Calculate clarifier surface overflow rate, detention time, weir loading, and flow-through velocity from tank dimensions and flow rate.
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Worked examples
These are the solver's own reference problems — the answers come from published sources or independent hand computation, never from the solver itself. The solution below is the live solver output for each.
Example 1
overflow rate + detention (the motivating exam problem)
Given
flowrate
10000 m^3/day
length
20 m
width
10 m
depth
3 m
Assumptions
Ideal horizontal-flow settling: the overflow rate equals the critical settling velocity that is just fully removed.
Solution steps
Surface overflow rate
Flow divided by plan area — dimensionally a velocity: particles settling faster than this are captured.
SOR = Q / A
SOR = 50 m per day (= 0.000579 m/s)
= 50
Detention time
Tank volume over flow — how long a parcel of water stays inside.
td = V/Q = A·d/Q
V = 600 m^3; td = 1.44 h
= 1.44 h
Results
Surface overflow rate (m³/m²·day = m/day)
50
Surface area
200m^2
Tank volume
600m^3
Detention time
1.44h
Horizontal flow-through velocity
0.003858m/s
Where this answer was checked
source
SOR = Q/A; td = A·d/Q — 10,000 m³/day tank, 20×10×3 m
verified by
hand-recomputed
derivation
A = 200 m²; SOR = 10000/200 = 50 m/day. V = 600 m³; td = 600/10000 day = 0.06 day = 1.44 h.
Example 2
US clarifier: 2 MGD over 4000 ft²
Given
flowrate
2 mgd
surface area
4000 ft^2
Assumptions
Ideal horizontal-flow settling: the overflow rate equals the critical settling velocity that is just fully removed.
Solution steps
Surface overflow rate
Flow divided by plan area — dimensionally a velocity: particles settling faster than this are captured.
SOR = Q / A
SOR = 20.37 m per day (= 0.000774 ft/s)
= 20.37
Results
Surface overflow rate (m³/m²·day = m/day)
20.37
Surface area
4000ft^2
Where this answer was checked
source
SOR = Q/A with unit conversion — MGD and square feet
verified by
hand-recomputed
derivation
Q = 7570.82 m³/day; A = 4000·0.092903 = 371.61 m²; SOR = 20.37 m/day.
Example 3
weir loading rate
Given
flowrate
5000 m^3/day
surface area
150 m^2
weir length
30 m
Assumptions
Ideal horizontal-flow settling: the overflow rate equals the critical settling velocity that is just fully removed.
Solution steps
Surface overflow rate
Flow divided by plan area — dimensionally a velocity: particles settling faster than this are captured.
SOR = Q / A
SOR = 33.33 m per day (= 0.000386 m/s)
= 33.33
Weir loading rate
Flow per length of effluent weir — controls outlet currents.