Quantity estimation

QUANTITY ESTIMATION OF DOMESTIC SEWAGE

Sewage is collected from municipal areas consists of wastewater generated from

• residences
• commercial centers
• recreational centers and
• institutions

Accurate estimation of sewage discharge is necessary for hydraulic design of sewers. Incorrect estimation of sewage leads to problems. Small estimate leads to inadequate sewer size that may not remain adequate for the entire design period while high estimate leads to large sewer size that affects the economy of the sewerage system and may not generate self cleansing velocities leading to deposition in sewers. Estimating discharge from sewers is made difficult due to leakage and unaccounted overflow.
Net quantity of sewage = 75 % to 80% of accounted water supplies +
                                           Addition due to private water supplies +
                                           Addition due to infiltration    -
                                           Subraction due to water losses  -
                                   Subtraction due to water not entering the sewerage system

For estimating design discharge, it is estimated that:
Maximum daily flow = Twice annual average daily flow
Maximum hourly flow = 1.5 times the maximum daily flow or thrice annual average daily flow
Minimum daily flow = 2/3 * Annual average daily flow
Minimum hourly flow = 1/2 * minimum daily flow or 1/3 * annual average daily flow
Per capita sewage generation is estimated as 75 to 80% of the per capita water supplied per day