Filtration Equations
Environmental Engineering · FE Reference Handbook section
Handbook notes for this section
Definitions and conditions exactly as the handbook states them.
- Filter equations can be used with any consistent set of units.
Core formulas for this FE topic
Definitions, applicability, units, assumptions and worked examples for each relation.
Worked exam-style examples
The four ways this section is written on the real exam — thoughts first, then equations, then substitution.
filtration equations used to size a rapid sand filter Given filtered flow rate (Q) = 99,010 m^3/day; filter area (A_f) = 372.0 m^2, determine the filtration rate (v_f) in m/day.
Given
Find
filtration rate (v_f), in m/day
Start with the thinking
- The governing relation printed in this handbook section is Filtration Equations.
- Everything except v_f is given, so isolate v_f symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- Filtration equations relate filtration rate to plant flow rate and total filter surface area in a granular media filter.
Figure 1 — schematic for Filtration Equations — solve for filtration rate — Filtration Equations
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for v_f:
Step 3 — List the givens: filtered flow rate (Q) = 99,010 m^3/day, filter area (A_f) = 372.0 m^2.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning v_f = 266.2 m/day to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 532.3 — kept a factor of two that cancels in the correct rearrangement.
- 133.1 — dropped that same factor in the other direction.
- 292.8 — rounded an intermediate value before the final step.
Reference: FE Handbook — Filtration Equations
filtration rate calculation for a granular media filter Given filter area (A_f) = 477.0 m^2; filtration rate (v_f) = 148.0 m/day, determine the filtered flow rate (Q) in m^3/day.
Given
Find
filtered flow rate (Q), in m^3/day
Start with the thinking
- The governing relation printed in this handbook section is Filtration Equations.
- Everything except Q is given, so isolate Q symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- Filtration equations relate filtration rate to plant flow rate and total filter surface area in a granular media filter.
Figure 2 — schematic for Filtration Equations — solve for filtered flow rate — Filtration Equations (2)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for Q:
Step 3
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Q = 70596\ \text{m^3/day}Step 6 — Check: returning Q = 70,596 m^3/day to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 141,192 — kept a factor of two that cancels in the correct rearrangement.
- 35,298 — dropped that same factor in the other direction.
- 77,656 — rounded an intermediate value before the final step.
Reference: FE Handbook — Filtration Equations
filtration equations applied to a water treatment plant filter bank Given filtered flow rate (Q) = 60,120 m^3/day; filtration rate (v_f) = 286.0 m/day, determine the filter area (A_f) in m^2.
Given
Find
filter area (A_f), in m^2
Start with the thinking
- The governing relation printed in this handbook section is Filtration Equations.
- Everything except A_f is given, so isolate A_f symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- Filtration equations relate filtration rate to plant flow rate and total filter surface area in a granular media filter.
Figure 3 — schematic for Filtration Equations — solve for filter area — Filtration Equations (3)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for A_f:
Step 3 — List the givens: filtered flow rate (Q) = 60,120 m^3/day, filtration rate (v_f) = 286.0 m/day.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
A_{f} = 210.2\ \text{m^2}Step 6 — Check: returning A_f = 210.2 m^2 to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 420.4 — kept a factor of two that cancels in the correct rearrangement.
- 105.1 — dropped that same factor in the other direction.
- 231.2 — rounded an intermediate value before the final step.
Reference: FE Handbook — Filtration Equations
filtration equations used to size a rapid sand filter Given filtered flow rate (Q) = 90,250 m^3/day; filter area (A_f) = 251.0 m^2, determine the filtration rate (v_f) in m/day.
Given
Find
filtration rate (v_f), in m/day
Start with the thinking
- The governing relation printed in this handbook section is Filtration Equations.
- Everything except v_f is given, so isolate v_f symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- Filtration equations relate filtration rate to plant flow rate and total filter surface area in a granular media filter.
Figure 4 — schematic for Filtration Equations — solve for filtration rate (case 2) — Filtration Equations (4)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for v_f:
Step 3 — List the givens: filtered flow rate (Q) = 90,250 m^3/day, filter area (A_f) = 251.0 m^2.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning v_f = 359.6 m/day to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 719.1 — kept a factor of two that cancels in the correct rearrangement.
- 179.8 — dropped that same factor in the other direction.
- 395.5 — rounded an intermediate value before the final step.
Reference: FE Handbook — Filtration Equations
filtration rate calculation for a granular media filter Given filter area (A_f) = 330.0 m^2; filtration rate (v_f) = 73.0000 m/day, determine the filtered flow rate (Q) in m^3/day.
Given
Find
filtered flow rate (Q), in m^3/day
Start with the thinking
- The governing relation printed in this handbook section is Filtration Equations.
- Everything except Q is given, so isolate Q symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- Filtration equations relate filtration rate to plant flow rate and total filter surface area in a granular media filter.
Figure 5 — schematic for Filtration Equations — solve for filtered flow rate (case 2) — Filtration Equations (5)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for Q:
Step 3
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Q = 24090\ \text{m^3/day}Step 6 — Check: returning Q = 24,090 m^3/day to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 48,180 — kept a factor of two that cancels in the correct rearrangement.
- 12,045 — dropped that same factor in the other direction.
- 26,499 — rounded an intermediate value before the final step.
Reference: FE Handbook — Filtration Equations
filtration equations applied to a water treatment plant filter bank Given filtered flow rate (Q) = 29,260 m^3/day; filtration rate (v_f) = 245.0 m/day, determine the filter area (A_f) in m^2.
Given
Find
filter area (A_f), in m^2
Start with the thinking
- The governing relation printed in this handbook section is Filtration Equations.
- Everything except A_f is given, so isolate A_f symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- Filtration equations relate filtration rate to plant flow rate and total filter surface area in a granular media filter.
Figure 6 — schematic for Filtration Equations — solve for filter area (case 2) — Filtration Equations (6)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for A_f:
Step 3 — List the givens: filtered flow rate (Q) = 29,260 m^3/day, filtration rate (v_f) = 245.0 m/day.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
A_{f} = 119.4\ \text{m^2}Step 6 — Check: returning A_f = 119.4 m^2 to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 238.9 — kept a factor of two that cancels in the correct rearrangement.
- 59.7143 — dropped that same factor in the other direction.
- 131.4 — rounded an intermediate value before the final step.
Reference: FE Handbook — Filtration Equations
filtration equations used to size a rapid sand filter Given filtered flow rate (Q) = 97,470 m^3/day; filter area (A_f) = 346.0 m^2, determine the filtration rate (v_f) in m/day.
Given
Find
filtration rate (v_f), in m/day
Start with the thinking
- The governing relation printed in this handbook section is Filtration Equations.
- Everything except v_f is given, so isolate v_f symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- Filtration equations relate filtration rate to plant flow rate and total filter surface area in a granular media filter.
Figure 7 — schematic for Filtration Equations — solve for filtration rate (case 3) — Filtration Equations (7)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for v_f:
Step 3 — List the givens: filtered flow rate (Q) = 97,470 m^3/day, filter area (A_f) = 346.0 m^2.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning v_f = 281.7 m/day to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 563.4 — kept a factor of two that cancels in the correct rearrangement.
- 140.9 — dropped that same factor in the other direction.
- 309.9 — rounded an intermediate value before the final step.
Reference: FE Handbook — Filtration Equations
filtration rate calculation for a granular media filter Given filter area (A_f) = 489.0 m^2; filtration rate (v_f) = 127.0 m/day, determine the filtered flow rate (Q) in m^3/day.
Given
Find
filtered flow rate (Q), in m^3/day
Start with the thinking
- The governing relation printed in this handbook section is Filtration Equations.
- Everything except Q is given, so isolate Q symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- Filtration equations relate filtration rate to plant flow rate and total filter surface area in a granular media filter.
Figure 8 — schematic for Filtration Equations — solve for filtered flow rate (case 3) — Filtration Equations (8)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for Q:
Step 3
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Q = 62103\ \text{m^3/day}Step 6 — Check: returning Q = 62,103 m^3/day to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 124,206 — kept a factor of two that cancels in the correct rearrangement.
- 31,052 — dropped that same factor in the other direction.
- 68,313 — rounded an intermediate value before the final step.
Reference: FE Handbook — Filtration Equations
filtration equations applied to a water treatment plant filter bank Given filtered flow rate (Q) = 70,690 m^3/day; filtration rate (v_f) = 105.0 m/day, determine the filter area (A_f) in m^2.
Given
Find
filter area (A_f), in m^2
Start with the thinking
- The governing relation printed in this handbook section is Filtration Equations.
- Everything except A_f is given, so isolate A_f symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- Filtration equations relate filtration rate to plant flow rate and total filter surface area in a granular media filter.
Figure 9 — schematic for Filtration Equations — solve for filter area (case 3) — Filtration Equations (9)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for A_f:
Step 3 — List the givens: filtered flow rate (Q) = 70,690 m^3/day, filtration rate (v_f) = 105.0 m/day.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
A_{f} = 673.2\ \text{m^2}Step 6 — Check: returning A_f = 673.2 m^2 to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 1,346 — kept a factor of two that cancels in the correct rearrangement.
- 336.6 — dropped that same factor in the other direction.
- 740.6 — rounded an intermediate value before the final step.
Reference: FE Handbook — Filtration Equations
filtration equations used to size a rapid sand filter Given filtered flow rate (Q) = 15,590 m^3/day; filter area (A_f) = 132.0 m^2, determine the filtration rate (v_f) in m/day.
Given
Find
filtration rate (v_f), in m/day
Start with the thinking
- The governing relation printed in this handbook section is Filtration Equations.
- Everything except v_f is given, so isolate v_f symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- Filtration equations relate filtration rate to plant flow rate and total filter surface area in a granular media filter.
Figure 10 — schematic for Filtration Equations — solve for filtration rate (case 4) — Filtration Equations (10)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for v_f:
Step 3 — List the givens: filtered flow rate (Q) = 15,590 m^3/day, filter area (A_f) = 132.0 m^2.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning v_f = 118.1 m/day to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 236.2 — kept a factor of two that cancels in the correct rearrangement.
- 59.0530 — dropped that same factor in the other direction.
- 129.9 — rounded an intermediate value before the final step.
Reference: FE Handbook — Filtration Equations