Transcript Wastewater Management - CE Meeting

Wastewater Management
Obj 6.3:
Sewage Generation
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.
Peak Sewage Flow Rate
Is the total flow from all generators of
sewage and includes:
domestic
commercial
institutional
infiltration
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
Peaking Factor
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 =
8640000
3
 100 L/s  0.1 m /s
24  60  60
3
0.22
m
/s
Peaking Factor =
 2.2
3
0.1 m /s
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
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
Commercial & Institutional
Sewage
Qcom/inst= AC x SGR x PF
AC = area characteristic
SGR = sewage generation rate
(m3/characteristic/day)
PF = peaking factor
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
Infiltration
 defective joints
 cracked pipes
 water table level
 manhole integrity
 construction and inspection
 maintenance and repair
Factors that
affect
infiltration
rates
Infiltration Flow Rates
Qinfiltration = A x IF
A = surface area (ha)
IF = infiltration rate (m3/ha/day)