A certain district of a city with a population of `50,000` over an area of `20` hectares is given Find design discharge of combined sewer line for following data :  [TU 2004] 

• Rate of water supply =`225` lpcd 
  
• Average impermeability coefficient for entire district=`0.3` 
  
• Time of entry =`10` minutes 
  
• Time of flow = `30` minutes. 
  

Solution:

Assuming 80% of supplied water contributes to sewage and peck factor to be 2.5.

The sanitary sewage discharge is,

`Q_(DWF)=(0.8**2.5**225**50000)/(1000**86400)`

`=0.2604\ m^3/s`

Here,

`t=10+30=40 min`

The intensity of rainfall is, `i=1020/(40+20)=17` mm/hr

Now, the storm sewage discharge is,

`Q_(WWF)=(0.3**17**20)/360`

`=0.233\ m^3/s`

Now, the design discharge for the combined system is,

`Q=0.233+0.2604`

`=0.4934\ m^3/s`

Solution:

Assuming 80% of supplied water contributes to sewage and peck factor to be 2.5.

The sanitary sewage discharge is,

`Q_(DWF)=(0.8**2.5**225**50000)/(1000**86400)`

`=0.2604\ m^3/s`

Here,

`t=10+30=40 min`

The intensity of rainfall is, `i=1020/(40+20)=17` mm/hr

Now, the storm sewage discharge is,

`Q_(WWF)=(0.3**17**20)/360`

`=0.233\ m^3/s`

Now, the design discharge for the combined system is,

`Q=0.233+0.2604`

`=0.4934\ m^3/s`