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Disinfection in water treatment plant
The document discusses various methods of disinfecting water, including their advantages and disadvantages. It describes boiling, ozone, bromine, iodine, UV rays, potassium permanganate, silver, and excess lime processes. Chlorine is highlighted as a widely used and effective disinfectant, though it can produce undesirable byproducts. The document also lists several purposes of chlorine in water treatment processes.
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Disinfection in water treatment plant
- 1. By Dr. M. PrasadPh.D.,
- 2. The processof destroying or killing the bacteria and other micro-organisms is Known as Disinfection. The chemicals used in this process are termed as Disinfectants.
- 3. In thewater treatment processes like sedimentation, coagulation, filtration, etc considered so far, all the bacteria from the water can not be removed. Moreover there is chance of getting the water contaminated during it flow through the water distribution system especially in case of intermittent supply, where the pipes remain empty for a considerable period The presence of turbidity’s, colour, minerals etc may not be dangerous but the presence of even single harmful organism will be definitely dangerous thereby making disinfection as the most important process.
- 4. The disinfectionnot only removes the existing bacteria from the water at the plant but also ensures their immediate killing even afterwards in the distribution system. The contamination of water during its transit from the treatment plant to the place of its consumption is also thus, prevented by disinfectants
- 5. disinfectants should be:- Destroy all the pathogenic bacteria and make the water potable. They should not take much time to kill the bacteria, under normal temperature conditions. Should be harmless, unobjectionable to tongue, economical, measurable by simple test.
- 6. Boiling ofwater By ozone Bromine iodine Ultra Violet rays Potassium permanganate Silver or electro- katadyn Excess lime process
- 7. Boiling ofwater 10-15 mins. at 100oC Bacteria get killed due to boiling Effective but not practically possible for public water supplies Kills existing germs but do not take care of future contamination. Not suitable for large scale treatments.
- 8. Ozone gasis unstable allotropic form of oxygen, with each of its molecules containing three oxygen items. It can be produced by passing high tension electric current through the stream of air in a closed chamber 3O2 under high electric arc voltage 2O3 Ozone breaks down into nascent oxygen as O3 O2 + O The nascent oxygen so produced is powerful oxidizing agent and removes the organic matter and bacteria from water.
- 9. Addition ofexcess lime kills bacteria in the waters Addition of 14-43 ppm of excess lime has been found to remove the bacterial load by about 99.3-100% from highly polluted waters Bacteria gets killed due to increased pH value resulted by the addition of lime Disadvantages Cannot protect water from recontamination, hence not used. Treatment like re-carbonation for the removal of excess lime for the further purification of water need to be done hence not useful.
- 10. The quantityof this disinfectants may be limited to about 8 ppm and contact period of 5 min. is generally enough. These disinfectants are now a days are also available in form of pills and are thus very handy. They are not used for treating any large scale public supplies but may be used for treating small water supplies for army troops, private plants, swimming pools etc.
- 11. Ultraviolet raysare invisible rays having wavelength 1000-4000 mμ and can be produced by passing electric current through mercury enclosed in quartz bulbs. The water to be treated with ultraviolet rays should, however, be less turbid and low in colour. Normally it should be colorless and turbidity should not exceed 15 mg/l The depth of water over the bulbs should not generally exceed 10cm or so because these rays can effectively penetrate through this much distance only.
- 12. Advantages Sterilization withUV-rays does not impart any addition taste or odour to water, as no chemicals are added. The method possesses ample scope for treating small quantities of water in hospitals and dispensaries for surgical uses or for drinking purposes for the place where cost is minor factor. Disadvantages Method is very costly, needs technical know how, and possesses possibilities of interruption due to failure of electricity.
- 13. This isused as popular disinfectant for disinfecting well water in villages which are generally contaminated with lesser amount of bacteria. Normal doses of this disinfectant varies between 1-2mg/l with a contact period of 4-6hrs. Advantages Besides killing bacteria it also helps in oxidizing the taste producing organic matter hence it is added in small doses to chlorinated water also. It has also been used as an algaecide and for removing colour and iron from water.
- 14. Potassium permanganatethough cheap , handy and useful yet can’t guarantee 100% removal of bacteria. It can possibly remove organisms causing cholera , but is of little use against other disease organisms. Water treated with potassium permanganate with the passage of time, produces a dark brown precipitate , which is noticeable as a coating on porcelain vessels and is difficult to remove without scouring.
- 15. Process In thismethod of disinfection metallic silver ions are introduced into the water by passing it through a tube containing solid silver electrodes which are connected to a DC supply of about 1.5 volts. The recommended silver dose may vary between 0.05 to 0.1 mg/l , and the required contact period may vary between 15 minutes to 3 hrs
- 16. Advantages The silvertreatment neither imparts any taste and odour to water nor it produces any harmful effects on human body. The method removes algae and its germicidal property is retained for a considerable time, thus allowing some safeguard against future contamination Disadvantages Use of silver is very costly and hence not adopted for treating for public supplies. Suspended organic matter and hydrogen sulphide should be removed before using this disinfectant hence it adds to cost of disinfection
- 18. • Time • pH •Temperature • Concentration of the disinfectant • Concentration of organisms • Nature of the disinfectant • Nature of the organisms to be inactivated • Nature of the suspending medium
- 19. 19 Chlorine has manyattractive features that contribute to its wide use in the industry. Four of the key attributes of chlorine are that it: • Effectively inactivates a wide range of pathogens commonly found in water; • Leaves a residual in the water that is easily measured and controlled; • Is economical; and
- 20. 20 • Has anextensive track record of successful use in improving water treatment operations. • There are, however, some concerns regarding chlorine usage that may impact its uses such as: • Chlorine reacts with many naturally occurring organic and inorganic compounds in water to produce undesirable disinfection byproducts (DBPs); • Hazards associated with using chlorine, specifically chlorine gas, require special treatment and response programs; and • High chlorine doses can cause taste and odor problems.
- 21. 112 21 • Chlorinepurposes in water treatment • Taste and odor control; • Prevention of algal growths; • Maintenance of clear filter media; • Removal of iron and manganese; • Destruction of hydrogen sulfide;
- 22. 22 • Bleaching ofcertain organic colors; • Maintenance of distribution system water quality by controlling slime growth; • Restoration and preservation of pipeline capacity; • Restoration of well capacity, water main sterilization; and • Improved coagulation by activated silica.