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Treatment of sewage
- 1. TREATMENT OF SEWAGE • Sewage before going to disposed in rivers or other on land, has to be treated , so as to make it safe. The degree of treatment is depends upon the characteristics of sewage. If sewage is no properly treated, the point of disposal became insanitary and may leads to air or waterborne diseases.
- 2. TREATMENT OF SEWAGE • Sewage can be treated in different ways. Treatment processes are often classified as 1. Preliminary Treatment 2. Primary Treatment 3. Secondary Treatment (Or) Biological Treatment 4. Complete Final Treatment.
- 3. TREATMENT OF SEWAGE • PRELIMINARY TREATMENT : • Preliminary treatment consists separating the floating materials like dead animals, tree branches papers, pieces of rags wood e.t.c,. And also removing the heavy inorganic solids. • This treatment reduces the B.O.D of wastewater by about 15 to 30 %.
- 4. TREATMENT OF SEWAGE • PRELIMINARY TREATMENT : • The processes consists of • 1. Screening for removing floating papers, rags, clothes e.t.c, • 2.Grit chambers or Detritus tanks for removing grit and sand • 3. Skimming tanks for removing oils and greases.
- 5. TREATMENT OF SEWAGE • PRIMARY TREATMENT : • Primary treatment consists in removing large suspended organic solids. • This is usually consists of settling basins to carry sedimentation process. • The liquid effluent from primary treatment contains a large amount of suspended organic material and has high BOD about 60 %. • Some times the preliminary treatment and primary treatment are classified under primary treatment.
- 6. TREATMENT OF SEWAGE • SECONDARY TREATMENT : • Secondary treatment involves further treatment of effluent coming from the primary sedimentation tank. • This is generally accomplished through biological decomposition of organic matter, which can be carried out either under aerobic or anaerobic conditions. In this process bacteria will decompose the fine organic matter to produce clearer effluent.
- 7. TREATMENT OF SEWAGE • The treatment reactors in which the organic matter decomposed by aerobic bacteria are known as aerobic biological units. Those are • 1. Filters, called trickling filters. • 2 . Aeration tanks • 3. Oxidation ponds and Aerated lagoons.
- 8. TREATMENT OF SEWAGE • The treatment reactors in which the organic matter is decomposed and stabilized by anaerobic bacteria are known as anaerobic biological units. Those are • 1. Anaerobic Lagoons • 2. Septic tanks • 3. Imhoof cones.
- 9. TREATMENT OF SEWAGE • The effluent from the secondary biological treatment will consist 5 to 10 % of BOD and may contain some ML of DO. • The organic solids or sludge separated in primary and secondary treatment processes will dispose of by stabilizing them under anaerobic process in a Sludge Digestion tank.
- 10. TREATMENT OF SEWAGE • COMPLETE FINAL TREATMENT: • This treatment is sometimes called as Tertiary treatment and consists in removing the organic load left after the secondary treatment, and particularly to kill the pathogenic bacteria. This is normally carried out by Chlorination.
- 11. PRILIMINARY TREATMENT SCREENING Screening is the first process operation carried out at a sewage treatment plant and consists of passing the sewage through different types of screens as to trap and removal of floating matter. Depending on the size of the openings, screens are classified as coarse screens, medium screens and fine screens.
- 12. PRILIMINARY TREATMENT • 1. COARSE SCREENS are also knows as RACKS and having the spacing between the bars about 50 MM or more. These screens do help in removing the large floating objects from sewage. • 2. MEDIUM SCREENS , the spacing between the bars is about 6 to 40 MM. the screens will ordinarily collect 30 to 9 liters of material per million liters of sewage.
- 13. PRILIMINARY TREATMENT • Fine screens have perforations of 1.5 to 3MM in size. The installations of these can remove 20% of suspended particles from the sewage. The screens will get clogged very frequently because of very low aperture size. Thus is require frequently cleaning , other wise the effeincy of the filter will be decrees.
- 17. PRILIMINARY TREATMENT GRIT CHAMBERS Grit chambers are used to remove the inorganic particles like sand, gravel, grit , egg shells, bones and other non biodegradable particles. Such type of particles may clog the channels or damage sewers due to abrasion.
- 18. PRILIMINARY TREATMENT • Generaly grit chambers are designed to remove the particles of higher specific gravity 2.65 and so. • The grit chambers are two types, depending on the direction of flow: those are • 1 Horizontal flow grit chamber. • 2. Vertical flow grit chamber.
- 23. PRILIMINARY TREATMENT • The horizontal grit chambers are to be designed with the velocity, should neither too low as to cause the silting of lighter particles nor too high as to cause the scour the chamber. • The critical scour velocity is calculated by using the expresion, 3 to 4.5(gd(G-1))0.5
- 24. PRIMARY TREATMENT • TYPE – I SETTLING • Plain sedimentation is carried in a special designed tank called settling tanks or settling basins or sedimentations tanks. • The components of the sedimentation of the sedimentation tanks are • 1. Enclosure tank • 2. Inlet and outlet arrangements • 3. Skimming troughs.
- 25. PRIMARY TREATMENT • CLEANING AND SLUDGE REMOVAL; The suspended organic matter contained in the sewage , settled in the bottom of the tank and have to be removed periodically other wise the capacity of the tank will be decrease and the organic matter will try to decompose by the bacteria thus evolve the foul gases which create the insanitary conditions at the sedimentation tank. The sludge collected from the bottom of the tank is send to the sludge digester. In early stages aerobic decomposition takes place after the consumption of all the oxygen the Anaerobic decomposition takes under closed conditions.
- 26. PRIMARY TREATMENT • The sludge collected from the bottom of the tank is send to the sludge digester. In early stages aerobic decomposition takes place after the consumption of all the oxygen the Anaerobic decomposition takes under closed conditions. After complete decomposition the sludge is removed from the digester and can used for land filling to elevate the low laying areas.
- 27. PRIMARY TREATMENT • TYPE –II SETTLING : • The larger suspended particles are been removed from the tank in type- I settling and remaining very fine colloidal particles will not settle down even though we offer a large detention periods. • The colloidal particles which are present in the sewage can be removed by adding chemicals called coagulation. • The chemicals which are used in the process of coagulation are called coagulants. • form as a big molecule and helps in the sedimention.
- 28. PRIMARY TREATMENT • As the coagulants added and mixing with the sewage, they will form a gelatinous substance called FLOC. These formed floc will attract the adjacent particle and form as a big molecule and helps in the sedimentation. • The floc will aslo neutralize the charge if the colloidal particle thus the particle can be come to rest. • The iron salts are majorly using as coagulant for the treatment of sewage through out the world.
- 29. PRIMARY TREATMENT • The coagulation process is generally not adopted in sewage treatment plants because of the reasons • 1. more advanced methods of sewage treatment based on biological treatment are available now a days and they are more preferable than coagulation • 2. the chemical used in the coagulation process can destroy the microorganisms, which help in the cleaning process. • 3. the cost of the chemicals added to the cost of the coagulation and thus the coagulation process will be costlier. • 4. the coagulation process require skill labor for proper adding and mixing of the coagulants to the sewage.
- 30. PRIMARY TREATMENT • However the process of coagulation is disadvantageous, it can give a clear effluent, which can be disposed off directly. • Coagulation can also remove phosphates from the sewage, which may help in the EUTROPHICATION of lakes.
- 37. SECONDARY TREATMENT • The secondary treatment of sewage is also called as biological treatment. • All the secondary treatment process are designed to work on Aerobic decomposition. • The secondary treatment is very important in the converting the complex organic matter into simple organic matter. • The efluent coming from primary treatment has contain 80 to 90% of BOD.
- 38. SECONDARY TREATMENT • The secondary treatment process mainly consists of filters, which consists of open beds of coarse aggregates. • The sewage is allowed to sprinkled intermittently on the filter beds. the necessary growth of the aerobic bacteria is provided by the aggregates in the bed, and aeration is provided by the nature. • There are various types of filters are used for the secondary treatment of sewage. All the filters try to oxidize the unstable organic matter into simple organic matter.
- 39. SECONDARY TREATMENT • There are different types of filter used in the secondary treatment are: • 1.Contact beds • 2. Intermittent sand filters • 3. Trickling filters • 4. Miscellaneous filters.
- 40. SECONDARY TREATMENT • CONTACT BEDS: • Contact beds are also called as contact filters, sewage is kept in contact with filter media for a certain period.
- 43. SECONDARY TREATMENT • INTERMITTENT SAND FILTER : • Intermittent sand filters are the earlier from of the biological units of sewage, now rarely use because of large surface area. • In intermittent sand filter the filter media is finer than the contact beds and their is no concrete lining around the filter.
- 46. SECONDARY TREATMENT • TRICKLING FILTER : • Trickling filters are also called as percolating filters or sprinkling filters. • They consists of tank of coarser filtermedia on which sewage is allowed to srpinkle ar trickled down. • The percolated sewage is collected at the bottom of the tank through a well designed under drain system.
- 47. SECONDARY TREATMENT • The microorganisms and bacteria which are already present in the sewage get attached to the filter media. • The organic matter present in the sewage will also adsorbed to the filter media, to form BIOLOGICAL FILM. • This formed bio layer is also called as SLIME layer. • As the microorganisms growth increases, the thickness of slime layer will also increase.
- 48. SECONDARY TREATMENT • The difffused oxygen is consumed by the bacteria present on the top layers of the Slime layer. • This create the oxygen deficiency in the bottom layers of the slime layer, which causes the anaerobic decomposition. • The liquid sewage will exerting Shearing action, then breakup some Slime layerfrom the media. But slime layer will grow continuously.
- 49. SECONDARY TREATMENT • The continuous growth and break up of the slime layer creates a blaance in thickness of the layer. • The breakup or detachment of the bio film from the slime layer is called SLOUGING. • The effluent obtained from the drain of the filters must be taken to the secondary sedimentation for settling out the Slougged Slime.
- 50. SECONDARY TREATMENT • CONSTRUCTION : • The trickling filter generally consists the following components, • 1. Rotary distribution • 2. Filter media • 3. Enclosure tank • 4. Under- drain system.
- 51. SECONDARY TREATMENT • The rate hydraulic loading rate of the high rate trickling filters has 40-200 cuM / Sqm. D • The wall of the filter media are made with honey-comb structures for circulating air into the layers of the filter media. • Depending on the rate of filteration, the trickling filters are classified into two types. • 1. standard rate filters • 2. High rate filters.
- 52. SECONDARY TREATMENT • OPERATIONAL TROUBLES: • There are some operational troubles which will arise while operating the filter. • 1. Fly nuisance • 2. Odour nuisance • 3. Ponding trouble.
- 58. SECONDARY TREATMENT • RECIRCULATION OF SEWAGE