1. Green Strategies for Desalination to Meet Future Potable Water Supply Needs while Minimizing Greenhouse Gas Emissions: Cooperative Geological and Engineering Solutions
Thomas M. Missimer1 and Gary L. Amy2
1Florida Gulf Coast University
U. A. Whitaker College of Engineering
2Clemson University
College of Engineering and Science
Annual Meeting of the Geological Society of America
Baltimore, Maryland
November 3, 2015

2. Seawater Desalination
Introduction
●Growing global water demand and climate change are collectively placing severe stress on existing freshwater supplies.
●Many regions of the world are developing seawater desalination systems to provide drinking water and in some cases irrigation water.
●Desalination is generally an energy intensive process and has a significant cost in comparison to conventional freshwater supply treatment.
Seawater Desalination

3. Seawater Desalination
Introduction
●Energy consumption during desalination of seawater contributes to GHG formation.
●Reverse osmosis is currently the least energy intensive technology used in large-scale seawater desalination.
●Use of electric energy consumption to convert seawater to freshwater ranges from 4-6 kw-hr/m3 and has a corresponding average cost range of $0.70 to $2.00/m3 depending on facility capacity and local electric cost.
Seawater Desalination

4. Seawater Desalination
Resource Depletion and Climate Change Require New Resource Management Strategies
Resource depletion is becoming critical in western Saudi Arabia where past water table fluctuations ranged from 1 to 3 m below surface and now are 10 to 30 m below surface. This region has the largest development of seawater desalination in the world.
Seawater Desalination

5. Current Facts on SWRO Desalination
●The cost of SWRO in large-capacity facilities has reduced from over $2-$3/m3 to an average under $1/m3 based on improvements to the membrane materials used in the primary process and in the use of modern energy recovery systems.
●While the electric energy consumption of the process has reduced to as low as 4 kw-hr/m3, the thermodynamic limit for electric use is 2.3 kw-hr/m3.
●Membrane biofouling and plant operations continue to be major problems.
Seawater Desalination

6. Seawater Desalination
How Can Further Reductions in Seawater Desalination Energy Use and Cost be Achieved?
●Renewable energy powered desalination-direct distillation processes
●Geothermal energy driven systems linking electric generation with multiple desalination processes and aquifer storage and recovery
●Improvement of raw water quality to SWRO systems using subsurface intake systems similar to bank filtration
●Link pressure-retarded osmosis to generate electricity and with seawater desalination
Seawater Desalination

7. Geothermal Energy Driven Direct Distillation
Hot-dry rock geothermal energy harvesting linked directly to provide heat to a multiple-effect distillation facility.
Seawater Distillation

8. Geothermal Energy Electricity-Desalination-Storage Campus
Hot dry rock geothermal energy harvesting is linked to electric generation, multiple effect distillation, adsorption desalination, seawater reverse osmosis desalination, and aquifer storage and recovery.
Seawater Desalination

9. Improvement of Raw Water Quality to SWRO Facilities
Improvement of the raw water quality can eliminate most of the SWRO pretreatment processes, thereby reducing energy consumption and biofouling of the membranes.
Seawater Desalination

10. Improvement of Raw Water Quality to SWRO Facilities
One type of subsurface intake uses wells to force raw seawater through a coastal aquifer before entrance into the SWRO plant.
Seawater Desalination

11. Improvement of Raw Water Quality to SWRO Facilities
All of the algae, most of the bacteria, and significant percentages of the TOC, biopolymer fraction of NOM, and both TEP types are removed by the natural system. The bacteria, biopolymers and TEP are all important contributors to membrane biofouling.
Seawater Desalination

12. Improvement of Raw Water Quality to SWRO Facilities
New and innovative well collection systems need to be tested to assess there potential use for large-capacity seawater desalination systems.
Seawater Desalination

13. Improvement of Raw Water Quality to SWRO Facilities
Seabed gallery intake design
Beach gallery intake design
New gallery intake designs need to be developed to meet the raw water requirements of large-capacity desalination systems. The seabed gallery concept was invented in 1982, but the first large-scale system was built in Fukuoka, Japan in 2006 (23.6 MGD).
Seawater Desalination

14. Pressure Retarded Osmosis
Seawater Desalination

15. Salinity Gradient Energy: Pressure Retarded Osmosis (PRO); A Special Case of FO
Pressure created by flow of freshwater into salt water
Pressure used to run a turbine  Blue energy
In Norway, River Water and Seawater
(Stadtkraft)
Research Questions
Develop PRO Membrane (PRO  FO)
Improve Power Efficiency (W/m2)
Increased Mechanical Strength over FO
Identify Applications
Desalination Brine & Wastewater Effluent
Theoretical Yields *
Seawater

16. Osmotic Power Generation + RO Retentate = Energy + Water (Chung,2015)
38.5 bars: a waterfall of meters in a hydropower plant
The semi-permeable membrane
RO retentate
8-8.8% NaCl
Singapore desalination plant
RO plant
NEWater retentate
(waste of recycled water)
Seawater Desalination
T. S. Chung, S. Zhang, K. Y. Wang, J. C. Su, M. M. Ling, Forward osmosis processes: yesterday, today and tomorrow, Desalination (2012)

17. Opportunity for PRO in Coastal City (Childress, 2013)
Seawater Desalination

18. Opportunity for PRO in Coastal City (Childress, 2013)
Also Brine Dilution (environmental impact )
Seawater Desalination

19. Seawater Desalination
Conclusions
●Improvements to the desalination processes in terms of lowering energy consumption and cost require interdisciplinary research, using both geologists and engineers to find solutions.
●Linked geothermal energy development with desalination and storage would lead to greatly improved desalination costs and lower GHG emissions
Seawater Desalination

20. Seawater Desalination
Conclusions
●The energy consumption of SWRO must be reduced from the current 4-6 kW-hr/m3 closer to the thermodynamic limit of 2.3 kW-hr/m3.
●Use of subsurface intake where feasible (favorable hydrogeology) lowers the energy use and cost of SWRO and PRO.
●Development of the pressure-retarded osmosis technology could harness the lost energy of freshwater discharge to tidal seawater and create electricity/desalination campuses.
Seawater Desalination