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Filtration Equations

Environmental Engineering · FE Reference Handbook section

Environmental Engineering
4 formulas
10 exam-style examples
~53 min
All Environmental Engineering lectures

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.

Example 1
Filtration Equations — solve for filtration rate — Filtration Equations

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

  • filteredflowrate(Q)=99,010m3/dayfiltered flow rate (Q) = 99,010 m^3/day
  • filterarea(Af)=372.0m2filter area (A_f) = 372.0 m^2

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.
granular filter

Figure 1 — schematic for Filtration Equations — solve for filtration rate — Filtration Equations

Step-by-step solution

  1. Step 1 — State the governing relation:

    vf=QAfv_f = \dfrac{Q}{A_f}
  2. Step 2 — Rearrange symbolically for v_f:

    vf=QAfv_{f} = \dfrac{Q}{A_f}
  3. Step 3 — List the givens: filtered flow rate (Q) = 99,010 m^3/day, filter area (A_f) = 372.0 m^2.

  4. Step 4 — Substitute the given values:

    vf=99010Afv_{f} = \dfrac{99010}{A_f}
  5. Step 5 — Evaluate:

    vf=266.2 m/dayv_{f} = 266.2\ \text{m/day}
  6. Step 6 — Check: returning v_f = 266.2 m/day to

    vf=QAfv_f = \dfrac{Q}{A_f}

    reproduces the given quantities, and both sides carry the same units.

Answer:
vf=266.2 m/dayv_{f} = 266.2\ \text{m/day}

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

Example 2
Filtration Equations — solve for filtered flow rate — Filtration Equations (2)

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

  • filterarea(Af)=477.0m2filter area (A_f) = 477.0 m^2
  • filtrationrate(vf)=148.0m/dayfiltration rate (v_f) = 148.0 m/day

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.
granular filter

Figure 2 — schematic for Filtration Equations — solve for filtered flow rate — Filtration Equations (2)

Step-by-step solution

  1. Step 1 — State the governing relation:

    vf=QAfv_f = \dfrac{Q}{A_f}
  2. Step 2 — Rearrange symbolically for Q:

    Q=vfAfQ = v_f A_f
  3. Step 3

    Listthegivens:filterarea(Af)=477.0m2,filtrationrate(vf)=148.0m/dayList the givens: filter area (A_f) = 477.0 m^2, filtration rate (v_f) = 148.0 m/day
  4. Step 4 — Substitute the given values:

    Q=vfAfQ = v_f A_f
  5. Step 5 — Evaluate:

    Q = 70596\ \text{m^3/day}
  6. Step 6 — Check: returning Q = 70,596 m^3/day to

    vf=QAfv_f = \dfrac{Q}{A_f}

    reproduces the given quantities, and both sides carry the same units.

Answer:
Q = 70596\ \text{m^3/day}

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

Example 3
Filtration Equations — solve for filter area — Filtration Equations (3)

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

  • filteredflowrate(Q)=60,120m3/dayfiltered flow rate (Q) = 60,120 m^3/day
  • filtrationrate(vf)=286.0m/dayfiltration rate (v_f) = 286.0 m/day

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.
granular filter

Figure 3 — schematic for Filtration Equations — solve for filter area — Filtration Equations (3)

Step-by-step solution

  1. Step 1 — State the governing relation:

    vf=QAfv_f = \dfrac{Q}{A_f}
  2. Step 2 — Rearrange symbolically for A_f:

    Af=QvfA_{f} = \dfrac{Q}{v_f}
  3. Step 3 — List the givens: filtered flow rate (Q) = 60,120 m^3/day, filtration rate (v_f) = 286.0 m/day.

  4. Step 4 — Substitute the given values:

    Af=60120vfA_{f} = \dfrac{60120}{v_f}
  5. Step 5 — Evaluate:

    A_{f} = 210.2\ \text{m^2}
  6. Step 6 — Check: returning A_f = 210.2 m^2 to

    vf=QAfv_f = \dfrac{Q}{A_f}

    reproduces the given quantities, and both sides carry the same units.

Answer:
A_{f} = 210.2\ \text{m^2}

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

Example 4
Filtration Equations — solve for filtration rate (case 2) — Filtration Equations (4)

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

  • filteredflowrate(Q)=90,250m3/dayfiltered flow rate (Q) = 90,250 m^3/day
  • filterarea(Af)=251.0m2filter area (A_f) = 251.0 m^2

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.
granular filter

Figure 4 — schematic for Filtration Equations — solve for filtration rate (case 2) — Filtration Equations (4)

Step-by-step solution

  1. Step 1 — State the governing relation:

    vf=QAfv_f = \dfrac{Q}{A_f}
  2. Step 2 — Rearrange symbolically for v_f:

    vf=QAfv_{f} = \dfrac{Q}{A_f}
  3. Step 3 — List the givens: filtered flow rate (Q) = 90,250 m^3/day, filter area (A_f) = 251.0 m^2.

  4. Step 4 — Substitute the given values:

    vf=90250Afv_{f} = \dfrac{90250}{A_f}
  5. Step 5 — Evaluate:

    vf=359.6 m/dayv_{f} = 359.6\ \text{m/day}
  6. Step 6 — Check: returning v_f = 359.6 m/day to

    vf=QAfv_f = \dfrac{Q}{A_f}

    reproduces the given quantities, and both sides carry the same units.

Answer:
vf=359.6 m/dayv_{f} = 359.6\ \text{m/day}

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

Example 5
Filtration Equations — solve for filtered flow rate (case 2) — Filtration Equations (5)

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

  • filterarea(Af)=330.0m2filter area (A_f) = 330.0 m^2
  • filtrationrate(vf)=73.0000m/dayfiltration rate (v_f) = 73.0000 m/day

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.
granular filter

Figure 5 — schematic for Filtration Equations — solve for filtered flow rate (case 2) — Filtration Equations (5)

Step-by-step solution

  1. Step 1 — State the governing relation:

    vf=QAfv_f = \dfrac{Q}{A_f}
  2. Step 2 — Rearrange symbolically for Q:

    Q=vfAfQ = v_f A_f
  3. Step 3

    Listthegivens:filterarea(Af)=330.0m2,filtrationrate(vf)=73.0000m/dayList the givens: filter area (A_f) = 330.0 m^2, filtration rate (v_f) = 73.0000 m/day
  4. Step 4 — Substitute the given values:

    Q=vfAfQ = v_f A_f
  5. Step 5 — Evaluate:

    Q = 24090\ \text{m^3/day}
  6. Step 6 — Check: returning Q = 24,090 m^3/day to

    vf=QAfv_f = \dfrac{Q}{A_f}

    reproduces the given quantities, and both sides carry the same units.

Answer:
Q = 24090\ \text{m^3/day}

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

Example 6
Filtration Equations — solve for filter area (case 2) — Filtration Equations (6)

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

  • filteredflowrate(Q)=29,260m3/dayfiltered flow rate (Q) = 29,260 m^3/day
  • filtrationrate(vf)=245.0m/dayfiltration rate (v_f) = 245.0 m/day

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.
granular filter

Figure 6 — schematic for Filtration Equations — solve for filter area (case 2) — Filtration Equations (6)

Step-by-step solution

  1. Step 1 — State the governing relation:

    vf=QAfv_f = \dfrac{Q}{A_f}
  2. Step 2 — Rearrange symbolically for A_f:

    Af=QvfA_{f} = \dfrac{Q}{v_f}
  3. Step 3 — List the givens: filtered flow rate (Q) = 29,260 m^3/day, filtration rate (v_f) = 245.0 m/day.

  4. Step 4 — Substitute the given values:

    Af=29260vfA_{f} = \dfrac{29260}{v_f}
  5. Step 5 — Evaluate:

    A_{f} = 119.4\ \text{m^2}
  6. Step 6 — Check: returning A_f = 119.4 m^2 to

    vf=QAfv_f = \dfrac{Q}{A_f}

    reproduces the given quantities, and both sides carry the same units.

Answer:
A_{f} = 119.4\ \text{m^2}

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

Example 7
Filtration Equations — solve for filtration rate (case 3) — Filtration Equations (7)

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

  • filteredflowrate(Q)=97,470m3/dayfiltered flow rate (Q) = 97,470 m^3/day
  • filterarea(Af)=346.0m2filter area (A_f) = 346.0 m^2

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.
granular filter

Figure 7 — schematic for Filtration Equations — solve for filtration rate (case 3) — Filtration Equations (7)

Step-by-step solution

  1. Step 1 — State the governing relation:

    vf=QAfv_f = \dfrac{Q}{A_f}
  2. Step 2 — Rearrange symbolically for v_f:

    vf=QAfv_{f} = \dfrac{Q}{A_f}
  3. Step 3 — List the givens: filtered flow rate (Q) = 97,470 m^3/day, filter area (A_f) = 346.0 m^2.

  4. Step 4 — Substitute the given values:

    vf=97470Afv_{f} = \dfrac{97470}{A_f}
  5. Step 5 — Evaluate:

    vf=281.7 m/dayv_{f} = 281.7\ \text{m/day}
  6. Step 6 — Check: returning v_f = 281.7 m/day to

    vf=QAfv_f = \dfrac{Q}{A_f}

    reproduces the given quantities, and both sides carry the same units.

Answer:
vf=281.7 m/dayv_{f} = 281.7\ \text{m/day}

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

Example 8
Filtration Equations — solve for filtered flow rate (case 3) — Filtration Equations (8)

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

  • filterarea(Af)=489.0m2filter area (A_f) = 489.0 m^2
  • filtrationrate(vf)=127.0m/dayfiltration rate (v_f) = 127.0 m/day

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.
granular filter

Figure 8 — schematic for Filtration Equations — solve for filtered flow rate (case 3) — Filtration Equations (8)

Step-by-step solution

  1. Step 1 — State the governing relation:

    vf=QAfv_f = \dfrac{Q}{A_f}
  2. Step 2 — Rearrange symbolically for Q:

    Q=vfAfQ = v_f A_f
  3. Step 3

    Listthegivens:filterarea(Af)=489.0m2,filtrationrate(vf)=127.0m/dayList the givens: filter area (A_f) = 489.0 m^2, filtration rate (v_f) = 127.0 m/day
  4. Step 4 — Substitute the given values:

    Q=vfAfQ = v_f A_f
  5. Step 5 — Evaluate:

    Q = 62103\ \text{m^3/day}
  6. Step 6 — Check: returning Q = 62,103 m^3/day to

    vf=QAfv_f = \dfrac{Q}{A_f}

    reproduces the given quantities, and both sides carry the same units.

Answer:
Q = 62103\ \text{m^3/day}

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

Example 9
Filtration Equations — solve for filter area (case 3) — Filtration Equations (9)

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

  • filteredflowrate(Q)=70,690m3/dayfiltered flow rate (Q) = 70,690 m^3/day
  • filtrationrate(vf)=105.0m/dayfiltration rate (v_f) = 105.0 m/day

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.
granular filter

Figure 9 — schematic for Filtration Equations — solve for filter area (case 3) — Filtration Equations (9)

Step-by-step solution

  1. Step 1 — State the governing relation:

    vf=QAfv_f = \dfrac{Q}{A_f}
  2. Step 2 — Rearrange symbolically for A_f:

    Af=QvfA_{f} = \dfrac{Q}{v_f}
  3. Step 3 — List the givens: filtered flow rate (Q) = 70,690 m^3/day, filtration rate (v_f) = 105.0 m/day.

  4. Step 4 — Substitute the given values:

    Af=70690vfA_{f} = \dfrac{70690}{v_f}
  5. Step 5 — Evaluate:

    A_{f} = 673.2\ \text{m^2}
  6. Step 6 — Check: returning A_f = 673.2 m^2 to

    vf=QAfv_f = \dfrac{Q}{A_f}

    reproduces the given quantities, and both sides carry the same units.

Answer:
A_{f} = 673.2\ \text{m^2}

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

Example 10
Filtration Equations — solve for filtration rate (case 4) — Filtration Equations (10)

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

  • filteredflowrate(Q)=15,590m3/dayfiltered flow rate (Q) = 15,590 m^3/day
  • filterarea(Af)=132.0m2filter area (A_f) = 132.0 m^2

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.
granular filter

Figure 10 — schematic for Filtration Equations — solve for filtration rate (case 4) — Filtration Equations (10)

Step-by-step solution

  1. Step 1 — State the governing relation:

    vf=QAfv_f = \dfrac{Q}{A_f}
  2. Step 2 — Rearrange symbolically for v_f:

    vf=QAfv_{f} = \dfrac{Q}{A_f}
  3. Step 3 — List the givens: filtered flow rate (Q) = 15,590 m^3/day, filter area (A_f) = 132.0 m^2.

  4. Step 4 — Substitute the given values:

    vf=15590Afv_{f} = \dfrac{15590}{A_f}
  5. Step 5 — Evaluate:

    vf=118.1 m/dayv_{f} = 118.1\ \text{m/day}
  6. Step 6 — Check: returning v_f = 118.1 m/day to

    vf=QAfv_f = \dfrac{Q}{A_f}

    reproduces the given quantities, and both sides carry the same units.

Answer:
vf=118.1 m/dayv_{f} = 118.1\ \text{m/day}

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

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