Guidelines for Establishing Transfer Stations for Municipal Solid Waste
Transfer stations are facilities at which municipal solid waste is dropped off by relatively small vehicles, loaded into larger containers or onto larger vehicles, and hauled to an off-site management facility for further processing or final disposal. There are many different methods and combinations of methods for solid waste transfer. The purpose of this report is to describe transfer station methodologies, illustrated by examples in British Columbia and Alberta, and to recommend siting, design and operational guidelines for establishing transfer stations. A second purpose is to provide cost models that compare direct haul in collection trucks with transfer haul to a landfill, and that compare rural landfills with rural transfer stations. It is intended that these cost models be used as an aid in deciding whether a transfer station is justified in given, particular conditions.
There are two principal reasons for constructing a transfer station:
- Economics - If the destination of the wastes is far away from the area in which they are collected, then it may be more economical to transfer the wastes to large vehicles for haulage than to haul them directly in the original collection vehicles. This situation is becoming increasingly common, as landfills become more difficult to site and, therefore, more remote from populated areas.
- Service - For a rural area without a garbage collection service, a transfer station is often provided as a service to local residents, so that they do not have far to drive to drop off their wastes. A transfer station is often established at a landfill after it has been closed because people are accustomed to taking their waste to that location. Such a transfer station may or may not be economical.
Ideally, a transfer station should be sited as close as possible to the centroid of the population served, in order to minimize collection costs, or some distance along the haul route to the landfill. The transfer station should be sited and operated so as to create no environmental or health hazard, and no nuisance.
1. Green Box - This rural system is shown in Figure 1, at the end of this section. It is similar to that used for commercial establishments in urban areas. Metal containers with hinged lids, varying in size from 2.3 to 6.1 cubic metres (three to eight cubic yards) are placed at strategic locations such as cross-roads, city works yards and rural stores. The containers are picked up and emptied by front, rear, or side loading compaction trucks. One cubic metre of packer truck capacity would equal about three cubic metres of bin capacity. Therefore, as an example, a 22 m3 truck could service eleven 6 m3 bins on one trip.
Although economical in terms of capital cost, the relatively small bins are unable to accommodate large items such as furniture and demolition/land clearing/construction (DLC) waste. They are awkward to use because waste must be lifted up to be dumped. A problem with multiple bins (i.e. more than three) is that people become frustrated on finding successive bins full, and may dump their waste indiscriminately. A transfer station employing small bins is normally considered suitable only for small annual tonnages, say less than 100 tonnes/year, and for serving areas that have some other convenient alternative for disposing of bulky waste.
2. Dedicated Truck - Some rural areas have found it convenient to arrange for a compaction waste collection truck to be available at a specified location, on a regular schedule, for an advertised time period, usually once per week. Local residents bring their waste to the truck, and are charged a prearranged rate per bag or can by the truck driver. Although this system is not a "transfer station" it can be a substitute for one, and has the advantages of requiring no capital cost, assuming a collection contractor is available, only minimal operating cost for a subsidy and advertising, and users pay much of the cost directly for the service. The major disadvantages are that it is relatively expensive, and that service can usually only be afforded for limited periods, say one day per week or less.
3. Rolloff Container - This rural system, illustrated in Figure 2, uses large steel containers, typically varying from eleven to thirty-eight cubic metres (fifteen to fifty cubic yards). Full containers are picked up by a rollon/rolloff tilt frame truck, and transported singly or in pairs by a truck/pup arrangement, to the landfill. An empty container is deposited by the same truck that picks up the full one. Rolloff bins often achieve their legal load limit without compaction. For example, the legal payload for a 38 m3 (50 cu yd) bin is about 8 tonnes, which is equivalent to a density of about 210 kg/m3.
The best rolloff station designs incorporate elevated ramps, with the bins sitting at a lower level, so that waste can be dropped down into the bin, and hinged counterweighted lids that are easy to move. A sheet metal or screened cover is often used over the bin to reduce blowing litter and exclude birds and animals. Site development can include fencing, a lockable gate, and paved roads.
This system is fairly economical in terms of capital cost, is capable of accepting all household solid waste, is uncomplicated, is flexible because more containers can be added when volumes increase, and is generally well accepted by the public. However, the bins cannot successfully receive waste from standard collection trucks. These trucks must direct haul to the landfill. Scheduling is the major concern with this system. Haul costs can be high because containers may not be completely filled. In summary, rolloff stations are the most common and accepted system in BC.
4. Hydraulically Tippable Containers - These come in a wide range of sizes. The smallest are up to three cubic metre roadside units that use a quick-connect hydraulic system on a side loading collection truck to tip the bins into the truck. Larger units, as shown in Figure 3, with a capacity of about thirty cubic metres, use their own hydraulic system to tip their contents into a large transfer trailer, typically holding 90 m, and hauled by a tractor. The large units are set up similar to rolloff stations, with a ramp leading to an upper level, so that waste can be thrown down into the container. The transfer trailer parks at the lower level to receive waste. The advantages of this type of system, compared to a rolloff system, are that it can receive waste from standard collection trucks, and that only the waste is hauled. The expense of hauling containers is avoided. Disadvantages of this system, compared to rolloff bins, are problems caused by cold weather on the hydraulic cylinders, potential damage to the hydraulic systems resulting from vandalism and fire, and problems that arise from overloading with heavy material, which becomes jammed in the hopper.
5. Direct Dump - Sometimes called a "push pit" system, these urban transfer stations, as shown in Figure 5 at the end of this chapter, allow waste collection trucks to dump their loads either directly to a large transfer trailer parked at a lower level, or to a tipping floor, from which it is usually pushed by a loader or Bobcat into a 90 m3 trailer. A variation on this theme is for the waste to be lifted from the tipping floor or bunker by a crane, thus eliminating the need for a lower level for the transfer trailer. The tipping floor and trailer are usually housed in a building. Other amenities generally provided at a larger station include weigh scales, bins for receiving recyclables, a storage area for white goods, and an office, washroom, and lunchroom for staff.
6. Compaction - The use of compaction at a transfer station may be economically advantageous, since it allows a greater weight to be hauled in a given container. The economic viability of compaction depends on the nature of the wastes, the type of vehicle used to collect wastes, and the distance from the transfer station to the landfill. Wastes containing a significant amount of dense material, and/or waste collected in packer trucks (even though it rebounds upon dumping) may already achieve legal truck weight limits without compaction. The fundamental question in deciding whether to use compaction or not is this: Can the legal gross vehicle weight of the transport units be reached without compaction?
Compactors may be used even at small facilities. Rolloff compactors are available and are sometimes used at rural transfer stations, as shown in Figure 4. These compactors typically achieve a compaction ratio of about 6:1. They are limited as to the size and type of waste they can accept, so often a standard rolloff container is provided to receive bulky objects and demolition debris. There is a variety of compactors available for urban direct dump transfer stations; waste may be compacted directly in the trailer that receives it, or in a separate receiving compactor that then discharges to the transfer trailer.
Figure 1. Typical Green Box Site
Figure 2. Typical Rolloff Bin Site
Adapted from Alberta Environment Transfer Station Manual
Figure 3. Transfer Station with Hydraulically Tippable (Transtor) Bin
Adapted from Alberta Environment Transfer Station Manual
Figure 4. Typical Compaction Type Rolloff Facility
Figure 5. Transfer Station Push Pit System