The separation systems for processing municipal solid waste have been developed widely; they are mainly classified under three categories: density separation, electric and magnetic field separation and size separation.
Density separation is a technique widely used to separate materials based on their density and aerodynamic characteristics. This technique has been applied to the separation of shredded MSW. Generally, the system can separate waste into two major fractions: 1. Light fraction, e.g., paper, plastics and organics. 2. Heavy fraction, e.g., metals, wood and other relatively dense organics.
Magnetic and electric field techniques use the electrical and magnetic properties of waste materials, such as electrostatic charge and magnetic permeability.
Size separation, or screening, involves the separation of a mixture of materials into two or more portions by means of one or more screening surfaces, which are used as go or no-go indicators. Trommelling is one of the size separation techniques commonly used in MSW separation. The trommel is a screening device that incorporates a rotating perforated drum as its main component. The perforations or drilled holes incrementally increase in size along the length of the cylinder, allowing smaller materials to drop out early in the process. Larger items are carried further along as the rotation continues, dropping through openings of increasing diameter as their size permits. Items too large for any of the openings pass through the trommel and can be moved to various areas by a conveyor or other means.
