Biomedical Engineering Reference
In-Depth Information
Introduction
Process modelling has become an important tool in biological wastewater treatment
engineering and models are being used for design, control, teaching and research. Biofilm and
floc structure have played different roles in biological wastewater treatment modelling.
Biofilm structure has been strongly emphasized over the past decades in biofilm research
whilst state of the art activated sludge models (ASMs) do not take floc structure into account.
It is the aim of this article to analyse and discuss the reasons for the different importance
dedicated to biofilm and floc structure in biological wastewater treatment modelling. The role
of diffusion as described by Fick's laws of diffusion is discussed and the use and meaning of
Monod kinetics in biological wastewater treatment modelling is outlined, since biofilm and
floc structure are interrelated to diffusion and Monod kinetics when modelling microbial
growth. Both concepts, i.e. Monod kinetics and Fick's laws of diffusion are introduced in the
following paragraphs.
Monod Kinetics
Monod kinetics are widely used for modelling microbial growth on a given substrate. The
Monod equation (Eq. 1) gives a functional relation between substrate uptake rate (μ),
substrate concentration (S), Monod affinity constant or half-saturation coefficient (K
S
), and
maximum specific uptake rate (μ
max
) [1]. The functional relation given by the Monod
equation is illustrated in figure 1.
120
substrate uptake rate
maximum specific uptake rate
100
80
60
40
20
0
0
50
100
150
200
K
S
Substrate Concentration
Figure 1.
Functional relation between substrate uptake rate and substrate concentration according to the
Monod equation (μ
max
= 100, K
S
= 20).
