Membrane Processes to Address the Global Challenge of Desalination

Transcription

1 Membrane Processes to Address the Global Challenge of Desalination Amy E. Childress Department of Civil and Environmental Engineering University of Nevada, Reno 2007 U.. Frontiers of Engineering ymposium Redmond, WA eptember 26, 2007

2 Outline alinity The Global Challenge Conventional Processes: Reverse Osmosis and Distillation Novel Processes: Forward Osmosis and Membrane Distillation Water Reuse Direct Potable Reuse Mind Over Matter? NAA Test ystem for Long-Term pace Missions ustainability: Water and Energy Brine Concentration to Achieve Zero Liquid Discharge Membrane Distillation driven by Renewable Energy Concluding Remarks

3 alinity What is it? Presence of soluble salts in soils and waters odium, calcium, magnesium, chloride, carbonate, bicarbonate, sulfate, silica What are typical concentrations? Drinking Water: <500 mg/l total dissolved solids Fresh water: <1,500 mg/l Brackish water: 1,500-20,000 mg/l eawater: 35,000-41,000 mg/l Brine or concentrate: >40,000 mg/l Why is it an issue? alts do not degrade naturally over time; accumulate until removed Increasing salinity is exacerbated by human activities Rising salinity levels have environmental and economic costs

4 Why are Engineers Concerned with alinity? Engineered ystems for drinking water treatment to achieve total maximumdaily loads for wastewater discharges Natural ystems Increased salinity in terminal lakes Mono Lake, CA

5 Desalination Today Countries with more than 1% of global desalinationcapacity U.. desalination capacity ource: Wagnick/GWI 2005

6 Desalination Capacity by Processes Global U.. ME Distillation 3% Other 5% VC 5% ED 5% Reverse Osmosis 46% Reverse Osmosis 69% MF Distillation 36% MF 1% ED 9% VC 3% Other 2% MED 1% Nanofiltration 15% ource: Wagnick/GWI 2005

7 Desalination Capacity by ource Global U.. Brine <1% Pure 5% Waste 6% River 9% eawater 56% Brackish 24% Brackish 51% River 26% Waste 9% Pure 7% Brine <1% eawater 7% ource: Wagnick/GWI 2005

8 Reverse Osmosis eparation Membrane Feed Permeate DP Produces water with <500 mg/l salts Less energy intensive than distillation (~10x less) But complicated by membrane fouling issues Possible solution: forward osmosis as pretreatment for reverse osmosis

9 Osmosis and Forward Osmosis membrane osmotic pressure Brine Water Brine Water Brine Water/ Feed Osmosis Equilibrium Brine Draw olution (D) Forward Osmosis (FO)

10 Impaired Water Forward Osmosis as Pretreatment for Reverse Osmosis Forward Osmosis 5-9% alt D Reverse Osmosis salt water 3-5% alt D Concentrated Impaired water Clean Water

11 Water Reuse Indirect nonpotable aquifer recharge for subsequent nonpotable use Direct nonpotable water reclaimed for watering golf courses, public parks, Indirect potable aquifer recharge for subsequent potable use (e.g., OCWD) or when a drinking water intake lies downstream of another municipality s wastewater facility (e.g., Las Vegas wash) Direct potable reuse

12 Waterworld Test Unit

13 NAA Test Unit

14 Water and Wastewater in pace Fresh water supply: hort missions full supply taken from earth International pace tation (I) periodic resupply Long-range, long-duration MUT RECYCLE AND REUE Without careful recycling, 40,000 pounds of water from Earth would be required to resupply a minimum of four crewmembers per year

15 pace Water Recycling ystem needs to reclaim wastewater from several sources: Hygiene (~25 l/person/day) Humidity condensed from the air (~1.8 l/person/day) Urine (~2 l/person/day) needs to: be reliable, durable, redundant, capable of high recoveries, economical, and lightweight operate autonomically with low maintenance have minimal consumables

16 Membrane Processes and specifically, the reverse osmosis process Advantages: High rejection, durability, small footprint, simple operation, minimal resupply of consumables Disadvantages: usceptible to fouling by dissolved and particulate materials such as surfactants Allows the passage of small molecules such as urea and endocrine disrupting compounds Must be used in combination with other processes

17 Original Direct Osmotic Concentration Concept

18 Original NAA DOC ystem

19 Comparison of ystem Performance I Water Recycling ystem Bio-Reactor VPCAR Direct Osmotic Concentration ystem Re-supply 413 kg/year 119 kg/year 0 kg/year? # of Independent Processors Feed treams Weight 193 kg 396 kg 68 kg 163 kg Volume 1.1 m m m m 3 Total subsystem power 61.5 Whr/kg 1108 Whr/kg Whr/kg? Recovery Rate 99% % 97%? cheduled Maintenance every 50 days Unknown 0?

20 chematic of Original DOC Test Unit Hygiene WW + Humidity Condensate Forward Osmosis Forward Osmosis/ Osmotic Distillation Conc. WW + Urine Reverse Osmosis Catalytic Oxidation Final Waste Developed under NAA BIR by Hydration Technologies, Inc.

21 Forward Osmosis/Osmotic Distillation Dual-Membrane Contactor emi-permeable Forward Osmosis Membrane diffusion Microporous Osmotic Distillation Membrane evaporation

22 Dual-Membrane Contactor Microporous Osmotic Distillation emi- Permeable Forward Osmosis

23 The RO ubsystem Brine Tank P F Pass 1A DOC#1 ŒDP ŒDP R Pass 1B DOC#2 ØDP ØDP Concentrated Draw olution P Pass 2 F R P Pass 3 F Pass 4 R P Product Water

24 Comparison of ystem Performance I Water Recycling ystem Bio-Reactor VPCAR Direct Osmotic Concentration ystem Re-supply 413 kg/year 119 kg/year 0 kg/year ~20 kg/year # of Independent Processors Feed treams Weight 193 kg 396 kg 68 kg 163 kg Volume 1.1 m m m m 3 Total subsystem power 61.5 Whr/kg 1108 Whr/kg Whr/kg Wh/kg Recovery Rate 99% % 97% > 92% cheduled Maintenance every 50 days Unknown 0 Unknown

25 Major Issue: Low Mass Transport in Dual Membrane Contactor Low mass transport in forward osmosis/osmotic distillation subsystem Low flux and recovery (was designed to recover approximately 10% of the wastewater; practically recover less than 2%) Flooding of osmotic distillation membrane resulting in passage of urea Potential solution: replace dual forward osmosis/osmotic distillation process with membrane distillation

26 Membrane Distillation Flux vapors diffuse through pores and directly condense into cold stream J = A * * ( wf wp P P )

27 Membrane Distillation Compared to distillation, requires only small temperature differences Can use low-grade energy/waste heat sources Compared to reverse osmosis, does not allow the passage of small non-volatile molecules Can provide removal of urea and endocrine-disrupting chemicals Compared to osmotic distillation, has much higher driving force for mass transfer Will produce higher fluxes

28 Improved DOC Concept

29 FO/MD Potable Reuse Test Unit Hygiene WW Forward Osmosis Membrane Distillation Humidity Condensate + Urine Reverse Osmosis Catalytic Oxidation Final Waste

30 Membrane Distillation for Urea Removal Water Flux, L/m 2 -hr T f = 40 C, T p = 20 C operating at 95% recovery Water Flux Water Recovery operating at 96% recovery Water Recovery, % Elapsed Time, hr ample Water Recovery % Rejection, % Urea Ammonia >99.9 >99.9 >99.9 >99.9 >99.9 >99.9

31 Endocrine Disrupting Chemicals The effect in fish has been proven; but is the effect transferable to humans? During long-term space missions, crew members will consume water that is continuously recycled; contaminants may be concentrated Trace contaminants, and particularly endocrinedisrupting chemicals (EDCs), must be removed

32 Endocrine Disrupting Chemical Rejection by Membrane Distillation Water Flux, l/m 2 -hr water flux E1 rejection E2 rejection Elapsed Time, hr Rejection, %

33 Where is the Technology Now? In terms of NAA undergoing long-term testing at NAA ARC going into competition in 2008 (against 3 distillation processes) In terms of terrestrial applications MD for seawater desalination FO as pretreatment for desalination MD and FO for brine concentration FO for centrate treatment MD for solar pond energy recovery

34 Water and Energy: Inextricably Bound Brine Concentration to Achieve Zero Liquid Discharge Membrane Distillation Driven by Renewable Energy

35 Cross Flow Operation Zero Liquid Discharge Feed Concentrate Permeate To achieve zero liquid discharge, the reverse osmosis concentrate stream needs to be further treated This can become energy intensive

36 Driving Force in Membrane Distillation

37 Effect of Feed alt Concentration on Flux in Membrane Distillation T f = 40 C, T p = 20 C, P f = 1.1 atm, P p = 0.64 atm Water Flux, kg/m 2 -hr T45 T22 PP22 Water Flux, kg/m 2 -hr T45 T22 PP NaCl Concentration, g/l ea alt Concentration, g/l

38 Brine Concentration Brine A Brine B Water Flux, L/m 2 -hr High Temperature VEDCMD T = 40 o C Brine A Brine B Low Temperature VEDCMD T = 20 o C Brine A Brine B Feed Concentration, g/l T Water Flux, L/m 2 -hr High Temperature VEDCMD Low Temperature VEDCMD FO Feed Concentration, g/l T

39 olar-powered Membrane Distillation Targeting remote, developing regions mall-scale, autonomous solutions Combination of two technologies Energy conversion Desalination Desalination by using alternative energy: Review and state of the art E. Mathioulakis, V. Belessiotis, and E. Delyannis Desalination 203 (2007)

40 Membrane Distillation Powered by olar Pond Promising solution to treat concentrate from membrane processes or to decrease salinity in terminal lakes saline water concentrated in solar pond pond provides thermal storage and energy to drive membrane distillation salinity of lake is diluted and slowly reduced Incident solar radiation (100%) Heat losses to atmosphere (84%) UCZ NCZ LCZ Heat losses to ground (2%) Useful heat (14%)

41 Concluding Remarks There is no single best method for desalination Hybrid technologies We will use direct potable reuse. one day! Immediate applications of membrane distillation appear to be more niche-type applications instead of large-scale seawater desalination Forward osmosis as pretreatment for reverse osmosis (or other desalination processes) has numerous applications Elimelech research group at Yale University studying novel NH 3 /CO 2 forward osmosis process Needs New membranes specifically developed for membrane distillation Commercial competition for forward osmosis membrane New membrane modules / packing for forward osmosis and membrane distillation

42 Acknowledgements Dr. Tzahi Cath, Riz Martinetti, Josh Cartinella, Pancho uarez, Mark Hausner National Aeronautics and pace Administration Office of Naval Research Bureau of Reclamation Carollo Engineers Eastern Municipal Water District Department of Energy Hydration Technologies, Inc.