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* Additional components available
About Septic Tanks
A septic tank system usually comprises two major components
- The septic tank.
- The final disposal system, which is usually a subsoil percolation system.
Each of these components has a specific function and should be designed accordingly.
The function of the components of the system
The function of the septic tank is to condition raw sewage, which has a clogging effect on the soil, thereby reducing the effective absorbency capacity of the subsoil. When the raw sewage enters the tank some of the suspended solids settle to the bottom of the tank and some collect at the surface, with the result that three distinctive layers are formed in the tank – a layer of sludge at the bottom, a floating layer of scum on top and a relative clear liquid layer in between. The organic solids and dissolved material in the sewage are attacked by bacteria so that the volume the scum and sludge is reduced by liquefaction and gasification.
The only function of the final disposal system is to get rid of the effluent from the septic tank in a safe and in offensive way.
- The tank must function as both a sedimentation tank and a digester.
- The capacity must allow for ample retention time for incoming sewage.
- Blockages must be minimised at inlet and outlet.
- Provision must be made for ventilation to allow escape of gases.
- The escape of scum and sludge to the soil percolation system must be minimised.
Final disposal system
- The nature of the soil must be determined as it has an influence on the shape and size of the
- The system must not create a danger to public health.
- Clogging effect of absorptive soil surfaces must be minimised. (d) Full use must be made of available infiltration areas.
* Malan W M a guide to the use of septic tank systems in South Africa. CSIR research report 219, Pretoria CSIR, 1964, 39p.
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