9420.pdf

5.2.4 Contaminant Reduction
Several of the measures recommended for water conservation will also lead to a reduction
of the contaminant loadings. The guiding principle for achieving contaminant reduction
is dry clean-up (segregation of offal and blood from process water).
Overall, the segregation of offal and blood from process water can reduce the organic
loading from a fish processing facility by about 50 to 60 % and even more, depending on
the extent of measures adopted.
5.3 Wastewater Treatment
5.3..1 General
Wastewater treatment options for fish processing plants can be divided into physical,
chemical and biological treatment. Physical treatment options make use of differences
in physical properties between water and contaminants for their separation. Chemical
treatment is generally required to improve removal efficiencies. With the exception of
ultrafiltration (see Section 5.3.6. 1) physical treatment methods cannot remove BOD which
is associated with dissolved substances. This fraction of the overall BOD can be
substantial and can only be removed by chemical and/or biological treatment.
5.3.2 Physical Treatment
Screening is the most prevalent method of physical treatment in the fish processing
industry. Most fish processing plants screen their effluent prior to discharge to a receiving
environment or municipal sewer. The types of screens used include:
. tangential screens (sidehill screens); ,/-
. rotary drum screens with spray water and, in some cases, counter flow helical
brushes for cleaning of screen;
. filter belt screens;
. wheel filters with solids scrappers and warm water spray.
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