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Lessons Learned from the Development of
Advanced Life Support Systems for Space
Applications
Emerging Applications for Water Treatment and
Potable Water Reuse
Tzahi Y. Cath
Environmental Science and Engineering Division
Colorado School of Mines
2006 International Conference on Environmental SystemsJuly 17-20, 2006
Presentation Outline
Overview of Membrane Processes for Water Treatment
Pressure-driven membrane processes
Membrane contactor processes
Combination of processes for process intensification
Potable Reuse of Wastewater
Volume Minimization of Wastewater
Brackish Water Desalination
Summary and Future Directions
Pressure-Driven Membrane Processes
SolventParticle or Solute Molecule
Membrane
PermeateFeed
P
Pressure-Driven Membrane Processes
Suspended Solids (Particles)
Macromolecules (Humics)
Multivalent Ions (Hardness)
Monovalent Ions (Na+,Cl-)
UFUF NFNFRROO
MMFF
Water Molecules
Limitations of Pressure-Driven Membrane Processes
Membrane fouling Limited application
Membrane scaling Limited water recovery
Energy
Membrane Fouling
particlesmacromolecules ionsmicrobes
Membrane Fouling
MFMF UFUF NFNF RORO
Membrane Scaling
Osmotic- and Thermally-Driven Membrane Processes
Process Mass Transport Driving Force
Forward Osmosis (FO) Diffusion Osmotic Pressure
Membrane Distillation (MD)
Evaporation Partial Vapor Pressure
The driving force is temperature or concentration gradients across the membrane
Combination with each other and with pressure-driven membrane processes
Osmosis / Forward Osmosis
Brine Water
Equilibrium
osmoticpressure
Brine Water
membrane
Osmosis
Water/Feed
Forward Osmosis(FO)
Brine
Brine ≡ Draw Solution (DS)
Draw Solutions
0 2 4 6 8 100
400
800
1200
1600O
smot
ic P
ress
ure
(@25
o C),
atm
Concentration, M
MgCl2
CaCl2
NaCl KCl sucrose KNO
3
NH4HCO
3
Forward Osmosis Pretreatment for Reverse Osmosis
Concentrated DS
Diluted DS
solute
ReverseOsmosis
ForwardOsmosis
RawFeed Solution
ConcentratedSolution Clean
Water
Membrane Distillation
adapted from: http://www.water-technology.net/
**pfm PPAJ
heated aqueous feed solution is
brought into contact with feed side of
hydrophobic, microporous membrane
hydrophobic nature of membrane
prevents penetration of aqueous
solution into pores
cold pure water is in contact with
permeate side of membrane
vapors diffuse through pores and
directly condense into cold stream
Vapor Pressure and Partial Vapor Pressure in Microporous Membrane Evaporation Processes
Water +NaCl
Vacuum Enhanced Direct Contact Membrane Distillation
P F
Traditional DCMD
P F
VEDCMD
Effect of Permeate-Side Vacuum on FluxΔT = 20C
vf = vp = 1.4 m/sec
Pf = 1.1 bar (abs)
- + Results from Traditional Configuration
New Hybrid System for Fouling-Protected MD
0 5 10 15 20 25 300.0
0.5
1.0
1.5
2.0
2.5
3.0
Wat
er F
lux,
L/m
2 -hr
Elapsed Time, hr
MD Water Flux
DS ~ 50 g/l NaCl DS ~ 200 g/l NaCl
Advantages of Membrane Contactors
High rejection of wide range of contaminants/solutes
Low-grade energy / waste heat sources can be used
Reduced fouling potential – less pretreatment required
Operate at low pressure – less constraints / safety issues
In MD, driving force not reduced by osmotic pressure
Can provide enhanced recovery through brine desalination
Evaluation of
Forward (Direct) Osmosis Concentration (DOC)
for Direct Potable Reuse of Wastewater in
Long-Term Space Missions
Project History
Mid 1990s – Forward osmosis incorporated into a water reclamation systems
1999 – Osmotek Inc. completed first phase of technology demonstration
2002-2003 – University of Nevada, Reno completed optimization study with recommendations to modify DOC architecture
2004-2007 – Rapid Technology Development Team (RTDT) program to develop a more reliable system – appropriate for human testing at TRL 5-6
Original DOC Concept
Integration of three membrane processes in one system Reverse osmosis – core process Forward osmosis – pretreatment for RO Forward osmosis/osmotic distillation – pretreatment for RO
Treat variety of wastewater streams, including: Hygiene wastewater Humidity condensate (HC) Urine
MembraneContactors
Schematic of Original DOC Test Unit
DOC #1 DOC #2
Final Waste
RO
Hygiene WW
+HC
Catalytic Oxidation
Conc. WW
+ Urine
Schematic of New DOC Test Unit
FO MD
Final Waste
RO
Hygiene WW
Hum.Cond.
+ Urine
Catalytic Oxidation
Construction of New Prototypes
Performance of Forward Osmosis feedDSmmw APAJ )(
MD for Potable Reuse of Urine and Humidity Condensate
(Tf = 40ºC, Tp = 20ºC)
Specific Power Consumption
Removal of Endocrine Disrupting Chemicals (EDCs)
Continually released to environment by humans and most often not destroyed by conventional wastewater treatment
May be a significant problem in closed water reclamation systems
Estrone (E1)Estrone (E1)17-17-ββ Estradiol (E2) Estradiol (E2)
Hormone Rejection by Membrane Distillation
Wastewater FeedDI Water Feed(urine + humidity condensate)
Hormone Rejection by Forward Osmosis
0 10 20 30 40 50 60 70 8050
60
70
80
90
100
ED
C R
ejec
tion,
%
Water Recovery, %
H2 in Soap Solution E1 in Soap Solution E1 in DI Water
Forward Osmosis for Concentration of Liquids from Anaerobic Digester
Anaerobic Digesters
Liquid fraction (“centrate”) recycled back to beginning of treatment process
Problems: High loading of organic matter, nutrients, and suspended
solid to the main treatment train Increased operating cost Difficult to employ pressure-driven membrane processes Environmental concerns
Potential benefits: commercial products ?
FO Performance Tests
FO Performance Tests
Pretreated CentrateRaw Centrate
11
22
33
44
55
66
77
88
99
FO Performance Tests
Average Rejection (%)
Ammonia TKNOrtho-
phosphate
>87 >89 >99.5
Forward Osmosis vs. Reverse Osmosis
MembraneMembraneCleaningCleaning
FO for Brackish Water Desalination
Performance of VEDCMD
CDS = 55 g/l NaCl
Tfeed = 20C
Tlow = 40C
Thigh = 60ºC
Performance of VEDCMD
Forward Osmosis vs. VEDCMD
CDS = 55 g/l NaCl
Tfeed = 20C
Tlow = 40C
Thigh = 60ºC
Scale Inhibition Study
Summary and Future Directions
Membrane contactors perform very well and are suited for unique applications as the treatment process or as pretreatment
Integration of membrane contactors or membrane contactors with pressure-driven membrane processes can lead to process enhancement
Further development of membranes for MD and FO is crucial for future advancement of these processes and their potential applications
Acknowledgements
NASA, Ames Research Center
DOD, Office of Naval Research
Prof. Glenn Miller and Prof. Ken Hunter at UNR
Joshua Cartinella, Ryan Holloway, Riz Martinetti
Thank You