The densification of raw material into fuel briquettes is one of the routes to convert biomass into energy. This method provides uniformity to the solid fuel, better physical and energy properties, facilitating its storage and transport, in addition to more homogeneous combustion. Given the importance of these characteristics, this work presents a literature review, emphasizing the experimental levels of the variables of the briquetting process, as well as on the most relevant quality parameters for obtaining briquettes. We also carry out a survey of the main technologies used in the production of briquettes, as well as the experimental methodologies and statistical analysis used in the planning and validation of processes. It was observed among the studies that the raw material granulometry, followed by pressure, initial moisture, compaction time and binder are the most used process variables for the production of briquettes. Other factors, such as the proportion of biomass, process temperature and thermal pre-treatments are used to obtain greater energetic and physical responses. Among the works, divergences were observed regarding the relevance and interaction of some process variables on the quality variables of the briquettes, indicating the need for the experiments to be mathematically modeled.

Rail transportation plays a crucial role in reducing carbon emissions from the transportation system, making a significant contribution to environmental impact mitigation due to the efficiency of passenger and freight rail transportation. Accurate assessment of carbon emissions resulting from rail transit is essential to quantify the positive impact of this mode of transportation on overall urban transport emission reduction. Given that measuring carbon emissions throughout the lifecycle of rail transportation involves a wide array of factors, adopting a systematic framework for analyzing these aspects is crucial. This study conducts a comprehensive review of existing research related to carbon emissions in rail transportation and its mitigation. Initially, the distinct characteristics of carbon emissions associated with rail transportation are identified, along with the complexity involved in accurately measuring these emissions. Subsequently, a comparison and analysis are conducted regarding various models for measuring carbon emissions in rail transportation. Finally, the study examines some greenhouse gas emission measurement research within the railway system. Redirecting research efforts toward measuring carbon emissions in the rail transportation system is essential to help the development of robust and effective public policies. This measure will play a crucial role in emission reduction, climate change mitigation, and the promotion of more sustainable transportation. Furthermore, the identified results propose which LCA methodology offers a valuable framework improving the quality of railway transportation emissions for future generations.

In recent years, the issue of climate change has gained significant attention and become a focal point of discussion in various sectors of civil society. Governments, individuals, and scientists worldwide are increasingly concerned about the observed changes in climate patterns, often attributed to the rising levels of greenhouse gases. In this context, the main objective of this study is to assess the greenhouse gas emissions associated with the railway system in the state of Pernambuco, Brazil, and compare them with other national case studies, aiming to obtain greenhouse gas emission parameters specific to the railway system and propose mitigation models to address this environmental impact in the air. To achieve this goal, a comprehensive life cycle assessment (LCA) methodology was employed to examine the life cycle of the Pernambuco Metro. This involved conducting an inventory of resource inputs and emissions using actual observed data. Additionally, a comparative analysis of greenhouse gas emissions across different urban rail transport systems is presented to provide valuable contextual insights. The study findings reveal that the total greenhouse gas emissions from the Pernambuco rail system amount to 6170.54 t CO₂e. Considering a projected total service life of 50 years, the estimated greenhouse gas emissions for the entire life cycle of the system’s operation and maintenance reach 308,550 t CO₂e. The interdisciplinary nature of this research highlights the significance of studying the atmospheric effects of the Pernambuco railway system as a crucial parameter for designing strategies and technologies aimed at reducing air pollution within the region. Through quantifying and analyzing the greenhouse gas emissions of the Pernambuco rail system, this study provides valuable insights that contribute to addressing concerns related to climate change and promoting sustainable practices. It underscores the importance of developing effective strategies to mitigate air pollution and facilitates informed decision-making for the future of urban transportation systems.

A retrospective bibliometric analysis of the railway sector covering the 20-year period between 2002 and 2021 was carried out to better understand the characteristics of the railway research. The Scopus database contained 1918 articles published with the keywords “Rail System”. VOSviewer software was used to create network maps from each of the variables studied. The results showed a huge increase in the number of publications over this period—notably, work written by Zhang, Y.T., who was found to be the most productive author. Engineering was found to be the most studied subject area of knowledge; Transportation Research Record was the journal with the highest number of publications; and China was revealed to be the leading country regarding this research field, Southwest Jiaotong University being the leading institution in this topic. Finally, there was a lack of research on the environmental impact and sustainability of railway systems, an area that could be opened up for future study.

This article addresses the developing of a framework to obtain specific GHG emissions for the railway system and proposes mitigation strategies. To achieve this purpose, a comprehensive life cycle assessment (LCA) method was employed with input data from various sources to analyze the contribution of energy consumption and the emissions of the railway system. This paper included gathering data from an infrastructure operation and maintenance for detailed GHG emissions impact. This study also presents a comparative analysis of the GHG emissions in different urban railway transportation systems in Northeast Brazil, providing valuable contextual insights. As a result of the combination of total GHG emissions analysis from the states of the Northeast Brazil railway system, a total of 11,996.11 metric tons of CO₂ equivalent (tCO₂e) was estimated. The main line traction was a prominent source of the greenhouse gas footprint, especially for the diesel traction systems at Paraiba. The proposed framework shows that significant environmental benefits can be realized with proper decision-making to increase the number of passengers–kilometer transported by rail.

MgCr₂O₄ nanospinel samples were synthesized using a modified Pechini method, followed by controlled calcination. The resulting materials were evaluated in terms of crystal structure, particle morphology, and optical and electronic properties. Their oxidative activity towards the degradation of organic dyes was investigated via photocatalysis, Fenton-like, and photon-Fenton-like processes. Various analytical techniques were employed to characterize the samples, including X-ray diffraction (XRD) with Rietveld refinements, infrared (IR) spectroscopy, UV–Vis spectroscopy, colorimetry, and transmission and high-resolution transmission electron microscopy (TEM/HRTEM). Structural characterization revealed that MgCr₂O₄ crystallized after calcination at 600 °C, and Rietveld refinements confirmed cubic Fd-3m symmetry. IR spectra confirmed the short-range order through the presence of vibrational modes assigned to CrO₆^2- octahedra. UV–Vis spectroscopy indicated mixed Cr valences (Cr³+/Cr⁶+) for samples calcined at temperatures below 900 °C, with Cr⁶+ eliminated at higher temperatures, confirmed by electron paramagnetic resonance (EPR) spectroscopy. This suggests that an oxidation reaction occurred due to oxygen vacancies in the lattice. Optical bandgap (Eg) increased with temperature. Samples calcined at low temperatures were dark green and became more saturated at temperatures above 900 °C, suggesting photoresponse to visible light, as indicated by the Eg values. The oxidative activity of the nanospinels in degrading the dyes methylene blue (MB) and rhodamine B (RhB) under visible light depended on the nature of the dye, the catalyst concentration, and the use of H₂O₂ in the process to improve the formation of hydroxyl radicals (•OH), as confirmed by photohydroxylation of terephthalic acid (TA). The highest degradation rate was observed in the photo-Fenton-like process, with 96% and 97% degradation of RhB and MB dyes in 60 min, reaching a kinetic rate constant (${\mathit{K}}_{app}$) of 0.055 min⁻¹ and 0.051 min⁻¹, respectively. This study highlights the importance of controlling various parameters to promote the formation of reactive oxygen species (ROS) required for oxidative degradation by nanospinels.