1. Electrodialysis/Reverse Osmosis to Recover Dissolved Organics from Seawater
Peter H. Pfromm, Tarl Vetter
Department of Chemical Engineering,
Kansas State University
Manhattan, Kansas
E. Michael Perdue, Ellery Ingall, Jean-François Koprivnjak
School of Earth and Atmospheric Sciences
Georgia Institute of Technology
Atlanta, Georgia

2. Overview Introduction and Motivation Electrodialysis Reverse Osmosis
Combined Process
Process Characterization
Experiments/Results
Conclusions and Outlook

3. DOC ~ 1ppm Units: Gigatons C, GtC/yr (1 GtC= 109 tons of carbon)
Source: NASA

4. 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

5. 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:
Aminosugars
Aromatics
Polysaccharides
Humic Species

6. 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.

7. The issue: recover pure DOC for scientific analysis. The problem: salt
Water
Process ?
Solid DOC sample
Salt
35 g/L salts
~ g/L=1 ppm DOC

8. State of the Art Recovery?
Ultrafiltration
Adsorption Methods
Seawater
Tangential Flow
Porous Non-polar Resin
Salt
~30% DOC
Pore
Resin Columns
Water Salt LMW DOC μm
Seawater with remaining DOC
Only recovers High Molecular Weight DOC (>1000 Da)
Salt still present in final sample
Only recovers select species (humic, etc)
Must use pH or other method to desorb

9. New Approach: Water Reverse Osmosis Process Electro-dialysis
RO removes fresh water concentrating salt and DOC
Water
Reverse Osmosis
Electro-dialysis
Process
Freeze Dry
Solid DOC sample
Salt
35 g/L salts
~ 1 ppm DOC
ED removes salt with minimal loss of uncharged species

10. RO ED
The Processes
Electrodialysis
Reverse Osmosis

11. Electrodialysis Spacers and Membranes
Astom AMX/CMX

12. Electrodialysis - + - - Concentrate + C A Diluate/Feed Diluate Return
Na+
Cl-
Diluate/Feed
Diluate Return
Cathode
Anode
Concentrate Return + C A -
Na+
Cl-
Diluate/Feed
Diluate Return
Cathode
Anode
Concentrate Return + -

13. Electrodialysis Characterization Limiting Current (Ilim)
Limiting Current (Amps)
Temperature: 25°C

14. RO ED
The Processes
Electrodialysis
Reverse Osmosis

15. Reverse Osmosis ~ Pure Water High Pressure
Higher Concentration Retentate
Flow
Polyamide barrier
0.2 μm
Water
Salt
Water
Microporous polysulfone
40 μm
Polyester fabric
120 μm
Salt
Water
Discarded Permeate
Low Concentration Feed

16. Spiral Wound RO Module

17. Reverse Osmosis Characterization
Permeate
Retentate
High Feed Flow Rate
Low Feed Flow Rate
Small Stage Cut
Large Stage Cut

18. Combined Process Operation
Unit
Electrodialysis Stack

19. Overall Retrieve seawater sample (200- 400 l) Drive to site
Purge ED/RO
systems
ED/RO
200 l seawater
Freeze
~10 l
Freeze dry
NMR....
Hope for good weather!

20. Experimentation

21. Examples:
Three shipboard
experiments
Start with 200 liter
seawater

22. ED: follow the limiting current density

23. Summary Brackish Seawater 103 7 15 6 3 14 21 26 24 15 6 21 21 2 17 Lab
5-26
6-8
7-3
7-18
7-19
7-20
7-21
7-22
7-24
7-25
7-26
7-27
8-14
8-18
103 7 6 15
Final DOC ppm 3 14 21 26 24 15 6 21 21 2 17
Brackish
Seawater
Lab

24. 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

25. 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)?

26. Acknowledgements
This work is supported by the National Science Foundation, Grants No and (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.