Air pollution emissions from Pyrolysis plants: A systematic mapping

Pyrolysis plants are gaining popularity for their ability to process various waste materials, such as sewage sludge, plastics, biomass, and tires, for waste management and energy generation. However, the environmental and health impacts of the gas emissions generated by these plants have yet to be extensively studied, and the available evidence needs to be more comprehensive and cohesive. The current systematic mapping critically evaluates the existing literature on air pollution emissions from pyrolysis plants, synthesizing the available evidence to identify the essential findings and research gaps in the field. The review examines the potential pollutants emitted by pyrolysis plants according to the feedstocks, process parameters, and APC system applied. The review highlights that pyrolysis plants can emit a wide range of air pollutants depending on the feedstock and operating conditions of the pyrolysis plants; in particular, they include: a. Particulate Matter (PM) Depending on the plant's design and efficiency of control measures, PM emissions can range from a few milligrams (1.11e-3 mg/Nm3 [85]) to hundred milligrams per cubic meter (mg/m³) of exhaust gas (72.50 mg/Nm3 [71]). b. Nitrogen Oxides (NOx) NOx emissions from studied pyrolysis plants ranged from 1.1138 mg/Nm3 to 131 mg/Nm3. [75, 53]. c. Volatile Organic Compounds (VOC) VOC emissions can range from a few ppm to several hundred ppm. d. Polycyclic Aromatic Hydrocarbons (PAHs) PAH emissions can range from trace amounts to a few milligrams per cubic meter (mg/m³) of exhaust gas. The magnitude and composition of the emissions depend on the feedstock and operating conditions of the pyrolysis plants. The review also identifies several areas for improvement in the current knowledge on this topic. For example, there needs to be more emission measurement and reporting standardization, making it challenging to compare results across studies. Additionally, few studies have investigated the long-term health effects of exposure to pyrolysis plant emissions, and further research is needed to understand better the impacts of these emissions on vulnerable populations, such as children and the elderly. It is worth noting that while health assessments are essential for understanding the potential human and environmental impact of these emissions, the current scope of this thesis primarily focuses on emission data and their implications. To address these gaps, the review recommends that future research should focus on the development of standardized methods for emission measurement and reporting, the investigation of the long-term health effects of exposure to pyrolysis plant emissions, and the identification and implementation of effective mitigation measures to reduce the environmental and health impacts of these emissions. In conclusion, this systematic mapping review offers a comprehensive assessment of the current knowledge concerning air pollution emissions from pyrolysis plants. The collective evidence underscores that pyrolysis plants produce notable air pollution emissions, necessitating continued investigation and effective mitigation measures to mitigate the associated environmental ramifications. It is noteworthy, however, that when compared to conventional combustion plants, pyrolysis processes generally yield emissions at comparatively lower levels, thereby presenting pyrolysis as a potentially more environmentally friendly option, although the full extent of its advantages warrants ongoing scholarly inquiry.