The seawater reverse osmosis (SWRO) desalination process is proven, mature and deployed globally. However, it remains the subject of many misconceptions and outdated views. Here are some commonly-asked questions about SWRO.
What is seawater desalination?
It is a process that turns ocean water into fresh drinking water by removing salt and impurities.
How is this process accomplished
Historically, this process relied on thermal distillation technologies, i.e., energy-intensive evaporation and condensation. In the late 20th century, advances in membrane technology enabled the use of much more energy-efficient reverse osmosis (RO) techniques. Poseidon's projects, including the Carlsbad project now in operation and the Huntington Beach project in advanced development, use RO technology.
How does reverse osmosis (RO) work
Water is pushed under high pressure through a semi-permeable membrane to separate salts and other solids from the water molecules. The membrane acts like a microscopic strainer that allows only the small water molecules to pass thorough.
Can the salt and minerals extracted be used
Natural seawater contains about three percent salt. The concentrated seawater by product from the desalination process contains six percent salt and 94 percent water. In order to recover the salt and minerals in the concentrated seawater, the remaining water thus needs to be evaporated using energy intensive distillation technology. Mineral harvesting only makes sense in limited circumstances. Evaporative salt harvesting has long been conducted at large, remote desert or coastal sites. At Poseidon’s compact sites in densely-settled coastal Southern California, though, water production is valued at a premium while the amount of salt generated is simply too great to be processed on-site. The quantity and value of minerals is also too small to justify the expense of additional processing.
Does weather affect the availability of water for desalination
No.The desalination process is conducted in an enclosed, highly-controlled environment and is based on an inexhaustible, local supply of seawater. The process is unaffected by drought, snowpack, rainfall or other weather conditions.
Where else has desalination been successful?
Desalination facilities have been operating in arid coastal regions throughout the world for several decades. It is most common in the arid Middle East, where over 50% of global desalination capacity is concentrated. In addition, 17% of desalination capacity is in North America, and approximately 10% in each of the regions of Europe, Asia and North Africa.
If desalination makes so much sense, why aren't there more plants in the United States
Until recently, capital and energy costs, and the abundance of freshwater, limited the use of desalination. Steady technological improvements since the 1980s have made desalination much more cost-effective. At the same time, conventional water supplies have come under increased pressure due to rising populations, falling water tables and changing weather patterns.
What kinds of improvements have taken place in RO technology?
The reverse osmosis membranes used today last longer, cost less and require significantly less energy than they did just a decade ago. Co-location of desalination facilities with existing coastal power plants enables joint use of existing intake and outfall facilities, resulting in large cost savings.
What is the quality of the water produced?
Desalinated water from the SWRO process yields drinking water of the highest quality that meets or exceeds all local, state and federal drinking water standards. The RO process is commonly used by bottling plants to produce premium drinking water from a number of sources.
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