Page 40 - Statistics presented by Dr. Sara Ismail Aborass
P. 40

9/8/2023

            CHEMICAL TREATMENT FOR WATER PURIFICATION :

                1) Coagulation and Flocculation :
               - Many impurities in water are present as colloidal solids

                  which will not settle during sedimentation process. Their
                  removal is achieved by the addition of harmless chemicals
                  (coagulants).
               - The coagulant is a metal salt which reacts with alkalinity in
                  water to produce gelatinous (metal hydroxide) precipitate
                  which incorporates the colloidal impurities. This fine
                  precipitate is then flocculated, by means of gentle motion,
                  to produce settlable solids. Examples of coagulants are Al3+
                  and Fe3+ salts.
               ⚫ Al2 (SO4)3. 18H2O known as alum is the most commonly
                  used coagulant.

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               2) Disinfection :
               Chlorine (Cl2 )(and its compounds) is widely used
               -Chlorine

              -Monochloramine and Dichloramine
                          Cl2 + NH3 → NH2Cl + HCl
                                       Monochloramine

                            NH2Cl + Cl2→ NHCl2 + HCl
                                           Dichloramine

                Ammonia may be present in water or added as
                solution NH4OH or (NH4)2SO4.

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