Humans need water to live, but not all water is created equal. Most of the world’s water supply is full of salt, which means that it isn’t terribly healthy for humans. Desalination is the process by which salt is taken out of the water to make it safe to drink. Thermal desalination is one of the leading methods at the moment, and it is important enough that everyone should try to understand the basics.
The Basic Method
Thermal desalination is fundamentally similar to the ancient process of distillation. In most cases, water is boiled to turn the liquid into a gas, which leaves all of the salt and other contaminants behind. The water vapor is then collected in a new container and allowed to condense back into liquid form. Since the salt never turned into a gas, the condensed water is pure and drinkable.
This is a very simple process, but it does require a lot of energy to use. That has led it to be the dominant form of desalination in areas where energy is cheap, often due to abundant solar power. In some cases, sunlight can even be focused and used to heat the water directly on a small scale!
The boiling point of water varies depending on the level of pressure in the local environment. In nature, this will rarely lead to a change of more than a few degrees in either direction. Humans can make the change much more extreme in a mechanical environment, which makes it easier to boil water for desalination without a gigantic investment of energy. In extreme cases, they can even increase the pressure so much that the water will boil at the ambient temperature, without adding any additional heat to the system!
This process is known as low-temperature thermal desalination, and it is one of the factors that makes the process economically viable. The precise balance between changing temperature and changing pressure will vary depending on the desalination plant that is doing the work, and will always be calibrated to fit the needs and economic situation of the communities that the plant serves.
It Can Be Green
Thermal desalination can be great for the environment. Fresh water is in short supply, and most regions are using it faster than the reserves can recover. Desalination reduces strain on the water supply, which allows people to meet their needs without damaging the environment to extract more water.
The main environmental cost comes from energy usage, but that isn’t a problem in places that use green energy. Since that type of energy is becoming more common, the environmental benefits of thermal desalination are continuing to grow, which is likely to make it a key part of sustainable design in the future.