County brings processing in house, cuts costs
At its Woody Waste Recycling Facility, the Solid Waste Authority of Palm Beach County, Fla. (SWA) is chopping costs as well as waste. The agency has installed an integrated system of equipment that eliminates much of the manual handling previously required for waste processing. In addition to reducing labor, the system brings grinding in house, allowing SWA to lower its operating costs substantially.
SWA accepts approximately 170,000 tons of yard trimmings and clean lumber each year. The Woody Waste Recycling Facility processes approximately 100,000 tons of that, producing screened mulch for SWA’s compost facility as well as boiler fuel and material for erosion control.
Prior to integrating its processing system, SWA’s waste-handling methods were “basic by anyone’s standards,” says Pat Byers, the authority’s director for composting and vegetation services. Workers off-loaded waste from delivery trucks, shaking out each bag by hand and removing the bags from the waste stream. They spread the waste on the ground, removing contaminants and stockpiling the remaining material to let it dry.
For years, SWA had outsourced its grinding, but that option became increasingly cumbersome. “We were contracting services from a local grinding company that would come in with a tub grinder, reduce [the waste] and then pass it along to be screened to the one-and-one-quarter inches we needed for composting,” Byers explains. “As the volumes coming into the facility continued to rise, we realized that … hand sorting and tub grinding were simply not going to make it.”
Intent on improving efficiency, SWA hired Melville, N.Y.-based RRT Design & Construction to develop a conceptual design for an integrated processing system. Based on its design, the firm issued Requests for Proposals and specifically sought vendors that could provide one-stop assembly of the complete system. “A single vendor can better understand how one modification will affect a downstream function and make adjustments for that change,” Byers says. “There is simply a much better understanding of how the full system operates.”
SWA selected Newton, N.H.-based Continental Biomass Industries to construct its new processing system. Construction began in May 2000, and the system was online by October 2000.
Today, the Woody Waste Recycling Facility is processing 50 to 60 tons of infeed per hour. A grapple-equipped handler dumps the yard waste and feeds it to a pre-screener that doubles as a feed hopper for the system. The pre-screener uses heavy-duty discs to remove material measuring three inches or less in diameter, and that material is either conveyed away from the system or propelled to the picking station.
The picking station can be manned by as many as eight workers who remove contaminants from the waste before it enters the grinder. Material exits the grinder and cascades over four 10-foot screen decks, where it is separated again according to size. (Material measuring one-and-one-quarter inches or less in diameter is mixed with dewatered sludge in preparation for composting; larger material is used for boiler fuel and erosion control applications, or it is made available to the general public as a soil amendment.) Material designated for mulch is sent to a 48-inch wide stacking conveyor.
(Composted material goes through an additional screening process, passing over a bivi-TEC screen manufactured by Gleisdorf, Austria-based Binder+Co AG and supplied by Leola, Pa.-based Aggregates Equipment. That process allows SWA to produce various grades of compost, which is marketed by Houston-based Synagro to soil blenders, landscapers, construction project contractors, golf courses and smaller niche markets.)
By integrating its processing and reducing the labor required for handling woody wastes, SWA has reduced operational costs to such a degree that capital expenditures for the project will likely be recovered within five years. In-house grinding alone has made an eye-opening difference, Byers says. “In 2000, we spent about $650,000 to have someone come in to do our grinding; in 2001 we will save that much,” he notes.