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Depth of Sorption Zone

Environmental Engineering · FE Reference Handbook section

Environmental Engineering
8 formulas
10 exam-style examples
~60 min
All Environmental Engineering lectures

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
Depth of Sorption Zone — solve for sorption zone depth — Depth of Sorption Zone

depth of sorption zone in a granular activated carbon column Given carbon bed depth (D) = 4.2000 m; time to total exhaustion (t_t) = 177.0 day; time to breakthrough (t_b) = 82.0000 day, determine the sorption zone depth (D_s) in m.

Given

  • carbonbeddepth(D)=4.2000mcarbon bed depth (D) = 4.2000 m
  • timetototalexhaustion(tt)=177.0daytime to total exhaustion (t_t) = 177.0 day
  • timetobreakthrough(tb)=82.0000daytime to breakthrough (t_b) = 82.0000 day

Find

sorption zone depth (D_s), in m

Start with the thinking

  • The governing relation printed in this handbook section is Depth of Sorption Zone.
  • Everything except D_s is given, so isolate D_s 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.
  • Depth of sorption zone in a carbon adsorption column is derived from breakthrough and exhaustion times of the bed.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Ds=D(tt−tbtt−0.5tb)D_s = D\left(\dfrac{t_t - t_b}{t_t - 0.5 t_b}\right)
  2. Step 2 — Rearrange symbolically for D_s:

    Ds=D(tt−tbtt−0.5tb)D_{s} = D\left(\dfrac{t_t-t_b}{t_t-0.5t_b}\right)
  3. Step 3 — List the givens: carbon bed depth (D) = 4.2000 m, time to total exhaustion (t_t) = 177.0 day, time to breakthrough (t_b) = 82.0000 day.

  4. Step 4 — Substitute the given values:

    Ds=4.2000(tt−tbtt−0.5tb)D_{s} = 4.2000\left(\dfrac{t_t-t_b}{t_t-0.5t_b}\right)
  5. Step 5 — Evaluate:

    Ds=2.9338 mD_{s} = 2.9338\ \text{m}
  6. Step 6 — Check: returning D_s = 2.9338 m to

    Ds=D(tt−tbtt−0.5tb)D_s = D\left(\dfrac{t_t - t_b}{t_t - 0.5 t_b}\right)

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

Answer:
Ds=2.9338 mD_{s} = 2.9338\ \text{m}

Why the other options are there

  • 5.8676 — kept a factor of two that cancels in the correct rearrangement.
  • 1.4669 — dropped that same factor in the other direction.
  • 3.2272 — rounded an intermediate value before the final step.

Reference: FE Handbook — Depth of Sorption Zone

Example 2
Depth of Sorption Zone — solve for carbon bed depth — Depth of Sorption Zone (2)

depth of sorption zone calculated from breakthrough curve data Given time to total exhaustion (t_t) = 42.0000 day; time to breakthrough (t_b) = 112.0 day; sorption zone depth (D_s) = 1.8100 m, determine the carbon bed depth (D) in m.

Given

  • timetototalexhaustion(tt)=42.0000daytime to total exhaustion (t_t) = 42.0000 day
  • timetobreakthrough(tb)=112.0daytime to breakthrough (t_b) = 112.0 day
  • sorptionzonedepth(Ds)=1.8100msorption zone depth (D_s) = 1.8100 m

Find

carbon bed depth (D), in m

Start with the thinking

  • The governing relation printed in this handbook section is Depth of Sorption Zone.
  • Everything except D is given, so isolate D 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.
  • Depth of sorption zone in a carbon adsorption column is derived from breakthrough and exhaustion times of the bed.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Ds=D(tt−tbtt−0.5tb)D_s = D\left(\dfrac{t_t - t_b}{t_t - 0.5 t_b}\right)
  2. Step 2 — Rearrange symbolically for D:

    D=Ds(tt−0.5tbtt−tb)D = D_s\left(\dfrac{t_t-0.5t_b}{t_t-t_b}\right)
  3. Step 3 — List the givens: time to total exhaustion (t_t) = 42.0000 day, time to breakthrough (t_b) = 112.0 day, sorption zone depth (D_s) = 1.8100 m.

  4. Step 4 — Substitute the given values:

    D=Ds(tt−0.5tbtt−tb)D = D_s\left(\dfrac{t_t-0.5t_b}{t_t-t_b}\right)
  5. Step 5 — Evaluate:

    D=0.3620 mD = 0.3620\ \text{m}
  6. Step 6 — Check: returning D = 0.3620 m to

    Ds=D(tt−tbtt−0.5tb)D_s = D\left(\dfrac{t_t - t_b}{t_t - 0.5 t_b}\right)

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

Answer:
D=0.3620 mD = 0.3620\ \text{m}

Why the other options are there

  • 0.7240 — kept a factor of two that cancels in the correct rearrangement.
  • 0.1810 — dropped that same factor in the other direction.
  • 0.3982 — rounded an intermediate value before the final step.

Reference: FE Handbook — Depth of Sorption Zone

Example 3
Depth of Sorption Zone — solve for sorption zone depth (case 2) — Depth of Sorption Zone (3)

sorption zone depth used to design carbon bed replacement schedule Given carbon bed depth (D) = 2.4500 m; time to total exhaustion (t_t) = 144.0 day; time to breakthrough (t_b) = 117.0 day, determine the sorption zone depth (D_s) in m.

Given

  • carbonbeddepth(D)=2.4500mcarbon bed depth (D) = 2.4500 m
  • timetototalexhaustion(tt)=144.0daytime to total exhaustion (t_t) = 144.0 day
  • timetobreakthrough(tb)=117.0daytime to breakthrough (t_b) = 117.0 day

Find

sorption zone depth (D_s), in m

Start with the thinking

  • The governing relation printed in this handbook section is Depth of Sorption Zone.
  • Everything except D_s is given, so isolate D_s 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.
  • Depth of sorption zone in a carbon adsorption column is derived from breakthrough and exhaustion times of the bed.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Ds=D(tt−tbtt−0.5tb)D_s = D\left(\dfrac{t_t - t_b}{t_t - 0.5 t_b}\right)
  2. Step 2 — Rearrange symbolically for D_s:

    Ds=D(tt−tbtt−0.5tb)D_{s} = D\left(\dfrac{t_t-t_b}{t_t-0.5t_b}\right)
  3. Step 3 — List the givens: carbon bed depth (D) = 2.4500 m, time to total exhaustion (t_t) = 144.0 day, time to breakthrough (t_b) = 117.0 day.

  4. Step 4 — Substitute the given values:

    Ds=2.4500(tt−tbtt−0.5tb)D_{s} = 2.4500\left(\dfrac{t_t-t_b}{t_t-0.5t_b}\right)
  5. Step 5 — Evaluate:

    Ds=0.7737 mD_{s} = 0.7737\ \text{m}
  6. Step 6 — Check: returning D_s = 0.7737 m to

    Ds=D(tt−tbtt−0.5tb)D_s = D\left(\dfrac{t_t - t_b}{t_t - 0.5 t_b}\right)

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

Answer:
Ds=0.7737 mD_{s} = 0.7737\ \text{m}

Why the other options are there

  • 1.5474 — kept a factor of two that cancels in the correct rearrangement.
  • 0.3868 — dropped that same factor in the other direction.
  • 0.8511 — rounded an intermediate value before the final step.

Reference: FE Handbook — Depth of Sorption Zone

Example 4
Depth of Sorption Zone — solve for carbon bed depth (case 2) — Depth of Sorption Zone (4)

depth of sorption zone in a granular activated carbon column Given time to total exhaustion (t_t) = 66.0000 day; time to breakthrough (t_b) = 41.0000 day; sorption zone depth (D_s) = 2.7700 m, determine the carbon bed depth (D) in m.

Given

  • timetototalexhaustion(tt)=66.0000daytime to total exhaustion (t_t) = 66.0000 day
  • timetobreakthrough(tb)=41.0000daytime to breakthrough (t_b) = 41.0000 day
  • sorptionzonedepth(Ds)=2.7700msorption zone depth (D_s) = 2.7700 m

Find

carbon bed depth (D), in m

Start with the thinking

  • The governing relation printed in this handbook section is Depth of Sorption Zone.
  • Everything except D is given, so isolate D 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.
  • Depth of sorption zone in a carbon adsorption column is derived from breakthrough and exhaustion times of the bed.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Ds=D(tt−tbtt−0.5tb)D_s = D\left(\dfrac{t_t - t_b}{t_t - 0.5 t_b}\right)
  2. Step 2 — Rearrange symbolically for D:

    D=Ds(tt−0.5tbtt−tb)D = D_s\left(\dfrac{t_t-0.5t_b}{t_t-t_b}\right)
  3. Step 3 — List the givens: time to total exhaustion (t_t) = 66.0000 day, time to breakthrough (t_b) = 41.0000 day, sorption zone depth (D_s) = 2.7700 m.

  4. Step 4 — Substitute the given values:

    D=Ds(tt−0.5tbtt−tb)D = D_s\left(\dfrac{t_t-0.5t_b}{t_t-t_b}\right)
  5. Step 5 — Evaluate:

    D=5.0414 mD = 5.0414\ \text{m}
  6. Step 6 — Check: returning D = 5.0414 m to

    Ds=D(tt−tbtt−0.5tb)D_s = D\left(\dfrac{t_t - t_b}{t_t - 0.5 t_b}\right)

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

Answer:
D=5.0414 mD = 5.0414\ \text{m}

Why the other options are there

  • 10.0828 — kept a factor of two that cancels in the correct rearrangement.
  • 2.5207 — dropped that same factor in the other direction.
  • 5.5455 — rounded an intermediate value before the final step.

Reference: FE Handbook — Depth of Sorption Zone

Example 5
Depth of Sorption Zone — solve for sorption zone depth (case 3) — Depth of Sorption Zone (5)

depth of sorption zone calculated from breakthrough curve data Given carbon bed depth (D) = 4.4000 m; time to total exhaustion (t_t) = 185.0 day; time to breakthrough (t_b) = 95.0000 day, determine the sorption zone depth (D_s) in m.

Given

  • carbonbeddepth(D)=4.4000mcarbon bed depth (D) = 4.4000 m
  • timetototalexhaustion(tt)=185.0daytime to total exhaustion (t_t) = 185.0 day
  • timetobreakthrough(tb)=95.0000daytime to breakthrough (t_b) = 95.0000 day

Find

sorption zone depth (D_s), in m

Start with the thinking

  • The governing relation printed in this handbook section is Depth of Sorption Zone.
  • Everything except D_s is given, so isolate D_s 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.
  • Depth of sorption zone in a carbon adsorption column is derived from breakthrough and exhaustion times of the bed.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Ds=D(tt−tbtt−0.5tb)D_s = D\left(\dfrac{t_t - t_b}{t_t - 0.5 t_b}\right)
  2. Step 2 — Rearrange symbolically for D_s:

    Ds=D(tt−tbtt−0.5tb)D_{s} = D\left(\dfrac{t_t-t_b}{t_t-0.5t_b}\right)
  3. Step 3 — List the givens: carbon bed depth (D) = 4.4000 m, time to total exhaustion (t_t) = 185.0 day, time to breakthrough (t_b) = 95.0000 day.

  4. Step 4 — Substitute the given values:

    Ds=4.4000(tt−tbtt−0.5tb)D_{s} = 4.4000\left(\dfrac{t_t-t_b}{t_t-0.5t_b}\right)
  5. Step 5 — Evaluate:

    Ds=2.8800 mD_{s} = 2.8800\ \text{m}
  6. Step 6 — Check: returning D_s = 2.8800 m to

    Ds=D(tt−tbtt−0.5tb)D_s = D\left(\dfrac{t_t - t_b}{t_t - 0.5 t_b}\right)

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

Answer:
Ds=2.8800 mD_{s} = 2.8800\ \text{m}

Why the other options are there

  • 5.7600 — kept a factor of two that cancels in the correct rearrangement.
  • 1.4400 — dropped that same factor in the other direction.
  • 3.1680 — rounded an intermediate value before the final step.

Reference: FE Handbook — Depth of Sorption Zone

Example 6
Depth of Sorption Zone — solve for carbon bed depth (case 3) — Depth of Sorption Zone (6)

sorption zone depth used to design carbon bed replacement schedule Given time to total exhaustion (t_t) = 132.0 day; time to breakthrough (t_b) = 40.0000 day; sorption zone depth (D_s) = 2.0200 m, determine the carbon bed depth (D) in m.

Given

  • timetototalexhaustion(tt)=132.0daytime to total exhaustion (t_t) = 132.0 day
  • timetobreakthrough(tb)=40.0000daytime to breakthrough (t_b) = 40.0000 day
  • sorptionzonedepth(Ds)=2.0200msorption zone depth (D_s) = 2.0200 m

Find

carbon bed depth (D), in m

Start with the thinking

  • The governing relation printed in this handbook section is Depth of Sorption Zone.
  • Everything except D is given, so isolate D 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.
  • Depth of sorption zone in a carbon adsorption column is derived from breakthrough and exhaustion times of the bed.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Ds=D(tt−tbtt−0.5tb)D_s = D\left(\dfrac{t_t - t_b}{t_t - 0.5 t_b}\right)
  2. Step 2 — Rearrange symbolically for D:

    D=Ds(tt−0.5tbtt−tb)D = D_s\left(\dfrac{t_t-0.5t_b}{t_t-t_b}\right)
  3. Step 3 — List the givens: time to total exhaustion (t_t) = 132.0 day, time to breakthrough (t_b) = 40.0000 day, sorption zone depth (D_s) = 2.0200 m.

  4. Step 4 — Substitute the given values:

    D=Ds(tt−0.5tbtt−tb)D = D_s\left(\dfrac{t_t-0.5t_b}{t_t-t_b}\right)
  5. Step 5 — Evaluate:

    D=2.4591 mD = 2.4591\ \text{m}
  6. Step 6 — Check: returning D = 2.4591 m to

    Ds=D(tt−tbtt−0.5tb)D_s = D\left(\dfrac{t_t - t_b}{t_t - 0.5 t_b}\right)

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

Answer:
D=2.4591 mD = 2.4591\ \text{m}

Why the other options are there

  • 4.9183 — kept a factor of two that cancels in the correct rearrangement.
  • 1.2296 — dropped that same factor in the other direction.
  • 2.7050 — rounded an intermediate value before the final step.

Reference: FE Handbook — Depth of Sorption Zone

Example 7
Depth of Sorption Zone — solve for sorption zone depth (case 4) — Depth of Sorption Zone (7)

depth of sorption zone in a granular activated carbon column Given carbon bed depth (D) = 1.7000 m; time to total exhaustion (t_t) = 188.0 day; time to breakthrough (t_b) = 64.0000 day, determine the sorption zone depth (D_s) in m.

Given

  • carbonbeddepth(D)=1.7000mcarbon bed depth (D) = 1.7000 m
  • timetototalexhaustion(tt)=188.0daytime to total exhaustion (t_t) = 188.0 day
  • timetobreakthrough(tb)=64.0000daytime to breakthrough (t_b) = 64.0000 day

Find

sorption zone depth (D_s), in m

Start with the thinking

  • The governing relation printed in this handbook section is Depth of Sorption Zone.
  • Everything except D_s is given, so isolate D_s 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.
  • Depth of sorption zone in a carbon adsorption column is derived from breakthrough and exhaustion times of the bed.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Ds=D(tt−tbtt−0.5tb)D_s = D\left(\dfrac{t_t - t_b}{t_t - 0.5 t_b}\right)
  2. Step 2 — Rearrange symbolically for D_s:

    Ds=D(tt−tbtt−0.5tb)D_{s} = D\left(\dfrac{t_t-t_b}{t_t-0.5t_b}\right)
  3. Step 3 — List the givens: carbon bed depth (D) = 1.7000 m, time to total exhaustion (t_t) = 188.0 day, time to breakthrough (t_b) = 64.0000 day.

  4. Step 4 — Substitute the given values:

    Ds=1.7000(tt−tbtt−0.5tb)D_{s} = 1.7000\left(\dfrac{t_t-t_b}{t_t-0.5t_b}\right)
  5. Step 5 — Evaluate:

    Ds=1.3513 mD_{s} = 1.3513\ \text{m}
  6. Step 6 — Check: returning D_s = 1.3513 m to

    Ds=D(tt−tbtt−0.5tb)D_s = D\left(\dfrac{t_t - t_b}{t_t - 0.5 t_b}\right)

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

Answer:
Ds=1.3513 mD_{s} = 1.3513\ \text{m}

Why the other options are there

  • 2.7026 — kept a factor of two that cancels in the correct rearrangement.
  • 0.6756 — dropped that same factor in the other direction.
  • 1.4864 — rounded an intermediate value before the final step.

Reference: FE Handbook — Depth of Sorption Zone

Example 8
Depth of Sorption Zone — solve for carbon bed depth (case 4) — Depth of Sorption Zone (8)

depth of sorption zone calculated from breakthrough curve data Given time to total exhaustion (t_t) = 153.0 day; time to breakthrough (t_b) = 9.0000 day; sorption zone depth (D_s) = 0.9700 m, determine the carbon bed depth (D) in m.

Given

  • timetototalexhaustion(tt)=153.0daytime to total exhaustion (t_t) = 153.0 day
  • timetobreakthrough(tb)=9.0000daytime to breakthrough (t_b) = 9.0000 day
  • sorptionzonedepth(Ds)=0.9700msorption zone depth (D_s) = 0.9700 m

Find

carbon bed depth (D), in m

Start with the thinking

  • The governing relation printed in this handbook section is Depth of Sorption Zone.
  • Everything except D is given, so isolate D 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.
  • Depth of sorption zone in a carbon adsorption column is derived from breakthrough and exhaustion times of the bed.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Ds=D(tt−tbtt−0.5tb)D_s = D\left(\dfrac{t_t - t_b}{t_t - 0.5 t_b}\right)
  2. Step 2 — Rearrange symbolically for D:

    D=Ds(tt−0.5tbtt−tb)D = D_s\left(\dfrac{t_t-0.5t_b}{t_t-t_b}\right)
  3. Step 3 — List the givens: time to total exhaustion (t_t) = 153.0 day, time to breakthrough (t_b) = 9.0000 day, sorption zone depth (D_s) = 0.9700 m.

  4. Step 4 — Substitute the given values:

    D=Ds(tt−0.5tbtt−tb)D = D_s\left(\dfrac{t_t-0.5t_b}{t_t-t_b}\right)
  5. Step 5 — Evaluate:

    D=1.0003 mD = 1.0003\ \text{m}
  6. Step 6 — Check: returning D = 1.0003 m to

    Ds=D(tt−tbtt−0.5tb)D_s = D\left(\dfrac{t_t - t_b}{t_t - 0.5 t_b}\right)

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

Answer:
D=1.0003 mD = 1.0003\ \text{m}

Why the other options are there

  • 2.0006 — kept a factor of two that cancels in the correct rearrangement.
  • 0.5002 — dropped that same factor in the other direction.
  • 1.1003 — rounded an intermediate value before the final step.

Reference: FE Handbook — Depth of Sorption Zone

Example 9
Depth of Sorption Zone — solve for sorption zone depth (case 5) — Depth of Sorption Zone (9)

sorption zone depth used to design carbon bed replacement schedule Given carbon bed depth (D) = 2.2000 m; time to total exhaustion (t_t) = 74.0000 day; time to breakthrough (t_b) = 7.0000 day, determine the sorption zone depth (D_s) in m.

Given

  • carbonbeddepth(D)=2.2000mcarbon bed depth (D) = 2.2000 m
  • timetototalexhaustion(tt)=74.0000daytime to total exhaustion (t_t) = 74.0000 day
  • timetobreakthrough(tb)=7.0000daytime to breakthrough (t_b) = 7.0000 day

Find

sorption zone depth (D_s), in m

Start with the thinking

  • The governing relation printed in this handbook section is Depth of Sorption Zone.
  • Everything except D_s is given, so isolate D_s 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.
  • Depth of sorption zone in a carbon adsorption column is derived from breakthrough and exhaustion times of the bed.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Ds=D(tt−tbtt−0.5tb)D_s = D\left(\dfrac{t_t - t_b}{t_t - 0.5 t_b}\right)
  2. Step 2 — Rearrange symbolically for D_s:

    Ds=D(tt−tbtt−0.5tb)D_{s} = D\left(\dfrac{t_t-t_b}{t_t-0.5t_b}\right)
  3. Step 3 — List the givens: carbon bed depth (D) = 2.2000 m, time to total exhaustion (t_t) = 74.0000 day, time to breakthrough (t_b) = 7.0000 day.

  4. Step 4 — Substitute the given values:

    Ds=2.2000(tt−tbtt−0.5tb)D_{s} = 2.2000\left(\dfrac{t_t-t_b}{t_t-0.5t_b}\right)
  5. Step 5 — Evaluate:

    Ds=2.0908 mD_{s} = 2.0908\ \text{m}
  6. Step 6 — Check: returning D_s = 2.0908 m to

    Ds=D(tt−tbtt−0.5tb)D_s = D\left(\dfrac{t_t - t_b}{t_t - 0.5 t_b}\right)

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

Answer:
Ds=2.0908 mD_{s} = 2.0908\ \text{m}

Why the other options are there

  • 4.1816 — kept a factor of two that cancels in the correct rearrangement.
  • 1.0454 — dropped that same factor in the other direction.
  • 2.2999 — rounded an intermediate value before the final step.

Reference: FE Handbook — Depth of Sorption Zone

Example 10
Depth of Sorption Zone — solve for carbon bed depth (case 5) — Depth of Sorption Zone (10)

depth of sorption zone in a granular activated carbon column Given time to total exhaustion (t_t) = 26.0000 day; time to breakthrough (t_b) = 8.0000 day; sorption zone depth (D_s) = 2.7000 m, determine the carbon bed depth (D) in m.

Given

  • timetototalexhaustion(tt)=26.0000daytime to total exhaustion (t_t) = 26.0000 day
  • timetobreakthrough(tb)=8.0000daytime to breakthrough (t_b) = 8.0000 day
  • sorptionzonedepth(Ds)=2.7000msorption zone depth (D_s) = 2.7000 m

Find

carbon bed depth (D), in m

Start with the thinking

  • The governing relation printed in this handbook section is Depth of Sorption Zone.
  • Everything except D is given, so isolate D 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.
  • Depth of sorption zone in a carbon adsorption column is derived from breakthrough and exhaustion times of the bed.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Ds=D(tt−tbtt−0.5tb)D_s = D\left(\dfrac{t_t - t_b}{t_t - 0.5 t_b}\right)
  2. Step 2 — Rearrange symbolically for D:

    D=Ds(tt−0.5tbtt−tb)D = D_s\left(\dfrac{t_t-0.5t_b}{t_t-t_b}\right)
  3. Step 3 — List the givens: time to total exhaustion (t_t) = 26.0000 day, time to breakthrough (t_b) = 8.0000 day, sorption zone depth (D_s) = 2.7000 m.

  4. Step 4 — Substitute the given values:

    D=Ds(tt−0.5tbtt−tb)D = D_s\left(\dfrac{t_t-0.5t_b}{t_t-t_b}\right)
  5. Step 5 — Evaluate:

    D=3.3000 mD = 3.3000\ \text{m}
  6. Step 6 — Check: returning D = 3.3000 m to

    Ds=D(tt−tbtt−0.5tb)D_s = D\left(\dfrac{t_t - t_b}{t_t - 0.5 t_b}\right)

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

Answer:
D=3.3000 mD = 3.3000\ \text{m}

Why the other options are there

  • 6.6000 — kept a factor of two that cancels in the correct rearrangement.
  • 1.6500 — dropped that same factor in the other direction.
  • 3.6300 — rounded an intermediate value before the final step.

Reference: FE Handbook — Depth of Sorption Zone

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