Some useful construction tips to design a septic tank easily
There are various methods to design Septic System or Septic Tanks. In this construction article, most easiest method is described to design a septic tank in quickest possible time. Besides, the article also explains how to define the size of the septic tank precisely.
Design of Septic Tank: While going to design any septic system, size plays an important role as the total required capacity of the septic tank can be determined with it.
The capacity of septic tank is based on number of users and span of sludge extraction. Usually sludge is extracted every 2 years. The water consumption of the tank is considered as 130 liters to 70 liters per head. For small number of users 130ltr per head is consumed.
The construction of a septic tank is generally done with brick wall in which cement mortar having thickness [not under 20cm (9 inch)] is used and the foundation floor developed with cement concrete 1:2:4. Both interior and exterior faces of the wall and top of the floor are plastered maintaining lowest thickness of 12mm (one-half inch) thick cement mortar 1:3 mix.
All interior corners of septic tank are rounded. Water resistant agent like Impermo, Cem-seal or Accoproof etc. is included to the mortar at the rate of 2% of the cement weight. Water proofing agent should be included in equal ratio to the concrete for developing floor of the tank.
For right convenience in collection and removal of the sludge, the floor of septic tank is supported with a slope of 1:10 to 1:20 around the inlet side. It signifies that floor of the outlet side remains on the higher elevation as compared to the floor at inlet side.
Volume of Septic Tank Components:
i) Length, Width and Depth of Septic Tank
Width = 750mm(min)
Length = 2 to 4 times width
Depth = 1000 to 1300mm. (min under water level) + 300 to 450mm free board
Maximum depth = 1800mm + 450 mm free board
Capacity = 1 cubic meter (10 cubic feet) minimum
ii) Detention period
Detention period of 24hrs usually is taken in septic tank design. The rate of flow of effluent should be similar to the rate of flow of influent.
iii) Inlet and outlet pipes
An elbow or T pipe having 100mm diameter is sunken to a depth of 250-600mm under the liquid level. For outlet pipe an elbow or T type of 100mm diameter pipe is sunken to a depth of 200-500mm under the liquid level. Pipes may made of stone ware or asbestos.