Biomedical Engineering Reference
In-Depth Information
tangential flow in cross-flow filtration can wash through the membrane surface, thus limit the
formation of concentration polarization and other membrane fouling. The cross-flow filtration
is more widely employed, especially in the industrial applications.
The transmission of a partially rejected solute through a membrane is expressed by the
apparent sieving coefficient conveniently (Ghosh and Cui, 2000).
C
(4)
P
S
=
a
C
b
where
C
b
is the solute concentration in the bulk feed;
C
p
is the solute concentration in
permeate.
The diamensionless ratio of sieving coefficients has been termed as selectivity (Reis and
Saksena, 1997) and it is defined as:
S
(5)
a
Ψ=
1
S
a
2
where Ψ is the selectivity, and
S
a1
and
S
a2
are the observed sieving coefficients for the lesser-
and greater- retained solute, respectively.
From equation (5), a larger value of Ψ is correlated with a better separation between two
solutes.
With great potential for concentration, fractionation, and purification of soluble and
insoluble materials, pressure-driven membrane processes have been beginning to emerge for
applications in fishery industry. As mentioned above, pressure-driven membrane process is
based on separation of the substances by passing the liquid under pressure through a
membrane. This method provides two essential characteristics: (a) it is a purely physical
separation principle; and (b) it is a modular design. Membrane process is therefore an ideal
choice for waste treatment in fishery industry, since it allows removing contaminants,
recovering dissolved or suspended high value components (protein, pigment and enzyme,
etc), and allows water reuse for certain applications (Rautenbach and Linn, 1995).
3. Application of Pressure- Driven Membrane Process
in the Fishery Industry
3.1. Microfiltration
Although the exact size range is a matter of debate, microfiltration is generally accepted
as a means of filtering colloidal or fine particles having approximate range of 0.02 to 10 μm
(Davis, 1992). Microfiltration is not basically different from ultrafiltration, reverse osmosis or
nanofiltration, except the size range of retained molecules. Microfiltration is suited to separate
larger sizes, such as suspended solids, particulates, and microorganisms. This is accomplished
because microfiltration membranes are thought to act like a physical seive. The membranes
are highly porous and have discernible pores even the surface skins are asymetric. Therefore,
