Technology Brief

Evaluation of the Potential for Composting Gypsum Wallboard Scraps

This technology report evaluates the potential for using composting as a means of recycling clean scrap gypsum wallboard and scrap wallboard paper.

Gypsum wallboard can technically and economically be recycled into new wallboard, but there are limited areas with nearby wallboard manufacturing facilities. Additonally, wallboard manufacturers can use only the gypsum powder leaving waste paper remains, which contain both gypsum and paper. Options for recycling the wallboard gypsum and paper together are important alternative markets.

This study, issued by the Clean Washington Center (CWC) and E&A Environmental Consultants, Inc., examines the feasibility of recycling scrap gypsum wallboard and scrap wallboard wastepaper as a bulking agent in a composting process.

PROJECT APPROACH

Mixing the composting feedstocks with a bulking agent is a critical task in composting. Bulking agents in the mix aid in providing the necessary porosity, balancing the carbon to nitrogen ratio, and absorbing excess moisture. The CWC study utilized a biosolids composting facility, but the results are applicable to yard and animal waste composting operations as well.

In this study, four compost mixes were examined with different mix ratios of gypsum, yard debris, and biosolids, in 21 cubic foot composting bins. Since the function of mixing is to combine the biosolids and bulking agents to create a uniform, compostable mass, the mix ratio, as well as the method of combining the biosolids and bulking agent, will affect the physical properties of the mixture.

The mixes were loaded manually into bin composters and composted/cured for an eight-week period in which porosity, temperature, oxygen, moisture, odor, decomposition, visual, and pH were monitored and maintained within optimum ranges. There were not significant differences in odor production between mixes.

PRODUCT ANALYSIS

At the end of the test, the volume and weight of the product was determined. In addition, the product was screened manually and tested for several product quality parameters (e.g., calcium, boron, and organic content) to determine the benefits or detrimental effects of the addition of the gypsum wallboard to a composting process. All mixes reached temperatures suitable for pathogen destruction (per EPA regulations). A germination test was done to see if the material had any toxic effects.

The study also compared the rates of degradation of the small (less than one-quarter inch) and the larger pieces of paper (approximately 2-inch diameter) during the compost process. The smaller pieces degraded almost completely, and the larger pieces degraded an average of 40% by weight during the process.

The screened end product had some noticeable differences, such as the presence of gypsum powder in greater quantities as the mix ratio of gypsum scrap was increased. There was no paper present in the screened product, and little remained in the overs.

APPLICATIONS

The composting industry may consider using gypsum wallboard scrap and the wastepaper remains as a resource to supplement other bulking agents. For facilities composting biosolids, gypsum can be utilized as the bulking agent to provide necessary porosity, balance the carbon to nitrogen ratio of the mix, and absorb excess water present in the biosolids.

Yardwaste composting facilities which receive high volumes of grass during one part of the season and do not have an adequate supply of woody bulking material to provide porosity, may find that a mix supplemented with chipped wallboard is an appropriate aeration component to help prevent the generation of odors.

Additionally, it is feasible to compost the scrap paper removed from wallboard which is recycled and processed for reintroduction into wallboard manufacturing. The paper serves as a carbon source and a moisture absorber.

CONCLUSION

This study illustrates that gypsum wallboard can be successfully incorporated into the composting process without hindering end product quality. As with all composting operations, aerobic conditions must be maintained (through aeration or mix porosity) in order to limit odors. Product end use, process control, and grinding optimization efforts are important factors affecting successful incorporation of gypsum wallboard into a compost operation.

This technology brief was prepared by the Clean Washington Center. The Clean Washington Center is the Managing Partner of the Recycling Technology Assistance Partnership (ReTAP). ReTAP's mission is to advance industry's use of recycled materials through technology extension services. ReTAP is an affiliate of the national Manufacturing Extension Partnership (MEP), a program of the U.S. Commerce Department's National Institute of Standards and Technology. ReTAP is also funded by the U.S. Environmental Protection Agency and the American Plastics Council.

Fact Sheet Issue Date: October 1997