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Chlorination - Disinfecting agent used in water treatment
- 1. CHLORINATION By PradumnBalaji Suryakar Government college of engineering aurangabad BE17F01F049
- 2. Introduction Presence ofturbidities,colour, or minerals etc may not be dangerous But presence of even a single harmful organism will definitely prove dangerous So disinfection is the most important process Chemical used as a disinfectant must be able to give the RESIDUAL STERILISING EFFECT ,so chlorine is most ideal disinfectant
- 3. Minor methods ofDisinfetion 1. Boiling of water 2. Treatment with excess lime 3. Treatment with Ozone 4. Treatment with iodine and bromine 5. Treatment with ultra-violet rays 6. Treatment with potassium permangate 7. Treatment with silver , called Electro-Katadyn process
- 4. Chlorination Advantages Cheap Reliable Easy to handle Easily measurable Capable of providing residual disinfecting effect Disadvantage When used in more amount it imparts bitter taste to the water
- 5. Doses of Chlorine Dose depends upon the inorganic and organic impurities present in water Inorganic impurities like S ,Fe ,Mn ,etc convert chlorine to chloride (no residual oxidising power) Excess chlorine is consumed by ammonia to form chloramines (combined chlorine) Chlorine consumed in above reaction represent the chlorine demand of water Once it is satisfied , the chlorine will appear as free chlorine
- 6. Free chlorineas well as the combined chlorine(Chloramines) will cause germicidal action on bacteria and pathogens. The free chlorine will instantaneously kill pathogens ,while the combined chlorine will provide long term germicidal effect Chlorine dose is increased during Rainy season and epidemics
- 7. Advantages of freechlorine 1. Can be easily stored for long period 2. Quite cheap and easily available 3. Occupies less space for storage 4. Low initial cost of installation 5. Very powerful disinfectant and may remain as residual 6. No need of skilled supervision 7. No sludge is formed
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- 9. Plain chlorination Onlythe chlorine treatment is given to water ,no other treatment is given Helps in removing bacteria ,organic matter, and colour Used when turbidity is less than 20-30 mg/l May be used in emergencies also Normal dose of chlorine=0.5 mg/l
- 10. Pre chlorination Processof applying chlorine to the water before filtration or sedimentation –coagulation Helps in coagulation and reduces loads on filters Reduces taste ,odour ,algae , other organisms Normal dose of chlorine=5-10 mg/l Post chlorination Normal process of applying chlorine in the end,when all the other treatments have been completed In water supplies ,it is adopted after filtration Residual chlorine = 0.1 - 0.2 mg/l
- 11. Double chlorination Wateris chlorinated twice Pre chlorination and Post chlorination is used Used when the water is highly turbid and contaminated
- 12. Break point chlorination Dose of chlorination beyond which any further addition of chlorine will equally appear as free residual chlorine Chlorine reacts with ammonia present in water DPD test will indicate quantum of total residual chlorine Graph of Residual chlorine Vs Applied Chlorine is plotted and shown
- 14. Details of graph Amount of residual chlorine is slightly less than that of addes (AB) Beyond point B ,organic matter present in water starts getting oxidised, so R.C. starts falling (BC) Beyond C, any further addition appear as free chlorine i.e nothing is utilised….so C is called Break point Addition of chlorine beyond break point is called break point chlorination
- 15. It isessential to add chlorine beyond break point to ensure residual effect Residual chorine is not easily removed except by sunlight So it take care of the future recontamination of water in the distribution system
- 16. Super chorination Indicatesthe addition of excessive amount of chlorine Required in special cases of highly polluted water, during epidemics of water borne diseases Used when water contains cysts of histolytica (organism) Residual chlorine = 1-2 mg/l Can be removed by dechlorinating agents like sodium thiosulphate , activated carbon ,sulphur dioxide ,etc
- 17. Dechlorination Removal ofchlorine from water Required when superchlorination is done Amount of residual chlorine changes from 1-2 mg/l to 0.1- 0.2 mg/l Economical dechlorinator=Ammonia Dechlorinating agents 1. Sulphur dioxide gas 2. Activated carbon 3. Sodium thiosulphate 4. Sodium metabisulphate 5. Sodium sulphite 6. Sodium bisulphite 7. Ammonia
- 18. Tests to determineChlorine Residuals 1. Orthotolidine test 2. D.P.D. test 3. Chlorotex test 4. Starch-iodide test
- 19. Reference Water supply Engineeringby S.K.Garg
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