Dynamic DuoDynamic Duo
December 1, 2002
When St. Lucie County, Fla., recognized it was facing the all-too-familiar problem of dwindling landfill space, it sought a solution in short order. The community of about 140,000 was sending approximately 470 tons per day of municipal solid waste (MSW) to the St. Lucie county landfill, and only an estimated 20 landfill years were left.
Working with Camp, Dresser & McKee (CDM), Cambridge, Mass, the county decided to build a new facility: the St. Lucie County recycling and baling facility in Ft. Pierce, Fla. Located about 1 mile from the landfill, the transfer station has been a catalyst for drastic improvements since it began operating in August 2001.
“We broke ground in August 2000 and had the ribbon-cutting ceremony a year later. So far, the facility is operating above expectations,” says Alex Makled, CDM's consultant in charge of implementing the project.
Initially, county officials just wanted to continue accepting waste more efficiently. Officials visited about a dozen facilities to examine the possibilities. And the county considered continuing with conventional landfilling or incinerating waste. Based on recommendations, the county eventually decided its best option was to convert the landfill into a balefill and use a transfer station to sort and bale waste.
“We chose baling because it increased landfill life, costs less to operate, and there was no increase in tipping fees for residents and customers,” says Ron Roberts, St. Lucie county's assistant solid waste manager. “Also, it doubled the life of our facility from 20 to 40 years.”
The Board of County Commissioners approved the facility's design and construction, which totaled approximately $10 million. Then St. Lucie hired Adams Robinson's offices in Dayton, Ohio, and Orlando, Fla., to manage construction. Disposal continued at the former landfill during construction.
The major challenge of the new facility, Makled says, was to make the transfer station large enough to not only bale municipal solid waste (MSW) but also to incorporate the facility's recycling programs. “When we visited [other] facilities, we asked what they would do over again if they could,” Roberts says. “Virtually all said they needed more room. Our tipping floor at the time was more than 50 percent larger than the largest we visited, and they were taking in about 1,000 tons more per day than we were.” St. Lucie also had to consider processing capacity per hour, bale densities per cubic yard, baler warranty and manufacturer support, Roberts adds.
Additionally, the county wanted to provide better traffic flow. With the previous system, which did not include a transfer station, trucks would drive to the scales then take a 2-mile ride to the St. Lucie landfill face to dump waste, Roberts explains. “[Trucks] would drive over mud and get flats, and we would have to help pull them out,” he says. The new transfer station tipping floor is dry, so haulers no longer get stuck.
Although it typically only processes about 400 tons per day, the new facility can accept up to 800 tons per day of waste. It features a 50,000-square-foot tipping floor about the size of a football field, a second level that houses two Milan, Italy-based Macpresse International balers, a leachate recycling system, and a recycling drop-off center for residents and customers. Inside the roof of the tipping floor, 10 exhaust fans change the air from the outside every six minutes to reduce or eliminate odors and dust.
Haulers drive to the tipping floor where they are weighed and then are directed by staff members where to dump. After emptying their loads, trucks return to the weigh station. The floor has a metal aggregate coating, called Anvil Top 300, instead of concrete, which was worn out at many of the facilities officials visited, Roberts says. “After 15 months, [our] floor looks like it did the day we opened it,” he says.
Once waste is dumped, loaders roll the loads over and inspect them for prohibited materials and pull out corrugated cardboard and metal that can be sold. Waste then heads up a conveyor, travels 13 feet down onto the baling floor and enters the baler hopper, where it is compressed with 250 tons of force. This squeezes out most of the water and produces bales measuring approximately 2.3 cubic yards each. Bales are wrapped with five pieces of wire and are loaded onto roll-off trucks. “Each bale of waste contains about two years' worth of waste generated in an average St. Lucie home,” Roberts says.
To manage liquid emitted during baling, a leachate system that includes a conveyor transports the gas and transfers it back to the waste where it is absorbed. This minimizes leachate generation from the baling process, Roberts says.
All of the processes are housed under one roof. The new facility also has significantly improved the county's disposal costs and efficiency, Makled says.
Before using the balefill, the county modified its operating permit to comply with its new system, as well as to reduce daily cover use. Currently, the facility uses a spray-on ConCover 180, which the Erie, Mich.-based manufacturer New Waste Concepts says lasts up to one year. “We don't have to use daily or intermediate cover anymore,” Roberts says. “Daily cover is 6 inches per day of dirt, which takes up about 25 percent of the space.” This reduced the county's dirt costs by 15 percent and saves balefill space because the facility is only using about 5 percent of the dirt that was required before, Roberts says.
The facility also is “nicer to look at,” Roberts says. With conventional landfilling, garbage is loose and some tends to fly away, he explains. But because St. Lucie now bales the waste in dense cubes that are tied, this virtually has eliminated birds and blowing litter. “It's aesthetically more pleasing because when you have to make an outside slope, the traffic can see the loose garbage,” Roberts says. “When you're baling, you're stacking the bales like stairs, and it looks almost like a dirt wall to passersby.”
Efficiency-wise, the balefill uses 45 percent less airspace and requires 60 percent less diesel fuel — 3,000 gallons less per month — because machines are not working at the landfill as long.
“Solid waste compactors and dozers use a large amount of fuel,” Roberts explains. “Now we run trucks to haul the bales to the working face, which is a 4-mile round trip.” Prior to baling, the county used more than 8,300 gallons of fuel per month. Now it uses a little more than 5,000 per month.
The time haulers are onsite also has been reduced by about 80 percent, and landfill density has increased by 39 percent. “Our in-place density prior to baling was 1,149 pounds per cubic yard,” Roberts says. “After six months of operating as a balefill, the in-place density increased to 1,680 pounds per cubic yard.” Roberts expects the next flyover of the landfill, scheduled for March 2003, to show a density of close to 2,000 pounds per cubic yard.
To conduct a flyover, the facility determined how many cubic yards of space were used during a given time frame. To calculate how many pounds of waste were in each cubic yard of space, officials then determined how many tons of waste went into the space used.
Economic and environmental evaluations — conducted every six months to help the county review waste densities, operational costs, savings and revenue generated from recyclables — indicate the county is saving money and having less of a presence on neighbors.
The cost of conventional landfilling was approximately $1 per ton higher than baling costs, Roberts says. The facility estimates that it will process about 150,000 tons per year, a cost savings of $150,000 per year. This does not take into account the revenue received from recovered cardboard and metal. The new baling facility recovers approximately 6 tons of cardboard per day, a 600 percent recovery increase compared to the former landfill; 8 tons of metal per day, a 400 percent increase; and 1 ton of end-of-life electronics per day. All loads are inspected for prohibited materials, which aids with recovery.
Because all baling and waste handling and transfer is confined to the indoors, weather and birds are not a factor, and leachate, odors and landfill gas have been reduced. Litter has been eliminated, and community relations have improved because neighbors no longer see the garbage. Environmental analyses consider aesthetics, litter, odors, gas generation and leachate inspections.
Although long-term benefits already have surfaced, Makled says the facility can function as a traditional transfer station in the future if the county decides it no longer wants to bale waste. “After the design life has expired, the facility easily can be converted to a traditional transfer station, so the county does not have to build another one down the road,” he says.
However, it's unlikely St. Lucie will abandon its balefill and transfer station. The county recently received honorable mention from the Florida Institute of Consulting Engineers' engineering excellence awards in January 2002 — less than six months after the facility began operating.
“The project was a joint effort in terms of the idea and in looking for ways to extend the useful life of the landfill. I give St. Lucie credit to being the pioneers in this field,” Makled says, indicating he believes the project is a great success model. “People really need to look into their current ways of handling waste and not be afraid to try new things.”
Danielle Jackson is a Waste Age contributing editor based in Davenport, Iowa.