Biofilm kinetic parameters
s
rv,xB = !!max s + Ks . XB
where V is understood as the volume inside the biofilm. This is analogized by the
substrate removal. For the substrate removal, the following zero order and first
order approximations apply:
kovf
!!max
= rv ,s = - - . XB
Ymax
!!max S
k1vf·S = rv,s = - - . - X B
Ymax Ks
(5.25)
In these expressions, kinetic constants as those known from suspended cultures can
be used.
Compared with suspended cultures the difference is the concentration of bacteria
which is much higher in a biofilm than in a suspension. In activated sludge plants,
the concentration varies from 2 to 6 kg VSSim 3 . In biofilms the concentration varies
from 10 to 60 kg VSS I m 3 . The only new parameter which comes into use is therefore
the diffusion coefficient D. The measurement of this coefficient in the biofilm is
uncertain and should not be relied upon. In practice, the diffusion coefficient can be
put equal to or a little lower than the molecular diffusion coefficient which can be
looked up in standard reference books, for example 151. Table 5.1 shows relevant
diffusion coefficients in pure water. Often a reduction factor of 0.8 is used, see Table
5.2; it should be stressed, however, that the variation is wide, depending for example
on the surface structure of the biofilm I 6 I.
Substance
D
Substance
D
Substance
D
O:z
2.1
CH.3CCXr
1.0
NH!
1.7
CO:z
1.6
CJ11206
0.6
N02
0.9
HC03
1.0
N03
1.6
c~0.4
Table 5.1
Diffusion coefficients in pure water at zsoc. Unit 10 4 m 2 /d.
Substance
D
vm;;•
koVf
10 4 m 2 /d
gCOD/gO:z
kgCOD/(m 3 ·d)
Oxygen
1.7-2.1
-
25-200
Acetic acid
0.3-0.7
2.1
230-300
Methanol
0.8-4
1.2
40-110
Glucose
0.1-0.7
2.4
350-550
unspec.COD
0.3-0.6
1.4-2
50-500
unspec. BOD
0.3-0.6
0.8-1.2
25-250
• in connection with biological growth.
Table 5.2
Diffusion coefficients for oxygen and organic substrates, stoichiometric conditions, and estimated removal
rate internally in biofilms. The estimates are uncertain and should not be relied upon.
152
s
rv,xB = !!max s + Ks . XB
where V is understood as the volume inside the biofilm. This is analogized by the
substrate removal. For the substrate removal, the following zero order and first
order approximations apply:
kovf
!!max
= rv ,s = - - . XB
Ymax
!!max S
k1vf·S = rv,s = - - . - X B
Ymax Ks
(5.25)
In these expressions, kinetic constants as those known from suspended cultures can
be used.
Compared with suspended cultures the difference is the concentration of bacteria
which is much higher in a biofilm than in a suspension. In activated sludge plants,
the concentration varies from 2 to 6 kg VSSim 3 . In biofilms the concentration varies
from 10 to 60 kg VSS I m 3 . The only new parameter which comes into use is therefore
the diffusion coefficient D. The measurement of this coefficient in the biofilm is
uncertain and should not be relied upon. In practice, the diffusion coefficient can be
put equal to or a little lower than the molecular diffusion coefficient which can be
looked up in standard reference books, for example 151. Table 5.1 shows relevant
diffusion coefficients in pure water. Often a reduction factor of 0.8 is used, see Table
5.2; it should be stressed, however, that the variation is wide, depending for example
on the surface structure of the biofilm I 6 I.
Substance
D
Substance
D
Substance
D
O:z
2.1
CH.3CCXr
1.0
NH!
1.7
CO:z
1.6
CJ11206
0.6
N02
0.9
HC03
1.0
N03
1.6
c~0.4
Table 5.1
Diffusion coefficients in pure water at zsoc. Unit 10 4 m 2 /d.
Substance
D
vm;;•
koVf
10 4 m 2 /d
gCOD/gO:z
kgCOD/(m 3 ·d)
Oxygen
1.7-2.1
-
25-200
Acetic acid
0.3-0.7
2.1
230-300
Methanol
0.8-4
1.2
40-110
Glucose
0.1-0.7
2.4
350-550
unspec.COD
0.3-0.6
1.4-2
50-500
unspec. BOD
0.3-0.6
0.8-1.2
25-250
• in connection with biological growth.
Table 5.2
Diffusion coefficients for oxygen and organic substrates, stoichiometric conditions, and estimated removal
rate internally in biofilms. The estimates are uncertain and should not be relied upon.
152