Integrierte Vermeidung und Verminderung der Umweltverschmutzung

Chapter 3
3.3.2.1 Water consumption
To meet quality and hygiene standards, the fish sector uses high quantities of water. It is mainly
consumed for cleaning operations and washing, cooling, and transportation of fish. Fish canning
and fish filleting consume large quantities of water, e.g. to clean and lubricate the filleting
machinery. Typical figures for fresh water consumption are for thawing, about 1 m 3 /t fish; for
filleting 5 to 11 m 3 /t fish, and for canning, 15 m 3 /t fish. Water is used for transporting fish and
viscera, for cleaning the installation and the equipment, for washing raw materials and products,
and for thawing. Reported water consumption and specific COD loads for traditional fish
processing are summarised in Table 3.16.
Production
Water
consumption
COD
(m 3 /t raw fish) (kg/t raw fish)
Herring filleting 3.3 – 10 Up to 95
Mackerel
Cleaning and head cut 20 270
Thawing included 26 – 32
White fish processing
Fresh fish 4.8 5 – 36
Thawing included 9.8
Shrimp processing 23 – 32 100 – 130
Table 3.16: Specific water consumption and organic load in Nordic countries
[28, Nordic Council of Ministers, 1997]
3.3.2.2 Waste water
Most of the water consumed during fish processing becomes waste water. The process related
waste water is produced in different processing steps, e.g. thawing, washing, head cutting,
filleting, skinning and trimming, and in cleaning the equipment and the installation.
When frozen fish is used as a raw material, a thawing step is needed. The organic pollution of
the waste water is relatively small. Scaling normally takes place in rotating perforated drums.
Scales are flushed away using large amounts of water – 10 to 15 m 3 /t fish. Large volumes of
waste water and organic pollution are generated. If the fillets are to be skinned, scaling is not
necessary. In automated filleting and eviscerating processes, water is used to lubricate fish while
passing through the machine. For some species such as mackerel, a warm caustic bath is
necessary to remove the skin and the waste water needs to be neutralised before it is discharged.
Water is used for washing and rinsing the fish, giving rise to waste water carrying fish scraps
and viscera. Viscera from oily fish contain high levels of oil and soluble matter, thus waste
waters from their filleting normally have higher COD levels (3000 – 60000 mg/l) than those
from white fish filleting (2000 – 6000 mg/l). The highly polluted waste water is generated due
to the time that solid wastes are in contact with the water which contains blood and fat. In
automated skinning, the fillet is pulled over a freezing drum. Water is used to clean and
lubricate the machine. The skinning of fatty fish releases large quantities of oil to the waste
water. The skinning process contributes about one third of the overall organic pollution in the
waste water of filleting installations.
As the evisceration of fatty fish takes place at the processing installation, and white fish are
eviscerated at sea, this also adds to the reason for the waste water having higher COD and TSS
levels. Table 3.17 shows the reported waste water characteristics from fish filleting.
156 January 2006 RHC/EIPPCB/FDM_BREF_FINAL