Wastewater Characterization of Fish Processing Plant Effluents

2 REVIEW OF TYPICAL FISH PROCESSING OPERATIONS
2.1 Vessel Unloading
Vessel unloading can be done with wet or dry pumps, or with buckets or baskets. Dry pumps result
in rough handling of the fish and are generally only used for ground fish due to the relatively
low commercial value of the fish. Wet pumps are much gentler and are used for freshly caught
salmon which are kept in water inside the holds of fishing boats and fish packer vessels during
transport. The pumps use large diameter hoses to pump water and whole fish out of the vessels'
holds. Water and fish are then discharged onto grating to allow the separation of fish and water.
A certain amount of water is recirculated to the vessels to ensure sufficient water for the
operation of the pumps and to be able to remove all fish. The water level in the vessel is
continually lowered during the unloading operation and the vessel, generally, is almost
completely empty when all fish have been unloaded.
Conveyors pick up the fish after their separation from the vessel hold water and transport them
to grading stations, where the fish are manually sorted according to their species. After
sorting, fish are kept in chilled water for intermediate storage until they can be further
processed.
Baskets or buckets are also used to unload vessels but are, generally, used only if small
quantities of fish need to be unloaded, or to offload frozen fish. Baskets are lowered into the
vessels holds by a crane and filled with frozen fish.
2.2 Butchering for the Fresh and Frozen Fish Market
A typical flow diagram depicting freezer - dressing of salmon and associated processes is shown
in Figure 2. The equipment used for salmon butchering (also referred to as "dressing") depends
on the requirements for further processing. Dressing fish for freezing involves the removal of
FREMP 03/21/1994
Fish Processing Plant Effluent 7