Biofilters
Find the order of reaction and the rate of reaction.
S/Ks = 10/10 = 1.0
The change in the order of reaction takes place at S/Ks = 2; hence it is a first order process. The change from a half order to a first order takes place at S = 20 g/m 3 .
The internal first order rate constant is
k1Vt = kovt/Ks = 300 · 10 3 /10 = 30,000 a 1
It is estimated that the biofilm is only slightly penetrated because
a= L ~k1Vf = 200 · 10-6 ...J 30 • 000 = 5.5
D
0.4 · 10-4
E =..!_= 0.18
a
The removal per surface area without diffusional limitation (e - 1) would be
k1A = k1Vt · L = 30,000 d- 1 · 200 · 10-6m= 6 rn/d
rA = k1A Sorg = k1Vt LS0 , 9 = 60 g/(m 2 · d)(without limitation)
Due to the diffusional limitation, the removal has been reduced to
k1A = 6 · 0.18 = 1.1 rn/d
rA = 60 · 0.18 = 11.0 g/(m 2 · d) (with diffusional limitation)
These theories for diffusional limitation of reactions in biomass, specifically biofilms
and bioflocs, can be generalized to a random process of order n. Hence it proves that
the generally governing parameter can be written:
(5.22)
For zero order we get:
(5.23)
For first order we get:
(5.24)
The quantity «l> is called the Thiele module.
5.2. Biofilm kinetic parameters
The removal of a substrate in a biofilm takes place through bacterial reactions inside
the biofilm where the individual bacterium behaves in the same manner as bacteria
in suspension. For the bacterial growth applies:
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