Electrodialysis Metathesis (EDM) to Prevent Scaling

in Desalination of Gypsum-rich Groundwater

Thomas A. Davis, Director

Center for Inland Desalination Systems

DesalTech/ August 29, 2015

© The University of Texas at El Paso

Outline

• Desalination in Alamogordo, NM

• Groundwater saturated with gypsum

• Desal Prize at BGNDRF

• Plans for Honduras

© The University of Texas at El Paso

Alamogordo Water Supplies

Fresh Groundwater (local)

Surface water

Springs (local)

Bonito Lake (~60 miles northeast)

• Unavailable since June 2012; Might open 2017

Brackish Groundwater (~25 miles north)

• 1-MGD temporary plant planned

• 4-6 MGD plant in future

© The University of Texas at El Paso

Composition of City of Alamogordo

groundwater

Ion mg/L meq/L

Calcium 413 20.63

Magnesium 88 7.21

Potassium 4.7 0.12

Sodium 164 7.15

Bicarbonate 108 1.77

Chloride 133 3.74

Sulfate 1433 29.84

Silica 28 0.46

TDS 2500

© The University of Texas at El Paso

The ZDD* process (Zero Discharge Desalination)

* T. A. Davis is a principal in ZDD Inc., licensee of the ZDD technology.

Mixed Sodium

Mixed Chloride

NaCl

Finished WaterBrackish Water

NF/RO Concentrate

2% of

original

volume

Electrodialysis

Metathesis

(EDM)

© The University of Texas at El Paso

CaSO4 is problematic for ED. anode

feed solution

concentrate

diluate

cath

ode

O2

OH-

H2

H+

AEM CEM

concentrate

_ +

Cell Pair

SO42- SO4

2- SO42- SO4

2-

Ca2+ Ca2+ Ca2+ Ca2+

+ + + + _ _ _ _

© The University of Texas at El Paso

Electrodialysis Metathesis (EDM)

© The University of Texas at El Paso

EDM exploits solubility of Cl & Na

salts.

© The University of Texas at El Paso

ZDD process with solar salt recovery

Finished Water

Brackish Water

Mg(OH)2

CaSO4

NaCl

Ca(OH)2

© The University of Texas at El Paso

Recovery of NaCl improves

economics of ZDD process

• Purchase of NaCl is 40% of the ZDD operating

cost.

• NaCl must have low levels of Ca & SO4.

• NaCl in supernatant can be recovered and

purified from EDM concentrate streams.

• Target NaCl recovery is 90%.

• Cost reduction of 25-30% possible

• Evaporation ponds can be used for solar salt

recovery, achieving Zero Liquid Discharge.

© The University of Texas at El Paso

The Desal Prize

Sponsors: USAID, Swedish International Development

Agency, Ministry of Foreign Affairs of the Kingdom of the

Netherlands

• Bureau of Reclamation was a partner

Site: BGNDRF in Alamogordo, N. M.

Purpose: Incentivize innovation in desalination for farmers in

developing nations

Outcome: UTEP team placed 2nd (MIT 1st)

Next Phase: Demonstration in Honduras

© The University of Texas at El Paso

ZDD & The Desal Prize: Achieving High Recovery for Rural Farmers

© The University of Texas at El Paso

UTEP Desal Prize Team

© The University of Texas at El Paso

Conclusions

• ZDD process removes CaSO4 as a solid

byproduct.

• ZDD has achieved 98% recovery compared

to 75% recovery with BWRO alone.

• Recovery of NaCl from CaSO4 supernatant

improves the economics of ZDD.

• Evaporation improves the purity and

concentration of recovered NaCl.

© The University of Texas at El Paso

Acknowledgement

• Funding

• Bureau of Reclamation

• El Paso Water Utilities

• The Team

• Malynda Cappelle – UTEP

• Shane Walker – UTEP

• Bernie Mack – Veolia

• Lucy Camacho – TAMU Kingsville

© The University of Texas at El Paso

Thank you

Questions?