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Collection and estimation of sewage


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Different types of sewers, design period, variations in sewage flow,
estimation of waste water discharge.

Published in: Education, Technology, Business
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  • Vacuum is generated in the vacuum station and the sewage in the pipeline is sucked into the collecting pit or tank in the vacuum station. The collected sewage is transferred by pumps to a sewage treatment plant. There are two options as for vacuum generation. The one is ejector system and the other vacuum pump. With the ejector system, the sewage in the collecting pit is recalculated by the circulation pumps through the special ejector which generates the vacuum. Read more ……..
    Name: Ricky YD
    Vacuum Sewer Engineer
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  • VACUFLOW ® Technology
    The vacuum sewerage system is a dry weather system which means that rain water may not be connected. The VACUFLOW ® System requires no use of so called “inspection points”. The most characteristic features of the VACUFLOW ® Technology is the guaranteed simultaneous suction and transport of sewage and air through a closed pipe network under constant negative pressure and it’s highly sophisticated, empiric adjusted, friction and static loss calculations in pipe lines.
    In addition, the VACUFLOW ® system is virtually maintenance and because it operates within a closed and leak proof vacuum system, the environment will benefit too. No sewage can escape to pollute surrounding areas.
    The vacuum system is perfect for a wide range of applications, particularly where expensive and tractate construction work is to be avoided. Think of areas under ground fill or shallow topsoil as well as areas with a high water table or where the environment is fragile.
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Collection and estimation of sewage

  1. 1. Module IIICollection and Estimation of Sewage Bibhabasu Mohanty Asst. Prof. Dept. of civil Engineering SALITER, Ahmedabad
  2. 2. Course Content Different types of sewers, design period, variations in sewage flow, estimation of waste water discharge.
  3. 3. Introduction… Sewage is water-carried waste, in solution or suspension, that is intended to be removed from a community. Also known as wastewater, it is more than 99% water and is characterized by volume or rate of flow, physical condition, chemical constituents and the bacteriological organisms that it contains.
  4. 4.  The system of pipes used to collect and carry rain, waste water and trade waste away for treatment and disposal is called the sewerage or the waste water system. There are three types of public sewers, each classified according to the kind of wastes it is required to handle.
  5. 5.  Combined sewers Sanitary sewers Strom sewers
  6. 6. Combined sewers Combination public sewers are the oldest variety of the three types of sewers and they are required to carry storm and sanitary wastes to some safe terminal. Rain water should be carried to some terminal not associated with the disposal plant
  7. 7. Sanitary sewers Sanitary sewers are those which are required to carry domestic sanitary wastes only. All rain water must be excluded from them. Combination and sanitary sewers generally are placed about ten feet under the street grade and usually are found below the centre line of the street.
  8. 8. Strom sewersStorm sewers are a comparatively new installation, made necessary because of sewage treatment.These sewers are made to carry only storm water and may terminate at any natural drainage area.
  9. 9. Problems in sewer systemThe per capita water supply (including the local and individual sources) to the population is less than the minimum requirement of water supply for the efficient performance of the sewerage system, i.e., 100 Lpcd.This will cause the operation and maintenance problems with frequent clogging, due to silting in the absence of self cleansing velocity;
  10. 10.  The topography of the town is flat necessitating deeper excavation of trenches and more number of sewage pumping stations. Either ground water table is high or the substrata are made up of hard rock, leading to difficult construction of sewerage system.
  11. 11. Sanitary sewer systemPublic sanitary sewers perform two primary functions:  Safely carry the design peak discharge,  Transport suspended materials to prevent deposition in the sewer.3 types of sanitary wastewater collection systems based on hydraulic characteristics and purpose:
  12. 12.  Gravity sewer system Pressure sewer system Vacuum sewer system
  13. 13. Gravity Sanitary Sewer Most common. Wastewater transported by gravity. Used to collect wastewater from residential, commercial, industrial, and institutional sources. Conveyance capacity allowances must be made for groundwater infiltration and unavoidable inflow.
  14. 14. Gravity sewer system
  15. 15. Pressure (Pumped) Sanitary Sewer Economical and environmentally friendly way of collecting, transporting and disposing of wastewater from households. They are often used in areas when the landscape is either very hilly or very flat, in areas that regularly flood or have high water tables, or where it is impractical to install other types of sewerage systems.
  16. 16.  A pressure sewer system is made up of a network of fully sealed pipes which are fed by pumping units located at each connected property. The pumping unit processes the household wastewater and transfers it to the pressure sewer located in the street via a small pipeline within the property.
  17. 17.  The pressure sewer system is made of four key elements. These elements are:  The pumping unit  The boundary valve kit  The house service line  The control panel
  18. 18. Pressure sewer system
  19. 19. Advantages Being smaller in diameter are installed at shallower depths than conventional sewers. They need not be laid on a precise grade as in gravity sewers, but can often go over hill below the hydraulic gradient line. Since there are no elements such as access manholes and sewer line is under pressure, the inflow from storm runoff is virtually eliminated. The system is cheaper than conventional sewerage where unfavourable conditions prevail.
  20. 20. Disadvantages They are to be differentiated from the water supply distribution system with proper colour code. Awareness among the public is required about the hazard risk of the pressure sewer system if they are tampered. Each and every house should have a collection sump and pumping facilities.
  21. 21. Vacuum Sewerage System The wastewater is being delivered by a gravity system to the pre tank of the domestic shaft. While the pre-tank being filled, an electronic sensor opens the interface valve. During the opening air flows into the mixing chamber and is being mixed with the wastewater and leaves the valve flowing into the vacuum pipe network as a water- air mixture.
  22. 22.  There are also pneumatically controlled valves that open and close depending on the vacuum in the pipe network. The vacuum pump produces a vacuum in the wastewater collection tank as well as the pipe network by which the wastewater is sucked from the pipe network to the collection tank at the pumping station.
  23. 23. Vacuum sewer system
  24. 24. Sewer Pipes Profiles circular egg-shaped (inverted) egg-shaped mouth-shaped square trapezoidal
  25. 25. Sewer Pipes Materials Concrete, Reinforced concrete, Prestressed concrete Ceramics Asbestos cement Cast iron Steel Plastics - PVC, PE, PP, reinforced with fibre-glass Resins - epoxy resin, reinforced with fibre-glass
  28. 28. Design approach Where does the wastewater come from? How much wastewater flow is there going to be? How is the wastewater going to be removed and treated?
  29. 29. Where does the wastewater come from?
  30. 30. Two main categories: Sanitary Wastewater  Wastewater from residential, commercial, institutional and industrial sources. Storm water Runoff  Wastewater resulting from rainfall running off streets, roofs, and other impervious surfaces.
  31. 31. Components of a Community’s Wastewater Domestic (sanitary) wastewater – wastewater discharged from residences and from commercial, institutional and similar facilities. Industrial wastewater – wastewater in which industrial wastes predominate.
  32. 32.  Infiltration/Inflow (I/I) – extraneous water that enters the sewer system from the ground through various means, and storm water that is discharged from sources such as roof leaders, foundation drains, and storm sewers. Storm water – runoff resulting from rainfall and snow melt
  33. 33. Infiltration to Sanitary Sewer Systems Groundwater/percolating water in the subsurface entering a sewer system through:  Defective pipes  Leaking pipe joints  Poor connections  Cracked manhole walls etc.
  34. 34. Inflow to Sanitary Sewer SystemsWater entering a sewer system from surface sources such as:  Leaking manhole covers  Directly connected roof gutters  Cellar or foundation drains  Cross connections from storm drains and combined sewers  Yard and area drains  Cooling-water discharges  Drains from springs and swampy areas  Street wash water
  35. 35. Sanitary Sewer Overflows Heavy rains overload the system though inflow and infiltration into cracks, ill-fitting joints, and leaky manholes. To prevent hydraulic overload of treatment plants, the excessive sewage bypasses the plant and is discharged without treatment.
  36. 36. Effects of SSOsEnvironmentalNutrients and toxicants may cause algal blooms and harm wildlife. Algal blooms remove O2 from water, smothering aquatic life.Decrease in water quality reduces number and range of plants and fish.
  37. 37. Public Health Direct contact with water containing sewage can cause skin and ear infections and gastroenteritis, and cuts become infected. Illnesses result from eating fish/shellfish that swim in sewage contaminated waters.Inhalation and skin absorption can also cause disease.
  38. 38. How much wastewater flow is there going to be?
  39. 39. Sources and Rates of Domestic WastewaterFlows Small residential districts – wastewater flows determined based on population density and average per capita contribution of wastewater. Large residential districts – wastewater flows developed based on land use areas and anticipated population density (typically rates are based on wastewater flows from nearby areas).If data is unavailable, estimate 70% of the domestic water-withdrawal rate is returned to the sanitary sewer system.
  40. 40. The quantity of sewage produced depends upon the quantity of water use.Generally;Average daily flow = (70 – 80) % average water consumption i.e.Average Daily Flow (ADF) of Sewage = 75%Average Daily Demand (ADD) of water consumption = 0.75 ADD
  41. 41. The flows in sanitary sewers vary seasonably monthly, daily, hourly. For areas of moderate sizes be expressed as;Maximum Daily Flow = 1.5 x ADF Where1.5 varies from place to placeMaximum hourly flow = (2 – 4) ADFThis is actually the peak flow
  42. 42.  Sewers are designed on peak flow basis, however the minimum flow passing through the sewer is also important in the design of a particular sewer because at low flow the velocity will be reduced considerably which may cause silting. So the sewers must be checked for minimum velocities at their minimum hourly flows. Generally for a moderate area the following minimum flows may be assumed.  Minimum Daily Flow = 2/3 ADF  Minimum Hourly Flow = 1/3 ADF
  43. 43. Relation Between water and waste water flow
  44. 44. Daily/Weakly variations in residential waste water flows fordry/ wet periods
  45. 45. Typical hourly variations in residential area waste water flows
  46. 46. Average Wastewater Flows from ResidentialSources
  47. 47. Average Wastewater Flows fromcommercial Sources
  48. 48. Industrial Wastewater Estimation Industries without internal reuse programs: approximately 85 to 95% of water used will be returned to the sanitary sewer system. Large industries with internal-water-reuse programs: need data on how much water is reused internally.
  49. 49. Average Wastewater Flows fromInstitutional Sources
  50. 50. Contd…
  51. 51. How is the wastewater going to beremoved and treated?
  52. 52. Types of Sewer Pipes in a Typical SeparateSanitary Collection System Sanitary sewers must be laid near all occupied buildings in order to collect wastewater. Building Connecting Pipes  Connects the building plumbing to the public sanitary wastewater collection system.  Convey wastewater from the buildings to lateral or branch sewer, or any other sewer except another building sewer.  Normally begins outside the building foundation
  53. 53. Lateral or Branch Sewers  Forms the first element of a wastewater collection system.  Usually in streets or special utility easements.  Used to collect wastewater from one or more building sewers and convey it to a main sewer.Main Sewers  Main sewers are used to convey wastewater from one or more lateral sewers to trunk sewers or to intercepting sewers.
  54. 54.  Trunk Sewers  Trunk sewers are large sewers that are used to convey wastewater from main sewers to treatment or other disposal facilities, or to large intercepting sewers.Interceptor Sewers  Intercepting sewers are large sewers that are used to intercept a number of main or trunk sewers and convey the wastewater to treatment or other disposal facilities