Sea water can be converted into fresh, drinkable water by removing the salt and other minerals through desalination, which is a process that separates the salt from the water. The separation of salt can be done by four methods, filtering, freezing, boiling, and vacuum evaporation. Each process has positive and negative aspects that affect the favorability of one over the others.
In the process of filtering the sea water, salt water is pumped from a container through a series of filters that help screen the heavier salt and dissolved minerals from the water that is allowed to pass through. Due to the miniscule size of the filter gaps, water has to be forced with enough pressure that ensures the water to pass through; otherwise it would never do so on its own. Because of the pressure requirement, the filter complexity, and the controlled quantity at any one time, this method consumes a lot of time, energy, and has a small output.
During the freezing of sea water, the dissolved salt and other minerals are ejected from the crystallizing water. This process occurs naturally in Earth’s oceans where the formation of sea ice occurs, and the ejection of the salt-concentrated water, known as brine, helps influence the flow of cold water currents. Unfortunately, not all the salt is ejected, as some of the salt remains trapped in pockets within the ice. Because this amount of salt remains in a natural setting, it is also possible to remain in an artificial process, which would require a melting process, before being frozen again. Multiple freezing and unfreezing sessions in different chambers would eventually yield ice that would be devoid of the salt, which could be later melted for drinking water. The fresh water could be ascertained by having the ability to freeze at a normal freezing point of 32 degrees Fahrenheit/0 degrees Celsius, due to the salt’s lowering of the freezing point.
By far the easiest method, boiling sea water evaporates the water and leaves the salt behind. Steam can be piped into a condenser or another chamber separate from the boiler, and cool into a liquid form. The cooled water should be devoid of salt. Additionally, large amounts of water can be added to the main boiler continuously. This means that so long as there is a heat source, the supply of fresh water can be maintained. The main problem is the heat source.
Similar to evaporation through heat addition, a vacuum process uses a barometric pressure principle to create a vacuum in a tall tube with warm water. Because of the vacuum and decrease in pressure, water will evaporate at lower temperatures, and the resulting steam will be collected in a condenser in order to be converted back to liquid form. The system uses less energy to operate, and is also more efficient. To date, this is the best solution for the global community, often when waste heat from other applications is used to warm the water that is to be evaporated.
