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 â€“ 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 â€“ 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 â€“ 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 â€“ 6 hours The flocculants precipitate before enter the last step
Filtration : the residual alum â€“ floc is held back on the sand befit form slimy layer witch absorbs bacteria .
Flow diagram of a rapid sand filtration plant Flocculation chamber
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
HCL + HOCLH2o + CL2
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