A Convergence of Wastestreams

It sounds simple enough. Collected waste is hauled to a centrally located facility, called a transfer station, instead of being taken directly to a landfill. At the transfer station, the waste from multiple collection routes gets deposited on a tipping floor, where front-end loaders and other equipment push it into large, open-topped transfer trailers parked and waiting in a bay below.

The aim is basic to any successful business: save money. Consolidating larger amounts of waste into fewer transport platforms achieves economies of scale that reduce overall transportation costs. Measured in cost per ton-mile, it is far cheaper to move waste in larger semi-trailers designed for long-distance hauling than in multiple waste-collection trucks designed to gather and compact waste at pickup points along a relatively short collection route. The former requires less labor (fewer drivers), less maintenance (fewer and simpler vehicles requires less extensive maintenance), and a more efficient power plant (utilizing fewer gallons of diesel per mile when loaded).

However, the devil is always in the details. Creating a work space where the waste from multiple collection trucks can be consolidated and transferred to fewer, larger transport trucks involves more than just pouring the concrete for a tipping floor and pushing the waste into the transport truck with a front-end loader. The waste material has to be prepared for shipping and accurately weighed; loading and offloading waste has to be done in the most efficient manner possible; communication with the hauling trucks has to be continuous to ensure timely routing and dispatching; access and exit movements by trucks have to be properly choreographed to ensure steady material flows.

Why Transfer Stations?
It is too often forgotten that companies—even waste management companies—are in business to make money. It is inherently inefficient (that is, expensive) in term of dollars per ton of waste times the mileage traveled to the haul waste long distances in relatively small waste-collection trucks. The trucks that pull up to your curb once a week and pick up your household waste are not designed for long-haul transport. They are designed to efficiently gather and compact relatively large quantities of loose waste and then haul it the comparatively short distance to the local landfill.

Transfer stations are relatively compact structures consisting of a few basic structural elements. Entrance to the facility is via an access roadway or ramp that directs truck traffic to the open bay(s) of the transfer station. These bays typically consist of reinforced concrete floors enclosed by prefabricated metal building structures. The floors are not reinforced with steel rebar only. Further protection from the impacts of dropping and pushing waste and the movement of heavy equipment is often provided by steel rails set in the surface of the concrete floors. These rails are oriented in the direction of waste movement (towards the lower bay) and extend slightly above the concrete surface.

Depositing waste from collection trucks and loading waste into transfer trucks both occur on the transfer station’s tipping floor. Adjacent to and below the tipping floor is the receiving bay. This is a recessed ramp long enough to contain at least one transfer truck and deep enough so that the surface of the tipping floor is somewhat higher than the top of the truck’s trailer. Safety rails and guide bars are used to direct personnel and workflow. The preferred method of moving deposited waste from the tipping floor to the trucks is the front-end loader.

Loading and Offloading
This front-end loader is the workhorse of the transfer station. Unlike its tracked cousin operating at the working face of a landfill, the front-end loaders utilized by transfer stations are equipped with wheels to prevent damage to the concrete surface of the tipping floor. Equipped with an oversized bucket originally designed to scoop up and lift large quantities of relatively low-density materials, the front-end loader can be easily modified for operations in a transfer station. The first modification would be to replace the standard bucket with a specially designed refuse bucket. The refuse bucket has an additional spill plate welded onto the back of the bucket to protect the operator from being struck by spillage.

This is especially important since waste is very heterogeneous, both in material characteristics and object sizes. Often, parts of the waste material are so light and low-density that they can easily fall off or even get blown off the heaped pile of waste being pushed by the bucket. Airborne parts and materials can cause serious damage to the front-end loader’s drive train by clogging air intakes and covering up the radiator, causing he engine to overheat. In addition to protecting the driver and the cooling system, wheeled front-end loaders are also equipped with strike bars that prevent waste from wrapping around the axles.

Material Preparation
Some material preparation occurs in the waste-collection trucks themselves as they compact their loads during pickup and delivery. On average (with wide variations, however) waste at the curbside has an average density of 0.10 to 0.17 tons per cubic yard (approximately 7–12 pounds per cubic foot). Compactors inside the waste-collection trucks reduce the volume of waste by about 50%, effectively doubling the density of the waste to approximately 0.20 to 0.35 tons per cubic yard (roughly 15–25 pounds per cubic foot). Additional compaction is rarely done at transfer stations that utilize truck transport. However, baling operations that compact and bundle waste into tight “bricks” are often performed at rail transfer stations. The loads of compacted waste are lifted via a fixed crane into the open top of the train’s freight cars.

Weighing
Waste loads are weighed by having the waste-collection trucks drive over truck scales installed at the transfer station. In-ground scales can be installed in recessed pits or else directly on flat ground. In the first case, the elevation of the surface of the scale is flushed with the adjacent pavement. In the second case, the scale’s surface is somewhat higher than the pavement and can be accessed by means of approach ramps.

The weight of the truckload is measured by a series of load cells attached to strategic points on the frame of the scale structure. The weight of the loaded truck either deforms the load cells or increases their internal pressures. Deformation is a function of the stiffness of the load cell’s materials. In most cases, the load cells deform slightly under the applied loads and elastically return to their original shape once the load is removed. Electrical sensors measure the deformation of the load cells’ body and send electrical or (if the load cell is pressure activated) hydrostatic signals to a monitoring station. By tallying the readings from all the individual load cells in the scale, relating the measured deformations to the load cell material’s elasticity, the station can determine and display the vehicle’s weight. The trucks are weighed twice: once when they enter the facility to get a weight when fully loaded and once when leaving the facility to get a weight when empty. The difference between the two weights is the weight of the waste load deposited at the transfer station.

A good example of a truck-weighing system that has been successfully integrated into transfer station operations is that of the Survivor truck scales manufactured by Rice Lake Weighing Systems. Designed for durability and long-term performance, these scales are constructed of structural steel arranged in a support structure whose innovative design is intended to promote greater accuracy, less downtime, and greater operational lifetime. Several different models are available (aboveground, recessed pit, and portable) and can be custom built to exact specifications.

Results of the weighing operations are clearly indicated (even in direct sunlight) on the unit’s M-Series remote display. Its Intellibright feature uses a photo sensor to read available ambient light and adjusts the brightness of the display accordingly. The display apparatus provides readings from the unit’s MHMI digital weight indicators. The company’s Model 920i programmable HMI Indicator/Controller provides open connectivity to standard networking interfaces. A single 920i indicator is capable of handling multiple scales, storing, manipulating, and reporting data. Hard copies of this accumulated data are issued from Rice Lake’s ATK automated ticketing kiosks. The quick availability of weight tickets produced by a user-friendly interface reduces truck queuing and increases material movement efficiencies.

Dispatching
Communications with incoming waste-collection trucks and outgoing waste-transfer trucks is important to avoid unnecessary waiting caused by queues. Timing is everything, and detailed scheduling is established and ensured by communications and GPS tracking of incoming and outgoing traffic to ensure proper timing. Communicating with your vehicle fleet is not just a simple matter of talking to the driver over a two-way radio; a traditional CB radio will do that.

Today’s dispatching operations require more sophisticated tools to facilitate broader integration between operations and real-time data transfer. As solid waste operators continue to struggle with rising costs, the need to integrate systems and measure performance has never been greater. An example of a product that allows for this higher level of communication is the system provided by Routeware. Led by experienced solid waste industry veterans, Routeware recently unveiled its “Smart Truck” technology, which is designed to manage key operating variables in real time. What’s more, the system is capable of integrating with key elements of a transfer station operation to seamlessly link truck weights and scale systems.

The fully integrated “brains” of the system, the DMS 5000, integrates with a GIS-based routing system to route vehicles and show locations efficiently, all in real time, while capturing relevant service data and exceptions. This data enables the fleet to operate and dispatch more effectively from pickup to the transfer station. Routeware also has the ability to create custom packages and reports that leverage a wide array of add-on features, including: scale integration, digital camera and video capability, maintenance diagnostics, and RFID technology for service verification or container inventory purposes. The DMS 5000 is capable of organizing operational data into one easy-to-access-and-utilize package that is based on the operational and reporting needs of the customer. Wi-Fi allows for the real-time transmission of all of the integrated activities, making it simple to monitor the progression of routes and facilitate changes.

The addition of scale integration is a significant feature of the Smart Truck technology because it allows for onsite verification of container weight and collation of customer data, which can be critical to maintaining proper customer pricing. In addition, the scale integration feature can provide the means to monitor and optimize available truck capacity and to avoid dangerous and costly overweight situations on route and transfer vehicles. Weight data captured by the onboard scale system can also be directly integrated with third-party scales at a transfer station, landfill, or other destination.

Truck-mounted cameras can record virtually all route activities and serve as proof of service exceptions, eligible for additional charges. The digital photo function allows the operator to save and organize photos by customer, location or other service records specified by the operator, creating a visual record of the service rendered. The DMS 5000 can be integrated with a maintenance diagnostics program to monitor engine hours as a precursor to preventative maintenance schedules. The RFID feature automatically reads passive tags on containers to match and verify loads to customers and locations, and to create a daily log relative to containers or other assets located in the field.

Routing
Routing is the planning performed prior to dispatching the trucks on their collection and hauling routes. It is done to determine the optimum routes to be traveled by the collection and transfer trucks entering and leaving the transfer station. Until the advent of intelligent software, this task was usually more art than science. Routing software searches out the most efficient routes possible (routes that avoid dead ends and backtracking). Any truck movement that results in a truck retracing its steps is wasted movement and a loss of time and money.

Soft-Pak Inc. provides an entire suite of software management systems for the waste industry in general and truck routing in particular. Its “i-Pak” integrated software system that emphasizes inventory tracking, routing, and productivity. i-Pak’s Vehicle Management module tracks the performance of rolling stock (trucks, equipment, and vehicles) and stationary support equipment (bailers, compactors and container). So, in addition to choosing the most profitable route from a time and distance point of view, i-Pak can also track the actual productivity of individual trucks and the profitability of their various routes. e-Pak is a secure Web-based extension of the i-Pak system that allows complete i-Pak functionality without the need for additional hardware. e-Pak can work with existing personal computers with the option to use offsite data backups.

MarBorg Industries is a 75-year-old Santa Barbara, CA–based solid waste and recycling company that has utilized Soft-Pak systems since 1997. Derek Carlson, business manager for MarBorg, has this to say about Soft-Pak and the advantages it provides his company:

“Many things have changed in the industry in the past decade, but Soft-Pak has always enabled us to stay ahead of the curve. The most valuable benefit of using Soft-Pak is that it is a comprehensive turnkey system that links and tracks every line of our business so we do not have to waste time and money duplicating our efforts across different systems. A prime example of this integration is the development of the company’s Scale-Pak module, which takes the transactions from transfer stations, landfills, and recycling centers and automatically updates customer accounts for billing, tracks material inventory in and out, gives jurisdictional reporting and, of course, generates certified weight tickets. Before we utilized Scale-Pak, we would have to double- and triple-enter the same information to get all the benefits that we now receive automatically by using Soft-Pak in conjunction with Scale-Pak. We used to take the weight tickets that were generated at the various facilities and re-enter them into our billing system and then enter the information again in order to track inventory and perform our diversion reporting. Now, once the transaction has been completed at the scale, all of this information is automatically disseminated throughout the system, updating customer accounts, inventory, and diversion reports. We have saved hundreds of thousands of dollars in operational and administrative efficiencies over the past several years by using the fully integrated Soft-Pak systems.”

Desert Micro also provides a software package that can be utilized by waste haulers to optimize collection truck routes. Its Route Manager combines the tasks of managing billing, collections, dispatching, routing, and operations.

In addition to a complete customer database and the daily tracking of truck operations, Route Manager provides routing layouts and a transaction history of route changes and their effects on the bottom line. It can mange and integrate an unlimited number of routes. Route sequencing can be done in real time with stop highlighting, route splitting, or route combination. Each stop along the truck route can be annotated with detailed notes and comments, facilitating both operations and planning.

Operations
Inside the transfer station, waste-handling operations are performed to efficiently transfer waste from the smaller collection trucks to the larger transfer trucks. Here, the human element comes into prominence, as spotters and operators must coordinate and communicate effectively to prevent waste from building up on the tipping floor.

Transfer trailers are the end point of the station operations. All the deposited waste is directed to the open top of a transfer trailer parked in a lower bay adjacent to the tipping floor. The ability to quickly and efficiently top-load a transfer trailer increases dramatically with an East Manufacturing Genesis tipping-platform transfer trailer. The design of the Genesis sidewall eliminates the need for the center bar or pipe that has traditionally bridged the sidewalls’ midsection across the top.

To avoid damage to the cross-pipe when top-loading a trailer, an equipment operator is forced to load at the front and the back of the trailer, creating two uneven mounds of material. A center bar decreases loading efficiency by effectively splitting the trailer’s loading zone in two and making packing a challenge.

Without a crossbar in the way, East Genesis tipping-platform transfer trailers can be loaded faster, cleaner, and more efficiently. And a more even distribution of the load allows operators to improve load densities, yielding higher profits.

In addition, the Genesis has a smooth-sided design that maximizes load capacity and improves operational aerodynamics to improve gas mileage. Structural strength is ensured by 2-inch-thick sidewalls supported by internal ribs every 3 inches. Additional width of up to 4 inches increases the overall volume capacity of this model by up to 5.75 cubic feet compared to a traditional sheet-and-post sidewall. The East Genesis Tipper’s advanced design—extruded sidewall panels, floor-to-wall junction, and heavy-duty top rail—combine to add the extra strength needed to keep wall flexing to a minimum.

Unloading the transfer trailers when they reach their destination is made simpler with the use of live floors. Live floors may seem complex, but in principle they are actually quite simple. The floor of the transfer trailer is equipped with planks or slats that extend horizontally along the trailer floor. The planks are grouped together in units of three and move back and forth lengthwise in the trailer.

The first group of every third plank moves back toward the truck cab and away from the discharge opening in the trailer rear. Then, the second group of every third plank moves into position, which is then followed by the third group. By doing this movement in intervals of three, the truck’s load is not forced back into the trailer since two out of the three planks (and the loads on top of them) remain stationary. When all three groups have been moved back into the trailer, all the planks then move forward toward the open end of the trailer. This carries out the load toward the open end, where it is partially discharged. The truck itself inches forward as the load comes out the back. The process is repeated until the entire load is discharged. This mechanism allows for the easy offloading of large transfer-trailer loads without the need for hydraulic jacks to tilt the load like a dump truck.

Keith Manufacturing Co.’s Walking Floor system uses fewer moving parts in order to minimize wear and tear, maintenance, and repair. This hydraulically powered system stores waste material until it is ready to be conveyed to a compactor or other processing equipment.

Custom-engineered to the specific needs of each transfer station, Keith systems can withstand the impact of heavy materials and loading equipment. Power requirements are low, and no additional energy is needed for startup. In addition to municipal solid waste, the Walking Floor systems are suitable for scrap tires, scrap metal, cardboard, plastic, aluminum, and baled paper. A wide variety of floor slats are available to handle highly abrasive loads, such as construction and demolition debris.

Trailers outfitted with a Keith Walking Floor unloader improve transfer station efficiencies through the ability to unload quickly and indoors. Floor slats run the length of the trailer and are powered by a tractor-mounted power takeoff hydraulic pump to unload the material.

Trailers located at the dumping areas in the transfer station provide an inexpensive and simple solution to waste collection and disposal. Trailers store the waste until it is ready to be transported to the landfill. Then the trailers are taken to the landfill, where the waste is easily unloaded.

Once fully loaded, the semi-trailers carrying the accumulated waste are usually covered with tarps. Tarps perform double duty, protecting the load from the elements while they protect motorists from objects falling from the truckloads. The need for tarps is codified into every state law and regulation concerning roadway safety and protection from litter.

Tarps can be manually deployed and tied down by the station crew, or else mechanically deployed by the truck driver, as with rolling tarps. In most cases, automated rolling tarps are preferred for their greater efficiency and enhanced operational safety. These rolling tarps consist of a support structure made of a series of bowed frames, each of which is anchored to the truck sidewalls by rollers that allow them to slide forward and backward—expanding and contracting like an accordion. Being bowed or arched allows the frame to avoid contact with (and abrasive wear and tear from) the accumulated waste load.

Cramaro Tarpaulin Systems of Newark, NJ, provides a complete product line of tarp covers for transfer trailers.

The company’s “Slide ‘N Go” system covers and uncovers a heaped waste load in only a few seconds. A flexible cable design allows for safe on-ground operation.

The opening and closing operation is performed manually by a foldaway hand crank connected to a belt or chain drive, or else by a 1.3- to 1.8-horsepower electrical motor with heavy-duty gearing and 6-gauge duplex wiring for high-current loads. The bows of the cover frame are designed for long-term durability, covered with plastic sleeves and arranged in a configuration that allows compaction to a width of only 18 inches when not deployed. The tarps are vinyl, waterproof, one-piece construction sheets with out seams.

Landfill Gatekeeping
A transfer station, like any other industrial or construction site, is inherently dangerous to people who are unfamiliar with its operations. In order to protect the public, transfer stations are usually sited in isolated locations and/or surrounded by security fencing. The use of security fencing can also serve to keep blown litter in as it keeps trespassers out. Fences can also be equipped with litter-screen extensions made out of fine mesh that will protect adjoining properties from blown debris. A properly installed fence will also be dug into the ground to help repel burrowing vermin.