(755d) Thermal Analysis and Characterization of Municipal Solid Waste Bottom Ash to Assess the Viability for Beneficial Use

Waste to Energy (WtE) ash is the byproduct of the controlled combustion of municipal solid waste (MSW) that are thermally converted to product heat and power. Every year approximately 9 million tons of WTE ash is generated in the US from nearly 80 facilities. According to the Environmental Protection Agency (EPA), only a small percentage of the total generated ash is utilized in these applications and almost all of the ash is being landfilled. This amount of material can be incorporated into the commercial sector for beneficial use. Therefore, it is important to understand the physical characteristic and thermal properties of the ash and possible reactions in landfill environment as well as in the ambient environment.

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 may result in reactions at the gas-solid interface such as corrosion of incorporated metals and hydration of certain minerals. 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 temperatures in landfills. It is also important to study the characteristics of MSW ash and the its contribution in reaction processes occurring in a landfill. The detailed properties of bottom ash were thoroughly examined in this study by combined methods of thermal analysis and characterization. The bottom ash used in this study was collected from the LabUSA Roosevelt metal recovery facility before and after metal recovery.

The first part of the talk focuses on understanding the characteristics of ash such as elemental distribution and quantitative phase analysis. Electron Dispersive Spectroscopy (EDS) was used for elemental mapping and quantitative elemental concentration. Scanning electron Microscopy (SEM) was used for imaging of the ash before and after exposure to carbon dioxide, landfill gas (50:50 mixture of methane and carbon dioxide), and nitrogen. Xray Diffraction (XRD) was used for phase identification before and after exposure to landfill gas and carbon dioxide. Reitvield XRD was used for quantitative analysis of the phases present. Moisture analysis was done on the ash according to ASTM protocol.

The second part of the talk focuses on thermal analysis of the ash. Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA) was used as methods of thermal analysis of bottom ash. Simultaneous DSC and TGA tests show endothermic behavior in temperatures below 200C, and exothermic reactions above 400C that are attributed to the pyrolysis of the organic matter present in ash. The mass loss from TGA analysis and heat flow in DSC were compared to get detailed interpretation of the processes taking place during the exposure to different gases under controlled temperatures. The characterization of the ash combined with the thermal analysis allow for a detailed interpretation of reactions occurring in waste to energy ash in landfill environment as well as during storage and transportation.