Florida’s Palm Beach County Solid Waste Authority believes a transfer station should be dedicated to just that.

By Charles D. Bader

Transfer stations have been in widespread use for many years now. The appeal of these useful facilities has been understandable. Particularly for municipalities that must rely on remote landfills, the use of strategically located transfer stations that effectively integrate a fleet of collection trucks with a fleet of large transfer vehicles can result in significant economies in both hard and soft dollars. The hard-dollar savings result primarily from the shorter runs per route by the collection vehicles and include

• lower driver labor costs;
• reduced fuel consumption;
• reduced maintenance costs; and
• more efficient trailer operations.

Among the soft-dollar costs that are important to the municipality, its solid waste division, and its contractors are

• reduced emissions;
• less traffic congestion;
• reduced mileage and hence wear on local roads;
• shorter wait lines at disposal facilities; and
• more convenient resident drop-off points than at a landfill.

All of these advantages accrue from the traditional use of transfer stations for transfer of waste from the collection trucks to the large trailers. However, the use of transfer stations has become so ubiquitous that some municipalities have endeavored to increase the utility of these facilities by expanding their functions beyond just transfer. In some cases they have turned transfer stations into dirty MRFs or other types of macro processing centers. This approach was persuasively presented in this magazine by Lynn Merrill (see “Transfer Trailer Now Leaving Gate 4A: The Transitioning Transfer Station”), who wrote:

While the immediate design need for a transfer station is to move MSW quickly through the building, transfer stations can be designed to allow a community to maximize waste diversion opportunities. As with a regional airport hub, with collection trucks acting like commuter aircraft and transfer trailers like jumbo jets, a transfer station can become a gateway in which macroseparation of loads can occur that are then dispatched to other facilities that can perform microseparations into marketable commodities. Through proper site selection and sizing, it becomes feasible for the facility to become a catalyst that maximizes route efficiencies while opening new market opportunities by not constraining the system to construction and demolition (C&D) processing facilities, material recovery facilities (MRFs), and composting facilities that are within driving range of the collection truck.

While the possibilities are intriguing, not every municipality believes that this is the best use of transfer stations. Notable among these is the Palm Beach County Solid Waste Authority. Director of Operations Mark Eyeington is most emphatic about this, saying, “The goals of our five transfer stations are, one, to accept incoming wastestreams with maximum efficiency; two, to quickly transfer these streams to the proper trailers without mingling them; three, to maximize the trailer loads to the legal over-the-road weight limits; four, to achieve an overall ratio of four and a half collection truck loads to each trailer load; and five, to route these trailers to the county’s processing/disposal facilities. Our transfer stations are integral to our overall waste handling system, and they must operate at peak efficiency to enable our overall system to handle the volume of waste that Palm Beach County generates each day. That’s challenge enough.”

Palm Beach County does indeed present quite a challenge. The county has a population of 1.25 million residents and sprawls over a 2,000-square-mile area. Since 72% of all waste generated in the county passes through these five transfer stations, the throughput requirements are tremendous (1,332,549 tons in fiscal year 2004 as shown in Table 1). And on peak days (usually Mondays), these transfer stations receive as much as 6,300 tons of incoming waste from all over the county. At a recent presentation to SWANA, Assistant Director of Transportation Mike Berg reported that the fleets coming to and leaving the five transfer stations log 2.85 million miles each year!

“For that reason,” Berg says, “virtually our total effort must be expended to rapidly and efficiently transfer each stream of waste—solid waste, vegetation, and corrugated and commingled recyclables—to the proper processing facilities: our waste-to-energy plant, our woody waste recycling facility, and our MRFs. About the only function we perform that is not exclusively a transfer is to serve as a drop-off location for the convenience of residents.”

Residents bring their recyclables (i.e., all plastic containers #1–#7, glass bottles and jars, aluminum cans, aluminum foil, aluminum pie plates, newspapers, corrugated cardboard, magazines, catalogs, brown paper bags, milk and juice cartons, and drink boxes). In addition, residents may drop off antifreeze, fluorescent bulbs, used motor oil and filters, household and automotive batteries, propane tanks (household size), and electronics (computers, monitors, keyboards, televisions, stereos, printers, fax machines, scanners, VCRs, DVD/CD players, video cameras, and cell phones) daily at all transfer stations.

Transfer Station Design
Since the five transfer stations were built at different times, their configurations differ somewhat from one another. The greatest revision is now underway as the Lantana station is being expanded and modified to handle its wastestreams. Under construction is a new co-located building that will feature six loading pits and be dedicated to unloading truckloads of MSW and vegetative waste and reloading each of those wastestreams into trailers. The existing Lantana building will then be devoted to handling recyclables (separate streams of corrugated and commingled recyclables). A third building (actually a canopy-covered drive-through) will accept and transfer household hazardous waste.

It should be emphasized that while the five transfer stations differ in detail, the overall transfer methods and flows are quite similar. All are designed for high throughput, top-loading operations. Each site has multiple steel-covered concrete drive-in pits into which the top-loading trailers enter. Each pit is 8 feet deep, so the top of the trailer in the pit is 1 foot below the tipping floor level. Collection vehicles normally deposit their loads on the tipping floor adjacent to each pit where the accumulated inventory awaits the arrival of the trailer returning from one of the processing/disposal facilities (the waste-to-energy facility, one of the MRFs, the woody waste recycling facility, or the landfill). While some trailers are being loaded, others may be getting tarped or weighed out on the platform scale before proceeding to the scalehouse for a transaction ticket prior to departure to the disposal/unloading location.

“Each of the loader operators manages the material deposited on the floor by the four to five trucks unloading at any one time,” Berg explains. “Operators can stage the waste in front of any designated pit, and either load a trailer directly or inventory the waste while waiting for a trailer to return to the terminal area for loading. Radio communication is used by all employees at the transfer stations.

“We try to position the streams to keep them separate, so for example, we designate different pits for corrugated and commingled recyclables. To accommodate collection trucks that collect mixed loads of recyclables (corrugated on one side of the truck and commingled on the other), the unloading corridors are so designated that the truck driver can dump loads from each side of his compartments to the cordoned-off areas appropriate for each waste recycling category for later loading into segregated trailers. The loader operator makes sure that when a truck unloads the corrugated, there is no commingled inventory nearby, and vice versa. The same precaution is made to keep MSW from getting mixed with vegetative waste.”

When the trailer is in place, a front-end loader begins to push the material into that pit. “As the material is deposited into the trailer, a mobile or stationary excavator equipped with a clamshell grapple evenly distributes and compacts the material in the trailer,” Berg says. “The excavator uses that clamshell-like attachment to pack the waste down, a process that is necessary to maximize the trailer’s payload of light-density garbage and trash. The excavator packs out a trailer to approximately the correct weight, which may be 300 to 400 pounds less than the 80,000-pound over-the-road limit. The operator monitors a scale indicator in order to load approximately the correct payload without going over the gross weight limit. If a vehicle is over or significantly under the weight limit, material can be added or removed to reach the optimum weight.”

The load is then ready for tarping to ensure that waste does not blow off during transit. A scissors lift at each transfer station is used to elevate an employee to adjust a tarp. It can also be used to enable him to cut off any protruding branch that is preventing a tarp from unwinding to secure the load. Berg says the entire fleet of trailers is being converted to 12-V tarp motors to prevent shoulder injuries to employees doing the tarping.

Handling Vegetative Waste
Vegetative waste is handled somewhat differently because of the nature of the material and the sheer magnitude of vegetation in Florida. Under state regulations, this type of waste cannot be landfilled so it must be processed in other ways. There is so much vegetative waste in Florida that it represents 22% of the total waste handled at the transfer stations, and the transfer stations only handle a portion of it. Transfer stations cannot accept C&D waste or land-clearing debris primarily because of the oversize of the material, which could damage the trailer. For this reason, C&D waste and land-clearing debris is trucked directly to the landfill.

“The yardwaste and other small vegetative waste is accepted at the transfer stations and transferred to trailers in much the same way MSW is handled,” Berg says. “The trailers take these loads to our woody waste recycling facility, which also accepts residential and commercial deliveries. There, approximately 100,000 tons per year is processed into a screened mulch for the authority’s compost facility or for use as a soil amendment. The woody waste recycling facility processing includes contaminant removal, drying, mulching, and screening prior to end use by other authority operations. Processed yardwaste is transported to the authority’s compost facility in 100-cubic-yard walking trailers (the same ones used at the transfer stations).”

Hurricane Overload
“Last year’s unusually severe hurricane season almost literally swamped the capacity of Palm Beach County’s transfer stations,” Berg says. “We were able to ramp up about 10% over our normal capacity to handle some of this additional vegetative waste, but the 3 million yards of the hurricane-produced vegetative waste (which included large amounts of spoiled food) was the equivalent of four to five years of normal vegetative waste generated in the county. The load was too great, both for our transfer stations and our woody waste recycling facility, so we had to devise another method of handling it.”

“We identified 10 temporary debris sites that could be used to accept the overload of vegetative waste generated by the hurricanes,” Eyeington recalls. “We contracted out services to private contractors who accepted the debris as it was trucked in, stockpiled it, and eventually ground it or otherwise processed it into a form that our other facilities could accept as mulch for compost or land application or as RDF for fuel for nearby cogeneration facilities. Despite the magnitude of this output, we had no problem in placing it without resorting to landfilling. I recall that the sugar cane mulch was particularly popular because it also put organics back into the soil.”

2004 Transfer Station Results
Including its share of the hurricane-produced vegetative waste, Palm Beach County’s 98-employee transfer station system processed 293,538 incoming truckloads of waste and loaded and delivered 64,106 trailer loads of MSW, vegetative waste, and recyclables last year. Remarkably, costs were less than $9 per ton for transportation and handling. And in the process, it supplied critical services for the other elements of the overall Palm Beach County Solid Waste Authority system and the residents of the county. For example, the transfer stations reliably supplied feedstock to the county’s waste-to-energy facility that burns it 24 hours a day, seven days a week, generating enough energy to power all of the Solid Waste Authority’s facilities as well as 30,000 homes in Palm Beach County. And perhaps most impressive, those transfer stations played an important role in Palm Beach County’s 80% landfill diversion rate.

Charles D. Bader is with Dateline II Communications in Los Angeles, CA.

MSW - Elements 2006