Seawater desalination is unequivocally the future of drinking water production for coastal communities and island nations in current times of water scarcity. It is already used quite heavily in a few countries. Saudi Arabia, the United Arab Emirates, and the U.S. are the top three desalination producers of drinking water by capacity in the world, followed by Australia, China, and Kuwait.
These countries benefit from desalination systems because they have particularly dry climates with few freshwater sources, or they require an expansion of water resources above their existing water sources available. Knowing the alchemy of desalination’s history, the cost effectiveness of reverse osmosis in desalination, the origins of its development along with its pros and cons is how we at Waterworld USA appreciate the reliable performance and long-lasting nature of our RO membrane product selection for your needs.
The Alchemy of Desalination
The global water crisis is unlikely to be solved without widespread use of desalinated water. Today, in an accelerating migration trend, nearly half of the world’s population lives a relatively short water pipeline away from a seashore. Countries benefit from desalination systems when they have particularly dry climates with few freshwater sources, or they require an expansion of water resources above their existing water sources available. So why do some countries utilize this advanced treatment technology, while others do not?
Desalination has the feel of science, engineering, and alchemy combined. The medieval alchemist tried to take lead, a product of scant value, and transform it into one of great worth, gold. So, too, the desalination process tries to take seawater (or inland, brackish water), strip it of its worthless elements, and change it into a lifesaving product of enormous value.
The ancient Romans tried to purify seawater for their army, but their efforts never went far.
During World War II, American scientists also began thinking about ways to either take the salt out of the water or the water out of the salt, which sounds like the same thing, but which require completely different approaches and scientific techniques. The problem with either approach, they realized, was that it might make sense in limited military applications where expense is of little concern, but the enormous amount of energy needed to produce pure water from seawater would have made it impossibly expensive for civilian use.
The ROI of RO
From a limited usage in removing salt and minerals from inland brackish water, reverse osmosis today is the dominant technology, already responsible for purifying sixty percent of the salty water desalinated at facilities around the world. As older desalination plants are retired, the role of membrane filtration will only grow.
Yet desalinated water is manufactured, and will always be more expensive than natural sources like rain, lakes, rivers, or even aquifers. Andt due to the use of RO membranes, desalinated water isn’t just the highest quality water to be found in terms of cleanliness, low salinity, and high clarity; it also turns out to be about fifty percent cheaper.
Seawater is a mixture of pure water, salt, and other minerals. When seawater goes through reverse osmosis, the water is pushed through a membrane with the pure water sent in one direction and the salt molecules in another. The segregated salty slush that remains is called brine and is returned to the sea. The same process can be used to take minerals or other unwanted material out of the source water. But whatever the particles to be removed are, the essential element is the membrane.
The RO membrane wasn’t originally created with seawater in mind, but rather for brackish water. Less salty than seawater, brackish water is found in so-called fossil aquifers that hold water collected in prior geologic eras and left undisturbed long enough for greater or lesser amounts of salt and minerals to leach into the underground water source. Brackish water is also created when seawater and freshwater come into contact with each other, as when a river meets the sea.
In his mid-forties, the Kansas-born Sidney Loeb began pursuing a Ph.D. at UCLA in the early 1960s in an evolving field of chemical engineering. Loeb was investigating whether brackish water might be purified to drinkable freshwater via a specially constructed membrane. Working with a lab partner, Loeb developed a membrane that had nano-sized holes that were large enough to allow pure water to pass through but small enough to block particles of salt and other dissolved minerals.
In 1965, Loeb’s membrane was brought to the small California town of Coalinga for a test. The town’s available water was so densely laden with minerals that it was undrinkable. Whatever water the town needed had to be delivered by train from another town. The test not only changed the future of Coalinga, but also of desalination—as Loeb’s membrane successfully purified the previously non-potable water. Sidney Loeb was to reverse osmosis what the Wright Brothers were to aviation, Henry Ford to the car, and Thomas Edison to the lightbulb. For sure, others have made all of these better after they started it, but they were the founders. Here are some of the pros and cons of his reverse osmosis seawater desalination for drinking water:
Modular systems are designed to be compact and easy to move and install in order to reduce capital costs. They are great for municipal or commercial drinking water applications (such as hotels) where space may be limited, but they need to provide for a large number of people.
Expansion of drinking water sources
The driving force behind desalination. Being more sustainably minded about the state of our current water sources is important, but alternatives are also essential when they are available. The ocean just so happens to be a very big alternative. With the world’s oceans as a viable source for drinking water, that would expand humanity’s most valuable resource by an exponential margin. Keep in mind that the oceans account for about 95+ percent of all the water on Earth.
The only other currently used desalination treatment is of the thermal variety. It works the same way as the water cycle, evaporating water into steam and when it is condensed it provides clean water. This approach is very effective at removing unwanted particles, but collecting and condensing steam is inefficient and produces much lower yields of pure water than RO. For the same output volume of water, thermal processes would require nearly three times as much seawater.
Very pure water
After reverse osmosis, the water is so pure we actually have to put minerals back into it. The process removes the minerals of water that humans need as well as the tastes we are familiar with. Therefore, the post remineralization process takes care of this and regulates pH.
Reverse osmosis membranes are very sensitive. So, unless some more resistant membrane material is developed, pretreatment is an important requirement. Without it, the membrane can become practically useless, decreasing yield or producing impure water. Improperly pretreated seawater can deposit particulate matter on the membrane. These contaminants affect proper membrane flow and pressure which increases operating cost.
Higher energy use
Reverse osmosis systems are constant flow processes so fluids are constantly being pumped and pressure is continually being applied to the cylindrical membrane vessels. However, the osmotic pressure energy stored in the concentrate solution can actually be recovered to reduce the overall energy costs. A commonly used technology is the rotary pressure exchanger. Influent seawater is pressurized by pistons within channels inside the exchanger that are depressed by the high-pressure concentrate reject stream from the RO unit. This reuse of kinetic energy from the brine water can reduce the energy cost efficiently.
Can Be Costly for Developing Nations
Regardless of any energy saving, many nations of the world don’t have the capability or resources to construct and operate desalination projects. The drinking water produced from the seawater desalination process is typically more expensive than treated groundwater, brackish water or surface water sources.