Advance water treatment
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- 2. AERATOR It is a mechanical process of bringing water in intimate contact with air, so as to absorb oxygen and to remove carbon dioxide gas. It may also help in killing bacteria to a certain extent. It may also helps in removing H2S gas, and iron and manganese to a certain extent, from the treated water. 2
- 3. It serves, To increase dissolved oxygen content. To remove tastes and odours. To remove hydrogen sulphide. To decrease carbon-di-oxide. To convert iron and manganese from soluble to insoluble states. To kill bacterias to some extent. 3
- 4. METHODS OF AERATION The methods aeration of water can be carried out in one of the following ways: By using spray nozzels By permitting water to trickle over cascades By air diffusion By using trickling bed 4
- 5. 1. By using spray nozzels: In this method, water is sprinkled in air or atmosphere through special nozzles which breaks the water into droplets, thus permitting the escape of dissolved gases. CO2 gas is removed( upto 90% or so) in this method. 5
- 6. 2. By permitting water to trickle over cascades: It is a waterfall and a simple cascade consists of a series of three or four steps. The steps may be of concrete or metal. The water is made to fall through a certain height (1 to3m) over a series of steps (3 to 10) with a fall of about 0.15 to 0.3 m in each step. The structure so formed is know as a freefall aerator. The simplest type of a freefall aerator is know as a cascade aerator. 6
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- 8. 3. By air diffusion: In this method, compressed air is bubbled through the water, so as to thoroughly mix it with water. Perforated pipes are installed at the bottom of the settling tanks, and the compressed air is blown through them. The air bubbles while coming up from the bottom of tank and aeration of water is thus achieved. The depth of aeration tanks is generally kept as about 2.5 to 3m . they work on the principle of continuous flow with minimum detention period of 15 minutes. 8
- 9. The quantity of air consumed per 1000 litres of water varies from 0.3m3 to 0.6 m3 9
- 10. 4. By using trickling bed: In this method, the water is allowed to trickle down the beds of coke, supported over perforated trays, and arranged vertically in series. Three beds are used, the depth of each being about 0.6m. The water is applied from the top through perforated distribution pipes and allowed to trickle down, up to the bottom bed. 10
- 11. During this downward motion, the water gets mixed up with air, and aeration takes place. The size of the coke varies from 50mm to 75mm. This method is found to be less effective than that of “spray nozzles”. But it gives better results than what can be obtained by “cascades” 11
- 12. WATER SOFTENING It is the process of reduction or removal of hardness from water. Advantage of softening Reduction of soap consumption Lowered cost in maintaining plumbing fixtures Improved taste of food preparation. To avoid corrosion and incrustation of pipes 12
- 13. TYPES OF HARDNESS: Following are the two types of hardness: Temporary hardness or carbonate hardness Permanent hardness or non-carbonate hardness 13
- 14. TEMPORARY HARDNESS OR CARBONATE HARDNESS The temporary hardness is caused by the bicarbonate and carbonate of calcium and magnesium are present in water. It can be removed either By Boling By addition of lime 14
- 15. By Boling: Calcium carbonate soluble in water, usually exist in water as calcium bicarbonate, because it easily dissolved in natural water containing CO2. Water is boiled, the CO2 gas will get out, leading to the precipitation of CaCO3, which can be sedimented out in settling tank. The reaction can be represented as Ca(HCO3)2 + Heat CaCO3 + CO2 + H2O Cal.bicarbonate Cal.Carbonate 15
- 16. PERMANENT HARDNESS: The permanent or non-carbonate hardness which is caused by the sulphates, chlorides and nitrates of calcium and magnesium. The permanent hardness is more permanent and difficult to remove. The methods of removing permanent hardness are Lime-Soda process Base-Exchange process or Zeolite process Demineralisation process 16
- 17. LIME-SODA PROCESS In this process, lime and soda ash are used to remove permanent hardness from water. It react with calcium and magnesium salts and form insoluble precipitates of CaCO3 and Mg(OH)2 The precipitates can be removed by sedimentation. 17
- 18. ADVANTAGES OF LIME-SODA PROCESS: The pH value of treated water increases which reducing the corrosion of the distribution system. Minimises coagulant dosage Removes iron and manganese to some extent Reduces total mineral content of water Removes pathogenic bacteria by some amount The process is economical 18
- 19. DISADVANTAGE: Disposal of the sludge formed is very difficult. Requires skilled supervision. Requires recarbonation. Cannot produce zero hardness 19
- 20. ZEOLITE OR BASE-EXCHAGE PROCESS : The zeolite or base-exchage process or cation- exchange process is also one of the removal of hardness. Zeolite are the natural salts or clays which are hydrated silicates of sodium and aluminium The zeolite or Resins are exchanging their cations, and during softening operation. The sodium ions of the zeolite get replaced by the Ca & Mg ions present in hard waters. 20
- 21. It may be gravity or pressure filters. Pressure filter type zeolite softeners being more common. It consists of closed steel Cyclinder. Tk of bed – 0.75 to 2m Rate of filtration- 100-300lit/sq.m/min It will results in a water of zero hardness, not Suitable for public supplies. 21
- 22. ADVANTAGES OF ZEOLITE PROCESS: Water of zero hardness, and useful for sp. Uses in textile indutries, boliers etc.., The plant is compact automatically and easy to operate. No sludge is formed The RMO(running, maintenance and operation) cost is quite less. Removes ferrous iron and manganese from H2O No problem of incrustation of pipes of the distribution system. No difficult to treating H2O 22