Treatment of Fresh Water Lec. 1

قال تعالى : ” وَجَعَلْنَا مِنَ الْمَاء كُلَّ شَيْءٍ حَيٍّ أَفَلا يُؤْمِنُونَ “ سورة الأنبياء 30

Introduction Water means life. Water has unique properties. Salt water or seawater has characteristics similar to fresh water with some noticeable differences because of the salts that are dissolved in water. Activities which directly or indirectly involve the use of water, often in very large quantities. e.g. 1. all industrial activities, 2. in agriculture and 3. for domestic purposes.

Limit of Water Consumption Average water consumptions reach values of up to 400 liter per person per day in the USA, while they may drop to 150 l in other western countries, where actions have been successfully implemented to reduce freshwater demand. in some African countries, where serious water shortages are experienced fresh- water consumptions are in the range of 20 l per day. The World Health Organization (WHO) recommends a lower limit for survival of 15–20 l per person per day, which is able to guarantee only basic needs such as drinking, food preparation, personal hygiene and laundry. This minimum amount needs to be increased significantly, up to 50 l per person per day, in order to guarantee needs beyond individual ones, such as those connected to hospitals, schools, basic infrastructures, etc.

Efficiency of Water Utilization it is expected that by the year 2040 the world demand for freshwater will be greater than the amount available. A future scenario such as this, requires the utmost consideration and all possible efforts should be made in order to ensure constant freshwater demand fulfilment. considerable effort has been made by scientists and technicians to optimize the management of conventional water resources in order to achieve optimum efficiency of water utilization. it is now evident that alternative sources of freshwater are necessary to meet the current and future trend in freshwater demand.

Efficiency of Water Utilization In the past, freshwater was considered as a naturally available resource, unmanufactured, and at most to be treated by means of some simple physico-chemical process in order to achieve the characteristics required for its final use. Only recently has freshwater started to be considered as a product that can be manufactured, with quality standards depending on the specific use. As such, a non conventional, yet sustainable route for freshwater production could be that offered by seawater desalination. Desalination processes make freshwater from the separation of salt from seawater or brackish water (water that has more salinity than fresh water, but not as much as seawater). As detailed in the following paragraphs,salinity seawater, constitutes a reliable sustainable source of freshwater, with high potential to fulfil the continuously increasing freshwater demand of the future.

Water Resources and Data The total amount of water provides a figure of about 1.4×10 9 km 3. Seawater is about 97.5% of the total available water, while the remaining 2.5% is constituted by underground and surface waters. A remarkable 80% of the latter is frozen water in glaciers, so that only 0.5% of the total amount available is to be found in lakes, rivers and underground.

TDS in different types of water Freshwaters differ significantly from seawaters by the relative amount of salts found in them.

Water Treatment Plant A typical water treatment plant is designed to remove odors, color, and turbidity as well as bacteria and other contaminants. FIGURE 1. water treatment plant 9Dr. Ola Abdelwahab

Coagulation and Flocculation Raw water entering a treatment plant usually has significant turbidity caused by colloidal clay and silt particles. These particles carry an electrostatic charge that keeps them in continual motion and prevents them from colliding and sticking together. Chemicals like Alum (aluminum sulfate) are added to the water both to neutralize the particles electrically and to aid in making them "sticky" so that they can coalesce and form large particles called flocs. This process is called coagulation and flocculation and is represented in stages I and II 10Dr. Ola Abdelwahab

SETTLING When the flocs have been formed they must be separated from the water. This is invariably done in gravity-settling tanks that allow the heavier-than-water particles to settle to the bottom. Settling tanks are designed to minimize turbulence and allow the particles to fall to the bottom. 11Dr. Ola Abdelwahab

FILTRATION 12 The movement of water into the ground and through soil particles, which helps in filtering the groundwater, and this principle is applied to water treatment. In almost all cases, filtration is performed by a rapid sand filter. As the sand filter removes the impurities, the sand grains get dirty and must be cleaned. The process of rapid sand filtration therefore involves two operations: 1. filtration and 2. backwashing. Water from the settling basins enters the filter and seeps through the sand and gravel bed, through a false floor, and out into a clear well that stores the finished water.

DISINFECTION Dr. Ola Abdelwahab13 After filtration, the finished water is disinfected, often with chlorine (step 5 in Figure 1). Disinfection kills the remaining microorganisms in the water, some of which may be pathogenic. Chlorine gas from bottles or drums is fed in correct proportions to the water to obtain a desired level of chlorine in the finished water. When chlorine comes in contact with organic matter, including microorganisms, Free available chlorine kills pathogenic bacteria and thus disinfects the water. Many water plant operators prefer to maintain a residual of chlorine in the water; that is, have some available chlorine left over once the chlorine has reacted with the currently available organics. Then, if organic matter like bacteria enters the distribution system, there is sufficient chlorine present to eliminate this potential health hazard. Tasting chlorine in drinking water indicates that the water has maintained its chlorine residual.