Post on 16-Jul-2015
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Made by- Made by- Rahul VermaRahul Verma
IX-BIX-B
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Electro dialysis/Reverse Osmosis to Electro dialysis/Reverse Osmosis to Recover Dissolved Organics from Recover Dissolved Organics from
SeawaterSeawater
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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)
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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
µρvRh
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
Reverse Osmosis
Water
Polyester fabric
120 μm
40 μmMicroporous polysulfone
Polyamide barrier
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Spiral Wound RO Module
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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
∆=m
ss 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
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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.
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THANK YOU
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