How to design a Septic Tank?
A Septic Tank is a small scale sewage treatment system used in areas which have no connection to the main sewage pipes that are provided by the Local governments or private Corporations.
In this article, we will detail out all the calculations that are to be performed to get the required volume of a Septic Tank with the help of examples.
Schematic Diagram of a Septic Tank
We would begin with a small scale example so that your concept of Septic tank design is clear.
Here are the thumb rules to be kept in mind which will help you in calculating the volume of a Septic Tank.
For a three bedroom house:
The quantity of sewage considered for a three bedroom house should not be less than 900 gallons.
For a two bedroom House:
The quantity of sewage to be considered for the design of Septic Tank should not be less than 700 gallons.
For one bedroom unit:
The quantity of sewage to be considered for the design of a Septic Tank should not be less than 550 gallons.
Let’s begin with an example of a three bedroom residence.
Septic Tank calculations for a three bedroom Residence
As per the thumb rule;
Quantity of sewage to be considered for the design of a Septic Tank = 900 gallons
1 gallon of liquid = 3.78 litres
Quantity of sewage in litres = 900×3.78 = 3402litres
Volume of Sewage in Cubic metres
3402/1000 = 3.402 cubic metres
Volume of Sewage in Cubic feet
3402/28.52 = 119.28 cubic feet
Dimensions of a Septic Tank in metres:
Width of the Septic Tank = 1.70m
Depth of the Septic Tank = 1.00m
Length of the Septic Tank = 2.00m
Dimensions of a Septic Tank in feet:
Width of the Septic Tank = 5.61’
Depth of the Septic Tank = 3.3’
Length of the Septic Tank = 6.6’
In our next article, we will move on with a discussion on “Septic Tank Design Calculations for an Office Complex“
#1 by Toksadeh on September 19, 2011 - 1:51 am
Kindly explain how you determined the length, width and depth of septic tank from the result of your calculation. Thanks