Modeling of Hydrogen Sulfide Generation from Landfills Beneficially Utilizing Processed Construction and Demolition Materials
Investigators: University of New Hampshire
Recycling of construction and demolition (C&D) debris has increased in recent times, with positive environmental and economic benefits being realized from utilizing C&D “waste” materials as resources. Resulting policies at the federal and state levels and economic structures have supported this increase in recycling. For example, tipping fees and regulatory structure (waste bans in Massachusetts) have expanded the C&D processing industry in the northeast. One of the products produced from C&D recycling is C&D fines, which often include some quantity of sulfate from gypsum drywall. Use of fines containing sulfate in an anaerobic environment can result in the formation of hydrogen sulfide (H2S). Because of H2S concerns, there is a growing problem in the Northeast relative to recycling or disposal of C&D fines. The long term focus of Massachusetts Department of Environmental Protection (MassDEP) and other State solid waste regulators in the Northeast is to improve management of C&D fines and to develop improved end markets that are less dependent on landfills. In the short term, however, regulators must continue to work with C&D processors and landfill operators to improve the management of C&D fines and residuals at active and inactive landfills.
Increasingly over the past decade, C&D debris processing residuals and fines have been used as landfill daily cover material and to close and cap old landfills. C&D debris processing residuals and fines (C&D fines) are favored by numerous landfill operators as an alternate daily cover material (ADC) as they are superior in many ways to traditional soil cover materials. However, one potential issue with use of C&D fines has been the increase in landfill gas (LFG) odors due to production of H2S and other reduced sulfur compounds. Increases in generation of reduced sulfur compounds in the LFG stems from the small pieces of gypsum wallboard contained in the fines. These LFG issues were unexpected and many landfill operations had to increase resources in LFG management and odor abatement as a result. Regulators have become involved in several states, implementing policies for use of C&D fines, management of LFG and control of odors. As a result, some landfills have stopped utilizing C&D fines altogether.
This research project had the following objectives:
-Compile and evaluate existing LFG, hydrogen sulfide and C&D fines data at nine northeastern landfills.
-Where necessary, conduct supplemental testing of H2S gas concentrations and determine sulfate content of C&D fines, if still being accepted by the site.
-From the empirical data, develop a first order model to predict H2S generation in MSW landfills in the northeast resulting from disposal or use of C&D fines in the landfill.
Development of a model to predict H2S generation resulting from acceptance of C&D fines in a typical MSW landfill provides valuable information for C&D processors, landfill operators and regulators. Since the model is based upon total sulfur input, C&D processors can refine their operations to reduce gypsum content in fines or reduce the production of fines. Landfill operators can better evaluate allowable quantities of C&D fines that may not impact LFG significantly or weigh the potential impacts of increased LFG management against the economic benefits of accepting the fines.