Conversions in biological treatment plants
hydrolysis
hydrolysis
biological growth
hydrolysis
b+s
very easily degradable material
growth
b;+.,
death
Fig3.3
Bisubstrate model, biological conversion in treatment plants. Can be used in the
process description of conventional activated sludge plants, nitrifying and denitrifying
plants and anaerobic plants. The trisubstrate model is particularly applicable for the
description of biological phosphorous removal.
Fig 3.3 shows two model representations which combine the conversions concerned. What really happens in a biological treatment plant is far more complicated
than what is shown in the figure. The figure represent a degree of detailing which is
suitable in many process descriptions.
The crucial problem in most biological conversions is that only a certain part of the
material to be removed/treated in the process is immediately accessible for microbial removal.
Below, the three processes, biological growth, hydrolysis and decay, are discussed,
and in chapters 4-9 they are used to describe the biological processes.
3.2.1 Biological growth
Bacteria in wastewater treatment processes are assumed only to be able to utilize
very small and simply built molecules for growth. It may be substances such as
acetic acid, ethanol, methanol, propionic acids, glucose, ammonium, nitrite etc.
The process can be described using the following expression:
rv;xs = J.l.max · f(S) · Xs
rv;xB
is the volumetric biological growth rate
(dimension M · L - 3 · T -I, unit for example kg COD(B)/(m 3 ·d))
J.l.max
is the maximum specific growth rate
(dimension T-1, unit for example h- 1 or d- 1 )
62
(3.1)
hydrolysis
hydrolysis
biological growth
hydrolysis
b+s
very easily degradable material
growth
b;+.,
death
Fig3.3
Bisubstrate model, biological conversion in treatment plants. Can be used in the
process description of conventional activated sludge plants, nitrifying and denitrifying
plants and anaerobic plants. The trisubstrate model is particularly applicable for the
description of biological phosphorous removal.
Fig 3.3 shows two model representations which combine the conversions concerned. What really happens in a biological treatment plant is far more complicated
than what is shown in the figure. The figure represent a degree of detailing which is
suitable in many process descriptions.
The crucial problem in most biological conversions is that only a certain part of the
material to be removed/treated in the process is immediately accessible for microbial removal.
Below, the three processes, biological growth, hydrolysis and decay, are discussed,
and in chapters 4-9 they are used to describe the biological processes.
3.2.1 Biological growth
Bacteria in wastewater treatment processes are assumed only to be able to utilize
very small and simply built molecules for growth. It may be substances such as
acetic acid, ethanol, methanol, propionic acids, glucose, ammonium, nitrite etc.
The process can be described using the following expression:
rv;xs = J.l.max · f(S) · Xs
rv;xB
is the volumetric biological growth rate
(dimension M · L - 3 · T -I, unit for example kg COD(B)/(m 3 ·d))
J.l.max
is the maximum specific growth rate
(dimension T-1, unit for example h- 1 or d- 1 )
62
(3.1)