298 94 307/02 Untersuchungen zum Stand der Umsetzung des ...

Teil 3 Seite 8-33
Table 8-3: Performance data of the stripping plant for ammonium (average values from
Parameter Influent Effluent
daily mixed samples; n = 14)
February July
In~/decreas
e %
Influent Effluent In~/decreas
e %
pH-value 7,6 12,1 + 59,7 5,7 12,5 + 119
spec. conductivity
mS/cm 3,67 8,45 + 130 6,08 14,8 + 144
COD total mg/l 6.168 5.553 - 10 14.016 12.780 - 8,8
NH4-N mg/l 647 64,3 - 90,1 931 95,4 - 89,7
Ammonia conversion
Another option to reduce the ammonium nitrogen in the part-stream is the ammonia con-
version. In contrast to the stripping, there the volatile ammonia contained in the exhaust
vapours is removed already. The ammonia is conveyed with the exhaust vapours into a
washing tower (converter) in a counter-current to a nitrous solution of 50-60 %, which re-
sults in a solution of the ammonium nitrate. The converter consists of a filter tower,
through which the concentrated ammonium nitrate solution is pumped into the recircula-
tion. The ammonium nitrate is extracted from the swamp of the filter tower when the de-
sired concentration has been reached. The exhaust vapours freed from the ammonia are
then, as usual, condensated in a condensator into acid exhaust vapours.
By adding a certain amount of urea, the ammonium nitrate solution gained in this way
can be turned into a ammonium-nitrate urea solution of 28 % (AHL 28), which can be
used in agriculture as fertiliser with a high nitrogen ratio.
For the operation of such a converter, it is necessary that the exhaust vapours do not
carry any solids. Thus, cyclones or other suitable separation implements must be installed
before the converters. Moreover, the exhaust vapours should have as low concentrations
of volatile carbon acids as possible, which are mainly caused by high temperatures (>
130°C) during the drying process.
Elimination of hydrogen sulphide
For wastewater with high sulphide concentrations, for instance the part-streams from the
feathers processing, another preliminary treatment target is the reduction of the hydrogen
sulphide concentrations. Contents from about 80 to 100 mg/l of sulphide will already im-
pair the activated sludge biocoenosis and thus the biological treatment process in the fol-
lowing biological stage.
For the treatment of sulphide-containing wastewater, the oxidation with hydrogen perox-
ide is particularly eligible. There, for the oxidation of 1 kg sulphide stoichiometrically about
13 l of 30 % hydrogen peroxide are needed. The reaction time should amount to 10 min-
utes.
8.2.4.1.1 Grease traps and oil traps ( DIN 4040 ) (Kurztechniken C.)