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Driving force for implementation
Example plants
Teil 3 Seite 4-31
At the Kraftisried animal carcass disposal plant, a flotation system is in use for as yet
unhomogenised waste water (system by the company Mangold), in which air is injected
through submersed aerators. The flotation objects are removed from the surface by
means of a paddle stirring device. An automatic spraying system prevents the possibly
substantial formation of foam during flotation. Given a dimension for Q of a maximum of
15 m 3 /h, it exhibits a volume of 12 m 3 and a surface area of 8 m 2 . Concerning fat content,
an elimination rate of 76% is achieved, and the COD (homogenised) is reduced by up to
42%. Table 4-4 illustrates the entire elimination capacity of the mechanical/physical-
chemical stage, consisting of fat separators, cylindrical sieves and flotation.
Table 4-4: Inflow and outflow values in terms of mechanical/physical-chemical effluent
pre-treatment at the Kraftisried animal carcass disposal plant (mean value on
the basis of daily composite samples; n = 3 to 111)
Parameters Inflow Outflow In-/decrease %
ces
pH 9,0 - 9,5 7,7 - 11 -
filterable substan-
mg/l 1.530 570 - 62,7
COD total mg/l 5.024 3.416 - 32
Fat mg/l 1.590 199 - 87,5
NH4-N mg/l 943 648 - 31,3
org.-N mg/l 119 39 - 66,9
At the Oberding animal carcass disposal plant flotation takes place on the basis of a mix-
ing and equalising basin. It is dimensioned for a constant effluent inflow of up to 8 m 3 /h. At
this plant, a fat elimination rate of 50% was achieved. The COD (homogenised) is only
reduced by 16%, since the excess sludge from the biological treatment plant simultane-
ously reaches the flotation plant. This can lead to temporary overloading, so that even an
increase in organic content material may result in comparison to in-flowing effluent.
In terms of flotation plants, stripping of ammonia cannot be avoided due to a high con-
tent of ammonia/ammonia concentrations in the effluent. At the Oberding animal carcass
disposal plant the N-elimination carried out in this way amounted to 10%; at the Kraftisried
animal carcass disposal plant, with higher initial values in the effluent, it amounted to
approx. 30 to 40%. This means high ammonia contamination of the air in the enclosed
flotation area, and therefore also the endangerment of personnel, since the permissible
MAC values are exceeded by a wide margin. In addition, flotation plants are generally a
source of strong odour emissions. In terms of enclosed accommodation of such a flotation
plant, sufficient air extraction is therefore recommended. The air extracted from the en-