In normal areas and in case ‘of isolated building and institutions, hotels, hospitals schools, small residential colonies, an underground sewerage system with provision for complete treatment of sewage may be neither feasible nor economical even though water supply facilities exist. In such cases, septic tanks and subsurface disposal of effluent are provided.
The septic tank should be located as far as possible away from buildings. It should not be located in swampy areas or areas prone to flooding. Where there 15 clayey or nonporous soil or where houses are closely built suitably designed loading pits may have to be used a septic tank cannot be avoided. Where the soil IS heavily porous the septic tank is effective.
The septic tank 15 a water-tight, single-storeyed, underground tank 111 which sewage is retained for a long period. Here sedimentation and sludge digestion take place simultaneously. The tank is generally rectangular in shape with R.C.C. roofing.
Usually, it has two chambers separated by a baffle wall. Sewage enters the front chamber known as the grit or screen chamber. The other is the anaerobic chamber. The tank should be properly ventilated with the provision of air vent pipes. A manhole is provided in the roof for inspection and cleaning: Sludge accumulated at the bottom of the tank is removed at intervals either by manual labor or by pumping.