Water Online the Magazine gives Water & Wastewater Engineers and end-users a venue to find project solutions and source valuable product information. We aim to educate the engineering and operations community on important issues and trends.
Issue link: http://wateronline.epubxp.com/i/129556
Technology Reverse Osmosis Desalination: A Feasible Alternative For Potable Water Supply Recent technology advances are making desalination less energy-intensive and less costly, bringing us closer to a long-sought solution to water scarcity. By James N. Smith, P.E. F reshwater is the liquid of life. Without it and flux properties have been key to the widespread the planet would be a barren wasteland. use of RO for desalination. Continued research and The supply of freshwater is finite, but the development of new fouling-resistant and energydemand is rising rapidly as world population efficient membranes is underway. Over the last grows and as global water use per capita increases. decade, advances in RO membranes have allowed Freshwater su pplies are not distributed evenly them to become more permeable, thereby allowing around the globe, higher flow rates throughout the seasons, at lower pressures or from year to year. than previously Fully two-thirds of the achieved. Higher world population — 4 permeability lowers billion people — lives the power cost for within 250 miles of the same amount a seacoast; just over of filtered water. half of the world Advanced materials population occupies a have reduced foulcoastal strip 120 miles ing rates, resulting wide, representing only in reduced cleaning 10% of the earth's land cost and increased surface. A solution to replacement interthe burgeoning use vals. Other recent of freshwater would work has focused be to tap the almost on integrating RO limitless volume of with electrodialyReverse osmosis (RO) installation in Dauphin Island, AL ocean water and inland sis (ED) to improve brackish water using recovery of valuable desalination processes. deionized products or to minimize concentrate volReverse osmosis (RO) filtration by means of ume requiring discharge or disposal. semipermeable membranes is the leading technology Possibly the greatest energy savings breakthrough used in drinking water desalination. Advances in in the last two decades is the result of integrating reverse osmosis treatment and membrane materials energy recovery devices (ERDs) into the operation have created systems that typically use less energy of desalination RO systems. Thanks to ERDs, it is than other desalination processes. The key to possible to reuse the energy from the concentrate expanding the use of RO desalination has come flow. The concentrate is directed to the ERDs, where down to finding ways to reduce the energy required it directly transfers its energy in part to the feed flow. to overcome the osmotic forces applied to the ERDs include energy recovery turbines, which can membrane. These improvements have led to an provide power savings of 30-40% over standard RO overall reduction in desalination treatment costs over units not equipped with ERDs. Furthermore, in the the past decade. last decade innovations in pressure exchanger (PX) Advancements in membrane technologies continue technology have created increased energy savings of to lower energy usage and the costs associated with 50-60% over non-ERD equipped RO units. desalination. Developments such as thin-film comPX technology utilizes isobaric energy recovery posite (TFC) membranes with advanced permeability technologies with the two-stage RO desalination 12 wateronline.com ■ Water Online The Magazine