ESTIMATION OF SEWAGE FLOW AND STORM RUNOFF

SOURCES OF WASTEWATER

The wastewater is generated from domestic, industrial and agricultural activities. From domestic sources the wastewaters are generated from toilet known as excreta or black water and from kitchen and bathroom as sullage or gray water. If excreta and sullage are mixed together and collected in a collection system for transporting away from the dwelling area, it is called sewage. The underground conduit for the collection of sewage is called sewer. A network of sewer pipes laid in order to carry the sewage from all the houses in a town to a sewage treatment plant, is called sewerage system.

 QUANTITY OF SEWAGE

Theoretically, the quantity of sewage that is likely to enter the sewerage system should be equal to certain proportionate quantity of water supplied to the contributing area. The net quantity of sewage generated will be about 80% of the water supply as per the CPHEEO Manual on Sewerage and Sewage Treatment.

But in actual practice, apart from certain portion of the quantity of water supply, certain additions and subtractions do take place from it, as explained below.

Addition due to private water supplies:

• Some private wells may sometimes be used by the public, commercial organizations and industries for their needs and these sources may add additional waster water flow to the system.
•  The quantity of water used by the. people of the town from private water supplies is generally small, unless there is an inadequate supply from the municipal water supply;
• It there is a large number of industries having private water supply.

 Addition due to infiltration:

•  Whenever, the sewers laid below the groundwater table, certain amount of groundwater infiltrates in to them, through the leaky joints or cracks in the pipes or manholes due to poor construction.
• However, if the groundwater table is well below the sewer, the infiltration can occur only after rain, the exact quantity of groundwater infiltrating into sewer pipes cannot be estimated precisely.
• Hence only a nominal allowance based upon experimental results may be made

 Subtraction due to water losses:

• The water lost due to leakage in the water supply transmission and distribution system and house service connections of the water supply system does not reach the consumers, and hence, never appears as sewage.

 Subtraction  from water supply not entering the sewerage system:

• Certain quantity of water, which may be used by the public and industries for such uses or processes, which may not produce any wastewater at all.