Water Desalination: An Essay for Dr. Athraa Hameed Turki Date: 22/09/2020 | Views: 1544

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Water scarcity has become a fast-growing major global challenge that is linked to climate change. Desalination is a source of freshwater tapping into the vast reserves of seawater and brackish water. There are various emerging technologies for water desalination. Firstly we define the water, as a colorless, tasteless, and odorless liquid, and it consists mainly of molecules each of which contains one oxygen atom and two hydrogen atoms and is symbolized by the symbol (H2O). Water is one of the most abundant resources on the earth's surface, occupying approximately 72% of its surface area. Therefore, planet Earth is sometimes called the blue planet, and water makes up 70% of the adult human body, 75% of the bird's body, and 80% of the fruits and vegetables. Despite the simplicity of the installation of the water, it is one of the most unusual and exceptional substances in nature, as water is the largest solvent on Earth's surface and has variable physical properties. Water contains different types of salts that are found in the form of chlorides, sulfates, or carbonates, such as sodium, calcium, and magnesium, and these salts are not suitable for human use such as drinking, washing, and cooking. Many countries that are located in desert and arid regions seek to desalinate seawater to get rid of dissolved salts and make it suitable for drinking and human use. The world today faces great challenges to meet the growing needs for drinking water and various human activities, as the quantities of potable water are still far below the level required to meet personal needs, especially in developing countries and poor countries. Therefore, scientists and researchers have resorted to developing a system by which saltwater in the seas and oceans is converted into water suitable for human use, which is known as the process of (desalination). The desalination process mainly depends on removing the excess salinity from the water and converting it into safe drinking water. Also, the salinity of the water may be reduced for use in the irrigation of agricultural crops and industrial processes. There are many different ways and methods by which water desalination can be done, and to determine the method used, several things must be known at the desalination site, namely:
1- Geographical location conditions.
2 - Analysis of available water, whether it is seas, lakes, or wells.
3- Study the population and development activities surrounding the study area.
4- Knowing the current and expected consumption pattern during the next twenty years.
5- Knowing the sources of saltwater and the stability of its chemical and natural composition.
6- Determine the available conventional energy sources.
7- Identify available alternatives to energy sources, such as solar and wind energy.
Solar desalination water is one of the promising methods to convert saline water into freshwater by converting solar energy into heat. There are two basic methods to achieve desalination using this technology, direct and indirect. Solar water desalination is very similar to the natural hydrological process in which the sun heats the oceans and sea, then the water is evaporated through the free convection to form clouds. when The cloud is condensed the water is obtained as rainfall. The saline water is heated by the heat of the sun through an inexpensive and simple device called (home desalination device), it is formed as a pyramid basin and its surface is made of glass or transparent plastic to allow the passage of solar radiation to the bottom of the basin. the basin must be covered with matte black paint to absorb the solar radiation and keep the heat inside it. the result of the rising temperature of the saline water, it turns from a liquid to a gaseous state (evaporation process), where the vapor rises to the top. As a result of the surface of the cover being colder than the vapor, the condensation process occurs on the top cover of the glass or plastic and then the distilled water is collected in a separate collection tank, while the salts remain in the bottom of the basin. The freshwater amounted by this process is proportional to the transparent cover's surface area so that the productivity of the freshwater increases with increasing the area in which the water vapor collects. the average amount of fresh water produced from solar water desalination per square meter of the surface area of condensation is about (2- 3) liters. These amounts may change due to the weather conditions and the change in the position of the sun during the day. The quantity of the freshwater producing from desalination using direct solar energy is comparatively small, and it may be suitable for personal and household needs only, so the indirect desalination method was used to increase the productivity of freshwater. the indirect desalination method is done by combining two different technologies, where solar panels are used to collect solar radiation, solar energy, and a specific method of desalination such as multi-effect evaporation method (MEE), reverse osmosis (RO) method, or multi-stage distillation (MSF). Therefore the solar energy is one of the most important renewable energy sources that reduce dependence on fossil fuels as an energy source that leads to reduce the costs needed to operate desalination plants.