Index 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

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

Index 3 Source: NASA Units: Gigatons C, GtC/yr (1 GtC= 10 9 tons of carbon)

Index 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

Index 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: Humic Species Aminosugars Polysaccharides Aromatics

Index 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 CO 2 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.

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

Index 8 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 μm

Index 9 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

Index 10 RO ED The Processes Electrodialysis Reverse Osmosis

Index 11 Electrodialysis Spacers and Membranes Astom AMX/CMX

Index 12 Electrodialysis + CCCCAA - Na + Cl - Na + Diluate/Feed Diluate Return CathodeAnode Concentrate Return Concentrate + CCCCAA - Na + Cl - Na + Diluate/Feed Diluate Return CathodeAnode Na + Concentrate Return + -

Index 13 Electrodialysis Characterization Limiting Current (I lim ) Limiting Current (Amps) Temperature: 25°C

Index 14 RO ED The Processes Electrodialysis Reverse Osmosis

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

Index 16 Spiral Wound RO Module

Index 17 PermeateRetentatePermeateRetentate High Feed Flow Rate Low Feed Flow Rate Small Stage Cut Large Stage Cut Reverse Osmosis Characterization

Index 18 RO Unit Electrodialysis Stack Combined Process Operation

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

Index 20 Experimentation

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

Index 22 ED: follow the limiting current density

Index Brackish Seawater Lab Summary Final DOC ppm

Index 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

Index 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)?

Index 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.