1. Wastewater Management
Obj 6.3:
Sewage Generation

2. 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.

3. 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

4. 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

5. Peaking Factor

6. 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 =

7. 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

8. 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

9. Commercial & Institutional Sewage
Qcom/inst= AC x SGR x PF
AC = area characteristic
SGR = sewage generation rate (m3/characteristic/day)
PF = peaking factor

10. 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

11. 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

12. Infiltration Flow Rates
Qinfiltration = A x IF
A = surface area (ha)
IF = infiltration rate (m3/ha/day)