(405e) Investigation of Reactions at the Gas/Solid Interface of Municipal Solid Waste Residues

Reactions at the gas-solid interfaces are present during the treatment/combustion of municipal solid waste (MSW) in waste-to-energy facilities, leaving a solid residue, ash, that has significant potential to valorize. Storage and transport of MSW ash after combustion in waste-to-energy facilities allows for reactions at the gas-solid interface such as corrosion and hydration. These reactions can potentially lead to issues such as production of undesirable gases, rise in temperature above regulation limits, and the consumption of recoverable metals and minerals from the ash. The issues of crucial concern in the waste management industry are elevated temperature in landfills, and the production of hydrogen from ash.

In order to minimize these issues in MSW management, it is necessary to understand the effect temperature, pressure, moisture content, and ash content on the rates of reaction and the products of the reactions. It is also important to study the characteristics of MSW ash and the its contribution in the reactions occurring in a landfill.

The first part of the talk focuses on understanding the impact of pressure, moisture, and temperature on MSW pyrolysis as a possible cause for elevated temperature in landfills (ETLFs). MSW provided from landfills is tested under simulated landfill conditions in controlled temperature and pressure environment. The effect on landfill gas concentrations (CH₄ and CO₂) in the reactors over a range of temperatures (49 to 177 °C) and moisture content (40 to 60 wt.%) in the presence of biological inhibitors are studied. Results from these tests identify a range of moisture content that impact the gas concentration during MSW decomposition. Gas analysis using microGC (gas chromatography) from these experiments identify the presence of hydrogen during MSW decomposition, which is also observed in elevated temperature landfills.

The second part of the talk focuses on characterization of MSW ash, and the reactions at the gas-solid interface of waste-to-energy ash after metal recovery. The ferrous and non-ferrous metals recovered from waste-to-energy ash are characterized using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). Hydrogen evolution resulting from the gas-solid interface reactions in MSW ash are recorded over time in controlled environment using gas analysis. The hydrogen production rate shows correlation with the loss of aluminum from MSW ash. Results also show higher hydrogen concentration in ash samples containing higher metal fractions, which points to ash hydration and carbonation as plausible reactions causing the elevated temperature behavior in landfills with co-disposal of ash.