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1. Chapter (4) Water treatment

2. Chapter content: Introduction to water uses in industry. Sources of water. Sources of impurities of water. Nature of impurities of water. Water treatment methods. Boilers. 136

3. 1. Industrial uses of water Water is usually used in industries for different applications such as: Process water. Cooling water. Boiler feedwater. 1 3 7

4. 2. Sources of water Sea water. Surface water. Rivers and lakes. Ground water. Rain water. 138

5. 2. Sources of water Water distribution on earth 139

6. 140

7. 3. Sources of impurities in water Impurities exist in water from the following: From ground. Sewage and industrial waste. 141

8. 4. Nature of impurities in water Impurities exist in water in any of the following forms: Suspended solids. Colloidal solids. Soluble salts. Dissolved gases (i.e., CO 2 , O 2 , etc.) 142 Insoluble

9. 5. Water treatment methods 143 (1) Suspended solids Suspended solids are removed by settling (also called sedimentation ) process.

10. 5. Water treatment methods (1) Suspended solids Water is allowed to settle in large tanks (called settlers), so any suspended material will settle down. 144

11. 5. Water treatment methods (2) Colloidal solids Colloidal solids are very small solid particles that will not settle alone in sedimentation tanks (settlers). Therefore, coagulants must be added to allow settling of these colloidal particles. Examples of coagulants : salts of sulfate and aluminum (alum). (i.e., Al 2 (SO 4 ) 3 .18H 2 O) 145

12. 5. Water treatment methods (2) Colloidal solids Coagulation is defined as agglomeration and settling of colloidal particles by addition of coagulants. 146

13. 5. Water treatment methods Water treatment methods The treatment methods used for removal of suspended and colloidal solids are: Sedimentation. … removal of coarse suspended solids … Coagulation and sedimentation. … removal of colloidal solids … 147

14. 5. Water treatment methods Water treatment methods The previous two processes are associated with: Filtration. … removal of remaining solids … It is carried out by passing water through rapid filter medium in order to remove any suspended and colloidal matter remaining. 148

15. 5. Water treatment methods 149

16. 5. Water treatment methods (3) Soluble salts For industrial uses, water should not contain certain soluble salts such as calcium, magnesium, etc. Presence of these salts cause water to be known as hard water. Removal of these soluble salts called softening of hard water. 150

17. 5. Water treatment methods (3) Soluble salts Types of water hardness: Temporary hardness : It is caused by the presence of bicarbonates of metals such as: Ca(HCO 3 ) 2 , Mg(HCO 3 ) 2 . Permanent hardness : It is caused by the presence of sulfates, chlorides, nitrates of calcium and magnesium such as: CaSO 4 , MgSO 4 , CaCl 2 , MgCl 2 , etc. 151

18. 5. Water treatment methods   152