Search Results (591)

Natural bentonite, dominated by montmorillonite-type layered aluminosilicates, is increasingly considered as an inexpensive and environmentally acceptable support or catalyst for the thermochemical conversion of waste carbon streams. Its relevance to catalysis arises from a combination of cation-exchange capacity, swelling behavior, hierarchical porosity after modification, and the possibility of generating Brønsted, Lewis, redox and metallic active sites. This review critically evaluates bentonite modification strategies—acid activation, alkaline and sodium exchange, inorganic oxide pillaring, transition- and noble-metal impregnation, organosilane or surfactant functionalization, and carbon-based hybridization—with emphasis on their consequences for texture, acidity, thermal stability, metal dispersion and catalytic behavior. The review then connects these structure–property relationships with the emerging application of modified bentonites in plastic-waste thermocatalysis and hydrogen-rich product formation. The recent literature indicates that acid-modified bentonite can substantially improve liquid hydrocarbon formation from polyethylene, binder-free bentonite pellets can operate at kilogram-batch scale for drop-in fuels, and Ni-, Fe- or Ni–Fe-modified bentonite-type catalysts can promote tar cracking, reforming and gas upgrading. However, direct evidence for high hydrogen yields from plastic waste over bentonite remains narrower than the evidence for liquid-fuel production, biomass pyrolysis or model-compound reforming. Therefore, this article distinguishes between direct plastic-waste evidence and transferable evidence from biomass, acetic acid, tar and hydrocarbon reforming studies. The analysis identifies Ni-impregnated acid-activated or pillared bentonite, Ni–Fe/bentonite, and La/Ca-promoted Ni/bentonite as the most promising routes for plastic-derived hydrogen-rich syngas, while acid activation alone is best regarded as a pretreatment rather than a complete catalyst design. Key limitations include catalyst deactivation by coke, metal sintering, chloride poisoning from PVC, inconsistent reporting of gas yields, and insufficient life-cycle and techno-economic analysis. A roadmap is proposed for designing reproducible, scalable bentonite catalysts for circular plastic-waste valorization. Full article

Winery residues generated by the wine industry represent an important sustainability challenge but also a valuable resource for producing vermicompost-derived products with potential agricultural applications through vermicomposting. This study evaluated the effects of aqueous vermicompost extracts produced from winery residues on the early in vitro development and physiological performance of garden cress (Lepidium sativum L.) and cucumber (Cucumis sativus L.) seedlings. Seedlings were cultivated on peat-based pellets (Jiffy-7^®) under controlled conditions and treated with two extract concentrations (10% and 20%, w/v) or distilled water (control). After 30 days, morphological traits (shoot height, leaf number and biomass) and biochemical parameters (photosynthetic pigments and total phenolics) were assessed. Both species showed high survival rates (>85%) and no phytotoxic symptoms. Compared with the control, VE20% increased chlorophyll a, chlorophyll b, and total chlorophyll contents in garden cress by 40.3%, 35.9%, and 38.9%, respectively, whereas VE10% increased chlorophyll a, total chlorophyll, and carotenoid contents in cucumber by 15.7%, 11.5%, and 25.0%, respectively. Total phenolic content did not differ significantly among treatments in either species (p > 0.05). These findings indicate that vermicompost extracts produced from winery residues exhibited low phytotoxic potential under the experimental conditions tested and influenced photosynthetic pigment accumulation without adversely affecting seedling growth. These responses warrant further investigation under ex vitro and field conditions to determine whether the observed physiological changes translate into relevant agronomic effects. Full article

Computational fluid dynamics provides detailed spatial distributions of physical fields in biomass boiler combustion, but the computational cost of each simulation limits its application in parametric studies and near-real-time workflows. This work investigates whether a Graph Neural Operator (GNO) can serve as a fast surrogate model that maps boiler operating parameters to six coupled CFD field distributions simultaneously. The reference case is a 10 kW wood-pellet boiler with internal flue gas recirculation (FGR), described and experimentally validated in an earlier publication by the authors. CFD data were collected on the symmetry plane of the combustion chamber for 80 operating points defined by the thermal load ratio (P/P₀) and the excess air ratio λ. A GNO surrogate was trained on 64 cases to predict temperature, velocity magnitude, static pressure, and mole fractions of CO, O₂, and CO₂ at each node of an unstructured spatial graph. On a held-out validation set of 16 operating cases, the model achieved R² values of 0.988 for temperature, 0.919 for velocity magnitude, 0.982 for pressure, 0.999 for CO, 0.992 for O₂, and 0.985 for CO₂. After training, each prediction is generated in a single forward pass, providing a computationally efficient approximation compared to the full CFD solver. A dedicated generalisation study on independent off-grid CFD cases confirmed that the surrogate interpolates within the parameter domain with essentially no loss of accuracy and degrades only moderately when extrapolated towards a higher thermal load and leaner mixtures. The results demonstrate that a baseline GNO surrogate can capture the spatial structure of coupled thermo-fluid and species fields in a realistic combustion geometry within the investigated parameter range and suggest applicability to digital-twin-oriented workflows where repeated parametric queries of boiler operation are required. Full article

Residential heater replacement programs in Chile have been evaluated primarily through fine particulate matter (PM) reduction metrics, without considering chemical speciation of the organic aerosols. This screening-level study characterized and compared particle-bound polycyclic aromatic hydrocarbon (PAH) and nitro-PAH emission factors from a residential firewood and a wood pellet heater, under controlled combustion conditions, and assessed their potential toxic equivalency (BaP-TEQ). Compound quantification used 1-nitropyrene as an index calibration compound; all results are semi-quantitative estimates with a combined analytical uncertainty of approximately 13–32%. Firewood combustion yielded a PAH-dominated emission profile with a total BaP-TEQ EF of 187.8 ng/kg, driven primarily by benzo[a]pyrene (BaP; individual contribution: 183.9 ng/kg). Wood pellet combustion showed a nitro-PAH-dominated profile under the applied semi-quantitative analytical conditions, with concentrations expressed as 1-nitropyrene-equivalent estimates and several compounds identified tentatively by NIST library matching, yielding a total screening-level BaP-TEQ EF of 972.1 ng/kg, approximately five-fold higher than firewood under the applied TEF framework and driven primarily by 6-nitrochrysene (toxic equivalency factor, TEF = 10). This screening-level estimate should not be interpreted as a direct human health risk between the two heating systems. Mean PM emission factors were 1.05 ± 0.55 g/kg for firewood combustion and 0.69 ± 0.15 g/kg for pellet combustion (approximately 1.5-fold difference). These results are reported descriptively given the screening-level nature of the analysis. The shift in particulate chemical profile from PAH-dominated in the firewood system to nitro-PAH-dominated in the pellet system suggests that wood pellets from pine may not be a sustainable approach to address air quality problems in Chile, since reductions in PM emissions alone may not capture relevant differences in the organic toxicological profile between these combustion systems. These findings provide a regional baseline for the chemical speciation of residential biomass emissions in Chile. Full article

Since 2024, most electricity production on Réunion Island has been achieved through combustion of biomass, using either imported wood pellets or locally produced bagasse. Their combustion generates two types of ash, depending on the biomass source: Wood Biomass Fly Ash (WBFA) and SugarCane Bagasse Ash (SCBA). Their chemical compositions differ significantly, leading to different potential applications. The composition of SCBA is similar to that of Coal Fly Ash (CFA), with low variability between batches. Therefore, SCBA could be used as an alternative to CFA, as a Supplementary Cementitious Material (SCM) or in composite cements. SCBA also meets most of the requirements of the NF EN 450-1 standard. However, grinding of SCBA appears necessary to achieve mechanical performance required by the standard. In contrast, WBFA exhibits variable chemical composition, mainly due to differences in pellet origin prior to combustion. Nevertheless, WBFA contains significant levels of chloride ions and sulfate, which may act as activators for materials such as GGBS or metakaolin (MK). Although the high unburned carbon content of WBFA increases water demand, their incorporation into GGBS-based binders (SSC or CEM III) or metakaolin-based systems shows promising potential, particularly for improving early strength. Full article

The study evaluated 6 mm pellets derived from whole hemp plants (Cannabis sativa L., cv. Futura 75) to assess their potential as a solid biofuel. The pellets had a low moisture content of 6.3–7.0% on an analytical basis, which is favorable for storage and combustion. Ash content was approximately 4.0–4.3%, while gross calorific values ranged from 17.3 MJ·kg⁻¹ as received to 19.4 MJ·kg⁻¹ on a dry ash-free basis. The net calorific values ranged from 16.1 to 17.5 MJ·kg⁻¹. Based on the elemental analysis, the carbon content was 46.8–49.4%, the hydrogen content was 5.5%, the nitrogen content was 0.68–0.73%, and the sulfur content was 0.05%. Compared with many agricultural biomass fuels, hemp pellets contained relatively low sulfur and moderate nitrogen contents. Hemp pellets from whole plants show favorable physicochemical properties, making them a viable renewable solid biofuel resource. Full article

Microalgae–fungal pellets have been studied as a versatile and robust biotechnological platform, offering significant advantages for microalgal biomass harvesting, wastewater treatment, biofuels production and/or obtaining of value-added products. This review presents an integrated analysis of the mechanisms governing the formation, stability, and functionality of these systems, combining physicochemical, biological, and mathematical modelling approaches and aims to describe the current state of the art and main research needs. The aggregation process is strongly influenced by the complementarity of the surface properties of microalgae and filamentous fungi, including electrostatic interactions, production of extracellular polymeric substances (EPSs), and modifications in surface roughness. Recent advances in multiscale characterization techniques, such as confocal microscopy, micro-computed tomography, atomic force microscopy, and X-ray photoelectron spectroscopy, have allowed a more precise elucidation of the internal architecture and surface chemistry of the pellets. In parallel, biological characterization through enzymatic assays, oxidative stress biomarkers, and photosynthetic activity analyses has provided relevant information on the metabolic responses and functional resilience of the consortium. Additionally, the incorporation of mathematical flocculation models can contribute to the prediction of pellet growth, density, and stability, supporting process optimization and application. The understanding of these interaction phenomena is important for the design of high-yield and efficient systems, including their development and validation, to expand the use of microalgae–fungal pellets in bioprocesses, as evidenced by this review. Full article

In this study, total ammonia nitrogen (TAN) excretion rates were quantified in juvenile (mean weight: 1.79 ± 0.17 g) and adult (mean weight: 15.91 ± 0.63 g) prawns (Macrobrachium caementarius) reared under recirculating aquaculture system (RAS) conditions representative of small-scale farming operations. Prawns were fed a commercial dry pelleted diet (48.5% crude protein) at a daily ration equivalent to 5% of total biomass. Water quality parameters were maintained within species-specific tolerance ranges to ensure normal physiological and metabolic function. TAN excretion rates were estimated using a mass balance approach under closed-flow batch conditions. A significant difference in TAN excretion was observed between life stages (p = 0.008): juveniles excreted 0.009 ± 0.006 mg TAN g⁻¹ h⁻¹ (0.22 ± 0.18 mg TAN g⁻¹ day⁻¹), whereas adults excreted 0.03 ± 0.01 mg TAN g⁻¹ h⁻¹ (0.73 ± 0.06 mg TAN g⁻¹ day⁻¹). Distinct diel postprandial patterns were evident in both life stages, with peak TAN release occurring 1–2 h after each feeding event, followed by a gradual decline. These life-stage differences have direct implications for RAS design and biofilter management and should be interpreted in the context of the dietary conditions used. The quantified excretion rates provide baseline bioengineering parameters for sizing biofilters, estimating nitrogen loading, and optimizing water quality management for this emerging aquaculture species. Full article

Alfalfa densification is a critical step in feed utilization and biomass energy conversion because it directly affects the transport efficiency, storage stability, and energy consumption of biomass processing systems. However, the thermodynamic behavior of the densification process remains poorly understood, especially under open-die conditions without external heating. This study investigated the thermo-mechanical characteristics of alfalfa pellet open-die densification without external heating by combining experimental measurements with ANSYS macro-continuum simulation. Stress transmission and temperature field distributions were analyzed. The results showed that the pellet quality index under different process conditions remained above 800, meeting the requirements for pelleted feed. Moisture content had a more significant effect on forming pressure than other factors; as moisture content increased, the forming pressure decreased. At an aspect ratio of 5.0, the forming pressure was below 45 kN. Simulation results further indicated that aspect ratio had a stronger influence on frictional behavior during densification. Under an aspect ratio of 5.0, the energy consumption was 888.53 J, and the heat flux reached 0.0062 W/mm². These results indicate that frictional dissipation driven by radial force is the dominant mechanism governing thermo-mechanical coupling. Moisture content and aspect ratio significantly affected both peak compression force and coupling intensity. Although reducing moisture content or increasing aspect ratio improved pellet quality, it also increased die load due to enhanced radial force. The coupling intensity followed the order: peak pressure stage > moving stage > compression stage. These findings reveal the evolution of stress and temperature fields during alfalfa densification, offering critical theoretical guidance for optimizing densification process parameters. Full article

As the Italian hop industry undergoes consolidation, assessing the environmental pressure of diverse cultivation and processing models is essential for sustainable growth. This study characterizes the Product Environmental Footprint (PEF) of Italian hop production through a multi-case analysis of eight representative farms. A primary data collection tool was utilized to quantify resource inputs, including water management, nutritional strategies, and phytosanitary defense. Following a rigorous thermodynamic consistency screening of the field data to eliminate unrepresentative parameters, the life cycle inventory focused on two validated regional anchor cases. The findings reveal a high degree of management heterogeneity, with dry cone yields ranging from 400 to 1673 kg of dry matter per hectare. Two functional units were defined: 1 kg of fresh hop cones (FU1) to assess cultivation impacts, and 1 kg of processed products (FU2) at the brewery gate to evaluate the full supply chain. Integrating deterministic life cycle impact outputs with a probabilistic Monte Carlo uncertainty analysis, the results indicate that the environmental impact varies significantly across commercial formats: Cryogenic Powder (2.33 ± 0.34 mPt/kg) represents the most resource-intensive format, while Raw Bales and T90 Pellets from high-yield models exhibit scores as low as 1.36 and 1.55 mPt/kg, respectively. The study identifies the agricultural phase as the primary environmental hotspot, driven predominantly by water deprivation. To address these burdens, a Sustainable Italian Hop (SIH) integrated scenario was developed. By combining precision irrigation, thermal decarbonization via biomass valorization, and a direct-to-pellet processing flow, this model achieved a 70% total reduction in the environmental footprint score (0.465 ± 0.076 mPt/kg) and an 86% reduction in water use impacts. Finally, the socio-technical and financial barriers to implementing the SIH framework are qualitatively evaluated. These results provide actionable benchmarks for aligning the emerging Italian hop supply chain with European Union climate neutrality objectives. Full article

Biomass pellets and briquettes are commonly treated as compacted solid biofuels, but their potential extends beyond direct combustion and heat generation. This review aims to synthesise current knowledge on pellets and briquettes as both energy carriers and functional materials for agro-environmental, biological, sorption, and material applications. A structured narrative review was conducted using Web of Science, Scopus, and OpenAlex, complemented by targeted searches of standards, life-cycle assessment studies, and recent experimental literature. This review discusses key physicochemical, mechanical, and environmental properties, including density, moisture content, durability, ash content, higher heating value, elemental composition, storage stability, and biodegradability. It also compares major energy pathways, including combustion, combined heat and power, torrefaction, hydrothermal carbonisation, pyrolysis, and gasification, with non-combustion uses such as fertiliser and microbial carriers, sorbents, bedding materials, mushroom substrates, biocomposites, and lightweight building components. Published studies indicate that the environmental performance of densified biomass depends strongly on feedstock origin, drying energy, transport, end-use technology, and system boundaries. The review proposes a quality-to-function framework in which pellet and briquette quality is interpreted in relation to the intended application rather than through a single universal fuel-quality criterion. This approach supports more precise biomass valorisation within circular bioeconomy systems. Full article

The co-gasification of biomass and municipal solid waste (MSW) has high potential for sustainable energy generation and waste-to-energy applications. Calliandra calothyrsus (CC) and MSW pellets have complementary thermochemical properties, although there are few experimental studies on their co-gasification in downdraft reactors. This study analyzed the effect of the feedstock composition on the temperature distribution inside the reactor, the syngas composition, and the quality of syngas energy in a 1–2.5 kg/h downdraft gasifier during co-gasification. Six feedstock blend compositions were experimentally evaluated: they were 100 CC, 70 CC–30 MSW, 60 CC–40 MSW, 40 CC–60 MSW, 30 CC–70 MSW, and 100 MSW. The criteria considered for measuring include reactor temperature distribution, syngas composition (CO, H₂, CO₂, and C_nH_m), and lower heating value (LHV). The results indicated that the 70 CC–30 MSW blend had the best syngas performance with a higher oxidation-zone temperature, greater CO concentration, reasonably steady H₂ generation, lower C_nH_m concentration, and the highest syngas LHV compared to other feedstock compositions. In the gasification process, the increase in the proportion of CC was beneficial to char reactivity, oxidation–reduction reaction, and tar cracking. The increase in MSW fractions decreased syngas quality due to the increase in ash and moisture content. The results show that co-gasification of Calliandra calothyrsus and bio-dried MSW pellets can increase syngas quality and provide practical insight into the optimization of biomass–MSW blending for downdraft gasification systems. Full article

The development of sustainable and efficient plant growth substrates is crucial for modern agriculture. This study assessed the potential of plant pellets formulated from various lignocellulosic residues, either with or without bamboo biochar (BB-char) and arbuscular mycorrhizal fungi (AMF), to support seed germination and early seedling growth. Four types of residues, including coconut coir (CO), corn cob (CC), leaves from the genus Dipterocarpus (DL), and teak leaves (TL), were combined with soil and paper waste to produce eight pellet formulations, with commercial peat pellets serving as a control. Chemical analyses revealed significant variation among the pellet types, with pH values ranging from 6.40 to 7.65, electrical conductivity (EC) from 3.64 to 11.62 mS cm⁻¹, and differences in organic matter, carbon, and nutrient contents [nitrogen (N), phosphorus (P), potassium (K)], reflecting the influence of residue type and the addition of BB-char and AMF. Phytotoxicity screening using aqueous extracts demonstrated species-specific responses, with cucumber exhibiting high tolerance across treatments, whereas chili seeds were more sensitive. Final germination percentage (FGP) and seedling growth assays in greenhouse conditions showed that pellets derived from CC and CO, particularly when combined with BB-char and AMF (T6 and T7), enhanced shoot and root development in carrot, chili, cucumber, and tomato, approaching the performance of commercial peat pellets. In contrast, DL- and TL-based pellets resulted in lower germination and growth. These findings indicate that both the physicochemical properties of lignocellulosic wastes and the combination of BB-char and AMF are important factors influencing pellet efficacy, highlighting the potential of CC- and CO-based pellets as sustainable peat alternatives for early-stage plant cultivation. Full article

The valorization of agro-industrial residues and sewage sludge into value-added products through vermicomposting represents a promising strategy for nutrient recycling and waste reduction. This study evaluated the effects of aqueous extracts obtained from five vermicomposts (VC1-VC5) produced from different mixtures of vineyard and winery residues and sewage sludge on cucumber (Cucumis sativus L.) seedlings grown under in vitro conditions. The aqueous extracts (10%, w/v) were characterized in terms of pH, electrical conductivity, and total polyphenolic content, and applied to cucumber seedlings cultivated for 30 days under sterile and controlled in vitro conditions using commercially available peat pellets (Jiffy-7^®). Seedling development was monitored throughout the experiment, and morphological and biochemical parameters were assessed at the end of the 30-day assay. All extracts supported seedling development, with no evidence of phytotoxicity. The application of VC2 and VC4 extracts resulted in significant increases in fresh and dry weight, while VC2 led to higher chlorophyll and carotenoid contents. Conversely, VC3 and VC5 extracts were associated with slight reductions in growth parameters and photosynthetic pigment content. Correlation analysis suggested positive associations between biomass accumulation and chlorophyll content, and negative association between total polyphenolic content and stem growth. Overall, the results indicate that aqueous vermicompost extracts were not phytotoxic under the tested conditions, although their effects appear to depend on extract composition, highlighting the importance of feedstock selection for sustainable horticultural applications. Full article

The world’s energy matrix faces challenges in replacing fossil fuels and reducing greenhouse gas emissions. Pellet production is effective for the correct disposal of agricultural waste through the production of biofuels. The objective of this work was to produce and characterize pellets from blends of pine and coffee straw residues, in addition to their compliance with ISO 17225-6/2021. The biomasses were subjected to analysis of dry and wet base moisture, bulk density, upper and lower calorific value (HCV and LCV dry), immediate, structural and elemental chemistry, chloride content, and thermogravimetric behavior. The pellets were produced in nine blends with the Amandus Kahl pellet mill, model 14-175, being submitted to analysis of productivity, moisture in dry and wet base, HCV and LCV dry, chloride, immediate chemistry, hardness, diameter and length, durability and percentage of fines, the analyses were compared by the Scott-knott test at the level of 95% probability. The blends that presented the best overall performance were 100% pine and a mixture of 87.5% pine and 12.5% coffee straws, especially for the higher calorific value (20.65 and 20.65 MJ/kg), moisture (8.98 and 9.17%), and ash (0.22 and 1%), but had limitations regarding mechanical durability (96.74 and 97.12%). The use of blends in pellet production is promising to promote the sustainable use of agricultural waste and the generation of clean energy. Full article