Investigation of Reactions Occurring in Municipal Solid Waste Residues
Each year more than 290 million tons of municipal solid waste (MSW) is generated in the U.S. Understanding the reactions occurring in waste during disposal, transport, and storage is important to move towards an integrated waste management strategy. Recently some landfills in the U.S. have been reported to exceed the regulatory temperature range, causing numerous regulatory challenges. The reason for this phenomenon is still unidentified. In addition, the co-disposal of the MSW ash in landfills lead to various reactions which can impact the landfill environment. Understanding the reactions occurring in the MSW and in ash is essential to minimize and prevent numerous issues in the current waste management system. This work focuses mainly on two key aspects that can help with better understanding of the reactions occurring in different steps of the waste management process. The first phenomenon studied is the issue of elevated temperature landfills (ETLFs). A method was developed to conduct experiments in lab using synthetic MSW to establish the performance of thermal pyrolytic reactions similar to landfills. The first set of experiments were conducted under controlled temperature environment to understand the impact of pressure, moisture, and temperature on MSW pyrolysis under simulated landfill conditions. In the second set of experiments, controlled heat input approach was used on the same type of waste. Under the controlled conditions, the critical process indicators such as CH4/CO2 gas composition ratio, hydrogen concentration, temperature, and pressure were investigated. The experimental findings enabled the identification of moisture windows that encourage the reactions producing undesirable gases from the waste. The results also show that the hydrogen generation in the waste is highly dependent on the availability of methane. A thorough understanding of the impact of different parameters on ETLF conditions was achieved. These experimental findings provide practical knowledge on trends in gas concentration changes and energy changes in abiotic processes in waste occurring in landfills. The second aspect studied was the reactions occurring in MSW combustion ash at different temperature ranges. The aim of the study was to identify the species participating in the reactions causing mass loss and heat release and the gases produced from these reactions. MSW ash was studied using material characterization and thermal analysis. Gas analysis was used to quantify generation of hydrogen from the ash in the lab in conditions same as during transportation. The combined analysis identified the decomposition and dehydration reactions occurring in ash that are responsible for increase in temperature and production of undesirable gases at different temperatures. These experiments provide useful data for MSW ash handling and re-use. As an effort to enhance the MSW ash, additives such as gypsum was studied for solid residue improvement. These experiments focused on improving MSW ash with additives to render it inert and to enable better extraction of recoverable metals. Insights from these experiments can lead to a way of profitably combining materials with MSW ash that can open a new avenue increasing the value of thermal processing facilities and help divert MSW from going directly to landfills.
Elevated Temperature Landfills, Abiotic Landfill Decomposition, Municipal Solid Waste, Solid Waste Management, Waste-to-Energy Ash, Thermal Analysis, Other Chemical Engineering
City University of New York - City College
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