Introduction

• Sewage is water-carried waste, in solution or suspension, that is intended to be removed from a community.
• Also known as wastewater, it is more than 99% water and is characterized by volume or rate of flow, physical condition, chemical constituents and the bacteriological organism that it contains.
• The system of pipes used to collect and carry rain, waste water and trade waste away for treatment and disposal is called the sewerage or the waste water system.
• There are three types of public sewers, each classified according to the kind of wastes it is required to handle.

Combined Sewers

• Combination public sewers are the oldest variety of the three types of sewers and they are required to carry storm and sanitary wastes to some safe terminal.
• Rain water should be carried to some terminal not associated with the disposal plant.

Sanitary Sewers

• Sanitary sewers are those which are required to carry domestic sanitary waste only. All rain water must be excluded from them.
• Combination and sanitary sewers generally are placed about ten feet under the street grade and usually are found below the centre line of the street.

Strom Sewers

• Storm sewers are a comparatively new installation, made necessary because of sewage treatment.
• These sewers are made to carry only storm water and may terminate at any natural drainage area.

Problems in Sewer System

• The per capita water supply (including the local and individual sources) to the population is less than the minimum requirement of water supply for the efficient performance of the sewerage system, i.e., 100LPCD.
• This will cause the operation and maintenance problems with frequent clogging, due to silting in the absence of self cleansing velocity.
• The topography of the town is flat necessitating deeper excavation of trenches and more number of sewage pumping stations.

Gravity Sanitary Sewer

• Most common.
• Wastewater transported by gravity.
• Used to collect wastewater from residual, commercial, industrial, and institutional sources.
• Conveyance capacity allowances must be made for groundwater infiltration and unavoidable inflow.

Pressure (Pumped) sanitary sewer

• Economical and environmentally friendly way of collecting, transporting and disposing of wastewater from households.
• They are often used in areas when the landscape is either very hilly or very flat, in areas that regularly flood or have high water tables, or where it is impractical to install other types of sewerage systems.
• A pressure sewer system is made up of a network of fully sealed pipes which are fed by pumping units located at each connected property.

Advantages

• Being smaller in diameter are installed at shallower depths than conventional sewers.
• They need not be laid on a precise grade as in gravity sewers, but can often go over hill below the hydraulic gradient line.
• Since there are no elements such as access manholes and sewer line is under pressure, the inflow from storm runoff is virtually eliminated.

Disadvantages

• They are to be differentiated from the water supply distribution system with proper color code.
• Awareness among the public is required about the hazard risk of the pressure sewer system if they are tampered.
• Each and every house should have a collection sump and pumping facilities.