Mass balances, nitrifying plants
Fig6.6
mole HC03
6
mole NH!
5
Ammonia
limitation
4
3.4
3
Alkalinity limitation =
2
pH-inhibition
0
0
2 2.4
1.4
Oxygen limitation
3
4
mole HC03
mole 0 2
The ratio between the components consumed in a biofilm determines which component
will be rate limiting /3!
Example 6.3
Wastewater having an alkalinity of 2 eqv/m 3 is to be nitrified. What is the highest ammonium concentration acceptable in the influent?
According to Expression (3.28) approx. 2 moles of HC03 are consumed for each mole
of ammonium. In the influent of the nitrifying plant only
1 mol NH;t = 1 mol N/m 3 = 14 g NH;\-N/m 3 can be accepted.
The wastewater is treated in an ideally mixed tank, where an ammonium concentration of
max. 2 g NH;\-N/m 3 is required in the bulk water.
The oxygen concentration in the bulk water is 4 g/m 3 . Oxygen is the rate limiting substrate
because the molar ratio is~ 1-f4 = 0.88 < 1.4.
Due to the diffusional limitation, an alkalinity above
2.4 · ~ = 0.30 eqv/m 3 is required.
Hence only 2.0- 0.3 = 1.7 eqv/m 3 , corresponding to
12 g NH;\-N/m 3 , may be removed- unless lime is added.
6.1.2 Combined removal of organic matter and
ammoruum
Activated sludge
The mass balance of nitrifying sludge is equal to Expression (6.1). Expression (6.4)
can be used for calculating the ammonium concentration in a nitrifying activated
sludge treabnent plant.
204
Fig6.6
mole HC03
6
mole NH!
5
Ammonia
limitation
4
3.4
3
Alkalinity limitation =
2
pH-inhibition
0
0
2 2.4
1.4
Oxygen limitation
3
4
mole HC03
mole 0 2
The ratio between the components consumed in a biofilm determines which component
will be rate limiting /3!
Example 6.3
Wastewater having an alkalinity of 2 eqv/m 3 is to be nitrified. What is the highest ammonium concentration acceptable in the influent?
According to Expression (3.28) approx. 2 moles of HC03 are consumed for each mole
of ammonium. In the influent of the nitrifying plant only
1 mol NH;t = 1 mol N/m 3 = 14 g NH;\-N/m 3 can be accepted.
The wastewater is treated in an ideally mixed tank, where an ammonium concentration of
max. 2 g NH;\-N/m 3 is required in the bulk water.
The oxygen concentration in the bulk water is 4 g/m 3 . Oxygen is the rate limiting substrate
because the molar ratio is~ 1-f4 = 0.88 < 1.4.
Due to the diffusional limitation, an alkalinity above
2.4 · ~ = 0.30 eqv/m 3 is required.
Hence only 2.0- 0.3 = 1.7 eqv/m 3 , corresponding to
12 g NH;\-N/m 3 , may be removed- unless lime is added.
6.1.2 Combined removal of organic matter and
ammoruum
Activated sludge
The mass balance of nitrifying sludge is equal to Expression (6.1). Expression (6.4)
can be used for calculating the ammonium concentration in a nitrifying activated
sludge treabnent plant.
204