ElectrodialysisReverse Osmosis to Recover Dissolved Organics from Seawater

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

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

• DOC 1ppm

• Source NASA
• http//earthobservatory.nasa.gov/Library/CarbonCyc
  le

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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)
  gt1000 Da
• 70wt of DOC is low molecular weight (LMW)
  lt1000 Da
• DOC is composed of many types of molecules,
  examples

Aminosugars
Aromatics
Polysaccharides
Humic Species
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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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The issue recover pure DOC for scientific
analysis. The problem salt
Water

• ?

Solid DOC sample
Salt
35 g/L salts 0.001 g/L1 ppm DOC
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State of the Art Recovery
Ultrafiltration
Adsorption Methods
Seawater
Porous Non-polar Resin
Salt 30 DOC
Resin Columns
Pore
100-300 µm
Seawater with remaining DOC

• Only recovers High Molecular Weight DOC (gt1000
  Da)
• Salt still present in final sample

• Only recovers select species (humic, etc)
• Must use pH or other method to desorb

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New Approach
RO removes fresh water concentrating salt and DOC
Water
Process
Freeze Dry
Solid DOC sample
Salt
35 g/L salts 1 ppm DOC
ED removes salt with minimal loss of uncharged
species
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The Processes
Electrodialysis
Reverse Osmosis
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Electrodialysis Spacers and Membranes
Astom AMX/CMX
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Electrodialysis
-

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Electrodialysis Characterization Limiting Current
(Ilim)
Limiting Current (Amps)
Temperature 25C
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The Processes
Electrodialysis
Reverse Osmosis
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Reverse Osmosis
Pure Water
Higher Concentration Retentate
Polyamide barrier
0.2 µm
Salt
Water
Water
Microporous polysulfone
40 µm
Polyester fabric
120 µm
Salt
Water
Discarded Permeate
Low Concentration Feed
http//www.dow.com/PublishedLiterature/
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Spiral Wound RO Module
http//www.purewaterplanet.com/images/ROMembrane.j
pg
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Reverse Osmosis Characterization
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Combined Process Operation
RO Unit
Electrodialysis Stack
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Overall
Retrieve seawater sample (200- 400 l)
Drive to site
Purge ED/RO systems
ED/RO 200 l seawater
Hope for good weather!
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Experimentation
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Examples Three shipboard experiments Start
with 200 liter seawater
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ED follow the limiting current density
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Summary
103
7
15
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Final DOC ppm
3
14
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21
24
15
6
21
21
2
17
Brackish
Seawater
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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.