ENCYCLOPEDIA OF ENVIRONMENTAL SCIENCE AND ENGINEERING - WATER AND WASTE MANAGEMENT SYSTEMS IN SPACE ppt

W WATER AND WASTE MANAGEMENT SYSTEMS IN SPACE INTRODUCTION Environmental Control and Life Support System ECLSS is the NASA terminology for the systems which allow people to exist and

W WATER AND WASTE MANAGEMENT SYSTEMS IN SPACE

INTRODUCTION

Environmental Control and Life Support System (ECLSS) is

the NASA terminology for the systems which allow people

to exist and work in confined spaces and in uninhabited

loca-tions and hostile environments These systems supply air,

water, temperature and humidity controls to enable personnel

to survive and work under hostile conditions The purpose

of this paper is to review the various devices that have been

developed for the recovery and reuse of liquid wastes in

spacecraft and space stations, and their possible terrestrial

applications

A SHORT HISTORY OF U.S SPACECRAFT

ECLS SYSTEMS

The U.S spacecraft ECLS systems have grown in

capa-bilities and complexity as the spacecraft have grown and

the duration of their missions has been extended Initial

removal in a closed loop There was no recycling of water

or wastes On the Orbiter, water is not recycled, but is

vented overboard Air is recycled Solid wastes are returned

to the earth This system will be changed as the Orbiter

is reconfigured for longer duration missions Due to the

high cost of transporting fresh water and oxygen into orbit,

the space station is designed to operate in an almost

com-pletely closed loop mode Only solid body waste and trash

will be returned to the earth Air and liquid wastes will be

recycled

Regenerative systems have been evaluated by NASA for

the different functions of the ECLSS (Figure 1) 1 A partial list

of the various technologies is given in Table 1 The emphasis

is on purification and recycling the air and wastewater streams

for atmosphere revitalization and water recovery and

manage-ment The high cost of transporting mass into orbit,

approxi-mately $22,000/kg, causes NASA to place a premium on low

weight, low volume, high efficiency, and low maintenance

requirements. 2

DRINKING WATER QUALITY STANDARDS

NASA has very strict standards for water consumed on the shuttle, and even stricter standards for the proposed space station This is logical, as the water on the space station will

be continuously recycled, and hence the astronauts will be exposed to this water for an extended duration Table 2 lists the present potable water standards for the shuttle and Space Station Freedom (SSF), and compares these to the existing EPA potable water standards The SSF hygiene water stan-dards are also shown in the table These stanstan-dards were established early in the program. 3

In order that hardware designers should have constant reference solutions to use when testing their equipment, NASA found it necessary to determine the compositions of urine and wastewater that would be produced on the space station Hence NASA analyzed average urine composi-tion, and determined a chemical model for urine, which could be made up and used to test recycling equipment

Similarly, a chemical model formula for hygiene water, i.e., water used for personal washing, laundry, and food preparation, was derived These model compositions for urine and wastewater were then used to test individual items

of hardware and complete processing systems However, the final evaluation tests must include the processing of urine and wastewater obtained from volunteers living in a closed test environment

TECHNOLOGIES TESTED FOR USE IN THE ECLSS

Various technologies were tested and/or evaluated for the ECLSS systems, with the emphasis on the water and air revi-talization systems Less attention has been paid to the treat-ment of solid waste, as this will only be required for long space voyages and for long term inhabitation of stations on the moon and planets A number of water recovery and waste management systems have been tested for application in the space station These systems have been evaluated by com-paring them to the baseline technology that was originally

ECLSS

Temperature and Humidity Control (THC)

Atmosphere Control and Supply (ACS)

Atmosphere Revitalization (AR)

Fire Detection and Suppression (FDS)

Water Recovery and Management (WRM)

Waste Management (WM)

Air Temperature Control Humidity Control Air Particulate Control Ventilation Intermodule Ventilation Avionics Air Cooling

Refrigerator/

Freezers

EVA Support

Urine Processing Combined Potable/Hygiene Processing Online Water Quality

Monitoring EVA Support Fuel Cell Water Transfer/Storage Contamination Recovery Experiment Support

Waste Storage &

Return Fecal Waste Processing Urine

Collection and Pretreatment

Vent & Relief

O2/N2 Pressure Control

O2/N2 Storage

O2/N2 Distribution Experiment Support Contingency Gas

Support

CO2 Removal

CO2 Venting Trace Contaminant Control Major Constituent Monitoring Trace Contaminant Monitoring

Fire Detection Fire

Suppression

Water Distribution Water Venting

O2 Generation

CO2 Reduction (SCAR)

FIGURE 1 Space Station Alpha Environmental Control and Life Support System (ECLSS) Functions Source: Ref 4.

selected for the space station The original baseline system

was the Thermoelectric Integrated Membrane Evaporation

Subsystem (TIMES) This was replaced by a new baseline

subsystem which is a combination of multibed filtration

(Unibed) and Vapor Compression Distillation (VCD) These

baseline systems along with many other promising

technolo-gies are described below

In all cases urine is pretreated immediately upon collec-tion to minimize bacterial growth and possible damage to collection and handling equipment In addition to inhibiting bacteria, the treatment is intended to control ammonia, sta-bilize dissolved solids to prevent precipitation, and allow the overall subsystem to function in a zero-gravity environment

Present pretreatment comprises the injection of either Oxone

TABLE 1 ECLSS Technologies Used or Evaluated

Atmosphere revitalisation Used LiOH

Used Molecular sieve Used Sabatier reactor Used Static feed water electrolysis Evaluated Solid amine fixed bed Evaluated Liquid sorbent closed loop Evaluated Bosch system

Evaluated Algal bioreactor Evaluated Growing green plants Trace Contaminant Removal Used Activated charcoal

Used Catalytic oxidiser Used Particulate filters Water recovery and management Used * Vapor compression distillation

Used Chlorine Used Sodium hypochlorite injection Used Iodine injection

Used Heat sterilisation Used Fuel cell by-product water Evaluated * Unibed filter

Evaluated * TIMES membrane filter Evaluated * Reverse osmosis Evaluated * Electrodialysis Evaluated * Electrooxidation Evaluation * Supercritical water oxidation Evaluation * Electrodeionisation Evaluation * Air evaporation Evaluation * Vapor phase catalytic ammonia removal Evaluation * Immobilized cell or enzyme bioreactors Evaluation * Plant transpiration and water recovery Temperature and humidity control Used Condensing heat exchangers

Used Water cooled suits Atmosphere control and supply Used Compressed gas storage

Used Cryogenic gas storage Waste management Used Urine stored in bags

Used Feces stored in bags Used Urine vented Used Feces stored in bags and vacuum dried Used Urine stored in tank and vented Used Feces stored in bags and compacted

* Described in this paper

TABLE 2 Water Quality Standards Comparison

TOTAL SOLIDS (mg/L) 5 to 10 500 100 500

“COLOR, TRUE (Pt/Co units)” 15 15 15 15

PARTICULATES (max size—microns)

pH Reference only 6.5–8.5 6.0–8.5 5.0–8.5

DISSOLVED GAS (free @ 37 ° C) None at 1 AT — (see Note 1) N/A FREE GAS (@ STP) — — (see Note 1) Note 1

INORGANIC CONSTITUENTS (mg/L)(see Notes 2 and 5)

CHLORINE (Total—Includes chloride)

IODINE (Total—Includes organic iodine)

Reference only — 15 15

RESIDUAL IODINE (minimum)

Reference only — 0.5 0.5

RESIDUAL IODINE (maximum)

(continued)

(a potassium monopersulfate compound) combined with

sul-furic acid, or hypochlorite (bleach) before distillation

Thermoelectric Integrated Membrane

Subsystem (TIMES)

This was the original baseline water recovery subsystem for

the space station (Figure 2) Wastewater is heated to 66⬚C

in a heat exchanger, and is then pumped through bundles of

small diameter hollow Nafion fiber membranes in the

evap-orator module The Nafion allows only water, gases, and

small neutral molecules to pass through The pressure on the

exterior of the membrane is reduced to 17 kPa (2.5 psi) to

assist in both transport through the membrane, and

subse-quent evaporation The water vapor is then condensed, and

the latent heat of condensation is conducted to the input heat

exchanger The TIMES system was found to produce poorer

quality water than the VCD. 4,5

Vapor Compression Distillation (VCD)

The VCD process involves spreading a thin film of the waste-water on the inside wall of a thin-walled rotating drum under low pressure, typically about 4.8 kPa (0.7 psi) The VCD is

slightly above ambient temperature Heat is applied to the outside of the wall causing the thin film of water to boil The vapor is extracted from the drum interior and compressed

by a pump The compressed vapor is then condensed on the exterior wall of the drum The compressed vapor condenses

at a higher temperature than that at which it had originally evaporated The latent heat of condensation thus supplied the heat required to evaporate the original feed water in the inside of the drum The unevaporated brine, heavily loaded with contaminants, is recycled back to the inflow stream, or passed to another subsystem

TABLE 2 (continued)

YEAST and MOLD (CFU/100 mL)

RADIOACTIVE CONSTITUENTS (pCi/L)

NRC LIMITS (see Note3) — —

ORGANIC PARAMETERS (mg/L) (See Note 2)

CYANIDE (total including organic cyanides)

HALOGENATED HYDROCARBONS — 0.1 (THM) * 10 10

TOTAL ORGANIC CARBON (TOC) Reference only — 500 10000

Note 1: No detectable gas using a volumetric gas vs fluid measurement system This excludes CO2 used for aesthetics purposes.

Note 2: MCLs considered independently of others.

Note 3: The maximum contaminant levels for radioactive constituents in potable and personal hygiene water shall

conform to Nuclear Regulatory Commission (NRC) regulations (10CFR20, et al.) These maximum contaminant levels

are listed in the “Federal Register Vol 51, No: 6, 1986, Appendix B, Table 2.

Note 4: Total organic carbon minus identifiable organic contaminants.

Note 5: MCLs for others, if found, will be established as necessary.

* THM = Trihalomethanes SSF = Space Station Freedom Source: Ref 3.

Thermoelectric Regenerator Waste

water

Purified Water

Membrane Evaporator Wastewater

Heat Exchanger Thermoelectric Elements

Condenser Latent

Heat

Hollow Fiber Membranes Water Vapor

Waste water

FIGURE 2 Schematic diagram of the TIMES (Thermoelectric Integrated Membrane Subsystem) Source: Ref 4.

Reverse Osmosis (RO)

Reverse osmosis is a process in which pressure is applied

to a concentrated solution which is on one side of a

semi-permeable membrane The pressure forces the molecules of

solvent through the membrane to the pure solvent or more

dilute solution on the other side Greater concentration

dif-ferential between the two solutions on either side of the

membrane require greater pressure A test unit containing

a bundle of tubes, capable of operating at up to 4140 kPa

(600 psi), was evaluated When wash water containing soap

was processed a soap gel film formed on the membrane

quality water A combination of several systems, including

RO, produced water that met National Committee for Clinic

Laboratory Standards. 13,14

Multifiltration (Unibed)

The multifiltration system comprises a heat sterilization unit

to kill microorganisms, followed by a series of progressively

finer particulate filters down to 0.5 microns to avoid

par-ticulates clogging the sorbent beds. 15 The water then enters

the Unibeds which remove the dissolved contaminants The

Unibed is a single replaceable unit which utilizes a set of beds

of different sorptive materials arranged in a specified

specified types and amounts of contaminants from a known

waste stream in such a way that all the beds are exhausted at

the same time A sequence of Unibeds of identical design,

each comprising three five-tube replaceable subunits, may be

used Unidentified compounds are generally removed by a

mixture of several types of activated charcoal and nonionic

sorbents near the outlet from the bed Microbial control to

avoid bacterial fouling of the various beds is achieved by iodinated resin beds at the inlet and outlet of each Unibed

Detailed discussions of the system may be found in Refs 11, and 14–16

Electrooxidation—Combined Electrolysis and Electrodialysis

Electrodialysis alone removes ions more efficiently than does reverse osmosis (RO); however, when combined with elec-trolysis the organic compounds are oxidized in the electroly-sis and the inorganic salts are removed by the electrodialyelectroly-sis. 7

A combined electrolytic and electrodialytic cell is illustrated

in Figure 5 No chemicals are used Low voltages are used to avoid unwanted side effects such as the production of chlorine,

or the formation of insoluble salts Various types of electrode materials have been tested Efficiency was increased consider-ably when the polarity across the electrodes was periodically reversed This procedure is termed Periodic Reverse Pulsed Electrolysis (PRPE) The process has theoretical advantages over RO, as increasing the brine concentration improves the conductivity, and hence the efficiency of the process

Electrooxidation effectively kills bacteria in the feed. 17

Supercritical Water Oxidation (SCWO)

Wastewater is heated to a temperature of 650⬚C under pressures

of 250 atmospheres When water is above its critical point, its properties as a solvent change Organic compounds which are insoluble at normal temperature and pressure become soluble

The addition of sufficient oxygen then leads to the complete oxidation of these compounds Most atmospheric gases and trace contaminant gases are also soluble in supercritical water, and will also be oxidized The process also has the potential

for oxidizing much of the organic solid wastes produced on

the space station. 18 Inorganic salts are produced when human

metabolic wastes are subjected to supercritical water

oxida-tion These salts have very low solubility in supercritical water

and precipitate out, and thus can be removed. 19 Metals are also

precipitated out, with the exception of mercury, which

car-ries over in the vapor phase, and has to be removed by ion

adsorption. 20

Electrodeionisation

Feed water moves through an ion exchange resin bed

which selectively removes certain ions from the water

Simultaneously, the resin is regenerated by the action of

an electric field imposed upon the resin bed. 21 A schematic

process diagram may be found in Ref 21 Bacteria are not

completely removed It appears that this process works best

to remove ionic contaminants It is a candidate for the

pro-duction of reagent grade water Both benchtop and industrial

capacity units are available

Air Evaporation

A system with a heat pump and solar collectors for

evapora-tive heat was tested The system is capable of 100% water

recovery from numerous types of contaminated sources The

wastewater is pretreated with a chemical solution to

pre-vent decomposition and bacterial growth It is then pumped

through a wick filter to remove particles, in a series of pulses

The timing of the pulses is such that the liquid from one pulse

is distributed along the wick by capillary action before the next pulse arrives A heated air stream evaporates the water from the wick, leaving the solids behind When the wick is full of solids, it is dried and replaced by a new wick The air and vapor stream passes through a condensing heat exchanger and then through a water separator to extract the free water from the stream and test it for quality It is then transferred to the post-treatment filter section and thence to the main water storage and distribution system The wick system can be ster-ilized by heating it to 121⬚C while in a dry state. 22

Vapor Phase Catalytic Ammonia Removal (VPCAR)

Neither pre-treatment nor post-treatment of the feed and product water are required The high temperature employed also destroys microbes to a very great extent. 23 The present design utilizes the thin film evaporation technique of the VCD process in a rotating disk evaporator, combined with catalytic reactors for vapor phase chemical reactions The ammonia and volatile hydrocarbons which are evaporated along with the water vapor are oxidized to innocuous gases

by catalytic chemical reactions carried out in the vapor phase

The overall system schematic is shown in Figure 6. 10,11 The vapor from the VCD boiler passes over two catalytic beds

oxidize organic volatiles to CO 2 and water, and ammonia to

the NO to N 2 and O 2 The O 2 produced is more than sufficient

utilization This high temperature vapor or steam supplies the

Outer Shell Rotating Drum

Evaporator Motor

Compressor

Condenser

2

FIGURE 3 Cross section of a VCD (Vapor Compression Distillation) still Source: Ref 4.

heat to evaporate the feed, condensing to form the product

water The residual concentrated feed, or brine, is sent to a

supercritical water oxidizer (SWCO) to remove the

remain-ing contaminants Bacterial growth is suppressed because

bacteria do not thrive in the concentrated brine due to the

buildup of both toxic compounds and of heavy metals in the

brine The vapor phase provides a barrier to non-airborne

micro-organisms. 10

Plant Transpiration and Water Recovery

The use of plants to produce clean water by transpiration

is being examined by NASA It is believed that plants can

process wastewater, and transpire it with minimal

contami-nants However, any volatile contaminants must be removed

first, so that they cannot evaporate directly from the wastewater

into the air The type of pretreatment required will depend upon the waste steam being treated Plant nutrients will have

to be added to the water Preliminary experiments using only a plant nutrient solution indicated that the amount of total organic carbon (TOC) in transpired water vapor from unstressed plants was very low, about 1.4 mg/L in the water that was collected in condensers outside the plant cham-ber Water collected in the plant chamber had higher TOC values, averaging 2.5 mg/L Stressed plants transpired water with TOC values of up to 7 mg/L The average TOC level

of tap water was 1.6 mg/L Insect infestation stressed the plants, causing higher TOC levels in the transpired water

It was not clear if any of the increased TOC was derived from the insects themselves There are many questions about the feasibility of using a compact growth facility to treat the wastewater These questions need to be examined carefully

TOP OF UNIBED MEDIA TYPE PROCESS FUNCTION

BOTTOM OF UNIBED

Diatomaceous Earth Coarse Diatomaceous Earth Fine MCV Iodinated Resin Dowex-1

Mixed Bed Resin

Carbon/Adsorbent Silicalite Mixture Weak Base Anion

MCV Iodinated Resin

+30 US Mesh -30 US Mesh Iodinated SBA Anion Dowex-1 SBA Anion

Coarse Filtration Fine Filtration Iodine Injection Absorption Cleansing Agents

Ion Exchange

Turbidity Removal Turbidity Removal Microbial Control Organic Scavenging

Reduction Inorganic Salts

Mixed Resin SAC/SBA

Adsorbant Section Methacrylic Weak Base Gel Type Resin Iodinated SBA Anion

Adsorption

Ion Exchange Weak Organic Acids Iodine Injection

TOC Removal/Reduction Reduction Organic acids

Microbial Control

FIGURE 4 Multifiltration unibed schematic and process details Source: Ref 15.

Discussions on these and related topics may be found in

Refs 24–27

Immobilized Cell or Enzyme Bioreactors

Immobilized microorganisms convert contaminants into

simpler molecules at near ambient temperatures The

immo-bilized cells can treat a wide variety of contaminants This

technology is under development, but it may have significant

terrestrial uses. 28 – 30 These biological systems require little

energy, and may leave little waste residue Prototype reactors

were tested using a packing of diatomaceous earth When

tested with feed containing 10 and 100 mg/L phenol in an

oxygenated solution, they were able to produce an effluent

with phenol content below the detection limit of 0.01 mg/L

The report did not say what organisms were used, nor how

they were arranged for the test. 30 Immobilized microbial cell

bioreactors have been used in industrial wastewater treatment

applications In a comparative test processing feed from a

coal tar plant, a reactor using a porous polymeric biomass

support achieved effluent phenol levels 100 times lower than those achieved by a commercial bioreactor utilizing a non-porous polyethylene support Similar results were observed for minor contaminants, and the sludge output was about 20% of that from the nonporous system

A bioreactor test using a consortium of enriched aero-bic microorganisms immobilized in packed bed reactors was conducted, utilizing a simulated wastewater feed

A porous polymeric biomass support was used in the reactor

Influent concentrations were nominally 600 mg/L COD, and

1000 mg/L urea COD reductions of 95% or more, and urea reductions of 95–99% were achieved when using hydraulic retention times of 24 or 48 hours Effluent total suspended solids ranged from 1 to 3 mg/L. 28

Tests have shown that low-molecular weight, polar, non-ionic contaminants can be removed from solution by immobi-lized enzymes which catalyze the oxidation of various organic compounds, such as alcohols, aldehydes, and so on, to organic acids, for subsequent removal by ion exchange Hence exist-ing ion exchange technology (multifiltration Unibeds) can be

Electrolysis + Electrodialysis

RO Brine Stream

Bleed to waste

Anion Exchange Membrane

Cation Exchange Membrane

RO Recycle Stream

Negative Electrode

Positive Electrode

Brine Drain FIGURE 5 Electrooxidation—combined electrolytic and electrodialytic cell Source: Ref 7.

made more effective The enzymes are bound to support,

usu-ally, a silica-based material, which is in a form that makes it

easy to utilize in a Unibed Specific enzymes are used

depend-ing upon the compound or class of compound, to be removed

These Unibeds have to include iodine removers at the inlet,

and iodinating resin beds at the outlets to maintain bacterial

control in the water supply system of the spacecraft. 29

Fuel Cell Product Water

When hydrogen and oxygen are combined in a fuel cell to

produce electric power, pure water is also produced This

system was used in both the Apollo and Orbiter spacecraft. 5

Urine and wastewater can be electrolyzed to produce

hydro-gen and oxyhydro-gen, thus providing a closed loop system (see

Electrooxidation above)

COMPARATIVE PERFORMANCE OF TECHNOLOGIES

Many promising technologies for wastewater treatment and

water recovery aboard the space station have been described

briefly Their performance levels vary depending upon the

characteristics of the wastewater feed The performance levels

and the basic features of each system are compared in Table 3

WATER QUALITY CONTROL

A major problem in these regenerative systems is bacterial

contamination and biofilms forming on the internal surfaces

of the water supply system These biofilms are the result

of colonies of bacteria forming on the surface They occur even in nutrient-limited environments Biofilms accelerate corrosion and are difficult to remove, or to prevent from

sur-vive in sterile water and at elevated temperatures for many hours. 32 This bacterial contamination poses both health and long term mechanical problems in any recycling system

Adequate continuous sterilization procedures and equip-ment will be required in any recycling system A high con-centration of micro-organisms is found in shower water, reinforcing the necessity of ensuring the disinfection of the recycled potable water supply A special soap is used for all washing on the Orbiter and is proposed for use on the space station, which reduces foaming and consequent problems in the recycling process. 33 Great care is taken to avoid the possibility of contamination due to cross con-nection of wastewater and processed water systems

Pre- and Post-Treatment of Recycled Water

Pre- and post-treatment of water is generally necessary in order to obtain the desired water quality after the treatment

of recycled water NASA concentrated much of its research effort on distillation processes The combination of distil-lation and ion exchange is quite successful in removing inorganic contaminants but is less successful in remov-ing volatile organic contaminants These volatiles must be removed to avoid their accumulation to toxic levels Organic

TO AIR REVITALIZATION SUBSYSTEM

N2, CO2 & H20 OXYGEN

URINE &

FLUSH HYGIENE &

WASH WATER

SOLID WASTE SLURRY (IF DESIRED)

Heavy Liquids Processor

RESIDUAL INORGANIC SOLIDS SCWO PRODUCT WATER OXYGEN

POTABLE WATER VENT GASES

VPCAR BRINE

VAPOR PHASE CATALYTIC AMMONIA REMOVAL UNIT (VPCAR)

New VPCAR Processor

SUPERCRITICAL WATER OXIDATION UNIT (SCWO) SCWO

FIGURE 6 Schematic flow diagram of integrated water reclamation system utilizing a combination of VPCAR unit and

SCWO unit Source: Refs 10 and 11.