Basic Biological Processes
In combination with (3.14), we have a double Monod expression:
52
502.2
ll<>bs = Jlmax - 5 K · 5
K
2 + 5 02.2 + 5,02
(3.17)
The saturation constant, K5,02t depends on floc size/biofilm thickness and on
temperature as it reflects diffusional limitations for oxygen into flocs/biofilm.
pH
The aerobic conversions are pH dependent, see Fig 3.6. The rather unusual shape of
the curve is due to a combination of the pH dependency of the micro-organisms
and the selection of individual micro-organisms.
The kinetics of pH can be described as follows:
KpH
Jlmax (pH)= Jlmax(opt.pH) · _ _.___
l where KpH is the pH constant.
I= 10 1optimunpH-pHI_ 1
(3.18)
Normally it is only the low pH values which cause problems in biological treatment
processes.
Apart from the fact that low pH values may be caused by the pH in the raw
wastewater, low pH values may arise in connection with nitrification, see Section
3.4, and possibly in connection with chemical precipitation of phosphorus.
Fig 3.6
Growth rate
4
5
6
7
8
9
The pH dependency for aerobic heterotrophic processes.
Model: KpH = 200 (see Expression (3.18)).
pH
73