Suppression of polycyclic aromatic hydrocarbon formation during pyrolytic production of lignin-based biochar via nitrogen and boron co-doping

Review on biochar as a sustainable green resource for the rehabilitation of petroleum hydrocarbon-contaminated soil

Petroleum pollution is one of the primary threats to the environment and public health. Therefore, it is essential to create new strategies and enhance current ones. The process of biological reclamation, which utilizes a biological agent to eliminate harmful substances from polluted soil, has drawn much interest. Biochars are inexpensive, environmentally beneficial carbon compounds extensively employed to remove petroleum hydrocarbons from the environment. Biochar has demonstrated an excellent capability to remediate soil pollutants because of its abundant supply of the required raw materials, sustainability, affordability, high efficacy, substantial specific surface area, and desired physical-chemical surface characteristics. This paper reviews biochar's methods, effectiveness, and possible toxic effects on the natural environment, amended biochar, and their integration with other remediating materials towards sustainable remediation of petroleum-polluted soil environments. Efforts are being undertaken to enhance the effectiveness of biochar in the hydrocarbon-based rehabilitation approach by altering its characteristics. Additionally, the adsorption, biodegradability, chemical breakdown, and regenerative facets of biochar amendment and combined usage culminated in augmenting the remedial effectiveness. Lastly, several shortcomings of the prevailing methods and prospective directions were provided to overcome the constraints in tailored biochar studies for long-term performance stability and ecological sustainability towards restoring petroleum hydrocarbon adultered soil environments.

Functional use of carbon dioxide for the sustainable valorization of orange peel in the pyrolysis process

Although biomass is carbon-neutral, its use as a primary feedstock faces challenges arising from inconsistent supply chains. Therefore, it becomes crucial to explore alternatives with reliable availability. This study proposes a strategic approach for the thermochemical valorization of food processing waste, which is abundantly generated at single sites within large-scale processing plants. As a model biomass waste from the food industry, orange peel waste was particularly chosen considering its substantial consumption. To impart sustainability to the pyrolysis system, CO2, a key greenhouse gas, was introduced. As such, this study highlights elucidating the functionality of CO2 as a reactive feedstock. Specifically, CO2 has the potential to react with volatile pyrolysates evolved from orange peel waste, leading to CO formation at ≥490 °C. The formation of chemical constituents, encompassing acids, ketones, furans, phenols, and aromatics, simultaneously decreased by 15.1 area% in the presence of CO2. To activate the efficacy of CO2 at the broader temperature spectrum, supplementary measures, such as an additional heating element (700 °C) and a nickel-based catalyst (Ni/Al2O3), were implemented. These configurations promote thermal cracking of the volatiles and their reaction kinetics with CO2, representing an opportunity for enhanced carbon utilization in the form of CO. Finally, the integrated process of CO2-assisted catalytic pyrolysis and water-gas shift reaction was proposed. A potential revenue when maximizing the productivity of H2 was estimated as 2.62 billion USD, equivalent to 1.11 times higher than the results from the inert (N2) environment. Therefore, utilizing CO2 in the pyrolysis system creates a promising approach for enhancing the sustainability of the thermochemical valorization platform while maximizing carbon utilization in the form of CO.

A critical review of biochar as an environmental functional material in soil ecosystems for migration and transformation mechanisms and ecological risk assessment

At present, biochar has a large application potential in soil amelioration, pollution remediation, carbon sequestration and emission reduction, and research on the effect of biochar on soil ecology and environment has made positive progress. However, under natural and anthropogenic perturbations, biochar may undergo a series of environmental behaviors such as migratory transformation, mineralization and decomposition, and synergistic transport, thus posing certain potential risks. This paper outlines the multi-interfacial migration pathway of biochar in "air-soil-plant-animal-water", and analyzes the migration process and mechanism at different interfaces during the preparation, transportation and application of biochar. The two stages of the biochar mineralization process (mineralization of easily degradable aliphatic carbon components in the early stage and mineralization of relatively stable aromatic carbon components in the later stage) were described, the self-influencing factors and external environmental factors of biochar mineralization were analyzed, and the mineral stabilization mechanism and positive/negative excitation effects of biochar into the soil were elucidated. The proximity between field natural and artificially simulated aging of biochar were analyzed, and the change of its properties showed a trend of biological aging > chemical aging > physical aging > natural aging, and in order to improve the simulation and prediction, the artificially simulated aging party needs to be changed from a qualitative method to a quantitative method. The technical advantages, application scope and potential drawbacks of different biochar modification methods were compared, and biological modification can create new materials with enhanced environmental application. The stability performance of modified biochar was compared, indicating that raw materials, pyrolysis temperature and modification method were the key factors affecting the stability of biochar. The potential risks to the soil environment from different pollutants carried by biochar were summarized, the levels of pollutants released from biochar in the soil environment were highlighted, and a comprehensive selection of ecological risk assessment methods was suggested in terms of evaluation requirements, data acquisition and operation difficulty. Dynamic tracing of migration decomposition behavior, long-term assessment of pollution remediation effects, and directional design of modified composite biochar materials were proposed as scientific issues worthy of focused attention. The results can provide a certain reference basis for the theoretical research and technological development of biochar.

Microwave-Assisted Pyrolysis-A New Way for the Sustainable Recycling and Upgrading of Plastic and Biomass: A Review

The efficient utilization of organic solid waste resources can help reducing the consumption of conventional fossil fuels, mitigating environmental pollution, and achieving green sustainable development. Due to its dual nature of being both a resource and a source of pollution, it is crucial to implement suitable recycling technologies throughout the recycling and upgrading processes for plastics and biomass, which are organic solid wastes with complex mixture of components. The conventional pyrolysis and hydropyrolysis were summarized for recycling plastics and biomass into high-value fuels, chemicals, and materials. To enhance reaction efficiency and improve product selectivity, microwave-assisted pyrolysis was introduced to the upgrading of plastics and biomass through efficient energy supply especially with the aid of catalysts and microwave absorbers. This review provides a detail summary of microwave-assisted pyrolysis for plastics and biomass from the technical, applied, and mechanistic perspectives. Based on the recent technological advances, the future directions for the development of microwave-assisted pyrolysis technologies are predicted.

Formation mechanisms and degradation methods of polycyclic aromatic hydrocarbons in biochar: A review

Biochar has been widely used in soil amendment and environmental remediation. Polycyclic aromatic hydrocarbons (PAHs) could be produced in preparation of biochar, which may pose potential risks to the environment and human health. At present, most studies focus on the ecotoxicity potential of biochar, while there are few systematic reviews on the formation mechanisms and mitigation strategies of PAHs in biochar. Therefore, a systematical understanding of the distribution, formation mechanisms, risk assessment, and degradation approaches of PAHs in biochar is highly needed. In this paper, the distribution and content of the total and bioavailable PAHs in biochar are reviewed. Then the formation mechanisms, influencing factors, and potential risk assessment of PAHs in biochar are systematically explored. After that, the effective strategies to alleviate PAHs in biochar are summarized. Finally, suggestions and perspectives for future studies are proposed. This review provides a guide for reducing the formation of biochar-associated PAHs and their toxicity, which is beneficial for the development and large-scale safe use of environmentally friendly biochar.

Biochar-based materials as remediation strategy in petroleum hydrocarbon-contaminated soil and water: Performances, mechanisms, and environmental impact

Petroleum contamination is considered as a major risk to the health of humans and environment. Biochars as low-cost and eco-friendly carbon materials, have been widely used for the removal of petroleum hydrocarbon in the environment. The purpose of this paper is to review the performance, mechanisms, and potential environmental toxicity of biochar, modified biochar and its integration use with other materials in petroleum contaminated soil and water. Specifically, the use of biochar in oil-contaminated water and soil as well as the factors that could influence the removal ability of biochar were systematically evaluated. In addition, the modification and integrated use of biochar for improving the removal efficiency were summarized from the aspects of sorption, biodegradation, chemical degradation, and reusability. Moreover, the functional impacts and associated ecotoxicity of pristine and modified biochars in various environments were demonstrated. Finally, some shortcoming of current approaches, and future research needs were provided for the future direction and challenges of modified biochar research. Overall, this paper gain insight into biochar application in petroleum remediation from the perspectives of performance enhancement and environmental sustainability.

Carbon-based adsorbents for the mitigation of polycyclic aromatic hydrocarbon: a review of recent research

Accumulation of polycyclic aromatic hydrocarbons (PAH) poses significant dangers to the environment and human health. The advancement of technology for cleaning up PAH-contaminated environments is receiving more attention. Adsorption is the preferred and most favorable approach for cleaning up sediments polluted with PAH. Due to their affordability and environmental friendliness, carbonaceous adsorbents (CAs) have been regarded as promising for adsorbing PAH. However, adsorbent qualities, environmental features, and factors may all significantly impact how well CAs remove PAH. According to growing data, CAs, most of which come from laboratory tests, may be utilized to decontaminate PAH in aquatic setups. However, their full potential has not yet been established, especially concerning field applications. This review aims to concisely summarize recent developments in CA, PAH stabilization processes, and essential field application-controlling variables. This review analysis emphasizes activated carbon, biochar, Graphene, carbon nanotubes, and carbon-nanomaterials composite since these CAs are most often utilized as adsorbents for PAH in aquatic systems.

Facile heteroatoms modification biochar production from mahogany (Swietenia macrophylla King) pericarps for enhanced the suppression of polycyclic aromatic hydrocarbon pollutants

Polycyclic aromatic hydrocarbons (PAHs) are critical environmental concerns due to their intrinsic toxic aromatic nature and concomitant circumstances that potentially harm the ecological and human health. In this study, converting mahogany (Swietenia macrophylla King) pericarps to value-added biochar by pyrolysis for evaluating the potential formation/destruction of biochar-bound PAHs was studied for the first time. This study designed and optimized the thermal processing conditions at 300-900 °C in the CO2 or N2 atmosphere, and heteroatoms (N, O, B, NB, and NS) were modified for mahogany pericarps biochar (MPBC) production. The MPBC500 exhibited significantly higher pyrolysis products of PAHs (2780 ± 38 ng g-1) than that of MPBC900 (78 ± 6 ng g-1) under N2 without introducing modified elements. Specifically, the inhibition capacity of MPBC500 for PAHs under CO2 was improved most efficiently by the active nitrogen species of the pyridinic N and pyrrolic N groups. The pyrolysis conditions and heteroatom modification of MPBC altered its physicochemical properties, that is, aromaticity and hydrophobicity, affecting the PAH concentration and composition in the pyrolysis products. This study reveals sustainable approaches to reduce the environmental footprint of biochar by focusing on increases in PAHs pollution in sustainable biochar produced from a low-carbon bioeconomy perspective.

Metal-free nitrogen and sulfur binary-doped cellulose-based biochar for efficient suppression of priority organic pollutants and environmental application

Biochar production from cellulose biomass is an alternative solution in the search for clean and renewable biofuel. However, the rational design of cellulose biochar (CLBC) for polycyclic aromatic hydrocarbons (PAHs) reduction by integrating pyrolysis process parameters and introducing heteroatoms as inhibitors remains to be studied. Therefore, exogenous heteroatoms (N, B, S, SB, NB, and NS) were used to modify CLBC for the first time. CLBC300 pyrolyzed at 300 °C in a CO2 atmosphere achieved the highest concentrations of PAHs (4982 ± 271 ng g-1), compared with that of CLBC700 (3615 ± 71 ng g-1) formed in a N2 atmosphere without heteroatom doping. The results showed that binary nitrogen- and sulfur-doped CLBC exhibited remarkable PAH-removal performance of 99 % with the lowest toxic equivalency (TEQ) value of 9 ng g-1. Overall, this study presents novel insights into the development of a heteroatom-based modification approach for reducing CLBC-borne PAHs and creating value-added products from cellulose biomass.

Pyrolysis processes affecting polycyclic aromatic hydrocarbon profile of pineapple leaf biochar exemplified by atmosphere/temperature and heteroatom doping

The content of polycyclic aromatic hydrocarbons in pineapple leaf biochar was examined as a function of pyrolysis atmosphere (CO₂ or N₂), pyrolysis temperature (300-900 °C), and heteroatom (N, B, O, P, NP, or NS) doping. Without doping, the polycyclic aromatic hydrocarbon production was maximal (1332 ± 27 ng/g) in CO₂ at 300 °C and minimal (157 ± 2 ng/g) in N₂ at 700 °C. The main components naphthalene and acenaphthylene accounted for about 91% of the total polycyclic aromatic hydrocarbon in the biochar prepared under CO₂ at 300 °C. Under the maximal polycyclic aromatic hydrocarbon production conditions (CO₂, 300 °C), doping decreased the total hydrocarbon content by 49% (N), 61% (B), 73% (O), 92% (P), 93% (NB), and 96% (NS). The results shed new light on the management of polycyclic aromatic hydrocarbons in BC production by controlling the pyrolysis atmosphere and temperature in addition to heteroatom doping. Results significantly contributed to the development of circular bioeconomy.

Effects of pyrolysis conditions and heteroatom modification on the polycyclic aromatic hydrocarbons profile of biochar prepared from sorghum distillery residues

The formation of 2- to 6-ring polycyclic aromatic hydrocarbons (PAHs) in sorghum distillery residue-derived biochar (SDRBC) was evaluated under different thermochemical pyrolysis conditions of carbonization atmosphere (N2 or CO2), temperature (300-900 °C) and doping with nonmetallic elements, i.e., N, B, O, P, N + B, and N + S. The results indicated that without surface modification, PAHs formation was 944 ± 74 ng g-1, the highest level, and 181 ± 16 ng g-1, the lowest level, at 300 °C in N2 and CO2 atmosphere, respectively. Boron doping of SDRBC significantly reduced the PAHs content (by 97%) under N2 at 300 °C. Results demonstrated that boron modified SDRBC exhibited the highest degree of PAH reduction. Combined pyrolysis temperature and atmosphere in addition to heteroatom doping is a robust and viable strategy for efficient suppression of PAHs formation and high-value utilization of pyrolysis products of low carbon footprint.

Activation of calcium peroxide by nitrogen and sulfur co-doped metal-free lignin biochar for enhancing the removal of emerging organic contaminants from waste activated sludge

The accumulation of emerging organic contaminants (EOCs) in waste activated sludge (WAS) is a global concern. In this study, a multi-heteroatom nitrogen and sulfur was successfully embedded into lignin-based biochar (N-S-LGBC) and used it to activate calcium peroxide (CP) for the degradation of 4-nonylphenol (4-NP) in WAS. N-S-LGBC/CP was effective in degrading 85 % of 4-NP within 12 h through the activation of CP owing to hydroxyl radicals and singlet oxygen species generated from the synergism among pyrrolic-N, thiophenic-S, and lattice oxygen, i.e., active sites responsible for 4-NP degradation. These results highlight substrate biodegradability for subsequent bioprocesses that improves WAS treatment in EOC degradation by the N-S-LGBC/CP-mediated process. There was abundance of distinct Aggregatilinea genus within the phylum Chloroflexi during N-S-LGBC/CP treatment, indicating high 4-NP pretreatment efficiency in WAS. This work provides a new understanding of N-S-co-doped carbocatalysts in green and sustainable hydroxyl radical-driven carbon advanced oxidation (HR-CAOP) platforms for WAS remediation.

A review on lignin pyrolysis: pyrolytic behavior, mechanism, and relevant upgrading for improving process efficiency

Lignin is a promising alternative to traditional fossil resources for producing biofuels due to its aromaticity and renewability. Pyrolysis is an efficient technology to convert lignin to valuable chemicals, which is beneficial for improving lignin valorization. In this review, pyrolytic behaviors of various lignin were included, as well as the pyrolytic mechanism consisting of initial, primary, and charring stages were also introduced. Several parallel reactions, such as demethoxylation, demethylation, decarboxylation, and decarbonylation of lignin side chains to form light gases, major lignin structure decomposition to generate phenolic compounds, and polymerization of active lignin intermediates to yield char, can be observed through the whole pyrolysis process. Several parameters, such as pyrolytic temperature, time, lignin type, and functional groups (hydroxyl, methoxy), were also investigated to figure out their effects on lignin pyrolysis. On the other hand, zeolite-driven lignin catalytic pyrolysis and lignin co-pyrolysis with other hydrogen-rich co-feedings were also introduced for improving process efficiency to produce more aromatic hydrocarbons (AHs). During the pyrolysis process, phenolic compounds and/or AHs can be produced, showing promising applications in biochemical intermediates and biofuel additives. Finally, some challenges and future perspectives for lignin pyrolysis have been discussed.

Bioremediation pretreatment of waste-activated sludge using microalgae Spirulina platensis derived biochar coupled with sodium sulfite: Performance and microbial community dynamics

4-Nonylphenol is a typical endocrine-disrupting compound found in waste-activated sludge. This study evaluates the feasibility of blue-green algae (Spirulina platensis)-based biochar as a carbon-neutral material to improve sodium sulfite (S(IV))-mediated sludge purification. Blue-green algae-based biochar is an effective activator (at 500 °C and 3 × 10^-6 M) of sodium sulfite and removed 75 % of 4-nonylphenol at pH 6 using at 1.7 g/L of dosage. Possible synergistic relationships among the coexisting oxidizing species (SO₃^•-, SO₄^•-, HO•, and ¹O₂), obvious defect structure, and abundant carbonyl oxygen groups on the surface of the biochar together dived advanced oxidation process. The bacterial consortia promoted the decomposition of biologically available substrates in the biosolid mixture, which led to the enrichment of Denitratisoma, and boosted 4-nonylphenol biodegradation. This study outlines a potential carbon-neutral, cost-effective, and sustainable sludge treatment strategy using renewable blue-green algae-based biochar, aiding 4-nonylphenol biodegradation in waste-activated sludge.

Brewer’s Spent Grain Biochar: Grinding Method Matters

The present work is based on the principle of biomass waste valorization. Brewer’s spent grains (BSG) come from breweries as by-products. Their huge amount of production on an industrial scale should focus our attention on their valorization, which creates challenges as well as opportunities. One way to valorize BSG by-products is to convert them into biochar, a functional material with multiple potential applications. With an emphasis on sustainable development and the circular economy, in this work, we focused on a comparative study of the different mechanical processes of BSG grinding and their effect on the resulting biochar formed after pyrolysis. Home appliances such as blenders, coffee mills, and mortar and pestles were used for this purpose. FESEM images confirmed the successful creation of five different morphologies from the same BSG under the same pyrolysis conditions. Interestingly, a novel Chinese tea leaf egg-like biochar was also formed. It was found that a series of physical pretreatments of the biomass resulted in the reduced roughness of the biochar surface, i.e., they became smoother, thus negatively affecting the quality of the biochar. XRD revealed that the biomass physical treatments were also reflected in the crystallinity of some biochar. Via a Raman study, we witnessed the effect of mechanical pressure on the biomass for affecting the biochar features through pressure-induced modifications of the biomass’s internal structure. This induced enhanced biochar graphitization. This is a good example of the role of mechanochemistry. DSC revealed the thermochemical transformation of the five samples to be exothermic reactions. This study opens up an interesting possibility for the synthesis of biochar with controlled morphology, crystallinity, degree of graphitization, and heat capacity.

Ecological responses of coral reef to polyethylene microplastics in community structure and extracellular polymeric substances

The relationships and interactions between extracellular polymeric substances (EPS) and microplastics (MPs) in coral reef ecosystems were symmetrically investigated. The current study aims to investigate the responses of scleractinian coral (Goniopora columna) to exposure of model MPs, exemplified by polyethylene (PE), in the size range of 40-48 μm as affected by MPs concentration of MP in the range between 0 and 300 mg L^-1 for 14 days. The structure of EPS-associated microbial community was studied using a series of techniques including high-throughput sequencing of 16 S rRNA, transmission electron microscopy (TEM), hydrodynamic diameter, surface charge (via zeta potential), X-ray diffraction (XRD), attenuated total reflectance‒Fourier transform infrared (ATR‒FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and fluorescence excitation-emission matrix (FEEM) spectroscopy. Microbial interactions between PE-MPs and coral caused aggregation and formation of EPS matrix, which resulted in increase and decrease in the relative abundance of Donghicola (Proteobacteria phylum) and Marivita (Proteobacteria phylum) in PE-MP-associated EPS, respectively. Particle size, electrostatic interactions, and complexation with the functional groups of the EPS-based matrix affected the humification index. FEEM spectroscopy analyses suggested the presence of humic- and fulvic-like fluorophores in EPS and dissolved organic matter (DOM) in PE-MP-derived DOM. The findings provided insights into the potential environmental implications of coral-based EPS and co-existing microbial assemblages due to EPS-PE-MP-microbiome interactions throughout the dynamic PE-MP exposure process.