Freshening, desalination, or desalination is a series of industrial processes conducted to remove all or part of excess salts and minerals from water. This term may be used to remove salts and minerals dissolved in water. Sea water can be desalinated so that it can be used in practical life such as agriculture, drinking and industry.
A large number of countries that suffer from water shortages are now interested in this applied science, and it is expected that during the next ten years, the application of this science will grow significantly due to the expected occurrence of water crises in many countries of the world, as some statistics indicate the death of hundreds of thousands annually due to scarcity of pure water for human use. The Arab Gulf countries desalinate sea water on an industrial level.
Currently, California suffers from a significant lack of rainfall and a state of drought during the past years, and for this they are starting to establish 17 water desalination plants on an industrial level.
The desalination process requires techniques that consume a lot of energy and money, with harmful effects on the environment. Energy consumption in the desalination process is considered one of the important problems and difficult obstacles that need to be overcome. It is one of the goals that are being worked on in scientific centers that focus on finding alternatives with less energy consumption, more effective and environmentally friendly.
The current world trend varies between seawater desalination or wastewater and rainwater treatment and reuse. We find that most of the water desalination plants are located in the Arabian Gulf and Libya, while most of the treatment plants are located in separate regions of the world such as the United States of America, Singapore and European countries.
The desalination process takes place in three basic stages before the distribution and pumping process in the network, as follows:
The methods currently used for water desalination revolve around two methods, namely:
Using membranes: In the desalination process, a semi-permeable membrane known as the reverse osmosis membrane is used, as this membrane allows the passage of fresh water in the direction of low pressure and the salt and bacteria do not pass through it. This requires increasing the pressure on the part of the membrane that is filled with sea water, and this pressure is about 70 bar (70 atmospheric pressure). This pressure is usually produced by electric pumps. Other membranes are also used for this process, such as electrophoresis. There are other types being researched, such as forward osmosis, nanofilters, and desalination membranes. Most of the existing researches focus on finding better and more effective membranes. Water desalination is expected to spread in many places during the next twenty-five years.
Distillation: This process consists in raising the temperature of salty water to a boiling point and forming water vapor, which is then condensed into distilled water, so the distilled water is free of salt. This distilled water has no taste, and then it is treated with additives to make it suitable for drinking or irrigation. This technology is often used when semi-free water treatment is required for industrial, chemical, biological applications...etc.
The thermal energy used may come from natural gas, coal, or a nuclear reactor, and the water evaporation process is used.
There are four types of distillation used in the desalination process:
This method is used in desalination plants with small production capacities.