ecycling and solid waste management R professionals identify construction and demolition (C&D) debris as a waste stream with potential for greater materials recovety and reuse. Across the state of Florida, for example, several components of the C&D debris stream currently possess viable end markets. Portland cement concrete is recov- ered, processed and reused as road base and other construction purposes., The asphalt paving industry utilizes milled asphalt as an ingredient in new hot-mix asphalt. Several markets exist for wood, most notably boiler fuel and colored mulch production.

One major C&D debris component not currently recycled in Florida, however, is gyp- sum drywall. This material can account for up to 30 percent or more in some types of con- struction. The results of a recent examina-

01 gy ILcyciing projects among three counties in Florida is presented here.

r

Motivation Florida’s population continues to grow at a rapid pace. New construction activity accom- panies this population increase and results in the production of construction debris. This material, combined with debris from demo- lition, renovation and storm damage, results in a sizable waste stream.

As elsewhere, current regulations in Flori- da allow disposal of C&D debris in permit-

drywall reeyeling by Timothy Townsend

and Chuck McLendon

ted, unlined sanitary landfills. Several recy- cling facilities, especially in southern Flori- da, remove valuable commodities prior to dis- posal. Concrete, asphalt, wood, metal, fines (soil) and cardboard frequently are removed, but gypsum drywall is not. The gypsum either is landfilled with the residual or ends up in one of the other recovered streams (e.g., fines) as an impurity.

Several incentives provide a motivating force for the development of gypsum drywall recycling programs. Gypsum represents the largest component of the C&D debris that currently does not have a market. Waste com- position studies show that gypsum drywall is often the second most prevalent waste type (by weight) produced during new construc- tion activities.

Several benefits also may be cited to keep- ing gypsum out or a ianar7fl. w nen CUSpOSed, gypsum dissolves and releases sulfate into water that percolates through the landfill mate- rial. In an anaerobic landfill environment where organic matter is present, microor- ganisms convert the sulfate to hydrogen sul- fide gas and other reduced sulfur gases. Hydrogen sulfide gas possesses the charac- teristics of having a “rotten-egg’’ odor notice-

- _.

With developing markets and available technology, gypsum drywall recycling needs only a viable collection infrastructure to succeed.

able at low concentrations. This gas also has adverse human health effects at high con- centrations. Several landfills around the U.S. are in the midst of lawsuits or remedial activ- ities as a result of neighbor complaints result- ing from these gases. In most of these cases, the source of the odor has been cited as dis- posed gypsum drywall in the landfill. The presence of gypsum drywall in processed C&D debris or fines used for daily cover at municipal solid waste landfills also has result- ed in severe odors in a number of cases. Some of these communities have reacted by limit- ing disposal of gypsum drywall in some types of landfills.

Markets Several possible markets have been proposed for the reuse of gypsum drywall, and a few 01 these are in practice in ditterent areas of the country. Markets discussed here for gyp- sum drywall typically apply to drywall from new construction activities. The potential for contamination with items such as asbestos, lead-based paint and other waste components limits the acceptability of drywall from ren- ovation and demolition, and so most recy- cling efforts focus on clean waste streams.

Timothy Townsend is assistant professor in the Department of Environmental Engineering Sciences at the University of Florida in Gainesville. He may be reached at (352) 392-0846 or ttown@ufl.edu. Chuck McLendon is a senior director at R.W. Beck, Inc. in Orlando, Florida. He may be reached at cmclen don@rwbeck.com.

Resource Recycling December 2000

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New cPywal1. Gypsum recovered from scrap drywall can be processed into new dry- wall. The material must be processed prop- erly to remove the paper and other impuri- ties. New drywall production is one of the larger drywall recycling markets in the north- western U.S. and western Canada.

A limitation cited at these locations, though, is that the gypsum plants have enough of their own scrap drywall to meet their needs. Utilizing scrap processed internally also pro- vides greater assurance as to the quality of the material. In addition, the companies that own and operate gypsum wallboard plants also own gypsum mining operations, and thus the cost and supply of raw material is not as much of an issue as if they were purchasing the raw gypsum elsewhere.

A trend in the drywall manufacturing industry, however, is to use synthetic gypsum produced by acid gas scrubbing from power plants. An air pollution filter traps sulfur com- pounds in a reaction with lime to form gyp- sum. Since new drywall plants are being located adjacent to such facilities, the avail- ability of this waste material may limit the reuse of scrap gypsum from construction in some areas.

Farm applications. Many agricultural uses exist for gypsum. Farmers apply gyp- sum in many locations as a source of sulfur and calcium for crops. Gypsum also imparts many beneficial qualities to soils. Gypsum aids in providing drainage for clay soils, helps to reclaim sodic soils and promotes healthy root growth. Gypsum has been applied to crops such as corn, soybeans, peanuts and vegetables. The biggest challenge faced by the gypsum drywall processor is educating local farmers and extension agents as to the benefits of using this material.

Cement content. Portland cement man- ufacture represents another major market for gypsum drywall. Mineral gypsum is added to Portland cement clinker when the cement is crushed in a ball mill. Gypsum aids in the control of setting times for Portland cement concrete and typically is present in cement at about 6 percent by weight. Cement manu- facturers often reuse scrap materials as min- eral resources, and gypsum drywall current- ly serves as a partial substitute for virgin gyp-

Important issues to the cement plant are adequate drywall processing (separation from the paper and reasonable size reduction) and a constant and reliable supply. Because the physical nature of the scrap gypsum drywall differs from the virgin rock gypsum, handling and conveying equipment modifications may be required to accommodate scrap drywall. These adjustments (such as the size of the hopper opening or the speed of the convey- or) are not a major problem, but the source of material needs to be consistent so that adjust- ments are not made continually.

Further prospects. Other potential mar-

~ l _ _ l l sum at a number of f d t i e s . __--

kets for gypsum include use in construction, both for construction materials such as bricks and blocks as well as for the construction of roads. Minor markets include grease absorber and cat litter. Markets for the paper from recovered drywall still require further development.

Incentives for development In Florida, several counties recently received innovative recycling grants (IRGs) from the Florida Department of Environmental Pro- tection (Tallahassee). The IRG program con- sists of competitive grants that provide finan- cial support to counties interested in explor-

ing new and innovative recycling activities. To date, three IRGs have been awarded for the specific purpose of examining the recy- cling of gypsum drywall from new construc- tion activities.

Citrus County was awarded a grant to examine recovery and reuse of gypsum in the production of new gypsum drywall and as an ingredient in the production of Portland cement. Citrus County partnered with Agri- cycle, Inc. (Columbus, Ohio) and Florida Crushed Stone (Brooksville, Florida) to estab- lish a drywall recycling program. The New River Solid Waste Association (Baker, Brad- ford and Union counties) was awarded a grant

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Reader service # 87 Resource Recycling December 2 0 0 0 m

Reader service # 173

to investigate use of scrap drywall in agriculture and+k the cw- struction of roads. Okaloosa County’s grant examined utilizing gypsum drywall as an amendment to compost for peanut farm- ing. While all of these programs examine slightly different end use markets, one of the biggest issues they all share is collection and processing.

lessons learned to date Although these three projects will not wrap up until early 2001, a number of lessons learned in the process can be shared.

Markets. The two most promising markets identified for Florida are agriculture and the cement manufacturing industry. Cement plants in the state have said the material is acceptable for reuse and would be willing to purchase such material if provid- ed as a constant, reliable commodity. The biggest challenge, then, is how to accomplish this.

A number of agricultural operations currently apply gypsum as part of farming operations. Some of these farmers also use synthetic gypsum from power plants and phosphate fertilizer manufacturers. Further development of this market would require education and outreach activities and would require assistance of county agricultural extension agents.

Processing. Processing of scrap drywall was one of the major concerns faced by the IRG projects. Several companies, includ- ing Andela Products (Richfield Springs, New York), American Pulverizer (St. Louis) and Shred-Tech (Cambridge, Ontario) among others, manufacture equipment specifically designed for processing drywall. Issues in processing include dust control and the separation of paper from the gypsum. Different processing techniques were investigated as part of the project, and it was determined that many types of existing equipment can be applied. A typical machine grinding drywall will produce about 93 per-

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c p t gyppgpm powder and 7 percent shredded paper, by weight. A hammermill normally used for grinding yard debris was applied

at the Okaloosa County project. Since the paper did not need to be removed prior to composting, screening the material was not nec- essary. For markets that require paper separation, screening is a necessary step. A trommel screen, for example, can be used to do both size reduction and screening in the same step because rotating the trommel causes the gypsum to break and be separated from the paper.

Dust is always an issue when processing drywall and can be con- trolled to some extent by using water misting, but the best strategy is to process material in a location where dust is not a major con- cern (appropriate regulations should be investigated). Larger-capac- ity equipment also can minimize dust by reducing processing time.

Collection and economics. Economics typically control whether a recycling program will work. In Florida, separation and collec- tion of scrap drywall from a construction site are what tend to dic- tate economics. Viability of recycling depends on landfill tipping fees; the costs of transportation, collection and processing; and the market value of the recycled gypsum. The economics and logistics of drywall recycling from commercial construction sites, where multiple loads of drywall could be sourced from a single project, typically are more favorable than residential projects.

The economics of the New River Solid Waste Association proj- ect were especially favorable because the primary source of scrap drywall was manufactured housing. Since drywall was the major component of the waste stream at the plant, plant operators were willing to separate the material if the tipping fee was lower than the landfill's and the same degree of service could be provided.

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into one box and hauled to the landfill when full. An econorpic analy; sis shows that even when the tipping fee is eliminated for source: separated loads of drywall, the contractor has little or no cost advan- tage to separate.

The difficult economic situation relative to site separation of dry- wall at the residential construction sites in Citrus County raised the question, “How are other areas of the country economically recov- ering drywall from new construction?’ Examination of systems in Ohio and North Carolina reveal that the success of the drywall recy- cling program results from the way in which waste is managed by contractors and subcontractors.

In many areas, for example, it is standard practice for drywall sub- contractors to be responsible for their own waste. They do not dis- pose of their waste in a container provided by the general contractor, but rather they remove and dispose of the waste themselves. In some cases, drywall companies decide that the time of their employees is better spent installing drywall than picking up waste, so they hire a scraping or clean-up service to remove the waste. In either case, the drywall scrap already is separated because of the existing system, and those disposing of the material have a definite economic advan- tage to find a cheaper disposal option. In fact, a number of the clean- up services also conduct drywall recycling themselves.

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The bottom line Florida continues its efforts to become a state where drywall recy- cling is a reality. Markets do exist, though in some cases a good deal of education and development is necessary. Processing technology does not have to be as elaborate or expensive as once thought. What it really comes down to is how to separate and collect the material.

RR More information on Florida’s Innovative Recycling Grant Program can be found on the Web at www.dep.state.fl.us/dwm/programs/recycling/directo ry.htm.

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