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Water purification presented by Dr . Amel A. rahim suliman

The purpose of water treatment is to provide safe and wholesome water The stages of purification are :(1) Storage (2) Filtration (3) Disinfection Storage :Is natural purification , the water drown out from the source in the artificial reservoir there is 3 point of view :a/ physical : the suspended impurities settle down in 24 hours by gravity so water become clear , allow penetration of light

b/ chemical :during storage the aerobic bacteria oxidized the organic matter with aid of .dissolved oxygen c/ biological : by storage the pathogenic organism gradually die ,the optimum storage of water about 10 -14 days , 90% of bacteria die in the first 5 -7 day . Storage for longer period developed vegetable growth witch produce bad .color and smell :-Filtration Is important stage because 98 – 99% of the . bacteria are removed by filtration

:-There is 2 type of filtration 1/ Biological or slow sand filter 2/ mechanical or rapid filter . :-Slow sand filters The elements of slow sand filter are :  Supernatant ( raw ) water .  Abed of graded sand .  An – under drainage system .  Filter control valves .

:-supernatant water/ 1 :Its above the sand bed survey 2 important purposes  promote down ward flow of water through the sand bed .  it provides waiting period 3 - 12 hours for raw water to under go partial purification by sedimentation and oxidation . 2/ sand bed :The thickness of it, is 1 meter , diameter between 0.2 – 0.3 mm should be clean and free from clay and organic matter . It presents a vast surface area . The purification processes are mechanical straining ,sedimentation , adsorption , oxidation and bacterial action .

Vital layer : is slimy gelatinous layer and consist . of thread like algae , bacteria ,and plankton This layer formed after several days in new filter :-Uses of vital layer ďƒ˜ removes organic matter . ďƒ˜ holds back bacteria . ďƒ˜ oxidized ammonia cal nitrogen into nitrates. 3/under drainage system :Witch is found at the bottom of the filter bed it consist of perforated pipes permit water passage

Criteria of filter box : Is an open box usually rectangular shape from 2.5 – 4 meter deep and the built wholly or partially below ground, the walls made of stone , bricks or cement . 4/ filter control :The filter is equipped with certain valves and devices witch are incorporated in the out letpipe system , the purpose of these devices is to maintain a constant rate of filtration

2/ Rapid sand or mechanical filter:The steps involved in purification of water by rapid sand filter are : a/ coagulation . b/ rapid mixing . c/ flocculation . d/ sedimentation . e/ filtration . ďƒ˜ coagulation witch is the 1st step , the raw water treated with chemical coagulation such as alum the dose 5 – 40mg/ liter depending up on the turbidity , color . Temperature and PH of water

Rapid mixing : the treated water is subjected to violent agitation in a mixing chamber for few minutes this allows quick dissemination of alum through out the water . Flocculation : it involves a slow and gentle stirring of the treated water in flocculation chamber for about 30 minutes. this processes result in the formation of thick , copious ,white flocculants precipitate of aluminum hydroxide . Sedimentation :the coagulant water inter into sedimentation tanks where stays for 2 – 6 hours The flocculants precipitate before enter the last step

Filtration : the residual alum – floc is held back on the sand befit form slimy layer witch absorbs bacteria .

Riv er

Flow diagram of a rapid sand filtration plant Flocculation chamber

Sedimentation Tank


Mixing Chamber

Filters Chlorine


Clear water storage

Rapid Space Rate of


Treatment Removal of bacteria Washing

Occupies small area

Slow Large area

Rapid should be characterized by : Chemical treatment

% 99- 98 By back washing

Slow Simple sedimentation % 99.9 By scraping the sand bed


: The chemical used as disinfectant in water should be characterized by  should destroy the pathogenic organism present with contact time and not / 1 . unduly influenced by water temperature , PH and mineral content . should not leave products of reaction that made water toxic/ 2  .should be available at reasonable cost/ 3  should have property of leaving residual concentration to deal with small / 4 .possible recontamination should be tested by simple technique to detect the efficiency of the / 5  .disinfectant :-Chlorination   .It of great value in water purification )Chlorine has germicidal effect ( virus need high dose  .It oxidized iron , manganese and hydrogen sulphate  .It control algae and slime organism  :-Action of chlorine  When chlorine is added to the water formation of hydrochloric acid and  . hypochlorus acid occur 




The disinfection action of chlorine is mainly due to the hypochlorous acid  witch is the most effective form of chlorine .its effectively is 70- 80 times than .the hypochlorite iron Chlorine is best acting when the PH of water around 7  :-Principles of chlorination  .the treated water by chlorination should be clear and free from turbidity / 1  the chlorine demand of water should be estimated (is difference between / 2  the amount of chlorine added to the water and the amount of residual chlorine remaining at the specific period 60-minute) at given temperature .and PH of water contact period . The presence of free residual chlorine for a contact period / 3  . at least 1 hour essential to kill bacteria and virus as . the minum amount of residual chlorine is 0.5 mg/l for 1 hour / 4  the sum of the chlorine demand of the specific water +the free residual / 5  .chlorine = the correct dose of chlorine to be applied

:-Method of chlorination  .chlorine gas/ 1  .chloramine/ 2  .perchloron/3  chlorine gas commonly used because is cheap quick in action and easy to apply . Disadvantage: has an .irritant to eyes and poisonous :-Ozonation  Is an unstable gas witch is apowerfull oxidizing agent . The dosage required 0.5-1.5 mg/l :-Ultraviolet  Is germicidal rays. The water should be free from  turbidity disadvantage has no residual effect of rays

:-Purification in small scale  .boiling/ 1  chemical disinfection/ 2  .Chlorine tabs .Chlorine solution .Bleaching power .Iodine filtration/ 3

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