       Introduction                                   5

   3       Experimental Method                           13

   4       Nitrate Transport                             19

   5       Nitrate Transport-Mathematical Model          39

   6       Phosphate Transport                           55

   7       Combined Nitrate-Phosphate Transport          75

   8       Economic Feasibility of the Nitrate
           Phosphate Removal System        '              79

   9       Preliminary Nitrate-Phosphate Pilot Plant     85

  10       Operation of Pilot Plant (Lawrence)           95

  11       Nitrate-Phosphate Membrane Tests             125

  12       Ammonium Transport                           129

  13       Economic Feasibility of the Ammonium
           Removal System                               141

  14       Ammonium Removal Pilot Cell                  145

  15       Acknowledgements                             153

  16       References                                   155
                            v

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                        FIGURES

                                                      Page
                                                        ^^ —

 1      Nutrient (Nitrate/Phosphate)  Removal
        System Schematic                                6

 2      Selective N-P Removal Principal                 8

 3      Schematic of Apparatus Used For Selective
        Nitrate and Phosphate Removal                  14

 4      A-l Type Spacer                                15

 5      Nitrate-Phosphate Test Cell,  Type A-3, Port
        Sample Being Withdrawn for Analysis            16

 6      Nitrate-Phosphate Test Cell,  Type A-3
        Disassembled, Showing Spacer Configuration and
        Sampling Port Locations                        17

 7      Flux vs Time                                   20

 8      Permeability vs Velocity                       23

 9      Permeability vs Product of Velocity and Anion
        Concentration in the Feed Stream               24

10      Nitrate Concentration Profile                  26

11      Hypothetical Concentration Profile             27

12      Nitrate Flux as a Function of Path Length      31

13      Affinity vs Path Length                        32

14      Permeability (J/AJ as a Function of Path
        Length                                         33

15      Experiment No.  50768-1                         34

16      Experiment No.  50704-2                         35

17      Experiment No.  50720-2                         36

18      Membrane Transport Model                       40

19      Nitrate Concentration Profile; Experiment
        No. 50704-2                                    47
                            VI

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                       FIGURES

                                                      Page
20     Nitrate Concentration Profile;  Experiment
       No. 50708-2                                     48

21     Nitrate Concentration Profile;  Experiment
       No. 50720-2                                     49

22     Nitrate Concentration Profile;  Experiment
       No. 50725-2                                     50

23     Nitrate Concentration Profile;  Experiment
       No. 50730-2                                     51

24     (A°) versus (A° + B°/Kg)  Plots  for Varying Kg
       Values                                          52

25     Film Controlled Data Plot                       54

26     Stability Diagram of Phosphate  Solution         56

27     Phosphate Concentration Profile;  Experiment
       No. 50742-2                                     59

28     Phosphate Concentration Profile;  Experiment
       No. 50749-2                                     60

29     Phosphate Concentration Profile;  Experiment
       No. 50753-2                                     61

30     Phosphate Concentration Profile;  Experiment
       No. 50763-2                                     62

31     Phosphate Concentration Profile;  Experiment
       No. 50766-2                                     63

32     Phosphate Concentration Profile;  Experiment
       No. 50769-2                                     64

33     Phosphate Concentration Profile;  Experiment
       No. 50775-2                                     65

34     Phosphate Concentration Profile;  Experiment
       No. 50772-2                                     66

35     Phosphate Transport Data as a Function of pH
       Differentials                                   68
                          vn

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                        FIGURES

                                                     Page_

36     D-Type Spacer Configuration                     70

37     Film Controlled Data Plot (A)                    72

38     Film; Controlled .Data, Plot (-B)                    73

39     Hypothetical Phosphate and Nitrate Removal
       System                                          80

40     Exchange ' Multicell;;.-Schematic.                    86

41     Exchange Multicell                              87

42     Schematic Flow Diagram for N-P Pilot Plant
       at Leominster                                   88

43     Nitrate Removal                                 89

44     Phosphate Removal                               90

45     Port Samples for 5/21/69                        93

46     Lawrence Experiment Station - Activated
       Sludge Plant                                    96

47     Lawrence Experiment Station   Activated
       Sludge Plant   Aeration Tank at Upper Right     97

48     Clarifier Section   Activated Sludge Plant      98

49     Sand Filter Section   Activated Sludge Plant
       Clarifier in Rear                               99

50     Lawrence Experiment Station   Aeration at
       Right   Feed to EXD Unit at Left               100

51     Serpentine Nitrate-Phosphate Spacer            101

52     EXD Nitrate-Phosphate Removal Prototype Cell
       During Assembly                                103

53     Open EXD Nitrate-Phosphate Removal Prototype
       Cell   Top End-Block in Foreground             104

54     Completed EXD Nitrate-Phosphate Removal
       Multicell                                      105
                          VI11

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                       FIGURES

                                                     Page

55     Completed EXD Prototype Cell                   106

56     Subunit of Prototype Nitrate-Phosphate
       Removal Cell                                   107

57     EXD Nitrate-Phosphate Removal Unit Assembled
       as Single Cell Subunit                         108

58     Film Controlled Data                           127

59     Schematic of Apparatus Used for Airimonium
       Removal Studies                                130

60     Ammonium Transport vs Flow Velocity            133

61     Multistage EXD Spacer                          152
                          IX

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                        TABLES

No.                                                   Pag

 1     Flow Path Dimensions of Test Spacers           18

 2     Experiment No. 50753                           21

 3     NO, Driving Force Data; Cl  Driving            22

 4     Steady State Analytical Data                   29

 5     Flux and Driving Force Computations            30

 6     Estimation of Phosphate Driving Forces         57

 7     Phosphate Transport Data                       67

 8     Phosphate   Chloride Exchange Data; D-3
       Test Cell                                      71

 9     N-P Transport in Multi-Component System        76

10     Nitrate Transport in Nitrate-Chloride System;
       Phosphate Transport in Phosphate-Chloride
       System                                         77

11     Nutrient Removal Design Illustration           83

12     Leominster Pilot Plant Operation               91

15     Synthetic Secondary Effluent                  109

14     EXD Phosphate Removal-Pilot Cell              112

15     Nutrient Removal   Exchange Diffusion Pilot
       Cell                                          113

16     EXD Nutrient Removal   Pilot Cell,
       Operating Data                                115

17     EXD Nutrient Removal   Pilot Cell
       Operating Data                                116

18     EXD Nitrate/Phosphate Removal   Pilot Cell,
       Operating Data                                118

19     EXD Nitrate/Phosphate Removal   Pilot Cell
       Removal Data                                  119

20     EXD Nitrate/Phosphate Removal   Pilot Csll
       Operating Data                                122

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                        TABLES

No.                                                 Page
21     EXD Nitrate/Phosphate Removal - Pilot Cell,
       Removal Data                                  123

22     Membrane Tests; EXD Nitrate-Phosphate
       Removal                                       126

23     Ammonium Transport Data                       132

24     NH* Removal                                   134

25     Ammonium Transport; Run 51026                 135

26     Ammonium Transport; Run 51033 A               137

27     Ammonium Transport; Run 51033B                138

28     Ammonium Transport; Run 51035                 139

29     EXD Ammonium Removal - Pilot Cell             146

30     EXD Ammonium Removal   Pilot Cell             148

31     EXD Ammonium Removal - Pilot Cell             150
                          XI

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                      Section 1

           CONCLUSIONS AND RECOMMENDATIONS

The technique used for selective nutrient (nitrate, phosphate,
ammonia) removal was based on the exploitation of Gibbs-
Donnan equilibrium considerations in ion-exchange membranes.
From the results of laboratory and pilot plant field tests,
the technical feasibility of nutrient removal via this Ex-
change-Diffusion Process (EXD) appears to be established, at
least to the extent that this preliminary investigation was
intended to reach.  For ammonia and nitrate, the process
also appears promising from economic considerations, especial
ly in view of the extremely conservative cost procedures used
in the initial estimates.  Further work should be directed
toward the reduction of these costs by the design of improved
cell configurations, the development of improved membranes
and in optimizing operating conditions.  Such efforts will
also improve the costs prospects for phosphate removal.
The process should be demonstrated in the field on a larger
scale and for a longer time than was possible in this study.

Specifically work during this program has included:

1.  Construction and operation of a number of laboratory-
    scale test systems for the Exchange-Diffusion process;

2.  Collection of nitrate transport data over a concentration
    range from 10"4 to 10"1 molar and phosphate transport
    data over a concentration range from 2 x 10~4 to 10~3
    molar.  Phosphate removal has been shown to be strongly
    pH dependent; different driving forces act on the dif-
    ferent phosphate species according principally to their
    respective electrochemical valences;

3.  Examination of nitrate-chloride; phosphate-chloride;
    nitrate-sulfate-chloride; phosphate-sulfate-chloride; and
    nitrate-phosphate-sulfate-chloride systems, of varying
    concentrations, and has established that the exchange
    rate of any one ion-couple is not greatly impeded by the
    presence of a number of additional ionic species.  Con-
    clusions drawn from simple two-ion, i.e., nitrate-chlor-
    ide, experiments are therefore transferable to more
    complex multi-component systems.

4.  Measurement of transport rates of nitrate and phosphate
    ions in two different cell geometries, the so-called
    sheet and tortuous-path configurations, at flow
    velocities from 0.45 to 67 cm/sec.

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Operation of a bench-scale N-P system on an activated
sludge secondary sewage effluent (Leominster, MA.) for
approximately two weeks.  This unit was operated both
with and without an activated carbon pretreatment step,
and evidenced no serious membrane fouling problems during
its short test period.  The unit was desinged for, and
consistently achieved, a 90% reduction of phosphates.

Development of a preliminary process design example -
This design was based upon a limiting phosphate removal
of 90% with concurrent nitrate removal of 97% from a
typical secondary effluent.  The partial estimated cost
for this degree of removal was 9.87^/1,000  gal.   Design
and cost estimates were based upon phosphate and nitrate
transport data obtained in the laboratroy,  with conven-
tional, commercially available ion-exchange membranes.
More suitable membranes, more nearly optimal process  de-
sign, and a regenerant chemical recovery system are ex-
pected to result in significant cost reductions.

Testing of several modified or developmental membranes in
the nitrate-phosphate EXD system.  None of the commercial
membranes examined showed transport properties substantial
ly better than those originally selected.  However, a
proprietary ion-exchange membrane exhibited enhanced
phosphate flux, indicating that improved system perform-
ance can be obtained by this method.

Construction and operation of a 1,000-2,000 gpd prototype
nitrate-phosphate EXD unit on authentic activated sludge
effluent obtained from a small treatment plant constructed
for this purpose.  Experience with the prototype removal
unit over a three-month period delineated scale-up pro-
blems in sealing methods, flow path geometry, hydraulics,
and membrane selection.  Solutions to most of these diffi
culties have been devised and a 90% nitrate-phosphate
removal appears to be attainable by application of these
improvements.  Economics for combined nitrate-phosphate
removal, however, are marginal at present.

Operation of a laboratory scale ammonium removal EXD
system which successfully demonstrated the feasibility
of 75-95% removals from 10"3 molar ammonium feed stream
and a synthetic secondary effluent of similar ammonium
concentration.  The practicality of recirculating a basic
regenerant solution was shown.  This mode of operation
minimizes regenerant volume and cost.

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10.   Preparation of a preliminary cos-t estimation of the EXD
     ammonium removal process based on the laboratory results.
     This analysis indicates a cost of less than 3tf/l,000 gal.
     for the design example chosen.

11.   Confirmation of the ammonium removal laboratory data in
     a small -pilot cell operated on the same secondary efflu-
     ent used as feed in the nitrate-phosphate field tests.

The technical feasibility and promising economics for some
Exchange-Diffusion systems indicated in this preliminary study,
combined with the potential of the process for pollution con-
trol, seem to warrent further investigation.  Laboratory and
pilot scale test should be continued to optimize flow ratio
and rates and plate-and-frame cell geometry.  Alternate cell
configurations, notably spiral wound and tubular construc-
tions, should be tested and evaluated relative to previous
results, especially as applied to phosphate removal.  A dem-
onstration EXD unit with capacity of ca. 50,000 gpd should be
designed and installed at a site selected by EPA.  Initial
work would emphasize the ammonium removal system since this
appears to be less complex in operation, more immediately
useful as a pollution control procedure and more clearly
economical.  Nitrate-phosphate removal demonstrations could
subsequently be conducted on the same unit with minor
modifications.  Design and operation parameters for such a
demonstration plant would be determined on the basis of the
optimization and configuration studies.

Finally, a concurrent program to devise superior membranes
should be conducted on a laboratory scale.  Substantial
improvements seem to be possible on the basis of the explora-
tory membrane tests reported for the nitrate-phosphate sys-
tem.

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                      Section 2

                     INTRODUCTION

The desirability of removing algal nutrients particularly
nitrates and phosphates from waste waters discharged to
lakes or slow moving streams has, for some time, been evident.
The problem has been to achieve this removal within reason-
able limits of economy and practicality.  All separation
methods investigated to date appear to be wanting in some
respect, generally in terms of efficiency and often in terms
of cost.  Under this contract the technical and economic
feasibility of a novel membrane-based nutrient removal process
has been investigated.  It uses chemical energy only, supplied
by a concentration difference between a feed (nutrient con-
taining) stream and a regenerant (nutrient receiving) stream.

The techniques employed for the selective removal of nutrients
from waste waters in this work is based on Gibbs-Donnan equi-
librium considerations in ion-exchange membranes.  For the
removal of nitrates and phosphates, the system consists of a
sandwich of anion permeable membranes, with solution flowing
parallel to the membrane surfaces between each pair.  An
identical arrangement is employed for ammonium removal except
that cation-exchange membranes are used.  The subsequent
discussion, although nitrate and phosphate removal is general-
ly used as an example, applies to either system.  Each mem-
brane separates a "diluting" or nutrient rich stream from a
"concentrating" or regenerant stream.  The configuration
resembles closely an electrodialysis stack, except that all
membranes in the stack are the same type, and there are no
electrodes at the ends of the stack.  The "concentrating"
stream flows in the counter-current direction to the "dilut-
ing" stream.  A schematic diagram of a nitrate/phosphate
multicell arrangement is presented in Figure 1.  In this
figure, the "diluting" stream flows through the odd numbered
compartments , the "concentrating" stream flows through the
even numbered compartments.  The "concentrating" stream flow
rate is of the order of only 1% of the "diluting" stream
flow rate.  The "concentrating" stream concentrations are of
the order of 100 times those of the diluting stream.

The necessary driving force for the selective transport of
nitrate and phosphate ions is obtained by augmenting the
"concentrating" stream with all the various anions present
in the "diluting" stream, with the exception of nitrate and
phosphate.  Nitrates and phosphatesin the"diluting" stream
willthus be exchanged for the various other anions in the
"concentrating" stream to satisfy the Donnan equilibrium.

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 FdC,
F C
 C „ CO
             >
             *S»-
            ->
                                          End Plate
AM

AM




AM

AM

AM
__. A k i
AM

AM

End Plate

( .
r
s &
i BK
\ •>.
-/

       compartment  number

       dilute stream flow rate

       concentrate  stream flow rate

       influent dilute stream  concentration
Cci  =
                                                 FcCci  FdCdo
       effluent concentrate stream concentration

                            FIGURE  I
         NUTRIENT (NITRATE/PHOSPHATE)REMOVAL SYSTEM  SCHEMATIC

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The fundamental operation of the nutrient removal process is
illustrated in Figure 2.  Nitrate or phosphate and chloride
concentration profiles are shown through a cross -section of
an anion-exchange membrane interposed between feed and re-
generant solutions.  Nutrients are transported from the feed to
the regenerant side of the membrane, against their overall
concentration gradient, because of coupling to the chloride
ions flowing in the opposite direction.  This coupling of the
two flows is the result of the system requirement of no net
charge transfer (zero electrical current) combined with the
Donnan exclusion of positively charged ions from the anion-
exchange membrane.  The requirement for zero electrical current
can be expressed:

          Sz . j. = i = 0                            (1)
          j D  J   F

where the summation is over all species j , both positive and
negative and:                   r

     J. = transport rate (flux) of species j, moles/cm2 -sec

     Z . = electrochemical valence of species j

     i  = current density, amps/cm2

     F  = Faraday's constant, 96,500 coulomb/equivalent.

If positive ions are effectively excluded from the membrane
because of the high ratio of fixed membrane charge to solution
concentration, then the positive ion (co-ion) flux will be
effectively zero and, if chloride; nitrate and phosphate are
assumed to be the only negative ions (counter- ions)  present,
equation 1 will reduce to:


          2JHP04+ JN03 + JC1 = °                   ^

Thus, when two solutions of differing concentrations and
compositions are separated by a permselective (ion-exchange)
membrane, transfer of the various ionic species will take
place across the membrane until a partial equilibrium is es
tablished between the two solutions.  This sort of equili
brium is established between solutions 1 and 2 of ions A,
B and C when:
          A2    A    B2          2
                  "          ~    '

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    2 —
2
   RT InE
                     Regenerant
                             N03 or P
                        4
                       32
                          1/2
                       2~} 1/2

                      4  *2
              (CI-),  (NO-)
        3 12
             FIGURE 2
O[™ I  e_
t_ t_c

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In this state, no net transfer of any of the negative species
A, B or C, will occur (still assuming zero co-ion flux).
The driving force for the removal process is the magnitude of
the system's displacement from this condition of Donnan equi-
librium.  A quantitative expression for this displacement can
be derived from the concepts of irreversible thermodynamics
(1).  The dynamics of the system shown in Figure 2 can be des-
cribed as an exchange reaction between feed and regenerant
"phases".

If_the ions of concern in the two solutions are, for example,
NO  and Cl , then the exchange of the two species across the
membrane can be described by a form of ion-exchange reaction:

          (NO")  + (Cl")  +  (NO")  +  (Cl")
               1        2        2        1

The driving force or "affinity" for this reaction can be ex-
pressed:

          .A. — ~" LJ **  11 *                              f *7 ~\
               i i                                 *• J

where:
          y . = y . + RT  In a.                       (4)
and:
     A = driving force, or  "affinity", of reaction, joules/mole

    y. = chemical potential of species i, joules/mole

     o
    yi = standard chemical  potential of speices  i,  joules/mole
                                                    o
     R = universal gas constant,  8.314 joules/mole/ K
                               o
     T = absolute temperature,  K

    a. = activity of species i


or, for the nitrate-chloride exchange as written:

                     (NOT)     (CO
          A = RT In  (	——  ' 	—-)
                     (N0")2    (Cl-)1


As long as the ratio of chloride  concentrations  exceeds  the

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ratio of nitrate concentrations, the reaction will proceed
as written-from left to right.  Equilibrium, and no further
transport, is achieved when:

          CGI")    (NOJ
          	2 =      2

          (CO    (NO")
               1        1

It can be seen from this relationship that, at a chloride
concentration ratio of 100:1, nitrate will be transported
against its concentration gradient until its concentration in
solution 2_is100timesthatin solution 1.  Divalent phos-
phate (Hpo^) will be transported against its concentration
gradient until its concentration in solution 2 is 10,000
times tTTat in solution 1; trivalent phosphate (PO^) will ac-
cumulate in solution 2 until its concentration is 1,000,000
times that in solution 1.

Through appropriate process design and operation, this pheno-
menon can be exploited to achieve selectively any desired de-
gree of nitrate and/or phosphate removal.

The rate of the exchange can be expressed as the product of
the above affinity and a "permeability" term:

          ZAJA = " ZBJB = P A' ecl/cm2/sec         (5)

The permeability term, P, is a function of ion mobilities and
concentrations and of membrane and boundary film thicknesses.
More correctly, the "permeability" will be a combination of
terms reflecting the permeabilities of the membrane and of
the boundary films at each interface:

          7T=-7T—      •"•
           A A   " ^B B ~ ~=
                              + =— +
                                Pm
The_experimental nitrate and phosphate removal program was
designed to determine nitrate and phosphate transport rates
as a function of:   driving force, A; nitrate and phosphate
concentrations;  membrane properties (thickness, exchange ca-
pacity, conductivity, etc.); and system hydraulics.

"Concentrate" stream concentrations and flow characteristics
were  generally maintained such that any film limiting trans-
port  would occur at the interfaces between the "dilute" stream
and its adjacent membranes.   Under these conditions, the
                          10

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transport rates would be described by a modified form  of
equation 6:

          7 T  = _ 7  T  = 	
           A 7      "DTJ   —T	1	

                          ^+F^                 (7)

From previous work on limiting current densities in electro-
dialysis systems (2,3) it was expected that an expression
for P_p  might resemble:


          Pf  = Kf C, Vn                           (8)
            d

where K,- would reflect certain hydraulic properties of the spacer
design, and the exponent, n, would vary between 1/3 for laminar
flow (4) and 2/3 for  turbulent flow  (3,5).

Rearrangement of equations 7 and 8 gives:

          A    1.1
          ZJ   P    v r vn                          (9)
                m   KfCjV

Plotting the flux versus velocity data  according  to  this
equation would be expected to give a  sequence  of  linear
curves depending upon the properties  (Pm)  of the  membranes
used. The intercepts in this type plot  would represent
1/P  ; the slopes (at the intercept) would  represent  l/K^C-,,
                           11

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                     Section 3

                 EXPERIMENTAL METHOD

According to our initial formulation of the system, nitrate
and/or phosphate flux across an anion permeable membrane
would be described by the product of an affinity and a per-
meability term.  Again, ammonium flux across a cation permeable
membrane could be described by an analogous formulation.
Investigations of nitrate transport were conducted first,
with initial emphasis on permeability as a function of flow
velocity.

The experimental apparatus was constructed according to the
diagram shown in Figure 3.  The apparatus included two Eastern
Industries Model P-7 pumps, and two high density polyethylene
reservoirs having a capacity of six gallons each.  The pres-
sure gauges were bourdon type from the United States Gauge
Company, with the range 0-60 psig.  The two flowmeters were
made by the Fisher-Porter Company for the Manostat Company,
catalog No. 36-541-30.  Two needle valves made by the Manostat
Company, catalog No. 78-425-01, were used for flow rate ad-
justment.  The temperature gauges were ASTM 45 mm immersion
thermometers, No. 36C, and covered the range -2 to +68 - 0.2°C
and ASTM 51 mm immersion thermometers No. 33C covering the
range  38 to +42 - 0.2°C for inlet and outlet of the streams,
respectively.

Three different sized experimental systems were assembled.
The pertinent flow path dimensions of the spacers used in
each of these systems are listed in Table 1.  The only va-
riable was flow path length.  The path width, thickness and
turbulence promoting aspects of the path were the same in
all three.  The flow path spacer for system Type A-l is shown
in Figure 4.  These systems employ the so-called "tortuous
path" type spacer design.  Figures 5 and 6 show two views of
the type A-3 test cell, in operation and disassembled, re-
spectively .

The choice of flow path length for a particular experiment
was determined by the desired nutrient removal for the planned
test conditions.  The removal was kept sufficiently small
that the value of the "affinity" terms at the beginning and
at the end of the flow path were not appreciably different.

Chloride was analyzed by titrating with Fisher standardized
silver nitrate solution (1 ml = 0.5 mg Cl"), according to
the Argentometric Method, in Standard Methods (6).

Considerable effort was expended in deciding on an appropriate
                           13

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         Feed Reservoir
         FIGURE 3
SCHEMATIC OF APPARATUS
 USED FOR  SELECTIVE
NITRATE AND PHOSPHATE
       REMOVAL
                          \r
                          A
                                    AM
                                      Or
                                 Flowmeters
                              T
r
        Regenerant  Reservoir
     \ i
     A
   Overall
   System
(P) Pressure Gauge
(?) Thermometer
AM Anion Membrane
O Pump
 Si  Needle Valve
 X  Valve

-------
     J.
4
4
I
12345
          FIGURE 4

       A-I TYPE SPACER
           15

-------
                 FIGURE 5

  NITRATE-PHOSPHATE TEST CELL, TYPE A-3,
PORT  SAMPLE BEING WITHDRAWN  FOR ANALYSIS
                  16

-------
       ////////ffffiiiiiiiiiiiiiinm\\\i\\\\\\\\\\\
      WWfHHMHIl I Hill HHmWU\\\\\\\\\
      //////////I/IIIIIIII
                 FIGURE  6

  NITRATE-PHOSPHATE TEST  CELL, TYPE  A-3,
DISASSEMBLED, SHOWING SPACER CONFIGURATION
        AND SAMPLING PORT LOCATIONS
                   17

-------
                       TABLE 1
         FLOW PATH DIMENSIONS OF TEST SPACERS

                                                  Overall
                                       Effective  Spacer
Spacer Type  Thickness  Width  Length    Area    Dimensions
   A-l

   A-2

   A-3
 cm

0 . 10

0.10

0 . 10
 cm

0 . 56

0 .56

0 .56
 cm

 85

442

972
cm2
51
256
584

12
23
23
cm
X
X
X

23
31
60
analytical technique for nitrate ion.  One method investigated
was a potentiometric determination, using a nitrate specific
electrode (manufactured by Orion Research, Incorporated,
Cambridge, Massachusetts).   Rapid analysis was the main con-
sideration in this method.   This electrode was subject to
chloride interference and,  at concentrations present in the
regenerant stream, behaved in fact as a chloride specific
electrode.  Other difficulties observed were drifting with
time and a pronounced sensitivity to the rate of stirring.

The standard Brucine Method was finally adopted for nitrate
determinations  (6).  The high chloride levels in the re-
generant stream were found to inhibit the development of the
characteristic yellow color produced in this method, although
the technique is reported to be insensitive to chloride.  It
was necessary to include the appropriate concentrations of
chloride in the standards for the calibration curve, in order
to obtain meaningful nitrate data.

The technique for phosphate analysis was the standard Aminona-
phthol-sulfonic acid Method for orthophosphate determination
in Standard Methods (6).  Slight deviations from Beer's Law
at very low phosphate concentrations were observed, and sam-
ples were diluted so as to fall within the range of 10 to 20
mg/1.   The high chloride concentrations in the regenerant
stream were not found to interfere with the phosphate analysis,

-------
                      Section 4

                  NITRATE TRANSPORT

Initial experiments were performed with the A-2 test cell.
Some of the first studies were conducted by removing chloride
from the feed stream by means of a nitrate concentration
potential.  This technique was employed because of temporary
nitrate analytical problems.  Since the ionic mobilities of
nitrate and chloride are very nearly the same, such a system
should behave the same as if the ionic roles were reversed.

Steady state flux values were determined as follows.  First,
keeping flow velocities constant and identical in both regen-
erant and feed streams, outlet samples were analyzed periodi-
cally for the appropriate ionic concentrations.  Flux values
were then computed and plotted versus time, as shown in Figure
7.  When both feed and regenerant fluxes reached an identical
and steady value, then that value was assigned for the flow
velocity, concentration, and driving force conditions of the
experiment.  Complete data for one experimental run are
shown in Table 2.

Collected steady state flux and system permeabilities for
various flow velocity and concentration conditions, are
presented in Table 3.

System permeability  (J/A) data from all runs conducted with
the A-2 system are plotted in Figure 8,  as a function of flow
path velocity.   It is apparent from this data that feed
stream concentration is also a significant parameter, both
flux and permeability increasing with this concentration.
As a tentative effort to include this parameter, system
permeabilities are replotted in Figure 9, against the product
of velocity and  concentration.

Later work on nitrate transport utilized experimental system
Type A-3 which had a path length of 972 cm.  Eight small
ports were placed along this flow path to obtain samples as
a function of flow path length (see Figures 5 and 6).  Each
port was 1/32 in. in diameter.

Flux values at different driving forces were determined as
follows:  keeping flow velocities constant and identical in
both regenerate  and  feed streams, the system was allowed to
run for six to seven hours to achieve steady state conditions
and mass balances between the two streams.  Outlet samples
were analyzed periodically to determine when steady-state
conditions were  achieved.  Each port was then sampled, starting
                          19

-------
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      4
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                 1.0   1.5  2.0  2.5  3.0   3.5


                     Time, hr

                         A = JR , Flux on regenerate
                             R  side

                         o = Jp , Flux on feed side



                  FIGURE 7
              FLUX VS TIME
                 20

-------
TABLE   2
EXPERIMENT NO. 50753
Inlet Cl~ in Feed = 0.0095 mole/liter
Inlet Cl in Regenerant = 0.0097 mole/liter
Inlet NO in Feed = 0.53 mole/liter
Inlet NO" in Regenerant = 0.0098 mole/liter
3 2
Membrane area = 256 cm
Flow
Rate Flow Rate Chloride Chloride Chloride Chloride Flux on
Time Feed Regenerate in Outlet in Outlet Gain by Loss Regenerate
T,hr FF1 FR1 Feed2 Regenerate2 Regenerate2 by Feed2 Side, J 3
.K
0.5 248
1.0 248
1.5 248
2 .0 250
2 .5 248
3 .0 250
3 .5 248
* ml /mi n
2mole/liter
•3 ^
•'mole/cm- sec
251 0.0088 0.0102 0.0005 0.0007 9.21
246 0.0088 0.0104 0.0007 0.0007 11.29
248 0.0088 0.0104 0.0007 0.0007 11.38
249 0.0088 0.0103 0 . 0 O'O 6 0.0007 10.28
247 0.0088 0.0104 0.0007 0.0007 11.34
248 0.0089 0.0104 0.0007 0.0006 11.38
246 0.00885 0.0103 0.0006 0.00065 10.16


(x 109)
Flux on
Feed Side
V
12.52
11.38
11.38
11.47
11.38
10.33
11.38



-------
                         TABLE 3
                 NO  DRIVING FORCE DATA
                                 = 0.0095M  = 0.01M

                                 = 0 . 527  M  = 0.50M

      Regenerant Inlet  Cl   Cone = 0.0097M  = 0.01M
Feed Inlet  Cl   Cone
Feed Inlet  NO   Cone
      Regenerant Inlet NO~  Cone = 0.0098M  =  0.01M
No .
50729
50714
50753
Flow Rate
ml /m in
100
150
250
Veloci ty
cm/sec
27 .8
41.7
69 . 4
Affinity
A
9068
9209
9281
Flux
J(x 10 )
mole/cm2 -sec
8. 072
9.78
11 . 36
i U 10"
P ermeabi 1
mole/cm2 -s
8.9
10 . 5
12. 2
)
ity
ec



                 Cl  DRIVING FORCE DATA

      Feed Inlet Cl~ Cone        = 0.0039  M  = 140 mg/1

                                 = 0.00038M  =  25 mg/1

      Regenerant Inlet  Cl   Cone = 0.5M
Feed Inlet  NO  Cone
     Regenerant Inlet NO   Cone = 0.00038M  =  25 mg/1
                                            Flux
                                                           <*
      Flow  Rate  Velocity   Affinity     J(x  10  )       Permeability
No.     ml/min     cm/sec       Amole/cm2-sec  mole/cm2-sec
50761
50756
100
250
27 .8
69 . 4
10741
11572
0 . 96
1 . 51
0 .90
1 .31

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                        FIGURE 8


           PERMEABILITY VS VELOCITY
                                           1000
                     23

-------
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12 3 4 5 i 1 39 2 3456789 2 34547S9
"5 io4 ,63 ,o
            V-C AN|ON' MOLES/CM2/SEC
                   FIGURE  9
PERMEABILITY VS PRODUCT OF VELOCITY  AND  ANION CONCENTRATION
IN THE FEED STREAM.
                     24

-------
from the outlet of the apparatus and progressing toward the
inlet.  This was done slowly so as not to disturb flow rates.
This experimental technique was employed to obtain relation-
ships between flux, system permeability and feed concentra-
tions along the entire flow path length.  Although lengthy,
it had two advantages.  First nitrate flux data were obtained
as a continuous profile over a wide range of concentrations
and driving forces, i.e., along the path length.  Second, a
convenient check on the nitrate analyses was obtained.  Assuming
that concentrations change in a regular  and smooth fashion
over the path length  (see Figure 10), a curve fitted through
the concentration data probably was more reliable than indivi
dual data points.

A least-squares data  fitting technique was employed to develop
an empirical relation between concentration of the feed and
path length in the form a + bL + cL2.  In plotting this con-
centration profile, the number of data points was doubled by
including feed stream concentration values computed from re-
generant stream data  according to the following method.  Be-
cause of steady state mass-balance considerations, the sum
of nitrate ions in the feed and regenerant streams would be
constant at any point along the flow path, i.e.,
            R.
where:
     C-  = concentration of NO, in feed at any position i;
     CD  = concentration of N0_ in regnerant at any position i;
      Ri                      6

     CT  = total concentration of N0_ at position i.
      1 .                            O
Also at steady state:
            _ =  FR.ACR_
                                      (ID
where:

     F
      F

     AC
       F.
flow rate of feed;

loss of nitrate by feed at any position i;
                           25

-------
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^^





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AF"c»r?r!

O Regenerant


^^-0" 	


— 	 A. 	


n
— — 	 u


A

),0) 200 400 600 800 IOC
FLOW PATH LENGTH , cm
FIGURE 10
NITRATE CONCENTRATION VS. PATH LENGTH
                  Run NO. 50763-I

-------
          =  flow  rate of regenerant;
     AC^  =  gain  of nitrate by regenerant at any position  i.
        i


All experiments were conducted with  equal feed and regenerant
flow rates:
     FF =  FR
Therefore,

This is illustrated in Figure 11.
            z
            o
            cc
            I—
            z
            LJ
A
\/
AC,
                      PATH  LENGTH
                     (12)
                       FIGURE  I I

     HYPOTHETICAL CONCENTRATION   PROFILE
                         27

-------
c,  in this figure, is defined as one-half the average of the
experimental values of C  :
                                                   (14)

where:

     n = total number of sample pairs (feed and regenerant)

The steady state feed stream concentration profile should  there-
fore be a mirror image of the regenerant stream concentration
profile rotated about the value of c.

     c   CF  = CR  - c                             (15)
           i     i

Using the equation (15), computed values of Cp  would be:
                                              i

     (C  )     = 2c   (C  )
        i comp           i exp                     (16)

where:

     (Cp )     = computed values of Cp
        i comp                        i

     (CD )     = analytical values of CD
       K -                               K •
        i exp                           i

Cp  values determined analytically and Cp  values  computed
  i                                      i
from analytical CD  values,  by equation (16) were  then utili
                 K. -
zed in the least squares type analysis to obtain best fit  feed
stream concentration profiles.

Data from one experiment in this series is presented in Tables
4 and 5 and concentrations,  fluxes and affinities  are plotted
against flow path length in Figures 10, 12 and 13, respectively.
System permeability (J/A) computations at various  path lengths
are plotted in Figure 14.

Experimental data and computed feed stream concentration
profiles are shown for this  and other experiments  in Figures
15,  16  and 17.
                          28

-------
                  TABLE  4
       STEADY STATE  ANALYTICAL DATA




          Experiment No.  50768-1





Inlet Chloride  in  Feed       = 0.00416 M





Inlet Chloride  in  Regenerant = 0.514   M
Inlet Nitrate  in  Feed




Inlet Nitrate  in  Regenerant




Flow Rate of Feed




Flow Rate of Regenerant
= O.C00367M




= 0.000477M




= 100 ml/min




= 100 ml/min
                                    Incremental
                     Incremental
Port
No .
Inlet
8
7
6
5
4
3
2
1
Outlet
Path
Length
cm
0
40
93
147
219
291
381
506
685
971
.0
.07
.98
.89
.67
.67
.10
.99
.49
. 71
Area (NO )
2 3
cm x
0
24
56
88
131
174
228
303
411
583
.0
. 04
.39
.73
.80
.87
.66
.89
.29
.03
3
3
2
2
2
2
1
1
1
0
in- Feed*
101*
.677
.386
.999
.741
.419
.128
.903
.598
.096
.613
(N°3)
X
4
5
5
5
6
6
6
7
7
8
in Reg.
101*
.798
.120
.483
.741
.096
.418
.693
.047
.531
.128
(NO
* by
X
2
3
2
3
2
2
3
4
4

) Loss*
Feed
105
.91
.87
.58
.22
.91
.25
.55
.52
.83

(NO ) Gain*
by Reg .
x 105
3
3
2
3
3
2
3
4
4

.22
.63
.57
.55
.22
.75
.54
.84
.84


-------
                         TABLE  5
FLUX AND DRIVING FORCE COMPUTATIONS
Experimental Run No. 50768-1
Port
No .
Inlet
8
7
6
5
4
3
2
1
Outlet
Incremental NO *
Affinity Flux on Feed Side
x 10 ^ x 10 9
1
1
1
0
0
0
0
0
0
0
.121 2 .012
.083 1 . 994
. 034 L . 329
. 999 1 . 248
.952 1. 123
. 906 0 . 700
.866 0.786
.801 0 .701
. 697 0 „ 470
. 532
Incremental NO *
Flux on Regenerate Side
X 10 5
2 . 236
1 .869
1 . 329
1.373
1 . 248
0 .849
0.786
0 ,751
0 . 597

*mole/liter
                           30

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                          0
200      400      600      800
       FLOW PATH  LENGTHt cm


          FIGURE 13
                                      AFFINITY V§ PATH LENGTH
                                               Run NO. 50768-!
1000

-------
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    2.00
     .75
    1.25
    1.00
    .075
       (0,5)
                200
  400      600      800

FLOW PATH  LENGTH,cm



   FIGURE  14
tooo
 PERMEABILITY (J/A) AS  A FUNCTION  OF PATH LENGTH

                            Run NO. 50768-I

-------
     4.0
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£ uul .806
200
                            400        600
                          PATH  LENGTH , Ucln
                            FIGURE  I 5
                 EXPERIMENT NO. 50768
800       1000
k  ANALYTICAL FEED
  CONCENTRATION, Cc
                                                  COMPUTED FEED
                                CONCENTRATION Cp.
                                                                  iCOMP
        INLET CHLORIDE  IN FEED           = 0.004I6M
        INLET CHLORIDE  IN RE6ENERANT     = 0.5I4M
        FLOW RATE (FEED AND RE6ENERANT )  = IOOML/MI!

-------
     4.03

     3.224
<  QC
£  K 2.418
LU
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   LU
     1.612
q
"  u^ .801
                 Y= 3.7x I04-3.365*I07XL+8.93XIO'!*L2
         0
 200       400       600
        PATH LENGTH, L,
           FIGURE  16

EXPERIMENT NO- 50704-2
 80O      - I 000
  ANALYTICAL FEED
k CONCENTRATION Cc

                                                   COMPUTED FEED
                                                   CONCENTRATION  Cp
                                                                    COMP
        INLET CHLORIDE IN FEED           = 0.004I2M
        INLET CHLORIDE  IN REGENERANT    -0-II4M
        FLOW RATE (FEED AND REGENERANT) ~IOO ML/MIN

-------
 0
 200       4OO      600
        PATH LENGTH,L,Chi

          FIGURE  17


EXPERIMENT NO. 50720-2
800      1000
 ANALYTICAL FEED
 CONCENTRATION, C

 COMPUTED FEED
 CONCENTRATIONS
                                                        "\ COMP
INLET CHLORIDE IN FEED           - 0-00387M
INLET CHLORIDE IN RE6ENERANT      = 0.875M
FLOW RATE ( FEED AND REGENERANTJ  - IOOML/MIN

-------
Experimental exchange rates can be computed from the slopes
of these concentration profiles:


     J = u ' W                                 (17)

where:
                               2
     J = exchange rate, mole/cm -sec;

     F = flow rate, liter/sec;

     a) = flow path width, cm;

     C = concentration, moles/liter;

     L = distance along flow path length, cm.

Affinities (driving force) can be computed also at any point,
L, along these concentration profiles:
                          K-y
      A = affinity (driving force), joule/mole;
                     2
      y = a + bL + cL , i.e., feed concentration profile,
          mole/liter;

     KD = inlet regenerant chloride, mole/liter;
      K

     Kp = inlet feed chloride, mole/liter;

      R = gas constant, joule/mole,°K;

      T = temperature of the system, °K.

Two experiments were conducted to ecamine the effects of sul-
fate interference on nitrate transport.  One was performed
with 120 mg/1 of sulfate in the feed and regenerant streams
and the other with zero sulfate.  All other experimental
conditions were maintained constant.  Concentration profiles
from these experiments are presented on semi log plots (see
Section 5 on Mathematical Model Development) in Figures 22
and 23.  From Figure 22 a value for J/NO^p of 1.8 x 10"3
cm/sec is obtained for the case where the only anions present
are nitrate and chloride.  Computations based on Figure 23
indicate that in the presence of sulfate, J/fNOp was de-
                         37

-------
creased by only 3 percent, to 1.74 x 10   cm/sec.  This
nitrate flux was maintained, furthermore, in the presence of
significant sulfate transfer.*  Feed .stream sulfate was reduced
from an inffluent 120 mg/1 to an effluent 25 mg/1 through the
cell.
                          38

-------
                       Section 5

          NITRATE TRANSPORT - MATHEMATICAL MODEL

From the data accumulated on the nitrate-chloride system, a
descriptive, or predictive, model of the steady state per-
formance of a nitrate removal system has been developed,
based upon the following approximations:

     1)  Concentration gradients in both boundary films and
         membranes are assumed linear.  This is likely to
         be reasonable for the nitrate-chloride system be-
         cause of their similar diffusion coefficients, va-
         lences, etc., but might not be realistic for, say,
         a phosphate-chloride system;

     2)  The nitrate-chloride ion exchange selectivity coef-
         ficient is assumed constant, and identical on both
         sides of the membrane, i.e., independent of concen-
         tration or composition.  Again, this seems reasonable
         for the nitrate-chloride system (see, for example
         Gregor, H.P., 
-------
Feed Solution
B
  J
   A'
Ac
          JB
film
fj|m
Regenerant
Solution
                                                    R
                       fJGURE  18

             MEMBRANE TRANSPORT MODEL
                       40

-------
By Pick's  Law:




     •**-T~1    J\   ~  *J /
                   DA                               (21a)
     A1   A"  =  J  -

                  D                                 (21b)
           R     A                                  (21c)


and:



     B°  - B'  =  J -AL
     ^    E     J
     B"   R°  =  l   &"
           R    B  DR                                (2If)




At the two membrane-solution interfaces:



           -  ZB    ZA    -   ZB    ZA              f22)
      A    A'    "R '        A "    "R M                 v   J
     TV-.TV 	 /"   "\   r   ~\    	  r  "\   f  ~\

      B    A1    g,        A"    gn




From equations  19,  20,  and 21d:



              V   7  A !

     B'       X   ZA A
     B'   Z R°  +  Z  J  6'
          ZBBF    ZAJAD^"                            (23)




Substituting equations  23  and 21a into equation  22:
     A' =  (K-)   -[  /   A6,]  A  B[A°   JA « ]    (24)


                   BF  +  JA-D^




For the nitrate-chloride system, Z. = Zg = 1, so:


                  X(KA)[A°   J  -11]                (25)

     Ai= 	^   ^   A DA	


         (KB) [AF   JA^~]  +  CBF + JA"3T
                           41

-------
Similarly, for A":
     r\.     T""~
         CK-A-, r,o    T   6",    fRo    T  6",
         (Kg) [AR + JA-^-]  +  [BR  -  JA-j5j]





Substituting  these expressions for A1  and A" into equation  21b

yields:
     j I =
       f.    , ,,. r . o
       D    (KB) [Ap

                     J
             iJ   K    A UA       K




For simplification of notation,  let:



     c  =  (<)



     c  _ D X

     n    T~
     b- -DA
     b  ~ rr




     a    yrr



          DR
     h" =  B
     D    I77



Substituting these expressions  into  equation 27, and rearrang

ing:

-------
he   c  [A--] [A+] +c [ [A--]
Rearranging  equation 28:
  ,O-nO  A°-R°-

  F R  R  F-
 A° B° A° B(
r2F V 21 +lj

kb" a' b1 a'



r 1     1 -v
                                      he
                                o ^CK
                                he
J


O , -nO-
                                he
                                                      -£
                                                                     (28)
                  _-_     -_
               ra' b'  a"  b"-, T3
               L     —i        J J
                      he
and finally:
 A° B°
 JA.-M-, JJ -,-,
                     A
                            A
                            A
       AOO
                             °  °
                J5
                                               K

                A°    B°r
               r &  .   ^

                                                                                      (29)

-------
In the experiments  conducted on nitrate removal  (A  -

B = Cl") :




     Bn =  10   mole/cm
      K




     B° »  10~5 mole/cm3





     A° =  A° = 10"6  mole/cm3
      K    r




     D. *  D  - 10"5  cm2/sec
      A    D




     6' =  6" - 5  x  10    cm (equal flow rates)




     t  *  5 x  10  2  cm




     KA -  3





     D  =«  10"6 cm2/sec




     X  *  2 x  10~3  eq/cm3
Then:


      K
       "R    1            ^
      [_£    ±_] K  2  x 10  sec/cm
and:


        t         7    2
      (—T—j)  ta  10   cm -sec/eq
                                                  - 9         2
For  the  flux  magnitudes obtained to date  (J  -  10    mole/cm

sec) ,  the  third order term on the right hand  side of equation 29

becomes  negligible.
Also:
       A°    B°        A°   B°
       /A. -pi     T1        *~^- T)    T)

                "
 and:




      (AD  +  BD)  * (^A°+ B°) = B°
                            44

-------
If, therefore:
                         A- -
       A  O     O     A '   Ixr>-u^            r
      (KBAp  +  BF).«(g--)(-|—) * 6 x  10 "b



then  the  first term on the R.H.S. of  equation 29 would be a

function  of film properties only, i.e.,  the system will be

film  diffusion controlled.


      Conversely,  if:


                         A- -

      f V A ^  _i_  ~D ^ "\   f ® * f &  >.

      (KBAp  +  ^J^D-^-t—)'



the system will  be membrane diffusion  controlled.



      For  the  experimental conditions  employed here, equation

29 can be closely approximated by:



r^O-nO A ^ "R ^ "1 —  rA^4-T2^~l      C  ^ \ C V^- A O  T> ^ ^ f V-A- A O T) 0 ^ 1 T
  r x\  r\  p       K.  iv JJ     T,.A.^ -,%   13 F  p   R R  R
Dividing by A°B°:

                ,u  .u   K"rtflY   JJ i1  r   JDT3IJ     A

                5R      KB A             aR     AF         (31)
Rearranging  this  expression:

                            A 0~O
                            A R
     J  .                    AF^
     A°       A°
      JT    r f -i . I\^
               B°      KDX             B°                 (32)
      AR
Since — «1, this  expression is approximated  by
     J_ ^ 	1	


     AF " &W+  ^HKAAX)                           (33)
                 KBDX
                            45

-------
which, under the experimental conditions used, should  be
virtually constant.  By definition:

         Fp dA°

     J ~ ~ dlT                                          (34)
where:
        = feed stream flow rate, cm /sec
     to  = flow path width, cm

     L  = distance along flow path, cm

or:

     J_ = F d ln AF
     .0   to   cTL
     AF                                                  (35)

     If — is constant, as suggested by  equation  33,  then a

        AF
semi-log plot of concentration versus path  length should be
linear.  Data from the Type A-3 cell is  presented in  semi
log form in Figures 19, 20, 21, 22, and  23,  and is  in fact
linear, as this model predicts.

Equation 33 can also be written:

     »o                   ~o
                DX       KB                             (36)

The first term on the R.H.S. of equation  36  is  a function of
film properties and the second term  is  a  function of membrane
properties only.  Each of these terms was  examined separately,
                                                  A°
                                                   F
According to equation 36,  an arithmetic  plot  of  (-T—)  versus
      B°                                          J
 (Ap + —£-) , at  constant velocity, would be  expected  to result


 in a straight  line.  Such  a plot is  shown  in  Figure 24 for

different assumed values of KR.   (Values of K^ used for the
                             -tJ                /A.
 chloride  transport data are assumed  to be  the reciprocal of

Kg used for the nitrate transport  data).  This plot is linear
                           46

-------
£ 9

~ 8
J^
lr
<
a:
LU
o
o

UJ
  10
              /-
A ANALYTICAL FEED CONCENTRATIONS
                     •O  COMPUTED1
           FEED  CONCENTRATIONS
                            COMP

                      !=  In (3. 79
          x IO"4) -  I.J093X
   0        200      400      600      800
                      FLOW PATH LENGTH,LNcm

                        FIGURE 19

         NITRATE  CONCENTRATION  PROFILE
                Experiment  NO. 507Q4-2
          INLET  CHLORIDE CONCENTRATION!
                 Feed      -  0.004I2M
                 Regenerant ~  O.II4M

                   FLOW RATES
                 Feed      -  100 ml /min
                 Regenerant ^  100 ml/min
                           1000
                    47

-------
a>
10
9
8

7
o>   6
"o
I ro
 c
 O   i
.—   o
 c
 o>
 o
 §  2
O
    10





\ A
r^

-4


^



xln(N03)F
&
"N



^ Analytical
(N03)F ~j
> Computed
(NO^corr

= ln(3 ,94x
\^



Feed Cone
Feed Cone
ip

IO~4)-MI8

A


;entrations
.


xlO~3 L

^^\ °
A
      0
          200     400     600     800
                 Flow Path Length , L , cm
1000
                       FIGURE 20

        NITRATE  CONCENTRATION  PROFILE
                  Experiment  NO. 50708-2
          INLET CHLORIDE  CONCENTRATIONS
                 Feed     =0.0038M
                 Regenerant =0.8IM
                  FLOW  RATES
                 Feed     =99nnl/min
                 Regenerant =99ml  min
                     48

-------
    10

w.   9
0)
~   8

^   7


I   6
      -3
 c
 O
 c
 0>
 o
 c
 o
 O

 QJ  2

 D
    10






>
^
^^
^^vH
A
-4


/:




^InfNOj)
o^^\
A ^^^^
°^^\
A
8


i Analytical
(N03V |
) Computed
(NOi)com


F=ln (2,83
^^

Feed Cone
Feed Cone
P


xicr4) - i.
-,


entrations
;entrations-


088x10-3 L

      0
200      400      600     800

       Flow Path Length, L, cm
1000
                       FIGURE  21


         NITRATE  CONCENTRATION  PROFILE

                  Experiment NO. 50720-2

          INLET CHLORIDE CONCENTRATIONS

                 Feed      =0.00387 M
                 Regenerant  = 0.875M

                  FLOW  RATES

                 Feed      =IOOml/min

                 Regeneraot = 99 ml/ mi n
                         49

-------

-------
O
I tO
o
2
cr
t-
UJ

o
o
tu
(
i
10
9
8
7
6
*5
4
3
10
»
k >\Q
Nj.
a\






ln(NO-3 )p
-4
A ANALYTICAL FEED CONCENTRATIONS
(NO^p
o
A
§V 0
\J >v
A




- In(l2.74
COMPUTED
CN03)COMF

N^
\



FEED CONC
i



^ A
IX
N^
0
7432 x 10 -3
ENTRATIONS





V

) 200 400 600 800 I0(
FLOW PATH LENGTH L cm
                       FIGURE  23

                  CONCENTRATION  PROFILE
                Experiment  NO.  50730-2
         INLET  CHLORIDE CONCENTRATION
                 Feed       z 0.003M
                 Reqengran,  ~ 0.474M
                  INLET  PH
                 Feed     ,  - 0.0012M
                 Regenerant ~ O.OOI2M
                  FLOW  RATES
                 Feed       ~ 49ml/min
                 Reqenerant  z 49m!/min
                    51

-------
en

t-o
                    0
                                               MOLES/Chi3
200
                                                                             FIGURE  24
                                                                          A
                                                                           °
                                                                            F      o   F
                                                                         (-f ) V5(Ap+ ± ) PLOTS
       J
      FOR VARYING
                                                                                      K
                                                                                       B
                                                                                         VALUES
                                                                          FLOW VELOCITY=27.8chvkEC



                                                                          Kg^ASSUMED NITRATE

                                                                              CHLORIDE EXCHANGE

                                                                              CONSTANT

-------
for K  = 2.0.  The slope of the K  = 2.0 line indicates a
           t             72
value for -i— of 3.0 x 10  cm -sec/eq.
          D X
                     t       A
Using the values of 	 and KR, indicated by Figure 24, values of
                    D X      *
A°          B°
•
-------
     4.0
     3.0
 o
 , U-
  IQ
5< n
 LJ
     1.0
       10
                O
                                               O Exp. NO. 50714
20
30
40    50   60   70  80 90 100
                                 FLOW PATH VELOCITY . cm/sec
                                    FIGURE  25
                           FILM  CONTROLLED DATA  PLOT

-------
                      Section 6

                 PHOSPHATE TRANSPORT

Investigations of phosphate-chloride exchange rates across an
anion permeable membrane were also done using the A-3 cell
geometry.  It was anticipated that phosphate transport would
be particularly complex due to the number of phosphate
species and their respective pH dependencies.

Equilibrium concentrations of phosphate species as a function
of pH are shown in the stability diagram for a 10"3 molar
phosphate solution (7) in Figure 26.  The necessary driving
force for the selective transport of phosphate ions can be
defined as:

                P, 1/Zp  C */Zc
     A = RT In (pi)     (*)
                 r       Lf                      (37)

where:

     A  = driving force or affinity; joule/mole

     R  = gas constant; joule/mole/°K

     T  = temperature; °K

     P_p = concentration of the pb.osph.ate ions in the feed
          stream; moles/liter

     P  = concentration of the phosphate ions in the regenerant
          stream; mole/liter

     Z  = valency of the phosphate ions


     Cr = concentration of the chloride ions in the feed
          stream; moles/liter

     Z  = valency of the chloride ions

Three forms of transferable phosphate ions are present in
solution and the driving force associated with each form va
ries with pH.  Keeping the pH of the feed solution constant
at 8 and varying the pH of the regenerant solution at similar
concentrations, computed values of driving forces for each
phosphate species are shown in Table 6.  Under such conditions,
the feed stream mostly contains divalent phosphate ions and
the driving force for this species increases as the regenerant
stream pH is lowered.
                           55

-------
0
10   II   12   13   14
	
                          FIGURE    26
                        STABILITY DIAGRAM
                               OF
                        PHOSPHATE SOLUTION

-------
                  TABLE  6


    ESTIMATION OF PHOSPHATE  DRIVING FORCES


                                    — "^
Total phosphate  concentrations = 10   moles/liter


                                    2
Chloride in the regenerant
  Chloride in the  feed
                                _

Universal gas  constant          = 8.314 joule/mole- K


Temperature of both  streams     = 296 K


           Feed  Concentrations at pH 8


           HPO~               ~              ~
     P =1.4 x  10~4   P  =8.6 x 10~
                                     P = 2.0 x 10
                                                ~
8. 0
7 .0
6.0
5.0
4.0
3 . 0
11,
7,
6,
6,
6,
6,
320
660
630
500
480
480
11
12
14
17
20
23
,320
, 330
, 690
, 400
, 230
, 060
11,
19,
24,
30,
35,
41,
320
350
490
200
600
000
                       57

-------
Experiments were concerned with the examination of phosphate
and chloride exchange rates, as a function of feed and re-
generant solutions pH's.   The analytical and computed feed
stream phosphate concentrations as a function of flow path
length are shown in Figures 27 through 34, respectively.

These exchange experiments were conducted with a variety of
pH values in feed and regenerant streams and the exchange
rates were compared with  the pH difference between feed and
regenerant streams.  For  this comparison, the following nom-
enclature was adopted:

     J   = exchange rate,  moles/cm2-sec;
     P   = total phosphate concentration in the feed stream,
           moles/cm3;
     ApH = the difference between inlet feed and regenerant
           pH values.

     values for all of the phosphate experiments to date were
computed from equation 35 and are tabulated with solution
pH' s in Table 7.  These J/P-p values are plotted versus ApH
in Figure 35.  In this figure, open circles represent a flow
rate of 100 ml/min; triangles represent 50 ml/min; and squares
represent 150 ml/min.   For the 100 ml/min data, J/Pj increased
rapidly with ApH until a value of ApH of about 4, whereupon
the increased driving force represented by the pH difference
ceased to have much effect.  J/P-p for the experiments 50763-2,
50766-2 and 50769-2 were virtually constnat at 1.7 x 10~3 cm/
sec., even with increasing ApH.   This J/PT value was inter-
preted as representing the boundary film limited exchange rate
for the 100 ml/min flow rate (velocity = 27.8 cm/sec).  Another
experiment under the same pH conditions of 50769-2 was then
conducted, after increasing the  flow rate to 150 ml/min (ve-
locity = 41.7 cm/sec).  The concentration profile for this
experiment is shown in Figure 34.  It has been indicated
above (see Figure 25)  that the limiting J/P-p value should in-
crease with about the square root of flow path velocity.  The
increase in J/PT for the 150 ml/min experiment over those
limiting at 100 ml/min was almost exactly what would be pre-
dicted using this square root rule.

Additional phosphate transport data were obtained in a some-
what  different type of system,  designated the D-3 Test Cell.
This cell had a path length of 52 cm with a path width of 18
cm.   It used a so-called "sheet-flow" type spacer, with an
extruded plastic (polypropylene)  netting for membrane support
and for turbulence promotion.  A picture of this general type

-------
PHOSPHATE CONCENTRATION mole /liter
3 fO C>J •£• Ul ff^ -S CD U3 O
-3






- 	 A
"" 5—
-4








•*-a___3
O
A








	 5 	
ANALYTICAL
COMPUTED








L — "= — ——£>
. FEED CGNC
FEED CONG








-^
ENTRAT10NS
ENTRATIONS
0       200      400      600      800
                  FLOW PATH LENGTH ^cm

                   FIGURE 27

  PHOSPHATE  CONCENTRATION  PROFILE
            Experiment  NO. 50742-2
      INLET  CHLORIDE CONCENTRATION!
             Feed     - .0025M
             Regenenanf ~ ,726M

              INLET  PH
             Feed     -5.2
             Regenerant ~ 4.75
              FLOW  RATES:
             Feed     - 48ml /min
             Regencr^nt - 48ml/min
1000
                 59

-------
o
E

z"
g
i-

oc
h-
z
Id
o
z
o
o

UJ
>-

X
Q.

o
X
Q.
                         ANALYTICAL FEED CONCENTRATIONS
                                  FEED CONCENTRATIONS
             200      400       600      800

                        FLOW PATH  LENGTH xLNcm

                         F_I_GURE_28.

       PHOSPHATE  CONCENTRATION  PROFILE

                 Experiment  NO 50749-2

           INLET  CHLORIDE CONCENTRATION.'

                   Feed      - .004I5M

                   Regenerant ~ .413M

                   INLET   PH

                   Feed      - 7.1
                   Regenerant = 4,9

                   FLOW   RATES!

                   Feed      = 100nnI /min
                   Regenervinf - lOOml/min
1000
                      60

-------
o

 *•>

o



-------
a
bj

<
X
CL
!/J
O
X
Q.
      200      400      600      800
                FLOW PATH LENGTH,L,cm
                  FIGURE 30

PHOSPHATE  CONCENTRATION  PROFILE
          Experiment  NO. 50763-2
    INLET CHLORIDE CONCENTRATION!
           Feed      - .00395M
           Regenerant ~ ,84M
            INLET   PH
           Feed      —8.1
           Regenerant =44
            FLOW  RATES:
           Feed      - 100 ml /min
           Rcgenerant = !00mI/min
                                                1000
                     62

-------
e
RATION, mole
LJ
O
z
o

-------
o
E

z~
o
or
UJ
o
z
o
UJ

<
X
DL
to
o
X
a.
10
l<
9
8
7
6
5
4
3
2
0
-3
k
^~~~~-^-_







-4


^^^^_^






o
A









ANALYTICAL
COMPUTED



"~T
^-^




FEED CON a
FEED CONG




^-— ^ . i




ENTRATIONS
ENTRATKDNS
0       200      400      600      800
                  FLOW PATH LENGTH ^cm

                    FIGURE 32

  PHOSPHATE  CONCENTRATION  PROFILE
            Experiment  NO. 50769-2

      INLET CHLORIDE CONCENTRATION!

             Feed      -.004M
             Regeneranf - .865M

              INLET   PH

             Feed      =9.5
             Regener^nt =: 3,9

              FLOW  RATES:
             Feed      =  iOOml/min
             Rccjenerant -  iOOml/min
                                                1000
                      64

-------
—
o
£

z
o
or
f-
z
UJ
O
•z.
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9
8
7
6
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in
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ANALYTICAL
COMPUTED




Z?-"Hft_^




. FEED CONG
FEED CONG




8— QL
^ — A
Vj



ENTRATIONS
ENTRATIONS
,
0
200
                      400      600      800
                       FLOW PATH LENGTH N

                         FIGURE 33
1000
       PHOSPHATE  CONCENTRATION  PROFILE
                 Experiment  NO. 50775-2

           INLET CHLORIDE CONCENTRATION!

                  Feed      - .0042M
                  Regeneranl — .83M

                   INLET   PH
                  Feed      - 8.1
                  Regenerant =: 6.6

                   FLOW  RATES:
                  Feed      — 99ml /min
                  Regener^nt = 99ml  min
                      65

-------
&>
4-



\


W

"o
•z.
o

<
or
yj
o
z
o
o

Jjj
»-
<
X
CL
(/»
o
I
Q.
fsj
O
      (BO A
                      o
                  ANALYTICAL FEED CONCENTRATIONS
                         COMPUTED
                           FEED  CONCENTRATIONS
o        200
PHOSPHATE
                      400      600       800
                       FLOW  PATH LENGTH NL,cm

                         FIGURE 34

                   CONCENTRATION
                                            1000
                                PROFILE
             Experiment  NO. 50772-2

      INLET  CHLORIDE CONCENTRATION!

              Feed      - .0042M
              Regener^nf ~ .84M

              INLET  PH

              Feed      - 9.5
              Regenerdnt ~ 3.9

               FLOW  RATES:
              Feed      ~ 150ml /min
              Regenerant - I50mi/min
                      66

-------
                        TABLE  7
PHOSPHATE
Exp .
No .
50732
50742
50749
50753
50763
50766
50769
50772
50775
Chloride
In Inlet
Regener ant*
-2
-2
-2
-2
-2
-2
-2
-2
-2
0
0
0
0
0
0
0
0
0
. 73
-73
.42
.52
.84
. 84
.865
.84
.83
3
3
1
1
9
9
9
1
1
TRANSPORT DATA
Phosphate
In Inlet
Feed ^
.2 x 10~4
.2 x 10 4
.085 x 10~3
.066 x 10~3
.66 x 10 H
.4 x 10 ^
.95 x 10 ^
.025 x 10~3
. 0 x 10~3
pH in
Inlet
Feed
5
5
7
6
8
8
9
9
8
.13
.18
.1
. 4
. 1
.1
.5
.5
.1
   pH
   Inlet
Regenerant

   4 . 76

   4 .76

   4 .9

   6 .35

   4 .4

   3 . 2

   3 .9

   3 .9

   6 .6
                                                       cm/sec
                                                        x 1014
                                                        5 .55

                                                        3 .47

                                                       13 .8

                                                        7 .32

                                                       17 . 0

                                                       17 .0

                                                       16 . 8

                                                       20 . 2

                                                       14.1
*mole/liter
                            67

-------
ON

00
                  20
                   [8
                   16
g

X
o

t/1
               t-
               O.
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                   12
                   10
               ~   8
                   4
                   0


0.83M
tQOnn

/
/


-ci /^
/rrunrr
/~


O0.52M-O
99m!/min
/
/ o °-72!
/ lOOn
A °'72f
"48m

vs-ci
Ti/min
^-Cl
I/ min


s*
^-^

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0.42M-CI
lOOml/mir






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0 84M-CI
I00m!/rni
T






— •"
O.
]
0 84M-C
n 99ml/n







0.84M-C!
150m! /min

0 86
Tin iQOr







M-CS - •
nl /min







                    01          2345
                                            ApHlpH  feed - pH  Reqenzrant) in

                                                     FSGURE 35
                        PHOSPHATE TRANSPORT DATA AS A FUNCTION OF pH DIFFERENTIAL

-------
of spacer is shown in Figure 36.  Steady state values for
exchange rates were determined as described previously.  Data
from six experimental runs with this system are shown in
Table 8.  The behavior of the parameter J/PX was examined at
various flow path velocities.  J/PT values for these experi-
ments are plotted in Figure 37 as a function of flow rate.
The slope of the best fit line through this data shows the
phosphate-chloride exchange rate varying with the 0.55 power
of flow path velocity.
All reported values of J/PT  (or J/N for nitrate-chloride ex-
changes) are plotted versus  flow path velocity in Figure 38.
This plot again shows all exchange rates varying approximately
with the 0.55 power of flow  path velocity.  Figure 38 also
shows that the type D-3 spacer, which has greater turbulence
promoting properties, results in 2 . 4 times the exchange rate
provided by the A-3 type spacer, under similar flow conditions
                           69

-------
           FIGURE  36
D-TYPE SPACER  CONFIGURATION
           70

-------
                                             TABLE  8
PHOSPHATE-
Inlet
Phosphate
Concentration
Expe r imen t
Number
50715
50718
50719
50723
50725
50725
-3(B)
-3
-3
-3
-3(A)
-3(B)
Fe
10
9
9
10
10
10
ed1
. 3
.7
.8
. 1
. 2
. 2
Reg . l
10
10
9
10
10
10
. 5
. 4
. 9
. 1
. 2
. 2
-CHLORIDE EXCHANGE DATA; D-3 TEST
Outlet Inlet
Phosphate Chloride
Concentration Concentration
Feed1
7
6
5
5
6
7
. 80
. 85
. 45
. 95
.69
. 30
Reg . 1
12 .8
13 . 2
14 . 2
14 . 3
13 .8
13 . 2
0
0
0
0
0
0
Feed2
.0042
. 0040
.0041
.0041
. 0041
. 0041
Reg . 2
0
0
0
0
0
0
.81
.81
.81
. 80
.81
.81
Fe
9
9
9
9
9
9
CELL
Inlet
ed
. 5
. 5
. 5
. 4
. 5
. 5
pH
Reg .
3
3
3
3
3
3
. 9
. 9
. 9
. 7
. 7
. 7
Flow
Feed3
250
199
50
75
99
150
Rate
Reg . 3
250
200
50
75
100
151
1mole/liter x
2mole/liter
3rnl/min

-------
    10
o
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7

6


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    3
                     3   456789 1.0        2     3

                                       FLOW VELOCITY , cm/sec


                                   FiGURE 37

                     FILM  CONTROLLED  DATA  PLOT (A)
                                                          56789 10.0

-------
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             FIGURE 38
FILM CONTROLLED DATA PLOT (B)
3  4  5 6 7 89100

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                      Section 7

         COMBINED NITRATE-PHOSPHATE TRANSPORT

Limited data were obtained for nutrient removal from multi
component solutions, for comparison with the results from
the simpler nitrate-chloride, and phosphate-chloride systems.
Typical results are presented in Table 9.  In this experiment,
the A-3 test cell was used, with a flow velocity of 30 cm/sec
and a regenerant stream chloride concentration of 0.8M.  Com-
parative data from two-ion systems for nitrate and phosphate
removal are shown in Table 10.  The presence of the addition-
al ionic species reduced the nitrate and phosphate removals
by 4.590 and 5.5%, respectively.  This is not considered sig-
nificant, since the regenerant stream chloride concentration,
i.e., driving force; in the multi-component system was small
er by about this amount than in either of the two-ion systems.
The conclusion is that no significant reduction in N-P trans-
port rates results from the presence of competing ions.  The
transport of these competing ions, however, does present an
additional demand on regenerant chloride which could be re-
duced by a more selective membrane.

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                         TABLE 9

       N-P  TRANSPORT IN  MULTI-COMPONENT  SYSTEM
                   (Run  No.  50728-3)

   Regenerant Chloride  Inlet = 0.8M
   Regenerant pH Inlet        = 3.8
   Flow Velocity              = 30 cm/sec
   Spacer Type                = A-3
   Membrane Type              = Tokuyama  Soda AV-4T
   Temperature                = 22.8°C

  Feed Concentrations,  mole/liter

          Inlet                   Outlet            % Removed

Chloride        4.12 x 10~3     6.85 x 10~3

Nitrate         3.97 x lo"4     1.34 x 10~4             66

Sulfate        10.40X10"11     2.92x10"^             73

Phosphate      10.23 x I0~k     6.59 x I0~k             36

PH              9.5             7.9
                            76

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                         TABLE 10

     NITRATE TRANSPORT  IN NITRATE-CHLORIDE SYSTEM
                    (Run  No. 50708-2)

    Feed  Concentrations,  mole/liter

             Inlet                   Outlet            % Removed

Chloride          3.8  x  10~3       4.1   x 10~3          	

Nitrate           4.2  x  lo"*4       1.24 x lo"4           75

Regenerant  Chloride  Inlet = 0.81M
Flow Velocity              = 30 cm/sec
Spacer Type                = A-3
Membrane  Type              = Tokuyama  Soda AV-4T
Temperature                = 22.0°C
   PHOSPHATE TRANSPORT  IN PHOSPHATE-CHLORIDE SYSTEM
                       (Run 50769-2)

    Feed  Concentrations,  mole/liter

             Inlet                   Outlet            % Removed

Chloride          4.   x  10~3          	              	

Phosphate        9.9  x  lo"4       5.8  x lo"4          41.5

pH                9.5               8.3

Regenerant  Chloride  Inlet = 0.865M
Regenerant  pH Inlet        = 3.9
Flow Velocity              = 30 cm/sec
Spacer  Type                = A-3
Membrane  Type              = Tokuyama  Soda AV-4T
Temperature                = 22.4°C
                            77

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                      Section 8

              ECONOMIC FEASIBILITY OF THE

           NITRATE-PHOSPHATE REMOVAL SYSTEM

From the data presented in Figure 38, a reasonable estimate
of the economics involved in the proposed nutrient scrubbing
process was developed.  For illustration, consider a treatment
scheme where:

     a.  901 of the influent phosphate is exchanged for chloride;

     b.  The ratio of feed to regenerant stream flow rates is
         50/1;

     c.  Process Configuration is plate-and-frame. counter-
         current flow;

     d.  Feed stream flow path velocity is 50 cm/sec.

Such a scheme is illustrated in Figure 39.

Since phosphate-chloride exchange rates appear to be slower
than  nitrate-chloride exchange rates, under similar experi
mental conditions, this design illustration will be controlled
by the phosphate removal requirement (901).  From Figure 38,
using a D-3 type spacer and extrapolating to a 50 cm/sec feed
stream velocity;

     (J/PT) = 7.0 x 10"3 cm/sec

Now since:

                FF d In (PTJ
                     ^L                            (38)

where:

     F-p = feed stream flow rate, cm3/sec
      r

     u  = flow path width, cm

equation 38 can be rewritten:

                           FL
     co. dx = d (Area) =    TT/'P "A ^  ^-n
                                                   (39)
or:
     Area =
              G
For a 90% phosphate removal, therefore:
                            79

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         Feed
    Concentrations*
Phosphate  = I0~4
Nitrate    =  4.0xlO"§
Chloride   =  6.l6xKT3
Sulphate   =  I0~3
            4-
                                    Regenerant
                                 Concentrations*
                             Phosphate =  10~3
                             Nitrate
                             Chloride
                              Sulphate
            4.0x10-4
            0.8
            2.25x!0~3
            3
   Outlet
    Inlet
                     AM
      Inlet
                                 Temperature = 24°C
                                    FC/R  = 50/1
                                     r   K
     Outlet
     Feed
Concentrations*
Phospate
Nitrate
Chloride
Sulphate
pH
= 10-3
= 4.0x10-4
= 4.0x10-3
= 10- 3
= 9




FIGURE 39
       Regenerant
    Concentrations *
Phosphate  = 4.5xlO~ 2
Nitrate    = |.8xlO"2
Chloride   = 0.692
Sulphate   = 2.25xlO"3
      * mole / liter
     HYPOTHETICAL  PHOSPHATE AND
       NITRATE  REMOVAL SYSTEM
                   80

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     Area      2.
            7.0 x
                                     J~ *
Figure 38 also shows that, with a 50 cm/sec velocity and an
A-3 type spacer, the nitrate flux would be:

     (J/N) = 4.5 x ItT3 cm/sec

As the D-3 type spacer provides 2.4 times the exchange rate
of the A 3 type spacer, the nitrate flux with the former spacer
type would be:

     (J/N) = 4.5 x 2.4 x 10 ~3 = 1.08 x 10 "2 cm/sec

From equation 38, therefore:

              =  iea x (J/N) +
                 F                  ^n             (40)

                  329 x 1.08 10"2 + ln(4.0 x 10"4)

                  3.55   7.81

                  11.36

       (N)   , = e n-36
       " }  out

So,  (N)  t

              = 1.17 x 10~5 mole/1

The nitrate removal, then, would be about 97%

If a preliminary nutrient removal process configuration  similar
to a plate-and-frame electrodialysis stack configuration is
assumed,  then about 600 membranes with  10 ft2  each of  available
transfer area would be employed in a typical module.   Based
upon large scale electrodialysis plant  estimates,  a pre-
liminary capital cost estimate for a comparable nutrient re-
moval plant would be $25,000 per module.
                            81

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At 1.55 x 104 ft2/MGD, the hydraulic capacity of a  single
module plant, designed for 90% P removal, would be:

     6i°-x 10  = Q.587 MGD
     1.55 x 10
The capital investment requirement would be:

     $25,000     =$00
     0.387 x 106   =
Amortized at 8 percent per year, with a 90 percent  load
factor, the investment retirement cost would be:

     (0.0646) (0 08)  (100) (1000) _ , 5? ./-, Q00   x
     ~      (365) (0.90)           ' -   y/ »     -s— '

If membrane costs and replacement rates are similar to
electrodialysis plants, i.e., $1.00/ft2 and 30%  replacement
per year, then membrane replacement costs would  be:

     (1.55 x IP") (100) (0.30)  =   4U/l5000  gal.
         (365) (0.90)  (1000)           y/ ;    b

Chemical costs would  include NaCl for regenerant  chemicals  and
R^SO^  for regenerant  stream pH control.  Sodium  chloride  costs,
at $16,50/ton bulk, would be:

     (G.8M) (58.46) (3785) =       ,,  OOQ   ,
                                    ' 1;UUU gdl °
            ( 4 5T)  (50/1)
     111.50)^(7.78) (100)  . 6.41,/1>000
Sulfur ic acid requirement, for adjustment of  inlet  regenerant
stream pH to 3, would be about 3 x 10 ~3 equivalents  per  liter
of regenerant stream.  Acid costs, at It/equivalent,  would  be

     I3jS_10t3785) (1) .
This design illustration is summarized  in Table  11.

The experimental data indicates that the process,  as  described
in  this illustration is technically feasible.  At  the above
cost estj.mate, 9 . 87^/1, 000 gal., it is probably not  economically
viable .
                          82

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                       TABLE  11
         NUTRIENT REMOVAL DESIGN  ILLUSTRATION
Feed Water  Characteristics
     Chloride
     Sulfate
     Nitrate
     Phosphate
     PH
4x10
   >M
    10~3M
4 x 10
    10~3M
142 mg/1
 96 mg/1
 25 mg/1
 31 mg/1
Nutrient  Removal
     Nitrates
     Phosphates
Capital Cost Estimate
Regenerant  Chemicals
Membrane  Area  Requirement
Feed Waste  Stream Ratio
    97%
    90%
    $64,600/MGD
7.78 Ib NaCl/1,000 gal
1.55
50/1
    1.55 x  10k  ft2  /MGD
Nutrient  Removal Cost Summary*
A.  Principal  Operating Costs
      Regenerant Chemicals  (NaCl)
      Acid  Feed
      Pumping  Energy
      Membrane Replacement
B.  Capital Costs(*8%/year)
        Total
               <:/!, OOP  gal

                   6 .41
                   0 .23
                   0 .25
                   1.41
                   1.57
                   9 .87
*Does not  include operating  and maintenance  labor  or any
general  and  administration costs.
                            83

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However,  a cost level of 5^/1,000 gal. may be eventually attain-
able since at least the capital and membrane replacement
cost estimates for this design illustration are likely to be
overly conservative.    This is for  the following reasons:

1.  These costs are based upon published estimates for
    brackish water electrodialysis  plants of conventional
    plate-and-frame designs;

2.  The nutrient removal module proposed here is a considerably
    less  complex design concept than an electrodialysis
    stack.  It does not require the two electrodes, separate
    electrode streams,  electrical insulation between mem-
    branes,  B.C. rectifiers,  substations, etc., all of which
    have  been included  in the $25,000/module cost figure.

3.  The nutrient removal module does not have to assume a
    plate-and-frame configuration,  but could be spiral-wound,
    cross-flow, tubular, or a variety of configuration one
    or any of which might well provide a more economical
    packaging configuration than the plate-and-frame used by
    the electrodialysis process;

4.  For the  purposes  of preliminary costing, both membrane
    costs and replacement rates were based upon electro-
    dialysis field experience.  Neither of these is necessarily
    applicable to the nutrient removal process, where the mem-
    branes are not subjected to nearly the same stresses as are
    those in the electrodialysis process.  It is likely that
    a less costly (by 50%)  membrane would be more desirable for
    the ultimate nutrient removal system and that such a mem-
    brane would stand up as well as, and perhaps perform
    better than, conventional electrodialysis membranes used
    to date.

5.  The design illustration presented here is based upon ex-
    perimental results  from a laboratory apparatus that like-
    ly did not resemble closely the optimal design for this
    particular process.  A more rigo'rous analysis of the de-
    sign concepts involved in this  nutrient removal process
    would, as has been  demonstrated for other membrane
    processes, result in reductions in both the membrane area
    and the  regenerant  chemicals requirement;

6.  No economic benefit whatsoever  has been assigned to the
    highly concentrated nutrient  solution that results from
    this  process, the chemical composition of which can be
    tailored or modified virtually  at will.
                          84

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                      Section 9

      PRELIMINARY NITRATE - PHOSPHATE PILOT PLANT

A small nutrient removal pilot plant was constructed and op-
erated for a brief period of time on secondary effluent from
the Leominster, Massachusetts activated sludge facility.
These tests were designed to demonstrate the feasibility of
selective nitrate and phosphate removal on an actual sewage
plant effluent and to evaluate any unanticipated problems
that might arise.  No attempt was made to optimize the opera-
tion and observations were primarily concerned with the amount
of nutrients removed and the tendency of the membranes to
foul.

The design of the test exchange-multicell is shown in Figure
40, and a photograph of the assembled unit in Figure 41.  A
schematic drawing of the complete test apparatus is presented
in Figure 42.  The multicell consisted of five exchange cells
separated by Lucite blocks, used to help minimize sealing pro-
blems.  Larger cells would, of course, use conventional gas-
keting.  Ports were provided for sampling both feed and re-
generant streams at several positions along the flow path.
Total membrane area was 2720 cm2, and the membranes used were
Tokuyama Soda Co., Ltd., anion exchange type AV-4T, the same
as those used in the laboratory studies.  Maximum flow was
about 40 GPD.

The plant was operated for seven days over the ten-day period
between 14-23 May, 1969.  Although usual start-up difficulties
were encountered, and the operational time was relatively
brief, the feasibility of 90% nitrate and/or phosphate re-
moval from secondary effluent was demonstrated.

Operation began on 5/14; nitrate and phosphate concentrations
are charted chronologically on the accompanying graphs, Fi
gure 43 and 44.  Flow rates on feed and regenerant sides
were maintained at 35-40 and 4-5 ml/min, respectively.  The
regenerant solution was made-up from tap  water to be 0.8N in
sodium chloride.  Feed solution was the effluent from the
final clarifier augmented by nitrate and phosphate salts to
approximately 10 mg/1 each.  A typical influent and effluent
analysis during good operation is given in Table 12.  In-
itially, an activated carbon filter was employed in the feed
stream ahead of the exchange cell.  This filter was bypassed
on the last two days of the test in order to observe the ten-
dency of the system to foul the membranes and to determine
the effect of any such fouling on nitrate-phosphate removal.

For the first two days of operation, the system appeared to
perform well, providing low effluent nutrient concentrations

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                            Regenerant  Feed

     AM   = Anion Transfer Membrane
     ^1 2   ~ ^eec' Port Sample
     ^12.. = R^generant Port  Sample
          FIGURE 40
EXCHANGE-MULTICELL SCHEMATIC
          86

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     FIGURE 41
EXCHANGE  MULTICELL
      87

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     Feed
  Reservoir
         Regenerant
         Reservoir

            Feed
           Effluent
Regenerant
Effluent
             FIGURE 42
SCHEMATIC FLOW  DIAGRAM  FOR
N-P PILOT  PLANT AT LEOMINSTER

-------
00
                         5/14
5/23
                                          FIGURE  43
                                      NITF
-------
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5/23
                                           TIME
                                           FIGURE 44
                                      PHOSPHATE REMOVAL

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                        TABLE  12
           LEOMINSTER PILOT PLANT OPERATION
                         Feed
Product
Removal
53
150
25
12.7
9 .82
9.8
472
9 .5
<1
0
0 .71
6 . 2
-__
94
96 +
96 +
93
_ -, _
Chloride  (Cl  )




Bicarbonate  (HCO )




Sulfate  (SO~)




Nitrate  (NO~)




Phosphate  (P)




PH
Feed Stream  Flow Rate =  15  gpd




Regenerant Stream Flow Rate  =  1.05 gpd




Regenerant Stream pH:  In =  1.6     Out = 6.2




Regenerant Stream Chloride  Concentration:   0.97M  =  34,500 mg/1
                            91

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and high percentage removal.   The performance then deteriorated
due to erratic operation caused by difficulties with pumps and
feed lines.  When these difficulties were corrected, satisfac-
tory operation was again attained.  Port samples taken at
this time along the length of the flow path indicated a very
rapid removal of nitrate with maximum reduction being realized
at the first port (972 cm path length) .   Phosphate was less
rapidly removed, the system achieving only a 701 cut at this
position.  Figure 45 shows these data.  As a result of bypas-
sing the carbon filter, phosphate removal was substantially
reduced and nitrate effluent concentration also increased at
first.  The poor nitrate removal may have been due to the
occurrence of denitrification in the reservoir and/or analy-
tical anomalies which gave inconsistent values for influent
concentration.  With fresh solution, good nitrate removal was
obtained on the final test day, although no improvement
occurred in phosphate removal.

In addition to the nutrient removal, sulfate concentrations
were reduced from 25-30 mg/1 to <_ mg/1 during the entire
test period.  The large increase in product water chloride
concentration indicates a cross-leak in the system between the
feed and regenerant compartments that did not exist in the
laboratory apparatus.  The removal achieved was in spite of
this leak and indicates that improved performance can be ex-
pected.

The completion of these preliminary field tests on nitrate-
phosphate removal from secondary effluent indicated, to the
extent possible at this stage, that the nutrient removal
process is indeed technically feasible.

Further work should be concerned with design modifications
and-membrane improvements directed toward the reduction of
process costs.  The demonstration of the process on a larger
scale, as described in the next section, has been of con-
siderable help in delineating such design changes.
                           92

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   12.7
INLET
 2        3
PORT NUMBER
                 FIGURE  45
      PORT SAMPLES  FOR  5/21/69
               93

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                      Section 10

         OPERATION OF PILOT PLANT (LAWRENCE)

Large scale field testing of the nitrate-phosphate removal
process was accomplished by the design and construction of
a multi-membrane pilot-scale prototype with design capacity
in the 1,000-2,500 gpd range.  Field studies utilizing this
cell were carried out at the Lawrence Experiment Station
(LES) of the Massachusetts Department of Public Health with whom
Process Research contracted for the use of certain facilities
and the services of certain personnel.  Approximately 200
square feet of experimental floor space at LES were utilized
for the construction and operation of a pilot scale activated
sludge waste treatment unit with final sand filtration and
small holding basin.  This unit provided sand-filtered sec-
ondary effluent for the EXD nitrate-phosphate and ammonium
removal systems on a continuous basis, throughout the field
test period.  Influent to the treatment plant was raw domestic
sewage drawn from a local interceptor of the City of Lawrence's
collection system.  Figures 46 and 47 are ground level views
of the activated sludge installation.  The two raised aera-
tion tanks are visible on the right in both pictures.  The
sand filter is on the extreme left with a temporary settling
basin under the floodlight.  The latter was subsequently
replaced by the clarifier section shown in Figures 48 and 49.
Figure 50 shows the overall pilot plant from a vantage point
on the second level of the experimental area.

Equipment layout and flow directions are more clearly seen
from this aspect.   The tank at lower left is a holding tank
from which the feed for the EXD units under test was taken.
When operating, the removal cells themselves were placed on
the concrete step just below the aeration tanks or on a rec-
tangular table next to the holding tank.  Pumps for the ex-
change units were also mounted on the concrete step or on
a shelf underneath the table.

The prototype EXD nitrate-phosphate removal unit was assembled
as a multicell stack in plate-and-frame configuration consist-
ing of 20 feed cells alternated with 21 regenerant cells.
Feed and regenerate streams were separated by Tokuyama AV-4T
anion transfer membranes; 40 membranes were required.  Cell
spacing and serpentine flow paths were formed by polyethylene
spacer/gaskets designed for this unit.  One of these spacers
is shown in Figure 51.  The serpentine flow path itself is
2.5 cm wide, 665 cm long and makes eight passes along the
length of the cell.  The regenerant spacer is 40 mil thick
with the flow path channel filled with 40 mil porous poly-
ethylene.  Feed spacers were of identical configuration but
only 20 mil thick and filled with open plastic mesh.  Overall
                          95

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          FIGURE 46

LAWRENCE  EXPERIMENT STATION
   ACTIVATED SLUDGE  PLANT
           96

-------
          FIGURE 47
LAWRENCE EXPERIMENT STATION
    ACTIVATED SLUDGE PLANT
 AERATION TANK AT UPPER RIGHT
          97

-------
       FIGURE 48

    CLARIFIER SECTION
ACTIVATED SLUDGE PLANT
        98

-------
       FIGURE  49

  SAND FILTER  SECTION
ACTIVATED SLUDGE PLANT
   CLARIFIER IN REAR
        99

-------
          FIGURE 50

LAWRENCE EXPERIMENT STATION
      AERATION AT RIGHT
  FEED TO EXD UNIT AT  LEFT
            100

-------
             FIGURE 51
SERPENTINE NITRATE-PHOSPHATE  SPACER
              101

-------
dimensions of spacers and membranes were 9.5 cm x 30.5 cm
with an active transport area of 61%, or 1690 cm2.  Poly-
vinylchloride end-blocks and aluminum end-plates were employed.
A drip channel was cut around the outer edge of the lower
end-block to carry off exuded liquid.  Eight aluminum bolts
were provided for sealing via brackets welded to each end-
plate.  Figure 52 shows the multicell during assembly with
about one-half the individual cells in place.  The bracing
on the underside of the top end-plate may be seen in Figure
53, which also shows the top end-block in front of the open
unit.  Figures 54 and 55 are two views of the completely
assembled EXD multicell.  Overall dimensions were approximate-
ly 43 cm x 102 cm x 46 cm high.   The prototype unit was de-
signed to operate at 2,600 ml/min feed flow rate, about 1,000
gal/day, and 50 ml/min regenerant flow rate.

Concurrent with end-plate design and fabrication for the pro-
totype multicell, a single feed  cell subunit was assembled
using full-size end-blocks, spacers and membranes.  The sub-
unit was constructed as a single feed cell flanked by two re-
generant streams with the whole  sandwich clamped between two
Lucite end-blocks.  The eight-pass serpentine spacer pictured
in Figure 51 was used for both feed and regenerant cells.
In the initial versions of the single cell subunit, plastic
mesh was used in all cell flow paths instead of the alterna-
tive porous polyethylene.  The feed stream was 40 mil thick
while the two regenerant streams were each 20 mil thick.  A
feed flow rate of 250 ml/min through the subunit was equivalent
to approximately 1,500-2,00 gal/day in a full-size prototype
with 15-20 feed cells.  Figure 56 illustrates the subunit as
it appeared during early testing.  In later trials using the
subunit configuration the PVC end-blocks and aluminum end-
plates designed for the full-size prototype were employed to
seal the cell rather than the array of C-clamps and channel
iron brackets seen in the Figure.  This latter arrangement
is shown in Figure 57.

Initial experiments on the single-cell assembly were run using
the synthetic secondary effluent listed in Table 13.  Data
from these runs indicated that 90% removal of nitrate (and
sulfate)  could be attained and that phosphate removals were,
in fact,  limiting,  fluctuating between 50 and 80%.
                          102

-------
                  FIGURE  52
EXD NITRATE-PHOSPHATE REMOVAL PROTOTYPE CELL
               DURING ASSEMBLY
                   103

-------
                   FIGURE  53

OPEN EXD NITRATE-PHOSPHATE REMOVAL PROTOTYPE CELL
       TOP  END-BLOCK  IN  FOREGROUND
                   104

-------
            FIGURE 54
COMPLETED  EXD NITRATE-PHOSPHATE
      REMOVAL MULTICELL
             105

-------
          FIGURE 55
COMPLETED EXD PROTOTYPE CELL
          106

-------
                FIGURE 56

                SUBUNIT OF
PROTOTYPE NITRATE-PHOSPHATE REMOVAL  CELL
                  107

-------
             FIGURE  57

EXD NITRATE  PHOSPHATE  REMOVAL UNIT
  ASSEMBLED  AS SINGLE CELL SUBUNIT
               108

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                       TABLE 13

             SYNTHETIC SECONDARY EFFLUENT

       Constituent              Concentration, mg/1
           Ca                            54

           Na                            48
           NH4  (as '-v                    14

           S04                           51

           P04                           30

           N°3                            8

           HC03                         170

           Cl                            48

Similar results were obtained with feed streams of both 90 and
30 mg/1 PC>4 and at the optimum pH difference of four or great-
er.

The regenerant solution was that of Table 13, augmented to
0.8M sodium chloride.  In addition to the somewhat low phos-
phate removal, two other problems were revealed by those first
trials.  The Tokuyama Soda Company AV-4T anion membranes
tended to discolor (turning a dark blue) at pH 9.3 or higher
and inter-and intrastream leakage was observed at the inlet
manifold holes.

On investigation of this disconcerting property of changing
color, it was found that the membranes could be restored to
their original tan color by leaching with methanol.  After
this treatment, no further color change could be produced.
We attributed this anomalous discoloration phenomenon to re-
sidual leak-test dye inadvertently left on the membranes af-
ter completion of the manufacturers quality control procedures
Extended correspondence with, and subsequent testing of,
samples of the anomalous membranes by Tokuyama eventually
elicited an opinion from them stating that the membranes were
"exactly standard material of AV-4T in color and quality."
Nevertheless, Tokuyama agreed to replace the membranes, and?
in the future, to provide material which did not discolor un-
der conditions of varying pH.  Moreover, it appeared that the
presence of such a colored substance was detrimental to the
anion exchange rate across the membrane and was a factor to
be considered in attempts to achieve a 90% phosphate removal.
                           109

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This was shown by the effects of the methanol decolorizing
treatment,  which generally improved the percent phosphate
removal.  The best removal efficiencies were obtained with
membranes that had been washed in methanol.   Normally this
treatment consisted of simply soaking the membranes overnight
in methanol.   A few small-scale confirmatory tests were run
using the A-3 cell.  These experiments duplicated the improve-
ment in phosphate removals obtained with methanol-treated mem-
branes and indicated that unless all the potential colored
material was  removed, use of an acid regenerant stream would
not produce the expected high exchange rates.  Since deco-
loring was  an uncertain procedure and it was equally uncer-
tain when and if non-colorable membranes would be available
from Tokuyama, operation with an essentially neutral feed
and regenerant stream appeared to be best with the available
membranes.

Analysis of the leakage occurring at the inlet manifolds in-
dicated that  the interstream leakage from feed to regenerant
was induced by the higher pressure in the feed stream rela-
tive to the regenerant stream (40:2 psi) near the regenerant
outlet, which caused the flexible Tokuyama membrane to bow
into the flow path, allowing feed solution to flow between
feed gasket and membrane into the regenerant manifold.  The
leak was corrected by extending the plastic screening to fill
the entire regenerant flow path area and supporting the low
pressure side of the membrane with a 3 mil stainless steel
insert glued  in place.  These measures effectively prevented
the membrane  from bowing.  A similar but less severe leak
occurred from the regenerant stream to the feed stream near
the feed outlet, the pressure differential being much less
at this point.  Solution to the problem in this area was to
provide additional gasketing around the manifold holes with
a silicone cement.  This material does not adhere permanently
to the membrane or the spacer/gasket, seals well, remains
pliable, and  cures when wet.

Intrastream leakage occurred at the feed inlet.  The feed
stream at 20  psi bowed the membrane into the regenerant flow
path, permitting feed solution to flow between spacer and
membrane to short-circuit the feed flow path.  A similar
situation was observed at the regenerant inlet.  Both defi
ciencies could be eliminated by applying silicone cement to
the appropriate spacer straps in order to improve the gasket-
ing properties.

While the procedures described above served to eliminate the
leaks and somewhat clarify the problem of the anomalous
                            110

-------
colorization of the anion membranes, phosphate removal effi
ciency continued to be inadequate, i.e., substantially less
than 90% removal.  Cell configuration was therefore modified
by replacing the plastic screening in the regenerant flow
path with solid, highly porous polyethylene sheet.  Hydraulic
tests had previously indicated that adequate liquid flows
could be maintained through this porous sheet.  The regener-
ant spacer gasket was retained at a 40 mil thickness, to match
the gauge of the porous  sheet.  Feed stream geometry was also
retained at 40 mil thickness.  Results from operation of the
subunit in this configuration are given in the first six en-
tries in Table 14.  Desired removal efficiencies were not
obtained at flow ratios of 50/1 and changing the ratio to 35/1
by decreasing the feed stream flow did not improve the results.
The feed stream configuration was then altered to provide a
20 mil thick flow path, filled with screening of the same
thickness.  The regenerant stream was retained at 40 mil to-
gether with the porous sheet inserts.  An experimental run
under these conditions (51061 in Table 14) gave a 90% phos-
phate removal at 120 ml/min feed stream flow, a ratio of 25/1.
This configuration was then made the basis of the full size
prototype cell described earlier in this section.

The pilot EXD unit was started-up at the Lawrence Experiment
Station on 28 April 1970.  However, initial hydraulic tests
indicated excessive leakage to the outside of the multicell
and an inability to attain the desired feed flow rates.  These
difficulties were diagnosed as unmatched thicknesses between
the feed stream spacer and the plastic screening in the feed
flow channel.  The entire multicell was therefore disassembled
for reconstruction of the feed cells.  These changes were
rapidly completed and the unit returned to operation on 8 May.

Nutrient removal trials commenced on 8 May with the cell oper-
ating at 2,700 ml/min (1,000 gpd) feed flow rate and continued
for six days.  LES personnel were in charge of daily operation
and maintenance, and performed all analyses of influent and
effluent streams.  The removal unit was started each morning
about 8:00 a.m. and shut down at the end of the day, approxi
mately 4:00 p.m.  This schedule provided 7-8 hours of running
time per day.  Results from this operational period are
given in Table 15.

During the run, feed flow rate varied from 2,700-2,300 ml/min
total flow, occasionally decreasing about an hour before shut-
down.  Regenerant flow rates were held between 50-70 ml/min,
giving a range of flow ratios of 46/1 to 38/1.  Difference  in
pH between the feed and regenerant solutions was maintained
at 1 2 pH units and both streams were used on a once-through
basis.  Sampling of the cell influent and effluent was done  at
                          111

-------
                                      TABLE 14
Experiment
  Number

51057A

51057B

51057C

51057D

51058

51059

51061
Flow Rate, ml/min
Feed	Regenerant
  240

  240

  200

  175

  240

  240

  120
REMOVAL - PILOT
rant: 0 . 8M NaCl
H Regenerant = 7
Phosphate Cone. ,
Feed In
2 . 90
10 .3
10 .3
10 . 3
3 .15
3 . 15
3 .05
CELL
.7-7.8


moles/liter x 1 (ft
Feed Out
1 .
3 .
4 .
3 .
1.
1.
0 .
80
47
13
75
26
02
2


POit
Removal , %
63
66
60
64
60
67
93

-------
TABLE    15
NUTRIENT REMOVAL -
Regener ant


Date
5/08/70
5/11/70
5/12/70
5/13/70
5/14/70
5/15/70

Date
5/08/70
5/11/70
5/12/70
5/13/70
5/14/70
5/15/70
: 0.8 mole/

Flow Rate,
ml/min
2700
2400
2300
2300
2300
2750-2100
Feed

P04 (P) ,
Ortho
14. 4/5 . 5
16. 7/5 . 5
17 . 5/6 . 4
17 . 0/7 . 0
8 . 2/2 .6
6 . 4/3 . 0
liter NaCl;

Ve loc i ty ,
cm/ se c
17 . 7
15 .8
15. 1
15. 1
15 . 1
18. 1-13
, In/Out

EXCHANGE DIFFUSION PILOT CELL
7-8 pH; 24-25°C;
Feed, In/Out

Conductivity
Mmhos/cm
740/740
700/740
680/680
640/640
700/700
.8 640/640
50-70 ml/min


PH
6 .7/6.0
7 .0/6.3
7 .2/6.4
7 . 1/6 . 8
7 . 3/6 .5
7 . 1/6 .3
total flow

Color Turbidity,
Units JTU
15/12 0.41/0.38
15/12 0.41/0.41
15/12 0.47/0.44
15/14 0.75/0.45
20/18 0.90/0.90
20/15 1.20/1.60
% Removal

mg/1 N03 (N) , S04
Total mg/1 mg/1
17 .5/7 .0
19 . 1/10 . 5 4
17 . 5/7 . 2 5
16 .8/7 . 2 8
9 .0/3.0 6
7 . 3/3 . 0 10
63/32
.6/0.8 64/0
.6/1.3 64/18
. 0/1 . 9 64/1
.4/0.8 72/16
.9/1.2 65/32

Ortho-P
63
67
63
59
68
53

N03 S04
49
83 100
77 72
76 98
87 78
89 51

-------
approximately 11:00 a.m.  daily and phosphate analysis as well
as conductivity,  pH and temperature measurements were then
available in the  afternoon so that operating adjustments to
the cell could be made if desired.  Nitrate and sulfate ana-
lyses were normally available the next day.  As seen in the
lower right columns of Table 15,  removal efficiencies were
not at the desired level, phosphate averaging 62% removal
and nitrate 82%.   As expected, phosphorous exchange was limiting
and was substantially below the 901 figure.  Nitrate removal
was markedly better than phosphate and very close to the re-
quired value.  Sulfate analyses and removal percentages are
included as a matter of interest  although not a primary con-
cern in this study.  During this  period they were quite erratic.

The initial period of operation for the prototype N-P removal-
cell was terminated after six days when the feed flow pump
failed due to a fractured impeller, but observations during
the test indicated the desirability of several modifications
in the system.  The PVC feed lines from the effluent reser-
voir to the exchange unit were distended and weakened from the
pumping pressure  and were replaced by rigid polyethylene
tubing.  The sand in the final filter was replaced with a
mixed filter media (Microfloc) and a surface washer instal
led near the top  of the filter column.  Changes were also
maded in the settling tank to eliminate stagnant areas, and
a sludge skimmer  and new sludge return pumps were installed.
The air distribution system in the aeration tanks was also
modified.

All repairs and modifications to  the EXD multicell and the
actiA^ated sludge  pilot plant were completed by 8 June and
operation was resumed at that time.  Procedures were the same
as those in force during the previous run except that the re-
generant solution was operated in a recirculating mode, with
periodic replacement of the entire solution.  A small inter-
stream leak from  feed to regenerant was present in the re-
assembled cell.  This amounted to approximately two liters
per hour as measured by total regenerant volume; about 1% of
the total feed volume and was considered insignificant.  Re-
sults for the period 8 June through 30 June are presented in
Tables 16 and 17.

From 6 June through 16 June, the  2,700 ml/min feed flow rate
(•"'-•1,000 gpd) used in the previous run was maintained while
the recirculated  regenerant solution was run first at 270
ml/min, a 10/1 ratio of flow rates, and later at 500 ml/min,
a 5/1 ratio.  Regenerant concentration was 0 . 8M Nad.  No
consistent significant improvement over the earlier once-through,
45/1 flow ratio operation was observed in nitrate/phosphate
removal efficiency.  Phosphate exchange was still limiting
                          114

-------
TABLE    16
EXD NUTRIENT REMOVAL - PILOT CELL, OPER,
Feed: Lawrence Secondary Effluent
Regenerant: 0 . 8M or 1 . 2M NaCl, recircul
Feed , In/out
Date
6/8 i
6/9
6/10
6/11
6/12
6/15
6/1*
6/17
6/18
6/19
6/22
6/23
6/24
6/25
6/26
6/29
6/30
(1)
(2)
Total
Flow Rate
ml/min
[1) 2640
2700
2700
2700
	
(1) 2650
2700
(1) 2000
2000
(2) 2100
2100
(3)
(3) 2000
(2) 2000
2000
(2) 2100
2100
New regenerant;
New regenerant;

7
7
7
7
7
7
7
7
7
6
7
7
6
7
6
7
0
1
pH

-4/7
.5/7
.6/7
.6/7
.3/6
.3/7
.3/6
.0/6
.1/6
.8/6
.1/7
.1/7
.6/6
. 0/6
.9/6
.0/6
. 8M
. 2M,

.0
. 1
.4
. 3
.7
. 3
. 3
.6
. 3
.6
.4
.0
.6
.3
. 5
. 4
NaCl
NaCl
Color
Units
	
65/65
65/65
65/60
60/60
55/55
55/55
55/40
60/50
45/40
55/50
55/50
55/50
60/55
60/50
55/45
60/50

(3)
Turbidi
JTU

0 .
1.
1 .
1 .
5 .
2 .
2 .
3 .
4 .
2 .
2 .
3 .
2 .
2 .
1 .
1 .

Sodium sul
	
9/0 .
2/0 .
6/1 .
0/9 .
0/5.
0/2 .
5/2.
1/2.
3/3.
6/2 .
6/2.
3/3.
3/2.
2/1.
5/1.
5/1.

fate
ty

9
8
6
8
0
0
4
7
6
3
1
0
5
5
3
4

u
                                                               25°C
Regenerant
Total
Flow Rate
ml/min
240
270
270
505
	
450
520
510
510
520
450
	
490
490
450
420
400



8
8
8
-
8
8
8
7
7
7
7
7
7
7
7
7
7


pH
.8
.6
.3
--
. 3
.0
.0
.5
.8
.7
.4
.4
. 6
.9
.9
.5
. 3
                                                                                           0 . 8M

-------
                                      TABLE 17
Date
6/8
6/9
6/10
6/11
6/11
6/12
6/15
6/16
6/16
6/17
6/18
6/19
6/22
6/23
6/24
6/25
6/26
6/29
6/30
(1)


a . m
p . m

(1)
a . m
p . m
(1)

(2)

(3)
(3)
(2)

(2)

(1)
(2)
(3)
New
Sodium
EXD NUTRIENT REMOVAL - PILOT CELL, REMOVA
Feed: Lawrence Secondary Effluent 25°
Regenerant: 0 . 8M or 1 . 2M NaCl, recirculatin
Feed, In/Out
Ortho

-PO .
d
(

P)

mg/1 "
8 .
20 .
23 .
23 .
27 .
28 .
31 .
21.
18 .
18 .
26 .
17 .
20 .
16 .
18 .
19 .
18 .
18 .
17 .
5/3.
0/7.
7/8.
6/7.
9/12
4/9 .
5/10
0/10
7/8.
5/5.
2/7.
5/5.
6/7.
5/13
3/14
6/6 .
0/6 .
0/6 .
6/5.
egener ant
egene
m sul
rant
fate
0
1
0
9
.
5
.
.
0
9
5
8
7
.
.
4
3
7
9
f
t
6
3
0

3
1
4 6
4 6

5
1
6
2
3 2
2 2
7
4
11
10
0 . 8M NaCl
1 . 2M NaCl
NO., (N
T.
rag /I
.5/0.
.2/0 .
.9/0 .
	
	
.2/0.
.5/0.
.6/4 .
	
.4/0 .
.1/0.
. 0/0 .
. 0/0 .
.9/0 .
.6/1.
. 0/0 .
.1/0.
.8/0 .
.9/1.


used as regeneran
)


3
8
7


7
3
8

1
7
3
6
7
8
8
4
6
1


t;


S04, mg/1
	
84/5
95/9
88/49
	
95/23
84/14
68/14
	
64/6
87/12
57/9
68/26
80/294
96/126
84/16
100/14
65/25
75/17


0 . 8M Na SO
                                                                  25°C
                                                                           % Removal
Ortho-P
65
65
66
67
57
67
67
51
57
68
71
67
63
19
21
67
65
63
67
NO3
94
75
22
--
--
92
95
27
--
98
36
95
70
76
31
89
90
95
90
304
—
94
91
44
--
76
83
79
--
91
86
84
62
--
--
81
86
62
77

-------
 and unchanged  at  60-65%  removal,  an  average  of  621.   Except
 for two  anomalously  low  values,  a 90%  nitrate removal was
 achieved on most  days, for  an  average  of  89%; an  apparent
 slight  improvement over  previous  data.  Sulfate removal  was
 again erratic  but remained  in  the 75-90%  removal  range ob-
 tained  at a 45/1  flow ratio.   A  fresh  regenerant  solution was
 prepared on 15 June  and  thereafter on  every  other operating
 day, but no significant  change in removal pattern was ob-
 served.   Initially small decreases in  exchange  efficiency
 appeared to correlate with  nutrient  build-up in the  regener-
 ant solution during  the  second eight hours recirculation, but
 later results  did not appear to  substantiate this.   It is a
 point that should be carefully checked in future  experiments.

On  17 June, the feed  flow rate was decreased to 2,000 ml/min
in  an effort to increase phosphate removal by providing longer
residence time in the exchange cell.   Regenerant flow rate
was maintaned at  500  ml/min.  A small improvement in removal
to  70%  was realized  on 17 18 June  and,  in  an attempt at furth-
er  improvement, the  regenerant concentration was increased to
1.2M NaCl on 19 June.  The enhanced  driving force produced no
additional phosphate  removal and nitrate and sulfate removal
appeared to be equally unaffected.   For the next two eight-
hour operating periods,  sodium sulfate was used in the regener-
ant solution at an 0.8M  concentration.   It was hoped that the
common ion would  suppress sulfate  transfer in favor of phos-
phate exchange.   This exception was  not realized;  only a 20%
average phosphate removal was obtained over the two-day trial.

A 1.2M sodium chloride regenerant  solution was  restored on 25
June with a 2,000 ml/min feed flow rate and 500 ml/min re-
generant flow and a  period of stable operation ensued for the
rest of the month.   Average phosphate,  nitrate,  and sulfate
removals were 66%, 91% and 77%, respectively.  A gradual de-
gradation of regenerant  pump performance was  observed over this
period,  manifest  by  a decrease in  the maximum attainable flow
rate, increase in pressure, and excessive  heating.  Several
lines were replaced  and  some replacement gauges were also re-
quired.   Removal  efficiencies were not affected by this pump-
ing irregularity  since 5/1 or 10/1 flow ratios appeared to be
equally effective.   The  treatment  pilot plant itself operated
satisfactorily although  color and  turbidity both increased
over the initial  operating period.   Twelve-hour filter runs  on
the Microfloc filter  were used as  a  standard procedure.  Tables
18  and 19 show data  for  the continuation into July of the
operating period  started on 8 June.

As  in previous data  phosphate exchange appears to be  limiting,
and its improvement  continued to be  used as a criterion for
evaluating  the effects of any changes in operating conditions.
                            117

-------
                                       TABLE  18

            EXD NITRATE/PHOSPHATE REMOVAL  - PILOT CELL,  OPERATING  DATA
                  Feed :
                  Regenerant:
 Lawrence  Secondary  Effluent,  2 5 c - 2 6 C
 1.2M NaCl,  recircula ting,  25  -  26 C

Feed, In/Out
                                                                          Regenerant
Total
Flow Rate
Date
7/1
7/2
7/3
7/6
7/7
7/8
7/13
7/14
7/15
7/16
7/20
7/21
7/22
7/23
7/24
7/28
7/29
7/30
7/31
8/3
ml/min pH
(1)

(1)

(1)



(1)

(1)
(1)

(1)

(2)
(2)
(2)
(2)
(2)
2100
2100
2000
2100
1800
1500
1800
1900
1850
1100
2000
2000
2000
2100
2100
2100
2100
2100
2200
1600
6
6
7
7
7
7
7
6
7
7
6
6
7
7
7
6
6
6
6
6
.7/6
.7/6
.2/6
.5/7
.3/6
.2/7
.2/7
.7/6
.3/6
.2/6
.3/6
.6/6
.0/6
.1/6
. 0/6
.6/6
. 9/6
.8/6
.8/6
.9/6
. 2
. 3
. 9
. 1
. 8
. 0
. 0
. 4
. 7
.6
. 2
. 3
.8
.6
. 5
. 2
. 1
.8
. 3
. 5
Color
Units
40/40
55/40
55/50
55/40
55/45
60/50
60/45
50/45
50/50
50/45
50/50
60/60
60/60
60/55
60/50
60/50
60/60
65/50
60/50
60/60
Turbidi ty

3
5
4
5
4
5
1
1
2
0
5
2
2
2
1
0
0
2
1
2
JTU
. 2/2
.5/4
. 6/4
. 0/4
.2/4
.0/5
.7/1
.5/1
-5/1
.6/0
.0/3
.1/2
.1/2
.0/1
.0/0
.6/0
. 2/0
.0/2
.5/1
.0/2

. 7
. 5
. 2
. 2
. 5
. 0
.5
. 5
. 2
.6
. 0
.0
. 0
. 8
.8
.6
. 2
. 0
.5
. 0
Total
Flow Rate
ml/min
360
320
370
305
510
400
325
330
350
420
350
400
300
380
300
100
125
300
320
350


EJL
7
7
7
7
7
7
7
7
7
7
6
7
7
7
7
3
3
3
2
2
. 1
. 1
. 6
.9
. 9
.9
.6
. 4
.6
. 7
. 9
. 0
. 2
. 3
. 6
. 5
. 5
. 5
. 0
. 0
(1)   New  Regenerant

(2)   Regenerant run  once-through

-------
                                       TABLE  19
Date

7/1
7 . 2
7/2
7/6
7/7
7/8
7/13
7/14
7/15
7/14
7/20
7/21
7/22
7/23
7/24
7/28
7/29
7/30
7/31
8/3
 1)
(1)
(1)
 (1)
 (1)

 (2)
 (2)
 (2)
 (2)
 (2)
XD NITRATE/PHOSPHATE REMOVAL - PILOT CELL, REMOVAL DATA
Feed: Lawrence Secondary Effluent 25°-26°C
Regenerant: 1.2M NaCl, rec ir cula t ing 25°-26°C
Feed, In/Out
Ortho-PO
4(P)
NO (N)
mg/1
16
16
16
14
8
19
19
17
18
16
17
13
18
22
21
20
23
17
17
17
.0/7.
.2/6.
. 6/6.
.5/3.
.0/2.
.8/5.
.1/6.
.5/4.
. 6/6 .
.9/3.
.3/7.
.5/4.
.2/7.
.2/9.
. 9/9 .
.3/8.
.3/9.
.5/8.
.5/8.
.7/7.
4
5
2
5
5
3
0
0
8
4
6
8
8
1
1
4
2
1
8
7
15
14
8
3
1
1
6
13
6
4
17
11
4
3
4
9
4
7
8
7
mg/
.0/1
.1/1
.3/0
.8/1
.7/0
. 8/0
. 0/0
.8/1
.6/1
.9/1
.2/1
.8/1
-9/1
. 8/0
. 0/0
.0/1
. 0/0
. 8/0
.3/0
.2/0
1
. 1
. 8
.8
.3
. 2
.4
. 3
. 2
. 1
. 2
. 2
. 2
. 1
.4
.7
. 0
.9
. 7
.6
.4
SO , mg/1
	 4 . - .
54/ 6
62/14
71/24
73/19
76/17
74/15
58/ 2
67/15
75/16
68/ 7
65/13
75/32
73/25
80/20
76/20
76/24
80/16
68/17
68/15
71/12
Ortho-P
54
60
63
76
69
73
69
77
63
80
56
64
57
59
59
59
61
54
50
57
% Removal
NO
3
93
87
90
66
88
78
95
91
83
76
93
90
78
90
83
89
78
91
93
94

SO
4
89
76
66
74
79
80
97
78
74
90
80
57
66
75
74
68
80
75
78
83
(1)   New Regenerant
(2)   Regenerant run once-through

-------
For the first four days of the July period, removals continued
much as they had been at the end of the previous reporting
period, i.e., an average of 63% phosphate, 841 nitrate and
76% sulfate removal efficiencies.   Feed to regenerant flow
ratios were 5/1.  From 7 July to 16 July,  various adjustments
were made in the feed flow rate in attempts to improve the
phosphate cut.   Flow rate was first reduced to 1,800 ml/min
and finally to 1,100 ml/min.  While the latter rate gave the
highest phosphate removal so far observed (801)  in the pilot
cell, the small total flow was unacceptable;  flow ratios
were as low as 2.5/1 and the membrane area required per gal
Ion of product much larger than economically practical for
large plants.  From 20 to 24 July, the original  operating
conditions were restored and, under reasonably stable opera-
tion, the average phosphate, nitrate and sulfate removals of
60%, 87% and 70% obtained were comparable to those of the 26
June to 6 July period.

From 28 July to 3 August, the pH of the regenerant stream was
adjusted to acidic values, first to 3.5 and then to 2.0.  The
aim was to determine if phosphate  transport could be increased
by creating a pH differential across the membrane, a procedure
shown to be useful during the earlier laboratory studies of
the EXD N-P removal process (see Table 7 and Figure 35) .

In the present instance, the anion exchange membranes used in
cell construction were of the anomalous, discolorable type
discussed earlier and shown to negate the effect of pH differen-
tials.  The test was nevertheless  made because of an impending
system shutdown and on the possibility that the  inhibiting
substance may have leached out after extended use.  The re-
generant solution was used on a once-through basis and at
flow ratios of 20/1 to 6/1 with 2,100 ml/min feed rate, and
4.5/1 at 1,600 ml/min feed rate.  Unfortunately, no improve-
ment in phosphate exchange was obtained under any of the con-
ditions used.

Over the entire period of July operation,  nitrate removal was
generally very good.  The average  overall removal efficiency
was 86%, and during ten of the twenty days of operation, a
>_ 90% nitrate removal was obtained.  The median value for the
period was 89%.  Sulfate removal average 77%.  Exchange of
neither moiety was affected by acidification of the regenerant.

Following completion of the N-P removal tests using an acidic
regenerant stream, the multicell was shut down and disassembled
to permit inspection of the membranes and spacers.  At this
time the unit has been in continuous contact with activated
sludge effluent for about three months and been run eight hours
a day for 43 days.  Most membranes and spacers were reasonably
unfouled.  No solid precipitate had formed or accumulated on
                           120

-------
the membranes or in the flow paths, although some of the membranes
had a thin slimy film on the feed face.  The flow path area
of all membranes had turned a very dark brown but no leaks
were found.  Several flow path screens also exhibited slight
sliming but were easily cleaned by rinsing in tap water.  The
porous sheet in the regenerant stream was stained a light-
brown for a few inches downstream from the inlet manifold but
was otherwise clean.  The multicell has reassembled with new
Tokuyama AV-4T anion-exchange membranes and original spacers,
screens and porous sheet.  Eighteen membranes were used, form-
ing nine feed cells and ten regenerant cells in the completed
multicell.  This is in contrast to twenty feed cells used in
the original multicell configuration.  The membranes used were
from a new supply and did not exhibit the anomolous coloration
of the previous membranes.  The smaller number of feed cells
was dictated by the unavailability of sufficient  of the  newer
membranes and the desire to limit total volumetric through
put in order to use less regenerant solution.

Following satisfactory tests on a new secondary clarifier for
the pilot activated sludge facility, the reassembled nitrate-
phosphate removal multicell was reinstalled at LES.  Operation
started on 17 August.  Conditions were essentially the same
as for the previous test period; recirculating 1. 2M sodium
chloride regenernat, secondary effluent from the pilot plant
as feed on a once-through basis.  The multicell was run 7-8
hours a day and the regenerant solution replaced periodically.
Results are presented in Tables 20 and 21.

Much improved removal of all three of the anions monitored was
obtained.  Excluding the last set of data for 1 September,
average removals were phosphate  84%, nitrate 97%, and sulfate
93%, with phosphate limiting, as usual.  Part of this improve-
ment in the removal efficiency was undoubtedly due to the low-
er feed flow rate in the newly reconstructed unit.  A total
flow of 500-600 ml/min was the maximum attainable at pressures
of 120-140 psig.  This was 56-67 ml/min per flow  path  compared
to 100 ml/min obtained earlier.  The new set of membranes
also contributed to the improvement, as discussed below in the
Section on membrane tests .  Various efforts to improve the
flow by adjustment of sealing pressure, pumping or start-up
sequence, and realignment of the membrane/spacer stack were
unavailing.  On 1 September a substantial leak developed which
produced an apparent high flow rate and a seriously degraded
removal efficiency.  Reworking of the unit was apparently
necessary and it was therefore decided to terminate the nitrate-
phosphate removal tests at this point, to permit completion
of the ammonium removal tests described below.  The removal
efficiencies obtained with the restructured cell were exceed-
ingly close to the design values for phospahte.  A 90%
                          121

-------
                                                           TABLE  20
t-o
to
EXD NITRATE/PHOSPHATE REMOVAL - PILOT CELL, OPERATING DATA
o o
Feed: Lawrence Secondary Effluent, 25 -26 C
Regenerant: 1 . 2M NaCl, r e c i r cula ti ng , 25 -26°C
Feed, In/Out Regenerant
Total Flow Rate
Date
8/17
8/18
8/21
8/24
8/25
8/26
8/27
8/28
8/31
9/1
(1)


(1)


(1)
(1)
(1)
(1)
ml/min
600
500
500
500
450
550
550
600
500
800

7
6
6
6
6
7
7
7
7
7
PH
.1/6
.4/5
.7/6
.7/6
. 9/6
.3/6
.2/6
.4/6
.6/7
.0/6

.6
.6
. 0
. 3
. 5
. 4
.8
. 7
. 0
.7
Co lor
Units
60/35
50/30
50/30
50/30
50/35
50/45
60/45
60/45
60/40
60/55
Turbidity Total Flow Rate
JTU
1 .0/1
1 .0/0
0 .3/0
0 . 2/0
0 .8/0
1. 3/0
0 .3/0
0 . 3/0
.15/.
• 9/.

. 0
. 9
.3
. 1
. 3
. 7
. 2
. 2
15
9
ml/rain
90
100
95
100
90
100
100
100
120
200

7
7
7
7
7
7
7
7
7
7
pH
. 7
. 2
. 1
.2
. 3
.2
. 3
. 6
.6
. 2
                (1)   New  Regenerant

-------
                                       TABLE  21

EXD
NITRATE/PHOSPHATE REMOVAL - PILOT CELL, REMOVAL DATA
Feed: Lawrence Secondary Effluent, 25 -26 C
Regenerant: 1 . 2M NaCl, r ecir cula ting , 25°-26°C
Feed, In/Out
Or tho-PO
Date
8/17
8/18
8/21
8/24 (1)
8/25
8/26
8/27 (1)
8/28 (1)
8/31
9/1 (1)
(P)

mg/1
20
13
17
14
12
16
16
19
18
16
/2
.4/1
.2/2
/2
.5/2
.7/3
.3/4
/2
.7/2
.6/8
. 3
.8
.6
.0
. 2
. 5
.0
. 6
.6
.6
1
5
4
7
7
6
7
6
8
8
NO3 C
N)
mg/1
. 0/0
.4/0
.0/0
. 0/0
.8/0
. 2/0
. 6/0
.0/0
.9/0
.6/1
. 1
. 1
. 1
.1
.1
. 2
. 2
. 2
. 2
.5


SO , mg/1
68/3
50/4
63/5
53/4
58/3
65/5
74/3
76/8
78/4
80/2
.0
. 0
.0
.0
.0
.0
. 0
.0
.0
0

Ortho-P
89
87
85
86
83
79
76
86
86
48
% Removal

NO.
3
90
98
98
98
98
97
97
97
98
83

S04
96
92
92
93
95
92
96
89
95
75
(1)   New Regenerant

-------
exchange appears to be attainable via flow path improvements
evolved from the ammonium tests and by utilizing advantages
to be obtained from improved membranes,  regenerant velocity
optimization and regenerant composition changes.  However,
the ratio of nutrient-free product water to membrane area and
the feed to regenerant flow ratios required for this removal
are substantially less than those used for the initial cost
estimate.  Since this estimate is economically acceptable only
in light of several mitigating assumptions, EXD phosphate re-
moval does not appear to be an economically competitive pro-
cess at this time.   Nitrate removal has  a more favorable
prognosis but both  systems require new membrane configurations
other than plate-and-frame in order to satisfy the contrasting
flow rate and velocity needs of the process.  Preliminary ex-
periments (8) indicate that a spiral wound configuration is
one effective solution to this problem.
                          124

-------
                      Section 11

           NITRATE-PHOSPHATE MEMBRANE TESTS

Several variations of the standard Tokuyama anion-exchange
membrane, which was used in all nitrate-phosphate EXD work
described so far in this report, were examined for exchange
efficiency with a composite phosphate, nitrate and sulfate
feed solution.   The experiments were run on an A-l type  cell
as described in  Section  3,  except  that  the  flow path
was 20 mil thick and filled with 20 mil polyethylene screen-
ing (compare Figure 4) heat-bonded to the gasket area of the
spacer.  The objective of these tests was to determine if
other readily available membranes would be more suitable for
nitrate-phosphate removal via the EXD process than the AV-4T
currently in use.  Results of these tests are given in the
top five rows of Table 22 which also show the calculated
values of J/conc, for all exchangeable species.   These data
indicate that the standard AV-4T membrane is the membrane
of choice for the nitrate-phosphate removal process.   Multi
valent anion transport is inhibited by the "-S" series mem-
branes; this may be a useful property in certain other appli
cations of EXD.  The ACP membrane has essentially the same
phosphate removal efficiency as the AV-4T but inferior nitrate
and sulfate efficiences.  It is claimed to have high resist-
ance to basic solutions but is substantially more expensive
than the standard membrane.  Also shown in Table 22 are N-P
removal results obtained in the A-l cell with anomalous AV-4T
membranes and with Aquion AE membranes, a proprietary anion
exchange membrane developed by Process Research,  Inc.  A plot
of J/P versus velocity for the membranes of interest, overlaid
on Figure 38, is shown in Figure 58.  The broken curves are
drawn on the two experimental points to approximate a slope
of 0.55.  It can be seen that the standard AV-4T membrane has
a distinct advantage over the anomalous variety by a factor
of 2.5.  The Aquion membrane produced a still further increase
in phosphate exchange rate and demonstrates the type of im-
provements that may be expected by employment of membranes
especially tailored for a given exchange.

Confirmation of superior performance for the standard AV-4T
membrane can be demonstrated with the data from the last N-P
prototype cell series.  Using the operating data for 17 August
and 25 June to represent standard and anomalous membranes re-
spectively, J/P may be computed for each type.  The results
give  14.5x10"^ cm/sec for the standard membrane and 11.2xlO~'+
cm/sec for the anomalous species.  Assuming that each of the
data points obtained lie on a log-log J/P vs. velocity curve
of slope 0.55,  and extrapolating to similar velocities, the
                            125

-------
TABLE    22
MEMBRANE TESTS:
EXD NITRATE-PHOSPHATE REMOVAL
Cell Type: A-l, Unitized Spacer
Regenerant: 0.8M Chloride? pH = 3.2
Average Feed: 4.12xlO~3M Cl; 3.47x10"^ NO ; 10.4x10"^ SO ;
10x23xlO~1+M PO; pH = 9.5
Average % Removal J/conc . x 10 ,
Flow Rate Velocity
Membrane
AVS-4T

AF-4T

AFS-4T

ACP

AV-4T
( Standard)
AV-4T
(Anomalous )
Aquion-ffi
(PRI)
ml/min
50
25
50
25
50
25
50
25
50
25
50
25
50
25
cm/
23
11
23
11
23
11
23
11
23
11
23
11
23
11
sec
.4
.7
. 4
,7
.4
.7
.4
. 7
.4
.7
.4
. 7
. 4-
. 7

PO4
0 .48
1.9
11
18
0.67
0 .67
13
25
16
25
7
13
38
37

NO,
45
64
54
73
41
65
41
60
43
67
45
56
33
49

S04
ft
7
11
20
20
0
3.2
27
48
56
70
36
45
41
S2

0
0
1
1
0
0
2
2
2
2
1
1
5
3


.085
. 156
.95
.70

.056
. 18
.35
.94
.44
. 18
.01
. 28
.80


N00
9
8
13
10
8
8
8
7
9
8
9
7
6
5
	 _>
. 98
. 54
.0
.9
.83
.78
.61
.49
. 33
.95
.60
. 18
.58
.37

cm/sec

so.
1
0
3
2
0
0
5
5
13
9
7
4
8
6
.21
.973
. 74
. 98

.272
.16
.34
.5
.95
. 30
.89
.31
.05

-------
to
x

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o
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                3  4 5 6 7 8 9 1.0
           2   3  458789 10
          FLOW VELOCITY, cm/sec

            FIGURE 58
FILM CONTROLLED DATA  PLOT
3  456739
           100

-------
standard membranes  appear to improve the exchange rate by a
factor of 1.6.   This  is  less than that obtained in the A-l
cell but the differences in the magnitude of the improvement
factor may be attributable to different regenerant stream
geometry and the fact that the A-l tests were run with low
regenerant pH.   Figure 35 indicates that a ApH>4 can increase
J/P by a factor of  3-4.   In any case,  a marked advantage seems
apparent in the use of the standard AV-4T membrane.
                          128

-------
                     Section 12

                 AMMONIUM TRANSPORT

Ammonia is not  only a nutrient material promoting algae growth,
but it is also a source of oxygen demand in a receiving water.
It was therefore of interest to investigate the possibility
of its removal from secondary effluents, in the form of the
ammonium ion, by the Exchange-Diffusion process; an exten-
sion of the concurrent EXD nitrate/phosphate removal studies
already described.  Equipment, operation and principles for
ammonium removal were essentially the same  as for N-P re-
moval, except that a cation-exchange membrane was employed
in the EXD cell to permit the ammonium-sodium exchange.

The exploratory experiments described below demonstrate the
technical feasibility of removing ammonium ions from second-
ary effluents by ionic exchange across a cation-transfer mem-
brane.  The driving force for the exchange was a concentra-
tion gradient set up by a high sodium concentration in the
regenerant or receiving stream of the exchange cell, rela-
tive to the ammonium concentration in the feed stream.  By
maintaining the regenerant stream basic via addition of lime
the ammonium removed could be air-stripped as ammonia and the
regenerating solution continuously recycled.  In addition,
ammonium removal efficiencies of 90% were obtained in a pilot
EXD cell using effluent from the small activated sludge plant
at LES as feed.

The ammonium removal studies were begun by examining the  para-
meter J/(NH+4Jat a variety of flow rates and regenerant
stream pH values.

The exchange cell used in the initial experiments was that
described above as type A-3.  This cell has "tortuous path"
flow-spacers 0.10 cm (40 mil) thick with a flow path 972 cm
long and 0.56 cm wide.  Effective transfer area is 584 cm2.
A cation-exchange membrane is held in plate-and-frame con-
figuration between the two spacers forming the feed and re-
generant compartments and the cell sealed via channel-iron
clamps bearing on one-inch thick Lucite  end-blocks.   Overall
cell dimensions are approximately 23 x 60 x 5.5 cm.  Photo-
graphs of the A-3 cell are shown in Figures 5 and 6.  The
flow schematic for the experimental set-up is shown in Figure
59 and is entirely similar to that used for the EXD work on
nitrate and phosphate.  The membrane employed was a Neosepta
C1-2.5T cation-exchange membrane manufactured by the Tokuyama
Soda Company.  All solutions were prepared from reagent grade
chemicals and deionized water.  Ammonium was analyzed via the
Direct Nesslerization method described in Standard Methods,
                          129

-------
Feed Reservoir
             r-«O-
                h=d
  FIGURE 59
    OF APPARATUS
  USED  FOR
    REMOVAL STUDIES
Regeneront  Reservoir
                                        Tesf Ce!
©
CM
Q
Pressure Gauge
Thermometer
Cation  Membrane
                                                  X    Valve

-------
and chloride by titration with mercuric nitrate or with a
specific ion electrode.  Sodium concentrations were determined
by difference.

Experiments were run by charging the feed and regenerant re-
servoirs with the appropriate solutions and pumping through
the exchange cell at constant flow rates, temperatures and
inlet concentrations until analysis showed the outlet con-
centrations were stable with time, i.e., a steady state had
been attained.  All measurements were taken after this point
had been reached.  Flow rates were identical for both feed
and regenerant streams in all laboratory runs and inlet
ammonium concentrations were held at approximately 10 3 molar.
The ratio J/NH^ was then calculated from the influent and
effluent feed concentrations according to:
                 dln(NH^)
     J/NH4 =   £ -^--1 , cm/sec


where, as before:

     J     = ammonium flux, moles/cm2-sec
     F     = feed stream flow rate, ml/sec

     to     = flow path width, cm

     (NH,) = ammonium concentration, moles/cm3

     L     = flow path length, cm

Results from the first runs are summarized in Table 23.  Data
are divided into groups with increasing velocity but with
the same pH and/or concentration in the regenerant stream.
In conformity with previous data, J/NHj increased with in
creasing velocity in the several pH and concentration ranges
examined.

This is also shown in Figure 60 where J/NH^ is plotted against
velocity.   The slope of the curve shows the exchange rate
increased with approximately the 0.55 power of the velocity,
typical of other film-controlled membrane processes and the
nitrate-phosphate data given previously.  The data also
indicate that the changes in regenerant concentration or in
regenerant pH shown in the Table had little, if any, effect
on J/NHl.   This is  interpreted to mean that J/NH| was  film-limited
at the low ammonia concentration and high affinities used,
i.e.,  lower regenerant concentration would have been equally
effective.  Percent ammonium removal was good in all of
these runs.  Table 24 gives some representative removal effi-
ciencies over the range of velocites studied.  Comparison
                          131

-------
                        TABLE  23
         Feed
       AMMONIUM TRANSPORT  DATA

              (NH )  ~ 0.001M;  (Na+)  = 0.003M
         Regenerant:   (NH ) =  0.001M
Exp.  No .
Feed pH =

    Flow,
   ml/min
5 . 5

Veloc ity,
 cm/sec
 J/NH^,
cm/sec
 Regenerant
 pH     (Na+),  mole/1
  51016
  51015
  51013
  51015
  51017
     25
     50
     75
    100
    150
    7
   15
   22
   29
   44
0 .00202
0 .00257
0 .00380
0 . 00425
0 . 00576
7 . 1
7 . 1
7 . 2
7 . 1
7 . 1
                       1 .0
                       1. 0
                       1 .0
                       1 .0
                       1 . 0
  51019A
  51019B
  51019C
     25
     50
     75
    7
   15
   22
0.00210
0 .00353
0 .00400
 7 . 1
 7 . 1
 7 .1
0 .3
0 . 3
0 . 3
  51023
  51020
  51022
     50
     75
    100
   15
   22
   29
0 .00337
0.00386
0.00495
   9
   9
   9
1 . 0
1 . 0
1.0
  51025
  51024A
  51026
  51024B
     25
     50
     50
    100
    7
   15
   15
   29
0 . 00168
0.00299
0.00328
0.00425
11
11
11
11
1 .0
1 . 0
                             152

-------
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          1.5   2  2.5  3    4   5  6  7  8 9 10    1.5   2  2,5  3


                                    V, cm/sec




                                  FIGURE 60


                AMMONIUM TRANSPORT  VS FLOW VELOCITY
5  6  7 8 9 10

-------
of the J/NH^ data in Figure 60 with the nitrate-chloride ex-
change data in Figure 38 indicates that the ammonium ion was
removed about 35% faster than the nitrate ion, under similar
hydrodynamic conditions.

                       TABLE 24

                     NH* REMOVAL

Feed Concentratior
mole/liter x Id4

In          Out  % Removal  Flow Rate,ml/min  Velocity,cm/sec

10          2.9       71           150              44
10          2.5       75           100              29
 9.3        1.8       81            75              22
 9.7        1.8       82            50              15
10          0.793            25               7

Several ammonium removal runs were also made with a continuously
recirculating regenerant solution to determine the feasibility
of minimizing regenerant effluent volume and chemical costs
by exchanging only the stoichiometrically required sodium
equivalents.  Regenerant pH was adjusted to 11 12 so that trans-
ferred ammonium ions would immediately be converted to ammonia
which was stripped from the regenerant solution by sparging
with compressed air or flowing over a baffled Lucite sheet.
A substantial and continuous driving force was thereby main-
tained for ammonium exchange.  In all the runs with recircu-
lating regenerant the feed and regenerant velocities were
again equal, with inlet ammonium concentrations in the feed of
0.0012-0.0014 mole/liter.   Table 25 gives operating data and
results for run 51026, which had a regenerant solution with
a sodium concentration of 1.0 mole/liter and a pH of 11.0,
adjusted with sodium hydroxide.  This experiment ran for 25
hours with an average NH^ removal from the feed stream of 87%.
Ammonium concentration in the regenerant reservoir remained
relatively constant, indicating effective removal by aeration.
Concentration of chloride in the outlet feed stream was 0.0048
mole/liter, a gain of 0.0008 mole/liter or 20%.

Exchange-Diffusion runs were also attempted using only excess
lime as the reagent in the recirculating regenerant stream.
This gave a regenerant pH of 12.4, which was expected to faci
litate ammonium removal and provide calcium ions for exchange.

Several feed stream velocities were examined but the desired
results were not obtained since all NH^ removal efficiencies
were less than 20%.
                           134

-------
             TABLE  25





  AMMONIUM TRANSPORT - RUN  51026





Flow  Rate = 50 ml/min =  14.6  cm/sec
Regenerant :
(Na
(NH|
= 11.0
) = 1.0 mole/liter
) = 0.0012 mole/liter
PH
Feed: pH =5
(Na|) = 0
(NH4) = 0
(C1-) = 0
Feed Out
% Removal
Time , Hr s .
1
1. 25
1. 50
18
19
20
21
22
23
24
25
Feed
5 .
5 .
5 .
5 .
5 .
5 .
5 .
5 .
5 .
5 .
5 .
In
50
50
45
50
59
55
55
55
55
55
60
Feed
6 .
6 .
6.
6 .
6 .
6 .
6 .
6 .
6 .
6 .
6 .
Out
10
10
18
40
40
40
40
40
30
25
40
Reg .
10 .
10.
10.
10.
10 .
10 .
10.
9 .
9.
9.
9.
In
89
89
85
15
15
00
00
99
90
90
85
Reg .
10
10
10
9
9
9
9
9
9
9
9
Out
.55
. 52
.52
.80
.70
.65
. 58
.60
.60
.60
.60
(
1


1

1
1
1
1
2
1
NH )
.4xlO~4M
	
	
. 29
	
.50
. 29
.43
.07
.21
.43
(NH+)
88
--
—
83
—
87
89
88
91
82
88
.5
.003 mole/liter
.0012 mole/liter
. 004/mole/liter
Regenerant

1


1

1
9


1

(NH+)
.OxlO~
	
	
.36x10
	
.21x10
.9x10"
	
	
. 21x10
	

3M


~3

~3
^


~3


-------
A saturated lime solution augmented by a 0.5 molar sodium
chloride concentration was then used as a recirculating re-
generant.   Table 26 gives data on an experiment in which cal
cium ion were also present in 0.0014 molar concentration on
the feed side of the membrane.  No ammonium ion was initially
present in the regenerant stream.  Average removal of ammonium
was 72%, somewhat less than in Experiment 51026.  This may
have been due to the higher average pH in the feed stream which
could convert some NH| to un-ionized NH3,, removing it from
Donnan equilibrium constraints.  Ammonium concentration in
the regenerant reservoir gradually increased indicating that
more efficient aeration may be required under these conditions.
No chloride leak from the regenerant to the feed stream was
observed at this regenerant concentration.

Run 51033B, Table 27, was similar to Run 51033A except that
the feed solution was adjusted to pH 6.3 by the addition of
HC1 and contained no calcium.   Removal of NH^ improved to
87% with more ammonium ion presumably available for transfer.
Regenerant ammonium concentration continued to increased
gradually.

It is apparent from these results that excellent removal
efficiencies for the ammonium ion can be obtained by employ-
ment of the Exchange-Diffusion process.

An extended ammonium removal run on synthetic secondary efflu-
ent was then made over a five day operating period.  Compo-
sition of the feed solution used is shown below:

                SYNTHETIC SECONDARY EFFLUENT
       Constituent                         Cone . ,  mg/1
          Ca
          Na
          NH4 as N
          304
          P04
          N03
          HC03
          Cl
                                                54
                                                48
                                                14
                                                51
                                                30
                                                 8
                                               170
                                                48
                                      .5 mole/liter sodium
                                       pH of 12 and was re-
The regenerant solution consisted of
chloride saturated with lime to give
circulated to a 110 liter reservoir with aeration between
the cell outlet and the reservoir.   Flow rates were 50 ml/min
in both feed and regenerant streams.  Results from this experi
ment are given in Table 28.  An ammonium removal averaging 80%
was obtained over the course of the run.  During the first
24 hours,  the inlet feed solution was adjusted to pH 6.4
7.0 by the addition of HC1, but this practice was discontinued
thereafter in order to determine the effect on the effluent.
                          156

-------
TABLE  26
Regenerant-.   pH
              (Na+)
      AMMONIUM TRANSPORT  -  RUN 51033A
Flow  Rate = 50 ml/min =  14.6  cm/sec
12 . 4                         Feed:  pH
0.5 mole/liter                      (NH
                     =  0
              (CaO)  =  saturated
                             6 .95
                             0.0014 mole/liter
                             0.0043 mole/liter
                             0.0014 mole/liter
Time , Hr s .
1
5
26
46
Feed
9
9
9
9
Out
.75
.70
,75
. 75
Regen. Out
12
12
12
12
.40
.40
. 35
.35
Feed Out % Removal
(NH+) (NH+)
4.26X1CTS,
3.57 74
3.57 74
77
Regenerant
(NH +
' " " --±
0
1 .15xlO~5
1 .78xlO~4
5 . 71x10^

-------
O!
00
              Regenerant:   pH
Time, Hrs

    21

    25

    44
                  73
                                       TABLE 27
                           AMMONIUM  TRANSPORT - RUN  51033B

                        Flow Rate  =  50 ml/min = 14.6  cm/sec

                       12.25                        Feed:   pH
                                                                               = 6.3
(Na+) =
(NH+) =
(CaO) =
Feed
9. 15
9. 15
9. 10
9. 15
9. 15
0 . 5 mol e/1 i ter
-4
5.71x10 mole/liter
saturated
PH
Out Regen. Out
12. 15
12. 19
12 . 05
11. 95
11.95


(
3 .
2 .
2 .
1.
0.
(NH*) = 0.0014
Feed Out
% Removal
NH^) (NH+)
30xlO~ M 77
12 85
12 85
25 91
72 95
mo le/liter

Regenerant
(NHj)
7 . 30xlO~4M
7 . 87
8 . 23
8. 20
1<5 .4

-------
                                 TABLE    28




       AMMONIUM  TRANSPORT   -   RUN   51035





Flow   Rate   =  50   ml/min   =   14.6    cm/sec





                 Temperature   =   19-24°C
Regener ant :
Time , Hr s .
0
3
5
22
26
29
46
50
53
75
99
120
(Na+) =
(CaO) =
pH
Feed
In
6
6
6
6
7
7
7
7
7
7

7
. 4
.4
.6
. 9
. 2
. 5
.8
.8
. 7
. 8
-
. 8
0.5 mole/liter
saturated
12 . 0
pH
Out
6 . 4
6 .4
6. 9
7 . 5
8. 1
8 . 4
8. 5
8. 4
8. 4
8 . 3
-
8. 4
Regen . In
(NH ) , ppm N



3
4
4
6
6
6
6
7
6
ND
ND
ND
'. 5
. 0
. 0
.0
. 3
. 3
.8
. 0
.6
Feed: (NH4) = 14.0 ppm as N
See text for other components
Feed Out
(NH+) , ppm N
3
2
3
2
2
2
2
2
2
3
2
2
. 75
.75
. 50
. 50
. 75
. 50
.01
.75
.00
. 20
.40
.,50
% (NH^)
7
Removal
4
80
7
8
4
1
80
8
8
8
1
4
1
86
7
8
8
8
3
2

-------
In neither instance was an excessive increase in feed stream
pH observed,  through the cell,  in contrast to a pH change of
about three units in earlier experiments also using a re-
circulating regenerant stream.   Aeration was accomplished by
spraying the  regenerant stream effluent into the reservoir
and/or by bubbling compressed air into the regenerant solution
The compressed air sparging was discontinued after three days
(50 hours)  with no apparent effect on the percent NH| removed
or further increase in regenerant ammonia concentration.
During the five-day run, a thin film built up on the regener-
ant face of the membrane but it was  not extensive enough to
interfere with the ammonium transport.   In any event, it could
be removed by a simple 10-15 minute  flush with tap water.

The data from run 51035 complement the excellent NHj removals
reported above from feed solutions containing only ammonium
cations.  The pilot plant work  described in Section 14 con-
firms the feasibility of ammonium removal from secondary
effluent by Exchange-Diffusion.
                          140

-------
                     Section 13

 ECONOMIC FEASIBILITY OF THE AMMONIUM REMOVAL SYSTEM

From the laboratory results on the Exchange-Diffusion ammo-
nium removal system described above, a preliminary cost
estimate was developed.  Calculations were based on a 0.001
molar ammonium feed concentration with 90% removal required.
Feed stream flow rate was taken at 50 cm/sec with a 50/1
flow ratio of feed to regenerant streams.

From Figure 60, J/NHJ is 6 x 10~3 cm/sec at a velocity of 50
cm/sec, with A-3 type spacers.  Data from the nitrate-
phosphate experiments show that a D-3 spacer results in a
transport rate 2.4 times that obtained with an A-3 spacer.
Thus J/NH^ = 6 x 10-3 x 2.4 = 1.4 x 10~2 cm/sec for D-3
geometry.

Rearranging the equation,
               F    dln(NH+)
     J/NH+ = - -1         4
         4     co   '    dL

yields, for 90% removal:

     Area   In (0.1)      2.3
          =         =
            (J/NHJ)   1.4 x
                                 = 1.64 x
                                 = 7.85 x 103 £t
                                              MGD

where the symbols have their usual meaning.

If, as previously, the EXD process configuration is assumed
to be similar to the familiar plate-and-frame electrodialysis
(ED) stacks, then about 600 membranes with 10 ft2 each of
available transfer area would be employed in a typical module
Based on large-scale ED plant cost estimates, a preliminary
capital cost estimate for a comparable ammonium removal plant
would by $25,000 per module.

Therefore, at 7.85 x 103 ft2/MGD, the hydraulic capacity of
a single module plant, for a 90% NH^ removal would be:


     600 x 10
     7.85 x 103
                = 0.765 MGD
                          141

-------
and the capital investment:


     $25'000 - - = $.0327/gpd
     0.765 x 10

amortized at 8% per year, with a 90% load  factor,  the  invest
ment retirement costs would be:

     Q.0527) (0.08) (100)  (1000) _ Q &Q  ,, QQQ   ,
     -           -- U.8U*/1,UUU gal.
Assuming membrane costs and replacement rates  are  also  simi
lar to ED plants, i.e., $1.00/ft2 and 30% replacement per
year, they would be:

     (7.85 x 103) (100) (0.30) _      /  OQO   ,
     - (365) (0.9) (1000)      0.72
-------
 Lime needed  to  convert  the  exchanged  ammonium  ions  to  ammonia
 would  be:

     10.001)  (0.9)  (28)^(10003  (3.785)  .  0_n  lb/MOO ga^ feed



                                         gal.


 A recirculating  system  would necessitate  air-stripping of  the
 ammonia  formed  in the regenerant  reservoir.  Costs  for this
 operation have  been reported  (9)  to be  2.3(^/1,000 gal. If
 the flow ratio  of the feed  to regenerant  stream  is  10:1  in
 the recirculating process,  the  stripping  operations would
 then amount  to  0.23
-------
                      Section 14

             AMMONIUM REMOVAL PILOT CELL

On 11 June 1970 an  EXD ammonium removal pilot cell was in-
stalled in the space leased from the Massachusetts Public
Health Department at the Lawrence Experiment Station (LES)
and testing started using effluent from the small-scale acti
vated sludge facility as feed.  The cell was constructed using
the serpentine spacer design also employed in concurrent
studies on a nitrate/phosphate EXD multicell, i.e., an eight-
pass flow path 2.54 cm wide and 665 cm long, die-cut into a
polyethylene sheet.  Only one feed and one regenerant stream
were used, separated by a Tokuyama CL-2.5T cation-transfer
membrane.   The feed stream was 20 mil thick with plastic mesh
in the flow path; the 40 mil regenerant stream was filled with
porous polyethylene sheet.  Lucite end-blocks and channel-iron
clamps were used to seal the cell, which had an overall size
of 3 x 1 feet.  Figure 51 shows the serpentine spacer and
Figure 52 is a view of a similar EXD cell during assembly.

Operating data for June are given in Table 29,  The cell was
started-up with a feed flow rate of 125 ml/min and regenerant
flow rate of 13 ml/min, a ratio of approximately 10/1.   The
regenerant solution was 0.8 molar sodium chloride recircula-
ting from a 50-liter reservoir maintained at pH 9-10 by addi
tion of lime.  A small filter with MicroFloc filter media
was used in the recirculation loop between the reservoir and
pump intake and the regenerant effluent from the cell flowed
over an aeration panel before returning to the reservoir.  The
unit was operated 7-8 hours a day using the same feed solution
as the nitrate/phosphate multicell and was shut down over-
night.  Analytical samples were taken about midway through the
daily operating period.  For the first seven days of the field
test, ammonium removal efficiencies of 70-80% were obtained,
comparable to the laboratory results on synthetic effluent.
Increase in regenerant flow rate to 30 ml/min on 24 June did
not improve the cut although manipulation of regenerant
velocities has been effective in increasing the efficiency
of exchange in other applications of the EXD process.

Excessive heating of the recirculating pump developed at this
time and the filter was removed and the height of the aeration
panel adjusted to minimize the load.  A slight increase in
the volume of the regenerant solution was observed initially,
caused by interstream leakage within the exchange cell.  The
leak was estimated at less than 101 of the feed influent volume
and progressively decreased as testing continued.  After 6-8
days operation virtually no leakage was taking place.  On  22
                           145

-------
                                      TABLE 29
EXD
Feed :
Regenerant :
S erpen tine
Regenerant
Date
6/11
6/16
6/17
6/18
6/19
6/22
6/23
6/24
6/25
6/29
6/30*
7/1
Flow Rate,
ml/min pH
13
13
13
13
13
13
13
30-35
30
30
25
33
9-
9-
9-
9-
9-
7
9-
9
10
9
10
10
10
10
10
10
10
. 1
10
.5


.5

AMMONIUM REMOVAL - PILOT CELL
Lawrence Secondary Effluent, 25°C
0.8M NaCl, r ecirculating , 25°C
Spacer
Feed
Flow Rate,
ml/min pH
12
12
12
12
12
12
12
12
12
12
5
5
5
5
5
5
5
5
5
0
100
9
6
7
7
7
7
6
7
7
7
7
6
7
6
.6
. 3
.0
. 1
.8
. 1
. 1
. 1
.0
. 9
. 0
.7
NH3-N in,
mg/1
40
15
15
18
7
30
16
20
16
17
19
16
NH3-N out,
mg/1
7
3
3
5
2
6
4
7
3
7
2
1
. 5
.7
. 0
. 0
.6
. 0
.0
. 0
.5
. 0
. 5
. 5
% N Removal
81
75
80
72
63
80
75
65
78
59
87
91
* New regenerant  solution

-------
June, the ammonia-N concentration in the regenerant reservoir
was  37.2 mg/1.

To examine the possibility of and to determine conditions for
attaining a 90% removal of ammonium ion from the feed, the
flow rate of the feed stream was decreased to 100 ml/min on
30 June, a new regenerant solution was prepared and the pH
maintained at 10-10.5 with more frequent monitoring and ad-
justment.  Regenerant flow rate was continued at 30 ml/min
although this rate was very close to the limit of the pump
capacity and fluctuations in the flow occurred.  These
changes produced a 90% ammonium removal efficiency on 30 June
and 1 July.

The EXD ammonium removal cell was continued in operation on
the Lawrence secondary effluent during July under similar con-
ditions.  Operating data are given in Table 30.  Changes insti
tuted at the end of June designed to produce a 90% ammonium
removal efficiency were continued.

A 90% removal was maintained through 2 July but on the follow-
ing four days the overheating and leakage of the regenerant
pump noted above became severe enough to cause extremely
erratic and limited flow in the regenerant stream, with re-
sultant decrease in ammonium removal efficiencies.  The ammo-
nium concentration in the effluent also increased at this
time and may have been a factor in the efficiency degradation.
Confirmation of any correlation will be attempted in subsequent
test programs.  Backflushing the regenerant flow path did not
improve the recirculation rate.  A marked buildup in the
volume of the regenerant tank occurred on 8 July indicating
excessive leakage from feed to regenerant streams.  Thereupon,
the cell was returned to the laboratory for disassembly, in-
spection and reconditioning.  All components were found to
be in excellent condition.  The membrane was leak-tight and
completely free of slime, precipitates, or deposits of any
kind.  The gaskets and the screening in the feed flow path
were also clean and undamaged.  The porous sheet in the re-
generant flow path appeared in satisfactory condition except
that the portion filling the first pass from the cell feed
inlet was stained a light-brown color.  This did not seem to
affect the flow.  The ammonium removal cell was reassemlbed
and returned to service on 13 July.  The same membrane, plas
tic screen,  and spacers were used after a suitable clean-up.
New polyethylene porous sheeting was employed in the regener-
ant flow path.  Initial start-up of the reinstalled cell was
on 13 July but repairs to the effluent holding tank delayed
resumption of sustained operation until 20 July.  A new 0.8M
sodium chloride regenerant solution was prepared and pH was
maintained at 10-10.5.  Thereafter, a 90% ammonium removal was
obtained through 24 July when the entire pilot treatment plant
                        147

-------
TABLE    30
EXD AMMONIUM REMOVAL - PILOT CELL
Feed: Lawrence Secondary Effluent 25°C
Regenerant: 0 . 8M NaCl, recirculating , 25°C
Serpentine Spacer
Date
7/1 a
7/1 p
7 . 2
7/3
7/6
7/7
7/8
7/13
7/20
7/21
7/22
7/23
7/24
Regenerant
Flow Rate,
ml/min
.m. 33
.m. 33
30
33
25
20
20
15
28
20
20
20
20

pH
10
10
10
10
10
10
10
10
10
10
10-10 .5
--
10 .2

Flow Rate,
ml/min
96
60
64
100
110
80
70
125
100
120
100
95
100

6
6
6
7
7
7
7
7
6
6
7
7
7

p_H
.7
.7
.7
.2
.5
.3
.2
.2
.3
.6
.0
.1
.0
Feed
NH3-N in,
mg/1
16
11
16
50
80
80
60
20
5
10
15
;LO
10

NH3-N out,
mg/1
1 . 5
0 .5
1.0
20
30
20
30
1
0 .5
1 .0
1.0
0 .8
1.1

% N Removal
91
95
94
60
63
75
50
95
90
90
93
92
89

-------
was shut down to permit installation of a new settling tank
for the activated sludge facility.  During this latter
period of operation, the cell was only run 3-4 hours a day,
compared to the previous 7-8 hours, in order to minimize
problems with excessive overheating of the pump.

Testing was recommenced on 17 August with fresh 0.8M NaCl and
a pH 10+ recirculating regenerant solution.  The new settling
tank for the activated sludge unit was in line and new high-
capacity turbine pumps had been installed on feed and re-
generant influent lines to the pilot cell.  Results for the
remainder of the month are shown in Table 31.  The cell per-
formed well initially, reproducing the 901 ammonium removal
attained before shut-down.  However, the regenerant stream
immediately developed a high pressure drop which severely
restricted regenerant flow and ammonium removal efficiency.
After cleaning, realignment, and hydraulic tests, the cell
was restarted on 25 August and for several days thereafter
gave ammonium removals in excess of the desired 90%.  Various
adjustments in the cell clamping pressure and feed pumping
pressure failed to produce an increase in feed flow rate
above about 65 ml/min.  On 1 September a leak developed
during an attempt to obtain a higher flow and the unit was
returned to Cambridge for rework and redesign of the flow
paths in order to obtain lower overall pressure drops at ac-
ceptable flow rates.

Modifications on the cell were completed on 8 September and
it was returned to service at LES.  Alterations consisted of
realigning and regasketing the feed and regenerant spacers,
enlarging the inlet ports in the end-blocks to accomodate
large diameter tubing and widening the manifold openings.
Cell configuration was retained at one feed and one regenerant
stream.  Serpentine spacers with plastic mesh in the feed
stream and porous polyethylene sheet in the regenerant stream
were again used to form the flow paths.  Operation was started
on 8 September and continued through 15 September.  The in-
tention was to run at the highest practical feed flow rate
consistent with a 90% ammonium removal.  This appeared to be
about 130 ml/min at a feed to regenerant flow ratio of 2/1 to
3/1, but flow and pressure readings were extremely erratic,
and the data were not considered representative.  Line pressures
were approximately 100 psig and 60-80 psig in feed and re-
generant respectively, conditions which caused periodic
rupture of the tubing connections and a feed to regenerant
leak  of about  one liter per hour.  It was also observed that
the regenerant reservoir gradually turned dark brown during
this series of runs and brownish slurry was expelled from the
regenerant side of the cell on morning start-up.

Cell configuration was now more drastically changed by re-
building with the externally manifolded multipass spacer
                           149

-------
TABLE    31
EXD AMMONIUM REMOVAL - PILOT CELL
Feed: Lawrence Secondary Effluent, 2S-26 C
Regenerant: 0 . 8M NaCl, re ci rculating , 25-26°C
Serpentine Spacer
Date
8/17
8/18
8/25
8/26
8/27
8/28
8/31
9/1
Regener an t
F low Rate ,
rol/rain
25
6
60
30
40
40
30
65

pH
10 .
10.
10 .
10 .
10.
10 .
10 .
10 .
2
1
2
1
3
2
2
3

Flow Rate,
ml/min
100
90
60
60
60
60
65
120


7
6
6
7
7
7
7
7

pH
. 1
.4
.9
. 3
. 2
.4
.6
.0
Feed
NH3-N in,
mg/1
25
2
4
12
20
20
15
13


NH3-N out,
mg/1
2 .
1.
1 .
1 .
1.
0 .
1 .
0 .
0
0
5
0
5
5
0
5

% Removal
92
50
63
92
93
98
93
96

-------
shown in Figure 61.  The four 6 cm x 76 cm parallel paths in
this design can be combined in several ways to provide one,
two or four effluent streams from a single spacer.  Various
combinations of these are also possible.  The configuration
selected for the ammonium cell consisted of one feed spacer
flanked by two regenerant spacers. All were 40 mil thick with
plastic  screening in the flow paths.  The feed spacer was
manifolded so that the feed influent was split into two
parallel streams, each using two spacer paths in series, i.e.
two 152 cm long parallel feed streams.  After passing through
the cell the split stream was recombined to provide a single
effluent.  Each regenerant stream was run in series through
the four paths of the regenerant spacer.  Cell operation
started on 19 October and continued on a 24 hour basis until
27 October, except for the week-end.  The regenerant solution
was recirculated and maintained at pH 10.5 by periodic spiking
with lime.  Initial results indicated that a 90% ammonium re-
moval could be accomplished at a feed flow rate of 125 ml/min
(3.5 cm/sec} and comparable velocity in the regenerant streams.

However, as in the previous test, the solution in the regener-
ant reservoir turned brown, apparently due to suspended iron
oxides, and a rust-colored sediment could be flushed out of
the regenerant spacers after a few hours operation.  The
contamination was ultimately traced to a carbon-steel align-
ment ring on the face of the "non-corrosive, all bronze" head
of the newly installed regenerant turbine pump.  On 21 October
this was replaced with an all-plastic vane pump and operation
of the cell continued with a fresh regenerant solution.  No
further discoloration of the regenerant reservoir was observed
and a 90% removal at 125 ml/min feed flow was confirmed.

Minimum regenerant flow was also 125 ml/min total feed for
the two regenerant streams, i.e., one-half the feed velocity.
Pressures were 25 psig in both streams but gradually increased
in the regenerant until no flow could be obtained.  Disassem-
bly of the cell disclosed substantial amounts of ferric hy-
droxide collected in the regenerant manifold which provided
flow restrictions and extensive iron coating on the regener-
ant flow path screening with occlusion of the membrane sur-
face.  Apparently this precipitate had accumulated during
operation with the turbine pump and eventually redistributed
to block the flow path.  Data on cell performance for the
multipass spacer is thus compromised and the experiments should
be repeated under more favorable conditions.  Such repetition
would be expected to show a significant improvement in cell
efficiency.
                           151

-------






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          FIGURE 61
MULTISTAGE EXD  SPACER

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                      Section 15

                   ACKNOWLEDGEMENTS

Thanks are extended for help and encouragement given by Dr.
Carl A. Brunner, Project Officer for the Advanced Waste Treat-
ment Laboratory and to the following personnel of the Lawrence
Experiment Station of the Massachusetts Department of Public
Health:  Barnett L. Rosenthal, John E. Delaney, Joseph E. O'Brien
and George Minasian.

Acknowledgement for dedicated and conscientious efforts over
the course of the project are due to Process Research, Inc.
employees:  Newman E. Walton and Stuart M. Raifman.
                           153

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                  Section  16

                  REFERENCES

Prigogine, I., "Thermodynamics  of  Irreversible  Processes".
Interscience  (1965) .

Smith, J. D., and Eisenmann,  J.  L.,  "Electrodialysis  in
Advanced Waste Treatment", U.S.  Department  of the In-
terior, Federal Water Pollution Control  Administration,
Publication WP-20-AWTR-18,  (February,  1967).

Smith, J. D.  and Eisenmann, J.  L.,  "Limiting  Current
Densities in  Waste Water Electrodialysis",  Proc.  Fifth
Ind. Water and Waste Conf., 141-164  (1965).

Rosenberg, N. W., and Tirrell,  C.  E.,  "Limiting Currents
in Membrane Cells", Ind. and  Engr.  Chem.,  49,  780,  (1957).

Mason, E. A., and Kirkham, T. A.,  "Design  of  Electrodialy-
sis Equipment", Chem. Engr. Progr.,  No.  24,  55, 173  (1959).

"Standard Methods for the  Analysis  of  Water and Wastewater",
12th Ed., American Public  Health Association, New York,
(1965) .

Stumm, W. , and Morgan,  J.  J., "Aquatic Chemistry", Wiley -
Interscience  (1970).

Exchange Diffusion as a Pretreatment to  Desalination
Processes, Final Report on Contract  14-01-001 1782,
Office of Saline Water, U.S.  Department  of  Interior  (1970).

Farrell, J. B., "Physical-Chemical Methods  of Nitrogen
Removal", Symposium on  Nutrient Removal  and Advanced Waste
Treatment, Orsanco, Cincinnati,  Ohio,  April 29-30, 1969.
                      155            »U.S. GOVERNMENT PRINTING OFFICE:1973 546-312/152 1-3

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  SELECTED WATER
  RESOURCES ABSTRACTS
  INPUT TRANSACTION FORM
                   1. Report No.
  4. T/t/
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