Latest Technologies in Water Desalination

Amy E. Childress

Department of Civil and Environmental Engineering

University of Nevada, Reno

1st Arab-American Frontiers Symposium

Kuwait Institute for Scientific Research and U.S. National Academies

October 17-19, 2011 in Kuwait City

Outline

S  Introduction

S  Fresh water scarcity

S  Alternate sources and new technologies

S  Desalination by reverse osmosis

S  Emerging Technologies for Desalination Applications

S  Membrane Distillation

S  Forward Osmosis

S  Pressure Retarded Osmosis

S  Final Remarks

Global Water Stress

Forcing water providers to rely more on alternative sources

Alternative Sources and New Technologies

Saline waters “Waste” waters

New concerns

Salinity

Recovery

Energy

Emerging Contaminants

Membrane Forward Pressure

Distillation Osmosis Retarded

Osmosis

(MD) (FO)

(PRO)

Desalination Applications and Salinity Levels

S  Seawater desalination (35-41 g\/L)

S  In-land groundwater desalination (2-6 g\/L)

S  RO brine (>40 g\/L)

S  Extreme salinity scenarios (>100 g\/L)

S  Oil and gas applications

S  Mineral mining (water is by-product)

Current Leading Desalination Technology:

Reverse Osmosis

Reverse Osmosis Separation

Concentrate Permeate

Feed ΔP

S  Produces water with <500 mg\/L salts

S  Less energy intensive than distillation (~10x less)

S  But… does have drawbacks → dual osmotic barrier (FO\/RO) or MD

1. passage of some contaminants

2. reduced driving force at high salt concentrations → osmotic dilution or MD

→ FO as pretreatment for RO

3. membrane fouling

In-Land Desalination

Drinking water

Concentrate

Brackish Groundwater Feed Drawback 4. Brine Disposal or Treatment

→ FO\/RO or MD

Seawater Desalination

Drinking water

Concentrate

High pressure

Low pressure

Pressurized Feed

Seawater Desalination

Drinking water

Concentrate

Pressure High pressure

Low pressure

Pressurized Feed

Seawater Desalination

Drinking water

Concentrate

High Salinity

Pressurized Feed Environmental Concern

Waste of Chemical Energy

Emerging Technologies:

Membrane Distillation (MD)

Forward Osmosis (FO)

Pressure Retarded Osmosis (PRO)

Direct Contact Membrane Distillation

Heated Feed Stream Cooler Distillate Stream

Hydrophobic, Microporous Membrane

Driving force: vapor pressure gradient

Driving Force in MD

Addresses RO Drawback 1: Reduced Driving Force at High Salt Concentration

Industrial Mineral Harvesting

Great Salt Lake, Utah

Tzahi Cath’s Lab at Colorado School of Mines

Desalination of

Hypersaline Lake Water

> 300 g\/L

Constituent g\/L 12 60

Cl 83 10 50

SO4 10 40

8 30

Ca 0.3 Water flux, LMH6 20

Batch recovery, %4 10

K 3 2 0

Li 0.03 0 60

Mg

Na 6 0

47

TDS

149 g\/L

20 40

Time, hr

Removal of Emerging Contaminants

Osmotic Processes Membrane Distillation

100 3.5 100

90EDC Rejection, % (a) 95

Water Flux, L\/m2-hr

EDC Rejection, %803.0water flux

70 2.5 estrone rejection 90

60 estradiol in Soap Solution 2.0 estradiol rejection

50 estrone in Soap Solution

estrone in DDW 1.5 85

0

10 20 30 40 50 60 70 80 1.0 80

0 10 20 30 40

Water Recovery, %

Elapsed Time, hr

Addresses RO Drawback 3: Passage of Some Contaminants

Membrane Distillation with Solar Energy

Salinity Gradient

Solar Pond

Membrane

Distillation

Solar Thermal, Geothermal

Waste Heat

Stand-alone energy collection\/storage and water desalination

Emerging Technologies:

Membrane Distillation (MD)

Forward Osmosis (FO)

Pressure Retarded Osmosis (PRO)

Emerging Technology:

Forward Osmosis

Osmosis and Forward Osmosis

membrane osmotic Conc Feed

pressure Draw Water

Brine Water Brine Water Solution

Osmosis Equilibrium Forward Osmosis

Impaired Water FO Pretreatment for RO

(General Concept)

Forward Concentrated Reverse

Osmosis Draw Solution Osmosis

water salt

Diluted

Draw Solution

Concentrated Clean Water

Impaired water

Addresses RO Drawback 3: Membrane Fouling

Addresses RO Drawback 3: Passage of Some Contaminants

Ammonia-Carbonate FO Process

Saline Membrane

Water

waste heat

Draw Column

Solution Distillation

NH3\/CO2

Brine Product

Water

Has potential to require less

energy than FO\/RO

Meny Elimelech’s Lab at Yale University

Emerging Technologies:

Membrane Distillation (MD)

Forward Osmosis (FO)

Pressure Retarded Osmosis (PRO)

What is Pressure-Retarded Osmosis?

S  An osmotically driven membrane process similar to RO and FO

membrane pressure>osmotic pressure pressure<osmotic pressure

Osmotic Brine Water Brine Water

pressure

Brine Water

Osmosis Reverse Osmosis Pressure Retarded

(RO) Osmosis (PRO)

What is Pressure-Retarded Osmosis?

S  An osmotically driven membrane process similar to RO and FO

S  A source of renewable and sustainable energy

PRECIPITATION

Seawater SALINATION Freshwater

Energy

global energy production from mixing in estuaries: 2,000 TWh\/y

current global energy production from all renewable sources: 10,000 TWh\/y

What is Pressure-Retarded Osmosis?

S  An osmotically driven membrane process similar to RO and FO

S  A source of renewable and sustainable energy

S  A process of capturing the energy released from the mixing of

freshwater with saltwater

River 5 g\/L Ocean 35 g\/L

What is Pressure-Retarded Osmosis?

S  An osmotically driven membrane process similar to RO and FO

S  A source of renewable and sustainable energy

S  A process of capturing the energy released from the mixing of

freshwater with saltwater

River Δπ=22.5 atm Ocean

What is Pressure-Retarded Osmosis?

S  An osmotically driven membrane process similar to RO and FO

S  A source of renewable and sustainable energy

S  A process of capturing the energy released from the mixing of

freshwater with saltwater

River

225 m

Ocean

Power Generation with PRO

chemical potential transformed to hydraulic potential

Norman, 1974

PRO System

Seawater Diluted seawater

Low L Pressure

pressure exchanger

pump

H Circulation

Seawater pump

Diluted seawater Hydroturbine and

generator

Draw solution side Diluted seawater

Membrane Low

pressure

Feed solution side

pump

Pumps Net power

Flushing Fresh water

solution

Achilli, Cath, Childress, 2009

Adapted from Loeb, 2002

Seawater Desalination

Drinking water

Concentrate

High Salinity

Pressurized Feed Environmental Concern

Waste of Chemical Energy

Proposed Energy Recovery

in Seawater Desalination

Drinking water

Impaired water

High pressure Osmotic pump

1

Feed 2

1- Energy generation

2 - Concentrate dilution

Final Remarks

S  There is no single best method for desalination

S  Water source and energy availability

S  Treatment needs

S  Sustainability considerations

S  The needs for all processes are similar:

S  Commercial competition for membranes

S  New membrane modules \/ packing

S  Cost models

S  MD, FO, and PRO have implications for wastewater

reuse

Acknowledgements

S  California Department of Water Resources

S  National Aeronautics and Space Administration

S  Office of Naval Research

S  U.S. Bureau of Reclamation

S  U.S. Department of Energy

S  Hydration Technology Innovations

S  Dr. Andrea Achilli

S  Dr. Tzahi Cath

S  Dr. Scott Tyler

S  Dr. Francisco Suarez

S  Katie Bowden, Jeri Prante,

Guiying Rao, Jeff Ruskowitz

amyec@unr.edu