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Electrodialysis Metathesis to Improve Desalination Yield from Gypsum-Rich Groundwater

Electrodialysis Metathesis to Improve Desalination Yield from Gypsum-Rich Groundwater. Thomas A. Davis Director, Center for Inland Desalination Systems University of Texas at El Paso, USA Presented to Multi-State Salinity Coalition January 27, 2012. We live in the desert.

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Electrodialysis Metathesis to Improve Desalination Yield from Gypsum-Rich Groundwater

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  1. Electrodialysis Metathesis to Improve Desalination Yield from Gypsum-Rich Groundwater Thomas A. Davis Director, Center for Inland Desalination Systems University of Texas at El Paso, USA Presented to Multi-State Salinity Coalition January 27, 2012

  2. We live in the desert.

  3. Tularosa Basin, NM Alamogordo, NM Satellite Image: White Sands National Monument and Missile Range Total Dissolved Solids (TDS) in groundwater ranges from 2 g/L to 10 g/L.

  4. 4 Each aquifer has unique composition, and there are variations within an aquifer. Snake Tank Wells BGNDRF

  5. Desalination of inland groundwater • RO produces two output streams: • Drinking water (permeate). • Waste water (concentrate), which contains the removed salts. • Minimizing the volume of RO concentrate: • Avoids wasting water. • Avoids/Minimizes expensive and environmentally challenging disposal processes: • Surface discharge • Evaporation ponds • Deep-well injection • Off-site hauling • Zero liquid discharge

  6. Limitations of Desalination Yield • High osmotic pressure (energy cost) • Solutes with limited solubility • Silica ~ 100 mg/L • CaCO3 > 15 mg/L, depends on pH • CaSO4 ~ 2 g/L, depends of salinity • BaSO4, SrSO4, CaF

  7. Approaches to Improve Yield • Use antiscalant to disrupt crystallization. • Contact supersaturated RO concentrate with seed crystals to reduce supersaturation. • Remove troublesome solutes by ion exchange or chemical softening. • Remove troublesome ions by electrodialysis. • Separation of useful salts is possible. • Salts can be concentrated to high levels.

  8. Standard electrodialysis (ED) Diluate Concentrated NaCl Diluate Concentrated NaCl C C A C A Cl- Na+ Na+ - + Cl- Na+ REPEATING CELL Rinse Na Cl Feed NaCl Feed Rinse

  9. Ca & SO4 in ED Diluate Concentrate Diluate Concentrate C C A C A Cl- Ca+ Na+ SO4= SO4= Ca+ - Ca+ + Na+ Cl- Na+ REPEATING CELL Rinse Brackish Water Feed Brackish Water Feed Rinse

  10. Limitation of Conventional ED • When CaSO4 is the dominant salt, it becomes supersaturated in the concentrate stream. • EDR is not as effective in highly saline solutions, because longer times are required to return to steady state after current reversal. • Others have mitigated supersaturation by contacted ED concentrate with seed crystals to remove CaSO4.

  11. EDM: Electrodialysis Metathesis EDM Diluate Mixed Cl (conc.) Dilute NaCl Mixed Na (conc.) C C A C A Cl- Na+ Na+ HCO3- Cl- - + SO42- Ca2+ Mg2+ Na+ REPEATING CELL (“QUAD”) Rinse EDM Feed NaCl Rinse

  12. Solubility of Salts in water CaCl2 Maximum 3.1M at 33°C NaCl Na2SO4 CaSO4 Highly soluble salts are producedby EDM.

  13. RO EDM treats RO concentrate to transferCa and SO4 into separate streams. Pretreated Feed Water NaCl + C A C A C - Na2SO4 CaCl2 NaCl Drinking Water Precipitation NaCl & MgCl2 Solution CaSO4 (solid)

  14. CaSO4 precipitated by mixing concentrated solutions from EDM

  15. The ZDD* process(Zero Discharge Desalination) • Treat RO concentrate with electrodialysis metathesis (EDM). • In EDM the ions of troublesome salts in RO concentrate exchange partners with NaCl to form highly soluble Na salts and Cl salts. • Each of the two EDM concentrate streams contains about 1% of the water from the original feed. • The other 98% is in the RO permeate. * T. A. Davis is a principal in ZDD Inc, licensee of the ZDD technology.

  16. Dealing with Silica • After CaSO4 was removed from the RO concentrate, silica became the limiting solute. • RO and EDM membranes are impermeable to silica, so silica builds up in circulating loop. • Methods to avoid silica precipitation: • Purge some of the solution to reduce silica. • Add antiscalant to delay precipitation. • Add NaOH to precipitate Mg(HSiO3)2, filter with ceramic membrane, and recycle purge solution. • Replace RO with Nanoflitration (NF) membrane.

  17. Latest ZDD Process Flow Diagram

  18. Compositions of ZDD processstreams, 4/15/11

  19. ZDD: Improvements in Recovery

  20. Conclusions • ZDD process can provide substantial improvements in yield of water from groundwater containing CaSO4. • EDM is the heart of the ZDD process. • Separate concentrated streams containing Ca++ and SO4= are produced in EDM. • Concentrated streams are mixed to produce CaSO4 byproduct. • NaCl can be recovered from supernatant. • Use of NF versus RO eliminates silica problem in EDM.

  21. Acknowledgements • Veolia Team: Brad Biagini, Larry Hart, Bud Krebs, Bernie Mack, Paul Choules, Mark Smock, Larry Jessup • UTEP/CIDS: Malynda Cappelle, Shane Walker, Lucy Camacho, Jesse Valles • Brackish Groundwater National Desalination Research Facility (BGNDRF) in Alamogordo, NM cids.utep.edu

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