Zero Liquid Discharge Desalination
Rick Bond, Vasu Veerapaneni
CONCENTRATE MANAGEMENT OPTIONS
• Direct discharge to surface water.
• Discharge to POTW.
• Underground injection.
• Zero Liquid Discharge.
Discharge
options
Where
discharge is
constrained or
restricted
2
MOTIVATION TO TREAT AND RECOVER
CONCENTRATE
• Discharge options that do not remove salt from the water
cycle are unsustainable.
• Viewed as a resource rather than waste, concentrate can
be treated to recover potable water and salt products.
• Complete treatment to recover all of the concentrate as
potable water is referred to as Zero Liquid Discharge (ZLD)
desalination.
3
ESTABLISHED ZLD TECHNOLOGIES ARE EXPENSIVE
• Thermal desalination –
expensive and energy
intensive.

Evaporation ponds –
expensive, require large
land areas, and
evaporated water is a
lost resource.
4
NEW ZLD APPROACHES HAVE FOUR BASIC STEPS
Product Water
Primary
Desalination
Concentrate
Recovery in RO
is limited by
sparingly
soluble salts
Concentrate
Treatment
Secondary
Desalination
salts
Concentrate is
treated to
remove salts
Final ZLD
Evaporation
salts
Allowing
further
recovery by
desalination
5
COSTS ARE MINIMIZED BY MAXIMIZING
RECOVERY IN SECONDARY DESALINATION
Product Water
Primary
Desalination
Concentrate
$2 -$3 /kgal
Concentrate
Treatment
Secondary
Desalination
salts
Final ZLD
Evaporation
$13 /kgal
salts
6
Final ZLD
Evaporation
Secondary
Desalination
Concentrate
Treatment
TECHNOLOGY OPTIONS
Chemical
Softening
RO
Thermal
Fluidized
Bed
Crystallizer
Electrodialysis
Reversal
Electrodialysis
Metathesis
Evaporation
Pond
Ion
Exchange
MIEX
Coagulation
Activated
Alumina
Vibratory ThermoMembrane Capacitative
Shear
Ionic
Enhanced
Distillation Distillation
Desalination
Process
Salt
Gradient
Solar Pond
Wind aided
intensified
evaporation
(WAIV)
Dewvaporation
Biological
Forward
Osmosis
Turbomister
7
RECOVERY IN SECONDARY DESALINATION IS
LIMITED BY MEMBRANE FOULING
• Inorganic scalants - CaCO3, BaSO4, CaSO4, SiO2.
• Natural organic matter (NOM).
• Fouling potential of NOM is increased by complexation
reactions between NOM and Ca.
8
TWO DIFFERENT APPROACHES WERE EVALUATED IN
RESEARCH CONDUCTED TO REDUCE ZLD COSTS
• Zero Liquid Discharge for Inland Desalination
• AwwaRF Project #3010 (2005 – 2007)
• Brackish groundwater, surface water, reclaimed water
• Zero Liquid Discharge Desalination of Waters with High Organic
Content
• Water Research Foundation Project #4163 (2008 – 2010)
• Brackish water with high concentrations of natural organic
matter
9
ZLD WITH FLUIDIZED BED CRYSTALLIZATION
(PROJECT #3010)
Primary RO
Product Water
Product Water
Filter
Secondary RO
Concentrate
Fluidized bed
crystallizer
Brine
Concentrator
Concentrate
Evaporation pond
10
FLUIDIZED BED CRYSTALLIZER (CRYSTALACTOR)
• Ca and Ba are removed by
precipitation onto CaCO3
crystals.
• Used extensively in Europe
for softening.
• Produces near anhydrous
crystals (90% dry) therefore
low solids volume.
• High loading rate, (80 m/h
(33 gpm/sf) small footprint.
11
FLUIDIZED BED CRYSTALLIZER VS. CHEMICAL
SOFTENING
1.2
Test 2 = Chemical softening
Test 3 = Fluidized bed crystallizer
Fraction remaining
1
Calcium and barium
removals in fluidized bed
crystallizer at pH 8.3
comparable to those in
chemical at pH 10.5.
0.8
0.6
Ca Test 2
Ca Test 3
Ba Test 2
Ba Test 3
0.4
0.2
0
7
8
9
10
11
12
pH
12
TREATMENT COSTS WERE REDUCED BY 50
TO 60 PERCENT
$14.00
Treatment cost ($/kgal)
$12.00
$10.00
$8.00
$6.00
$4.00
$2.00
$BH
SNWA
COP
Benchmark process
Scott
SAWS
Evaluated process
13
ENERGY CONSUMPTION WAS REDUCED BY
65 TO 75 PERCENT
Percent reduction (kWh/kgal product)
100%
80%
60%
40%
20%
0%
BH
SNWA
COP
Scott
SAWS
14
ZLD DESALINATION USING ELECTRODIALYSIS
METATHESIS (EDM) (PROJECT #4163)
Primary RO
product water
product water
EDM
concentrate
concentrate
Pond,
WAIV, or
thermal
salts
15
ELECTRODIALYSIS METATHESIS (EDM) IS A
NEW ELECTRODIALYSIS TECHNOLOGY
• Innovative arrangement of membranes used to separate
concentrate into two streams of highly soluble salts.
• Although this variation is new, the technology and the
membranes have been used for decades.
16
ELECTRODIALYSIS IS A MEMBRANE SEPARATION
PROCESS DRIVEN BY ELECTRIC POTENTIAL
• Driving force is electric
potential between anode
and cathode.
• Cell pair comprises cation
and anion exchange
membranes, diluate cell,
and concentrate cell.
• Ions are extracted from
diluate compartment and
held in concentrate
compartment.
cation
exchange
membrane
anion
exchange
membrane
diluate
-
-
(+)
-
-
+
+
anode
-
• A stack contains hundreds
of cell pairs.
+
+
+
feed
electrolyte
solution
concentrate
- +
(-)
-
+
+
-
cathode
+
concentrate
diluate
compartment
concentrate
compartment
repeating cell pair
17
IN BASIC ELECTRODIALYSIS ALL REMOVED
IONS ARE CONTAINED IN A SINGLE
CONCENTRATE STREAM
Cell pair
CaSO4
BaSO4
CaCO3
Diluate
Concentrate
C
C
A
Mg2+
(+)
anode
Na+
Cl-
(-)
SO42-
cathode
Ca2+
Concentrate
Feed
18
EDM CONCENTRATE IS SEPARATED INTO
TWO HIGHLY SOLUBLE STREAMS
Cell set (4 membranes, 4 cells)
Na with
anions
Cl with
cations
C
A
SC
SC
SA
Mg2+
(+)
Cl-
(-)
ClNa+
Na+
anode
cathode
SO42-
NaCl
Concentrate 1
Na with anions
Ca2+
Feed
Concentrate 2
Cl with cations
NaCl
19
SOLUBILITIES OF NA2SO4, CACL2, AND NACL
ARE 15 TO 35 TIMES SOLUBILITY OF CASO4
Solubility of Salts in water
CaCl2
Maximum 3.1M at 33°C
NaCl
Na2SO4
CaSO4
20
DEVELOPMENT OF SOLID PRODUCTS WITH
EDM APPROACH
product water
Primary RO
recycled NaCl
NaCl recycled to
EDM
concentrate
NaCl
EDM
NaOH
NaOH
Pond, WAIV,
or thermal
CaSO4
CaCO3
Mg(OH)2
salt
21
EDM WATER QUALITY RESULTS
• EDM effectively separated the concentrate into two streams
of highly soluble salts.
• Silica and TOC went through EDM largely unaffected and
therefore posed no membrane fouling risk.
• No inorganic or organic compound concentrations were
found in any of the EDM streams that would be considered
potential membrane fouling threats.
22
EDM PILOT RESULTS WITH NF CONCENTRATE
Analyte
EDM Feed
Concentrate 1
Concentrate 2
Calcium
284
51
14,900
Magnesium
69
5
2220
Sodium
376
38,600
14,000
Chloride
853
38,800
53,700
Sulfate
421
42,400
nondetect
Bicarbonate
29
350
nondetect
TOC
19
36
2
EDM concentrate was effectively separated into two
streams of highly soluble salts: sodium with anions
and chloride with cations.
23
EDM RECOVERY IN THE PILOT TESTS
EXCEEDED 99%
Concentrate
Source
EDM Recovery
Rate of water
transfer
(mol/eq)
NF
99.9%
7.7
RO
99.8%
7.4
EDR
99.9%
8.2
NF
99.9%
7.6
Recovery in EDM depends of the rate of water
transfer by osmosis and electroosmosis. The rate of
water transfer in electrodialysis is proportional to the
equivalents of ions transferred.
24
EDM RECOVERY DECREASED WITH TDS
100%
97% at 1400 mg/L TDS
87% at 5300 mg/L TDS
EDM recovery
80%
76% at 27,700 mg/L TDS
60%
40%
0
5000
10000
15000
20000
25000
30000
Raw water TDS (mg/L)
25
EDM ENERGY CONSUMPTION INCREASED
AS TDS INCREASED
140
y = 0.004x + 2.432
R² = 0.977
EDM energy (kWh/kgal)
120
100
80
60
40
20
0
0
5000
10000
15000
20000
25000
30000
Raw water TDS (mg/L)
26
EDM TREATMENT COSTS COMPARED WITH
THERMAL
$45
R2 = 0.97
ZLD treatment cost ($/kgal)
$40
EDM less
expensive
$35
Transition
range
Thermal less
expensive
$30
$25
R2 = 0.99
$20
$15
$10
$5
$0
5000
10000
15000
20000
25000
30000
Raw water TDS (mg/L)
EDM
thermal
27
EDM METHOD WAS PARTICULARLY COST
EFFECTIVE FOR LOW TDS SOURCES
ZLD Treatment Cost $ per 1000 gal Concentrate EDM vs. Thermal
Treatment cost ($/kgal concentrate)
$12.00
$10.00
$8.00
$6.00
EDM
Thermal
$4.00
$2.00
$560
630
750
1412
Raw Water TDS (mg/L)
28
SUMMARY
• Concentrate management will become increasingly
important as we strive to manage salinity and meet water
demands.
• Two ZLD methods were evaluated in AwwaRF/WRF research
projects: fluidized bed crystallization and EDM.
• Each showed potential to reduce ZLD treatment costs by
more than 50 percent.
• Best ZLD method may depend on water quality
characteristics and treatment goals.
29
ACKNOWLEDGEMENTS
• City of Phoenix
• Orlando Utilities Commission
• City of Scottsdale
• Tampa Bay Water
• San Antonio Water & Sewer
• South Florida WMD
• City of Beverly Hills
• Southwest Florida WMD
• SNWA
• St. Johns River WMD
• California Energy Commission
• Water Research Foundation
30
MSSC
2011 Annual Salinity Summit
FEBRUARY 17-18
SAN ANTONIO, TEXAS
Zero Liquid Discharge Desalination
Rick Bond
BondRG@bv.com
31