The History and Future of Desalination Plants
Oceans cover more than 70% of the earth’s surface and though they support the lives of millions of species of marine animals and plants, those briny waters are unable to sustain humans and other mammals or, indeed, most terrestrial life. The problem is the mineral content of seawater. Because it is higher than that in mammalian cells, the osmotic pressure difference causes water to migrate from them, resulting in dehydration and, in time, death. Today it has become common practice to address this osmotic imbalance and to produce fresh water the world over from the sea in desalination plants.
While the methodology employed for this purpose today may be more sophisticated, the principle itself is far from new and has been exploited in simpler ways for millennia. For example, it is known that the sailors of ancient Greece boiled water, condensing the steam on a cold surface to form droplets of fresh water that could then collected for later use. The Romans of that time adopted a slower process in which the seawater was allowed to permeate through clay pots, depositing the contained salts on their inner surfaces. More recently, in 1790, Thomas Jefferson, then the US Secretary of State, is claimed to have described a form of desalination plant suitable for use at sea and it became customary to display the instructions for its use on all seagoing vessels of the time. It was, however, only a comparatively short time later before the construction of the world’s first facility capable of producing potable water from the sea in quantities sufficient for more widespread distribution.
While most believe these facilities are a product of the 20th century, it was in the latter quarter of the 19th century when the first of the many large-scale desalination plants appeared that, for many years, would rely on distillation, the only sufficiently effective technology available at that time. This one was built in 1881 and housed in a converted section of Tigne Fort in the Maltese seaside town of Sliema. At the time, its purpose was to provide fresh water for the British soldiers garrisoned there. Unfortunately, the distillation process requires heat which, in turn, requires a source of energy and, in this case, that energy must be obtained from electricity. While there has been a succession of improvements, each designed to make distillation more efficient, it does not detract from the fact that a more cost-effective technology is required in order for the product of desalination plants to become more affordable for commercial distribution.
Today, there are around 15 000 such facilities operating in various parts of the globe, predominately in desert or semi-arid regions. However, given the current rate of population growth, the steady decline in potable water reserves, and the mounting threat climate change, it is likely that even those coastal countries which traditionally experience high levels of rainfall will also need to turn to the sea in order to protect them from the risk of a future decline in their current ability to meet consumer demands. A new technology is now being adopted by desalination plants. It is known as reverse osmosis, or RO, and it appears to offer the much sought-after alternative to costly distillation methods. Its main advantage stems from the fact that its energy requirements are far lower because RO systems function effectively at temperatures well below boiling point.
Removing the salt from seawater and brackish sources, however, is just one of the more recent applications of RO technology. In fact, it has become a preferred option, not just in the new generation of desalination plants, but wherever water of exceptionally high purity may be required. Typical RO users include pharmaceutical companies, manufacturers of semiconductors, the food and beverage industry, and municipal treatment plants. However, the technology is not limited to industrial and commercial applications. In the home, compact water purifiers serve to remove residual traces of chlorine and minerals from tap water to improve its taste, while aid workers and soldiers in the field employ similar but more portable RO devices designed to render water from contaminated local sources safe to drink.
While water from desalination plants that employ reverse osmosis remains more expensive than that from traditional treatment plants, technological advances are expected to see the price of desalinated water fall by 20% over the next five years, with even greater reductions to follow. Currently, world-class RO and other treatment systems are available from WaterIcon.