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.

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-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

Where,

• 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.