9420.pdf

Tangential and rotary screens have received wide acceptance due to their simplicity. The
mesh sizes of the screens installed in North American fish processing plants range from
0.15 to 1.52 mm, with 0.5 mm being the most widely used (pers. comm. with suppliers:
Mr. David Botwright of Sanitherm Engineering Ltd. and representative of Hycor and Mr.
Brian Graham of IPEC Industries, and review of MOELP Permits).
Typical solids removal rates achieved with tangential screens are presented in Table 5.5.
Aquametrix (1993a) reported 75 to 80 % solids removal efficiencies with 0.42 mm
internally fed rotoshear screen.
Wheel filter screens, in use mostly in Norway, can have mesh sizes as small as 10 pm
(NovaTec, 1993a).
Table 5.5 Solids Removal by 25 mesh (0.6 mm) Tangential Screens
Wastewater Source Flow rate [m Tm ~ Solids Removal [%]
Salmon canning 2.3 43
Groundfish 2.7 10
Herring I 1.1 I 50 II
Source: Riddle and Shikaze, 1973
Solids removal is an important step in wastewater treatment, as solids of organic origin
contribute to the BOD and TSS of “a wastewater. However, a substantial fraction of the
BOD of wastewater is due to dissolved substances (such as blood and soluble proteins)
which, together with particles smaller than the screen openings cannot be removed by
screening.
Screens used in fish processing can be divided into three categories according to mesh
size:
1.
2.
3.
coarse screens with mesh sizes above 600 ~m;
fine screens with mesh sizes from 150 to 600 ~m;
very fine screens with mesh sizes from 10 to 150 ~m.
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