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: pxu@nmsu.edu