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Newsletter and Technical Publications
<Municipal Solid Waste Management>
Sound Practices
Collection and transfer
1.3.3 Sound technical options - transfer
Transfer stations and transfer points
Transfer stations are centralized facilities where waste is unloaded from
smaller collection vehicles and re-loaded into larger vehicles (including in
some instances barges or railroads) for transport to a disposal or processing
site. This transfer of waste is frequentlyaccompanied by some removal,
separation, or handling of waste. In areas where wastes are not already dense,
they may be compacted at a transfer station.
Transfer stations represent sound practice when there is a need for vehicles
servicing a collection route to travel a shorter distance, unload, and return
quickly to their primary task of collecting the waste.
In industrialized countries, and for waste from large urban areas in
developing countries, larger, new landfills, incinerators, and composting
facilities are increasingly designed to serve a number of communities or an
entire region, with the result that they are sited at a considerable distance
from the collection service areas. In this circumstance, since transporting
waste from the route to the facility takes longer and uses more fuel, transfer
stations can be very attractive.
Transfer trailers or compacting vehicles can carry larger volumes of MSW than
regular collection trucks, which allows them to travel longer distances carrying
more waste. This lowers fuel costs, increases labor productivity, and saves on
vehicle wear.
Drawbacks to transfer stations include the additional capital costs of
purchasing trailers and building transfer stations, and the extra time, labor,
and energy needed for transferring waste from collection trucks to transfer
trailers.
Some developing countries have transfer stations of the type described above,
but there are also unmechanized, local transfer points that serve the special
needs of particular collection service areas. A micro-collection vehicle
designed to service a hilly area or a densely populated area with narrow or
congested streets can transfer its load to a larger vehicle or a stationary
container at such a transfer point. This can make it possible to service
collection areas that a truck could not enter. Such transfer points may also
degenerate into unregulated dumps in the absence of institutional commitment and
managerial capacity to ensure their efficient operation.
Elements of transfer
Siting
Sound practice for the siting of transfer points and transfer stations includes
the choice of a site accessible to collection vehicles and positioned for
staging of the larger trucks that will haul away the waste. Sound practices for
siting transfer points include the following:
- the neighborhood must be willing to accept the transfer point as designed
and located;
- agreements made with the surrounding community must be taken seriously and
honored by the relevant authorities; and
- odors, noise, leachate, and increased traffic must be minimized.
Larger-scale transfer stations should in general be sited:
- far enough from residential areas that odors, noise, leachate, and traffic
are not acute issues;
- close enough to the collection area that collection vehicles can quickly
return to the area;
- at sites that are zoned for commercial or industrial use;
- where there is easy access to major roads;
- on the site of a closed landfill, since the existing land uses and road
network around the landfill are already suitable for transfer stations; and
- where road restrictions (weight, noise, speed, surface, axle weight, truck
length) do not conflict with the expected usage related to transfer.
In some large or heavily populated areas, or in regions with dispersed
population centers separated by relatively sparsely populated areas, more than
one transfer station may be desirable. The appropriate number of transfer
stations depends primarily on the number and size of service areas covered by
the MSWM system, the distance between the areas, the volume of MSW generated,
the distance to disposal, the types of vehicles in use in primary collection,
and the size and type of transfer stations selected.
Transfer vehicles
A number of truck types are currently used for transporting wastes from transfer
points. At large transfer stations, large transfer trailers are used for bulk
transport of compacted waste to more remote disposal facilities. These can be
either open-top (usually a cover is required during waste transport) or
enclosed.
Large-scale transfer station design
Transfer station design in industrialized countries generally includes a tipping
floor serviced by bulldozers for pushing waste into transfer trailers or a
compactor blade for packing waste into trailers. Recyclables and special wastes
are increasingly being sorted and processed at transfer stations. There are
three common types of transfer station that represent sound practice.
Open tipping floor. In the open tipping floor design, collection
trucks unload uncompacted waste onto the tipping floor, and bulldozers organize
the waste and place it in open-top trailers.
Often the most appropriate choice for developing countries, this type of
facility:
- is more efficient for small volumes of waste than for large;
- can serve to transfer different materials at different times or into
different vehicles;
- can easily accommodate recovery of bulky wastes or of materials such as
cardboard;
- allows for waste picking at the transfer station; and
- maximizes the possibility of spreading the waste, ideally on concrete
platforms, in order to pre-dry or pre-compost it for a day or two before
transfer to a landfill or processing facility.
Open pit design. An open pit transfer station has the collection
trucks dump waste into an open pit, where bulldozers organize the waste and load
it into open-top trailers. Alternatively, the waste is compacted and loaded into
enclosed trailers. This design:
- allows multiple collection vehicles to unload at the same time that
loading and transfer operations are in process;
- can accommodate larger vehicles than an open tipping floor design;
- has higher capital and operating costs than an open tipping floor;
- is not ideal for pre-processing or separation of recoverable materials,
although this can be accommodated;
- is vulnerable to breakdown of compaction units, if they are used; and
- can incorporate waste picking only with difficulty, since the open pit is
hazardous.
Direct dumping transfer stations. In direct dumping, collection trucks
unload through hoppers directly into either open-top trailers or compactors.
This system:
- has no intermediate handling, which increases efficiency and decreases
labor;
- does not permit waste picking or any other type of intermediate handling,
and therefore effectively prevents recovery;
- requires an intermediate level of capital investment in the facility, but
a significant investment in the transfer trailers themselves;
- can be rapidly constructed and/or moved, since most of the capital
investment is in the vehicles, not in the facility itself;
- requires an abundance of extra trailers;
- is vulnerable to a shortage of trailers, since there is no buffer when
there are insufficient trailers available to load the waste; and therefore
- is a poor choice when equipment maintenance, repair, or replacement
represent significant difficulties within the system.
Some of the drawbacks to direct dumping can be solved in hybrid systems,
where vehicles discharge onto a tipping apron which allows brief access to the
waste before it is pushed by loaders or dozers into the hoppers that feed the
transfer trailers.
Distance to processing or final disposal. Since one of the main
reasons for including transfer in a waste system is to increase the efficiency
of hauling to disposal or processing, sound practice must include an assessment
of the distance from the collection service areas to these facilities in
comparison to direct haul to the disposal facility.
Health and environmental considerations of transfer
Environmental benefits of transfer. From a system-wide perspective,
transfer operations have the potential for environmental and health benefit, in
the following ways:
- They can reduce air emissions and fuel consumption because of increased
collection and transport efficiency and reduced energy use.
- Access to the materials for pre-processing, waste picking, or materials
recovery, together with removal of bulky or hazardous items, reduces fuel
use and increases recovery.
- Design for safe pre-processing and waste picking can improve the health
and working conditions of waste pickers who would otherwise be salvaging
materials from the landfill or open dump.
- The availability of transfer in a collection system means that landfill
siting becomes less dependent on considerations of accessibility for carts
and short-distance vehicles. Landfills can therefore be sited with more
consideration for public health and environmental factors such as
hydro-geological conditions, the containment of leachate and landfill gases,
and physical isolation of the facility to minimize the threat from disease
vectors such as rodents.
Environmental problems related to transfer. Transfer stations and
transfer points can also cause problems for human health and the environment.
- Negative neighborhood impacts can include noise, air emissions, and
leachate, and oil emissions from the collection and transfer vehicles, and
from truck maintenance facilities.
- Like other MSWM facilities, transfer stations and transfer points have
potential odor, litter, and disease vector problems. But, since they
facilitate greater and more timely collection, they often on balance
alleviate such problems.
- A lack of control can result in a neighborhood transfer point serving as a
place for uncontrolled dumping.
Summary of selection factors for transfer stations and transfer points
The following design and selection factors for transfer stations and transfer
points are associated with sound practice:
- Choose a transfer system that can accommodate the full range of collection
vehicles already in use or planned (even when the long-term desire might be
to phase out certain types).
- Site transfer stations and transfer points to minimize odor and noise and
to allow waste to be accumulated, if necessary, prior to long-haul
transport.
- Respect and abide by agreements with the neighborhood in which a transfer
point is sited.
- Select and design transfer systems that allow access to the waste for
pre-processing and removal of recyclables, compostables, or problem
materials, unless there is a compelling reason to do otherwise.
- For large-scale transfer stations, select locally made equipment, local
designs, and local expertise whenever possible, supplemented if
necessary by assistance from national or international experts.
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