Septic tank is an integral part of the drainage system of a home. A septic tank is a rectangular chamber of brickwork, plastered inside with cement or of RCC, usually built underground. The function of a septic tank is to produce certain biological and chemical changes by partial liquefaction and gasification of the human excreta discharged into it, through the action of anaerobic bacteria which flourish in the humidity, darkness, warmth and absence of free oxygen.
How does a Septic tank works?
During the course of action in a septic tank, the lighter matter (grease and fat etc.) rise to the surface and form a thick floating layer called “Scum”, while heavier matter sink to the bottom to form “Sludge”. The tanks are made water tight, air tight and light is also excluded to help decomposition of sewage. These layers of scum and sludge are not disturbed by the flow of water and the inflow and outflow from the tank are so arranged as to give least disturbance. Both the inlet and outlet pipes are bent downwards and should have their open ends midway in the water. The centre of the outlet pipe is generally kept about 150mm below the centre of the inlet. Inlets and outlets should be standard “T” fittings of glazed earthenware pipes. When the tank width is more than 1.5m, there should be two inlets. Another precaution taken against possible disturbance of the scum is by making a hanging vertical partition in the tank which is called “Baffle wall”. The baffle wall extends from above top water level to 45cm from the floor and from 25 to 45cm away from the inlet pipe. The baffle wall need not be made in the small septic tanks. In long tanks, a second baffle wall is sometimes provided which is built from the floor to a little below the water level in the tank and at a distance of about 60cm from the outlet end. The tanks are covered with precast concrete slabs with provision of manhole and ventilating pipe. An iron or PVC pipe called ventilating pipe, of diameter not less than 75mm is fixed on the precast cover slab to remove the gases formed inside the septic tank.