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Rapid Mix and Flocculator Design

Environmental Engineering · FE Reference Handbook section

Environmental Engineering
9 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
Rapid Mix and Flocculator Design — solve for velocity gradient — Rapid Mix and Flocculator Design

rapid mix and flocculator design velocity gradient for coagulation Given power input (P) = 19,090 W; dynamic viscosity (mu) = 0.0011 Pa*s; basin volume (V) = 1,460 m^3, determine the velocity gradient (G) in 1/s.

Given

  • powerinput(P)=19,090Wpower input (P) = 19,090 W
  • dynamicviscosity(mu)=0.0011Pa∗sdynamic viscosity (mu) = 0.0011 Pa*s
  • basinvolume(V)=1,460m3basin volume (V) = 1,460 m^3

Find

velocity gradient (G), in 1/s

Start with the thinking

  • The governing relation printed in this handbook section is Rapid Mix and Flocculator Design.
  • Everything except G is given, so isolate G 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.
  • Rapid mix and flocculator design uses the velocity gradient G to set power input for a coagulation-flocculation basin.
rapid mix / flocculator basin

Figure 1 — schematic for Rapid Mix and Flocculator Design — solve for velocity gradient — Rapid Mix and Flocculator Design

Step-by-step solution

  1. Step 1 — State the governing relation:

    G=PμVG = \sqrt{\dfrac{P}{\mu V}}
  2. Step 2 — Rearrange symbolically for G:

    G=PμVG = \sqrt{\dfrac{P}{\mu V}}
  3. Step 3 — List the givens: power input (P) = 19,090 W, dynamic viscosity (mu) = 0.0011 Pa*s, basin volume (V) = 1,460 m^3.

  4. Step 4 — Substitute the given values:

    G=190900.00111460G = \sqrt{\dfrac{19090}{0.0011 1460}}
  5. Step 5 — Evaluate:

    G=109.5 1/sG = 109.5\ \text{1/s}
  6. Step 6 — Check: returning G = 109.5 1/s to

    G=PμVG = \sqrt{\dfrac{P}{\mu V}}

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

Answer:
G=109.5 1/sG = 109.5\ \text{1/s}

Why the other options are there

  • 219.1 — kept a factor of two that cancels in the correct rearrangement.
  • 54.7625 — dropped that same factor in the other direction.
  • 120.5 — rounded an intermediate value before the final step.

Reference: FE Handbook — Rapid Mix and Flocculator Design

Example 2
Rapid Mix and Flocculator Design — solve for power input — Rapid Mix and Flocculator Design (2)

rapid mix basin design power input for a water treatment plant Given dynamic viscosity (mu) = 0.0011 Pa*s; basin volume (V) = 895.0 m^3; velocity gradient (G) = 917.0 1/s, determine the power input (P) in W.

Given

  • dynamicviscosity(mu)=0.0011Pa∗sdynamic viscosity (mu) = 0.0011 Pa*s
  • basinvolume(V)=895.0m3basin volume (V) = 895.0 m^3
  • velocitygradient(G)=917.01/svelocity gradient (G) = 917.0 1/s

Find

power input (P), in W

Start with the thinking

  • The governing relation printed in this handbook section is Rapid Mix and Flocculator Design.
  • Everything except P is given, so isolate P 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.
  • Rapid mix and flocculator design uses the velocity gradient G to set power input for a coagulation-flocculation basin.
rapid mix / flocculator basin

Figure 2 — schematic for Rapid Mix and Flocculator Design — solve for power input — Rapid Mix and Flocculator Design (2)

Step-by-step solution

  1. Step 1 — State the governing relation:

    G=PμVG = \sqrt{\dfrac{P}{\mu V}}
  2. Step 2 — Rearrange symbolically for P:

    P=G2μVP = G^2 \mu V
  3. Step 3 — List the givens: dynamic viscosity (mu) = 0.0011 Pa*s, basin volume (V) = 895.0 m^3, velocity gradient (G) = 917.0 1/s.

  4. Step 4 — Substitute the given values:

    P=917.020.0011895.0P = 917.0^2 0.0011 895.0
  5. Step 5 — Evaluate:

    P=850433 WP = 850433\ \text{W}
  6. Step 6 — Check: returning P = 850,433 W to

    G=PμVG = \sqrt{\dfrac{P}{\mu V}}

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

Answer:
P=850433 WP = 850433\ \text{W}

Why the other options are there

  • 1,700,866 — kept a factor of two that cancels in the correct rearrangement.
  • 425,217 — dropped that same factor in the other direction.
  • 935,476 — rounded an intermediate value before the final step.

Reference: FE Handbook — Rapid Mix and Flocculator Design

Example 3
Rapid Mix and Flocculator Design — solve for basin volume — Rapid Mix and Flocculator Design (3)

flocculator design velocity gradient and power requirement Given power input (P) = 6,150 W; dynamic viscosity (mu) = 0.0017 Pa*s; velocity gradient (G) = 247.0 1/s, determine the basin volume (V) in m^3.

Given

  • powerinput(P)=6,150Wpower input (P) = 6,150 W
  • dynamicviscosity(mu)=0.0017Pa∗sdynamic viscosity (mu) = 0.0017 Pa*s
  • velocitygradient(G)=247.01/svelocity gradient (G) = 247.0 1/s

Find

basin volume (V), in m^3

Start with the thinking

  • The governing relation printed in this handbook section is Rapid Mix and Flocculator Design.
  • Everything except V is given, so isolate V 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.
  • Rapid mix and flocculator design uses the velocity gradient G to set power input for a coagulation-flocculation basin.
rapid mix / flocculator basin

Figure 3 — schematic for Rapid Mix and Flocculator Design — solve for basin volume — Rapid Mix and Flocculator Design (3)

Step-by-step solution

  1. Step 1 — State the governing relation:

    G=PμVG = \sqrt{\dfrac{P}{\mu V}}
  2. Step 2 — Rearrange symbolically for V:

    V=PμG2V = \dfrac{P}{\mu G^2}
  3. Step 3 — List the givens: power input (P) = 6,150 W, dynamic viscosity (mu) = 0.0017 Pa*s, velocity gradient (G) = 247.0 1/s.

  4. Step 4 — Substitute the given values:

    V=61500.0017247.02V = \dfrac{6150}{0.0017 247.0^2}
  5. Step 5 — Evaluate:

    V = 60.3622\ \text{m^3}
  6. Step 6 — Check: returning V = 60.3622 m^3 to

    G=PμVG = \sqrt{\dfrac{P}{\mu V}}

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

Answer:
V = 60.3622\ \text{m^3}

Why the other options are there

  • 120.7 — kept a factor of two that cancels in the correct rearrangement.
  • 30.1811 — dropped that same factor in the other direction.
  • 66.3984 — rounded an intermediate value before the final step.

Reference: FE Handbook — Rapid Mix and Flocculator Design

Example 4
Rapid Mix and Flocculator Design — solve for velocity gradient (case 2) — Rapid Mix and Flocculator Design (4)

rapid mix and flocculator design velocity gradient for coagulation Given power input (P) = 4,900 W; dynamic viscosity (mu) = 0.0018 Pa*s; basin volume (V) = 1,858 m^3, determine the velocity gradient (G) in 1/s.

Given

  • powerinput(P)=4,900Wpower input (P) = 4,900 W
  • dynamicviscosity(mu)=0.0018Pa∗sdynamic viscosity (mu) = 0.0018 Pa*s
  • basinvolume(V)=1,858m3basin volume (V) = 1,858 m^3

Find

velocity gradient (G), in 1/s

Start with the thinking

  • The governing relation printed in this handbook section is Rapid Mix and Flocculator Design.
  • Everything except G is given, so isolate G 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.
  • Rapid mix and flocculator design uses the velocity gradient G to set power input for a coagulation-flocculation basin.
rapid mix / flocculator basin

Figure 4 — schematic for Rapid Mix and Flocculator Design — solve for velocity gradient (case 2) — Rapid Mix and Flocculator Design (4)

Step-by-step solution

  1. Step 1 — State the governing relation:

    G=PμVG = \sqrt{\dfrac{P}{\mu V}}
  2. Step 2 — Rearrange symbolically for G:

    G=PμVG = \sqrt{\dfrac{P}{\mu V}}
  3. Step 3 — List the givens: power input (P) = 4,900 W, dynamic viscosity (mu) = 0.0018 Pa*s, basin volume (V) = 1,858 m^3.

  4. Step 4 — Substitute the given values:

    G=49000.00181858G = \sqrt{\dfrac{4900}{0.0018 1858}}
  5. Step 5 — Evaluate:

    G=38.7096 1/sG = 38.7096\ \text{1/s}
  6. Step 6 — Check: returning G = 38.7096 1/s to

    G=PμVG = \sqrt{\dfrac{P}{\mu V}}

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

Answer:
G=38.7096 1/sG = 38.7096\ \text{1/s}

Why the other options are there

  • 77.4192 — kept a factor of two that cancels in the correct rearrangement.
  • 19.3548 — dropped that same factor in the other direction.
  • 42.5806 — rounded an intermediate value before the final step.

Reference: FE Handbook — Rapid Mix and Flocculator Design

Example 5
Rapid Mix and Flocculator Design — solve for power input (case 2) — Rapid Mix and Flocculator Design (5)

rapid mix basin design power input for a water treatment plant Given dynamic viscosity (mu) = 0.0017 Pa*s; basin volume (V) = 491.0 m^3; velocity gradient (G) = 53.0000 1/s, determine the power input (P) in W.

Given

  • dynamicviscosity(mu)=0.0017Pa∗sdynamic viscosity (mu) = 0.0017 Pa*s
  • basinvolume(V)=491.0m3basin volume (V) = 491.0 m^3
  • velocitygradient(G)=53.00001/svelocity gradient (G) = 53.0000 1/s

Find

power input (P), in W

Start with the thinking

  • The governing relation printed in this handbook section is Rapid Mix and Flocculator Design.
  • Everything except P is given, so isolate P 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.
  • Rapid mix and flocculator design uses the velocity gradient G to set power input for a coagulation-flocculation basin.
rapid mix / flocculator basin

Figure 5 — schematic for Rapid Mix and Flocculator Design — solve for power input (case 2) — Rapid Mix and Flocculator Design (5)

Step-by-step solution

  1. Step 1 — State the governing relation:

    G=PμVG = \sqrt{\dfrac{P}{\mu V}}
  2. Step 2 — Rearrange symbolically for P:

    P=G2μVP = G^2 \mu V
  3. Step 3 — List the givens: dynamic viscosity (mu) = 0.0017 Pa*s, basin volume (V) = 491.0 m^3, velocity gradient (G) = 53.0000 1/s.

  4. Step 4 — Substitute the given values:

    P=53.000020.0017491.0P = 53.0000^2 0.0017 491.0
  5. Step 5 — Evaluate:

    P=2331 WP = 2331\ \text{W}
  6. Step 6 — Check: returning P = 2,331 W to

    G=PμVG = \sqrt{\dfrac{P}{\mu V}}

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

Answer:
P=2331 WP = 2331\ \text{W}

Why the other options are there

  • 4,662 — kept a factor of two that cancels in the correct rearrangement.
  • 1,165 — dropped that same factor in the other direction.
  • 2,564 — rounded an intermediate value before the final step.

Reference: FE Handbook — Rapid Mix and Flocculator Design

Example 6
Rapid Mix and Flocculator Design — solve for basin volume (case 2) — Rapid Mix and Flocculator Design (6)

flocculator design velocity gradient and power requirement Given power input (P) = 17,610 W; dynamic viscosity (mu) = 0.0012 Pa*s; velocity gradient (G) = 454.0 1/s, determine the basin volume (V) in m^3.

Given

  • powerinput(P)=17,610Wpower input (P) = 17,610 W
  • dynamicviscosity(mu)=0.0012Pa∗sdynamic viscosity (mu) = 0.0012 Pa*s
  • velocitygradient(G)=454.01/svelocity gradient (G) = 454.0 1/s

Find

basin volume (V), in m^3

Start with the thinking

  • The governing relation printed in this handbook section is Rapid Mix and Flocculator Design.
  • Everything except V is given, so isolate V 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.
  • Rapid mix and flocculator design uses the velocity gradient G to set power input for a coagulation-flocculation basin.
rapid mix / flocculator basin

Figure 6 — schematic for Rapid Mix and Flocculator Design — solve for basin volume (case 2) — Rapid Mix and Flocculator Design (6)

Step-by-step solution

  1. Step 1 — State the governing relation:

    G=PμVG = \sqrt{\dfrac{P}{\mu V}}
  2. Step 2 — Rearrange symbolically for V:

    V=PμG2V = \dfrac{P}{\mu G^2}
  3. Step 3 — List the givens: power input (P) = 17,610 W, dynamic viscosity (mu) = 0.0012 Pa*s, velocity gradient (G) = 454.0 1/s.

  4. Step 4 — Substitute the given values:

    V=176100.0012454.02V = \dfrac{17610}{0.0012 454.0^2}
  5. Step 5 — Evaluate:

    V = 72.4045\ \text{m^3}
  6. Step 6 — Check: returning V = 72.4045 m^3 to

    G=PμVG = \sqrt{\dfrac{P}{\mu V}}

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

Answer:
V = 72.4045\ \text{m^3}

Why the other options are there

  • 144.8 — kept a factor of two that cancels in the correct rearrangement.
  • 36.2023 — dropped that same factor in the other direction.
  • 79.6450 — rounded an intermediate value before the final step.

Reference: FE Handbook — Rapid Mix and Flocculator Design

Example 7
Rapid Mix and Flocculator Design — solve for velocity gradient (case 3) — Rapid Mix and Flocculator Design (7)

rapid mix and flocculator design velocity gradient for coagulation Given power input (P) = 11,380 W; dynamic viscosity (mu) = 0.0018 Pa*s; basin volume (V) = 1,055 m^3, determine the velocity gradient (G) in 1/s.

Given

  • powerinput(P)=11,380Wpower input (P) = 11,380 W
  • dynamicviscosity(mu)=0.0018Pa∗sdynamic viscosity (mu) = 0.0018 Pa*s
  • basinvolume(V)=1,055m3basin volume (V) = 1,055 m^3

Find

velocity gradient (G), in 1/s

Start with the thinking

  • The governing relation printed in this handbook section is Rapid Mix and Flocculator Design.
  • Everything except G is given, so isolate G 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.
  • Rapid mix and flocculator design uses the velocity gradient G to set power input for a coagulation-flocculation basin.
rapid mix / flocculator basin

Figure 7 — schematic for Rapid Mix and Flocculator Design — solve for velocity gradient (case 3) — Rapid Mix and Flocculator Design (7)

Step-by-step solution

  1. Step 1 — State the governing relation:

    G=PμVG = \sqrt{\dfrac{P}{\mu V}}
  2. Step 2 — Rearrange symbolically for G:

    G=PμVG = \sqrt{\dfrac{P}{\mu V}}
  3. Step 3 — List the givens: power input (P) = 11,380 W, dynamic viscosity (mu) = 0.0018 Pa*s, basin volume (V) = 1,055 m^3.

  4. Step 4 — Substitute the given values:

    G=113800.00181055G = \sqrt{\dfrac{11380}{0.0018 1055}}
  5. Step 5 — Evaluate:

    G=77.6280 1/sG = 77.6280\ \text{1/s}
  6. Step 6 — Check: returning G = 77.6280 1/s to

    G=PμVG = \sqrt{\dfrac{P}{\mu V}}

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

Answer:
G=77.6280 1/sG = 77.6280\ \text{1/s}

Why the other options are there

  • 155.3 — kept a factor of two that cancels in the correct rearrangement.
  • 38.8140 — dropped that same factor in the other direction.
  • 85.3908 — rounded an intermediate value before the final step.

Reference: FE Handbook — Rapid Mix and Flocculator Design

Example 8
Rapid Mix and Flocculator Design — solve for power input (case 3) — Rapid Mix and Flocculator Design (8)

rapid mix basin design power input for a water treatment plant Given dynamic viscosity (mu) = 0.0012 Pa*s; basin volume (V) = 269.0 m^3; velocity gradient (G) = 863.0 1/s, determine the power input (P) in W.

Given

  • dynamicviscosity(mu)=0.0012Pa∗sdynamic viscosity (mu) = 0.0012 Pa*s
  • basinvolume(V)=269.0m3basin volume (V) = 269.0 m^3
  • velocitygradient(G)=863.01/svelocity gradient (G) = 863.0 1/s

Find

power input (P), in W

Start with the thinking

  • The governing relation printed in this handbook section is Rapid Mix and Flocculator Design.
  • Everything except P is given, so isolate P 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.
  • Rapid mix and flocculator design uses the velocity gradient G to set power input for a coagulation-flocculation basin.
rapid mix / flocculator basin

Figure 8 — schematic for Rapid Mix and Flocculator Design — solve for power input (case 3) — Rapid Mix and Flocculator Design (8)

Step-by-step solution

  1. Step 1 — State the governing relation:

    G=PμVG = \sqrt{\dfrac{P}{\mu V}}
  2. Step 2 — Rearrange symbolically for P:

    P=G2μVP = G^2 \mu V
  3. Step 3 — List the givens: dynamic viscosity (mu) = 0.0012 Pa*s, basin volume (V) = 269.0 m^3, velocity gradient (G) = 863.0 1/s.

  4. Step 4 — Substitute the given values:

    P=863.020.0012269.0P = 863.0^2 0.0012 269.0
  5. Step 5 — Evaluate:

    P=234401 WP = 234401\ \text{W}
  6. Step 6 — Check: returning P = 234,401 W to

    G=PμVG = \sqrt{\dfrac{P}{\mu V}}

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

Answer:
P=234401 WP = 234401\ \text{W}

Why the other options are there

  • 468,802 — kept a factor of two that cancels in the correct rearrangement.
  • 117,201 — dropped that same factor in the other direction.
  • 257,841 — rounded an intermediate value before the final step.

Reference: FE Handbook — Rapid Mix and Flocculator Design

Example 9
Rapid Mix and Flocculator Design — solve for basin volume (case 3) — Rapid Mix and Flocculator Design (9)

flocculator design velocity gradient and power requirement Given power input (P) = 16,330 W; dynamic viscosity (mu) = 0.0009 Pa*s; velocity gradient (G) = 488.0 1/s, determine the basin volume (V) in m^3.

Given

  • powerinput(P)=16,330Wpower input (P) = 16,330 W
  • dynamicviscosity(mu)=0.0009Pa∗sdynamic viscosity (mu) = 0.0009 Pa*s
  • velocitygradient(G)=488.01/svelocity gradient (G) = 488.0 1/s

Find

basin volume (V), in m^3

Start with the thinking

  • The governing relation printed in this handbook section is Rapid Mix and Flocculator Design.
  • Everything except V is given, so isolate V 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.
  • Rapid mix and flocculator design uses the velocity gradient G to set power input for a coagulation-flocculation basin.
rapid mix / flocculator basin

Figure 9 — schematic for Rapid Mix and Flocculator Design — solve for basin volume (case 3) — Rapid Mix and Flocculator Design (9)

Step-by-step solution

  1. Step 1 — State the governing relation:

    G=PμVG = \sqrt{\dfrac{P}{\mu V}}
  2. Step 2 — Rearrange symbolically for V:

    V=PμG2V = \dfrac{P}{\mu G^2}
  3. Step 3 — List the givens: power input (P) = 16,330 W, dynamic viscosity (mu) = 0.0009 Pa*s, velocity gradient (G) = 488.0 1/s.

  4. Step 4 — Substitute the given values:

    V=163300.0009488.02V = \dfrac{16330}{0.0009 488.0^2}
  5. Step 5 — Evaluate:

    V = 73.7333\ \text{m^3}
  6. Step 6 — Check: returning V = 73.7333 m^3 to

    G=PμVG = \sqrt{\dfrac{P}{\mu V}}

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

Answer:
V = 73.7333\ \text{m^3}

Why the other options are there

  • 147.5 — kept a factor of two that cancels in the correct rearrangement.
  • 36.8666 — dropped that same factor in the other direction.
  • 81.1066 — rounded an intermediate value before the final step.

Reference: FE Handbook — Rapid Mix and Flocculator Design

Example 10
Rapid Mix and Flocculator Design — solve for velocity gradient (case 4) — Rapid Mix and Flocculator Design (10)

rapid mix and flocculator design velocity gradient for coagulation Given power input (P) = 3,890 W; dynamic viscosity (mu) = 0.0017 Pa*s; basin volume (V) = 767.0 m^3, determine the velocity gradient (G) in 1/s.

Given

  • powerinput(P)=3,890Wpower input (P) = 3,890 W
  • dynamicviscosity(mu)=0.0017Pa∗sdynamic viscosity (mu) = 0.0017 Pa*s
  • basinvolume(V)=767.0m3basin volume (V) = 767.0 m^3

Find

velocity gradient (G), in 1/s

Start with the thinking

  • The governing relation printed in this handbook section is Rapid Mix and Flocculator Design.
  • Everything except G is given, so isolate G 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.
  • Rapid mix and flocculator design uses the velocity gradient G to set power input for a coagulation-flocculation basin.
rapid mix / flocculator basin

Figure 10 — schematic for Rapid Mix and Flocculator Design — solve for velocity gradient (case 4) — Rapid Mix and Flocculator Design (10)

Step-by-step solution

  1. Step 1 — State the governing relation:

    G=PμVG = \sqrt{\dfrac{P}{\mu V}}
  2. Step 2 — Rearrange symbolically for G:

    G=PμVG = \sqrt{\dfrac{P}{\mu V}}
  3. Step 3 — List the givens: power input (P) = 3,890 W, dynamic viscosity (mu) = 0.0017 Pa*s, basin volume (V) = 767.0 m^3.

  4. Step 4 — Substitute the given values:

    G=38900.0017767.0G = \sqrt{\dfrac{3890}{0.0017 767.0}}
  5. Step 5 — Evaluate:

    G=54.6201 1/sG = 54.6201\ \text{1/s}
  6. Step 6 — Check: returning G = 54.6201 1/s to

    G=PμVG = \sqrt{\dfrac{P}{\mu V}}

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

Answer:
G=54.6201 1/sG = 54.6201\ \text{1/s}

Why the other options are there

  • 109.2 — kept a factor of two that cancels in the correct rearrangement.
  • 27.3101 — dropped that same factor in the other direction.
  • 60.0821 — rounded an intermediate value before the final step.

Reference: FE Handbook — Rapid Mix and Flocculator Design

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