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Monod Kinetics—Substrate Limited Growth

Environmental Engineering · FE Reference Handbook section

Environmental Engineering
2 formulas
10 exam-style examples
~49 min
All Environmental Engineering lectures

Handbook notes for this section

Definitions and conditions exactly as the handbook states them.

  • Continuous flow systems where growth is limited by one substrate (chemostat):

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
Multiple Limiting Substrates (Monod) — solve for specific growth rate — Monod Kinetics—Substrate Limited Growth

Monod kinetics with multiple limiting substrates for microbial growth in a bioreactor Given maximum specific growth rate (mu_max) = 5.5000 1/day; limiting substrate concentration (S) = 86.0000 mg/L; half-saturation constant (K_s) = 57.0000 mg/L, determine the specific growth rate (mu) in 1/day.

Given

  • maximumspecificgrowthrate(mumax)=5.50001/daymaximum specific growth rate (mu_max) = 5.5000 1/day
  • limitingsubstrateconcentration(S)=86.0000mg/Llimiting substrate concentration (S) = 86.0000 mg/L
  • half−saturationconstant(Ks)=57.0000mg/Lhalf-saturation constant (K_s) = 57.0000 mg/L

Find

specific growth rate (mu), in 1/day

Start with the thinking

  • The governing relation printed in this handbook section is Multiple Limiting Substrates (Monod).
  • Everything except mu is given, so isolate mu 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.
  • Multiple limiting substrates growth kinetics use the Monod equation to relate specific growth rate to substrate concentration.

Step-by-step solution

  1. Step 1 — State the governing relation:

    μ=μmaxSKs+S\mu = \mu_{max} \dfrac{S}{K_s + S}
  2. Step 2 — Rearrange symbolically for mu:

    μ=μmaxSKs+S\mu = \mu_{max}\dfrac{S}{K_s+S}
  3. Step 3 — List the givens: maximum specific growth rate (mu_max) = 5.5000 1/day, limiting substrate concentration (S) = 86.0000 mg/L, half-saturation constant (K_s) = 57.0000 mg/L.

  4. Step 4 — Substitute the given values:

    μ=5.500086.0000Ks+86.0000\mu = 5.5000\dfrac{86.0000}{K_s+86.0000}
  5. Step 5 — Evaluate:

    μ=3.3077 1/day\mu = 3.3077\ \text{1/day}
  6. Step 6 — Check: returning mu = 3.3077 1/day to

    μ=μmaxSKs+S\mu = \mu_{max} \dfrac{S}{K_s + S}

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

Answer:
μ=3.3077 1/day\mu = 3.3077\ \text{1/day}

Why the other options are there

  • 6.6154 — kept a factor of two that cancels in the correct rearrangement.
  • 1.6538 — dropped that same factor in the other direction.
  • 3.6385 — rounded an intermediate value before the final step.

Reference: FE Handbook — Multiple Limiting Substrates (Monod Kinetics)

Example 2
Multiple Limiting Substrates (Monod) — solve for maximum specific growth rate — Monod Kinetics—Substrate Limited Growth (2)

Monod multiple limiting substrate model for activated sludge biomass growth Given limiting substrate concentration (S) = 14.0000 mg/L; half-saturation constant (K_s) = 11.0000 mg/L; specific growth rate (mu) = 6.1000 1/day, determine the maximum specific growth rate (mu_max) in 1/day.

Given

  • limitingsubstrateconcentration(S)=14.0000mg/Llimiting substrate concentration (S) = 14.0000 mg/L
  • half−saturationconstant(Ks)=11.0000mg/Lhalf-saturation constant (K_s) = 11.0000 mg/L
  • specificgrowthrate(mu)=6.10001/dayspecific growth rate (mu) = 6.1000 1/day

Find

maximum specific growth rate (mu_max), in 1/day

Start with the thinking

  • The governing relation printed in this handbook section is Multiple Limiting Substrates (Monod).
  • Everything except mu_max is given, so isolate mu_max 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.
  • Multiple limiting substrates growth kinetics use the Monod equation to relate specific growth rate to substrate concentration.

Step-by-step solution

  1. Step 1 — State the governing relation:

    μ=μmaxSKs+S\mu = \mu_{max} \dfrac{S}{K_s + S}
  2. Step 2 — Rearrange symbolically for mu_max:

    μmax=μ(Ks+S)S\mu_{max} = \dfrac{\mu (K_s+S)}{S}
  3. Step 3 — List the givens: limiting substrate concentration (S) = 14.0000 mg/L, half-saturation constant (K_s) = 11.0000 mg/L, specific growth rate (mu) = 6.1000 1/day.

  4. Step 4 — Substitute the given values:

    μmax=6.1000(Ks+14.0000)14.0000\mu_{max} = \dfrac{6.1000 (K_s+14.0000)}{14.0000}
  5. Step 5 — Evaluate:

    μmax=10.8929 1/day\mu_{max} = 10.8929\ \text{1/day}
  6. Step 6 — Check: returning mu_max = 10.8929 1/day to

    μ=μmaxSKs+S\mu = \mu_{max} \dfrac{S}{K_s + S}

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

Answer:
μmax=10.8929 1/day\mu_{max} = 10.8929\ \text{1/day}

Why the other options are there

  • 21.7857 — kept a factor of two that cancels in the correct rearrangement.
  • 5.4464 — dropped that same factor in the other direction.
  • 11.9821 — rounded an intermediate value before the final step.

Reference: FE Handbook — Multiple Limiting Substrates (Monod Kinetics)

Example 3
Multiple Limiting Substrates (Monod) — solve for half-saturation constant — Monod Kinetics—Substrate Limited Growth (3)

multiple limiting substrates Monod equation for nutrient-limited growth Given maximum specific growth rate (mu_max) = 2.2000 1/day; limiting substrate concentration (S) = 146.0 mg/L; specific growth rate (mu) = 2.8300 1/day, determine the half-saturation constant (K_s) in mg/L.

Given

  • maximumspecificgrowthrate(mumax)=2.20001/daymaximum specific growth rate (mu_max) = 2.2000 1/day
  • limitingsubstrateconcentration(S)=146.0mg/Llimiting substrate concentration (S) = 146.0 mg/L
  • specificgrowthrate(mu)=2.83001/dayspecific growth rate (mu) = 2.8300 1/day

Find

half-saturation constant (K_s), in mg/L

Start with the thinking

  • The governing relation printed in this handbook section is Multiple Limiting Substrates (Monod).
  • Everything except K_s is given, so isolate K_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.
  • Multiple limiting substrates growth kinetics use the Monod equation to relate specific growth rate to substrate concentration.

Step-by-step solution

  1. Step 1 — State the governing relation:

    μ=μmaxSKs+S\mu = \mu_{max} \dfrac{S}{K_s + S}
  2. Step 2 — Rearrange symbolically for K_s:

    Ks=S(μmaxμ−1)K_{s} = S\left(\dfrac{\mu_{max}}{\mu}-1\right)
  3. Step 3 — List the givens: maximum specific growth rate (mu_max) = 2.2000 1/day, limiting substrate concentration (S) = 146.0 mg/L, specific growth rate (mu) = 2.8300 1/day.

  4. Step 4 — Substitute the given values:

    Ks=146.0(2.20002.8300−1)K_{s} = 146.0\left(\dfrac{2.2000}{2.8300}-1\right)
  5. Step 5 — Evaluate:

    Ks=−32.5018 mg/LK_{s} = -32.5018\ \text{mg/L}
  6. Step 6 — Check: returning K_s = -32.5018 mg/L to

    μ=μmaxSKs+S\mu = \mu_{max} \dfrac{S}{K_s + S}

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

Answer:
Ks=−32.5018 mg/LK_{s} = -32.5018\ \text{mg/L}

Why the other options are there

  • -65.0035 — kept a factor of two that cancels in the correct rearrangement.
  • -16.2509 — dropped that same factor in the other direction.
  • -35.7519 — rounded an intermediate value before the final step.

Reference: FE Handbook — Multiple Limiting Substrates (Monod Kinetics)

Example 4
Multiple Limiting Substrates (Monod) — solve for specific growth rate (case 2) — Monod Kinetics—Substrate Limited Growth (4)

Monod kinetics with multiple limiting substrates for microbial growth in a bioreactor Given maximum specific growth rate (mu_max) = 8.2000 1/day; limiting substrate concentration (S) = 47.0000 mg/L; half-saturation constant (K_s) = 38.0000 mg/L, determine the specific growth rate (mu) in 1/day.

Given

  • maximumspecificgrowthrate(mumax)=8.20001/daymaximum specific growth rate (mu_max) = 8.2000 1/day
  • limitingsubstrateconcentration(S)=47.0000mg/Llimiting substrate concentration (S) = 47.0000 mg/L
  • half−saturationconstant(Ks)=38.0000mg/Lhalf-saturation constant (K_s) = 38.0000 mg/L

Find

specific growth rate (mu), in 1/day

Start with the thinking

  • The governing relation printed in this handbook section is Multiple Limiting Substrates (Monod).
  • Everything except mu is given, so isolate mu 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.
  • Multiple limiting substrates growth kinetics use the Monod equation to relate specific growth rate to substrate concentration.

Step-by-step solution

  1. Step 1 — State the governing relation:

    μ=μmaxSKs+S\mu = \mu_{max} \dfrac{S}{K_s + S}
  2. Step 2 — Rearrange symbolically for mu:

    μ=μmaxSKs+S\mu = \mu_{max}\dfrac{S}{K_s+S}
  3. Step 3 — List the givens: maximum specific growth rate (mu_max) = 8.2000 1/day, limiting substrate concentration (S) = 47.0000 mg/L, half-saturation constant (K_s) = 38.0000 mg/L.

  4. Step 4 — Substitute the given values:

    μ=8.200047.0000Ks+47.0000\mu = 8.2000\dfrac{47.0000}{K_s+47.0000}
  5. Step 5 — Evaluate:

    μ=4.5341 1/day\mu = 4.5341\ \text{1/day}
  6. Step 6 — Check: returning mu = 4.5341 1/day to

    μ=μmaxSKs+S\mu = \mu_{max} \dfrac{S}{K_s + S}

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

Answer:
μ=4.5341 1/day\mu = 4.5341\ \text{1/day}

Why the other options are there

  • 9.0682 — kept a factor of two that cancels in the correct rearrangement.
  • 2.2671 — dropped that same factor in the other direction.
  • 4.9875 — rounded an intermediate value before the final step.

Reference: FE Handbook — Multiple Limiting Substrates (Monod Kinetics)

Example 5
Multiple Limiting Substrates (Monod) — solve for maximum specific growth rate (case 2) — Monod Kinetics—Substrate Limited Growth (5)

Monod multiple limiting substrate model for activated sludge biomass growth Given limiting substrate concentration (S) = 129.0 mg/L; half-saturation constant (K_s) = 17.0000 mg/L; specific growth rate (mu) = 1.0800 1/day, determine the maximum specific growth rate (mu_max) in 1/day.

Given

  • limitingsubstrateconcentration(S)=129.0mg/Llimiting substrate concentration (S) = 129.0 mg/L
  • half−saturationconstant(Ks)=17.0000mg/Lhalf-saturation constant (K_s) = 17.0000 mg/L
  • specificgrowthrate(mu)=1.08001/dayspecific growth rate (mu) = 1.0800 1/day

Find

maximum specific growth rate (mu_max), in 1/day

Start with the thinking

  • The governing relation printed in this handbook section is Multiple Limiting Substrates (Monod).
  • Everything except mu_max is given, so isolate mu_max 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.
  • Multiple limiting substrates growth kinetics use the Monod equation to relate specific growth rate to substrate concentration.

Step-by-step solution

  1. Step 1 — State the governing relation:

    μ=μmaxSKs+S\mu = \mu_{max} \dfrac{S}{K_s + S}
  2. Step 2 — Rearrange symbolically for mu_max:

    μmax=μ(Ks+S)S\mu_{max} = \dfrac{\mu (K_s+S)}{S}
  3. Step 3 — List the givens: limiting substrate concentration (S) = 129.0 mg/L, half-saturation constant (K_s) = 17.0000 mg/L, specific growth rate (mu) = 1.0800 1/day.

  4. Step 4 — Substitute the given values:

    μmax=1.0800(Ks+129.0)129.0\mu_{max} = \dfrac{1.0800 (K_s+129.0)}{129.0}
  5. Step 5 — Evaluate:

    μmax=1.2223 1/day\mu_{max} = 1.2223\ \text{1/day}
  6. Step 6 — Check: returning mu_max = 1.2223 1/day to

    μ=μmaxSKs+S\mu = \mu_{max} \dfrac{S}{K_s + S}

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

Answer:
μmax=1.2223 1/day\mu_{max} = 1.2223\ \text{1/day}

Why the other options are there

  • 2.4447 — kept a factor of two that cancels in the correct rearrangement.
  • 0.6112 — dropped that same factor in the other direction.
  • 1.3446 — rounded an intermediate value before the final step.

Reference: FE Handbook — Multiple Limiting Substrates (Monod Kinetics)

Example 6
Multiple Limiting Substrates (Monod) — solve for half-saturation constant (case 2) — Monod Kinetics—Substrate Limited Growth (6)

multiple limiting substrates Monod equation for nutrient-limited growth Given maximum specific growth rate (mu_max) = 3.2000 1/day; limiting substrate concentration (S) = 114.0 mg/L; specific growth rate (mu) = 4.5900 1/day, determine the half-saturation constant (K_s) in mg/L.

Given

  • maximumspecificgrowthrate(mumax)=3.20001/daymaximum specific growth rate (mu_max) = 3.2000 1/day
  • limitingsubstrateconcentration(S)=114.0mg/Llimiting substrate concentration (S) = 114.0 mg/L
  • specificgrowthrate(mu)=4.59001/dayspecific growth rate (mu) = 4.5900 1/day

Find

half-saturation constant (K_s), in mg/L

Start with the thinking

  • The governing relation printed in this handbook section is Multiple Limiting Substrates (Monod).
  • Everything except K_s is given, so isolate K_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.
  • Multiple limiting substrates growth kinetics use the Monod equation to relate specific growth rate to substrate concentration.

Step-by-step solution

  1. Step 1 — State the governing relation:

    μ=μmaxSKs+S\mu = \mu_{max} \dfrac{S}{K_s + S}
  2. Step 2 — Rearrange symbolically for K_s:

    Ks=S(μmaxμ−1)K_{s} = S\left(\dfrac{\mu_{max}}{\mu}-1\right)
  3. Step 3 — List the givens: maximum specific growth rate (mu_max) = 3.2000 1/day, limiting substrate concentration (S) = 114.0 mg/L, specific growth rate (mu) = 4.5900 1/day.

  4. Step 4 — Substitute the given values:

    Ks=114.0(3.20004.5900−1)K_{s} = 114.0\left(\dfrac{3.2000}{4.5900}-1\right)
  5. Step 5 — Evaluate:

    Ks=−34.5229 mg/LK_{s} = -34.5229\ \text{mg/L}
  6. Step 6 — Check: returning K_s = -34.5229 mg/L to

    μ=μmaxSKs+S\mu = \mu_{max} \dfrac{S}{K_s + S}

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

Answer:
Ks=−34.5229 mg/LK_{s} = -34.5229\ \text{mg/L}

Why the other options are there

  • -69.0458 — kept a factor of two that cancels in the correct rearrangement.
  • -17.2614 — dropped that same factor in the other direction.
  • -37.9752 — rounded an intermediate value before the final step.

Reference: FE Handbook — Multiple Limiting Substrates (Monod Kinetics)

Example 7
Multiple Limiting Substrates (Monod) — solve for specific growth rate (case 3) — Monod Kinetics—Substrate Limited Growth (7)

Monod kinetics with multiple limiting substrates for microbial growth in a bioreactor Given maximum specific growth rate (mu_max) = 4.7000 1/day; limiting substrate concentration (S) = 9.0000 mg/L; half-saturation constant (K_s) = 90.0000 mg/L, determine the specific growth rate (mu) in 1/day.

Given

  • maximumspecificgrowthrate(mumax)=4.70001/daymaximum specific growth rate (mu_max) = 4.7000 1/day
  • limitingsubstrateconcentration(S)=9.0000mg/Llimiting substrate concentration (S) = 9.0000 mg/L
  • half−saturationconstant(Ks)=90.0000mg/Lhalf-saturation constant (K_s) = 90.0000 mg/L

Find

specific growth rate (mu), in 1/day

Start with the thinking

  • The governing relation printed in this handbook section is Multiple Limiting Substrates (Monod).
  • Everything except mu is given, so isolate mu 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.
  • Multiple limiting substrates growth kinetics use the Monod equation to relate specific growth rate to substrate concentration.

Step-by-step solution

  1. Step 1 — State the governing relation:

    μ=μmaxSKs+S\mu = \mu_{max} \dfrac{S}{K_s + S}
  2. Step 2 — Rearrange symbolically for mu:

    μ=μmaxSKs+S\mu = \mu_{max}\dfrac{S}{K_s+S}
  3. Step 3 — List the givens: maximum specific growth rate (mu_max) = 4.7000 1/day, limiting substrate concentration (S) = 9.0000 mg/L, half-saturation constant (K_s) = 90.0000 mg/L.

  4. Step 4 — Substitute the given values:

    μ=4.70009.0000Ks+9.0000\mu = 4.7000\dfrac{9.0000}{K_s+9.0000}
  5. Step 5 — Evaluate:

    μ=0.4273 1/day\mu = 0.4273\ \text{1/day}
  6. Step 6 — Check: returning mu = 0.4273 1/day to

    μ=μmaxSKs+S\mu = \mu_{max} \dfrac{S}{K_s + S}

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

Answer:
μ=0.4273 1/day\mu = 0.4273\ \text{1/day}

Why the other options are there

  • 0.8545 — kept a factor of two that cancels in the correct rearrangement.
  • 0.2136 — dropped that same factor in the other direction.
  • 0.4700 — rounded an intermediate value before the final step.

Reference: FE Handbook — Multiple Limiting Substrates (Monod Kinetics)

Example 8
Multiple Limiting Substrates (Monod) — solve for maximum specific growth rate (case 3) — Monod Kinetics—Substrate Limited Growth (8)

Monod multiple limiting substrate model for activated sludge biomass growth Given limiting substrate concentration (S) = 49.0000 mg/L; half-saturation constant (K_s) = 86.0000 mg/L; specific growth rate (mu) = 5.1600 1/day, determine the maximum specific growth rate (mu_max) in 1/day.

Given

  • limitingsubstrateconcentration(S)=49.0000mg/Llimiting substrate concentration (S) = 49.0000 mg/L
  • half−saturationconstant(Ks)=86.0000mg/Lhalf-saturation constant (K_s) = 86.0000 mg/L
  • specificgrowthrate(mu)=5.16001/dayspecific growth rate (mu) = 5.1600 1/day

Find

maximum specific growth rate (mu_max), in 1/day

Start with the thinking

  • The governing relation printed in this handbook section is Multiple Limiting Substrates (Monod).
  • Everything except mu_max is given, so isolate mu_max 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.
  • Multiple limiting substrates growth kinetics use the Monod equation to relate specific growth rate to substrate concentration.

Step-by-step solution

  1. Step 1 — State the governing relation:

    μ=μmaxSKs+S\mu = \mu_{max} \dfrac{S}{K_s + S}
  2. Step 2 — Rearrange symbolically for mu_max:

    μmax=μ(Ks+S)S\mu_{max} = \dfrac{\mu (K_s+S)}{S}
  3. Step 3 — List the givens: limiting substrate concentration (S) = 49.0000 mg/L, half-saturation constant (K_s) = 86.0000 mg/L, specific growth rate (mu) = 5.1600 1/day.

  4. Step 4 — Substitute the given values:

    μmax=5.1600(Ks+49.0000)49.0000\mu_{max} = \dfrac{5.1600 (K_s+49.0000)}{49.0000}
  5. Step 5 — Evaluate:

    μmax=14.2163 1/day\mu_{max} = 14.2163\ \text{1/day}
  6. Step 6 — Check: returning mu_max = 14.2163 1/day to

    μ=μmaxSKs+S\mu = \mu_{max} \dfrac{S}{K_s + S}

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

Answer:
μmax=14.2163 1/day\mu_{max} = 14.2163\ \text{1/day}

Why the other options are there

  • 28.4327 — kept a factor of two that cancels in the correct rearrangement.
  • 7.1082 — dropped that same factor in the other direction.
  • 15.6380 — rounded an intermediate value before the final step.

Reference: FE Handbook — Multiple Limiting Substrates (Monod Kinetics)

Example 9
Multiple Limiting Substrates (Monod) — solve for half-saturation constant (case 3) — Monod Kinetics—Substrate Limited Growth (9)

multiple limiting substrates Monod equation for nutrient-limited growth Given maximum specific growth rate (mu_max) = 4.3000 1/day; limiting substrate concentration (S) = 176.0 mg/L; specific growth rate (mu) = 8.2800 1/day, determine the half-saturation constant (K_s) in mg/L.

Given

  • maximumspecificgrowthrate(mumax)=4.30001/daymaximum specific growth rate (mu_max) = 4.3000 1/day
  • limitingsubstrateconcentration(S)=176.0mg/Llimiting substrate concentration (S) = 176.0 mg/L
  • specificgrowthrate(mu)=8.28001/dayspecific growth rate (mu) = 8.2800 1/day

Find

half-saturation constant (K_s), in mg/L

Start with the thinking

  • The governing relation printed in this handbook section is Multiple Limiting Substrates (Monod).
  • Everything except K_s is given, so isolate K_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.
  • Multiple limiting substrates growth kinetics use the Monod equation to relate specific growth rate to substrate concentration.

Step-by-step solution

  1. Step 1 — State the governing relation:

    μ=μmaxSKs+S\mu = \mu_{max} \dfrac{S}{K_s + S}
  2. Step 2 — Rearrange symbolically for K_s:

    Ks=S(μmaxμ−1)K_{s} = S\left(\dfrac{\mu_{max}}{\mu}-1\right)
  3. Step 3 — List the givens: maximum specific growth rate (mu_max) = 4.3000 1/day, limiting substrate concentration (S) = 176.0 mg/L, specific growth rate (mu) = 8.2800 1/day.

  4. Step 4 — Substitute the given values:

    Ks=176.0(4.30008.2800−1)K_{s} = 176.0\left(\dfrac{4.3000}{8.2800}-1\right)
  5. Step 5 — Evaluate:

    Ks=−84.5990 mg/LK_{s} = -84.5990\ \text{mg/L}
  6. Step 6 — Check: returning K_s = -84.5990 mg/L to

    μ=μmaxSKs+S\mu = \mu_{max} \dfrac{S}{K_s + S}

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

Answer:
Ks=−84.5990 mg/LK_{s} = -84.5990\ \text{mg/L}

Why the other options are there

  • -169.2 — kept a factor of two that cancels in the correct rearrangement.
  • -42.2995 — dropped that same factor in the other direction.
  • -93.0589 — rounded an intermediate value before the final step.

Reference: FE Handbook — Multiple Limiting Substrates (Monod Kinetics)

Example 10
Multiple Limiting Substrates (Monod) — solve for specific growth rate (case 4) — Monod Kinetics—Substrate Limited Growth (10)

Monod kinetics with multiple limiting substrates for microbial growth in a bioreactor Given maximum specific growth rate (mu_max) = 3.1000 1/day; limiting substrate concentration (S) = 110.0 mg/L; half-saturation constant (K_s) = 8.0000 mg/L, determine the specific growth rate (mu) in 1/day.

Given

  • maximumspecificgrowthrate(mumax)=3.10001/daymaximum specific growth rate (mu_max) = 3.1000 1/day
  • limitingsubstrateconcentration(S)=110.0mg/Llimiting substrate concentration (S) = 110.0 mg/L
  • half−saturationconstant(Ks)=8.0000mg/Lhalf-saturation constant (K_s) = 8.0000 mg/L

Find

specific growth rate (mu), in 1/day

Start with the thinking

  • The governing relation printed in this handbook section is Multiple Limiting Substrates (Monod).
  • Everything except mu is given, so isolate mu 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.
  • Multiple limiting substrates growth kinetics use the Monod equation to relate specific growth rate to substrate concentration.

Step-by-step solution

  1. Step 1 — State the governing relation:

    μ=μmaxSKs+S\mu = \mu_{max} \dfrac{S}{K_s + S}
  2. Step 2 — Rearrange symbolically for mu:

    μ=μmaxSKs+S\mu = \mu_{max}\dfrac{S}{K_s+S}
  3. Step 3 — List the givens: maximum specific growth rate (mu_max) = 3.1000 1/day, limiting substrate concentration (S) = 110.0 mg/L, half-saturation constant (K_s) = 8.0000 mg/L.

  4. Step 4 — Substitute the given values:

    μ=3.1000110.0Ks+110.0\mu = 3.1000\dfrac{110.0}{K_s+110.0}
  5. Step 5 — Evaluate:

    μ=2.8898 1/day\mu = 2.8898\ \text{1/day}
  6. Step 6 — Check: returning mu = 2.8898 1/day to

    μ=μmaxSKs+S\mu = \mu_{max} \dfrac{S}{K_s + S}

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

Answer:
μ=2.8898 1/day\mu = 2.8898\ \text{1/day}

Why the other options are there

  • 5.7797 — kept a factor of two that cancels in the correct rearrangement.
  • 1.4449 — dropped that same factor in the other direction.
  • 3.1788 — rounded an intermediate value before the final step.

Reference: FE Handbook — Multiple Limiting Substrates (Monod Kinetics)

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