IN FLORIDA, MOUNTAINS OF construction and demolition (C&D) debris are vying for space with picturesque natural preserves and sunny beaches. As visitors and new residents flock to the Sunshine State, construction is reaching a feverish pitch, and landfill operators are struggling to keep up with the byproducts of growth.
Gypsum drywall has been a problem material because it represents a significant portion of a growing C&D stream, and decomposing drywall has been blamed for foul odors at C&D landfills, according to the Florida Department of Environmental Protection (FDEP), Tallahassee. To help find a solution, the FDEP provided a recycling grant to fund a drywall pilot project conducted by R.W. Beck, Orlando, Fla., and SCS Engineers, Long Beach, Calif. The project examined two methods of collection and separation, and analyzed the economic potential for sustained drywall recycling.
Florida's Orange and Seminole counties were deemed optimal sites for the pilot. The population growth in both counties has caused an increased need for housing, which has meant increased construction waste.
The pilot compared two methods of collecting drywall for recycling: source separation and disposal site separation. With source separation, drywall is separated at the construction site and placed in a roll-off container or pile. The drywall then is collected by a hauler and delivered to a recycling location for processing.
General contractors in Florida are responsible for the collection and disposal of construction-site waste. This method does not lend itself to separation because waste materials from various construction phases are mixed together. In other areas of the country, drywall contractors, not general contractors, are responsible for their own waste. This helps with waste separation because most of the refuse at a job site is drywall with only a few contaminants.
The project coordinators then located several construction projects interested in participating in the source separation program and placed roll-off containers at the construction sites. But although Orange and Seminole counties announced they would waive tipping fees for segregated drywall loads brought to disposal facilities, few private sector haulers participated.
Because contractors and waste haulers had marginal success separating scrap drywall, Orange County, along with the Republic 545 Landfill, Winter Garden, Fla., decided to explore disposal site separation. Disposal site separation involves the manual or mechanical separation of drywall from mixed loads of C&D debris. This method of separation placed no requirements on the contractor or waste hauler.
Once drywall was collected, finding a market for the product was important. Three potential markets were approached: agriculture, cement and new drywall.
Many farms use gypsum as a soil amendment for crops. Gypsum contains calcium and sulfate, which act as a calcium supplement for many crops. Also, gypsum decreases the acidity of soils. The agriculture market does not require paper to be separated from gypsum material because paper will naturally breakdown in the soil. This end-market, however, prefers a fine material consistency that can be spread easily onto soil.
Gypsum also is used as an ingredient in Portland cement to help control the cement's setting time. Generally, 5 percent to 10 percent of cement consists of gypsum. Recycled gypsum, such as the gypsum core from drywall, can be used as a substitute for raw, mined gypsum. Also, gypsum from waste drywall can be recycled into new drywall. However, this market tolerates the least amount of paper or other contamination.
To process drywall into a saleable product, technologies such as trommel screens, horizontal end grinders, tub grinders, hammermills and various other types of equipment can be used.
Both the Orange County Landfill and the 545 Landfill used a trommel screen to reduce the size of the material and remove most of the paper. Four processing operations were held during the pilot project.
Prior to loading the scrap drywall into the trommel screen, the drywall was preprocessed. Preprocessing involves breaking the larger sheets of material into smaller fractions by running over and tossing the drywall pile with a front-end loader. Preprocessing drywall allows the paper backing to more easily separate from the gypsum while it is processed in the trommel screen.
For any type of waste stream, low tipping fees can make recycling a challenge. This is particularly true in many parts of Florida, where the average C&D disposal tipping fee is approximately $15 per ton to $20 per ton. With low tipping fees, the cost for disposal may be less than the cost to recycle, depending on location and any surcharge for contamination.
Also, hauling costs are proportional to distance. As distance to a site increases, hauling costs will increase. Thus, if the recycling facility is too far away, the material will not be recycled. Similarly, if the distance to the end-market is too far, recycling becomes infeasible.
Regardless of collection and processing techniques, recycling drywall must be economically sensible. Tipping fees, transportation costs and the costs of virgin material are the most important criteria to consider when mapping an economic strategy.
|▸ Cost-effective. This is the most cost-effective form of separation because it does not require extra processing to remove contaminants.|
▸ Efficient. It eliminates the need for downstream separation.
▸ Quality. If not contaminated, this method typically results in the highest quality end-product.
|▸ Requires a widespread education and/or system change. Contractors and workers are not accustomed to separating C&D onsite.|
▸ Space requirements. Requires another container, bin or pile to be placed onsite.
▸ Contamination. Site workers often do not discriminate between disposal and recycling containers.
|DISPOSAL SITE SEPARATION|
|▸ Easy implementation. There is no change to the current system for contractors and haulers, nor a need for promotion and education.|
▸ Additional materials. Allows for separation of other C&D recyclables, such as wood and metals.
|▸ More costly separation. More labor, time and equipment are needed to sort materials, as compared to source separation.|
▸ Space. Requires space to spread mixed C&D loads to pull out drywall.
▸ Contamination. There is a potential for drywall to become contaminated when mixed with other C&D debris.
|Chart courtesy of R.W. Beck|