Desalination as a Source of
Fresh Water
Desalination 101
Professor Tzahi Y. Cath
Colorado School of Mines
Department of Civil and Environmental Engineering
Advanced Water Technology Center (AQWATEC)
September 20, 2016
Presentation Overview
Source water requiring desalination
Properties of water and their impact on desalination
Desalination technologies
Water recovery and cost of desalination
Issues associated with desalination
Pre-treatment of source water
Energy demand and energy recovery
Concentrate management
Future technologies
Desalination of Impaired Water
Common water sources requiring desalination
Seawater
Brackish groundwater
Industrial water (high purity)
Domestic and industrial wastewater for advanced reuse
Surface water containing specific dissolved solids
Constituents requiring removal by desalination
Dissolved solids, simple salts/ions, heavy metals, nutrients,
hardness, organic contaminant of emerging concern, etc.
Colligative Properties of
Ionic Solutions Properties of solution that depend on the number of solute
molecules present, but not on the nature of the solute
Osmotic pressure, vapor pressure, freezing point
depression, and boiling point elevation are examples of
colligative properties
Osmotic pressure and vapor pressure are two properties of
solution that play a major role in desalination
Vapor Pressure of Water
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0 20 40 60 80 100
Part
ial vap
or
pre
ssu
re o
f w
ate
r, a
tm
Temperature, °C
DI
150,000 mg/L
300,000 mg/L
500,000 mg/L
Increases with
increasing
temperature
Minimally
decreases with
increasing
concentration
Multiple-effect Evaporator (MED)
Courtesy of Tom Pankratz, [email protected]
Multistage Flash Evaporation (MSF)
Courtesy of Tom Pankratz, [email protected]
Vapour Compression Brine
Concentrator
Centrifugal
Compressor Steam
Boiling
Chamber
Heat
Exchanger
Heat
Element
Distillate
Preheated
Feedwater
Feedwater
Heat Exchanger
Feedwater
Courtesy of Tom Pankratz, [email protected]
Osmotic Pressure of Solution
Osmosis
Brine Feed
Increases with increasing solute concentration
Increases with increasing temperature
Osmotic Pressure of Solution
Osmosis
DP=Dp
Brine Feed
Increases with increasing solute concentration
Increases with increasing temperature
GFD = LMH x 1.7
Ranges of Pressure and Flux
Process
Pressure Water Flux
PSI kPa gal/ft2/day
(GFD)
L/m2/hr
(LMH)
Nanofiltration 100 – 400 700 – 2800 15 – 30 20 – 50
Reverse Osmosis 200 – 1000 1400 – 7000 15 – 30 20 – 50
Desalination Technologies
1% 2% 3% 4% 75% 25% 50% 10% 5%
10
20
30
Sea Water RO
High Efficiency RO
Membrane • Limited Recovery • High Pressure • Simple/modular
% Total Dissolved Solids
• High recovery • Energy to boil water • Exotic metals
Crystallizer Thermal
Brine Concentrators
Sp
ecif
ic E
ner
gy, k
Wh
/m3
0
Adapted from: Oasys Water
ED/EDR
Contracted Capacity by Technology
Courtesy of Tom Pankratz, [email protected]
Water Recovery in
RO/NF Systems
Overall Recovery =10048.8 gal
100 gal
æ
èç
ö
ø÷ = 48.8%
Assuming each membrane (or each stage) operates at 20%
recovery
Total permeate from all membranes (stages) = 48.8 gal
100 gal
20 gal
80 gal
16 gal
64 gal
12.8 gal
51.2 gal
Overcoming Osmotic Pressure
+
350 psi
membrane
Seawater
35 g/L TDS
Deionized
water
Rule of thumb: 1 g/L salt ≈ 10 psi of osmotic pressure
Overcoming Osmotic Pressure
+
350 psi
700 psi
++
membrane
Seawater
35 g/L TDS
Deionized
water
Conc. Seawater
70 g/L TDS
Deionized
water
Rule of thumb: 1 g/L salt ≈ 10 psi of osmotic pressure
50% water
recovery
700 psi
++
Deionized
water
Conc. Seawater
70 g/L TDS
Overcoming Osmotic Pressure
+
350 psi
700 psi
++
membrane
Seawater
35 g/L TDS
Deionized
water
Conc. Seawater
70 g/L TDS
Deionized
water
Rule of thumb: 1 g/L salt ≈ 10 psi of osmotic pressure
50% water
recovery
700 psi
++
Deionized
water
Conc. Seawater
70 g/L TDS
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
Recovery (%)
Rela
tive O
pera
tin
g C
ost
of
Tre
atm
en
t
Brackish Water Reverse
Osmosis (BWRO)
Rela
tive B
rin
e D
isp
osal
Co
st
Moderate
High
Water Recovery and
Associated Costs
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
Recovery (%)
Rela
tive O
pera
tin
g C
ost
of
Tre
atm
en
t
Rela
tive B
rin
e D
isp
osal
Co
st
Low
High
Water Recovery and
Associated Costs
Zero Liquid Discharge (ZLD)
& Near-ZLD
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
Recovery (%)
Rela
tive O
pera
tin
g C
ost
of
Tre
atm
en
t
Rela
tive B
rin
e D
isp
osal
Co
st
Emerging
Technologies
Moderate - High
Moderate
Water Recovery and
Associated Costs
Relative Desalination Costs
Process Capital Cost
$/GPD
O&M Cost
$/kgal
Water Cost
$/kgal
($/m3)
Nanofiltration 1.00 – 1.30 0.40 – 0.70 0.60 – 1.00
(0.16 – 0.26)
Brackish water
Reverse Osmosis 1.20 – 2.50 0.80 – 1.50
1.50 – 3.00
(0.40 – 0.80)
Seawater Reverse
Osmosis 3.50 – 5.00 2.00 – 4.00
2.50 – 7.00
(0.66 – 1.85)
Courtesy of Tom Pankratz, [email protected]
GPD – gallon/day
kgal – 1,000 gallon
Seawater Reverse Osmosis
Desalination Plants
Adapted from: Global Water Intelligence (2010)
1.45
1.19
0.76 0.7 0.72
0.52 0.57 0.66
0.78
0.57
0.73
1.04 1.13
0.93
0.59 0.54
Bahamas Dhekelia Larnaca Taweelah Trinidad Ashkelon Tuas TampaBay
Skikda Hadera Cap Dijnet Chennai ShuweihatII
Ad Dur Tenes Soreq
Wate
r P
ric
e (
$/m
3)
Cost difference:
• Energy cost
• Concentrate management
• Project cost (engineering, permitting, etc.)
• Tax credits and other financial costs/incentives
• Size
Pre-treatment Removal of:
Suspended solids or emulsions
Microorganisms
Organic matter
Specific ions (iron, calcium, magnesium, silica, etc.)
From: R. J. Aaberg, Osmotic power - A new and powerful renewable energy source, ReFocus, 4 (2003) 48-50
Osmotic Power Energy Recovery:
Pressure Retarded Osmosis
Concentrate Management
Coastal
Ocean outfall
Inland
Surface discharge (bad!)
Sewer disposal (not good!)
Deep well injection
Land application/dust control
Zero liquid discharge (ZLD) (crystallization, expensive…)
Pipeline to ocean (not common)
Other Desalination Technologies:
Membrane Distillation
Heated aqueous feed solution is
brought into contact with the feed side
of a hydrophobic, microporous
membrane
Colder water or gas is in contact with
the distillate side of the membrane
Vapors diffuse through the pores and
condense in the colder stream
adapted from: http://www.water-technology.net/
Other Desalination Technologies:
Humidification-Dehumidification
Courtesy of Tom Pankratz, [email protected]
In summary…
Desalination is used for salt removal, but also for purification
of water and removal of other contaminants
Development of new membranes focuses on increasing
water flux, increasing solute rejection, and increasing
chemical resistance of membranes
Reverse osmosis is a core process to enable potable water
reuse
Desalination (especially reverse osmosis) is affordable and
provides a reliable source of potable water; and efficient
energy recovery makes it possible
Brine management is a prevailing problem, especially at
inland installations, and it drives development of high-
recovery desalination (ZLD)
Thank you
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Tzahi Cath, Ph.D.
Ben L. Fryrear Professor and AQWATEC Director
COLORADO SCHOOL OF MINES
Department of Civil and Environmental Engineering
1500 Illinois St., Golden, Colorado 80401-1887
Office: 303.273.3402
Cath URL: http://inside.mines.edu/~tcath/
AQWATEC URL: http://aqwatec.mines.edu/
ERC ReNUWIt URL: http://urbanwatererc.org/
CEE URL: http://cee.mines.edu/
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~