The Elements of Waste Transfer Operations
Transfer stations promote economies of scale in waste operations—efficient movement is key to their success.
Editor’s note: This article first appeared in the June 2016 issue of MSW Management.
Transfer trailers exist because of transfer stations. Transfer trailer trucks financially justify the building and operating of transfer stations, since their larger capacities achieve the necessary economies of scale that minimize the overall costs of over land bulk transport. Common sense and accounting show that it is less expensive to transport large quantities of waste long distance in fewer large trucks than smaller quantities of waste in smaller trucks (like the waste collection trucks used to pick up trash from a street corner). The cost advantage of fewer, larger trucks extends from lowered fuel and labor costs, to lower overhead with less maintenance and fleet upkeep.
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These transfer stations serve as links connecting a town’s local waste collection operations with the region’s final waste disposal facility (landfill, material recovery facility, waste-to-energy plant, or landfill). Though their basic functions are the same, waste transfer stations can vary widely in terms of ownership (public or private), size (in terms of tons of waste received daily, required floor space, and truck queuing lengths), and services offered (direct transfer to trailers, compaction bailing, recycling, and such). Transfer stations serve as nodes where collected wastestreams can be consolidated for long-distance transport. They don’t just load trailer trucks. At transfer stations, waste can be transferred to other forms of intermodal transportation such as rail cars and barges, depending on the station’s location and regional transport infrastructure.
The configuration of the transfer station’s floor plan varies with its operational scheme. The simplest layout has the transfer trailer with its open top 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. This type of operation usually requires larger transfer trailers (100-cubic-yard capacity or more) to allow for an economically large load since the waste is not compacted. There is no need for sophisticated, and costly, compaction or bailing equipment. So, this cost advantage makes it preferable for low-volume operations.
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In any case, 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 so as to handle peak waste flows from incoming waste collection trucks. It provides temporary storage capacity at peak hours so as 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’s density and the resultant payload deposited into the transfer trailer. While making for more efficient (with increased tonnage per trailer truck) transfer operations, this layout is not typically conducive to materials recover or waste screening operations.
More advanced compaction operations require a heavier-duty transfer trailer. One type of waste compactor is the stationary hydraulic ram. This equipment is used to compact waste into the transfer trailer. Due to the high pressure created by the ram’s hydraulic equipment, the typical transfer trailer needs to be modified to reset the applied forces. So the types or trailers that serve transfer stations with hydraulic rams are usually made from reinforced steel. However, the additional weight of the steel reduces the overall carrying capacity of the trailer. Due to the resultant limitations on waste loads that can be carried by the trailer, hauling is less economical.
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 are then moved by forklifts to flat bed trailers for transport. Being self contained (and typically wrapped in wire), these waste bundles do not need high side walls for safe transport. Since the capital costs are high (balers 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), only the largest transfer trailers can economically justify their use.
Transfer trailers that move waste to a disposal facility are typically 50 to 70 feet long. Larger ones have hauling capacities in excess of 100 cubic yards. Given their size and length, they require access roads with wide turning radii and gradual approach slopes. These features have to be worked into the exterior landscape design of the transfer station. Their weight load capacity ranges from 15 to 25 tons per trip. This is small compared to trains and barges that can typical haul thousands of tons, but provides greater operational flexibility and options for locating the transfer station itself. Since not every community is located near a major rail head or river transport, not every one 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 engines specifications (displacement, horsepower, fuel, and oil requirements), transmission and drive trains, and suspension systems. Waste transfer trailers also have unique structural requirements. This is especially true of the floor and sides at the rear of the trailer, which get the most wear and tear. Trailers that get top loaded at the transfer station also damage the top rail.
Despite the similar function and specifications, transfer trailers are not all the same. Each make and model has uniquely designed and constructed frames, alignments, and body designs. Cab layouts and operating systems can also vary significantly. No matter what the application, fleet managers need to devote rigorous and regular maintenance to their trucks. Customization for the particular tasks can greatly add to performance while reducing costs. As such, truck suppliers provide customized packages for tarp deployment mechanisms, suspensions, tires, and brakes, in addition to standard offerings.
East Manufacturing designs and manufacturers transfer trailers that transport garbage from the transfer station to landfill. These trailers are either built to use a tipping platform to empty their load at the landfill, or they come equipped with a Live or Walking Floor. To meet the increasing customer demand for smooth-sided transfer trailers, the East Genesis design with extruded 2-inch aluminum panels provides the same, or more, strength than 4-inch traditional external post-style walls. The aerodynamic design consists of unique 2-inch-thick, double-wall extruded aluminum panels, robotically welded vertically inside and out for superior strength and resistance to side bowing and to protect the outer wall from dents. Vertical panels are lighter than competitive horizontal-panel systems, resist bowing better, and reduce maintenance costs. In addition to maximum strength, welding inside and out reduces corrosion from road salt penetration. Advanced wall-to-floor construction secures the critical point for trailer strength—the welded union of cross members, floor plates, and sidewalls. For a super strong floor-to-wall attachment joint, cross members, and floor plates interlock into the bottom rub rail, forming a pocket to accept the sidewall panels. The 3-inch spacing of interior panel ribs give eight times more wall support than external posts positioned every 25 inches. And, the inside walls stay flatter resulting in longer life. East offers optional thicker aluminum in higher wear areas, like the inside last 4 feet of the trailer. East Genesis transfer trailers are more aerodynamic and easy to clean. In addition, the smooth-sided walls will not show any pings and dings on the outside like the traditional external post-style walls. In addition, Genesis increases the width of East’s tipping trailer by 4 inches for up to 7.75 cubic yards of extra payload.
When a traditional external post trailer fits a customer’s application, East has advantages in its welding process for its traditional external post-style wall trailers. Maximum strength sidewalls are thicker than most competitive models, and posts are continuously welded for greater durability. Side posts are welded directly to the bottom rail then dirt-shedding wedge plates are added for maximum attachment integrity with the bottom rail. A full-length boxed top rail interlocks with the sidewalls and side points, which prohibits the sidewalls from deflecting. And all outside joints are continuously welded for greater load-bearing strength and durability. Stronger 5-1/4-inch extruded I-beam floor cross members offer 30% more bending resistance than the 4-inch cross members used by competitors.
Mac Trailer Manufacturing produces both tipper and moving floor transfer trailers. Designed to withstand abrasive operations and demanding load conditions, their trailers can handle municipal solid waste and other bulk loads such as wood, agricultural products, recyclables, and scrap. The moving floor model can even handle crushed cars and scrap white goods. It comes in the original fully welded aluminum sheet and post with side skins to a gauge of 0.250, or the smooth sided “MVP” (MAC Vertical Panel) MACLOCK configuration that incorporates 2 ¼-inch hollow core aluminum extruded panels. The drive unit can be leak-proof or conventional, with its slats either aluminum for agricultural-wood materials, or high-impact steel for aggressive abrasive loads of scrap, white goods, crushed cars, or sand. Their tipping floor model maximizes load and volume capacity. The 53-foot-long MAC Tipper can provide volume up to 148 cubic yards. Even greater capacity is provided by their “MVP” MACLOCK extruded aluminum panel construction.
Manac Trailers US provides an advanced trailer design that includes side doors with alignment guides, a pair of bolted cross braces made of tubing with a tubular top rail, side wall and posts made of DOMEX 100 steel, coupler plate made of 100,000 PSI steel with bolted king pin Fabricated ”C” frame made of 80,000 PSI steel. The trailer has a 146-cubic-yard capacity and reinforced structure that evenly distributes loads.
Ruan works directly with waste disposal and recycling companies to identify efficiency opportunities and investigate productivity solutions. As a result, these customized trailers have improved improve payloads by 10 to 15% and have increased each driver’s daily turns from five or six round trips, to eight or 10.
Titan Trailers manufactures THINWALL, a patented double-wall extruded aluminum (6061-T6 aluminum alloy) panel that first introduced the trailer industry to smooth side technology back in 1996. The THINWALL panel is a hollow-core extrusion that achieves high strength with light weight, similar to the way that corrugation turns paper into a high-strength board. The inner wall is thicker than the outer wall to absorb load impacts and to prevent interior damage from penetrating to the outside. The aluminum web between the walls is integral to the extrusion, with no mechanical joining. Titan completes the welding for one side of an entire THINWALL assembly—up to 53 feet long—in a single automated pass. Then, we repeat the process on the other side. The result is highly consistent, 100% machine-welded seams inside and out. Titan’s horizontal interlocking panels gain extra strength and stability much like the walls of a log cabin. The end-to-end seams withstand flexing stresses better when the trailer rolls and twists over rough terrain. A horizontal structure also eliminates welding seams at stress points on multi-axle rigs. The same THINWALL technology is also used to construct the floors of the trailers.
Travis Body & Trailer, Inc. has developed their patented VerTex trailer design, which combines Vertical panels of an Extruded, dual-wall trailer. With aerodynamic smooth sides, this design can come in Frameless, Frame-type, or Quarter-Frame configurations. It is available in either live floor or tipper models. Its live floor models are built in coordination with Keith and Hallco.
Trinity Trailer’s “Bridge” design and construction provide a number of benefits unavailable in conventional self unloading belt trailers. Flexible design allows their “Eagle Bridge” Trailer to haul a variety of payloads. This frameless steel trailer design allows the trailer to flex and twist in response to changes in ground surface. Their newest trailer, equipped with a 4-foot-wide belt, unloads in less than four minutes. Its stainless steel belt surface (the only one in the industry) does not need to be scraped of sticky stains, or swept of debris. It is also resistant to acids, corrosive chemicals, and oxidation.
Western Trailers builds flat floor tipper trailers, drop center tipper trailers, and live floor trailers for the refuse industry since the early ’80s. Western’s trailers have a unitized high-strength steel frame that is finished with the highest-quality paint process in the industry. All of Western’s trailers use corrosion and wear resistant aluminum to keep trailer tare weights down and payloads maximized. Western’s drop center 48-foot tipper trailers have 17 more cubic yards capacity over a typical flat floor tipper trailer. This extra capacity allows for less compaction of the load to get up to weight and less trailer loading damage, an added benefit is less load hang up when unloading. For customers that require live floor trailers, Western offers a time proven design with floors from Hallco and Keith.
Wilkens Industries provides multiple solutions to waste and recycling hauling needs such as their WALKING FLOOR trailers, push-outs, or tipper. Each of these products can be custom built for a customer’s needs. Its latest advancement is the patented X Series Transfer Trailer. This design allows direct transfer into the trailer from the waste collection truck via a loading dock. This allows for multi-modal waste transport in remote rural areas and inner cities not serviced by a transfer station.
While dumping a transfer trailer load can be accomplished with tilting the entire floor using heavy duty lift jacks, live floors (or walking floors) provide another option for offloading waste at its final destination. Live floors (often augmented by pusher blades) allow the transfer trailer 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 do not need the capital expense associated with tippers. In general, live floors are preferred for depositing waste at remote locations (most landfills). More versatile than hydraulic lifting jacks, 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.
Hallco Industries, Inc. produces the Hallco LIVE FLOORS conveyor system. This consists of three sets of bidirectional moving floors slats that can be installed into any OEM’s transfer trailer or retrofitted into a smooth wall trailer. They can also be installed in stationary bunkers or bins used for storing and feeding material into MRFs. Its design allows for top loading, compactor loading, or baler loading. Standard decking is available in lengths up to 53 feet long and a single Hallco drive can go up to 10 feet wide. Custom applications and dimensions are also available. Ease of installation is provided by snap-on slats and single-unit construction. Hallco’s new patent-pending surface mount sub deck is designed to satisfy the needs of trailers hauling and safely unloading food waste and other material with a high moisture content. This allows for seamless integration between an OEM’s leak-proof end dump or tipper style trailer and Hallco’s Live Floors conveyor. With simplicity as its goal, Hallco has designed this new surface mount sub deck for installation directly on an existing sealed floor pan and spaced far enough apart to prevent waste from building up under the slats (similar to the Hallco W Floor leak-proof system). This system supports any of their off-the-shelf slats and bearings, making it versatile for many applications.
As mentioned elsewhere in the article, Keith Manufacturing’s WALKING FLOOR conveyor is used by many players in the trailer industry, either as a standard feature, or a retrofit into an operating truck. It is designed with unique horizontal unloading and loading system capabilities. As such, this system can provide pallet and bulk material handling services, and can handle almost any kind of each type of cargo. The refuse and recycling industries utilize both mobile WALKING FLOOR trailers and stationary WALKING FLOOR bins. Their system can be found worldwide in a variety of applications. At a recently opened material recovery facility (MRF) in Alabama, Keith’s WALKING FLOOR system is being used to move paper, mixed plastic, and ferrous metals. Citizen participation rates in the recycling operation are increased by ease of use. Residents can use only one bin for waste and recyclables. The system can temporarily store recyclables and then feed them into a baler. In Spain, a waste company has employed the Keith LeakProof system. Its ability to contain up to 12 inches of liquid allows them to meet more stringent regulations concerning load leakage. An Asian customer has adopted their V-18 floor system to provide rugged durability against wear and tear from waste loads. The organic waste system utilizes a traveling conveyor that feeds the system and ensures an even fill of waste materials. Capable of storing up to 300 metric tons of organic waste, it also operates automatically when human operators are not present. A European application utilizes WALKING FLOOR technology to automate unloading, improving cycle time compared to manual offloading, which took up to 60 minutes to complete.
Truck Tarping Systems
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 are hydraulically operated mechanism that use arms and 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.
Mountain Tarp’s Open Top Transfer Trailer covers are designed for trailers up to 45 feet in length. It comes with a double armed deployment mechanism for end dumps 37 feet to 45 feet long. The mechanism’s 3/4-thick tarp pivot work with dual 3,900-pounds springs. The whole system comes in a pre-assembled front assembly.
Pioneer, a Wastequip Company, provides Strong Arm tarping systems for waste industry trailer trucks. These systems come with telescoping low arms, fixed gantry, and a ROLLMASTER Roller Assembly. The strong arms are made from 3/16-inch A5 steel and are operated by external cylinders. Utilizing an enhanced rack and pinioned model, the system is applicable for hook lift and roll off boxes of various sizes.
Pulltarps Manufacturing invented the Pulltarp spring return truck tarp system to make tarping quicker, easier, and safer. Their specialized Telescoping Tower tarp deployer was specifically designed for the waste industry. Its power up and power down hydraulic system is operated by a self-contained hydraulic power pack. This system raises 10 feet to easily cover a trailer fill with up to 40 cubic yards of waste. At 102 inches wide, its housing can handle extra wide tarps.
Roll Rite designs and manufactures customized, state-of-the-art, automated tarp systems for the heavy-duty trucking industry serving the construction, agriculture, waste, and recycling markets. These systems quickly and reliably contain and protect payloads, create a safer work environment for drivers, and maximize return on investment by increasing revenues and reducing cost of ownership. Roll Rite’s side-to-side lockdown system for transfer trailers, with its patented front and rear arms, is able to climb over heaped loads and reliably secure whatever is being hauled, in a safe and effective way. This eliminates climbing and eliminates cranking, keeping drivers in a safer environment.
A trailer tipper allows an entire load from a transfer trailer to deposited efficiently at a preferred location. It simply lifts up and rotates the trailer so the load falls out of the open end. A tipper can be fixed or portable and allow 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.
But, separating the disposal mechanism from the trailer truck itself greatly reduces the truck 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. Further efficiencies are created at the work face, which can be reduced in size because of the concentrated unloading of the tipper and the decreased time need to offload each truck. Overall, it can result in significant operational cost savings.
The actual disposal operation with a tipper requires a series of steps. After the waste transfer trailer backs up into the tipper, its load bed is decoupled from the truck frame. As the truck cab and frame drive a short distance away, the tipper lifts the front end of the bed up to a 90-degree angle with the ground while keeping the open rear and lower near the surface. Gravity does the rest, with waste falling out of the tilted bed. This can be done in half the time it takes for a self unloading truck.
Columbia Industries LLC provides a low-profile and bulk material handling portable tipper. This tipper can be towed to different locations at a site or over the road to a new location entirely due to its ease of transport and four-axle spring suspension. Over its 15- to 20-year average operating life, their Low Profile Tipper can handle 10 to 12 trailers per hour at an average load of 2 tons more than a self unloading trailer. Total cycle time to unload a trailer is approximately three minutes, while operating at a tipping angle of 63 degrees to the horizontal. Units are operated by a pair of multi-stage telescopic hydraulic cylinders and range in size from 50- to 65-ton capacity models. Optional features include a hydraulically actuated rotating backstop, and a secure operator cab equipped with heating and air conditioning.
Phelps Industries manufactures a Low Profile Tipper configured for over-the-road transportation. It can be taken apart by unpinning several major components, allowing it to be removed as a second trailer load in less than 15 minutes. Each portable tipper comes with its own self contained diesel-powered hydraulic drive unit that makes it independent of local power supplies, a feature that is especially useful in remote locations. These portable units come in several different styles, from a standard unit that utilizes a long approach ramp, or a low-profile model that uses a short approach ramp when space is at a premium. Built on a strong rigid platform, the tipper is manufactured 10 feet wide by the desired length (with standard lengths of 35 to 75 feet, at 5-feet increments). Standard tilt angles vary from 36 degrees, 40 degrees, 5 degrees, and 63 degrees, allowing for variable operating configurations to match available space and clearance.
Suspensions and Safety Gear
Given the harsh operating conditions associated with waste hauling, special care must be taken to ensure a safe and smooth ride. This requires more extensive suspension systems that are normally found in long haul truck. Such suspension allow the waste hauling transfer trailer to operate on rough (often dirt) service roads at landfills, as well as smoothly paved highways.
Link Manufacturing, Ltd. produces the UltraRide, a complete chassis air suspension system designed for both light- and medium-duty trucks (Class 4 and 5). It is most often used in emergency vehicles and buses, but also in towing applications. It is a total replacement system for an existing truck’s rear suspension system, not just a helper spring or leveling system. Installation utilizes existing manufacturer frame holes. Additional cross members increase stability and reduce frame stress from rough surfaces. Optional online diagnostics ensure that proper ride height and lift are continuously monitored. Its electronic air kit dumps to a height rather than a pressure, allowing the system to maintain base pressure for quick recovery.