Treabnent Plants for Denitrification
bu lk aerobic anoxic
water
I
I
I
I
0 2
I
I
N0 3
anaerobic
I
I
I
aerobic' anoxic'
anaerobic
e removal $ production
Fig 7.27 Illustration of layers of redox zones in a biofilm.
In the internal, reduced zones, all relevant processes may take place under anaerobic conditions. These may comprise the well-known redox processes for an electron
potential less than p(c:t = 5.8, see for example /9 I . The most important processes in
connection with water treabnent are:
- Reduction of iron to ferro components which are soluble and hence may
diffuse into the outer zones.
- Reduction of organic matter to fatty acids. Several of the intermediate
products as well as the fatty acids themselves may diffuse to the outer zones.
- Reduction of sulphate to sulphide, as illustrated in the figure.
In connection with anaerobic degradation of organic matter, a release of ammonium
takes place which diffuses into the aerobic zones.
The reduction of sulphate in the biofilm or the oxidation of sulphide diffusing out
from anaerobic degradation of the organic matter is of special potential importance.
The produced sulphide can be precipitated with metals, for example iron, but it is
otherwise accessible for diffusion into the outer oxidizing zones.
The ultimate anaerobic reduction of organic matter is the conversion into methane
and carbon dioxide. The methane may diffuse out, to be oxidized in the outer zones.
269
bu lk aerobic anoxic
water
I
I
I
I
0 2
I
I
N0 3
anaerobic
I
I
I
aerobic' anoxic'
anaerobic
e removal $ production
Fig 7.27 Illustration of layers of redox zones in a biofilm.
In the internal, reduced zones, all relevant processes may take place under anaerobic conditions. These may comprise the well-known redox processes for an electron
potential less than p(c:t = 5.8, see for example /9 I . The most important processes in
connection with water treabnent are:
- Reduction of iron to ferro components which are soluble and hence may
diffuse into the outer zones.
- Reduction of organic matter to fatty acids. Several of the intermediate
products as well as the fatty acids themselves may diffuse to the outer zones.
- Reduction of sulphate to sulphide, as illustrated in the figure.
In connection with anaerobic degradation of organic matter, a release of ammonium
takes place which diffuses into the aerobic zones.
The reduction of sulphate in the biofilm or the oxidation of sulphide diffusing out
from anaerobic degradation of the organic matter is of special potential importance.
The produced sulphide can be precipitated with metals, for example iron, but it is
otherwise accessible for diffusion into the outer oxidizing zones.
The ultimate anaerobic reduction of organic matter is the conversion into methane
and carbon dioxide. The methane may diffuse out, to be oxidized in the outer zones.
269