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

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

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

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

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

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

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

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

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

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

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

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

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

Pressure Retarded Osmosis Seawater Desalination

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

Osmotic Power Generation + RO Retentate = Energy + Water (Chung,2015) 38.5 bars: a waterfall of 390 - 400 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) http://osmoticpower.com/ 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)

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

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

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

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