Thermal Reactions and Byproducts from the Waste-to-Energy Process of Flame Retardant-Containing Wastes—A Review

Review Thermal Reactions and Byproducts from the Waste-to-Energy Process of Flame Retardant-Containing Wastes—A Review Chun-Yun Hsiao and Sheng-Lun Lin * Department of Environmental Engineering, National Cheng Kung University, No.1, University Rd, East Dist, Tainan 70101, Taiwan * Correspondence: [email protected] or [email protected]; Tel.: +886-6-275-7575 (ext. 65845) Received: 14 February 2025; Revised: 27 April 2025; Accepted: 28 April 2025; Published: 8 May 2025 Abstract: The increasing global concern about global warming has spurred researchers and industries to actively explore low-carbon energy alternatives to reduce carbon emissions and lessen dependence on traditional energy sources. Waste-to-energy (WTE) conversion has emerged as a promising solution in this pursuit. However, the prevalence of flame retardants (FRs) in various household materials poses a challenge to WTE processes. FRs, commonly added to prevent fire hazards, include chlorine-, phosphorus-, and nitrogen-based variants, each with specific applications and fire suppression mechanisms. Thermal treatment technologies, such as incineration, pyrolysis, gasification, and hydrothermal treatment, are currently employed for energy conversion. While effective in reducing waste volume and degrading most FRs, these processes can generate secondary pollutants, including polychlorinated dioxins, with complex reaction pathways that are difficult to control. This necessitates stringent management measures to mitigate the associated environmental risks. In contrast, non-thermal degradation techniques, such as chemical degradation, photocatalysis, biodegradation, and electrochemical methods, offer more environmentally friendly alternatives. However, current technological limitations constrain their application scope and efficiency. This review aims to comprehensively examine the pollutant emission behaviors of FRs during thermal treatment processes for energy conversion, highlight the associated environmental risks, and assess the potential of non-thermal degradation techniques. By analyzing these aspects, the review seeks to provide scientific insights and technological support for achieving waste valorization and low-carbon sustainability.