Stabilization of Waste-to-Energy (WTE) fly ash for disposal in landfills or use as cement substitute

A review of cleaner production of glass-ceramics prepared from MSWI fly ash

Municipal solid waste incineration (MSWI) fly ash, classified as a hazardous waste due to its high toxicity, poses a significant environmental challenge that existing treatment methods struggle to manage effectively. Although high-temperature thermal treatment has proven effective in handling hazardous waste, its large-scale industrial adoption is hindered by the associated high costs and energy demands. A promising alternative is the conversion of MSWI fly ash into high-value glass-ceramic materials, which presents both environmental and economic benefits. This review provides insights into a cleaner production technique for glass-ceramics derived from MSWI fly ash. It begins with an analysis of the physical and chemical characteristics of MSWI fly ash and its environmental impact. The review then explores advancements in MSWI fly ash-based glass-ceramic production, mainly focusing on the processes of crystallization and the immobilization of heavy metals. Furthermore, the potential for heat recovery is considered, with a discussion on optimizing the heat treatment process for sustainable and cleaner production. The review concludes by proposing a systematic approach to reduce energy consumption, demonstrating the potential to save approximately 39.5 % at least compared to traditional methods.

Opportunities and challenges with implementing a recycling program for municipal solid waste incineration (MSWI) bottom ash as a construction aggregate: A programmatic review

The incineration of municipal solid waste (MSW) produces byproducts known as MSW incineration (MSWI) ash. The reuse of MSWI ash as a construction material prevails in several areas of the world, namely Europe and Asia, however, reuse in the United States (US) lags due to regulatory requirements for disposal practices. Developing a recycling program for MSWI ash provides an alternative end-of-life disposal scenario for material currently landfilled and supplements the reliability of mining of natural aggregates. This study provides a programmatic review of the past decade of challenges and opportunities a local government in the US has experienced to implement a recycling program for their MSWI bottom ash (BA) as a construction aggregate in road materials, such as hot mix asphalt, concrete pavement, and road base. The regulatory and practical challenges in the U.S. are presented, including meeting mechanical and environmental performance requirements (e.g., strength and leaching-to-groundwater). The novel approach to overcoming these challenges include blending MSWIBA from two facilities with common aggregates, creating suitable construction materials. Interfacing with local and state agencies, such as the Department of Environmental Protection and Transportation resulted in additional testing to establish the MSWIBA as a beneficial use material and obtain essential approvals for advancing reuse opportunities. This paper synthesizes available data regarding the challenges, opportunities, and implementation of this recycling program by reviewing the experiences of an MSWI facility in the US to provide fundamental guidance to those considering similar applications.Implications: The reuse of municipal solid waste incinerator bottom ash (MSWIBA) lags in the United States (US) due to regulatory limitations and lack of precedence. This manuscript details the steps of a local government in the US to establishing a novel recycling program for their MSWIBA, including performance evaluation, regulatory interfacing, and outreach. This critical review provides a comprehensive document containing appropriate considerations required to implement similar MSWIBA recycling programs in the US and offers lawmakers, policymakers, and MSWI operators knowledge regarding opportunities and challenges associated with pursuing this avenue.

Evaluating the impact of drying on leaching from a solidified/stabilized waste using a monolithic diffusion model

The release rates of constituents of potential concern from solidified/stabilized cementitious waste forms are potentially impacted by drying, which, however, is not well understood. This study aimed to identify the impacts of drying on subsequent leaching from Cast Stone as an example of a solidified cementitious waste form. The release fluxes of constituents from monoliths after aging under 100, 68, 40, and 15 % relative humidity for 16, 32, and 48 weeks, respectively, were derived from mass transfer tank leaching tests following EPA Method 1315. A monolithic diffusion model was calibrated based on the leaching test results to simulate the leaching of major and redox-sensitive constituents from monoliths after drying. The reduction in physical retention of constituents (tortuosity-factor) in the unsaturated zone was identified as the primary impact from drying on subsequent leaching. Fluxes of both major (i.e., OH^-, Na, K, Ca, Si, and Al) and redox-sensitive constituents (i.e., Tc, Cr, Fe, and S) from monoliths during leaching were well described by the model. The drying-induced reduction of tortuosity-factor and concomitant changes in porewater pH and redox conditions can significantly change the subsequent release fluxes of pH- and redox- sensitive constituents.

Energy Recovery from Polymeric 3D Printing Waste and Olive Pomace Mixtures via Thermal Gasification-Effect of Temperature

One of the polymeric materials used in the most common 3D printers is poly(ethylene terephthalate) glycol (PETG). It represents, in world terms, around 2.3% of polymeric raw material used in additive manufacturing. However, after processing this material, its properties change irreversibly. A significant amount of waste is produced around the world, and its disposal is usually destined for landfill or incineration, which can generate an important issue due to the high environmental risks. Polymer waste from 3D printing, hereinafter 3DPPW, has a relatively high calorific value and adequate characteristics to be valued in thermochemical processes. Gasification emerges as an innovative and alternative solution for recovering energy from 3DPPW, mixed with residues of lignocellulosic origin, and presents some environmental advantages compared to other types of thermochemical treatments, since the gasification process releases smaller amounts of NOx into the atmosphere, SOx, and CO₂. In the case of the study, co-gasification of olive pomace (OLB) was carried out with small additions of 3DPPW (10% and 20%) at different temperatures. Comparing the different gasifications (100% OLB, 90% OLB + 10% 3DPPW, 80% OLB + 20% 3DPPW), the best results for the synthesis gas were obtained for the mixture of 10% 3DPPW and 90% olive pomace (OLB), having a lower calorific value of 6.16 MJ/m³, synthesis gas yield of 3.19%, and cold gas efficiency of 87.85% for a gasification temperature of 750 °C. In addition, the results demonstrate that the addition of 3DPPW improved the quality of syngas, especially between temperatures of 750 and 850 °C. Including polymeric 3D printing materials in the context of the circular economy and extending their life cycle helps to improve the efficiency of subsequent industrial processes, reducing process costs in general, thanks to the new industrial value acquired by the generated by-products.

Evaluation of Fly Ash from Co-Combustion of Paper Mill Wastes and Coal as Supplementary Cementitious Materials

The applications of waste-derived fuel from paper mills in industrial boilers benefit the reduction of carbon emissions. However, the co-combustion of waste-derived fuel and coal causes significant changes in the characteristics of the ash and brings about the need to find possible means of the utilization of the ash produced. In this work fly, ash samples were collected from circulating fluidized bed (CFB) boilers co-combusting paper mill wastes with coal and analyzed in detail. The chemical, physical, and thermal characteristics of two different co-combustion fly ashes (CCFA) were investigated using X-ray fluorescence (XRF), X-ray diffraction (XRD), thermogravimetry (TG), and scanning electron microscope (SEM). The chemical composition of CCFA is largely affected by the fuel source type. Thermal analyses of CCFA show that the type of desulfurization system used by the boiler influences the form of sulfate present in the fly ash. The presence of calcium sulfite hemihydrate can cause a high loss in the ignition of CCFA. By comparing the physical requirements specified in the ASTM standard for coal fly ash to be used in concrete, the CCFA produced from paper mill wastes was found to show good potential as supplementary cementitious materials.