Basic Biological Processes
3.5.3 Nutrients, denitrification
The nutrient requirement of the denitrifying bacteria corresponds to that of the
aerobic, heterotrophic organisms. The organisms prefer ammonium to nitrate as a
nitrogen source in assimilation. In municipal wastewater there are usually sufficient
nutrients whereas industrial wastewater may be short of phosphorus.
3.5 .4 Alkalinity
The denitrification process increases the alkalinity of the water. For every mole of
nitrate converted, one equivalent alkalinity is produced which appears from Expression (3.31). If ammonium is used as a nitrogen source, this will reduce the
alkalinity production by one equivalent per mole of ammonium assimilated. It
appears from Expression (3.30) that the alkalinity production is 4.15 eqv /4.54 mol
N03-N corresponding to 0.91 eqv /mol NO)-N.
Example 3.8
By denitrification of wastewater, 25 g N03-N/m 3 are transformed. The process is assumed to follow Expression (3.30) which means that ammonium is used for assimilation.
The alkalinity of the water before the denitrification, TAL1, is 4.1 eqv/m 3 . What is the alkalinity, TAL3, after the denitrification process?
From Expression (3.30) it is found that 0.91 eqv alkalinity/mol NO:J-N converted is produced.
_
3 25 g N03-N!m 3
_
3
25 g N03-Nim =
1.79 mol N03-N/m
14 g N03-N/mol
The change in alkalinity, ~TAL, is then
~TAL= 0.91 eqv/mol N03-N · 1.79 mol N03-N/m 3 = 1.63 eqv/m 3
TAL3 = TAL1 +~TAL= 4.1 + 1.6 = 5.7 eqv/m 3
3.5.5 Kinetics, denitrification
Normally, the kinetics are described by a Monod expression, see Expression (3.14).
As it is nitrate we want to convert, we aim at a substrate with no limiting effects. In
such cases, a zero order expression, such as (3.15), can be used.
If an external substrate is added, for example acetic acid or methanol, it is possible
to prevent substrate limitation. If the existing content of organic matter in the
wastewater is used, it will, in many cases, result in a limitation of the removal rate.
This is not to be confused with an absolute limitation where the process stops due
to the shortage of substrate.
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3.5.3 Nutrients, denitrification
The nutrient requirement of the denitrifying bacteria corresponds to that of the
aerobic, heterotrophic organisms. The organisms prefer ammonium to nitrate as a
nitrogen source in assimilation. In municipal wastewater there are usually sufficient
nutrients whereas industrial wastewater may be short of phosphorus.
3.5 .4 Alkalinity
The denitrification process increases the alkalinity of the water. For every mole of
nitrate converted, one equivalent alkalinity is produced which appears from Expression (3.31). If ammonium is used as a nitrogen source, this will reduce the
alkalinity production by one equivalent per mole of ammonium assimilated. It
appears from Expression (3.30) that the alkalinity production is 4.15 eqv /4.54 mol
N03-N corresponding to 0.91 eqv /mol NO)-N.
Example 3.8
By denitrification of wastewater, 25 g N03-N/m 3 are transformed. The process is assumed to follow Expression (3.30) which means that ammonium is used for assimilation.
The alkalinity of the water before the denitrification, TAL1, is 4.1 eqv/m 3 . What is the alkalinity, TAL3, after the denitrification process?
From Expression (3.30) it is found that 0.91 eqv alkalinity/mol NO:J-N converted is produced.
_
3 25 g N03-N!m 3
_
3
25 g N03-Nim =
1.79 mol N03-N/m
14 g N03-N/mol
The change in alkalinity, ~TAL, is then
~TAL= 0.91 eqv/mol N03-N · 1.79 mol N03-N/m 3 = 1.63 eqv/m 3
TAL3 = TAL1 +~TAL= 4.1 + 1.6 = 5.7 eqv/m 3
3.5.5 Kinetics, denitrification
Normally, the kinetics are described by a Monod expression, see Expression (3.14).
As it is nitrate we want to convert, we aim at a substrate with no limiting effects. In
such cases, a zero order expression, such as (3.15), can be used.
If an external substrate is added, for example acetic acid or methanol, it is possible
to prevent substrate limitation. If the existing content of organic matter in the
wastewater is used, it will, in many cases, result in a limitation of the removal rate.
This is not to be confused with an absolute limitation where the process stops due
to the shortage of substrate.
89