Mass balances, nitrifying plants
gTKN
~ Removal rate, ~;_
....
....
....
....
....
....
....
....
.... ~\
1/2 -1/2 -1
k112A = 3.8(g0 2 ) m d
10
40
s
Oxygen concentration, g/m 3
Fig6.3
Obseroed nitrification rate per surface area of biofilm as a function of the oxygen
concentration in bulk water Ill
For a separate nitrifying biofilm plant the nitrification rate is limited either by the
oxygen concentration or by the ammonium concentration because, in practice, the
biofilm can be assumed to be only partially utilized (partially penetrated). The
criterion for the limitation is found when calculating Expression (5.32) for ammonium and oxygen.
Fig 6.4 shows the penetration conditions for NH4 and Oz in the two cases of
limitation, see Expression (5.32):
S~ > Doz
2.1-10-4 1
g .NH!-N/m 3
- - = - - · Voz NH4 =
· - - = 0.3 =-------:Soz < DNH4
'
1.7. 10-4 4.25
g 0 2 /m 3
ForSNH4> 0.3 · Sm, oxygen is the limiting factor, and the reaction rate in the tank is:
r A,NH4 = (k'(zA,02 IVNH4,02 ) · So2,2 Yz
(6.6)
where k1;2A,02
is the rate constant of oxygen,
VNH4,02
the stoichiometric coefficient between oxygen and ammonium
(4.25 g Oz/g NH;4-N),
So2,2
the oxygen concentration in the tank.
For SNH4 < 0.3 -Soz, ammonium is the potential limiting factor, and the reaction rate
in the tank is:
(6.7)
where kl/2A,NH4 is the rate constant of ammonium,
5NH4,2
is the ammonium concentration in the tank.
200