Sources and Rates of Domestic Wastewater Flows…………….

Sources and Rates of Domestic Wastewater Flows

  • Small Residential District- Wastewater flows determined based on population density and average per capita contribution of wastewater.
  • Large Residential District- Wastewater flows developed based on Land use areas and anticipated population density.
  • If data is unavailable, estimate 70% of the domestic water-withdrawal rate is returned to the sanitary sewer system.
  • The quantity of sewage produce depends upon the quantity of water use.


  • Average daily flow- (70-80)% average water consumption i.e.
  • Average Daily Flow (ADF) of Sewage- 75%
  • Average Daily Demand (ADD) of water consumption-75 ADD
  • The flows in sanitary sewers vary seasonably monthly, daily, hourly. For areas of moderate sizes be expressed as;
  • Maximum Daily Flow- 5 x ADF


  • 5 varies from place to place.
  • Maximum hourly flow= (2-4) ADF
  • This is actually the peak flow.
  • 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.
  1. Minimum Daily Flow= 2/3 ADF
  2. Minimum Hourly Flow= 1/3 ADF


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.


How is the waste water going to be removed and treated?

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.


Lateral 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.


Trunk Sewers

  • Trunk sewers are large 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.



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