# DESIGN OF SEPTIC TANK

DESIGN OF SEPTIC TANK
No. of people=75
Sewage /capital/day=120liters
De- sludging period=1 year
Length : width=4:1
Assume the detention period=24 hrs
Free board                       =300mm
Quantity of sewage produced per day=9000 liters/day
Quantity of sewage produced per day=9000 liters/day
Capacity of the tank=9000*24/24
=9000liters
Assuming the rate of sludge deposit =30liters/capita/day
The quantity of sludge deposited
=30*75*1
=2250liters
Total required capacity of the tank
=9000 /750
=12 m3
Assuming the depth of tank =1.5m
Area of tank =12/1.5
=8m2
4B2=8
B=1.4m
L=4*1.4 =5.6m
The dimensions of the tank will be =5.6m*1.5*(1.5+0.3)
=5.6m*1.5m*1.8m
DESIGN OF SOAK PIT:
Sewage  flow=9000 L/d
Percolation rate=1250 L/m3/d
Volume required for the  soak pit=9000/1250
=7.2m3
Assume the depth of soak pit =2m
Area of soak pit required        =7.2/2
=3.6m2
Diameter of soak pit   =√(3.6*4/π)
=2.14m
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