Selective and Anti-fouling Ion-Exchange
Membranes for Water Reuse and Desalination
Xuesong Xu, Guanyu Ma, Million Tesfai, Wenbin Jiang,
Lu Lin, Huiyao Wang, Pei Xu
2nd Annual WIN Workshop, BGNDRF
10/28/2019
EnLiTeEnvironmental Lab of Innovative Technologies
n US Bureau of Reclamation
n NSF Engineering Research Center
ReNUWIt
n BGNDRF
n Charlie He (Carollo Engineers)
n El Paso Water
n City of Scottsdale
n SUEZ Water Technologies & Solutions
Acknowledgements
Development of Alternative Water Supplies is Crucial for Water Security
Water Scarcity
Elevated SalinityHigh sodium adsorption ratio
Contaminants of emerging concerns
Desalination
Water Conservation
Water Reuse
Concentrate
High Sodium to Hardness Ratio Resulted in Reuse Challenges
n SAR = Sodium Adsorption RatioSAR = [Na+] / {([Ca2+] + [Mg2+]) / 2}1/2
≤3 6 to 9 > 9
(use meql units)
Concentrate
85%
15%
Cathode (-)
Anode (+)
Anion Exchange Membrane
Cation Exchange Membrane
Cation Exchange Membrane
- - - - - - - - - - - -
Feed+ + + + + + + + + + +
Electrodialysis (ED) Consists of Electrodes and A Stack of Membrane Cell Pairs
- - - - - - - - - - - -
- - - - - - - - - - - -
+ + + + + + + + + + +
Spacer
Spacer
RepeatingCell Pairs
Cathode (-)
Anode (+)
Cl-Na+
Na+
Anion Exchange Membrane
Cation Exchange Membrane
Cation Exchange Membrane
- - - - - - - - - - - -
Feed+ + + + + + + + + + +
Na+
Na+Na+
Cl-Cl-
Cl-
Cl-Na+
Na+
Na+
Desalted water
ED concentrate
- - - - - - - - - - - -
- - - - - - - - - - - -
+ + + + + + + + + + +
Saline water
Saline water
Electrodialysis (ED) with Normal Grade IX Membranes Removes Cations and Anions
SO42- Ca2+
Ca2+
Cathode (-)
Anode (+)
Cl-Na+
Na+
Anion Exchange Membrane
Cation Exchange Membrane
Cation Exchange Membrane
- - - - - - - - - - - -
Feed+ + + + + + + + + + +
Na+
Na+
Na+
Cl-Cl-
Cl-
Cl-Na+
Na+
Na+
Desalted water
ED concentrate
- - - - - - - - - - - -
- - - - - - - - - - - -
+ + + + + + + + + + +
Saline water
Saline water
Electrodialysis with Selective IX Membranes Remove Preferentially Monovalent Ions
SO42- Ca2+
Ca2+
Selective Electrodialysis for ZLD of Reclaimed Water
CaSO4MgCl2CaCl2
Ca2+
Mg2+
Ca2+
Mg2+
SO42-
Cl-
Na+ Cl-
Na+
SO42-
Ca2+
Irrigation
Cooling Water
Wetland
Salty Reclaimed Water
Na+Na+
Na+
Na+Na2SO4NaCl
SelectiveED
Reclaimed waterwith low hardness,
higher salinity
Reclaimed waterwith low sodium,
lower salinity
Modified Selective Membranes
Oxidation
Modification
Polyethyleneimine chain
CR67
Addition of epoxy group
Selective CR671
-------
Polyethyleneimine
+
+
+
+
+
+
+
Modified CEM
Na+
Ca2+
Na+
Na+
Na+
Ca2+
Ca2+
Ca2+
Na+
Na+
Na+
Ca2+
-------
CEM
Na+
Ca2+
Na+
Na+
Na+
Ca2+
Ca2+
Ca2+
Ca2+Na+
Ca2+
Ca2+
Ca2+
Bench-Scale Testing Results
0
2
4
6
8
10
0 2 4 6 8 10 12 14
Re
lative
tra
nsp
ort
nu
mb
er
Current density (mA/cm2)
2-electrical stage bench selective_Ca
2-electrical stage bench normal_Ca
2-electrical stage bench selective_Mg
2-electrical stage bench normal_Mg
Normal IX
membranes
Selective IX
membranes
Xu et al, Desalination 2018
Field Testing at Three Sites
Scottsdale Water Campus
El Paso KBH Desalination Plant
BGNDRF
Pilot Site Development
!
Selective Membrane Coating
Selective Membranes Demonstrate Better Selectivity of Monovalent Cations over Divalent than Normal Membrane
Xu et al, Separation & Purification Tech 2018
0
2
4
6
8
10
12
14
0.5 0.8 1.1 1.3 2.3
Perm
sele
ctiv
ity im
prov
emen
t
Current density (mA/cm2)
0%
20%
40%
60%
80%
100%
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
Con
duct
ivity
redu
ctio
n
Current density (mA/cm2)
2-stage Pilot
Selective membranesNormal membranes
Modeling and Full Scale Design
!
!
Bench Testing
Pilot Testing
Full ScaleDesign
Data Fitting and Mathematical Modeling
Water and Salt Balance, Process ModelingCost Analysis
WATSYS: Specialty EDR Projection Model by GE (Normal Grade Membrane Only)
Scottsdale Blending Analysis and Cost Comparison – 1 MGD Reclaimed Water (4-stage)
Baseline Alternative Alternative 1A Alternative 1 Alternative 2
UF + RO Normal EDR -WATSYS
Normal EDR -Testing Selective EDR
Feed Water Flow (mgd) 1Feed Water Sodium (mg/L) 235
Overall Recovery 88% 93% 92% 94%Unit Recovery 85% 90% 90% 90%
Product Water Sodium (mg/L) 110Product TDS (mg/L) 530 522 433 634Number of Stages - 4 4 4
Capital ($/gpd product flow) $6.1 $6.5 $7.6 $6.5O&M ($/kgal) $1.09 $0.88 $0.83 $0.81
Selective ED achieved higher water recovery and 26% cost reduction treating municipal
reclaimed water
Selectivity Decreased with Increasing
Salinity
BGNDRF Groundwater – Bench-scale
Well 1: TDS 1200 mg/L, SAR 11.5
Well 3: TDS 3600 mg/L, SAR 4.7
Well 4: TDS 4100 mg/L, SAR 4.7
0
1
2
3
4
5
6
7
0 2 4 6 8 10 12
Rel
ativ
e Tr
ansp
ort N
umbe
r
Current Density (mA/cm2)
CR671 - Ca/Na Well 1Well 3Well 4
Development of Antifouling Ion-exchange Membranes
Development of Antifouling Ion-exchange Membranes
Ø Compilation of brightest pixels for all spots
Raw CR671 CR671 w/ PEI
CR671 w/ PEI + 3% TiO2 CR671 w/ PEI + 5% TiO2
CR671 w/ PEI + 7.5% TiO2 CR671 w/ PEI + 10% TiO2
Electrochemical Characterization of Modified Ion-exchange Membranes
Electrical equivalent circuits and the schematic representation of the different transport layers for (a) the normal grade CR67 and (b) the modified CR671 with polyethyleneimine (PEI) coating. RM, RDL, RMO, and
RDBL represent the resistances of the membrane, the electrical double layer, the modification and the diffusion boundary layer, respectively. CDL and CMO represents the capacitances of the electrical double
layer and the modification. Q is the constant phase element from the diffusion boundary layer.
0
1
2
3
4
5
1.0E-02 1.0E+00 1.0E+02 1.0E+04
-Z" [
Ohm
]
Frequency [Hz]
0.05 M NaCl
0.1 M NaCl
0.5 M NaCl
12 Hz
8 Hz
0
0.3
1.0E-02 1.0E+00 1.0E+02
-Z" [
Ohm
]Frequency [Hz]
0.5 M NaCl
15 Hz
a)
Bode plots for different ionic strengths
solutions of CR671. (a) NaCl, (b) CaCl2, (c)
Mixed NaCl + CaCl2 (Na+/Ca2+, 7.2:1).
Concluding Remarks
Ø Selective ED is more cost effective to treat municipal wastewater for irrigation than RO
Ø Monovalent permselectivity of selective membranes decreased with increasing feed salinity and current density
Ø Coating polymers and nanoparticles (TiO2 and graphene oxides) can significantly reduce membrane biofouling increase monovalent permselectivity.
Pei Xu: [email protected]