GREEN STRATEGIES FOR DESALINATION TO MEET FUTURE POTABLE WATER SUPPLY NEEDS WHILE MINIMIZING GREENHOUSE GAS EMISSIONS: COOPERATIVE GEOLOGICAL AND ENGINEERING SOLUTIONS

Global warming will accelerate sea level rise and exacerbate climatic variability, particularly in arid regions. Increasingly intense droughts of long duration will cause depletion of conventional freshwater supplies, particularly surface and ground-water resources. Therefore, development of seawater desalination systems will become increasing necessary to meet potable water supply demands in the future. Using current strategies and designs, desalination of seawater is energy intensive and, if driven by electricity fossil fuels, will further increase greenhouse gas (GHG) emissions, thereby increasing the impacts of anthropogenic climate change. Use of new strategies and technologies must be implemented to achieve increased availability of freshwater using desalination while capping or reducing GHG emissions. Four strategies are suggested to achieve these objectives: 1) desalt seawater using the seawater reverse osmosis (SWRO) process driven by renewable energy sources, 2) use geothermal energy to generate electric power and link the steam discharge to one or more thermal desalination processes and add reverse osmosis and aquifer storage and recovery (ASR) to the same site, creating an energy generation/water supply “campus” to maximize efficiency in both processes, 3) improve the raw seawater quality used for treatment by the reverse osmosis process by integrating a form of natural-systems filtration using coastal wells or galleries installed in the beach littoral zone or in the seabed which tend to remove organic matter that causes biofouling of membranes and increases energy consumption and costs, and 4) further develop the concept of pressure retarded osmosis (PRO) to harness the potential (salinity gradient) energy from SWRO brines to generate electricity and to offset the energy consumption of SWRO or development of electric power plants using salinity difference in estuarine systems. Some of these strategies are implemented today, but at scales insufficient to make any impact on GHG emission goals. The geological community has the expertise to work with the engineering community to help implement large-scale applications of these improved desalination methods, particularly strategies 2 and 3, to achieve significant reductions in GHG emissions.