7. Treatment Plants for
Denitrification
By Jes la Cour Jansen, Paul Harremoes and Mogens Henze
In many countries it is today recognized that it is necessary to remove nitrogen from
wastewater. The discharge of nitrogen and phosphorus results in eutrophication of
the recipients and makes them unsuitable for fishing and bathing. At the same time
the discharge of nitrogen into fresh recipients means that these become unsuitable
as raw water supply for drinking water. In countries where the main part of the
drinking water comes from the groundwater, the latter problem is not yet urgent.
However, it is a crucial problem in countries where surface water is used as the
dominant resource of drinking water, such as in Central Europe, North America and
South Africa.
Nitrogen can be removed by physical, chemical and biological treatment methods
such as
-ion exchange (drinking water)
- reverse osmosis (drinking water)
- ammonia stripping (wastewater)
- chemical denitrification
- chemical precipitation, MgNlf4P04
- biological denitrification (drinking water and wastewater)
- assimilation
For wastewater, biological denitrification is the dominant process type.
Denitrification is the process by which bacteria convert nitrate into free nitrogen. As
the nitrogen components in ordinary municipal wastewater is present in the form
of reduced nitrogen, these components must be nitrified (see Chapter 6) before the
denitrification can be established. Therefore, the denitrification process can seldom
be looked at separately, but must be seen in relation to the preceding nitrification.
By denitrification, nitrate oxidizes an organic compound, that is, nitrate practically
replaces oxygen in the degradation of organic matter. This means that the denitrification process should also be viewed as a part of the removal of organic matter. This
relationship is stressed by the fact that many bacteria are able to immediately
replace oxygen by nitrate as an oxidant in the absence of oxygen.
This relationship between denitrification, nitrification and the removal of organic
matter has had an important impact on the development of processes for the
229
Denitrification
By Jes la Cour Jansen, Paul Harremoes and Mogens Henze
In many countries it is today recognized that it is necessary to remove nitrogen from
wastewater. The discharge of nitrogen and phosphorus results in eutrophication of
the recipients and makes them unsuitable for fishing and bathing. At the same time
the discharge of nitrogen into fresh recipients means that these become unsuitable
as raw water supply for drinking water. In countries where the main part of the
drinking water comes from the groundwater, the latter problem is not yet urgent.
However, it is a crucial problem in countries where surface water is used as the
dominant resource of drinking water, such as in Central Europe, North America and
South Africa.
Nitrogen can be removed by physical, chemical and biological treatment methods
such as
-ion exchange (drinking water)
- reverse osmosis (drinking water)
- ammonia stripping (wastewater)
- chemical denitrification
- chemical precipitation, MgNlf4P04
- biological denitrification (drinking water and wastewater)
- assimilation
For wastewater, biological denitrification is the dominant process type.
Denitrification is the process by which bacteria convert nitrate into free nitrogen. As
the nitrogen components in ordinary municipal wastewater is present in the form
of reduced nitrogen, these components must be nitrified (see Chapter 6) before the
denitrification can be established. Therefore, the denitrification process can seldom
be looked at separately, but must be seen in relation to the preceding nitrification.
By denitrification, nitrate oxidizes an organic compound, that is, nitrate practically
replaces oxygen in the degradation of organic matter. This means that the denitrification process should also be viewed as a part of the removal of organic matter. This
relationship is stressed by the fact that many bacteria are able to immediately
replace oxygen by nitrate as an oxidant in the absence of oxygen.
This relationship between denitrification, nitrification and the removal of organic
matter has had an important impact on the development of processes for the
229