Environmental Engineering FOURTH EDITION

286 ENVIRONMENTAL ENGINEERING

Magnets

Ferrous material may be removed from refuse using magnets, which continually extract
the ferrous material and reject the remainder. Figure 14-1 1 shows two types of magnets.
With the belt magnet, recovery of ferrous material is enhanced by placing the belt close
to the refuse; however, such placement decreases the purity of the product. The depth
of refuse on the belt can also pose difficulties, since the heavy ferrous particles tend to
settle to the bottom of the refuse on the conveyor and are then further from the magnet
than other refuse components.

Separation Equipment

Countless other unit operations for materials handling and storage have been tried. Jigs

have been used for removing glass, froth flotation has been successfully employed

to separate ceramics from glass, eddy current devices have recovered aluminum in

commercial quantities, and so on. As recovery operations evolve, more and better

materials separation and handling equipment will be introduced. Figure 14-12 is a

diagram of a typical MR.F.

Energy Recovery from the Organic Fraction of

Municipal Solid Waste

The organic fraction of refuse is a useful secondary fuel. Shredded and separated by

classification, it may be used in existing electric generating plants either as a fuel to

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Magnetics t t Nonmagnetics

Nonmagnetics Magnetics

Figure 14-11. Two types of magnets used for resource recovery.