3. Elaboration Question 2

Course subject(s) 3. Biological treatment

Question 2: Impact of temperature on microbial growth

Temperature is one of the key factors that influence microbial growth. Given that the average summer temperature is 20°C and the average winter temperature is 7°C, draw a graph representing the average heterotrophic bacteria growth rate for summer and winter using the information given below.

The Monod equation for bacterial growth is defined as :

\(\dfrac{dX}{dt}=\mu\cdot X\text{ with }\mu = \mu_{max}\dfrac{s}{(K_{s}+s)}\)


  • X = Biomass concentration
  • S = Substrate concentration
  • Ks = Monod coefficient (substrate affinity)
  • μ = Growth rate
  • μmax = temperature dependent and the relationship represented in the equation below:
  • \(\mu_{max,T}=\mu_{max,20}\theta^{(T-20)}\)

The different parameters are given in the table below. 

\(K_{s}\) 5 g BOD/m3
At 20 °C: \(\mu_{max}\) 6 g VSS/g Vss.d
At 20 °C: \(\theta\) for calculating: \(\mu_{max,T}\) 1.07 -

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