Ultrafiltration is examined for use as the first stage of a primary treatment process for spacecraft wastewater. It is hypothesized that ultrafiltration can effectively serve as pretreatment for a reverse osmosis system, removing the majority of organic material in a spacecraft wastewater. However, it is believed that the interaction between the membrane material and the surfactant found in the wastewater will have a significant impact on the fouling of the ultrafiltration membrane. In this study, five different ultrafiltration membrane materials are examined for the filtration of wastewater typical of that expected to be produced onboard the International Space Station. Membranes are used in an unstirred batch cell. Flux, organic carbon rejection, and recovery from fouling are measured. The results of this evaluation will be used to select the most promising membranes for further study

Pickering, Karen D.

Wiesner, Mark R.

NASA Technical Reports Server

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Abstract 
Evaluation of Ultrafiltration for Spacecraft Water Reuse 
Karen D. Pickering 
Project Manager, Advanced Water Recovery Systems 
Johnson Space Center 
Houston, Texas 
Mark R. Wiesner, Ph.D. 
Professor, Environmental Science and Engineering 
Rice University 
Houston, Texas 
Source of Acquisition 
NASA Johnson Space Center 
Ultrafiltration is examined for use as the first stage of a primary treatment process for 
spacecraft wastewater. It is hypothesized that ultrafiltration can effectively serve as 
pretreatment for a reverse osmosis system, removing the majority of organic material in a 
spacecraft wastewater. However, it is believed that the interaction between the membrane 
material and the surfactant found in the wastewater will have a significant impact on the 
fouling of the ultrafiltration membrane. In this study, five different ultrafiltration 
membrane materials are examined for the filtration of wastewater typical of that expected 
to be produced onboard the International Space Station. Membranes are used in an 
unstirred batch cell. Flux, organic carbon rejection, and recovery from fouling are 
measured. The results of this evaluation will be used to select the most promising 
membranes for further study. 
Introduction 
Worldwide, many communities have begun to consider water reuse the most 
economically feasible method for providing water to meet the needs of their populations. 
Industrial processes and landscape irrigation are common applications for recovered 
water. Some communities have begun to implement indirect potable reuse, in which 
treated wastewater effluent is discharged to a receiving water body that is the source of 
potable water for a community. The effluent receives some additional treatment due to 
the residence time of the water in the natural environment. 
The National Aeronautics and Space Administration (NASA) has a unique requirement 
for water reuse. Of the various consumables required to sustain human life in 
space, water accounts for the greatest percentage of material by mass. It is estimated by 
Skoog, et al (1989) that between 3.63 and 12.63 kg of water / person are required for each 
mission day. Both the available spacecraft volume and the cost of launching the required 
mass into orbit limit the amount of water that can be carried onboard spacecraft for 
extended duration missions. Clearly, water must be recycled in order to make long 
duration missions feasible. 
https://ntrs.nasa.gov/search.jsp?R=20100033381 2019-08-30T11:44:08+00:00Z
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NASA requires a direct potable reuse system that will reliably produce potable water for 
consumption by a spacecraft crew for extended durations. As plans for extended duration 
missions are developed, new technologies for the reuse of water onboard spacecraft must 
be considered. In many water reuse projects, a large volume of fairly dilute effluent from 
a wastewater plant wldergoes advanced water treatment processes to meet reclaimed 
water guidelines. In space applications, water recovery systems process a small volume 
of highly concentrated wastewater. In addition, power, volume, weight and chemical 
additions must be limited in order to meet the constraints of spaceflight. Finally, 
technologies used onboard space vehicles that transfer a crew between Earth and a 
planetary outpost must be capable of operating independent of gravity. 
Materials and Methods 
Membrane materials frequently used in the manufacture of ultrafiltration membranes 
include polysulfone (PS), polyethersulfone (PES), polyacrylonitrile (PAN), cellulose 
esters, polyimide (PI), polyetherimide (PEI) , polyamide, and polyvinylidene fluoride 
(PVDF) (Anselme and Jacobs, 1996). Five ultrafiltration membrane materials were 
evaluated in this study. All membranes were manufactured by Osmonics, Inc. 
(Minnetonka, MN). The ultrafiltration membranes vary somewhat in their pore size 
ratings. Membranes were selected as close to a molecular weight cut-off (MWCO) of 100 
kiloDaltons (kDa) as commercial availability allowed. Literature (Fane et ai, 1985; 
Jonsson and Jonsson, 1991) and previous NASA testing (Bagdigian et ai, 1992) indicated 
that polysulfone and polyethersulfone membranes experience significant fouling when 
exposed to ionic surfactants. Therefore, these membranes were not evaluated. 
Table 1. Membrane materials. 
Membrane material Part number Molecular Weight Cut-off 
(MWCO) 
Polyvinylidenefluoride (PVDF) SepaAN09 30K 
Polyacrylonitrile (PAN) SepaRM05 lOOK 
Ultrafillic (proprietary) SepaMX50 lOOK 
Thin-film composite (TFC) Sepa 0-80 10K 
Cellulose acetate (CA) Sepa SZ05 80K 
Wastewater used in this study was collected from the main wastewater feed tank that is 
part of the Water Research Facility (WRF) located in Building 7B at Johnson Space 
Center. This wastewater was collected from volunteer donors. The wastewater is 
representative of wastewater that will be produced by a crew aboard the International 
Space Station and consists of shower waste, lavatory waste, oral hygiene waste, urine, 
urine flush water, and a humidity condensate analog. 
There is substantial day-to-day variation in the concentration of both total organic carbon 
and dissolved solids in actual wastewater. The range of concentration and components of 
human urine produces in the most significant variability in the wastewater. In order to 
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minimize the effect of this variability, sufficient wastewater was collected at the start of 
the study for the entire set of membrane experiments. Wastewater was stored at 2 - 4°C 
(35.6 - 39.2°P) in a closed container when not in use to minimize biodegradation and 
volatilization of constituents. Composition of the wastewater is shown in Table 2. 
Table 2. Wastewater composition. Composition represents wastewater produced 
by 4 crewmembers / day. (MSFC Specification 2841C, Table I) 
Component Quantity (liters) 
Shower waste 10.9 
Lavatory waste 16.4 
Oral hygiene waste 1.5 
Urine 6.0 
Urine flush 2.0 
Humidity condensate 9.1 
Total volume 45.9 
NASA Whole Body Shower Soap (NWBSS) was used as the personal care product for 
both the shower and lavatory users. The composition of NWBSS is shown in Table 3. 
The primary ingredient of NWBSS is Geropon TC-42 (BASF), which is an anionic 
surfactant. 
Table 3. NASA Whole Body Shower Soap composition. 
(Ecolab, Inc. production specification, 1988) 
Component % composition (w/w) 
Trade name (Manufacturer) Generic name 
Geropon TC-42 (Rhodia) Sodium cocoyl-n-methyl taurate 98 .65 
Emulmetik 300 (Lucas Meyer) Lecithin 0.5 
Luviquat FC 550 (BASF) Polyquaternimn-16 0.75 
---- Formalin 0.1 
Since a true humidity condensate can only be obtained through closed environment 
testing, an analog for humidity condensate is used. This analog includes major 
compolmds found in actual hWllidity condensate collected from Space Shuttle missions, 
closed environmental chamber tests at Johnson Space Center, and the End-use Equipment 
Facility (EEF) at Marshall Space Flight Center. (Carter et ai, 1992, Muckle et ai, 1993; 
Straub et ai, 1995; Pierre et ai, 1996; Homan et ai, 1997) The composition of the 
simulated humidity condensate is presented in Table 4. 
Table 4. Composition of humidity condensate analog. 
Compound Concentration (mg/I) 
Ethanol 129.7 
2-Propanol 35.0 
1-2, Propanediol 71.5 
Caprolactam 26.1 
2-(2-butoxyethoxy) ethanol 3.8 
4-ethylmorpholine 4.2 
Methanol 7.5 
Formaldehyde 15.4 
Formic Acid 21.9 
Propionic acid 7.2 
Zinc Acetate Dihydrate 43.9 
Ammonium Bicarbonate 32.8 
Ammonium Carbonate 32.3 
The quality of the wastewater used in the filtration experiments is summarized in Table 5. 
Table 5. Average wastewater composition. 
Parameter 
pH 8.8 
Total organic carbon 353 mg/l 
Total suspended solids 
Total dissolved solids 
An unstirred batch filtration cell (Spectrum, model S-76-400, PIN 501819) was used for 
the experiments. This batch filtration cell employed dead-end filtration to produce 
permeate. By operating the system without stirring, the maximum adsorptive fouling of 
the membrane should be observed. Solute transport from the membrane into the bulk 
feed solution is due only to diffusive back transport. The conditions within the batch 
filtration cell at a given time are depicted in Figure 1. In this figure, Cbulk represents the 
solute concentration in the bulk liquid, C(x) is the solute concentration at distance X in 
concentration polarization layer; Cmem indicates the solute concentration at the membrane 
surface; and Cp represents the solute concentration in permeate. In addition, Jp in the flux 
of solvent through the membrane and P is the driving pressure. 
The cell used a 76 mm diameter flat sheet membrane. The maximum allowable working 
pressure (MA WP) of the cell is 5.8 bar (70 psig). The working pressure is provided by 
pressurized facility breathing air and was controlled by a regulator (Porter, PIN 8286). 
The experiments were conducted at 2 bar (15 psig). 
I~ 
1\ 
p 
Cbu1k 
~(X) Cm 
, . , 
[Concentration 
f polarization layer 
membrane<: 
Figure 1. Concentration polarization in a batch filtration cell. 
Each membrane was evaluated three times. A new membrane was used for each 
experiment. New membranes were rinsed with deionized water (DI), then soaked 
membrane-skin-down in DI water overnight (Cho et aI, 1998; Jones and O'Melia, 2000; 
Childress and Elimelech, 1998). The membrane was removed from the DI water and 
rinsed again immediately before installation into the filtration cell. 
The clean water flux of the membrane was measured prior to each dead-end filtration 
experiment. Two hundred and fifty milliliters of wastewater was then added to the 
filtration cell and filtered under constant pressure to at least 80% recovery. No makeup 
wastewater was added to the cell during the experiment. The mass of permeate collected 
over time was recorded with an electronic balance (Mettler-Toledo, PG-5002S) 
connected to a data acquisition system. At the completion of filtration, the concentrate 
was poured out of the cell and the membrane was rinsed with at least 250 ml ofDI water. 
The clean water flux of the fouled membrane was then measured. 
Results and Discussion 
Membrane Performance 
The steady-state flux through the membranes is illustrated in Figure 2. The thin-film 
composite membrane, although marketed as an ultrafiltration membrane, performed more 
like a nanofiltration membrane. The clean water flux of the membrane at an operating 
pressure of 2 bar was considerably lower than that of the other membranes; therefore, the 
membrane was not evaluated with wastewater. 
The PVDF membrane exhibited the greatest steady-state flux of the membranes tested; 
however, the ultrafillic membrane' s average steady-state flux was within the statistical 
error of the average flux of the PVDF membrane. Interestingly, the PVDF membrane 
had the lowest MWCO rating, at 30 kDa, of the membranes evaluated. This is contrary 
to the expected results, in which the higher MWCO membranes would yield the greatest 
steady-state flux. Similar results were report by Archer (1999), who observed that 
permeate flux is not related to MWCO in the filtration of surfactant solutions. 
18.0 
16.0 
14.0 T 
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6.0 
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4.0 - - --
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PVDF Ullrafi llic PAN cellulose acetate 
membrane material 
Figure 2. Steady-state flux of ultrafiltration membranes in dead-end filtration 
experiments. 
The clean water flux of each membrane, both before and after fouling, is presented in 
Figure 3. Of the evaluated membranes, the PVDF membrane and the cellulose acetate 
membrane had the greatest clean water flux, while the ultrafillic and cellulose acetate 
membranes had the highest clean water flux after fouling. The PVDF membrane showed 
substantial irreversible fouling, based upon the clean water flux measured after filtration 
of the wastewater. The percent flux reduction of each membrane is summarized in Table 
6. Very little correlation is observed between clean water flux reduction of a fouled 
membrane and the molecular weight cutoff as supplied by the manufacturer. The 
membranes that showed the greatest loss of flux after fouling were the two hydrophobic 
membranes, PVDF and PAN. This is likely due to the adsorption of surfactant to the 
hydrophobic surface of the membrane. Similar results have been reported in the literature 
(Laine et ai, 1989, Jonsson and Jonsson, 1991). 
Table 6. Molecular weight cutoff and flux reduction 
Membrane Material 
PVDF 
Cellulose acetate 
PAN 
"Ultrafillic" 
700.0 
600.0 
500.0 
I 400.0 
N 
~ 
~ 300.0 
<;:: 
200.0 
100.0 
0 .0 
-t 
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--
n 
PVDF 
MWCO 
(kDa) 
30 
80 
100 
100 
ri-
f--+-
Ultrafill ic 
surface % clean water flux 
reduction 
hydrophobic 86.6 
hydrophillic 21.2 
hydrophobic 71.7 
hydrophillic 58.8 
r+- Io new membran1--
lDafter rinse 
. ~" _1 
1 
." 
r-+ , 
h ,..----, 
PAN cellulose acetate thin-film composite 
membrane material 
Figure 3. Clean water flux of membranes, before and after fouling. 
Water Quality 
Very little difference was observed in the permeate water quality between each 
membrane. In all cases, the permeate total suspended solids was below detection limits. 
The permeate turbidity was reduced to less than 1 NTU The average permeate turbidity 
produced by each membrane is shown is Table 7. The turbidity of the permeate from the 
PVDF membrane was not measured. 
Total organic carbon was measured during each experiment; however, the results of these 
measurements are inconclusive. 
r-
, . 
------
Table 7. Average permeate turbidity. 
Membrane Material Turbidity 
PVDF --
Cellulose acetate 0.324 
PAN 0.296 
"Ultrafillic" 0.325 
Conclusions and Upcoming Work 
Based upon the data collected, the PVDF, ultrafillic, and cellulose acetate membranes 
will be the subjects of additional study. In general, the hydrophilic membranes were less 
susceptible to fouling than the hydrophobic membranes. Furthermore, molecular weight 
cut-off was not a useful indicator of either steady-state flux or susceptibility to fouling. 
Of the membranes evaluated, the proprietary "ultrafillic" membrane appears to be the 
most promising. The steady-state flux of the membrane measured during dead-end 
filtration experiments exceeds 14 11m2 -hr. In addition, it showed good recovery from 
fouling, based upon measurements of clean water flux. The cellulose acetate membrane 
demonstrated excellent recovery from fouling, although the steady-state flux was 30% 
less than the ultrafillic membrane. The PVDF membrane, despite significant irreversible 
fouling, had the greatest steady-state flux of the membranes evaluated. 
In upcoming work, a variety of surfactants frequently used in personal care products will 
be evaluated with the selected membranes. It is believed that an optimum combination of 
surfactants and membrane can be determined. The selected membranes will also be 
further characterized to confirm molecular weight cutoff and surface characteristics. 
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Evaluation of Ultrafiltration for Spacecraft Water Reuse

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