(best examples and good practices) on household organic waste ...

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material, <strong>and</strong> the gravitational force within a confined volume. In the
interaction, the drag force <strong>and</strong> the gravitational force are exerted in different
directions upon the particles. The result is that waste particles that have a large
drag to- weight ratio are suspended in the air stream, whereas components that
have a small ratio tend to settle out of the air stream. The suspended fraction
conventionally is referred to as the “air-classified light fraction” <strong>and</strong> the settled
fraction is termed “air classified heavy fraction”. The confined volume in which
the separation takes place is called an “air classifier”. (Tchobanoglous <strong>and</strong> Kreith,
2002)
In air classification of shredded mixed MSW, the paper <strong>and</strong> plastic materials
tend to be concentrated in the light fraction, <strong>and</strong> metals <strong>and</strong> glass are the
principal components of the heavy fraction.
Since the density of a material (e.g., paper) is not the only characteristic of a
particle that affects the air classification process, fine glass particles, by virtue
of their high drag-to-weight ratio, may appear in the light fraction. On the
other h<strong>and</strong>, flat, unshredded milk cartons or wet cardboard may appear in the
heavy fraction. Moisture affects the separation of the various components, as a
result of its influence on the density of a material. The influence can be
particularly pronounced in the case of paper where its density can approach
that of typically denser components, such as food waste that normally would
report to the heavy fraction. Air classifiers may be one of a number of designs.
All three require dust collection, blower, separator, <strong>and</strong> control facilities.
(Wastesum.,2010)
The velocity of the air stream required to lift a particle in a vertical column
(e.g., a vertical air classifier) must exceed a minimum value, termed the floating
(or terminal) velocity. The floating velocity is a function of a number of
parameters. The influence of the parameters on the floating velocity is
illustrated in (Table 6.) for a variety of waste components. (Tchobanoglous <strong>and</strong>
Kreith, 2002)