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

Specific O2 consumption for N 1,91 kg O2/kg BOD
Flow of return sludge 43 %
Teil 3 Seite 4-35
The introduction of air and the circulation of the biomass are achieved using 8 aerator
chains. The aerator chains consist of 7 floating aerators each, connected to one another
by means of air supply hoses. The air is introduced in the form of small bubbles, over the
basin floor. The required quantity of air is made available through sliding vane rotary com-
pressors. A compressor constantly runs on base load in order to ensure a specific mini-
mum level of circulation of the activated sludge. The connection of further compressors is
regulated by a timing programme and an automatic oxidation/reduction control. By vary-
ing the rate of oxygen introduced through different chains aerobic and anoxic zones are
produced. The rate of oxygen fed through the chains is altered periodically, so that over
time anoxic zones are intermittently created throughout entire basin.
The sludge is removed and the effluent is subject to further aeration and sedimentation.
Table 4-6 shows the emission levels achieved in the plant described in Table 4-5 during
the period 1992 to 1996.
Table 4-6: Emission levels achieved during the period 1992 - 1996
Parameters Aver-
BOD5 homogenised
mg/l
COD homogenised
mg/l
age
Minimum Maxi-
mum
3.1 1 8
65.4 35 125
NH4-N mg/l 10.0 0.3 29
NO3-N mg/l 2.4 0.3 7.7
NO2-N mg/l 1.8 0.7 4
P total mg/l 1.8 0.3 4.3
AOX mg/l 0.015 < 0.01 0.02
At a second rendering plant reportedly designed with a processing capacity of 580 t/d of
animal carcases and designed for full nitrogen elimination, 2 tanks are operated in parallel
with intermittent aeration. The process effluent is subject to fat separation and flotation
followed by mixing with non-process waste water. It is then treated in a clarification plant
and an equalisation basin (1.250 m³ with a reserve of 1.750 m³). It is then divided be-
tween 2 basins, each of 6.240 m³ capacity. The basins contain 1.365 meter tubes for air
intake, aerators and 3 stirring devices. The basins are in alternation supplied with air (aer-
ated) at or simply stirred (anoxic) to time ratio of approximately 2:1.