Sustainable Desalination of Seawater

The demand for fresh water continues to grow, driven by increasing population densities in urban areas that lack sufficient fresh water and an increasing global need for water for agriculture and industry. One of the ways to meet this demand for fresh water is desalination - removing dissolved salt from seawater. With the abundance of seawater on the planet, desalination is an attractive and viable long-term option. There are now 13,080 desalination plants in operation around the world according to the International Desalination Association. In California alone, some 20 seawater desalination plants have been proposed, including a $300 million facility near San Diego. Seawater reverse osmosis is an advanced desalination process used to filter water in which seawater is forced through a semi-permeable membrane, producing pure water on one side and concentrated brine on the other. The process, however, has historically been energy-intensive because of the high pressures that must be attained for it to work effectively. Recent technological advances, including the development of energy recovery devices, have dramatically improved the energy efficiency and reduced cost. Early energy recovery devices were only 50% to 75% efficient but newer ones can recover up to 98% of the energy from the high-pressure membrane reject stream. This paper describes seawater reverse osmosis processes, reviews the technologies used to minimize energy consumption and contrasts their efficacy. It also examines the role of energy recovery devices in improving the energy efficiency of high pressure water application beyond desalination.