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Electrodialysis/Reverse Osmosis to Electrodialysis/Reverse Osmosis to Recover Dissolved Organics from Recover Dissolved Organics from

SeawaterSeawater

Peter H. Pfromm, Tarl VetterPeter H. Pfromm, Tarl VetterDepartment of Chemical Engineering, Department of Chemical Engineering,

Kansas State UniversityKansas State UniversityManhattan, KansasManhattan, Kansas

E. Michael Perdue, Ellery Ingall, E. Michael Perdue, Ellery Ingall, Jean-FranJean-Franççois Koprivnjakois Koprivnjak

School of Earth and Atmospheric SciencesSchool of Earth and Atmospheric SciencesGeorgia Institute of TechnologyGeorgia Institute of Technology

Atlanta, GeorgiaAtlanta, Georgia

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Overview

• Introduction and Motivation• Electrodialysis• Reverse Osmosis• Combined Process• Process Characterization• Experiments/Results

• Conclusions and Outlook

3 Index•Source: NASA•http://earthobservatory.nasa.gov/Library/CarbonCycle

Units: Gigatons C, GtC/yr(1 GtC= 109 tons of carbon)

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Earth scientists would like to know: • Composition of carbon reservoirs• Origin/fate of carbon reservoirs

The problem with DOC in the oceans:

• Only 1 gram of carbon in 1000 liters of seawater......

• Salt

The approach: • Engineers and scientists collaborate• Develop a new separation approach

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What is marine dissolved organic carbon (DOC)?

~30wt% of DOC is “high molecular weight” (HMW) >1000 Da

~70wt% of DOC is “low molecular weight” (LMW) <1000 Da

DOC is composed of many types of molecules, examples:

Humic Species

Aminosugars

Polysaccharides

Aromatics

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How do you detect marine dissolved organic carbon (DOC)?

Not a trivial issue: reasonably accurate part-per-billion level analysis for organic carbon in a high-salt (chloride) matrix.

Shimadzu TOC-VCSN high-temperature catalytic oxidation analyzer

Sample is acidified to remove inorganic carbon, then combusted over Pt catalyst and CO2 is detected by infrared

Many papers, book chapters, and meetings are dedicated to this issue. Perdue at Georgia Tech is one of the well known experts on this.

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35 g/L salts

~ 0.001 g/L=1 ppm DOC

Solid DOC sample

Salt

Water

Process

The issue: recover pure DOC for scientific analysis. The problem: salt

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State of the Art Recovery

Ultrafiltration Adsorption Methods

Pore

Tangential Flow

Water Salt LMW DOC

Salt

~30% DOC

Only recovers High Molecular Weight DOC (>1000 Da)

Salt still present in final sample

Seawater

Resin Columns

Porous Non-polar

Resin

Seawater with remaining DOC

Only recovers select species (humic, etc)

Must use pH or other method to desorb

100-300 μm

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35 g/L salts

~ 1 ppm DOC

Solid DOC sample

Salt

Water

Process

Reverse Osmosis

Electro-dialysis

New Approach:RO removes fresh water concentrating

salt and DOC

ED removes salt with minimal loss of uncharged species

Freeze Dry

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RO

ED The Processes

Electrodialysis Reverse Osmosis

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Electrodialysis Spacers and Membranes

Astom AMX/CMX

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Electrodialysis

+

C C C CA A

-

Na+

Cl-

Cl-

Cl-Na+

Na+

Na+

Na+

Diluate/Feed

Diluate Return

CathodeAnode

Concentrate Return

Concentrate

+

C C C CA A

-

Na+

Cl-

Cl-

Cl-

Na+

Na+

Na+

Na+

Diluate/Feed

Diluate Return

CathodeAnode

Na+

Concentrate Return

+ -

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Electrodialysis Characterization Limiting Current (Ilim)

0

5

10

15

20

25

30

0 10 20 30 40 50

Conductivity (mS/cm)

Limiting Current Density (Amps)

Reapp = 38

Reapp = 90

vRh

apparent

4Re

Limiting Current (Amps)

Temperature: 25°C

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RO

ED The Processes

Electrodialysis Reverse Osmosis

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Water

Salt

~ Pure Water

Low Concentration

Feed

Higher Concentration

Retentate Water Salt

Flow

High Pressure

Discarded Permeate

0.2 μm

http://www.dow.com/PublishedLiterature/

Reverse Osmosis

Water

Polyester fabric

120 μm

40 μmMicroporous polysulfone

Polyamide barrier

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Spiral Wound RO Module

http://www.purewaterplanet.com/images/ROMembrane.jpg

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0

5

10

15

20

25

30

35

40

0 2 4 6 8 10 12 14 16 18

Conductivity (mS/cm)

Permeate Flowrate (mL/s)

180 psi

205 psi

150 psi

120 psi

90 psi

60 psi

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0 50 100 150 200

Operating Pressure (psi)

Stage Cut

0.99 mS/cm

4.11 mS/cm

7.80 mS/cm

12.12 mS/cm0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0 50 100 150 200

Operating Pressure (psi)

Stage Cut

0.99 mS/cm

4.11 mS/cm

7.80 mS/cm

12.12 mS/cm

0

5

10

15

20

25

30

35

40

0 2 4 6 8 10 12 14 16 18

Conductivity (mS/cm)

Permeate Flowrate (mL/s)

180 psi

205 psi

150 psi

120 psi

90 psi

60 psi

PermeateRetentate PermeateRetentate

High Feed Flow Rate

Low Feed Flow Rate

Small Stage Cut

Large Stage Cut

mss T

CAKQ

Reverse Osmosis Characterization

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RO

Unit

Electrodialysis Stack

Combined Process Operation

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Overall

Drive tosite

Purge ED/RO systems

Freeze~10 l

Freeze dryNMR....

Retrieveseawatersample(200- 400 l)

ED/RO 200 l seawater

Hope for good weather!

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Experiment Date Starting Concentration (ppm) Sample Type Experimental Objective7/12/2005 0.18 Artificial Seawater9/28/2005 0.11 Artificial Seawater10/18/2005 0.05 Artificial Seawater11/9/2005 0.01 Artificial Seawater3/6/2006 0.22 Artificial Seawater4/3/2006 0.06 Artificial Seawater5/26/2006 1.95 Brackish Water6/8/2006 2.24 Brackish Water7/3/2006 3.30 Brackish Water7/18/2006 1.20 Seawater (ship board)7/19/2006 0.93 Seawater (ship board)7/20/2006 1.19 Seawater (ship board)

7/20, 7/21/2006 1.21 Seawater (ship board)7/21/2006 0.82 Seawater (ship board)7/22/2006 1.10 Seawater (ship board)7/23/2006 0.20 Blank (ship board) Examine DOC leaching

7/24, 7/25/2006 1.22 Seawater (ship board) Adjustment of ED operation7/25, 7/26/2006 1.10 Seawater (ship board) Attempt total desalination7/26, 7/27/2006 1.02 Seawater (ship board) Examine high concentration

7/27/2006 5.08 Brackish Water (ship board) Comparison of DOC recovery8/14/2006 0.96 Seawater Lab reproduction of seawater8/18/2006 1.08 Seawater Test new membranes

Determination of operating parameters and modes

Examine recovery of natural DOC species

Recovery of DOC from various locations and depths

Experimentation

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Examples:

Three shipboardexperiments

Start with 200 literseawater

0

40

80

120

160

200

240

0 2 4 6

Time [hrs]

DOCretained

[mg]

ED & RO EDED

0

25

50

75

100

0 2 4 6

Time [hrs]

%removed

ED & RO EDED

S

Salt

Water

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0

2

4

6

8

10

12

14

16

18

20

0 10 20 30 40 50

Diluate (seawater) conductivity [mS/cm]

ED current

[A]

initialseawater sample

201 litersinitial ED only

RO&ED: water removalbalanced by salt removalto maintain conductivity

limiting current

applied current

final ED

ED: follow the limiting current density

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0

10

20

30

40

50

60

70

80

90

100

Diluate DOC Recovery (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Date of Experiment5-26 6-8 7-3 7-18 7-19 7-20 7-21 7-21 7-22 7-24 7-25 7-26 7-27 8-14 8-18

Brackish

Seawater Lab Lab Lab Lab Lab

Summary

24

1421

21

15

21

17

1526

1036 7

6

3

2

Final DOC ppm

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Conclusions• ED/RO can recover a significant

fraction of DOC from seawater (60%-90%)

• The process is fast, allowing treatment of large volumes of samples

• We are able to reduce salt concentration and water volume to make a sample ready for freeze drying

• Preliminary results by NMR: differences from the high MW fraction that was previously available.

• Scientists and engineers think differently but can communicate and collaborate successfully

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Outlook• Examine the impact of

temperature• Further minimize losses to the

ED concentrate, possibly with different membranes

• Examine modulation of the ED current to optimize DOC recovery

• Applications for recovery of sensitive molecules (proteins, enzymes)?

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Acknowledgements• This work is supported by the National Science

Foundation, Grants No. 0425624 and 0425603. (Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of NSF)

• Dr. Mary Rezac who initiated the contact between scientists and engineers that made this work possible.

• Poulomi Sannigrahi for help at sea and in the laboratory.

• We would especially like to thank Captain Raymond Sweatte and the excellent crew of the R/V Savannah for two great and productive cruises.