Waste transfer station process and machines

Transfer stations serve as links connecting local waste collection operations with a region’s final waste disposal facility, whether that’s a landfill, a material recovery facility or a waste-to-energy plant. Though their basic functions are the same, waste transfer stations can vary widely in terms of ownership, size and services offered.

Transfer stations serve as nodes where collected waste streams can be consolidated for long-distance transport. They don’t just load trailer trucks—at transfer stations, depending on the station’s location and regional transport infrastructure, waste can be transferred to other forms of intermodal transportation, such as rail cars and barges.

Transfer stations are designed to handle four primary tasks: arrival, unloading, sorting and reloading. Most activity at a transfer station occurs within the main transfer building. The configuration of the transfer station’s floor plan varies with its operational scheme. Understanding the fundamentals of the waste transfer station process can help in optimizing the facility, resulting in significant operational cost savings.

The simplest transfer station layout has the open top transfer trailer parked in a lower pit adjacent to the tipping floor where waste is deposited by the individual waste collection trucks. The waste piles are then pushed into the top of the transfer trailer trucks by wheeled dozers or front-end loaders.

Because the waste is not compacted, this type of operation usually requires larger transfer trailers (100-cubic-yard capacity or more) to allow for an economically large load. Sophisticated and costly compaction or baling equipment is not needed. This cost advantage makes it preferable for low-volume operations.

From there, the essential elements of transfer station design are considered.

The surge pit

Even relatively simple transfer stations can have a surge pit. This is not a loading technology, nor does it necessarily incorporate compacting equipment. A basic surge pit is simply an intermediate step designed and constructed to handle peak waste flows from incoming waste collection trucks.

The surge pit provides temporary storage capacity at peak hours to reduce the number of transfer trailers needed to efficiently service the station. A front end loader or bulldozer is used to compact the accumulated waste either by riding on top of it or by pushing it up against a side wall of the pit. This increases the waste density and the resultant payload deposited into the transfer trailer.

While making for more efficient transfer operations by increasing tonnage per trailer truck, this layout typically is not conducive to materials recovery or waste screening operations.

The waste compactor

At a transfer station, waste often is compacted to reduce its volume, then loaded into trailers for transportation to the final disposal site. Transfer station compactors are designed to handle extremely high volumes of waste. One type of waste compactor, the stationary hydraulic ram, uses hydraulic equipment to compact waste into the transfer trailer.

More advanced compaction operations require a heavier-duty transfer trailer. In light of the high pressure created by the ram, the typical transfer trailer needs to be modified to resist the applied forces.

The types of trailers that serve transfer stations with hydraulic rams usually are made from reinforced steel. However, the additional weight of the steel reduces the overall carrying capacity of the trailer. Given the resultant limitations on waste loads that can be carried by the trailer, hauling is less economical.

The baler

The baler provides a means to achieve high levels of waste density without the need for heavily reinforced truck bodies. This equipment compresses waste into high-density, self-contained bales, bricks or logs.

The compacted packages then are moved by forklifts to flat-bed trailers for transport. Being self-contained and typically wrapped in wire, these waste bundles do not need high sidewalls for safe transport.

Capital costs for balers are high. They can cost more than half a million dollars each, and most sites will require at least two, so one can operate while the other is down for maintenance and repair. Therefore, only the largest transfer trailers economically can justify their use.

The access road

Transfer trailers that move waste to a disposal facility are typically 50-70 feet long. Larger trailers have hauling capacities in excess of 150 cubic yards.

Given their size and length, they require access roads with wide turning radii and gradual approach slopes. These features must be worked into the exterior landscape design of the transfer station.

The transfer trailer

Transfer trailer weight-load capacity ranges from 15-25 tons per trip. This is small compared with trains and barges that can typically haul thousands of tons, but it provides greater operational flexibility and options for locating the transfer station itself.

Because not every community is near a major railhead or river transport, not every transfer station generates enough waste to justify the investment in barge or rail transport.

As a result, it is not uncommon to combine these modes of transportation with regional transfer stations loading transfer trailers, which, in turn, transport their loads to larger stations for barge or rail transport to the final location.

Given the harsh characteristics of the waste loads being carried, the design of waste transfer trailers differs from that of other over-the-road trucks performing mass-haul operations. Waste trailers will have different engine specifications, transmissions, drive trains and suspension systems. The floor and sides at the rear of the trailer, which experience the most wear and tear, also have unique structural requirements.

The live floor

While dumping a transfer trailer load can be accomplished by tilting the entire floor using heavy-duty lift jacks, live floors—or walking floors—provide another option for offloading waste at its final destination.

Often augmented by pusher blades, live floors allow transfer trailers to unload themselves. A live floor consists of a series of independently moving planks arranged horizontally the full length of the trailer floor.

The planks, usually three at a time, sequentially raise and lower themselves, creating a wave action that carries the waste out of the back of the trailer. This wave is repeated until the last of the waste has been deposited.

Live floors can be constructed integrally with a transfer trailer or retrofitted into existing trailers. Landfills receiving transfer trailers with live floors can avoid the capital expense associated with tippers. In general, live floors are preferred for depositing waste at remote locations (most landfills).

Live floors are more versatile than hydraulic lifting jacks, and not having to raise the trailer provides much needed operational flexibility and choice of disposal spot. This includes direct deposit at the landfill’s current working face, greatly improving waste disposal operation efficiency.

The tarping system

Open-top trailers must have their loads covered before they hit the road. Given the nature of waste, flying debris let loose during transport is a constant concern.

Automated tarping systems designed specifically for the waste and recycling markets are hydraulically operated mechanisms that use arms or telescoping cylinders to lift a heavy tarp up and over the mound of waste in the trailer.

Once positioned, rollers deploy the tarp over the rough and jagged surface of the waste without causing it to catch and tear. The tarp is then secured in place prior to transport.

The trailer tipper

A trailer tipper allows an entire load from a transfer trailer to be deposited efficiently at a preferred location. It lifts up and rotates the trailer so the load falls out of the open end.

A tipper can be fixed or portable, and it allows for controlled waste management near or on the current work face. It eliminates the need to equip each trailer truck in the fleet with a walking floor, but limiting waste disposal to only one location does limit operational flexibility at the landfill.

However, separating the disposal mechanism from the trailer truck itself greatly reduces the truck’s operating weight. This allows for heavier loads and more efficient transport, which, in turn, reduces truck queuing, traffic on neighboring roads and can make distant disposal sites economically viable.

This article originally ran in MSW Management, which Waste Today acquired in 2023.