DISPOSAL OF SEWAGE FROM THE SINGLE HOUSE AND FUNCTION OF THE SEPTIC TANKS .

SEPTIC TANK :-- A septic tank which is a settling tank must be rectangular chamber of RCC or the brick work with cement plastered insides usually built underground .The function of septic tank is to produce certain biological and chemical changes by partial liquefaction and gasification or decomposition of the human excreta discharged into it , through the action of anaerobic bacteria,which flourish in the absence of free oxygen, humidity, darkness and warmth,and which are the conditions created in a septic tank,thus reducing the bulk of the sewage. During the course of action in a septic tank the lighter matter ,grese 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 air tight ,water tight and light is also excluded to help decomposition of the sewage.These layers of scum and sewage 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 the out let pipes are bent downwards and should have their open ends midway in the water .The centre of the outlet pipe is generally kept about 150 mm below the centre of the inlet. A hanging baffle wall making a vertical partition must be arranged which should be 45 cm from the floor and 45 cm away from the inlet pipe however not required in the small tanks .For more design considerations we may follow recommendations given in the IS:2470 .