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

Teil 3 Seite 4-24
Both in terms of the float-off and wash water substance stream from the cleansing of car-
riages and stalls, as well as the slaughterhouse waste water, tripe waste water (yellow
line) and meat processing waste water (red line) substance streams, a coarse material
separator is generally required. The coarse materials should be removed as quickly as
possible.
On the basis of its content materials, fine sieves with a mesh size of 1 mm are predomi-
nantly utilised for the green line.
The coarse materials that are often also floated off in the red line (e.g. beef stomachs,
pieces of meat, hooves) may require the prior utilisation of a strainer rack with a rod spac-
ing of, for example, 20 mm and a subsequent fine sieve with a mesh size of 1 mm.
Blockages are to be avoided by means of automatic cleansing devices.
While determining dimensions, safety margins of approx. 30% above the manufacturer's
recommendation should be observed.
In the case of suppliers who have only recently entered the market, performance capaci-
ties should be tested in trials before implementation.
The following sieves are utilised:
- Fixed sieves : e.g. arc-shaped sieves
- Non-fixed sieves : e.g. cylindrical sieves
- Filtering
straining racks : e.g. filtering sieve
When implementing sieving systems and straining racks, it should be noted that these
are required to be walled in (including the collecting container). This is necessary in order
to avoid complications during winter operation (e.g. as a result of freezing) and to guard
against possible nuisance caused in the summer months through the occurrence of
odours and vermin.
Even during planning, care should be taken to ensure that the collecting container for the
sifted substances is placed directly under the delivery opening of the sifting installation.
The installation of additional conveyance devices can in this way be avoided.
Through the implementation of raking and sifting installations, it is possible to reduce the
solid refuse component of the effluent substantially. A prerequisite in this regard is of
course that the raked and sifted material is indeed retained and does not simply reach the
sewerage system in a smaller form. In accordance with manufacturer instructions, elimina-
tion rates of 50 to 90 % may be expected in terms of the disposable materials at a mesh
size of 1 mm and 10 to 40% in terms of BSB5 (biochemical oxygen requirements over 5
days).
Experimental values of the Niedersächsisches Wasseruntersuchungsamt (Lower Saxony
Water Research Office) in Hildesheim regarding the influence of organic loading of raw