Document text
Cife Systems, Jut \
ER-171-3- 2
DEVELOPMENT OF AN IODINE GENERATOR FOR
RECLAIMED WATER PURIFICATION
IN MANNED SPACECRAFT APPLICATIONS
FINAL REPORT
by
R. A. Wynveen, J. D. Powell
and F. H. Schubert
August, 1973
Distribution of this report is provided in the interest
of information exchange. Responsibility for the contents
resides in the authors or organization that prepared it.
Prepared Under Contract' No. NAS1-11765
by
LIFE SYSTEMS, INC.
Cleveland, Ohio 44122
for
JOHNSON SPACE CENTER
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
JCifc Systems, Jhc.
FOREWORD
The development work described herein was conducted by Life Systems, Inc.
during the period June 26, 1972 through August 28, 1973, under NASA Contract
NAS1-11765. The Program Manager was Dr. R. A. Wynveen. Technical support
was provided as follows.
Personnel
Area(s) of Responsibility
Fred C. Jensen
Iodine valve, accumulator and dispenser
design
Glenn A. Little
Ground Support Accessories layout and
fabrication
John E. Nemeth
Analytical, Parametric and Endurance
Testing
David E. Keck
Control and monitor instrumentation
design and fabrication
Manny H. Naft
Mechanical design and alternate iodine
generation designs
J. David Powell
Control and monitor instrumentation design
James L. Seago,
Ph.D.
Iodine chemistry, electrochemistry and
microbiology
John W. Shumar
Product Assurance and materials evaluation
Franz H. Schubert
Mechanical hardware, electrolytic valve
and Potable Water System Simulator
designs
Boris D. Cahan,
Ph.D.
Iodine electrochemistry and ion exchange
membrane technology
The program's technicians were R. A. Clark and M. L. Kruszynski. Secretarial
work was completed by C. A. Lucas and V. E. Szanati. Dr. Boris D. Cahan is
a Senior Research Associate within the Chemistry Department of Case Western
Reserve University, Cleveland, Ohio 44106.
The contract's Technical Monitor was 0. Karl Houck, NASA Johnson Space Center,
Houston, Texas 77058. The program was initially contracted with the NASA
Langley Research Center and subsequently transferred to the Johnson Space
Center.
Jdfe Systems, Jhc .
TABLE OF CONTENTS
PAGE
FOREWORD i
LIST OF FIGURES v
LIST OF TABLES vi
SUMMARY 1
INTRODUCTION ... 2
PROGRAM OBJECTIVES AND STRUCTURE 2
Primary Program Objectives 2
Primary Process Objective 3
Four Program Tasks ' . 3
IGDS Development (Task 1.0) 4
Ground Support Accessories (Task 2.0) 4
Research and Development Testing (Task 3.0) 5
Program Management (Task 4.0) 5
Program Additions 6
PREVIOUS RESEARCH AND DEVELOPMENT 7
Chlorogen 7
Conversion from Chlorine to Iodine 7
IODINE AS A BIOCIDE 10
Comparison Between Iodine and Chlorine Characteristics 10
Electrochemical 10
Physical and Chemical ..." 10
Biocidal 12
Iodine in Dilute Aqueous Solutions 12
Elemental Iodine ....... ........ 12
Hypoiodous Acid 14
Formation of Tri-iodide Ion 14
Formation of Iodate Ion 15
Desirable Potable Disinfecting Characteristics 15
Space Shuttle Application 15
Iodine Versus Silver Ion 15
DETERMINATION OF IODINE GENERATION REQUIREMENTS 16
Water Flow Requirements 16
continued-
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Table of Contents continued -
PAGE
Contractual Specification 16
Shuttle Orbiter Specification 16
Space Station Specification 17
Iodination Level Requirements 17
Selection of Water Flow Design Point 17
Prototype Iodine Generation Rate • . . 17
Iodine Storage Capacity . 20
Prototype Operating Modes 22
Operating Mode A 22
Operating Mode B 22
Operating Modes C and D 22
Operating Modes E and F 22
IODINE GENERATING AND DISPENSING SYSTEM BREADBOARD 24
IODINE GENERATING AND DISPENSING SYSTEM PROTOTYPE 27
Iodine Accumulator, Valve and Dispenser 27
Accumulator 27
Valve 27
Dispenser 31
IGDS Instrumentation 31
Control Concepts 33
Circuit Construction 39
Control Adjustment Summary 43
Mechanical Controller 45
GROUND SUPPORT ACCESSORIES ................. 45
Material Testing Setups 45
Experimental Cells 45
Potable Water System Simulator 45
Storage, Fill and Water in Use Tank Simulator ....... 51
Water Recirculation Pump 51
Iodine Detector Simulator 51
Packaged Monitor Instrumentation and Accessory Controls 51
Analytical Considerations 51
Measurement of Iodine Concentration 51
Hydrogen Ion Concentration 54
Iodide Ion Concentration 54
PRODUCT ASSURANCE . 54
Quality Control 55
iii
continued -
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Table of Contents continued -
PAGE
Maintainability 55
Safety 55
Iodine Generating and Dispensing System Materials Program .... 56
Survey Results 56
Material Testing . 56
Ninety- and 180-Day Membrane Exposure Tests 58
Material Compatibility with Flammability and Outgassing
Specification 61
Metallic and Nonmetallic Materials in the Potable
Water System 61
TEST RESULTS 61
Laboratory Breadboard Experiments 64
Solutions to the Acid Build-up Problem 66
The Leaching Problem 66
Supplementary Experiments To Quantify Leaching 67
Leach Rate versus Flow Rate 67
Leach Rate versus Temperature 67
Leach Rate versus Time 67
Minimizing Leach Rate 71
Material Experiments 71
Iodinated Water Taste Experiments 71
IGDS Experiments 71
Shakedown Test 72
Calibration Test 72
Design Verification Test 72
Endurance Test 74
Operating Conditions 74
Post-Test Inspection 86
Bacterial Challenge Experiments 88
OTHER PROGRAM ACTIVITIES 88
Mechanical Iodine Injection 88
Mechanical Approach Design 88
Advantages and Disadvantages 93
Mechanical Approach Work Terminated 93
Preliminary Comparison of Potable Water Disinfecting System ... 93
CONCLUSIONS 96
REFERENCES 97
APPENDIX A - REFERENCE DATA A-l
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LIST OF FIGURES
FIGURE PAGE
1 Chlorogen System Concept 8
2 Schematic of Chlorogen-Based IGDS Concept 9
3 Schematic of Selected IGDS Concept 9
4 Iodine Valve Operation 11
5 Inactivation of E. Coliform by Iodine and Chlorine at pH 6 . . 13
6 Iodine Required as a Function of Flow Rate and Concentration . 19
7 Block Diagram of Operating Modes A to D 23
8 Laboratory Chlorogen Hardware 25
9 Experimental Cell for I 2 Valve Characterizations . . 26
10 IGDS Block Diagram 28
11 Assembled Iodine Accumulator, Valve and Dispenser 29
12 Disassembled Iodine Accumulator, Valve and Dispenser 30
13 Control and Monitor Instrumentation Enclosure 32
14 Iodine Control System Block Diagram (Continuous Monitoring) . 34
15 Iodine Control System Block Diagram (Periodic Sampling) ... 36
16 Proportional Controller Operation 37
17 Proportional Controller Operating Flexibility 38
18 Electronic Construction and Mounting 40
19 Iodine Control Logic and Bipolar Current Source 41
20 Iodine Control Storage and Clock 42
21 Sensor Storage Block Diagram 44
22 Iodine Control Logic for Mechanical Injection 46
23 Potable Water System Simulator 47
24 Potable Water System Simulator, Front View 49
25 Potable Water System Simulator, Rear View 50
26 Potable Water System Simulator Water Tank 52
27 Iodine Sensor Simulator 53
28 Results of the 35-Day Characterization Test 65
29 Leach Rate as a Function of Water Flow 68
30 Leach Rate as a Function of Temperature 69
31 Leach Rate as a Function of Time 70
32 Current-Voltage Characterization: IGDS and Breadboard Valves . 73
33 Leach Rate of IGDS as a Function of Time 75
34 Effect of Current Density on Efficiency 76
35 Total Iodine Generated versus Current Density ~. . . . . . . . 77
36 Cell Voltage versus Current Density 78
37 Water Flow Rate Variations 79
38 PWSS Loop Water Pressure Variations 80
39 Water Temperature Variations 80
40 Iodine Production Variations 81
41 Leach Rate Variations 82
42 Efficiency Variations 82
43 pH Variations in Iodinated Water 83
44 Valve Voltage Variations 84
45 Mechanical IGDS 90
46 Possible Mechanical Injection System 91
47 Saturated Iodine Solution Flow Rates 92
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LIST OF TABLES
TABLE PAGE
1 Space Station Prototype Reclaimed Water Flow Rates 18
2 Six-Man Prototype Design Specification 21
3 Potable Water System Simulator Parts List 48
4 Iodine and Chlorine Material Compatibilities 57
5 Results of Saturated Iodine Soak Test (Room Temperature) ... 59
6 Results of Accelerated Iodine Soak Test, 338K (149F) 60
7 PWSS Material Contacting Iodinated Water 62
8 Materials Wetted by Iodinated Water in the PWSS 63
9 Endurance Test Parameters 85
10 Results of the Bacterial Challenge Experiments 89
11 Biocidal Agent Comparison 94
12 Comparison of Potable Water Biocidal Agent Systems 95
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SUMMARY
A four-task program culminated with a successful 30-day test of a prototype
Iodine Generating and Dispensing System (IGDS). The IGDS was sized to iodinate
the drinking water nominally consumed by six men, 4.5 to 13.6 kg (10 to 30 lb)
water per man-day with a ±10 to 20% variation with iodine (I^) levels of 0.5
to 20 parts per million (ppm). The 1 ^ treats reclaimed water to prevent or
eliminate microorganism contamination; Treatment is maintained with a residual
of I 2 within the manned spacecraft water supply. A simplified version of the
Chlorogen water disinfection concept, developed by Life Systems for on-site
generation of chlorine (C^), was used as a basis for IGDS development.
The IGDS consisted of (1) an I^ accumulator to store crystalline 1 ^; (2) an
electrochemical I„ valve to control I ^ flow; (3) a method for dispensing I^
into water; and (4) nominal controls. The accumulator had storage volume
adequate for 180 days. The I valve consisted of an anion exchange membrane
between two noble metal electrodes. The I^ dispenser consisted of a compartment
that passed untreated water over the 1 ^ generation electrode. The controller
allowed regulation of I^ flow in response to an I~ concentration to maintain
the desired residual I concentration. The IGDS design specification was selec-
ted for Space Shuttle Urbiter and Space Station applications. Six operating
modes were included to simulate all envisioned arrangements.
Preliminary development was completed with laboratory setups and a breadboard.
Ground Support Accessories were provided to check out IGDS materials of construc-
tion, obtain design data, simulate the potable water system, and measure I 2
concentration and related aqueous solution parameters.
A mini-Product Assurance Program was included so the impact of manned chamber
testing requirements would be included during the initial design activities.
Major emphasis was on IGDS materials selection and, based on several exposure
tests. Teflon and 316 stainless steel were selected.
An extensive test program was completed. Experiments with cells demonstrated
that current densities to 5 mA/cm were possible. Experiments with a bread-
board system, operated for 35 days, demonstrated construction material integrity
and the combining of I ^ storage, dispensing and valve functions into a single
assembly.- .
Information produced during this development effort identified the IGDS as a
contender for potable water microorganism control on future manned spacecraft.
It remains to reduce the basic design reported herein to a prototype approaching
flight specification. Experiments with the IGDS culminated in a 30-day endur-
ance test. The endurance test was operated at a 5 to 10 ppm I level at room
temperature, with a water flow of 27 kg (60 lb) per day and a pressure of 210
kN/in ? (30 psig) . The electrolytic valve operated at 1.6 watt and 6 mA (0.24
mA/cm (0.23 amp/ft )).
Potable water contaminated with abundant E. Coliform Group organisms was treated
by electrolytically generated at levels of 5 to 10 ppm. In all instances,
the E. coli were eliminated.
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Cifc Systems, Jhc.
Other program activities included (1) development of a mechanical injection
process and (2) a preliminary comparison between the IGDS and the silver ion
(Ag ) water treatment process. The comparison showed the IGDS was lighter,
smaller, and avoided the need to replace ion exchange columns. The electrolytic
I 2 valve required less than one watt of power.
INTRODUCTION
The potable water supply on future manned spacecraft will use recycled water
in the distribution system. Although pasteurization has been recommended as
a reliable method for sterilization, other approaches offer distinct advantages
in terms of weight, volume, cost and power consumption for maintaining water
quality. One such approach was investigated under NASA Contract NAS1-9917, ^ '
which lead to the development of a laboratory breadboard of an in-situ Cl^
generating device called the Chlorogen.
Other biocides, Ag + and I 2 , for instance, have merit and have received attention
in the manned space program. Iodine, because of its superior microorganism
annihilation potential at low dosages and dose rates, among other advantages,
is favored. However, development of suitable devices to dispense and measure
I 2 and its concentration in a manned spacecraft application has not occurred
except for treating potable water stores in the Lunar Excursion Module of the
Apollo and in the Skylab program. The program conducted under Contract NAS1-
11765 was, therefore, initiated for the "Development of an Iodine Generator
for Reclaimed Water Purification in Manned Spacecraft Applications." Technology
produced from the preceding Chlorogen development formed the basis of initial
studies for the I 2 generator development program which is described herein.
PROGRAM OBJECTIVES AND STRUCTURE
A program to develop a six-man prototype of an Iodine Generating and Dispensing
System (IGDS) was completed by Life Systems, Inc. The ultimate purpose of the
IGDS is to treat reclaimed water for microorganism- contamination in a manned
spacecraft application.
Primary Program Objectives
The primary program objectives were to
1. Convert the Laboratory Breadboard Model of the Chlorine
Generating Device^ ■'into one based upon I^ as the
biocidal agent.
2. Perform experimental research and development with the
laboratory breadboard to demonstrate the feasibility of the
ly generator prior to the development of a six-man prototype
or the device .
(1) The numbers shown in parentheses refer to references cited at the end of
this report .
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3. Design and develop (a) the method for storing a 180-day
supply of I 2 , (b) a mechanism for dispensing the generated
1 2 into water, and (c) the instrumentation to allow for auto-
matic I_ generation in response to a signal reflecting
residual I 2 level.
4. Design, develop, fabricate, assemble and functionally test a
prototype six-man system on the basis of the analytical and
experimental results obtained with the Laboratory Breadboard
Subsystem. (The prototype device was specifically designed
to iodinate the drinking water nominally consumed by six men
(selected in the range 4.5 to 13.6 kg (10 to 30 lb) per man-
day) with a ±10 to 20% variation.)
5. Endurance test the prototype subsystem having a goal of 30
days of continuous operation at the nominal design point.
Primary Process Objective
The primary process objective is to treat reclaimed water to prevent micro-
organism contamination in a zero gravity, manned spacecraft application, by
maintaining a preset residual concentration of This is to be accomplished
by integrating the IGDS with a residual I 2 analyzer. The analyzer is to pro-
vide a signal to activate the I 2 injection process when I 2 is needed to iodin-
ate reclaimed water or to maintain the pre-established residual level within
a potable water supply.
Four Program Tasks
The program was divided into four tasks.
1. Design, develop, fabricate, assemble and functionally check out
a breadboard and a six-man prototype of the IGDS.
2. Design, fabricate, assemble and functionally check out the Ground
Support Accessories (GSA) needed for the development of components
for the laboratory breadboard and the six-man subsystem.
3. Experimental research leading to and including development testing-
of the nominal six-man IGDS.
4. Program and data management, document preparation and submittal,
and contract administration including preparation for and atten-
dance at informal program reviews.
The program's activity was divided such that 54% was devoted to design,
development and fabrication of the breadboard and prototype units of the IGDS
(Task 1.0); 12% was associated with the GSA for both the breadboard and the
six-man system (Task 2.0); 24% was for research and development testing (Task
3.0); and 10% was for data requirements and management of the program to meet
cost, schedule and performance objectives (Task 4.0).
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IGDS Development (Task 1 . 0)
The IGDS development involved
1. Analytical studies on replacing the in-situ, biocidal agent
generating concept based on Cl 2 chemistry with one based on
I 2 chemistry and including
a. evaluation of the differences between I 2 and Cl 2
chemistry, electrochemistry and biological activity,
b. evaluation of the materials for applicability to the
I- system and modification, where required or appropri-
ate, to optimize system/hardware design and development,
c. preparation of a (i) short summary of the literature
defining the organisms that are killed or incapacitated
through iodination and chlorination, and the temperature,
contact time, solution pH and level of disinfecting agent
required, J (ii) list of organisms projected for the space-
craft environment, and (iii) cross comparison of iodin-
ation and chlorination procedure and concentration required
to kill organisms anticipated to be present in a manned
space mission,
d. analysis of approaches to be used for the measurement of
- I 2 in water,
e. finalization of the spacecraft water treatment requirements
for the selected mission and preparation of a specification
for the prototype unit in terms of capacity, capacity range,
and ranges in water pressure and temperature, and
f. preparation of mock-ups of two IGDS concepts and their
electronic control module.
2. Modification of the laboratory breadboard of the Cl 2 generating
device to enable using it to provide
- | a y
3. Design, develop and fabricate the nominal six-man IGDS V
including an I 2 accumulator, electrolytic I 2 flow control
valve (generator), I 2 dispenser, and instrumentation.
Ground Support Accessories (Task 2,0)
The activities devoted to designing and fabricating the GSA included
1. Provision for a potable water system to simulate the end-item
application .
(a) A mini -Product Assurance Program was also carried out during the prototype
IGDS development (see the Product Assurance section starting on page 54).
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Cife System, Jhc.
2. Provision for a 28 VDC power supply.
3. Provision for an electronic circuit to simulate an I 2 sensor,,
signal corresponding to a 0 to 20 ppm I 2 level (0 to 5 VDC) . ^
4. Establish methods to detect residual I^.
5. Provisions to allow evaluation of the effect of on metallic
and nonmetal lie materials.
These facilities have been called accessories instead of ground support equip-
ment because they would not be required for operation of the prototype system
in its end-item application. They are needed to simulate the interface between
the IGDS and the projected operating environment and to provide parametric
testing facilities.
Research and Development Testing (Task 3.0)
The experimental research leading to and including development testing of the
nominal six-man IGDS included
1. A series of experimental investigations carried out on laboratory
"set-ups," including a 35-day endurance test on a breadboard,
to evaluate application of the Cl 2 generator concept to I 2 generation.
2. Preliminary testing of the nominal six-man IGDS as a system
shakedown/debugging procedure.
3. Design Verification Testing (DVT) at 0.5, and 20 ppm and several
other concentrations in between.
4. Disassemble, inspect and reassemble for the 30-day endurance
test.
5. Continuous 30-day endurance test to establish operational parameters
for subsequent automated system operation.
6. Disassemble, inspect and refurbish after the 30-day test.
7. Experiments in which one or more of the E. Coliform Group of
bacterial organisms were challenged by the 1 ^ generated with the
breadboard and prototype units.
Program Management (Task 4.0)
The program management activities incorporated to meet NASA’s cost, schedule
and performance objectives and the data requirements included
(a) It was initially planned that the Iodine Colorimeter developed under
NAS9-11879 would be provided as Government Furnished Equipment (GFE)
to integrate with the IGDS. (3)
(b) No redesign or refurbishment was needed.
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Cife Systems, Jnc.
1. Monthly meetings with program personnel to discuss contractual
cost, schedule and performance objectives versus accomplishments.
2. Four meetings with the contract's Technical Monitor; two at Life
Systems' facility and two at the Johnson Space Center (JSC).
3. Preparation and submittal of the following series of data
requirements :
a. an initial Program Plan and its revision to cover the
modifications incorporated when the program was
transferred to JSC,
b. Monthly Technical Progress Report Letters, except during
the month when other interim type reports were submitted,
c. two Interim Technical Progress Reports: one on the
evaluation of the "Chlorogen" approach to I 2 generation
and the other on a comparison between C^ and 1 ^ for
maintaining biocidal conditions in water supplies,
d. Monthly Financial Management Reports,
e. one New Technology Report,
f. a report on additional areas for investigation, and
g. the Final Report.
Program Additions
After the program was transferred to JSC, several modifications were added,
including
1. Incorporation of a standard inspection procedure for use
during prototype fabrication and assembly.
2. Provisions for monitoring the nonmetal lie materials for
applicability to manned testing (later expanded to also
include monitoring metallic materials).
3. Provision for the 1 ^ sensor signal, sample and hold, and
synchronization clock since the ^ sensor projected for use
employed sampling on a periodic rather than a continuous
basis.
4. Incorporation of two additional challenge experiments in which
one or more of the E. Coliform Group of bacterial organisms
were incorporated into the water and subsequently challenged
with the electrochemically generated 1 ^.
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JCife Systems, Jnc.
PREVIOUS RESEARCH AND DEVELOPMENT
Chlorogen
The Chlorogen is an in-situ biocidal agent generator consisting of three
series-connected, electrolytic cells. The overall process is illustrated in
Figure 1;
One cell serves as a Cl^ generator and is based on an electrolysis process
where Cl 2 is evolved from an aqueous electrolyte made up of sodium chloride
(NaCl) and sulfuric acid. Chlorine is produced at the anode and hydrogen (H^)
is produced at the cathode according to the following reactions:
Anode:
2C1"
= C1 2
+ 2e"
E =
0
- 1 . 36v
(1)
Cathode :
2H + + 2e“
= H
E .=
O.OOv
(2)
Overall:
2C1‘ + 2H +
- «,
+
— o
E =
A
1 . 36v
(3)
o
The Cl- is produced at a flow rate proportional to current and at a quantity
proportional to the integration of current for the interval of time current
is flowing.
The Cl^ evolved at the anode is in the gas phase since Cl 2 is a gas above 238K
(31F) . The generated Cl 2 then passes to the second electrolytic cell which is
used as an electrolytic valve to control the flow of Cl-. Chlorine only flows
when current flows. Chlorine is consumed at a cathode {via the reverse of
reaction (1)) and generated at an anode (via reaction (1)). Starting and stop-
ping of the flow, therefore, results from the opening and closing of an electri-
cal circuit, a process much faster in response than mechanical valves. Because
of this feature, the concentration of Cl 2 required in the chlorination process
can be carefully regulated. The Cl- flow rate is directly proportional to the
current flowing because each side or the electrolytic valve contains Cl- and
the consumption and generation were found to occur with 100% current efficiency.
The by-product H 2 generated in the Cl 2 generation step (reaction (2)) is
eliminated immediately by electrochemical ly reacting it to produce water vapor
at the anode of the third electrolytic cell using ambient air as a source of
this cell's cathode reactant.
Conversion from Chlorine to Iodine
Figures 2 and 3 are schematics of two versions of the Chlorogen concept, based
on its conversion to They show component locations and their interface
with the reclaimed water. As part of the current program, three additional
functional components were added to the in-situ biocidal agent generator concept.
Additional components are (1) agent storage, (2) a diffuser for dispensing the
generated agent into water, and (3) instrumentation for control and monitoring
the process.
Figure 2 illustrates the approach in which the I 2 is stored as an acidified
iodide (e.g., potassium iodide) and subsequently converted into H 2 and I 2> The
7
Acidified
NaCl
JCife Systems, Jhc.
a> c
4-> -H
X
1A
•H *0
O
O 0)
Xl
V)
fH C X
O
<D
+J *H *rt
x:
X)
Orth
4->
o
<U 4-> *->
c
i— i a> rt
u
<
u G S
li
II
II
EZZZ)
8
FIGURE 1 CHLOROGEN SYSTEM CONCEPT
Cife Systems, Jhc.
Cifc Systems, Jhc.
formed in the process of forming I 2 from iodide (I ) is consumed in the H 2
Eliminator. The I 2 dispensing rate is controlled by the electrolytic valve
which is an electrochemical cell consisting of two metal screen electrodes sep-
arated by an electrolyte. The electrolyte is a potassium iodide soaked anion
exchange membrane. The reactions occurring at the electrodes are
Anode:
21"
= I 2 + 2e"
E = -0.54v
0
( 4 )
Cathode :
I„ + 2e"
= 21"
E = +0.54v
n
( 5 )
Overall :
I (solid)
= I» (aqueous)
V
E = O.OOv
n
(6)
The function of the valve is to accurately dispense I 2 into water.
Figure 3 illustrates a simpler, alternate approach, in which I 2 is stored as
a solid in contact with a saturated solution. An electrochemical cell is
not used to generate I„ and, therefore, the I 2 Generator and H 2 Eliminator
portions of the on-site, biocidal agent generator are dropped. The I 2 flow
rate is still controlled by the electrolytic valve and the accumulator, dif-
fuser, and instrumentation are still needed. A simpler subsystem was not
possible with Cl 2 because of the potential hazard of storing a 180-day supply
of gaseous Cl 2<
IODINE AS A BIOCIDE
Comparison Between Iodine and Chlorine Characteristics
In changing from Cl 2 to I 2 , consideration had to be given to their electro-
chemical, chemical and biocidal characteristics.
Electrochemical
The literature shows ^that a smaller potential is required to oxidize I to I 2
than to oxidize -Cl" to Cl 2 , _-0. 54 versus -1.36 volt, respectively. Electrical
current required for a six-man spacecraft application is less than one amp so
power reductions to use I 2 are negligible (less than one watt). The lower oxi-
dizing power of I 2 also means the competitive reaction between Cl 2 evolution
and oxygen (0 2 ) evolution is avoided. (Were it not for the high overvoltage
(i.e.’, voltage greater than oxidation potential) of the competing C> 2 evolution
reaction, efficient conversion of Cl to Cl 2 would not have been possible.)^
Figure 4 depicts the I 2 valve process. Electrical current regulates the
electrochemical reaction and the specific anion transferred determines the
process efficiency. If 100% of the current flow is via I", the current effi-
ciency will be 100%; via I ", the current efficiency will be 300%; and via OH ,
the current efficiency will be 0%. Actual practice indicates a complex combin-
ation of all three.
Physical and Chemical
One important difference between I 2 and Cl 2 is that I 2 is a solid at room tem-
perature while Cl 2 is a gas. Thus, I 2 formed through electrolytic generation
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Cife Systems, Jttc.
Anion Exchange Membrane (across which I - , I ~ and
other anions can transfer)
Iodinated
Water
Water to be
Treated
Cathode Reactions
Anode Reactions
I2 + 2e = 21 Electrochemical 21
I 2 «■ 2e
I 2 + 1 " *3
Competing
1 3 ~ = X 2 + 1
FIGURE 4
IODINE VALVE OPERATION
Cifc Systems, Jmc.
could not be transferred through the gas phase to the electrolytic valve as was
possible with This was the important difference that changed the approach
to the IGDS froni the three-cell concept to solid storage and on-site flow
regulation with’ one cell, i.e;, the electrolytic valve. Other differences be-
tween CI 2 and I- .chemistry have been reported elsewhere, including standard
chemistry texts 7 ^
Biocidal
A clear distinction between the effectiveness of and Cl^ in killing or
incapacitating organisms is difficult to make. The principal factors affecting
efficient destruction of microorganisms are
a. time of contact,
b. concentration of organisms,
c. concentration of disinfectant,
d . temperature , and
e. solution pH.
A review of the disinfecting literature indicated that both I_ and Cl 2 can be
effective biocidal agents provided the right combination of the above ^factors
exists. It was not an objective of the current program, however, to make a
decision or recommendation of the preferred biocidal agent . A report was pre-
pared which did provide a literature summary. ' The results, however, can be
illustrated in Figure 5 by comparing the inactivation of E. Coliform Group
microorganisms with I„ and Cl 2 at low concentrations and pH 6. Both biocidal
agents are about equally fast. Other comparisons^ , however, indicate that
either I 2 or CI 2 may have a faster speed of inactivation, depending upon oper-
ating conditions or microorganisms.
Figure A-l, Appendix A, illustrates that I 2 and the hypoiodous acid (HOI) formed
when I 2 dissolves in water have the broad disinfecting capacility needed for
a spacecraft potable water system.
Iodine in Dilute Aqueous Solut-ions ....
Evaluation of the effectiveness of any agent for the disinfection of water
requires a familiarity with all the chemical. reactions that the agent is likely
to undergo under actual conditions of use. ^ } In the case of I„, four different
substances must be considered. They are elemental I , HOI, tri-iodide (I ~),
and iodate (IO^ - ). The aqueous chemistry of these chemicals are all pH depen-
dent except for I^~ which has an indirect pH relationship.
Elemental Iodine
The reaction of ^ with water is
12
Survival, Log Percent
Cife Systems , Jhc.
FIGURE 5 INACTIVATION OF E. COLIFORM BY
IODINE AND CHLORINE AT pH 6( 7 )
13
JCife System, Jhc.
I 2 + H 2 0 = HIO + H + + I" (7)
with a hydrolysis constant at 298K (77F) of
= MQ-KH-Icri = 3 x 10- 13 (8)
U 2 J
Other chemistry is summarized in Appendix A, including
1. I 2 solubility in water significantly dependent on
temperature (Figure A-2),
2. pH of aqueous solutions of (Figure A-3),
3. conversion of concentration from ppm to molarity
(Figure A-4) , and
4. effect of 1 ^ and I” concentration on the reversible
oxidation potential for the I^/I couple (Figure A-5) .
Hypoiodous Acid
Hypoiodous acid is a primary disinfecting form of 1 ^. It undergoes ionization
to form the hypoiodite ion (10 ) according to the reaction
HOI = H + + 01
with an ionization constant at 298K (77F) of
K
a
(H + ) (10 )
(HIO)
-13
4.5 x 10
(9)
( 10 )
Hypoiodous acid is only slightly stronger than pure water as an acid and its
ionization is pH dependent
Formation of Tri-iodide Ion
In the presence of added I", an aqueous solution of 1 ^ forms the bactericidal ly
ineffective I^ via
*2 + 1 = V (11)
The equilibrium expression at 298K (77F) for the reaction is
(i 7 ) a') ,
K. = — = 1.4 x 10"° (12)
1
Because, as shown in Figure 4, the electrochemical reactions involve I - , the
formation of I^' becomes a greater factor than in normal I 2 disinfecting
processes.
14
JCife Systems, Jhc.
Formation of Iodate Ion
The conversion of HIO to 10^" occurs at high pH values (8.0 and over) according
to the reaction
3HI0 + 20H" = HI0 3 + 2H 2 0 + 21"
f9)
It has been shown that the 10 has no disinfecting ability. v 1
formation of 10 ” would, to the extent that it is formed by the
I^, lower the disinfecting ability of the dose of I,, added.
Desirable Potable Disinfecting Characteristics
Desirable characteristics of a potable water disinfecting agent include
a. techniques (s) available to monitor its concentration
(to ensure effectiveness),
b. no physiological side reactions,
c. applicability to all known organisms,
d. avoidance of corrosiveness,
e. palatability,
f. ease of use,
g. minimum loss of agent/potency on storage, and
h. avoidance of outgassing.
Iodine, in the required dosages, has these characteristics.
Space Shuttle Application
The sterilization procedures for microbiological control considered as applicable
for the shuttle water subsystem included pasteurization, addition of Cl?, bromine,
I 2 and Ag . Although the pasteurization method was' initally'serectedCluJas the
primary water microbiological control methode, I 2 chemical addition was recom-
mended for maintaining bacterial control of the stored backup water. The
latter recommendations resulted from the effectiveness of I 2 against a wide
spectrum of organisms over a wide pH range with little variation in concentration.
In addition^ it is compatible for use with all types of water evaporators. More
recently Ag has been selected for use aboard the space shuttle vehicle.
Iodine Versus Silver Ion
Results of the IGDS program indicate I- has the following advantages over
Ag + :
(13)
Any substantial
consumption of
15
Cifc Systems, Jhc.
1. more effective against a broader spectrum of organisms, including
viruses, bacteria, fungi (spores), protozoa, and algae, over a
wide pH range, with little variation in required concentration,
2. avoids the regular replacement of ion exchange filters used to
reduce the Ag + concentration prior to consumption of the water,
3. avoids the uncertainty regarding all the conditions (temperature,
pressure, pH, flow rate, water line materials, water contaminants,
etc.) under which Ag plates out or is reduced to Ag metal,
4. offers the potential for use within the waste water collection
cycle of regenerative systems,
5. avoids the difficult sensing of Ag + needed to ensure Ag + concen-
tration in the water tank and especially, it avoids the sensing
needed to ensure that the ion exchange filter has removed excess
Ag to the parts per billion range just prior to water consumption,
6. offers greater flexibility in providing an in-flight adjustable
dosage level (0.5 to greater than 20 ppm) with the level control-
lable through the electrolytic valve,
7. provides a simple, regulated process for feeding elemental I 2
into a water supply, and
8 . is unaffected by amines which may complex Ag + .
DETERMINATION OF IODINE GENERATION REQUIREMENTS
Both the quantity of water to be treated and the iodination level influence
the IGDS requirements.
Water Flow Requirements
The contractual. Shuttle Orbiter, and Space Station specifications all
influenced the water flow specification
Contractual Specification
The contract cited that the prototype was to be sized to iodinate the drinking
water nominally consumed by six men, selected within the range of 4.5-13.6 kg
(10-30 lb) water per man-day with a ±10 to 20% variation. The minimum water
flow rate would be six men x 4.5 kg (10 lb) water per day x 1.1 or 29.7 kg
(66 lb) per day. The maximum rate would be six men x 13.6 kg (30 lb) water per
day x 1.2 or 97.9 kg (216 lb) per day. (Figure Ag6 allows rapid conversion
of water flows from kg/day (lb/day) to ml/min (in /min)).
Shuttle Orbiter Specification
The amount of potable water required by a four-man, shuttle vehicle crew is
16
JCife Systems \ Jhc :
approximately 18.1 kg (40 lb) per day. This water is used for drinking (7.1
kg (15.6 lb)), food preparation (3.3. kg (7.3 lb)), washing (4.0 kg (8.8 lb))
and urinal flush (3.6 kg (8.0 lb)). The amount of water available from the
fuel cells, however, is determined by the power they generate and their
efficiency. For a 5.0 kw power output the projected water produced is 46.3
kg (102 lb) per day.
The difference between the water used by the crew and that generated by
the fuel cells is available for heat rejection or for other purposes. It is
projected, however, that the entire fuel cell-generated water would have to
be iodinated, establishing 54.4 kg (102 lb) per day as a design point for
the IGDS. taJ
Space Station Specification
Data presented within the Delta Preliminary Design Package of a Space Station
Prototype (SSP) Program^ ' indicated the range in water flows expected for
the six-man system as shown in Table 1. The range found is 22.8 to 77.6 kg
(50.3 to 171 lb) per day.
Iodination Level Requirements
The contract called for an ability,to operate the IGDS over a range of 0.5
to 20 ppm. Based on taste tests, 1 " J however, it appeared that water with con-
centrations of I 2 greater than 5 ppm might not be palatable for continuous,
long-term use (efg., 90 to 180 days). In addition, the literature indicates a
level of 5 ppm, or less if longer contact times are used, is adequate to kill
organisms contained in potable water (see Figure A-l) . It was concluded,
therefore, that the quantity eventually needed for water treatment will be
less than 20 ppm. In fact, a 5 ppm maximum concentration is recommended be-
cause of the previously cited taste and biocidal characteristics.
Selection of Water Flow Design Point
Selection of a water flow, at a 10% excess over the minimum 27.2 kg (60 lb) per
day at an iodination level of 20 ppm, results in an IGDS with a capacity that
is also compatible with a water flow of 120 kg (264 lb) per day at a 5 ppm level.
This latter water flow rate is large enough to satisfy the contractual, shuttle
and SSP requirements at the lower iodination level recommended for flight
application. Figure 6 presents the required as a function of I^ level (ppm)
for various water flow rates.
Prototype Iodine Generation Rate
The I 2 generation or feed rate is related to process water flow rate and I 2
concentration as noted above and is determined by the equation
(a) It was reported that the fuel cell water production rate would vary
from 54.4 to 76.2 kg (120 to 168 lb) per day.
(b) See section titled "Iodinated Water Taste Test," page 70.
17
Cife Systems, Jhc .
TABLE 1 SPACE STATION PROTOTYPE RECLAIMED
WATER FLOW RATES
Flow Rate, kg/Day (Lb/Day)
Source of Water
Minimum
Normal
Maximum
Urine Recovery
9.3
(20.5)
15.6
(34.5)
33.6
(74.1)
Cabin Temperature and Humidity
and Carbon Dioxide Reduction
Subsystems
9.7
(21.4)
18.0
(39.7)
31.2
(68.8)
Total
19.0
(41.9)
33.6
(74.2)
64.8
(142.9)
Plus 10% Excess
20.9
(46.1)
37.0
(81.6)
71.3
(157.2)
Plus 20% Excess
22.8
(50.3)
40.4
(89.0)
77.7
(171.4)
18
Iodine Required (x 10 ), Lb/Day
Cifc Systems, Jhc .
3.50
3.25
3.00
2.75
2.50
2.25
2.00
1.75
1.50
1.25
1.00
0. 75
0.50
0.25
0.00
w w TJ* V <-
Iodine, ppm
FIGURE 6 IODINE REQUIRED AS A FUNCTION OF FLOW RATE AND CONCENTRATION
9
Cife Systems, Jhc.
I 2 Generation Rate, kg/Day = (wt. water, kg/man-gay) (no. men)
(I 2 cone., ppm)(10~ D )
For the current application this becomes
I 2 Generation Rate = (4.5) (6) (20) (10*^)
0.54 x 10*3 fcg/cLay
1.20 x 10* 3 lb/day
0.54 gm/day
0.23 gm/hr
(14)
(15)
Another method for expressing the I 2 generation rate is in terms of electrical
current required, using Faraday's Law and assuming 100% current efficiency, i.e.,
— = moles
nF
where
( 16 )
I = current, amp
t = time, second
n = number of electrons
F = Faraday's constant, 96,500 amp-sec per equivalent weight of matter
For the prototype application this results in
(0.54 gm/day) (2 equiv/mole) (96, 500) (1000 mA/amp) . _ . n
(254 gm/mole) (24 hour/day) (3600 sec/hr) ~ ^ '
Figure A-7 presents the I 2 generated as a function of current, assuming 100%
current efficiency.
Iodine Storage Capacity
The I 2 that must be stored within the prototype depends upon the process water
flow rate, the operating time and the margin added for contingency. For the
six-man prototype the quantity of I 2 needed is
(0.54 gm/day) (180 days) (1.10) = 108 gm (0.238 lb) (18)
3 3
Since I„ has a density of 4.93 gm/cm (0.178 lb/in ), the minimum volume of
I 2 is 22 cin (1.33 in ) .
Iodine Generating and Dispensing System Design Specification
Table 2 presents the specification used to design the six-man prototype hardware.
20
Cife Systems, Jhc \
TABLE 2 SIX-MAN PROTOTYPE DESIGN SPECIFICATION
Process Water Flow Rate, kg (Lb) per Day
Nominal
Range (Min . -Max . )
I 2 Generation Rate
Nominal § 5 ppm Level
Range
Min. @0.5 ppm Level
Max. @ 20 ppm Level
Set Point
2
Water Pressure, kN/m (Psig)
Nominal
Range
Water Temperature, K (F)
Nominal
Range
2
Pressure Drop across Generator, kN/m (Psid)
Water Tank Capacity, kg (Lb)
(' 12 ')
Water Quality Specification 1 ' J
Water Circulation Rate, kg (Lb) per Hr
(b)
27.2 (60)
24.4-29.9 (54-66)
Gm/Hr
Lb/Day
0.14
3.0 x 10
-4
n-2
2.7 x 10
1.2 x 10
0.60 1.3 x 10
Manually Adjustable
210 (30)
196-224 (28-32)
294 (70)
289-300 (60-80)
-5
0.7 (0.1)
70 (154)
20 (45)
(a)
I 2 Level Sensor Signal Characteristics
0 to 20 ppm
Sample Frequency
Control Instrumentation
Power Source
I 2 Sensor
0 to 5 VDC (C)
TBD ( d )
60 to 400 Hz, 115 VAC,
Single Phase
Simulated
(a) Design goal with actual level to be less than value cited.
(b) Only applicable to operating modes B and C, see next section of text.
(c) Assumed to be linear although a nominal deviation from linearity is
expected at the high ^ concentration level.
(d) Design will tolerate any sample rate from continuous to 12 samplings
per hour.
21
Cife Systems, Jhc.
Prototype Operating Modes
The prototype was designed for a potable water system employing one or more
water storage tanks; for example, one tank being filled, one on storage
while it is being tested for sterility, and one tank being used. This required
that the IGDS be designed to fit each of the six operating modes described
below with the help of Figure 7.
fa")
Operating Mode A (water line to a tank being filled^ )
In this operating mode, water being reclaimed from various water reclamation
subsystems, is accumulated and passes through the IGDS for iodination. The
level is established by monitoring the I^ level downstream of the I ^ valve and
using a feedback loop to regulate the ^ xlow rate. The water passes into a
storage tank being filled.
Operating Mode B (water line to a tank being filled that contains residual
iodinated water from prior use at an unspecified I^ level)
Operating Mode B is the same as A except the potable water tank being filled
contains leftover iodinated water. Since the iodination level of this water
would be unknown, it is necessary to recirculate it along with the reclaimed
water through the IGDS. It then passes through the I 2 sensor that provides
the feedback signal to establish the I 2 injection rate.
Operating Modes C and D (recirculation loop of a tank being used or a tank
being used with water being consumed)
These operating modes assume that the IGDS is located in a recirculation loop,
including the potable water tank being used. The only difference between Mode
C and D is that Mode D assumes water is simultaneously being consumed. This
influences water flow rate.
These operating modes are needed when the materials utilized in the potable
water tank tend to cause continuous consumption/reaction with the residual I^.
If loss of I 2 from the loop did not occur, these operating modes would not be
required.
Operating Mo de s E and F (recirculation loop of a 'tank being used with water . .
being added 00 and consumed or a tank being used with water being added only^ J )
Operating Modes E and F were not included in the block diagram contained in
Figure 7 because they do not reflect operating modes of any projected space
missions. These modes are different from Modes C and D in that water is simul-
taneously being added to the tank being used .
(a) Contract baseline operating mode.
(b) Operating modes added between laboratory breadboard and prototype system
testing.
22
Cife Systems, Jhc .
Operating Mode D
(Dashed Line
do*
Potable H 2 0
Potable H 2 0
Potable H 2 0
Tank Being
Tank Being
Tank Being
Filled*
Tested*
Used
I 2 Level
Detector
ump
/
I i
Operating Mode C
(Without Dashed
Line)
Generator
Operating
Mode B (Dashed
Line Included)
Operating Mode A
^ (Without Dashed Line)
18 kg (39.7 Lb) per Day
15.6 kg/Day (34.5
Lb/Day}
210 kN/m 4 - (30 Psig)
I 2 Level
Detector
Generator
do
3.3 kg/Day (7.3 Lb/ Day)]
289-300K (60-80F)
■
i
t
H 2°
Consumption
14.7 kg/Day
(32.4 Lb/Day)
289-300K (60-80F)
Urine H 2 0
Sabatier
Cabin
Recovery
Reactor
Humidity
Process
Condensation
Condensation
''Tank capacity of 70 kg (154 Lb)
FIGURE 7 BLOCK DIAGRAM OF OPERATING MODES A TO D
23
Cifc System, Jhc.
IODINE GENERATING AND DISPENSING SYSTEM BREADBOARD
Prior to designing the prototype IGDS, a series of experiments were carried
out to yerify the concept. The tests were made on the breadboard hardware
available^ , as shown in Figure 8, and on various laboratory set-ups. The
major purposes were to
a. obtain technical data on the I ^ valve performance,
b. verify the acceptability of dispensing the generated
l ? into the water by flowing the water over the
electrode (anode) on which the I- was being generated,
and
c. verify the applicability of storing the solid I 2
immediately adjacent to the cell's cathode. ~
The breadboard consisted of an electrolytic I_ valve, two water reservoirs
(one serving as the supply, the other, the ioainated water receiver), a power
supply and a water circulation pump. Periodically, and for endurance testing,
the water was recirculated instead of a once- through gravity feed operation.
The experimental cells utilized to obtain preliminary data on the valve were
those used on the Chlorogen program and were described previously. ^ J They
employed electrodes with an active area of 7.62 x 2.54 cm (3.0 x 1.0 in).
Figure 9 is a photograph of one of the cells.
fa)
The cell consists of an anode, an anion exchange membrane, and a cathode.
Adjacent to the anode was a compartment through which the water to be iodinated
or reiodinated circulated. Adjacent to the cathode was a compartment where a
slurry of water and I„ crystals were retained. The cell housing was made of
plexiglass held together with stainless steel bolts.
The experimental results obtained are presented on page 63 in the section entitled
"Laboratory Breadboard Experiments." They indicated
a. an ^2 va ^ ve was practical,
b. I 2 could be stored adjacent to the cathode as- - —
a slurry ,
c. the flowing water leached small amounts of
from the membrane surface, and
d. a build-up of H + concentration occurred in the
I 2 accumulator compartment.
Regarding Item c, maximum leaching allowable is a function of water flow
rate through the ^ valve and the desired level. The larger the flow and
the higher the desired 1^ concentration, the smaller the contribution leaching
(a) A description of the cell parts is presented beginning on page 27.
24
Cifc Systems, Jhc.
25
FIGURE 8 LABORATORY CHLOROGEN HARDWARE
Cife Systems, Jnc.
Cathode
Electrical Connection
Plexi glass
Cell Housing
Iodinated H o 0 Outlet
0 Compartment
Feed H 2 0 Inlet
Assembly Bolts
Anode Electrical Connection
FIGURE 9 EXPERIMENTAL CELL FOR
I 2 VALVE CHARACTERIZATIONS
26
Cife System, Jhc.
has to the concentration of the processed water. For the IGDS specification
(4.5 kg minus 10% water per man-day and a lower I ^ level of 0.5 ppm) and
based on equation (13), the minimum needed amounts to
required = ^ (6) (0.5) (10 ^) = 12.4 x 10”^ kg/day (19)
-2 -5
or 1.2 x 10 gm (2.7 x 10 lb) per day. Expressed as electrical current this
leach rate amounts to 0.011 mA (per equation (16)).
Regarding Item d, a pH lower than 2 was measured.
IODINE GENERATING AND DISPENSING SYSTEM PROTOTYPE
The IGDS prototype consisted of an accumulator, the electrolytic I 2 valve,
the I^ dispenser and instrumentation. Figure 10 shows a block diagram of the
system integrated into a potable water system and with an I ^ concentration
detector .
Iodine Accumulator, Valve and Dispenser
The I„ accumulator, valve and dispenser functions were combined as shown
assembled in Figure 11 and disassembled in Figure 12.
Accumulator
3 3
The internal I_ accumulator volume was approximately 50 cm (3.0 in ) with
dimensions of 9.53 x 2.54 x 2.05 cm (3.75 x 1.0 x 0.81 in). Filled with I^
at the theoretical density of 4.93 gm/cm^ (0.178 lb/in^) provides storage of
244 gm (0.541 lb) of I . With 108 gm (0.238 lb) of I^, it has a storage capacity
of 409 days (based on at 100% density) or 180 days (based on a 56% void
volume) .
A fiberglass sheet was used to separate the crystals from directly contacting
the electrode. This was not done with all prior cells, but was done in the
prototype to determine if the direct contact of solid I„ against the cathode
electrode/membrane surface contributed to I^ leaching. “The change was found to
minimize, but not eliminate, the occurrence. A 316 stainless steel screen was
used to hold the fiberglass sheet against the plexiglass housing.
Valve
The I^ valve consisted of an anion exchange membrane between two 70 mesh noble
metal screen electrodes.
The primary function of the anion exchange membrane is to immobilize the
electrolyte and to prevent the water being iodinated from contacting the solid
I While the membrane is conductive to anions (I , I^”, and OH”), the cation
portion of the electrolyte is immobilized within the membrane. Hydrogen ions.
27
JCife System, Jhc.
Q
T3
28
FIGURE 10 IGDS BLOCK DIAGRAM
JCife Systems, Jhc.
Pt Reference
12 Crystals
Anode Lead
FIGURE 11 ASSEMBLED IODINE ACCUMULATOR, VALVE AND DISPENSER
29
Cife Systems, Jhc.
r::;::;;T:r:t:?;;::;?:
Sample Port
(e.g. , pH)
FIGURE 12 DISASSEMBLED IODINE ACC
VALVE AND DISPENSER
30
Cife System, Jhc.
water, I^, HOI, etc. do not pass through the membranes, as a result of the
anion exchange mechanism. They may diffuse through, but at an order of magnitude
lower rate.
The anion exchange membranes were conditioned prior to incorporation in the
cells. This pre-conditioning consisted of soaking the membranes in a stirred
solution of 0.6 normal potassium iodide solution for one-half hour. The
membranes were then rinsed and again soaked, this time in a 0.1 normal potas-
sium iodide solution for one-half hour. The second step was then repeated.
Membranes were always maintained in a wet state.
A reference electrode was included to enable determining at which electrode
the polarization occurred. It consisted of a platinum wire immersed in the
saturated solution in the accumulator adjacent to the cathode.
In the exploratory work the polarization, other than internal resistance, mainly
occurred at the anode (21 = I + 2e ) with little occurring at the cathode
where the slurry existed. In the IGDS more polarization occurred at the cathode
because the solid was retained 0.95 cm (0.38 in) away by the fiberglass sheet.
Dispenser
The I 2 dispenser distributed the water over the valve anode (21 = I ? + 2e )
which was supported on square pegs. The pegs also divided and distributed the
water and had 0.25 cm (0.1 inch) sides and were located on 0.64 cm (0.25 inch)
centers .
IGDS Instrumentation
The control and monitoring circuits for the IGDS were those necessary for a
laboratory/prototype development program but had limited sophistication. They
were initially breadboarded and used with the breadboard cell and system testing.
For the IGDS they were packaged into the enclosure shown in Figure 13. It
contained circuits which
a. monitored the I 2 valve current,
b. monitored the valve voltages, including anode-to-
reference, anode-to-cathode and reference-to-cathode ,
c .
d.
e .
f.
provided adjustable constant current to the 1^ valve,
provided. power for the circulation and water feed
pumps, ^
monitored the I 2 sensor signal input voltage,
provided the temporary storage for I 2 sensor signals, and
(a) See section entitled "Potable Water System Simulator," page 45.
31
Cifc Systems, Jhc.
CONCENTRATOR
CONTROL
Cife Systems, Jnc.
g. provided the sensor sample activation pulse so that
the I 2 level sampling and the internal signal storage
systems were synchronized.
The instrumentation has the following features:
1. Closed and open loop control of concentration.
2. Manually adjustable, level set point over a 0 to 20 ppm range.
3. Compatability with a 0 to 5 VDC level signal corresponding
to a 0 to 20 ppm concentration.
4. Sample and hold provisions for periodic sampling and avoiding
sensor noise during sampling.
5. Bipolar current supply, for current reversal, to stop losses
from valve.
6. Constant current source so variations in cell voltage do not
affect current flow.
7. Upper voltage limit adjustable to prevent 0 evolution.
8. Lower voltage limit adjustable to produce appropriate oxidation
potential .
9. Ammeter to monitor ^ valve current.
10. Meter to monitor sensor input voltage, cell anode-to-reference,
anode -to- cathode and reference-to-cathode voltages, using a high
impedance FET amplifier.
11. All control and monitoring instrumentation in one enclosure.
Control Concepts
Two control concepts were incorporated - integrating and proportional. Each
could be operated in a continuously monitoring or periodic monitoring mode.
Integrating, Continuous Monitoring of Iodine Level - A block diagram of the
control system with continuous monitoring is shown in Figure 14. A pump cir-
culates liquid to be iodinated through the valve, the sensor and the storage
tank. The I. level signal from the sensor (E ) is compared with the I_ level
set point signal established by the adjustable CONCENTRATION SET POT (E^) . LaJ
Any difference (E) between these two signals (the error) is sent to the u
integrator. The integrator has an output which is constant only when its input
(E) is zero. The integrator output signal is used to control the bipolar cur-
rent source circuit which, in turn, produces a constant current directly pro-
fa) The expressions in capitals refer to the labels used on the instrumentation
enclosure's front panel (see Figure 12).
33
JCifc Systems, Jhc.
portional to the signal received at its input. The valve generates I ^ and
dispenses it into the liquid loop as a function of current flowing through it.
For this system to be in equilibrium, and E^ must be equal which causes
the valve to release as much I ^ as is being consumed. If the level in
the circulating loop should decrease, the output from the error amplifier will
increase from zero which will cause the output of the integrator to start
increasing. This causes a higher current generation and, therefore, a higher
I ^ dispensing rate. When the rates of generation and consumption become
equal, the system will reach a new equilibrium and E will equal E^g with no
output from the error amplifier. However, the output from the integrator and
the current source will be at a new value and, in the case illustrated, this
value will be higher than the previous one. The system works with zero error,
thus the set point and level will always be identical. The integrator was
designed with a very long time constant to compensate for projected system lags.
Integrating, Cyclic Monitoring of Iodine Level - If the sensor is to measure
discontinously, a storage system must be inserted between the sensor and the
error amplifier, and a clock added as shown in Figure 15. The time constant
of the integrator and the rest of the system must be tailored so that rela-
tively small changes in the system operating levels will occur between sample
times .
Proportional Controller, Continuous and Cyclic Sampling - If the integrator
is replaced with an amplifier, the system will no longer operate with zero
error. A difference (i.e., E^g / E ) is required because a finite input
voltage to the amplifier is needed to provide an output voltage which drives
the current source. Figure 16 illustrates system operation.
Assume the control is adjusted to operate along the curve A, B, C, D, E and
F of Figure 16 and that the system is operating at point D. If the level
in the circulating loop decreases, the proportional controller will cause the
current to move up along the curve from point D and a new equilibrium point
will be established when the I 2 generator and consumption rates are again
equal, say point C. Note the 1 ^ concentration is now down to about 8 ppm while
the current is up to 10 mA. The error increased to accomplish this. (For
purposes of illustration the change was made large, 10 to 8 ppm. In actual
practice this difference would be kept very small.) With the proportional type
controller, a change in the concentration will vary the current in the cell
until generation and consumption are equal. In the integrating system
there would be no net change in concentration to accomplish the same results.
Therefore, the curve shown by the vertical dotted line through D in Figure 16,
represents the integrating system operation.
The actual error at any operating point and the error change in response to
changes in I„ level, depends upon the gain of the amplifier and current source
characteristics. Thus, the slope of line B-E (Figure 16) can be varied through
an adjustment in amplifier gain as shown in Figure 17. In addition, both
the maximum and minimum current levels can be changed by adjustment of circuit
components .
35
Page missing from available version
Iodine Valve Current
Cife Systems, Jnc.
Maximum Current Level
Internally Adjustable
FIGURE 17 PROPORTIONAL CONTROLLER OPERATING FLEXIBILITY
38
JCifc Systems, Jnc .
Both modes of operation were incorporated in the controller. The FEEDBACK
RESISTOR switch, when in the IN position, converts the integrator to an
amplifier. Since the control can be used in either operating mode, it will
be possible to study each in subsequent development.
Circuit Construction
The control and monitoring system electronics for the IGDS were constructed on
two assemblies:
1. The 1 ^ valve control logic including bipolar current source, and
2. The control storage and clock.
fal
An I„ control sensor simulator v 'and a mechanical ^ j-ioj ection control were also
added to the enclosure but are not part of the IGDS. ^ ' These four units were
assembled on vector boards and tested independent of each other and used when
needed during the breadboard testing. Following this, the four vector board
assemblies were installed in a cabinet as shown in Figure 18, along with per-
formance indicators and controls (see Figure 12) . Then, the complete package
was debugged and tested with the four electronic subassemblies connected to-
gether. Once the subassembly was functional, it became the prototype instru-
mentation .
Control Logic and Bipolar Current Source - A photograph of the I 2 control logic
and bipolar current source is shown in Figure 19.
Control Logic . The control logic circuit contains the error detecting
and amplifying circuit, as well as the integrator/ amplifier . This circuit pro-
duces an internal voltage which is proportional to the difference between the
I ^ level set point (CONCENTRATION SET POT on the front panel) and the concentra-
tion as measured (simulated) by the I^ sensor. This error signal is fed to
a circuit which, as described previously, can be used in either an integrating
or an amplifying (proportional) mode with a long lag time. In either mode, the
output from this circuit is sent to the bipolar current source.
Bipolar Current Source . The bipolar current source provides the elec-
trical current required by the I~ cell. It is a controlled, constant current
source which produces a current f independent of cell voltage) whose magnitude
and direction are controlled by the signal from the control logic. The magni-
tude of the maximum current in either direction is internally adjustable.
Circuits are also incorporated to limit the maximum voltage which can be
applied to the cell in either direction by internal component adjustment.
Storage and Clock - Figure 20 is a photograph of the Storage and Clock.
(a) Discussed in the section entitled "Ground Support Accessories," page 45.
(b) A mechanical I ^ injection concept was carried along in parallel until the
electrolytic valve concept successfully passed the 30-day test with the
breadboard hardware.
39
Cifc Sy stents, Jnc.
Logic
JCife Systems, Jhc.
41
FIGURE 19 IODINE CONTROL LOGIC AND BIPOLAR CURRENT SOURCE
JCife Systems, Jnc.
42
FIGURE 20 IODINE CONTROL STORAGE AND CLOCK
JCife Sy stents, Jnc,
Storage (Iodine Sensor) . The I sensor, being developed by NASA, measures
1 2 concentration at discrete time intervals of one minute or longer. (3) An
accurate measurement of I ^ concentration will only be available after each
measurement is made. The sensor signal storage circuit was, therefore, de-
veloped to accept an level signal and store it until a new sensor signal is
obtained.
Figure 21 is a block diagram of this storage system. When a signal from the
I 2 system is to be stored, a clock signal will cause the I„ sensor signal to
be converted to an eight-bit digital number that is then stored in eight bi-
stable devices. Output from the storage is converted from digital to analog
which is used in the I « control system. The stored signal is assumed to be
the latest I ^ concentration and will be maintained until a new clock signal
is received, at which time the system will store the updated I_ sensor signal.
By storing the digital form of the 1 ^ sensor signal, the length of time which
the signal is stored can be extended indefinitely. Conventional analog
storage techniques have a very limited storage time.
System Clock . The system clock, consisting of a free-running unijunction
oscillator feeding an eight-bit binary divider provides the means for synchro-
nizing the operation of the I ^ sensor with the storage circuit. Outputs from
the eight-bit divider are connected to two decoding arrays. One array provides
a signal to the I sensor to initiate a reading. The other decoding array pro-
vides a signal to initiate storage. These two clock output signals are set to
occur at different times. The sensor is automatically instructed to measure
After a time interval during which the measurement is taken and signals are
allowed to stabilize, the sensor storage system is automatically instructed to
store the stabilized level signal.
As assembled, the clock produced a sample signal to the I ^ sensor, followed by
a storage pulse to the storage circuits every 32 seconds. The time between
the store and sample pulses can be varied in one second increments and the
cycle time can be varied in one second increments up to a maximum of 256 sec-
onds, by retuning the decoding array circuits.
Control Adjustment Summary
Operation of the IGDS is automatic. No control adjustments are needed. Two
adjustments are provided, however, for system operating flexibility, the
CONCENTRATION SET POT and the I„ SENSOR SET POT. Once the instrumentation is
integrated with an I ^ sensor, only the CONCENTRATION SET POT will be needed.
Because this was a development program, several factory adjustments and wiring
modifications were provided which can change the performance characteristics
of the IGDS. These include
a. system clock timing (set at 32-second intervals),
b. maximum and minimum current of the bipolar current
source (set at +10 and -5 mA, respectively),
43
JCifc Systems, Jnc.
Clock
Signal
FIGURE 21 SENSOR STORAGE BLOCK DIAGRAM
Jtife Systems, Jnc.
c. the maximum voltage (positive and negative direction)
of the bipolar current source (set at +8 and -1 volt,
respectively) , and
d. the gain and time constant of the integrating amplifier
and control logic.
Mechanical Controller
The control system for mechanical injection was designed and the circuits
built (see Figure 22), tested and installed in the instrumentation package.
A variable speed pump, which can be used to mechanically dispense I 9 to the
circulating loop is operated by this system. The pump can be operated by
setting the CONCENTRATION CONTROL switch to the MECHANICAL position and plugging
the dispensing pump into the proper receptacle on the back of the package.
In this mode of operation the only modification is that the bipolar current
source is replaced with an adjustable, variable voltage supply that varies
pump speed.
The control logic, system clock, I sensor signal storage and sensor simulator
circuits all operate as previously described when integrated with the mechanical
controller.
GROUND SUPPORT ACCESSORIES
Ground Support Accessories were needed to (a) check out cell materials of
construction, (b) obtain exploratory data on cell operation, (c) simulate a
potable water system, and (d) measure concentration and aqueous solution
parameters .
Material Testing Setups
The procedure and setups used to test proposed IGDS materials of construction
are discussed in the Material Testing section on page 56.
Experimental Cells
The experimental cells and laboratory breadboard were discussed in the section.
Iodine Generating and Dispensing System Breadboard on page 24 and illustrated
in Figures 8 and 9.
Potable Water System Simulator
The Potable Water System Simulator (PWSS) was used to simulate the interface
between the IGDS and the projected operating environment. Figure 23 presents
its schematic. Table 3 identifies the PWSS components and indicates which are
needed as a function of the six operating modes described on page 22. In addi-
tion to providing a source of water to be iodinated, it also contained pro-
visions for monitoring flows, pressures and temperatures. It had taps for
obtaining water samples. Figures 24 and 25 are photographs of the front and
back of the PWSS. Major components of the PWSS were the water storage tank
and water recirculation pump.
45
JCife Systems, Jhc.
46
FIGURE 22 IODINE CONTROL LOGIC FOR MECHANICAL INJECTION
System Symbols
JCife Systems, Jhc.
figure ?3 POTABLE WATER SYSTEM SIMULATOR
TABLE 3 PUTABLE WATER SYSTEM SIMULATOR PARTS LIST
Cife Systems, Jhc .
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48
CELL OUTPUT
Cife Sy stents, Jnc.
B ackp ressure Re gulator
for Dump Mode
Water Feed F low Rate Indicator
and Controller,
Co ntrol an d Monitorin
Instrumentation
FIGURE 24 POTABLE WATER SYSTEM SIMULATOR, FRONT VIEW
Cife Systems, Jhc.
R ecirculating Flow Rat ej
Indicator and Controller
Iodine Accumulator
Valve and Dispenser
Control and Monito rin
■ Instrumentation S
Water Feed Pump
Water Recirculating
Pump
FIGURE 25 POTABLE WATER SYSTEM SIMULATOR, REAR VIEW
50
Cife System, Jnc.
Storage, Fill and Water In Use Tank Simulator
Figure 26 is a schematic of the tank design that was fabricated. It has a
usable water volume of 79 liters (2.8 ft ), which is sufficient to hold 69.9
kg (154 lb) of water with 13% ullage gas volume. The tank was made from 316
stainless steel. It employed an external glass tube for reading the liquid
level in one-liter intervals as calibrated by emptying the tank into a gradu-
ated 12 liter (0.42 ft -3 ) container (see Figure A-7) .
Water Recirculation Pump
A gear pump was used to circulate water within the PWSS. It has a capacity
of 3.8 liter/min (1 gal/min) at 210 kN/m (30 psig) . It is capable of oper-
ating up to 2100 kN/in (300 psig) at 366K (200F) . A magnetic coupling is used
to eliminate possible leakage.
Iodine Detector Simulator
A circuit was constructed to simulate the I~ sensor. signal (see Figure 27)
because the Iodine Colorimeter was not available. ^ J This allowed the system
to be operated in an open loop mode so system operating parameters could be
measured. The simulator was installed in the instrumentation enclosure (see
Figure 18) . The only parameters which could not be determined using the
detector simulator approach are the closed loop control stability and gain
requirements. (To determine these requires using the actual detector with
the feedback loop closed around the system.)
Packaged Monitor Instrumentation and Accessory Controls
Figures 13 and 18 present photographs of the packaged IGDS controller. The
controller also contains the PWSS pump controls, parameter monitor instru-
mentation, the mechanical feed controller, and power converters.
Analytical Considerations
During the course of the program, measurements were made of the concentration
of I 2 , I” and H in the various waters tested. Provisions for measuring I
concentration and pH were made, using an in-line plastic block to retain a
calomel, a glass electrode and I -specific electrode. Because the fiber liquid
junction of a standard calomel electrode is difficult to maintain in a flowing
solution, valves were installed with a bypass arrangement. Care was taken to
insure that the solution had stabilized, through the formation of a stable
liquid junction, before a meter reading was taken.
Measurement of Iodine Concentration
Two methods were used to measure the level of I 2 within the water: colorimetric
and thiosulfate titration. An evaluation was made of the interval between
taking a sample and its analysis. The purpose was to insure that samples
taken on Saturdays, but not analyzed until the following Monday morning,
51
Cife Systems, Jnc.
53
FIGURE 27 IODINE SENSOR SIMULATOR
JCife Systems, Jhc.
would not have a low I. level because of loss of I 2 from the solutidn. The
results indicated^' that analyses of I2 solutions, within the first 40 hours,
gave almost identical readings. As the storage time increased to beyond 50
hours, however, the.I- level measured decreased sufficiently to reflect a lower
level than that considered to be within experimental accuracy.
Colorimetric Method - Spectrophotometric measurements of concentration for
the potable water were made with a Fisher Electrophotometer II, Model 81.
The colorimetric procedure offers the advantages of , speed, simplicity, sensi-
tivity and lower cost over the amperometric method. * J
The procedure followed was essentially an adaptation of the procedure by
Black § Wittal. The colorimetric method was most suited for low concentra-
tions of I 2 . Figure A-10 presents the calibration curve obtained over the
concentration range 0.5 to 2.0 ppm, using an optical path of 23 mm. Figure A-ll
presents the calibration curve obtained over the concentration range 5 to
25 ppm, using an optical path of 50 mm.
Thiosulfate - Levels of concentration above 2 ppm were determined using
the standard thiosulfate process. ^ ^
Hydrogen Ion Concentration
The concentration of the H + (pH) of solutions were determined with a pH meter.
It was calibrated periodically as illustrated in Figure A-12.
Iodide Ion Concentration
Two methods were used to determine the concentration of I .
Specific Ion Electrodes - A specific ion, I electrode was used, employing a
pH meter to measure the electrode voltage. The electrode was calibrated as
illustrated in Figure A-13.
Oxidation to Iodine - Since I” is colorless and cannot be measured photometrically,
it had to be oxidized using an "Oxone" solution. A solution containing both
I 2 and I” was first photometrically analyzed for l„. Then "Oxone" was added
to oxidize the I - to I 2 and the solution again photometrically analyzed. The
difference between the readings was taken as the value of the I concentration.
PRODUCT ASSURANCE
A mini-Product Assurance Program was included so the impact of manned chamber
testing requirements would be included during the initial design activities.
The functions included were quality control, maintainability, safety and
nonmetallic material control. Quality control was added to ensure reproduc-
ibility of cell design and configuration during subsequent developmental
activities. Maintainability was included to ensure that the subsystem would
(a) See Figure A-9.
54
£ife Systems, Jhc.
have a design and configuration that could be operated and maintained by per-
sonnel not associated with its development. Safety was included in anticipation
of manned chamber requirements. Nonmetallic materials control was included in
preparation for the nonmetallic material and outgassing specification- J
required of equipment to be operated within manned spacecraft.
The Product Assurance Program was carried out during the prototype IGDS
development .
Quality Control
The Quality Control activities performed during the fabrication and assembly of
the prototype IGDS consisted of
1. performance and documentation of receiving inspections on
all vendor supplied parts,
2. maintaining a record of all rejected parts and authorized
rework,
3. insuring that assembly techniques specified in the design
drawings were complied with, and
4. configuration control on all design drawings.
This minimum activity insured that no defective components or parts were
incorporated into the IGDS and that design drawings correctly reflected the
progression of the design from the initial concepts through the final
engineering drawings .
Maintainability
The design was evaluated for maintainability. Only nominal considerations were
needed, however, since the application configuration remained unspecified. The
prototype's I^ accumulator was configured so that rapid filling with solid 1^
crystals was possible. The prototype interfaced with the PWSS using quick connect
fasteners.
Design analyses performed indicated no maintainability problems are anticipated
for a flight unit; e.g., no ion exchange cartridges need replacing, the I^
valve is a static device, etc.
Safety
The IGDS is inherently safe. A Safety Hazard Analysis, however, was used to
verify that no system or system component characteristics would be dangerous
to personnel or equipment. The disinfecting concept is essentially a static
device that operates at room temperature. It does not employ high voltages,
hot temperatures, rotating components, etc.
55
JCife Systems, Jhc.
Iodine Generating and Dispensing System Materials Program
The candidate materials control program conducted during the design and fabri-
cation of the IGDS included - •
1. surveying. the literature for materials compatibility to
and HOI 13 J l
2. performing compatibility tests above to verify acceptability
in the environment projected for the IGDS,
3. maintaining a record of all nonmetallic materials used, and
4. guiding the design so that only those materials or configurations
that meet the requirements of D-NA-022^ J are used.
Survey Results
The literature and vendor survey revealed that polypropylene, cast acrylic
(Plexiglas), Teflon, Viton, Fluorel, ethylene propylene, epoxy resins. R poly-
sulfone, polyamides and nylons were candidate nonmetallic materials. ^
Table 4 summarizes the results. The metallic materials: 316, 316L and 321.
stainless steel were selected as candidates. Under a separate contract,
it was found that of six nonmetallic materials studied (silastic, polyiso-
prene, butyl rubber, Nordel, Viton and polyurethane), silastic was the
most acceptable because of minimum I 2 sorption, I 2 conversion, or I substi-
tution reaction. Butyl rubber, Nordel and Viton were unacceptable Because of
the taste and odor they contribute to water when interacting with 1^. Poly-
isoprene and polyurethane were unacceptable because of continuous 1^ sorption.
Material Testing
To verify their acceptability, several of the materials listed above were
subjected to compatibility tests. Two tests were performed: one in which the
samples were placed in a saturated solution of I 2 (250 to 300 ppm) at room
temperature, and an accelerated reaction test in which the samples were placed
in a solution saturated with I 2 (1100 ppm) at 338K (149F), an arbitrarily
selected elevated temperature.
Room Temperature Test - A sample piece of the proposed material was placed in
a glass bottle with a ground-glass top containing a saturated I 2 solution.
Before exposing the material to the I 2 solution, each piece was cleaned with a
soap solution, dried at 339K (150F), weighed, and visually checked with the
naked eye and a 14X power microscope. Where appropriate, materials were also
dimensionally measured using a micrometer.
(a) In addition, chemical compatibility data was gathered for Cl 2 and hypo-
chlorous acid so that both the I 2 and C\„ generator approaches to water
purification could be compared from a materials point of view.
56
Cife Systems, Jhc.
TABLE 4 IODINE AND CHLORINE MATERIAL COMPATIBILITIES
Polyvinylchloride
Penton
Polypropylene
Polyethylene
Fiberglass Reinforced Epoxy
Viton
Teflon
Cast Acrylic (Plexiglas)
Polysulfone
Fluor el
Fluorocarbons
Iodine
10%
500 Ppm
Solid
Solution
Solution
U
S
t — V
O
CM
S
s
—
U
s
s (20)
S
--
U
s
s ( 2 ol
S
s
—
s (19)
--
s (2°)
--
--
u( 2 °)
—
s
S
--
s
S
s ( 18 ).
Chlorine
Satd.
Gas Water
U S
U U
U S
S S
s
s
s (19 >
F
S
s™ -
(a) All data was obtained from Ref. 16 except when noted.
(b) Key:
S = Satisfactory U = Unsatisfactory
F = Fair -- = No data available
57
Cife Systems, Jhc.
Test solutions were prepared by placing crystals in deionized water until
the solution was saturated. Only the saturated water (without any solid I.
crystals) was placed in the glass bottles. Every two weeks the solution was
standardized -to determine I ^ lost, then appropriately brought back to. the
initial concentration.
Table 5 presents the room temperature soak test results observed with the
saturated, aqueous solution. Teflon, polypropylene, polyvinylchloride and
Plexiglas were found to be acceptable nonmetallic materials. Only Teflon
failed to take on the brown, I-s tain or to continuously consume (remove) ^
from the saturated solution. The acceptable metallic materials were 316 stain-
less steel and platinum.
High Temperature Test - Sample pieces of the proposed materials were placed in a
single glass flask containing^ deionized water and I crystals. The flask was
heated to 338K (149F), resulting in an I- saturated solution of =1100 ppm.
(This is about four times the saturation level of water at 298K (77F)). The
test was continued for approximately three and a half months. Care was taken
to insure that solid I ^ crystals were always present within the water.
Table 6 presents the 338K (149F) accelerated soak test results observed with
the I- saturated, aqueous solution. Teflon, polypropylene and polyvinylchloride
were found acceptable. Only Teflon failed to take on the brown, stain.
Platinum was an acceptable metallic material. The 316 stainless steel had
marginal acceptability at the elevated temperature and was not acceptable when
exposed to I„ vapors. The latter. results were similar to those reported by
Kinman for 304 stainless steel. J
Ninety- and 180-Day Membrane Exposure Tests
An experiment was completed to investigate the long-term effects of I and water
upon the prototype anion exchange membrane. Since the intended usage ror the
IGDS is long duration missions, it was of interest to determine if membrane
degradation occurred on prolonged exposure to the aqueous slurry.
Procedure - Membranes 7.9 x 10.8 and 0.04 cm (3-1/8 x 4-1/4 and 0.017 in) thick
were conditioned in the normal manner and placed in a sealed container with
approximately 100 gm (0.22 lb) of I Sufficient water was included to insure
the membranes were completely immersed. The container was sealed and placed
in storage at room temperature.
At the end of 90 and 180 days, the membranes were removed and examined for
defects. No evidence of membrane deterioration was detected. After both
examinations, the membranes remained flexible with no cracks or evidence of
ion exchange material flaking off the matrix support grid. All membranes were
returned to the exposure container except one which was assembled in an experi-
mental cell. This membrane successfully passed the 21 kN/m (3 psi) pressure
differential test. The membrane's electrochemical performance was then tested.
In all cases it gave results similar to that observed on membranes not exposed.
58
TABLE 5 RESULTS OF SATURATED IODINE SOAK TEST (ROOM TEMPERATURE)
Cife Systems, Jnc.
59
TABLE 6 RESULTS OF ACCELERATED IODINE SOAK TEST, 338K (149F)
Cife Systems , Jnc.
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£ife Systems, Jnc.
Membrane exposure to an aqueous I ^ slurry does not affect the physical, ion
exchange, or electrochemical properties of the membrane. No problems are
anticipated due to membrane degradation. The test membranes have been returned
to the aqueous slurry environment to generate further data on long-term
exposure .
Material Compatibility with Flammability and Qutgassing Specification
An evaluation was made of the nonmetallic and metallic materials' acceptability
to the NASA flammability and outgassing specification for manned flight
vehicles. J The subsystem drawings were used as control documents. Efforts
were made to maximize the number of acceptable materials. However, in the
event an IGDS required material that would not have been acceptable or if data
on its flammability and outgassing did not exist, a specimen of the material
would have been sent to JSC for evaluation. The original material, however,
was to be used unless an acceptable alternate material was known and readily
available .
The following IGDS materials were found to meet the requirements of the
specification: Teflon, Viton A, anion exchange membrane, and 316 and 316L
stainless steel. The anion exchange membrane is acceptable by virtue of its
projected in-flight use configuration, where it will be immersed in an aqueous
solution and retained in a vented container.
The IGDS cell housing was fabricated of transparent Plexiglass, because of a
desire to visually observe cell operation. A flight system will have the
housing constructed of 316 stainless steel, since Plexiglass does not meet the
specification. If the system is to be exposed to elevated temperatures (e.g.,
338K (149F), the steel shall be Teflon-coated to avoid the slight pitting
observed.
Metallic and Nonmetallic Materials in the Potable Water System
An evaluation was made of the metallic and nonmetallic materials that come
in contact with iodinated water in the PWSS. The results of this analysis
are summarized in Table 7. Each component in the system^ J was evaluated.
Table 8 indicates the location of the materials.
TEST RESULTS
The following experiments were completed during the program:
1. laboratory breadboard to establish design data,
2. hardware material compatibility with the environment,
3. supplementary cell characterization,
4. IGDS design verficiation and endurance testing, and
(a) Reflected by Drawing LSI-D-605, Rev. A.
61
Cife Systems, Jhc.
TABLE 7 PWSS MATERIALS CONTACTING IODINATED WATER
Metallic Materials
316 Stainless Steel
304 Stainless Steel
302 Stainless Steel
Platinum
Nonmetallic Materials
Teflon
Viton A
Kel-F
Ceramic
Lucite
Ion Exchange Membrane
Iodine Crystals
62
Cife Systems, Jnc.
TABLE 8 MATERIALS WETTED BY IODINATED WATER IN THE PWSS
Part Identification
Number
Part Description
Materials) Exposed to Water
V-101, -102 and -103
Two-Way Ball Valve
316 Stainless Steel, Teflon
V-104 thru V-112 and
V-116
Manual Two-Way Valve
316 Stainless Steel, Teflon
V-I13, -114 and -115
Manual Three-Way Valve
316 Stainless Steel, Teflon
QC-101 and -102
Quick Connects
316 and 302 Stainless Steel,
Viton A
G-101 and -102
Pressure Gauge
316 Stainless Steel
PR-101 and -102
Backpressure Regulator
304 Stainless Steel, Teflon
P-101 and -102
Gear Pump
316 Stainless Steel, Teflon,
Ceramic
F-101 and -102
Flowmeter
316 Stainless Steel, Teflon,
Kel-F, Borosilicate Glass
TC-101, -102 and
-103
Sheathed Thermocouple
316 Stainless Steel
TK-101
Water Loop Tank
316 Stainless Steel
H-101
Tank Heater
316 Stainless Steel
LSI-D-611
IGDS
316 Stainless Steel, Plexiglas
Platinum, Ion Exchange
Membrane, Fiberglass, I 2
Crystals, Viton A, Teflon
- -
Tubing and Fittings
316 Stainless Steel
63
Cifc Systems, Jhc \
5. bacterial challenge.
Except for material studies which were discussed previously (page 56), results
of these experiments are presented below.
Laboratory Breadboard Experiments
Various tests were carried out to verify the electrochemical concept. These
included determining the effect of current on electrolyte I. valve voltage,
internal cell resistance, etc. Also, a 35-day test was performed using a lab-
oratory breadboard cell and the projected IGDS anion exchange membrane. These
experiments formed the basis of the IGDS design.
Primary purposes of the breadboard tests were to determine membrane and
material performances. In addition, it was desired to obtain other design
data on time effects, limiting current densities that could be drawn, vari-
ations in I^ generation current efficiency, and to evaluate the effect of
varying the process water flow rate.
Typical measurements and results of the 35-day test are shown in Figure 28.
Presented are the operating current, the cell's terminal voltage, anode-to-
reference voltage, calculated current efficiency, and the pH of the anode
solution and the saturated I ^ solution in the compartment adjacent to the
cathode. The cell was generally operated in a constant current mode. The
data indicated that operation from 5 mA to 20 mA was possible. During the
first eight days of the test, terminal voltage was relatively unstable, in-
dicating changes that were evidently occurring which influenced cell internal
resistance. The terminal voltage later became more dependent upon cell current
but gradually declined to about 1 volt at a 3 mA current level. Anode voltage
was less sensitive to current changes and did not appear to appreciably de-
cline as the test progressed. It may be inferred from this data that the anode
maintained its electrochemical stability throughout the test. Current effi-
ciency, determined by the equation
I 0 measured-I„ calculated . „„ „ .
2 - — cal culated 100 = Current Efficiency (20)
increased throughout the test and exceeded 100% at one period. This charac-
teristic is attributed to I 2 leaching and/or 1^" transfer across the membrane.
The pH of the iodinated solution declines more rapidly at the higher current
levels. It is expected that transfer of OH from the cathode compartment in-
stead of the generated I is responsible for this fall in pH. The abrupt rise
in pH in the cathode compartment on the 21st day resulted from draining and
refilling the compartment with fresh saturated water. The specific changes
in pH with time have little quantitative significance since they relate to
the quantity of liquid involved which was randomly varied.
Although the 35-day test was mainly completed to establish the lack of membrane
deterioration or electrode corrosion, it also was able to identify the build-
up of H in the cathode compartment and the leaching possibility.
64
Cife Systems, Jmc.
FIGURE 28 RESULTS OF THE 35-DAY CHARACTERIZATION TEST
Cife Systems, Jhc.
Solutions to the Acid Build-up Problem
Various possible solutions to the build-up of H + in the I 2 accumulator exist,
including
1. operating at 100% current efficiency by
a. lowering the current density or
b. increasing the area of electrode-membrane contact
at the anode .
2. Utilizing acid-resistant materials and employing a larger
I 2 accumulator volume for greater H tolerance,
3. neutralizing H + by adding alkali to the I 2 accumulator, and
4. consuming H + by an electrochemical reaction that needs H +
to operate.
Techniques 1 and 2 are feasible and straightforward. Technique 2 was followed
in the IGDS.
Addition of alkaline electrolyte (e.g., KOH) directly to the I 2 reservoir
or in a reservoir separated from the I 2 reservoir by an anion exchange
membrane, does not work because of the reaction of I 2 with alkaline media.
3I 2 + 6 KOH = KI0 3 + 5KI + 3H 2 0 (21)
Only the addition of a controller based on monitoring the increase in H + ,
together with controlled, but limited addition of alkali, will avoid the
acid build-up and reaction (21) above. Technique 3, therefore was not con-
sidered practical because of the complexity it adds.
Technique 4 was eliminated because of its complication and the development
needed.
The Leaching Problem
Analysis of these preliminary test results indicated that low current densities
were desired to maximize current efficiency and minimize the evolution of 0 2
caused by the transfer of OH - instead of I”. Since this increased the H and
I_ concentration, the amount of dissolved I 2 increased (tied up as ).
This indicated the membrane would become more susceptible to I- leaching on the
anode side which, on checking with low water flow rates, was then observed.
Initial tests for membrane leaching were made using very large water flow
rates of 500 to 570 kg (1100 to 1260 lb) per minute. These large rates were
initially expected to be the maximum recirculation rates that would be needed
3
(a) 350 to 400 ml/min (21.4 to 24.4 in /min).
66
Cife Systems, Jhc.
in the end-item application. Initial tests were, therefore, for the assumed
"worse case" condition. After the water flow rate specification was finalized
(see section entitled "Water Flow Requirements," page 16) at 30 kg (66 lb) per
day (21 ml/min), the occurrence of leaching became apparent. Supplementary
experiments were then carried out to quantify the leaching and the effect of
water flow, temperature and time.
Supplementary Experiments To Quantify Leaching
Between the time the initial valve and breadboard experiments were completed
and the IGDS was fabricated, a series of supplementary experiments were made.
Their purpose was to quantify experimental findings observed during testing
of I ^ valves. The supplementary experiments included
1. measurement of the effect of water flow rate on leach rate,
2. measurement of the effect of temperature (286, 296 and 349K
(55, 73 and 104F, respectively)) on I 2 leach rate (without
current flowing) , and
3. measurement of the effect of time on leach rate. .
Leach Rate versus Flow Rate
Figure 29 quantifies the effect water flow rate has on the leach rate. The
constant leach level at the high water flow rate explains why leaching was
not observed during the experimental work carried out prior to freezing the
IGDS design. The I 2 level resulting from leaching at the high flow rates used,
yielded an I 2 level below the detection limit.
Leach Rate versus Temperature
Experimenting with single cells indicated that the I 2 leach rate varied with
water temperature. An experiment, therefore, was undertaken to quantify this
effect. Results, shown in Figure 30, indicate the. leach rate increases with
increasing temperature with a rapid rise occurring at the more elevated
temperatures .
Leach Rate versus Time
Figure 31 quantifies the effect time has on the leach rate at a constant water
flow rate of 19 ml/min (1.1 in /min) . Results of two different tests are
indicated. Each test was carried out for nine days. The data indicated with
circles were obtained on a cell through which no current has ever passed. The
data indicated with triangles were obtained on a valve that had been operating
under continuous load but was put on to open circuit and, after 30 minutes,
the leach rate determined.
The results indicated an average leach rate of approximately 0.08 gm (1.8 x 10
lb) I 2 per day at a temperature of 296 ±5K (73 ±9F) .
67
Iodine Produced (x 10 ), Lb/Day
Cife Systems, Jhc.
Date
3/27/73
Test Series
Flow Rate
Cell
LSI-C1
Membrane
LSI-01
Current
0
Flow Rate
Varied
Pressure
Ambient
Temperature
23C
Flow. Rate, Ml /Min
Flow Rate, In /Min
FIGURE 29 LEACH RATE AS A FUNCTION OF WATER FLOW
Iodine Produced(x 10 ), Lb/Day
Cife Systems, Jhc ;
Iodine Produced (x 10 ), Lb/Day
Cifc Systems, Jhc.
1.0
2.00
—
• No load cell,
data taken after weekend
after nighttime
1.75
- 0.8
— O No load cell.
data taken during the day
1.50
- £
^ Operating cell placed on open circuit
Q
u 0. 6
- Date
3/15 to 3/23/73
1 . 25
MM «
Test Series
Leach Rate
o
o
Cell
LSI-C1
3
Membrane
LSI01
1.00
L o
~ fH
Current
0
Cl.
Flow Rate
19 Ml/Min NDP
g°. 4
- Pressure
Ambient
0.75
•H
O
Temperature
23C -SC
HH
0.50
0.2
A
A
O
0.25
•
•
O
tt>
6 • «g
•
0.00
0.0
1 1 L
1 J--: 1 L_
4 5 6
Time, Day
10
Avg.
-A
- O
FIGURE 31 LEACH RATE AS A FUNCTION OF TIME
70
Cife Systems, Jhc.
Minimizing Leach Rate
Operation and construction factors can minimize the leach rate.
The operation factors that minimize leaching are
1. slower water circulation rates that minimize flushing I 2
from the anode membrane surface (decreasing the diffusion
driving force) ,
2. lower water temperature,
3. greater operating current densities (decreasing the concentration
of I ? at the cathode surface and increasing the concentration of
at the anode surface), and
4. minimized concentration of H* in the accumulator (high
H concentrations yield high dissolved - ^ as Ig~)-
The construction factors that minimize leaching are
1. smaller membrane/electrode areas,
2. greater separation between the solid I 2 and the membrane, and
3. avoidance of incorporation of I during the membrane conditioning
process.
While not yet completely eliminated, the observed leaching appears to be
manageable and possibly can be eliminated totally.
Material Experiments
The material tests completed were reviewed in the IGDS Materials Program
seciton (page 56). This included material stability to saturated solutions
at room temperature and at 338K (149F). The membranes were characterized
after 90 and 180 days.
Iodinated Water Taste Experiments
Water samples, varying in level from 0.5 to 20 ppm, were tasted to determine
their palatability. This test indicated that flight systems would not utilize
residual I~ concentrations of 20 ppm. Even a 10 ppm specification seemed unlikely.
Taste at these levels is very "antiseptic." While tolerable for a short term,
the taste would become objectionable under continued, long-term use. It was
concluded, therefore, that the system specification would eventually assume a
lower I 2 level, probably 5 ppm.
IGDS Experiments
After the IGDS was fabricated, inspected and assembled, the following series of
tests were completed:
71
Cifc Systems, Jhc.
1. Shakedown,
2. Calibration,
3. Design Verification Test (DVT), and
4 . Endurance .
The unit was disassembled after the DVT and Endurance Tests and no change or
refurbishment was needed between these tests.
Shakedown Test
Upon assembly of the IGDS and its integration into the PWSS, various tests
were used to shake down the system. These included
1. The system was operated and all valves and connections, including
flowmeters and pressure regulators, were checked for leakage.
2
2. A 103 kN/m (15 psid) pressure differential was applied across the
flowmeter controller. (By design a differential of 207 kN/m2 (30
psid) is needed for control.)
2
3. The system was pressurized to 207 kN/m (30 psia) and found leak-
free .
The system was calibrated after all mechanical, electrochemical and electronic
components, including the valve, were found to be working properly.
Calibration Test
The calibration tests performed included
1. calibration of the PWSS water loop recirculation and water feed
flowmeters (R-6-15A and R-2-15-A, respectively) see Figures A-14
and A-15, and
2. calibration of the PWSS water supply tank sight tube (see Figure
A-8) .
Since the electronic meters were calibrated at the manufacturer (±3% full-scale
deflection error), no additional calibrations were made.
Design Verification Test
After the shakedown and calibration tests were completed the IGDS was charac-
terized. This included the following five experiments:
1 . A current density span was made to determine high and low limits
of I 2 production and to compare performance with the breadboard
valves (Figure 32). The higher voltage above 1 mA/cni with the
72
Cell Voltage,
Cife Systems, Jnc .
Cifc Systems, Jhc.
IGDS probably resulted from increased cathode polarization because
of the greater distance separating the solid I- from the cathode
when the fiberglass retaining sheet was used.
2. A leach rate test (Figure 33) versus time (21 days) was made
which indicated the phenomena began after six days and leveled
out shortly thereafter. The cause of the three scattered data
points is unknown.
3. An efficiency versus current density span (Figure 2 34) was made,
indicating a current density of 1.5 to >4.0 mA^cm was applicable
although a lower (Ocurrent density (0.23 mA/cin (0.24 ASF)) was
used as baseline to minimize loss of efficiency by OH - transfer.
4. Total and I - production versus current density runs (Figure 35)
were made to characterize IGDS capacity.
5. Cell voltage plus anode and cathode versus reference voltage tests
as a function of current density (Figure 36) was made for IGDS
power level characterization. The reason for the abrupt rise
in the cathode- to-reference voltage is not known.
The water sample to be analyzed was taken at the dump valve, downstream of
the flowmeter for all the parametric DVT tests presented. If the potable
water side of the IGDS was depressurized (sample taken), water saturated with
I 2 passed across the membrane as the water pressure in the I 2 accumulator
equilibrated with the (now lower pressure) potable water side of the IGDS.
Endurance Test
Following completion of the Shakedown, Calibration and Design Verification
Tests, the I 2 accumulator, valve and dispenser assembly was disassembled,
checked for integrity and reassembled when all components were found normal.
A 30-day endurance test at nominal conditions was then completed. Performance
data obtained from this test are presented in Figures 37 to 44.
Operating Conditions
During the test the parameters cited in Table 9 were held essentially constant,
although some variation occurred during the test as noted.
In Figure 37, citing the water flow rate variation, the difference between
the solid data points and the open circles is that the latter were calculated
based upon total water accumulated (generally over seven hours or a weekend)
divided by the time passed. The solid circles were flow measurements gen-
erally taken over a 5 to 15 minute period. The flow was maintained near
19.5 ml/min (28 kg (62 lb) per day).
In Figure 38, citing water loop pressure versus test time, the operating
pressure is shown to be approximately constant at the designed 210 kN/m
(30 psi), once a check at 238 kN/m (34 psi) was demonstrated.
74
Cife Systems, Jnc.
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IGDS Efficiency
Cifc Systems, Jhc.
0 1.0 2.0 3.0 4.0
Current Density, Amp/Ft^
FIGURE 34 EFFECT OF CURRENT DENSITY ON EFFICIENCY
76
Iodine Produced, Gm/Day
jCife Systems, Jnc.
Cell Voltage
Cifc Systems, Jnc.
Cife Systems, Jhc.
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FIGURE 37 WATER FLOW RATE VARIATIONS
280
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FIGURE 40 IODINE PRODUCTION VARIATIONS
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FIGURE 4? EFFICIENCY VARIATIONS
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Cife Systems, Jhc.
In Figure 39, citing the temperature variation, the difference between the
solid data points and the open circles is that the latter was measured first
thing in the morning and the latter after the system had equilibrated to room
temperature later in the day. Prior to the ninth day, only the one reading
was taken later in the day. No data point was taken after the system had
equilibrated on the 26th day. Thus, the crossover noted does not have quan-
titative significance.
Iodine Dispensed - The I dispensed was a result of that generated by the
valve and that leached by the water. As indicated in Figure 40, the pro-
duced varied from Jr ppm initially to 11 ppm, with the I 2 generated electro-
chemically contributing about a constant 4 ppm and the remainder resulting
from leaching. (Methods to minimize leaching were discussed on page 70.)
Leach Rate - The DVT (Figure 33) indicated an I 2 leach rate of 0.05 gm/day
(1.8 ppm at 28 kg (62 lb) water flow per day). After disassembly and reassembly
the leach rate increased to an initial 0.15 gm/day, 0.2 gm/day after ten days,
and leveled off at 0.3 gm/day after 17 days as shown in Figure 41. It is
uncertain if the increase was caused by the reassembly or by the acid build-up
and plexiglass attack cited in the "Post-Test Inspection," below. Insuf-
ficient controls were used to maintain such stable operation that the variations
cited could be quantitatively explained.
Iodine Generation Efficiency - The efficiency of the electrolytic portion of
the I 2 dispersion remained relatively constant at 15% (see Figure 42) and
tracked the I 2 produced electrolytically (see Figure 40) . When the leached
I 2 was included, the efficiency increased from 20% initially to 40 to 45%
from the fifteenth day on. Insufficient controls were used to maintain such
stable operation that the variations could be quantitatively explained.
Iodinated Water pH - The concentration of the H + (pH) of the iodinated water
remained relatively constant within the band 5.2 to 5.5 pH units (see Figure
43).
Valve Voltage - The valve's voltage started initially at about 1.6 volts
and e^ded at about ^ne-half this level, at a constant current of 6 mA (0.24
mA/cm (0.23 amp/ft j) as shown in Figure 44. Cathode- and anode-to-reference
voltage were measured but not plotted. The cathode-to-reference remained
essentially constant at 0.01 to 0.025 volt. The anode-to-reference tracked
the terminal voltage almost identically except for the cathode-to-reference
contribution .
Post-Test Inspection
After the 30-day endurance test, the IGDS was removed from the test stand and
the cathode fluid drained into a container. Its pH was measured and found to
be. 1.05.
The anode cavity was flushed with distilled water and the cover from the cathode
cavity was removed. It was observed that no solid I~ was left, although the
solution was very dark, indicating adequate availability of 1 ^. The bottom of
86
JCife Systems, Jnc .
the cell had approximately a 0.16 to 0.32 cm (1/16 to 1/8 in) thick layer of
sludge. The stainless steel screen and screen supports were in excellent
condition, being only slightly discolored by the sludge near the bottom.
The cathode compartment lid was stained. It was basically black near the
bottom of the cell, changing to a light brown near the top. The Helicoil
insert located in the bottom part of the cathode compartment lid, was partially
corroded away. The Viton A 0-ring used to seal the cathode compartment lid
appeared to have a slight set, but showed no signs of deterioration.
The bottom of the Plexiglass cathode cavity appeared to be attacked by the
acidified catholyte. A sludgy deposit was formed, consisting partially of the
Plexiglass itself. Discoloration of. the cathode compartment again was black-
ish at the bottom of the cell and dark cinnamon or amber at the top.
The platinum reference electrode was clean and the Teflon covering was
slightly tanned near the part that passed through the cathode compartment wall.
The Plexiglass plug, inserted with methylene chloride at the bottom of the cell
during fabrication, appeared to be swollen into the cavity about 0.16 cm (1/16 in).
This plug had been inserted to secure the lead from the reference electrode.
Plug material that had swollen into the cathode compartment was soft and readily
removable.
The cathode electrode looked very clean, as did the metallic stainless steel
part used to secure the electrode to the side of the compartment.
The fiberglass separator was discolored, but structurally intact. In separating
the valve's electrode-membrane-electrode sandwich, the membrane remained
attached to the anode and had two areas where a brownish, sludge- like deposit
was attached to it. This was opposite the two bottom slots of the cell and
appears to have been a transfer of the material noted above. The membrane
appeared slightly wrinkled, with the greatest wrinkling, about a 0.08 to 0.10
cm (0.03 to 0.04 in) depression, toward the bottom part of the cell, but showed
no other visible degradation. Sludge-like deposits were easily removed from
the membrane.
All parts were cleaned with sodium thiosulfate, rinsed with distilled water,
and stored.
Sludge formation and Plexiglass staining can be accounted for by the H + build-up.
As the acid concentration increased, it attacked the Plexiglas allowing
staining. As the H concentration increased, the amount of I 2 dissolved in
solution increased via
! 2 + r = V (22)
with the I being formed to balance the H + buildup. The H + concentration
increased when OH were removed from the catholyte as part of the current
carrying process due to the equilibrium
87
Cife Systems, Jhc.
H 2 0 = H + + OH" (23)
The variation in color (black at bottom to amber at top) resulted from the
gradual dissolution of solid I- and its diffusion upward with an increase in
I 2 concentration and staining tendency following this diffusion process.
Bacterial Challenge Experiments
Three experiments were completed in which one or more of the E. Coliform
Group of bacterial organisms were incorporated into the potable water and
subsequently challenged by I 2 . One experiment was conducted during the de-
velopment leading up to prototype system design. The other two were conducted
at the beginning and completion of the IGDSs 30-day endurance test. The
results are summarized in Table 10 and show that E. coli cannot survive in
the iodinated water with I 2 concentrations of 4.8 ppm or greater
OTHER PROGRAM ACTIVITIES
In addition to the activities discussed in the preceding sections, various
other experimental and analytical evaluations were made. They are reviewed
below.
Mechanical Iodine Injection
At the beginning of the program it was not known whether an electrochemical
I ? feed system could be developed within the program scope. As a backup,
therefore, a mechanical I_ injection system was designed and its control system
fabricated and tested. This activity lead to the following conclusions:
1. The mechanical injection approach is feasible.
2. The variable voltage approach to pump control is applicable.
3. The technology needed is available to fabricate such an approach
to I 2 injection.
Mechanical Approach Design
Two different designs were considered applicable. Schematics of these are
shown in Figures 45 and 46. The former is the preferred concept and employs
periodic pumping of water through a saturated I 2 solution until the I 2 level
meets specification. Figure 46 shows a mechanical concept based upon using
micro-pistons to cyclically inject saturated I 2 solution into the water.
Figure 47 illustrates the flow of saturated I 0 solution needed to raise the
I 2 level in water flowing at various rates.
The lower the desired I 2 level and the slower the water flow rate, the more
difficult it is for a mechanical system to establish a consistent I 2 level
because of the difficulty in reliabily pumping a fluid at low flow rates (e.g.,
5 ml/min (0.3 in /min)).
88
JCifc System, Jhc \
TABLE 10 RESULTS OF THE BACTERIAL CHALLENGE EXPERIMENTS
Experiment
Number
Iodine
Valve
Initial E. Coli.
Level ( a )
Iodine Level,
Ppm
Final E. Coli
Level
1
Exp. Cell
2.0 x 10 5
5.4
0
2
IGDS
3.8 x 10 5
10.2
0
3
IGDS
1.8 x 10 5
4.8
0
(a) In organisms per 100 ml.
Piston Drive Motor and
Gear Box
JCife Systems, Jhc.
91
FIGURE 46 POSSIBLE MECHANICAL INJECTION SYSTEM
Cife Systems, Jhc.
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92
FIGURE 47 SATURATED IODINE SOLUTION FLOW RATES
JCifc Systems, Jhc.
Advantages and Disadvantages
A limited comparison was made of the advantages and disadvantages of the
mechanical and electrochemical methods.
Electrochemical Approach - The electrochemical approach is attractive because
it
a. allows more accurate control of 1 2 injection,
b. has a lower power requirement,
c. has no moving parts,
d. is simple to scale-up, and
e. offers the potential of de-iodinating water treated with
excess I 2 to provide an overkill.
The disadvantage was the initial uncertain level of development risk.
Mechanical Approach - The mechanical approach was attractive because
a. it was able to iodinate at fast rates (but had difficulty
meeting I 2 feed regulation at low feed rates), and
b. its technology is more established, reflecting less
development risk.
The disadvantages were
a. it has a larger equivalent weight (larger system component
and power) and
b. it requires continuous or periodic operation of a pump.
Mechanical Approach Work Terminated
Effort directed toward the mechanical was terminated when the electrochemical
approach offered the more attractive solution to the I 2 feed requirement.
This occurred after test data indicated the process was feasible, and a 35-
day endurance capability was demonstrated with breadboard hardware.
Preliminary Comparison of Potable Water Disinfecting System
A preliminary system evaluation was made tjjetween the electrochemical I 2 system,
the mechanically fed I„ system, and an Ag system for an application requiring
33 kg (72 lb) water + per day at 20 ppm I 2 for 180 days and 33 kg (72 (lb) water
per day at 2 ppm Ag for 180 days. Results are summarized in Table 11.
Details are presented in Table 12. The I 2 approach has a lower weight be-
cause it avoids the need for ion exchange columns required to remove excess
Ag •
93
Cife Systems, Jhc,
TABLE 11 BIOCIDAL AGENT COMPARISON
Approach
Weight, kg
(Lb)
Volume, Liter
(Ft3)
Power ,
Watt
Electrolytic I 2
3.0 (6.7)
1.8 (0.06)
8
Mechanical I 2
5.1 (11.3)
2.9 (0.10)
67
Ag +
23.9 (52.8)
8.4 (0.30)
0
*
94
TABLE 12 COMPARISON OF POTABLE WATER BIOCIDAL AGENT SUBSYSTEMS
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component weight, volume and power.
(b) See Ref. 23.
(c) 30-Day replacement.
Cifc Systems, Jnc.
CONCLUSIONS
A program to develop a prototype Iodine Generating and Dispensing System
(IGDS) was successfully completed, including functional testing of the bread-
board and six-man prototype systems.
The program was initiated on the basis of using a previously developed chlorine
(C^) generating concept. Conversion of the on-site C^ generating concept to
an iodine- (I^) based device was successful. Two electrolytic components, the
hydrogen (H^) eliminator and disinfecting agent generator, were eliminated.
The electrochemical I_ valve developed during the program proved to be an
acceptable method of dispensing and controlling in simulated spacecraft
potable water stores. Iodine produced by the generator eliminated tracer E.
coli bacteria from simulated water stores.
Exploration of chemistry for the intended end application of controlling
microbial growth in spacecraft potable water stores showed, among other things,
that concentrations of 5 ppm or less will eliminate most microorganisms and
not adversely affect water "taste.”
A water flow rate of 120 kg (264 lb) per day can be iodinated to 5 ppm by the
prototype generator that measures 9.53 x 2.54 x 2.05 cm (3.75 x 1.0 x 0.81 in)
and contains, in addition to electrochemical components, enough I 2 for 180
days. Iodination is attained with less than 10 watts power being consumed by
the prototype whose design is compatible with the 78 kg (171 lb) and 46.3 kg
(102 lb) per day anticipated water flow rates of a Space Station and Space
Shuttle, and the possible water system operating modes for these spacecraft.
Other studies performed during the program indicated, for a variety of reasons,
that I 2 is a preferred biocide, in particular, for a Shuttle Orbiter application.
However, additional development is needed to avoid I 2 leaching from the generator
and to enhance generator performance. Other work is necessary to integrate an
improved I 2 generator with an I 2 level detector/monitor since the experiments
performed in this program were with a simulated detector. Analysis of the
development necessary indicates that a flight qualified electrochemical 1 ^ gen-
erator can be readied for Space Shuttle utilization.
96
Cife Systems, Jhc.
REFERENCES
1. Schubert, F. H. and Wynveen, R. A., "Development of a Laboratory Bread-
board Model of a Chlorine Generating Device to Chlorinate Reclaimed
Water on a Spacecraft," Final Report, NASA CR-111854, December, 1970.
2. "A Comparison Between Chlorine and Iodine to Maintain Biocidal Conditions
In Water Supplies," Life Systems, Inc., ER-171-7, November 10, 1972.
3. "Iodine Colorimeter," Beckman Instruments, Final Report, NAS9-11879,
July, 1971.
4. Latimer, W. M., "The Oxidation States of the Elements and Their Potentials
in Aqueous Solutions," Second Ed., Prentice-Hall, Inc., New York, 1952.
5. "Evaluation of Chlorogen Approach to Iodine Generation," Life Systems, Inc.,
ER-171-6, September 8, 1972.
6. Moeller, T., "Inorganic Chemistry," John Wiley § Sons, Inc., New York,
1954.
7. "Corrosion Control and Disinfection Studies in Spacecraft Water Systems,"
Engineering Science, Inc., NAS9-9431, March, 1972.
8. Black, A. P., Kinman, R. N. , Thomas, Jr., W. C., Freund, G., and Bird,
E. D., "Use of Iodine for Disinfection," J. AWWA, November, 1965.
9. Chang, Shih L., "The Use of Active Iodine as a Water Disinfectant,"
J. Am. Pharm. Assoc., 48 , 417, 1958.
10. "Space Shuttle Environmental Control/Life Support Systems," Hamilton
Standard, NASA CR-1981, May, 1972.
11. "Space Shuttle ETC/LSS System Definition," AiResearch Manufacturing
Company, NAS9-11592, May 20, 1972. - ... _
12. "Water and Waste Management Group," Delta Preliminary Design Package,
Space Station Prototype (SSP) Document No. A66, Hamilton Standard,
June, 1971.
13. "Potable Water Specification," NASA Johnson Space Center, SD-W-002, May
16, 1970.
14. Olivieri, V. P., Donovan, T. K. and Kawata, K., "Inactivation of Virus
in Sewage," J. San. Engr. Div., 97_, ASCE, 661, October, 1971.
15. Black, A. P. and Wittal, G. P., "New Methods for the Colometric Determin-
ation of Iodine Residuals, Part 1 - Iodine, Iodide and Iodate," J. AWWa,
59, pgs 471-490, April, 1967.
16. "Standard Methods for the Examination of Water and Wastewater," American
Public Health Assoc., Inc., 13 Ed., 1971.
97
Cifc Systems, Jhc.
17. "Procedures and Requirements for the Flammability and Offgassing Evalua-
tion of Manned Spacecraft Nonmetal lie Materials," D-NA-0002, NASA Manned
Spacecraft Center, July, 1968.
18. "The Encyclopedia of Plastics," Plastic Piping Systems, Inc., Newark,
New Jersey, 1972 .
19. "Seal Compound Manual," Parker Seal Co., Culver City, California, 1971.
o
20. "Valcourse Chemical Compatibility Chart," Valcor Engineering Corp.,
Kenilworth, New Jersey, 1967.
21. Private communication, J. W. Shumar, Life Systems, Inc. and R. N. Kinman,
College of Civil Engineering, University of Cincinnati, August, 1972.
22. "Modern Plastics Encyclopedia," No. A, 49_, McGraw-Hill Inc., New York,
1972.
23. "Water and Waste Management Group," Delta Preliminary Design Package
SSP Document Nos. 71, 114 and 142, Hamilton Standard, Appendix 1, pgs
102-103, June, 1971.
98
JCife Systems, Jhc.
APPENDIX A - REFERENCE DATA
FIGURE PAGE
A-l Time versus Concentration Relationship in the Destruction
(99.9%) of Cysts, Virus and Bacteria by I„ and HOI at
291K (64F) A-2
A-2 Iodine Solubility in Water A-3
A-3 pH of Aqueous Solutions of Iodine A-4
A- 4 Conversion of Iodine Concentration from PPM to Molarity . . A-5
A-5 Electrode Potential as a Function of pH and pl~ A-6
A-6 Conversion from Weight to Volume Flow A-7
A-7 Theoretical Iodine Generation Rate A-8
A-8 Calibration of Water Storage Tank A-9
A-9 Effect of Storage Time on Iodine Concentration A-10
A-10 Absorbancy versus Aqueous Iodine Concentration A-ll
A-ll Absorbancy versus Aqueous Iodine Concentration A- 12
A-12 Calibration of No. 11 Coming Glass Electrode Using
A GGF Calomel A-13
A-13 Iodide Ion Calibration Curve A-14
A-14 Calibration of R-6-15-A Flowmeter Tube A-15
A-1S Calibration of R-2-15-A Flowmeter A-16
A-l
Cife Systems, Jhc.
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A- 2
Iodine Concentration, ppm
Cife Systems, Jhc.
Temperature, C
FIGURE A-2. IODINE SOLUBILITY IN WATER*-* 5
(a) Black, A. P., Kinman, R. N., Thomas, Jr., W. C., Freund, Gerhard and
Bird, E. D., "Use of Iodine for Disinfection," J. AWWA, S7, pg. 1403,
Nov., 1965.
Iodine Cone
FIGURE A-3 pH OF AQUEOUS SOLUTIONS OF IODINE
A-4
Iodine Concentration, ppm
Cife S if stems, Jhc.
FIGURE A-4 CONVERSION OF IODINE CONCENTRATION FROM PPM TO MOLARITY
A-5
Electrode Potential
JCife Systems, Jnc.
FIGURE A-S ELECTRODE POTENTIAL AS A FUNCTION OF pH AND pi"
A-6
£ife Systems, Jhc.
Iodine Produced (x 10 ), Lb/Day
£ifc System, Jnc :
2.79
2.50
2.25
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0.00
Water Volume, Ft
Cife Systems, Jmc.
2.83
2.64
2.47
2.30
2.12
1.94
1.77
1.59
1.41
1.24
1.06
0.88
0.71
0.53
0.35
0.18
0.00
£ife Systems, Jhc.
FIGURE A-9 EFFECT OF STORAGE TIME ON IODINE CONCENTRATION
A-10
Absorbancy Units
Cife Systems, Jhc.
Iodine Concentration, Ppm
0 0.635 1.27 1.91 2.54 3.18
FIGURE A-10 ABSORBANCY VERSUS AQUEOUS IODINE CONCENTRATION
A-ll
Absorbency Units
Cife Systems, Jhc .
0.30
0.25
0.20
0.15
0.10
0.05
0.00
i
FI(
2
JCife Systems, Jhc.
FIGURE A-12 CALIBRATION OF NO. 11 CORNING GLASS
ELECTRODE USING A GGF CALOMEL
A-13
-300
JCife System, Jhc.
Cife Systems, Jhc.
FIGURE A-15 CALIBRATION OF R-2-15-A FLOWMETER
A- 16