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

salts

salts

PrimaryDesalination

Concentrate Treatment

SecondaryDesalination

Final ZLDEvaporation

Concentrate

5

Recovery in RO is limited by sparingly soluble salts

Concentrate is treated to remove salts Allowing

further recovery by desalination

COSTS ARE MINIMIZED BY MAXIMIZING RECOVERY IN SECONDARY DESALINATION

Product Water

salts

salts

PrimaryDesalination

Concentrate Treatment

SecondaryDesalinationConcentrate

Final ZLDEvaporation

$2 -$3 /kgal

$13 /kgal

6

TECHNOLOGY OPTIONS

ROElectro-dialysis Reversal

Electro-dialysis Metathesis

Vibratory Shear Enhanced Process

Forward Osmosis

Membrane Distillation

Thermo- Ionic Desalination

Capacitative Distillation

Seco

ndar

y De

salin

atio

n

Chemical Softening

Fluidized Bed Crystallizer

MIEX Ion Exchange Coagulation Activated

Alumina Biological

Conc

entra

te

Trea

tmen

t

Thermal Evaporation Pond

Salt Gradient Solar Pond

Wind aided intensified evaporation (WAIV)

Dew-vaporation Turbomister

Fina

l ZLD

Ev

apor

atio

n

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

Evaporation pond

Product Water

Fluidized bed crystallizer

Filter

BrineConcentrator

Secondary RO

Product Water

Concentrate

Concentrate

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

0

0.2

0.4

0.6

0.8

1

1.2

7 8 9 10 11 12

pH

Frac

tion

rem

aini

ng

Ca Test 2

Ca Test 3

Ba Test 2

Ba Test 3

Calcium and barium removals in fluidized bed crystallizer at pH 8.3 comparable to those in chemical at pH 10.5.

Test 2 = Chemical softeningTest 3 = Fluidized bed crystallizer

12

TREATMENT COSTS WERE REDUCED BY 50 TO 60 PERCENT

$-

$2.00

$4.00

$6.00

$8.00

$10.00

$12.00

$14.00

BH SNWA COP Scott SAWS

Trea

tmen

t cos

t ($/

kgal

)

Benchmark process Evaluated process13

ENERGY CONSUMPTION WAS REDUCED BY 65 TO 75 PERCENT

0%

20%

40%

60%

80%

100%

BH SNWA COP Scott SAWS

Per

cent

redu

ctio

n (k

Wh/

kgal

pro

duct

)

14

ZLD DESALINATION USING ELECTRODIALYSIS METATHESIS (EDM) (PROJECT #4163)

Primary RO

Pond, WAIV, or thermal

salts

EDMproduct water

product water

concentrate

concentrate

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.

• A stack contains hundreds of cell pairs.

+

+

+

-

-

-

+

+

+

-

-

-

-

+

-

++

-(-)

cathode

(+)

anode

concentratecompartment

diluatecompartment

cation exchange membrane

anion exchange membrane

electrolyte solution

repeating cell pair

concentrate

diluate

feed

concentrate

17

IN BASIC ELECTRODIALYSIS ALL REMOVED IONS ARE CONTAINED IN A SINGLE CONCENTRATE STREAM

Cell pair

C CA

FeedConcentrate

DiluateConcentrate

(+)

anode

(-)

cathodeSO42-

Cl-

Ca2+

Mg2+

Na+

CaSO4 BaSO4 CaCO3

18

EDM CONCENTRATE IS SEPARATED INTO TWO HIGHLY SOLUBLE STREAMS

Cell set (4 membranes, 4 cells)

SC CA

FeedConcentrate 1Na with anions

(+)

anode

(-)

cathode

SO42-

Cl-

Ca2+

Mg2+

Na+

SCSA

Concentrate 2Cl with cations

NaClNaCl

Na+

Cl-

Na with anions

Cl with cations

19

SOLUBILITIES OF NA2SO4, CACL2, AND NACL ARE 15 TO 35 TIMES SOLUBILITY OF CASO4

Solubility of Salts in water

Maximum 3.1M at 33°C

NaCl

CaCl2

CaSO4

Na2SO4

20

DEVELOPMENT OF SOLID PRODUCTS WITH EDM APPROACH

Primary RO

Pond, WAIV, or thermal

salt

EDM

CaSO4CaCO3 Mg(OH)2

NaCl recycled to EDM

recycled NaCl

product water

concentrate

NaOH NaOH

NaCl

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

40%

60%

80%

100%

0 5000 10000 15000 20000 25000 30000

ED

M re

cove

ry

Raw water TDS (mg/L)

97% at 1400 mg/L TDS

87% at 5300 mg/L TDS

76% at 27,700 mg/L TDS

25

EDM ENERGY CONSUMPTION INCREASED AS TDS INCREASED

26

y = 0.004x + 2.432R² = 0.977

0

20

40

60

80

100

120

140

0 5000 10000 15000 20000 25000 30000

ED

M e

nerg

y (k

Wh/

kgal

)

Raw water TDS (mg/L)

EDM TREATMENT COSTS COMPARED WITH THERMAL

R2 = 0.97

R2 = 0.99

$-

$5

$10

$15

$20

$25

$30

$35

$40

$45

0 5000 10000 15000 20000 25000 30000

ZLD

trea

tmen

t cos

t ($/

kgal

)

Raw water TDS (mg/L)

EDM thermal

EDM less expensive

Transition range

Thermal less expensive

27

EDM METHOD WAS PARTICULARLY COST EFFECTIVE FOR LOW TDS SOURCES

$-

$2.00

$4.00

$6.00

$8.00

$10.00

$12.00

560 630 750 1412

Trea

tmen

t cos

t ($/

kgal

con

cent

rate

)

Raw Water TDS (mg/L)

ZLD Treatment Cost $ per 1000 gal Concentrate EDM vs. Thermal

EDM

Thermal

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• City of Scottsdale• San Antonio Water & Sewer• City of Beverly Hills• SNWA• California Energy Commission

• Orlando Utilities Commission• Tampa Bay Water• South Florida WMD• Southwest Florida WMD• St. Johns River WMD• Water Research Foundation

30

MSSC2011 Annual Salinity SummitFEBRUARY 17-18SAN ANTONIO, TEXAS

Zero Liquid Discharge DesalinationRick BondBondRG@bv.com

31