Insight into biomass feedstock on formation of biochar-bound environmentally persistent free radicals under different pyrolysis temperatures

Formation and evolution of environmentally persistent free radicals in charcoal and soot generated from biomass materials

Environmentally persistent free radicals (EPFRs) are emerging pollutants that are highly reactive and toxic, posing potential health risks. Biomass burning is a significant source of EPFRs, but there has been a notable gap in research regarding the EPFRs present in charcoal and soot produced from the same combustion process. Our study detected EPFRs in both charcoal and soot, but there were significant differences in their characteristics. The EPFR concentrations in charcoal were much higher than that in soot, by approximately 2-4 orders of magnitude, suggesting that charcoal may be more chemically reactive. Differences in the formation mechanisms between charcoal and soot were found to result in variations in the characteristics of EPFRs observed in each material. Furthermore, the ability of EPFRs to generate reactive oxygen species (ROS) differed considerably between charcoal and soot. Charcoal exhibited a strong ability to produce ROS, including 1O2 and ·OH radicals, and the abundances of 1O2 was further enhanced (∼1.2 -2.1 times) after illumination. In contrast, only the 1O2 radical was found in soot produced at 300 °C. These findings enhanced our understanding of the environmental impact and potential toxicity of EPFRs, offering valuable insights for evaluating the risks associated with wildfires and agricultural burning.

Heracleum sosnowskyi pyrolysis - Energy and environmental aspects of biochar utilization

The Heracleum sosnowskyi is a highly invasive plant species known for its rapid spread and the significant threat it poses to the ecosystem and human health, primarily due to its furanocoumarin content. In the present study, for the first time the pyrolysis process (200-600 °C) of Heracleum was conducted, demonstrating its efficacy in utilizing the material as feedstock and generating valuable solid by-products. It was found that biochar produced at temperatures of 200-300 °C is suitable for solid fuel production (HHV 20.2-24.1 MJ·kg-1) and has strong hydrophobic properties, while pyrolysis over 400 °C promotes the improvement of fertilizing properties by increasing the content of micro and macronutrients (K=112.4 g·kg-1 at 600 °C). The mass and energy analysis proved that in specific conditions (for dry > 300 °C; for wet > 400 °C), pyrolysis can be an effective way for Heracleum biomass conversion into valuable biochar without the need for external energy.

Biochar-Derived Persistent Free Radicals: A Plethora of Environmental Applications in a Light and Shadows Scenario

Biochar (BC) is a carbonaceous material obtained by pyrolysis at 200-1000 °C in the limited presence of O2 from different vegetable and animal biomass feedstocks. BC has demonstrated great potential, mainly in environmental applications, due to its high sorption ability and persistent free radicals (PFRs) content. These characteristics enable BC to carry out the direct and PFRs-mediated removal/degradation of environmental organic and inorganic contaminants. The types of PFRs that are possibly present in BC depend mainly on the pyrolysis temperature and the kind of pristine biomass. Since they can also cause ecological and human damage, a systematic evaluation of the environmental behavior, risks, or management techniques of BC-derived PFRs is urgent. PFRs generally consist of a mixture of carbon- and oxygen-centered radicals and of oxygenated carbon-centered radicals, depending on the pyrolytic conditions. Here, to promote the more productive and beneficial use of BC and the related PFRs and to stimulate further studies to make them environmentally safer and less hazardous to humans, we have first reviewed the most common methods used to produce BC, its main environmental applications, and the primary mechanisms by which BC remove xenobiotics, as well as the reported mechanisms for PFR formation in BC. Secondly, we have discussed the environmental migration and transformation of PFRs; we have reported the main PFR-mediated application of BC to degrade inorganic and organic pollutants, the potential correlated environmental risks, and the possible strategies to limit them.

Persistent free radicals on biochar for its catalytic capability: A review

Biochar is an economical carbon material for water pollution control, which shows great promise to be applied in the up-scale wastewater remediation processes. Previous studies demonstrate that persistent free radicals (PFRs) on biochar are critical to its reactivity for wastewater remediation. A series of studies have revealed the important roles of PFRs when biochar was applied for organic pollutants degradation as well as the removal of Cr (VI) and As (III) from wastewater. Therefore, this review comprehensively concludes the significance of PFRs for the catalytic capabilities of biochar in advanced oxidation processes (AOPs)-driven organic pollutant removal, and applied in redox processes for Cr (VI) and As (III) remediation. In addition, the mechanisms for PFRs formation during biochar synthesis are discussed. The detection methods are reviewed for the quantification of PFRs on biochar. Future research directions were also proposed on underpinning the knowledge base to forward the applications of biochar in practical real wastewater treatment.

Degradation of organic pollutants from water by biochar-assisted advanced oxidation processes: Mechanisms and applications

Biochar has shown large potential in environmental remediation because of its low cost, large specific surface area, porosity, and high conductivity. Biochar-assisted advanced oxidation processes (BC-AOPs) have recently attracted increasing attention to the remediation of organic pollutants from water. However, the effects of biochar properties on catalytic performance need to be further explored. There are still controversial and knowledge gaps in the reaction mechanisms of BC-AOPs, and regeneration methods of biochar catalysts are lacking. Therefore, it is necessary to systematically review the latest research progress of BC-AOPs in the treatment of organic pollutants in water. In this review, first of all, the effects of biochar properties on catalytic activity are summarized. The biochar properties can be optimized by changing the feedstocks, preparation conditions, and modification methods. Secondly, the catalytic active sites and degradation mechanisms are explored in different BC-AOPs. Different influencing factors on the degradation process are analyzed. Then, the applications of BC-AOPs in environmental remediation and regeneration methods of different biochar catalysts are summarized. Finally, the development prospects and challenges of biochar catalysts in environmental remediation are put forward, and some suggestions for future development are proposed.

Citrus limetta fruit waste management by liquefaction using hydrogen-donor solvent

The liquefaction of Citrus limetta fruit waste (both pulp and peel) in a hydrogen-donor solvent has not been reported in the literature and authors considered the same as the objective of this work. Thus, results on waste management of this potential fruit wastes by liquefaction in hydrogen-donor methanol solvent at 260 °C temperature, residence time of 30 min, and 1 : 2, 1 : 3 and 1 : 4 biomass-to-solvent ratios were reported in this work. The aim was to achieve biofuels of high quantity and quality from this waste, which would otherwise be disposed of without any value addition. A maximum of 12.5 wt% of biocrude yield was found from Citrus limetta peel biomass, which was higher than that from the thermochemical conversion of other citrus fruit waste biomasses. Biocrude having higher heating value (HHV) of 26.76 MJ kg-1 from Citrus limetta pulp, when the feed biomass pulp-to-solvent ratio was 1 : 4, found to be the best outcome of this study. Biocrude and biochar have also been extremely characterized using several advanced techniques such as Gas Chromatography Mass Spectrometry (GC-MS), Fourier Transform Infrared Spectroscopy (FTIR), and Field Emission Scanning Electron Microscopy (FESEM), etc. Finally, the novelty of this work is not only obtaining higher yield of biocrude but also better HHV compared to other similar studies in the literature.