4 Community Water Supply Purification of Water:On Large Scale: Storage.Filtration Disinfection.Storage: Physical, Chemical, BiologicalFiltration: Slow Sand Filters/Biological FilterRapid Sand Filters orMechanical Filters
5 DisinfectionThe final stage of purification of water is disinfection ., the elimination of pathogens, and chlorination.Chlorination is the method of choice for sterilization of water, both on a large scale and small.When chlorine is added to water it forms hypochlorous acid and hydrochloric acid.H2O + CL2 = HOCL + HCL
6 The pH range of water is between 6. 5 -- 8. 0, and greater than 6 The pH range of water is between , and greater than 6.0 the hypochlorous acid:HOCL = H OCL-There are two broad groups of substances, those which form germicidal compounds and those which do not.Ammonia in water combines with chlorine to form, chloramines, and these are germicidal.Chlorine reacts with sulphides and ferrous salts, its germicidal power is destroyed.
7 Action of chlorine depends upon: Organic matter, metal and bacterial content.Temperature and pH of waterAmount of free residual chlorinePresence of suspended matter.
8 Methods of Chlorination: 1. Simple chlorination: The addition of chlorine to water in a regular controlled dose. Its use is generally restricted to waters which are pre-filtered, in which the residuum of free chlorine of 0.1 to 0.2 parts per million, after thirty minutes contact time, will ensure adequate sterilization.On a large scale chlorine gas or hypochlorite solutions are used, addition being done by means of a dosing apparatus.
9 2. ChlorinationAmmonia is added first to the water, followed by the addition of Chlorine. The latter exerts its rapid bactericidal action and then combines with ammonia to form chloramines Long action of at least 2 hours is necessary to kill bacteria.Suitable for chlorinating swimming pools.The ratio of ammonia to chlorine is usually 1:4 or 1:5.
10 Super chlorination followed by dechlorination: This process involves addition of a amount of chlorine, far in excess of the requirement. After a suitable contact time, chlorine is removed by an oxidizing agent like sulphur dioxide in the ration of 1 : 1, or sodium thiosulphite in the ratio of : 1 .This process satisfies the chlorine demand and eliminates cysts, ova and micro-organisms, not kill by simple chlorination.
11 4. Free residual or Break-point chlo - rination
12 This is applicable to waters containing ammonia, but have a low content of organic matter. The breakpoint is reached when the chloramines have been completely converted and destroyed by the excess of chlorine, and very little chlorine, free or combined is left in the water in an active form.Thus the oxidizing power of chlorine is fully utilized, and there is sufficient chlorine to satisfy the criteria of continuous disinfection.
13 When chlorine combines with organic matter in water, it forms trihalomethanes (THMs). These have been shown to cause cancer in laboratory animals.Chloroform is a common THM which has been linked to bladder cancer in those who drink from treated public water supplies.
14 Tests for Free Chlorine Orthotolidine test:This is carried out to find the pressence of both free chlorine and chloramines in water.On addition of the reagent (orthotolidine in 10% HCL)2. Orthotolidine - arsenite Test:This Is a refinement of the orthotlid -ine test, and determines separately the free and residual chlorine.
15 3. Starch iodide test:It is carried out to detect residual or free chlorine in tap water. Add 1 ml of freshly prepared starch solution to 5ml of water to be tested. A crystal of potassium iodide is added to it. If gree chlorine is present in water, a blue colour appears immediately.
16 Purification on Medium Scale Double Pot Chlorinator
17 Water for domestic use.when water is obtained from wells, springs and tanks. Disinfection is done by chlorination, usually by adding bleaching powder or chlorinated lime (CAO CaCOCl2 ).Cheap, reliable, easy to use and safe disinfecting agent. Chlorine content in fresh bleaching powder is 33 – 38 % but this reduces on storage to 25 or 20 %.
18 To disinfect a well or a tank, the quantity of water is found out and then bleaching powder at the rate of 2.5 g per 1000 liter of water is added. This gives about 0.7 mg of applied chlorine per liter.Double pot chlorinator:1 kg of bleaching powder is added to 2 kg of coarse sand. The pot is immersed in the well, and it is sufficient to provide chlorination to the well for 2-3 weeks at a time.
19 2. Horrock’s apparatus:This consists of one black and six white cups, of 200 ml capacity, a spoon of 2 gram capacity, a stirring rod, a special pipette and cadmium starch solution.The black cup, to make the “stock solution”. is filled with the water to be tested. 2g of the bleaching powder to be used, is added to this black cup.Fill the remaining 6 white cups with water up to the mark indicted.
20 Add with the help of the pipette one drop from the black cup to the first cup, 2 drops to the second and so on up to six drops to the last cup.Wait for half an hour.Add a drop or two of calcium iodide starch solution to each white cup and note which cup shows a bluish color first.The number of drops added in this cup gives the number of spoons of bleaching powder required for 450 liters of water to provide 1 PPM chloride.
21 Purification on Small Scale This can be done by following methods.Boiling:This is a simple and effective method . Roll boiling for 5 – 10 minutes kills off most microorganisms, and removes temporary hardnessDistillation:This method would get rid of all impurities however the water would be very soft, and insipid in taste. It is a very costly method
22 Chemicals:Bleaching powder. It can be kept as a strong solution, small quantities of which are used for adding to water in the dose of 200 grams to one liter to make a 5% solution.Chlorine tablets. They are also known as Halozone tablets.Iodine:Two drops of a 2% solution of iodine is sufficient to disinfect one liter of water.
23 Potassium Permanganate: It may be used by adding an amount just sufficient to give a pink coloration. It is effective against V.choleraAlum:It should be used in all turbid water, adding 0.1 to 0.4 per 5 liters of water.
25 Domestic Filtration:Three pot treatment system:In this method water which is to be utilized would have been stored for a minimum period of two days, providing sufficient time for suspende -d impurities to sediment, and improvement in quality.Pot No. 3 is the pot from which water is used for drinking purposeEach day when new water is brought into the house,Water in pot 2 is slowly poured into pot number 3, and pot 2 is washed out.Water in pot No.1 is slowly poured into pot 2, and the empty pot 1 is washed out.
26 Two pot filtration system Fresh water from the source of supply is collected in pot No.1, preferably, straining it through a clean muslin cloth.Two pot method:Two pot filtration system
27 Ceramic filters:These special micro filters in which water is made to pass through the micro pores of the candles placed inside the container. Bacteria are unable to pass through these micro pores.
29 Drinking Water:It must be calorie-free and sugar-free. Flavors, extracts or essences may be added to drinking water, but they must comprise less than 1% by-weight of the final product or the product will be considered a soft drink Drinking.water may be sodium-free or contain very low amount of sodium