2.4 Waste Diversion
45
2.4.1 Recycling at Material Recovery Facility (MRF)
The material recovery facility (MRF) receives, separates and prepares the recyclable
materials for later use as raw materials for remanufacturing and reprocessing. It can
also process wastes into a feedstock for biological conversion or into a fuel source
for energy production [31]. MRFs can be classified into two different types: clean
and dirty material recovery facilities. The clean MRFs use clean or source-separated
MSW generated by either residential or commercial sources and the dirty MRFs use
mixed or non-source separated waste stream [32]. Dirty MRFs have greater recovery
potential and a wider range of recoverable materials as some of the recoverable
materials might have been mistakenly put in the trash by the consumers. However,
they require more manual labor work for sorting the material.
The mixed wastes are inspected and the biodegradable materials are separated
from the recyclables and are sent to composting facilities or landfills. The sourceseparated wastes are inspected manually or mechanically for separation of valuable
recyclables such as paper and carton, tin cans, metals, plastics and glass [32]. Manual
sorting is usually performed in rural areas or small towns and mechanical sorting
is used in larger MRFs and provides lower labor costs, greater material recovery
and faster processing rates [31, 33]. The material recovery facility (MRF) consists
of four main sections: (1) receiving or tipping area, (2) sorting and processing area,
(3) storage area for recyclables and (4) residuals storage area. The general operating
procedures of an MRF are shown in Fig. 2.9.
In the sorting and processing area of automated facilities, a combination of
screens, magnetic separators, air classifiers and conveyor systems are used to sort
the recyclables [32].
Magnetic separation is used to remove the ferrous metals from the other materials. After separation, they will be either shredded or baled depending on market
specification [31]. Screening is another separation procedure to separate materials
of different sizes into various size distributions. Disc screens and trommels are the
main types of screens used in MRFs. Disc screens feed the materials into the screens
by means of rotating disks. They are most effective when the fine particles to be
removed are denser than the large materials. Trommels (as illustrated in Fig. 2.10)
are revolving screen cylinders that are inclined at a downward angle and utilize gravity
and centrifugal force to separate different material sizes from the waste stream [31].
In addition, air classification, a separation system that utilizes an airstream, may
also be utilized at an MRF to remove lightweight material and debris from the main
material stream. The light materials are lifted by the air stream due to differences in
particle shape and density and the heavier materials are discharged from the bottom.
The non-ferrous materials are separated from the waste stream based on conductivity through an eddy current. A rotating disk separator, which consists of parallel
rotating magnetic disks, creates high magnetic fluxes that generate electrical currents
within the free-falling non-ferrous metals. The conductivity of the metal determines
the strength of the produced eddy current. A wide range of non-ferrous metals such
45
2.4.1 Recycling at Material Recovery Facility (MRF)
The material recovery facility (MRF) receives, separates and prepares the recyclable
materials for later use as raw materials for remanufacturing and reprocessing. It can
also process wastes into a feedstock for biological conversion or into a fuel source
for energy production [31]. MRFs can be classified into two different types: clean
and dirty material recovery facilities. The clean MRFs use clean or source-separated
MSW generated by either residential or commercial sources and the dirty MRFs use
mixed or non-source separated waste stream [32]. Dirty MRFs have greater recovery
potential and a wider range of recoverable materials as some of the recoverable
materials might have been mistakenly put in the trash by the consumers. However,
they require more manual labor work for sorting the material.
The mixed wastes are inspected and the biodegradable materials are separated
from the recyclables and are sent to composting facilities or landfills. The sourceseparated wastes are inspected manually or mechanically for separation of valuable
recyclables such as paper and carton, tin cans, metals, plastics and glass [32]. Manual
sorting is usually performed in rural areas or small towns and mechanical sorting
is used in larger MRFs and provides lower labor costs, greater material recovery
and faster processing rates [31, 33]. The material recovery facility (MRF) consists
of four main sections: (1) receiving or tipping area, (2) sorting and processing area,
(3) storage area for recyclables and (4) residuals storage area. The general operating
procedures of an MRF are shown in Fig. 2.9.
In the sorting and processing area of automated facilities, a combination of
screens, magnetic separators, air classifiers and conveyor systems are used to sort
the recyclables [32].
Magnetic separation is used to remove the ferrous metals from the other materials. After separation, they will be either shredded or baled depending on market
specification [31]. Screening is another separation procedure to separate materials
of different sizes into various size distributions. Disc screens and trommels are the
main types of screens used in MRFs. Disc screens feed the materials into the screens
by means of rotating disks. They are most effective when the fine particles to be
removed are denser than the large materials. Trommels (as illustrated in Fig. 2.10)
are revolving screen cylinders that are inclined at a downward angle and utilize gravity
and centrifugal force to separate different material sizes from the waste stream [31].
In addition, air classification, a separation system that utilizes an airstream, may
also be utilized at an MRF to remove lightweight material and debris from the main
material stream. The light materials are lifted by the air stream due to differences in
particle shape and density and the heavier materials are discharged from the bottom.
The non-ferrous materials are separated from the waste stream based on conductivity through an eddy current. A rotating disk separator, which consists of parallel
rotating magnetic disks, creates high magnetic fluxes that generate electrical currents
within the free-falling non-ferrous metals. The conductivity of the metal determines
the strength of the produced eddy current. A wide range of non-ferrous metals such