Design Criteria Of Septic Tank

Septic Tank:

Septic tank is a tank where sewage is kept a long time for sedimentation of suspended solid by anaerobic microorganism activity.

Septic Tank Design
Septic Tank Design

Basically, the tank is rectangular in shape consisting of rooftop with two chambers, isolated from each other by a baffle wall. The first chamber is called grit chamber in which the sewage enters first and the rest one is called anaerobic chamber.

Inlet and outlet pipe should be fitted in such a manner that while entering or existing there should not be any unsettled influence in the sewage of anaerobic chamber. Sand, grit etc is settled down in the grit chamber before the sewage is directed to the anaerobic chamber. In the anaerobic chamber, natural solids settle at the base of the tank where anaerobic bacteria follows up on it and changes over complex unsteady mixes to more straightforward stable mixes.

Septic Tank Design:

The following measure should be kept in view to design a septic tank:


1. The floor zone of the git chamber must be adequate to decrease the speed of steam and to allow sedimentation.

2. The capacity of a septic tank should be sufficient to give a detainment period fluctuating from 12 hours to 3 days, 24 hours time frame is normally viewed as satisfactory.

3. The depth beneath segment divider opening should be adequate to allow aggregation for the predetermined period. A minimum area of 0.07 m2 for each client in grit chamber and minimum volumetric substance of the grit chamber of 0.02 m3 for every client is required.

4. The minimum width and depth of a septic tank should be 0.75 m and 1 meter underneath water level. The length should be 2 to 4 times of the width. The minimum capacity of a septic tank is granted 1 m3.

5. Every septic tank should be furnished with a ventilating channel minimum diameter of 5 cm.

Also Read – Design Procedure Of R.C.C Lintel
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