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.
-------
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
" ~ '
-------
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
-------
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
-------
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
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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
-------
o
x
o
a>
CVJ
o
o
E
»»
X
ZJ
20
18
14
12
10
8
4
0
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
-------
100
o
0$
>.CVI
±Te
— o
10
o>
CL
O
1.0
s
*s
^
S
^
x*"
^
x"
^
^
^
^
n
Jd
c
>i
A
^"
^X'
^
^S'
^
^
s*'
n
0
A
*s
^
C
C
N
c
c
c
0
£
hl(
N(
iti
Cl
hi
N
^
**
Dr
D
'0
01
0
x
X*
ic
3
t(
= (
•i
3~
X
•H"
j(
C
a
5
d
•^
^
3 Dr
).I05
Dri
.OIM
e Dr
3.8*
ivin
M
*/ing
(Se
vin(
io-
g
f
e
'4
Fc
•o
Fa
Fo
(S
)rc«
rce
ble
rce
>ee
3
3)
To
bl<
3
3
)
|0 2345 6789|00
Velocity, cm/sec
FIGURE 8
PERMEABILITY VS VELOCITY
1000
23
-------
lUUt
9
s
7
6
5
A
3
2
10
3
8
7
fe
C
4
•a
1.0
9
9
7
4
5
4
3
Z
O.I
10
ff"
<
— «»
i
D
X
/
•y
LU
0
1
a
5 CM1
Jj S
1 \
>l< i
X
^
?
X
x
X
X
X
/
x
^x
^
o
/
'
x
j
/
/
-
'
x
^X
X
X
ri
x^
a CHL
CNO
0 NIT
V CHI
CN(
Of
3
R/
i
.0
D2
^IDE DRIVING FORCE
= .I05M
ME DRIVING FORCE
0!M (SEE TABLE 3)
RIDE DRIVING FORCE
- 3.8XIO"4
(SEE TABLE 3)
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
-------
l_
4-
X
"o
E
2 iO.Oxlo"4
o
a 8.0
2
UJ
2 6.0
o
£ 4.0
QC
z 2-°
U
^^
^^_
j^—^^
u--0
^^
_—<>- — '
*&•• H
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
-------
o
X
o
in
1
CO
E
o
^ 2.5
o
E
x" 2.0
ID
U_
uj 1.5
oc
*" i n
z L0
0.5
(
-------
O)
INJ
12,000
| 11,000
10
- 10,000
o
v" 9,000
z
^ 8 000
tL, )
7,000
6,000
5000
)
\
O
X
N°\
o
°\
v
V°^
v°\
^0
0
200 400 600 800
FLOW PATH LENGTHt cm
FIGURE 13
AFFINITY V§ PATH LENGTH
Run NO. 50768-!
1000
-------
to
o
O
c>
III
I
™h
u
cvT-
^
~c
£
CD
u
2
or
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
i- ><
It
UJ _J
2» ^
O ^
O —I
LU *-
£ 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
O
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.
O
UJ
5
X
Q-
m
o
x
Q.
10
(
9
8
7
6
5
4
3
2
in
-3
);
-4
' ^-~^
O
A
^--ft
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.
N,
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*
^-^
O
0.42M-CI
lOOml/mir
^^^
O-
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
u
•y
in
\
e
o
p-
Q.
7
6
5
3
3 456789 1.0 2 3
FLOW VELOCITY , cm/sec
FiGURE 37
FILM CONTROLLED DATA PLOT (A)
56789 10.0
-------
O
tn
\
£
u
HJU
7
6
5
4
3
2
10
9
8
7
6
5
4
3
2
1
^
/
//
,pf
-^
r
••t
/
D-3 Type Sp
Phosphate-*
Exchan
s-
a
:i
g
->
c
Ti
e
^
x^ ^
?r •
oride
x^
'
/
-
/
^
'
*•
A-3 1
Nitra
Ex
^
^4-3
Pho
ype
re-a
chan
£{
^
s*
Typ«
sphal
Ex<
Spa
ilor
ge
^
- SP
re-(
:har
1
cer
ide
IX
^
rC
act
:KI
ige
s1
^
s/
tr
X
^
x
brid«
x
^^*
-"•
s1
3 4 5 6 7 891.0
2 345678910
FLOW VELOCITY , cm/see
FIGURE 38
FILM CONTROLLED DATA PLOT (B)
3 4 5 6 7 89100
-------
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.
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
Regenerant Feed
AM = Anion Transfer Membrane
^1 2 ~ ^eec' Port Sample
^12.. = R^generant Port Sample
FIGURE 40
EXCHANGE-MULTICELL SCHEMATIC
86
-------
FIGURE 41
EXCHANGE MULTICELL
87
-------
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
-------
UD
O
I-4-.U
lit (~i
1 9 n
l
0^^^
5/19
\
\
\
\
\
&&o
5/21
^e0^
5/22
5/23
TIME
FIGURE 44
PHOSPHATE REMOVAL
-------
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
-------
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
-------
12.7
INLET
2 3
PORT NUMBER
FIGURE 45
PORT SAMPLES FOR 5/21/69
93
-------
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
-------
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
-------
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
-------
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
E
o
X
— s
l_
o
9
8
7
G
5
4
3
2
1
9
8
7
6
5
4
3
2
|/
X^
1
n
x"
1 —
1
f
j
\
D
PI
X
_^
"ic
0
S
»s
/
O
^xX
x^./lf
1
Type Sp«
phate -C
Exchan
i
i
i
A-l 'Uni
^quion-Af
A-
1 Ur
;
tized Spacer
~- Membrane
^x
liti
" 0
-3T>
losph
F xr
acer
'ide.
^ x
\
-
^
^
T
a
h
/
v'
e
re
an
tized
r-4T 1
Y!<
SF
?m
x^
SP
-O
qe
>ac
brc
.X
^ -
x
/
ac
ilo
sr
in«
X
X
i
-
er
ri(
'
\
'
de
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
-------
PO
o
S
£
u
IU
9
8
7
5
4
3
2.5
2
1.5
i
KC.L
, n i
0 C
- o i
A
X
iENJ
a +
.0
).3
.0
'
[RANT
SIR
n W
..P"
ft q
7.1
1
^
' .1
.0
x-
EAW
^
^s
ff
A
-"
x"
ff
^^ O
//
^
aj
X^
^
X
>^
^x*
^
s"
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
-------
p"
'
s
r
\.
4
-f-
f
1
(
j
6
=) —
-}
/-
k
>
V
o
3/K
I
1
' im
ID 3/0 uiamerer or
J r\
i
Porous Plastic or Extruded Mesh
P|
^w 'ft"1
1OH
r
L
V.
— (:
— t
c^ -
/
y
' 1
^~
3—
7
}—
h—
-i
l
i
FIGURE 61
MULTISTAGE EXD SPACER
-------
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
-------
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
-------
SELECTED WATER
RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
1. Report No.
4. T/t/
------- |