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Wastewater Management
Obj 6.3: Sewage Generation
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Water Supply Usage for most municipalities the amount of sewage will be about 60-75% of the water supply used. demand for fresh water peaks around 6:00 pm this is typically when PEAK SEWAGE FLOW RATE occurs.
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Is the total flow from all generators of sewage and includes:
Peak Sewage Flow Rate Is the total flow from all generators of sewage and includes: domestic commercial institutional infiltration
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Qdomestic = A x PD x SGR x PF
Domestic Sewage Qdomestic = A x PD x SGR x PF A = residential area (ha) PD = population density (persons/ha) SGR = sewage generation rate (m3/person/day) PF = peaking factor
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Peaking Factor
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Peaking Factor If sewage flow monitored from a subdivision was measured at 8,640,000 L for a 24 hour period and the measured flow rate at the time of peak usage was 0.22 m3/s: Average flow rate = Peaking Factor =
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Peaking Factors (PF) small towns have higher peaking of water use (high peaking factor) 200% to 500% of average flow rate large towns have lower peaking of water use (low peaking factor) 150% to 250% of average flow rate
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Commercial and Institutional Sewage
wide variety of land use types and densities great variation in sewage generation Domestic Equivalent Estimation Method Sewage Generation Rate Method
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Commercial & Institutional Sewage
Qcom/inst= AC x SGR x PF AC = area characteristic SGR = sewage generation rate (m3/characteristic/day) PF = peaking factor
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Infiltration groundwater seeps into sanitary sewers through cracks and joints surface runoff finds its way into manholes infiltration amounts depend on quality of construction and age of system
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Infiltration Factors that affect infiltration rates defective joints
cracked pipes water table level manhole integrity construction and inspection maintenance and repair Factors that affect infiltration rates
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Infiltration Flow Rates
Qinfiltration = A x IF A = surface area (ha) IF = infiltration rate (m3/ha/day)
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