3. Basic Biological Processes
By Mogens Henze
"There must be some kind of unsatisfactory
sdentific explanation".
(Freely translated) (Leif Panduro, Danish author)
In this chapter we will discuss the most essential biological processes which are
present in biological wastewater treatment, that is, aerobic and anaerobic as well as
biological phosphorus removal. All descriptions have been simplified. However,
they are sufficiently detailed to describe the three processes. As an introduction, the
biology in biological treatment plants is discussed as well as the selection mechanisms which are utilized. In this chapter only conversion processes are discussed,
and for the purpose of our discussion they are always considered to be positive. In
the subsequent chapters, where mass balances are set up, the individual conversion
terms are signed.
3.1. The biology in biological treatment
plants
The biological processes in treatment plants are carried out by a very diversified
group of organisms. It is only possible roughly to list which species are present as it
proves that the fauna in a treatment plant is very dependent on the external
conditions. This will be further discussed under biological selection in the next
section.
3.1.1 The organisms
All organisms in a biological treatment plant must necessarily have there origin
from the outside, that is, they come from the wastewaters, from the air, the soil, or
from animals which live close to the plant (seagulls, flies, rats, etc.). An essential part
of the individual organisms have grown in the plant itself, and it is here the selection
described in the next section is important.
An important hygienic aspect in connection with biological treatment plants is the
presence of pathogenic organisms. These will not be further discussed in this
chapter, but it is important to know that large amounts of pathogenic organisms will
normally be present at all stages of biological treatment, with the exception of the
effluent resulting from an efficient disinfection process. In connection with the
danger of infection from the pathogenic organisms, the animals living in the vicinity
of a treatment plant contribute to the dispersion of these organisms in the environ55
By Mogens Henze
"There must be some kind of unsatisfactory
sdentific explanation".
(Freely translated) (Leif Panduro, Danish author)
In this chapter we will discuss the most essential biological processes which are
present in biological wastewater treatment, that is, aerobic and anaerobic as well as
biological phosphorus removal. All descriptions have been simplified. However,
they are sufficiently detailed to describe the three processes. As an introduction, the
biology in biological treatment plants is discussed as well as the selection mechanisms which are utilized. In this chapter only conversion processes are discussed,
and for the purpose of our discussion they are always considered to be positive. In
the subsequent chapters, where mass balances are set up, the individual conversion
terms are signed.
3.1. The biology in biological treatment
plants
The biological processes in treatment plants are carried out by a very diversified
group of organisms. It is only possible roughly to list which species are present as it
proves that the fauna in a treatment plant is very dependent on the external
conditions. This will be further discussed under biological selection in the next
section.
3.1.1 The organisms
All organisms in a biological treatment plant must necessarily have there origin
from the outside, that is, they come from the wastewaters, from the air, the soil, or
from animals which live close to the plant (seagulls, flies, rats, etc.). An essential part
of the individual organisms have grown in the plant itself, and it is here the selection
described in the next section is important.
An important hygienic aspect in connection with biological treatment plants is the
presence of pathogenic organisms. These will not be further discussed in this
chapter, but it is important to know that large amounts of pathogenic organisms will
normally be present at all stages of biological treatment, with the exception of the
effluent resulting from an efficient disinfection process. In connection with the
danger of infection from the pathogenic organisms, the animals living in the vicinity
of a treatment plant contribute to the dispersion of these organisms in the environ55