Biomass doi: 10.3390/biomass6030036

Authors: Juliana Dias de Oliveira Ana Carolina Amorim Orrico Luís Antonio Kioshi Aoki Inoue Michely Tomazi Tarcila Souza de Castro Silva Érika do Carmo Ota Cláudio Teodoro de Carvalho Ranielle Nogueira da Silva Vilela Marco Antonio Previdelli Orrico

Fish-processing residues represent a significant environmental challenge due to their high moisture and nitrogen contents, which favor greenhouse gas (GHG) emissions during degradation. This study evaluated how different waste management strategies affect GHG emissions from fish waste, including conventional composting (Bulk), composting amended with biochar (BulkBioch), burial with soil (S), and burial with soil plus sawdust (BulkS). Daily emissions of CH4, N2O, and CO2 were monitored, and cumulative emissions were modeled using generalized additive models. Composting treatments (Bulk and BulkBioch) released higher CO2, suggesting greater microbial degradation, while burial treatments developed earlier anaerobic conditions with reduced decomposition efficiency. Bulk showed the highest cumulative CH4 and CO2 emissions, whereas N2O fluxes were greater in burial methods, reaching 2.18 g N2O kg−1 TS in S. Biochar addition was associated with 15% and 10% lower CH4 and N2O emissions, respectively, and earlier stabilization of CH4 emissions. In global warming potential, BulkBioch presented the lowest climate impact (305 g CO2-eq kg−1 fish), followed by Bulk (338 g CO2-eq kg−1), whereas BulkS reached up to 599 g CO2-eq kg−1. The use of bulking agents in burial resulted in lower CH4 buildup and greater nutrient retention. Overall, combining bulking agents and biochar may represent a promising strategy to mitigate GHG emissions while supporting nutrient conservation.

Biomass doi: 10.3390/biomass6030035

Authors: Elif Nur Dilbirliği Mohamed Mehdi Yataghene Spyros Grigorakis Dimitris P. Makris

The examination presented herein aimed at developing a benign alkali-catalyzed organosolv treatment for efficacious recovery of antioxidant hydroxycinnamates from wheat straw (WS), which is a widespread agricultural residue, rich in lignocellulosic material. After an initial screening of aqueous mixtures of various common alcohols, 20% (v/v) 1-propanol was selected as the most efficient solvent, while a following trial indicated 1.5% sodium hydroxide as the most appropriate catalyst concentration. Using this system (20% 1propanol/1.5% sodium hydroxide), WS treatment was investigated by carrying out polyphenol recovery kinetics, estimating the effect of severity and performing treatment optimization with response surface methodology. It was shown that the yield in total polyphenols and the ferric-reducing power of the extracts produced were highly correlated with treatment severity, but the antiradical activity was less so. Under optimized conditions, the treatment afforded a total polyphenol yield of 30.0 ± 1.7 mg ferulic acid equivalents g−1 dry WS mass, at 300 min and 80 °C. Analysis of the extracts obtained under optimized conditions with liquid chromatography–tandem mass spectrometry revealed the instrumental role of the alkali catalyst in liberating major bound hydroxycinnamates, namely p-coumaric acid and ferulic acid. The corresponding yields of these two compounds were 4.01 and 2.55 mg g−1 dry WS mass, suggesting WS as a promising source of high value-added phytochemicals, with a significant prospect in food, pharmaceutical and cosmetics industry.

Biomass doi: 10.3390/biomass6030034

Authors: Kaizar Hossain Sayanti Kar Dipsita Hati Arpita Ghosh Sinjini Sengupta Souvik Paul Avik De Abhishek RoyChowdhury

The textile industry consumes a significant quantity of water and produces effluent containing water-soluble dyes and heavy metals such as Lead (Pb), Cadmium (Cd), Chromium (Cr), Copper (Cu), and Zinc (Zn), among others. Heavy metal contamination of water bodies and their impact on aquatic life, as well as on human health, is of prime importance. This review examined the potential of phytoremediation, a low-cost and eco-friendly process for removing contaminants from textile effluent. This review also investigated the impact of heavy metal toxicity on aquatic plants used for biogas production post phytoremediation application. This review evaluated textile effluent characteristics, efficiency evaluation of phytoremediation of textile wastewater, metal uptake mechanisms of aquatic plants, and anaerobic digestion processes with emphasis on Water hyacinth (Eichhornia crassipes), Duckweed (Lemna minor), and Water lettuce (Pistia stratiotes). The findings indicated that these aquatic plants possess immense potential for removing heavy metals and other impurities by employing phytoextraction and rhizofiltration methods. Their rapid growth rate makes them preferred candidates for anaerobic digestion. However, accumulation of heavy metals in plant tissues inhibits microbial activities during anaerobic digestion, resulting in fluctuations in biogas and methane production. Findings also showed that these aquatic plants are efficient in the removal of heavy metals in water while yielding considerable biomass that can be used to produce bioenergy through anaerobic digestion. However, the sequestration of heavy metals in plant biomass may affect the rate of methane generation efficiency. The findings of this review suggest that phytoremediation has promising potential for the recycling of textile wastewater and, when coupled with biogas production, contributes towards a circular bioeconomy, an approach that integrates closed-loop resource utilization with renewable biological systems to minimize waste.

Biomass doi: 10.3390/biomass6030033

Authors: Marco Antonio-Zarate Lizeth Rojas-Blanco Moises Moheno-Barrueta Marcela Arellano-Cortaza Ildefonso Zamudio-Torres Erik Ramirez-Morales

The growing demand for sustainable, decentralized energy solutions has heightened interest in biomass-based technologies for rural applications. In Mexico, the expansion of oil palm cultivation in humid tropical regions has generated large quantities of agro-industrial residues that remain largely underutilized. This review analyzes the potential of oil palm residues as feedstock for small-scale thermochemical conversion, with a particular focus on gasifier stove technologies. Key residues, including empty fruit bunches, mesocarp fiber, and palm kernel shells, exhibit favorable physicochemical properties, including adequate calorific values and high volatile matter content, which support their suitability for gasification processes. However, challenges related to moisture content, ash composition, and tar formation may affect system performance and require appropriate pre-treatment and operational control. Gasifier stoves, especially fixed-bed and top-lit updraft (TLUD) configurations, represent a viable solution for decentralized energy generation in rural settings, improving combustion efficiency and reducing emissions compared to traditional biomass use. Despite their potential, current bioenergy policies in Mexico remain primarily focused on large-scale biofuel production, limiting the deployment of small-scale technologies. Overall, oil palm residues constitute a promising feedstock for gasifier stove applications, although their successful implementation depends on feedstock optimization, appropriate stove design, and the development of policy frameworks that support decentralized bioenergy systems.

Biomass doi: 10.3390/biomass6020032

Authors: Gergana Peeva

Phosphorus is an essential and finite resource critical for global food production, yet its inefficient use and discharge from wastewater systems contribute to eutrophication and resource depletion. The transition from conventional wastewater treatment plants to water resource recovery facilities has intensified interest in technologies that enable phosphorus recovery within a circular economy framework. This review provides a critical and up-to-date synthesis of phosphorus recovery strategies from wastewater, with primary emphasis on struvite (MgNH4PO4·6H2O) crystallization as one of the most mature and practically implemented recovery routes. The occurrence and chemical forms of phosphorus in wastewater streams are discussed alongside conventional approaches, such as enhanced biological phosphorus removal and chemical precipitation, in order to position struvite recovery within the broader phosphorus management landscape. In addition to struvite crystallization, selected competing and complementary recovery pathways, including electrochemical systems, biochar-assisted processes, and sludge ash recovery, are discussed to compare technological maturity, recovery potential, and practical applicability. Particular attention is given to reactor configurations, full-scale applications, and commercial technologies to assess operational reliability, recovery performance, and fertilizer product quality. Life-cycle assessment results and regulatory developments are also discussed to contextualize sustainability claims, technology selection, and market integration. The review identifies key technical and economic challenges, particularly regarding magnesium supply, competing ions, wastewater matrix effects, and the feasibility of mainstream application. Overall, controlled sidestream struvite crystallization appears to offer the most favorable balance between recovery efficiency, operational reliability, and fertilizer product quality under suitable plant conditions.

Biomass doi: 10.3390/biomass6020031

Authors: Sri Hartini Diana Sari Didik Nurhardiyanto Muhammad Hisjam Benedictus Ardityawan Dhanius Sandi

Indonesia, particularly Central Java, generates substantial amounts of agricultural biomass residues, including melinjo shells, tobacco stalks, and cacao shells, which remain underutilized for energy applications. This study addresses the limited scientific evidence on the fuel properties and environmental performance of these residues by systematically evaluating their suitability as briquette feedstocks. A factorial experimental design was applied using three biomass types and two binders (tapioca starch and clay). The produced briquettes were characterized for moisture content, ash content, volatile matter, and higher heating value according to the Indonesian National Standard (SNI 01-6235-2000), and their environmental performance was assessed using a Life Cycle Assessment (LCA) approach to estimate associated environmental costs. The results indicate that briquettes made from melinjo shells with tapioca starch binder exhibited the most favorable performance, achieving a moisture content of 7.01%, ash content of 13.58%, volatile matter of 47.15%, and a calorific value of 5453.43 cal g−1. However, the ash and volatile matter contents exceeded the recommended limits for solid biofuels. These findings demonstrate that melinjo shells are a promising feedstock for briquette production due to their relatively high energy content, while further improvements in carbonization conditions and reductions in binder proportion are required to enhance fuel quality and environmental performance.

Biomass doi: 10.3390/biomass6020030

Authors: Rania Abbi Alexander Mikhalev Meryem Achira Ayoub Ainane Aise Deliboran Ayla Mumcu Khadija Oumaskour Tarik Ainane Rafail Isemin

This study evaluated the sustainability of removing phenolic compounds from olive mill effluents using a nanobiochar synthesized from olive pomace. Catechol, tyrosol, hydroxytyrosol, and homovanillic alcohol were chosen as model pollutants due to their presence in agro-industrial wastewater. The surface morphology, elemental composition, crystallographic structure, functional groups, porosity, and thermal stability of the nanobiochar were investigated by SEM, EDX, XRD, FTIR, BET analysis, and TGA/DTA. The developed nanobiochar exhibited a predominantly amorphous carbon structure, enriched in carbon (85.6%), with localized graphitic domains. Its mesoporous architecture (SBET = 15.478 m2 g−1; Dp = 2.14 nm) promotes accessibility to active sites, while its thermal stability confirmed its suitability for adsorption applications. In this batch adsorption study, the technological aspect considered is the influence of operating parameters on adsorption efficiency, using kinetic and equilibrium models. Pseudo-first-order and pseudo-second-order kinetic models, as well as Freundlich and Langmuir isotherms, were used to analyze the experimental data. The pseudo-second-order model proved to be the most suitable for describing adsorption, suggesting that the process is primarily dominated by chemisorption. Similarly, the Langmuir model gave the least satisfactory results regarding equilibrium data, indicating monolayer adsorption on homogeneous active sites. The adsorption capacity of phenolic compounds was variable. The highest adsorption capacities were observed for catechol (250 mg g−1), tyrosol (19.23 mg g−1), homovanillic alcohol (15.38 mg g−1), and hydroxytyrosol (13.16 mg g−1). The results of this research indicate that adsorption affinity depends on molecular structure and electronic properties. Furthermore, computer modeling based on molecular simulations and electronic descriptors was performed to explain the adsorption mechanism. Linear regression, principal component analysis, and elastic regression revealed strong correlations between adsorption parameters and molecular descriptors. These results demonstrate that olive pomace-based nanobiochar is an environmentally friendly adsorbent for the treatment of phenolic effluents, with adsorption primarily controlled by surface interactions.

Biomass doi: 10.3390/biomass6020029

Authors: Márcio D. N. Ramos João Pedro M. Souza Johan M. Thevelein José Renato Guimarães Thais S. Milessi

Consolidated Bioprocessing (CBP) is a promising technology that integrates enzyme production, biomass hydrolysis, and sugars fermentation. However, CBP is underexplored from a process engineering point of view. Considering that cell recycling can increase process economic viability and that the selection of a bioreactor is a key factor to ensure process effectiveness, this study demonstrates the feasibility of recycling cells during sugarcane bagasse CBP by using magnetic immobilized enzyme producer yeast and a low shear stress vortex flow bioreactor. In the first step, Ca-alginate immobilized strains achieved good productivities (0.48 g/L/h) and 5.7 g/L of ethanol in only 12 h, but cell recovery was hindered by residual solids. To overcome this limitation, magnetic particles were incorporated into the spheres, allowing for rapid post-fermentation, maintaining ethanol production and productivity (6.1 g/L and 0.51 g/L/h). Three repeated batches were successful performed (producing an average of 5.5 g/L of ethanol, 0.46 g/L/h) with complete cell recovery from the remaining solid after biomass hydrolysis, maintaining high cell viability and bead integrity, highlighting the robustness of the immobilization strategy and the suitability of the bioreactor for the process. The successful cell recovery accomplished overcomes a fundamental limitation of bioprocesses carried out in the presence of solids. This strategy represents an important step for biorefineries development, with potential applicability to other bioprocesses using solid substrates.

Biomass doi: 10.3390/biomass6020028

Authors: Joan G. Lynam Nazimuddin Wasiuddin Mostafa A. Elseifi Syed Ashik Ali Musharraf Zaman Md Reazul Islam Nafisa Tarannum Kenneth Hobson

Utilizing lignin from agricultural wastes as a partial replacement for asphalt binder used in pavement presents a sustainable option, as it is abundant in nature. The effects of the addition of lignin on the properties and performance of asphalt binder and asphalt mixes were studied. Lignin was produced from rice husks, using a hydrothermal carbonization (HTC) treatment process. The rice husk-derived lignin was then mixed with a PG 67-22 binder at 0%, 5% and 10% of the mass of the total binder. The HTC treatment of rice husks at 250 °C created a powdery substance with an increased acid-insoluble lignin content and a reduced cellulose and hemicellulose content. The addition of 10% lignin was found to produce an unstable modified binder due to phase separation between the lignin and binder, thus requiring continuous stirring before use. Asphalt mixes prepared with 5% lignin exhibited better moisture-induced damage resistance compared to the control mix. Also, an improved rutting resistance of asphalt mixes was observed with the use of a lignin-modified binder. Lignin from rice husks may constitute a sustainable partial substitute for a crude-oil-based binder.

Biomass doi: 10.3390/biomass6020027

Authors: Juana Fernández-Rodríguez Marta Muñoz Montserrat Perez

Rapid population growth is intensifying global energy demand and waste generation. Slaughterhouse waste is creating important environmental problems. Transforming this into renewable energy through technologies like anaerobic digestion offers a sustainable pathway to reduce environmental impacts and support the energy transition. The main objective of this study was to examine the biodegradability of the slaughterhouse semi-liquid fraction (S), slaughterhouse liquid fractions (L), and their mixtures (25%, 50%, and 75%) through a two-phase anaerobic co-digestion (TPAcD) process. Batch reactors were operated in two separate microbiological and thermal phases. In the first, a thermophilic 55 °C–acidogenic stage, biochemical hydrogen potential (BHP) assays were conducted to evaluate green hydrogen production, while in the second, a mesophilic 35 °C–methanogenic stage, biochemical methane potential (BMP) assays were carried out to assess biomethane generation. The most relevant findings revealed that while liquid fractions maximized hydrogen recovery, overall yields remained limited due to competitive metabolic pathways. Notably, the 25L:75S configuration optimized hydrolysis, with a 1280% increase in soluble COD, establishing the semi-liquid fraction as a critical organic reservoir for thermophilic–acidogenic activity. In the subsequent stage, the acidogenic pre-treatment significantly enhanced methanogenesis, where the same 25L:75S mixture exhibited a synergistic methane yield of 495.46 mL CH4/g VS. This 13.8% improvement over the theoretical additive potential confirms that strategic substrate balancing overcomes individual feedstock limitations, maximizing energy recovery in sequential anaerobic digestion. These results highlight the potential of phase-separated anaerobic co-digestion as a strategy to improve the valorization of slaughterhouse wastes.

Biomass doi: 10.3390/biomass6020026

Authors: Charith Akalanka Dodangodage Geethaka Nethsara Gamage Lakru C. Mallawa Jagath C. Kasturiarachchi Kavini Vindya Fernando Ranoda Hasandee Halwatura Thilini A. Perera Sanjitha Dilan Rajapakshe Sayuri S. Niyangoda Rangika Umesh Halwatura

The integration of microalgal cultivation with wastewater streams offers a promising pathway to enhance resource efficiency within circular bioeconomy frameworks. However, the suitability of clarified aquaponics sedimentation effluent for producing carbohydrate-rich microalgal biomass remains insufficiently evaluated, particularly with respect to nutrient recovery and bioethanol-relevant feedstock potential. In this study, clarified aquaponics sedimentation effluent was assessed as a cultivation medium for Chlorella sp. under controlled laboratory conditions. Biomass productivity, nutrient removal performance, and carbohydrate accumulation were systematically evaluated and compared with conventional synthetic medium. Chlorella sp. cultivated in clarified aquaponic effluent achieved a maximum biomass concentration of approximately 2.05 g L−1, exceeding that obtained in Bold’s Basal Medium. Carbohydrate content exceeded 40% of dry weight, indicating suitability for fermentable sugar production. Nitrate and phosphate removal efficiencies greater than 95% were achieved, with mass balance analysis confirming biological assimilation as the primary removal mechanism (~87.4%). This confirms the dual functionality of the system. The effective nutrient assimilation and confirmed the dual functionality of the system as both a biomass production and nutrient recovery process. Comparable performance under diluted and undiluted effluent conditions further indicated that freshwater dilution is not required following clarification. Light saturation was observed at 180–190 μmol m−2 s−1, providing guidance for energy-efficient operation. These findings demonstrate that clarified aquaponics effluent can serve as an effective alternative growth medium for producing carbohydrate-rich Chlorella sp. biomass while enabling nutrient recovery. The estimated bioethanol potential is theoretical, based on stoichiometric conversion assumptions, and experimental fermentation was not conducted. This work provides quantitative evidence supporting the integration of microalgae into aquaponic systems and establishes a foundation for future pilot-scale, techno-economic, and life-cycle assessments.

Biomass doi: 10.3390/biomass6020025

Authors: Jorge Emilio Hernández Ruydíaz Daniel David Otero Meza Juan José Cabello Eras Jairo Guadalupe Salcedo Mendoza Camilo Andrés Novoa Pérez Camilo Andrés Meza Sanmartín María José Lozano Polo Kleyder José Salgado Angulo Eduardo David Arroyo Dagobeth Lisbeth Cecilia Tuirán Romero

The transition towards a circular bioeconomy in developing regions is frequently hindered by operational failures caused by feedstock discontinuity. Whilst biochemical potential is traditionally the primary selection criterion, this study postulates that logistic reliability serves as the governing constraint. To validate this strategic reorientation, a decision-making framework was developed and applied to a representative tropical agro-industrial region. A sensitivity analysis comparing objective, subjective and neutral weighting scenarios identified annual residue production as the dominant factor. Results established cattle manure as the universal baseload substrate essential for mitigating seasonality, outweighing higher-yielding but intermittent agricultural residues. Spatial analysis revealed distinct territorial vocations, identifying a high-availability rice–livestock cluster in the south suitable for centralised industrial plants and dispersed cassava–livestock nodes in the centre favourable for decentralised digestion. Furthermore, the assessment of energy autonomy demonstrated that the prioritised co-digestion scenarios could cover local residential electricity demand between 1.5 times and 81 times. Crucially, residues favoured by expert judgement proved logistically unfeasible despite superior theoretical yields. This data-driven approach demonstrates that successful substrate selection must transcend theoretical yield maximisation to prioritise supply chain reliability, providing a robust roadmap for de-risking bioenergy investments and ensuring regional energy autonomy.

Biomass doi: 10.3390/biomass6020024

Authors: Masud Kabir Isabel López-Cortés Carlos Ferrer-Gisbert Diego-David Moposita-Vasquez Borja Velázquez-Martí

The growing global demand for sustainable energy has intensified interest in biomass residues as viable feedstocks for biofuels and bio-based production. This review systematically examines advances in the utilization of biomass residues, spanning upstream assessment through downstream conversion pathways. Using the PRISMA framework, 543 peer-reviewed articles published between 1990 and 2025 were analyzed from the Scopus and Web of Science databases. The review reveals a clear methodological evolution from early residue characterization and physicochemical analyses toward integrated techno-economic, environmental, and system-level assessments. Upstream research increasingly addresses feedstock identification, spatial dispersion, logistics optimization, and pretreatment efficiency, while downstream advances focus on biochemical, thermochemical, and hybrid conversion technologies. Although artificial intelligence and machine learning constitute approximately 2.5–3% of the total historical literature, they account for nearly 18–22% of recent studies in process modeling and yield prediction, achieving predictive accuracies frequently exceeding R2 > 0.95. Despite these advances, persistent challenges remain in biomass logistics, feedstock heterogeneity, and technology scaling. Emerging trends highlight hybrid frameworks that integrate data-driven and mechanistic models to enhance efficiency, circularity, and commercial feasibility in bioenergy systems.

Biomass doi: 10.3390/biomass6020023

Authors: Jing Fu Pieter Koster Amirhoushang Mahmoudi Artur Pozarlik

This paper builds a one-dimensional transient numerical model of mixed fuel of woody and non-woody biomass to simulate the multistage conversion process of biomass in a moving grate-fired bed, including drying, pyrolysis, gasification, and char combustion. Based on time and space discretization, the model comprehensively considers the conservation of mass, momentum, and energy. It also introduces reaction kinetics and freeboard radiation coupling effects to more accurately describe the bed temperature distribution and reaction process. The analysis focuses on the effects of different non-woody biomass mixing ratios and moisture content. This provides references for optimization of the design of future furnaces and operating parameters and mixed fuel composition. The simulation results show that, for pure woody biomass, the surface temperature reaches approximately 200 °C in the first zone, followed by char reactions with peak temperatures up to 592 °C. The whole conversion process takes about 62% of the grate length. Increasing the pepper mixing ratio leads to lower bed temperatures due to the higher moisture content. The maximum bed temperature in the first zone decreases from 592 °C for pure wood to 551 °C at 30 wt.% pepper, with delayed pyrolysis and a thinner char reaction zone. When the pepper mixing ratio is below 20 wt.%, the combustion process maintains a stable temperature gradient and a continuous reaction front, compared to the mixing ratio of 30% pepper case. This confirms the feasibility of non-woody biomass application to combustion technology. Although a higher pepper mixing ratio leads to a slight temperature decrease, the reaction remains stable along the grate, indicating reliable combustion performance.

Biomass doi: 10.3390/biomass6020022

Authors: Arly Morico Jeffrey Lavarias Wendy Mateo Antonio Barroga Melba Denson Kaye Papa Marvin Valentin Andrzej Białowiec

Waste is increasingly recognized as misplaced biomass, underscoring its potential for reintegration into sustainable environmental management strategies. Biomass pyrolysis has emerged as a promising value-adding process capable of enhancing material properties for diverse applications. In this study, discarded Pili (Canarium ovatum Engl.) nutshells (PS) were utilized as a pyrolysis feedstock to upgrade their fuel characteristics. Pyrolysis conditions were optimized using response surface methodology (RSM) based on a central composite design (CCD) to maximize fixed-carbon content and higher heating value (HHV). The optimized biochar achieved a maximum fixed-carbon content of 86.15% and an HHV of 32.10 MJ/kg at a pyrolysis temperature of 600 °C and a residence time of 60 min, values comparable to those of conventional coal. Under these optimized conditions, the fixed-carbon content and HHV of the precursor biomass were enhanced by up to 254.7% and 58.4%, respectively. Statistical analysis indicated that pyrolysis temperature was the most significant factor influencing both fixed-carbon content and HHV (p < 0.05). The optimized biochar exhibited low volatile matter (8.88%), low ash content (4.97%), and low atomic ratios (H:C = 0.291; O:C = 0.077), indicating a high degree of carbonization and thermal stability. Energy-dispersive X-ray (EDX) analysis identified alkali and alkaline earth metals (Ca, Mg, Na), which contributed to the ash fraction, with minor heavy metals present, predominantly Pb. Hence, these findings enhance understanding of how pyrolysis conditions affect PS–biochar properties, improving fuel quality indicators.

Biomass doi: 10.3390/biomass6020021

Authors: Anatoliy Angelov Svetlana Bratkova Polina Velichkova Katerina Nikolova Petia Genova Rosen Ivanov Sotir Plochev

In laboratory installations, wastewater from the distillery industry (ethanol stillage and vinasse) is treated via a two-stage combination of microbial sulfate reduction (MSR) and biomethanation, assisted by bioelectrochemical systems (BESs). In the first stage, a sulfidogenic bioreactor with an integrated microbial fuel cell (MFC) is used, which partially oxidizes the produced H2S and facilitates the conversion of organic compounds. Sulfate removal reaches 95.4% (stillage) and 92.8% (vinasse), with corresponding COD reductions of 30.6% and 36.5%, respectively. The polarization curves, power density, generated current, and coulombic efficiency are analyzed. The sulfidogenic bioreactor consortium is dominated by Deltaproteobacteria, which contributes to acetate accumulation during the MSR stage. Methanogens are dominated by the genus Methanofolis. In the second stage of anaerobic digestion, three treatment options are investigated: direct biomethanation, biomethanation after preliminary MSR, and biomethanation after MSR with a microbial electrolysis cell (AD-MEC). The highest COD conversion rates are achieved in the AD-MEC variants: 91.36% for ethanol stillage and 92.8% for vinasse. Microbial communities are dominated by acetoclastic methanogens of the genus Methanothrix. For stillage treated after MSR, biogas production is nearly double that from direct methanation. For vinasse, the largest amount of biogas is generated during by the integrated MEC system, followed direct methanation. Methane content is the highest in methanation after MSR in AD-MEC (93.4–93.6%).

Biomass doi: 10.3390/biomass6020020

Authors: Elisandra Rabelo da Silva Wallysson Wagner Vilela Santos Tatiana Souza Porto Suzana Pedroza da Silva Rodrigo Lira de Oliveira

Cellulases catalyze the hydrolysis of cellulose and can be produced through fermentation processes, such as sequential fermentation (SeqF), which combines submerged and solid-state fermentation. The objective of this study was to evaluate the production of cellulases (endoglucanase and β-glycosidase) by fungi of the genus Aspergillus using coffee husks as substrate. Three Aspergillus strains were evaluated, with A. japonicus URM5620 showing the highest endoglucanase (0.368 U mL−1) and β-glucosidase (0.652 U mL−1) activities by SeqF. Based on the complete factorial design 22, a 9-fold and 3-fold increase in the production of endoglucanase (3.44 U mL−1) and β-glucosidase (2.12 U mL−1), respectively, was observed. Both enzymes showed maximum activity at 60 °C and pH 5.0. The kinetic/thermodynamic parameters indicated a high affinity of the enzymes for their respective substrates and a high catalytic potential. In addition, the half-life and decimal reduction values demonstrate the good thermal stability of endoglucanase (t1/2 = 8.82 ± 0.34 and D = 29.32 ± 1.13 h) and β-glucosidase (t1/2 = 26.61 ± 0.74 and D = 88.38 ± 2.47 h) at 60 °C. The thermostability results indicate potential for use in the pretreatment of raw materials.

Biomass doi: 10.3390/biomass6020019

Authors: Ginevra Ganzi Andrea Pronti

The transition towards circular economy is now a key strategy to address the environmental issues we are facing. Within this framework, biochar, a carbon-rich material derived from residual agricultural pyrolysis, can represent a sustainable and circular solution. This paper aims at evaluating the possibility of implementing a local biochar-production system as part of an economic and social strategy of the redevelopment of an abandoned rural site, Borgo di Perolla, in Tuscany, Italy. A cost–benefits analysis (CBA) was conducted to evaluate the economic feasibility of three different scenarios of production and strategies: Scenario 1 considers revenues solely from the production and sale of biochar and wood vinegar; Scenario 2 additionally includes potential income from the sale of voluntary carbon credits; and Scenario 3 incorporates biochar credits within the European Union Emission Trading System (EU ETS). For each scenario, three indicators were calculated: Net-Present Value (NPV), Internal Rate of Return (IRR), and Breakeven point (BEP). The most evident result that emerged is that the sale of biochar and its by-products alone is not sufficient to ensure the project’s economic sustainability, mainly due to high production costs. Only through carbon-credit-trading markets biochar becomes not only an environmentally strategic tool but also an economically rewarding one. In this sense, market infrastructures, such as the ETS, are essential for the dissemination of circular models, like biochar, that generate both environmental and economic benefits. Previous studies on biochar have largely focused on its application and associated benefits, while cost–benefit analyses have primarily examined its economic feasibility through the commercialization of biochar as a soil amendment, particularly within the United States context. The present work contributes to this literature in three main ways. First, it provides a site-specific and replicable CBA framework applied to a real territorial regeneration project (Borgo di Perolla), grounded in primary data collected through field surveys, stakeholder interviews, and expert validation. Second, the study explicitly compares multiple market-access scenarios within the same analytical framework, ranging from biochar-only sales to voluntary carbon markets, allowing for a clear identification of the economic thresholds at which biochar becomes financially sustainable. Third, and most importantly, the main contribution of this work lies in the explicit modeling of biochar integration into the EU Emissions Trading System. This paper extends the analysis to a regulated carbon market scenario, assuming the recognition of biochar-based carbon removals within the EU ETS framework. From a methodological perspective, the study quantitatively assesses how ETS price dynamics affect the profitability, internal rate of return, and break-even point of a biochar project over a long-term horizon. From a policy perspective, the analysis anticipates recent regulatory developments, such as the EU Regulation 2024/3012, on establishing a Union certification framework for permanent carbon removals, carbon farming, and carbon storage in products, by showing how biochar could function as a fully market-integrated climate technology.

Biomass doi: 10.3390/biomass6020018

Authors: William Vera Jhonsson Luis Quevedo-Olaya César Samaniego-Rafaele Carlos Culqui-Arce Manuel Jesús Sánchez-Chero Grimaldo Wilfredo Quispe-Santivañez Rebeca Salvador-Reyes

The sustainable processing of coffee requires not only improving the efficiency of conventional operations but also advancing the recovery and valorization of bioactive compounds across the coffee value chain. In this context, emerging technologies offer eco-efficient alternatives to conventional extraction methods. This review summarizes recent advances in ultrasound-assisted extraction (UAE), high-pressure extraction (HPE), cold atmospheric plasma (CAP), and microwave-assisted extraction (MAE) applied to coffee beans and major coffee side streams, including pulp, husk, parchment, silverskin, and spent coffee grounds. The physicochemical principles of each technology, the main operating parameters, and their influence on extraction yield, phenolic composition, antioxidant capacity, and heat-sensitive compound preservation are discussed. Furthermore, potential synergies between combined techniques (UAE-MAE or HPE-UAE) and trends toward industrial scaling and integral valorization within a circular economy framework are highlighted. Overall, the evidence indicates that emerging technologies can intensify coffee extraction processes, increase phenolic recovery (often achieving up to two-fold improvements in total phenolic content compared to conventional techniques), and significantly reduce processing times (commonly reaching 2.5–15 min), supporting more sustainable and industrially relevant value chains.

Biomass doi: 10.3390/biomass6010017

Authors: Shaik Nasrullah Shareef Veera Gnaneswar Gude Mohammad Marufuzzaman

Renewable energy systems are increasingly critical for achieving decarbonization and long-term energy security, particularly in rural regions with abundant local resources. While solar and wind technologies have become cost-competitive, their intermittency limits reliability when deployed independently. Biomass, by contrast, offers dispatchable renewable power but faces economic challenges related to feedstock logistics. This study evaluates a biomass-led hybrid renewable energy system (HRES) for Grenada County, Mississippi, integrating biomass, solar photovoltaic (PV), and wind resources to enhance system reliability and reduce environmental impacts. System performance and optimization were assessed using the System Advisor Model (SAM) and the Hybrid Optimization of Multiple Energy Resources (HOMER). The proposed configuration comprises approximately 80% biomass, 10% solar PV, and the remaining share from wind, producing a total annual electricity output of about 423 GWh, sufficient to meet regional demand. The subsystem-level levelized cost of energy (LCOE) was estimated at 12.10 cents/kWh for biomass, 4.07 cents/kWh for solar PV, and 8.62 cents/kWh for wind, with the overall hybrid cost influenced primarily by biomass feedstock transportation and storage. Environmental impact assessment based on U.S. EPA eGRID and IPCC factors indicates that the hybrid system achieves a weighted emission intensity of approximately 28.4 kg CO2-eq/MWh, representing a reduction of over 94% compared to the regional grid. When scaled to annual generation, this corresponds to roughly 197,000 metric tons of avoided CO2-equivalent emissions per year, alongside 80–95% reductions in acidification and eutrophication impacts. The results demonstrate that biomass-anchored hybrid systems can provide a reliable, low-carbon pathway for rural energy development, with further cost reductions achievable through targeted policy incentives and financing support.

Biomass doi: 10.3390/biomass6010016

Authors: Nazim M. Bellal Ouacil Saouli Massimo Urciuolo Giovanna Ruoppolo Anna Basco Renata Migliaccio Biagio Ciccone Fabrizio Scala

This study investigates the potential of tomato waste (TW) and hot pepper waste (HPW) biomass from local food industries in Algeria as sustainable feedstocks for fluidized-bed air gasification. Conversion efficiency, syngas composition and energy content were evaluated under different operating conditions, including gasification temperature (750 and 850 °C) and bed material (silica sand, olivine, and a ZSM-5 zeolite catalyst/silica sand mixture). The results demonstrate that gasification of these biomasses in a bubbling fluidized-bed reactor is an effective waste-valorization route, producing a syngas rich in hydrogen and methane, suitable for power generation and biofuel applications. Under all operating conditions, hot pepper waste generated a syngas with higher energy content than tomato pomace.

Biomass doi: 10.3390/biomass6010015

Authors: Othmar J. Aguilar-Bautista Karina Aguilar-Arteaga Araceli Castañeda Ovando Yari Jaguey Hernández Gonzalo Velázquez de la Cruz Eduardo Morales Sánchez Prisciliano Hernández Martínez

In this study, barley biomass from the brewing industry was used to obtain fraction-rich arabinoxylans, polysaccharides that, due to their chemical and structural properties, can form films. The effect of adding three plasticizers at a concentration of 20% w/w on the mechanical, optical, and barrier properties of the thermoplasticized films was evaluated. Tensile strength (TS) and percent elongation (%E) tests were performed to determine the mechanical properties, water vapor transmission rate (WVTR) and water vapor permeability (WVP) were evaluated by gravimetric methods, the ΔE and color index (CI) were calculated with the chromatic coordinates of the CIE-L*a*b system, and structural morphology was determined by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR-ATR). The results show that plasticizers decrease the TS values and increase the %E, obtaining more flexible films compared to films made without plasticizers. The structural characteristics of plasticizers directly influence the CI of films. The values corresponding to %E and PVA were higher in the arabinoxylan films thermoplasticized with glycerol. Films’ stability was evaluated using electrochemical impedance spectroscopy. The results show that there are significant differences when the films are coated with polylactic acid.

Biomass doi: 10.3390/biomass6010014

Authors: Ivanka Stoycheva Bilyana Petrova Boyko Tsyntsarski Nartzislav Petrov Bogdan Ranguelov

This paper explores the complex interrelationships between biomass composition, thermochemical conversion pathways, carbon yield and other characteristics in order to expand the knowledge for biomass conversion processes and adapt them to specific requirements. A comprehensive characterization, chemical and thermal analysis of peach stone biomass, was performed. Thermogravimetric analysis, elemental analysis and low-temperature nitrogen sorption were also carried out in order to establish the composition and textural characteristics of the precursor material and obtained product. Carbon adsorbents were obtained from the studied biomass precursor under different conditions via one-step hydro-pyrolysis process by using steam activation at 800 °C. After research was conducted, it was established that cellulose is the main component, which influences the quantity and quality of the obtained adsorbent. The high content of hemicellulose reveals peach stones as a good candidate, especially for hydrothermal carbonization. High cellulose content (40%) in the biomass precursor is a prerequisite for the formation of porous texture in carbon adsorbent during hydro-pyrolysis. It was also shown that the carbon yield (26.70%) can be predicted and is highly dependent on the precursor composition. These results highlight the potential of peach stones as a valuable precursor for the production of sustainable, high-performance carbon adsorbents for environmental remediation.

Biomass doi: 10.3390/biomass6010013

Authors: Darlisson Santos Joyce Gueiros Wanderley Siqueira Marcos Gabriel Lopes da Silva Maria Donato Girleide da Silva Bruna Pratto Allan Almeida Albuquerque Emmanuel Damilano Dutra Jorge Luíz Silveira Sonego

This manuscript provides a comprehensive review of the enzymatic hydrolysis of lignocellulosic biomass, emphasizing how chemical composition, structural features, inhibitory compounds, and process configurations collectively influence the conversion of structural polysaccharides into fermentable sugars. Variability among herbaceous, woody, and residual biomasses results in differences in cellulose, hemicellulose, lignin content, and crystallinity, which strongly affect enzyme accessibility. The review discusses key inhibitory mechanisms, including nonproductive cellulase adsorption onto lignin, interference from phenolic derivatives and pretreatment by-products, and inhibition caused by accumulating mono- and oligosaccharides. Process configurations such as SHF, SSF, PSSF, and consolidated bioprocessing are compared, with SSF often achieving superior performance by mitigating end-product inhibition. The manuscript also highlights the growing relevance of computational modeling and simulation tools, which support kinetic prediction, the evaluation of transport limitations, and the optimization of operating conditions in high-solids systems. Additionally, recent advances in artificial intelligence are presented as powerful approaches for modeling nonlinear hydrolysis behavior, estimating kinetic parameters, identifying rate-limiting steps, and improving predictive accuracy in complex bioprocesses. Overall, the integration of experimental insights with advanced modeling, simulation, and AI-based strategies is essential for overcoming current limitations and enhancing the technical feasibility and industrial competitiveness of lignocellulosic bioconversion.

Biomass doi: 10.3390/biomass6010012

Authors: Ana Paula Yumi Nishimura Fernando Augusto Pedersen Voll Nadia Krieger David Alexander Mitchell

Kinetic models are important tools for guiding the design and optimization of lipase-catalyzed processes. These processes follow the Ping Pong bi bi mechanism, for which mechanistic kinetic equations can be derived. However, when there are several competing reactions, fully mechanistic models contain a large number of parameters, making it difficult to obtain reliable estimates, so simplified models are necessary. We present a two-step approach to developing semi-mechanistic models of such processes. The first step involves the estimation of the selectivities of the enzyme, using profiles for the reaction species plotted against the degree of reaction, while the second step involves empirical fitting to the same data, but plotted as a function of time. We demonstrate this two-step approach through four case studies based on the literature data for the lipase-catalyzed esterification of fatty acids with trimethylolpropane to produce biolubricants. The semi-mechanistic models were able to describe the data well. Our approach has the advantage of allowing selectivities to be estimated without confounding effects from phenomena such as enzyme denaturation and inhibition. It therefore provides a promising framework for developing models of enzyme-catalyzed processes that obey Ping Pong bi bi kinetics.

Biomass doi: 10.3390/biomass6010011

Authors: Lady Viviana Camargo Ovalle Alex Ricardo Schneider Aline Nunes Marcelo Maraschin

Kappaphycus alvarezii is an important source of carrageenan, a polysaccharide widely utilized for its gelling and stabilizing properties. However, understanding advancements in its application is crucial for broadening its biotechnological uses and promoting sustainable practices. This study aimed to conduct a systematic review of the applications of carrageenan from K. alvarezii, following PRISMA guidelines. A search was conducted in the CAPES Journals Portal and Scopus databases from 2010 to 2025, using the descriptors “Kappaphycus alvarezii” and “carrageenan.” Out of 491 analyzed articles, 38 met the inclusion criteria, categorized into health/medicine (n = 11), human food (n = 10), general industry (n = 8), animal nutrition (n = 6), and agriculture (n = 3). The findings reveal various applications, including scaffolds, antimicrobial agents, encapsulants, and wound dressings in health/medicine; edible films and food additives in human food; biomaterials and bioproducts, as well as applications in biorefinery in general industry; applications in aquaculture and livestock in animal nutrition; and as a defense inducer or biostimulant in agriculture. Despite a limited number of articles specifically addressing the direct applications of carrageenan from K. alvarezii, its uses are extensive across various industries.

Biomass doi: 10.3390/biomass6010010

Authors: Dalidys Rendón-Camargo Efrain Boom-Cárcamo Lina Buelvas-Gutiérrez Ana Maya-Gonzalez

This study analyzes the valorization of oil palm biomass residues within the framework of industrial symbiosis (IS), emphasizing their role in circular economy strategies and sustainable industrial development. Through a systematic literature review and snowball sampling, 156 articles indexed in Scopus and Web of Science were examined, classifying evidence by country, type of residue, derived products, economic sector (ISIC Rev. 4), and technological approach. The results show a strong geographical concentration of IS experiences in Asia, particularly Malaysia, Indonesia, and Thailand, where residues such as empty fruit bunches (EFB), palm kernel shells (PKS), oil palm mesocarp fibers, palm oil mill effluent (POME), and oil palm trunks (OPT) are integrated into processes for bioenergy, biochemicals, composite materials, construction products, biochar, and bioplastics. In contrast, applications in Latin America and Africa remain incipient, with high potential but limited industrial implementation due to infrastructural and regulatory gaps. Technological trends point toward thermo-chemical and biological conversion routes (pyrolysis, gasification, hydrothermal carbonization, anaerobic digestion), development of advanced materials and catalysts, and the emergence of integrated biorefinery models supported by computational optimization tools. The analysis highlights that palm biomass residues, far from being an environmental liability, constitute strategic resources for low-carbon value chains. However, scaling IS initiatives requires clear public policies, economic incentives, and stronger coordination between industry, government, and academia. The study provides a structured overview of current knowledge, identifies research gaps, and outlines future directions for leveraging oil palm residues as a key input for sustainable IS.

Biomass doi: 10.3390/biomass6010009

Authors: Adrián Fagundo-Mollineda Yolanda Freile-Pelegrín Román M. Vásquez-Elizondo Erika Vázquez-Delfín Daniel Robledo

The massive influx of pelagic Sargassum in the Caribbean poses a serious environmental, social, and economic problem, as the stranded biomass is often treated as waste and deposited in landfills. This literature review synthesizes recent research highlighting its potential for valorization in various industries, turning this challenge into an opportunity. Sargassum has low levels of protein and lipids. Still, it is particularly rich in carbohydrates, such as alginates, fucoidans, mannitol, and cellulose, as well as secondary metabolites, including phenolic compounds, flavonoids, pigments, and phytosterols with antioxidant and bioactive properties. These biochemical characteristics allow for its application in renewable energy (bioethanol, biogas, biodiesel, and combustion), agriculture (fertilizers and biostimulants), construction (composite materials, cement additives, and insulation), bioremediation (adsorption of heavy metals and dyes), and in the health sector (antioxidants, anti-inflammatories, and pharmacological uses). A major limitation is its high bioaccumulation capacity for heavy metals, particularly arsenic, which increases environmental and health risks and limits its direct use in food and feed. Therefore, innovative pretreatment and bioprocessing are essential to mitigate these risks. The most promising approach for its utilization is a biorefinery model, which allows for the sequential extraction of multiple high-value compounds and energy products to maximize benefits, reduce costs, and sustainably transform Sargassum from a coastal pest into a valuable industrial resource.

Biomass doi: 10.3390/biomass6010008

Authors: Juana Fernández-Rodríguez Montserrat Pérez Diana Francisco

The untreated discharge of dairy industry wastewater, characterized by high organic and nutrient loads, poses a severe eutrophication threat, leading to oxygen depletion and the disruption of aquatic ecosystems, which necessitates advanced treatment strategies. Anaerobic digestion (AD) represents an effective and sustainable alternative, converting organic matter into biogas while minimizing sludge production and contributing to Circular Economy strategies. This study investigated the effects of fat concentration and operational temperature on the anaerobic digestion of dairy effluents. Three types of effluents, skimmed, semi-skimmed, and whole substrates, were evaluated under mesophilic 35 °C and thermophilic 55 °C conditions to degrade substrates with different fat content. Low-fat effluents exhibited higher COD removal, shorter lag phases, and stable activity under mesophilic conditions, while high-fat substrates delayed start-up due to accumulation of fatty acids and brief methanogen inhibition. Thermophilic digestion accelerated hydrolysis and methane production but demonstrated increased sensitivity to lipid-induced inhibition. Kinetic modeling confirmed that the modified Gompertz model accurately described mesophilic digestion with rapid microbial adaptation, while the Cone model better captured thermophilic, hydrolysis-limited kinetics. The thermophilic operation significantly enhanced methane productivity, yielding 105–191 mL CH4 g−1VS compared to 54–70 mL CH4 g−1VS under mesophilic conditions by increasing apparent hydrolysis rates and reducing lag phases. However, the mesophilic process demonstrated superior operational stability and robustness during start-up with fat-rich effluents, which otherwise suffered delayed methane formation due to lipid hydrolysis and volatile fatty acid (VFA) inhibition. Overall, the synergistic interaction between temperature and fat concentration revealed a trade-off between methane productivity and process stability, with thermophilic digestion increasing methane yields up to 191 mL CH4 g−1 VS but reducing COD removal and robustness during start-up, whereas mesophilic operation ensured more stable performance despite lower methane yields.

Biomass doi: 10.3390/biomass6010007

Authors: Cesare Freda Emanuele Fanelli Assunta Romanelli Vito Valerio Adolfo Le Pera Miriam Sellaro Giacinto Cornacchia Giacobbe Braccio

Sewage sludge was pyrolyzed at mass rate of 500 g/h in a bench-scale rotary kiln for methane-rich syngas production. The tested process variables were the pyrolysis temperature (600, 700 and 800 °C) and the CaO addition to the process (0 and 0.2 CaO/dried sewage sludge). Product distribution (char, condensable product, and gas) as well as their chemical composition were determined. At CaO/dried sewage sludge mass ratio equal to 0, with the increasing pyrolysis temperature from 600 to 800 °C, the gas yield increased from 31.4% to 45.6 wt.%, while the char yield decreased from 41.3 to 37.5 wt.%. At CaO/dried sewage sludge mass ratio equal to 0.2, significantly different product distribution and chemical composition were detected. In fact, syngas showed a net CO2 concentration reduction (under 10 mol %), while methane concentration increased at 600 and 700 °C up to 54 and 42 mol %, respectively. The total gas yield increased, probably because of the CaO behavior as catalyst of volatiles conversion reactions (cracking and reforming). In fact, the condensable product yield decreased up to 7 wt.% at 800 °C. At CaO/dried sewage sludge equal to 0.2 and pyrolysis temperature of 700 °C, the maximum methane yield of 150 g/kg SS was detected.

Biomass doi: 10.3390/biomass6010006

Authors: Gennaro Pace Gianluigi Farru Fabiano Asunis Giovanna Cappai Angela De Bonis Maria Cristina Mascolo Donatella Caniani Ignazio Marcello Mancini Salvatore Masi Francesco Di Capua

Spent coffee grounds (SCGs) are abundantly produced worldwide as a by-product of coffee brewing, and production is surging following the rise in global coffee consumption. Although the adsorption properties of raw SCGs have been investigated in previous studies, limited attention has been paid to the use of SCG-derived hydrochars as engineered adsorbents. In this work, hydrochars produced via hydrothermal carbonization (HTC) of SCGs at different temperatures were systematically assessed for their capacity to remove methylene blue (MB) dye from aqueous solution. The effect of HTC temperature and soft alkaline activation on MB adsorption were evaluated through adsorption batch tests. The soft alkaline activation increased the experimental adsorption capacity from <20 mg g−1 for untreated hydrochars to approximately 100 mg g−1 at 20 °C, while Langmuir isotherm analysis yielded a monolayer capacity of 147.1 mg g−1 at the same temperature; experimental uptake further increased to 215.6 mg g−1 at 40 °C and high dye concentrations. Kinetic, isotherm, and thermodynamic tests were performed on selected materials to describe their adsorption behavior and potential mechanisms. Microscopic, diffraction, spectroscopic, and porosimetric analyses were performed to investigate the structural differences among the tested materials. This study shows that temperature regulation and soft alkaline activation can strongly improve the adsorption capacity of the hydrochars, producing competitive low-cost adsorbents from a waste material in compliance with the principles of the circular economy.

Biomass doi: 10.3390/biomass6010005

Authors: Dirléia dos Santos Lima Lucas Capello Manuela de Santana Santos Maria do Carmo Rangel

Aiming to obtain chemicals from renewable sources to mitigate global warming, the catalytic pyrolysis of tamarind pulp, obtained from juice industries, was studied. Catalysts based on HZSM-5 zeolite prepared from rice husk ash using ultrasound, microwaves, and a combination of both were used. The catalysts were characterized by elemental analysis, X-ray diffraction, specific surface area and porosity measurements, scanning electron microscopy, and acidity measurements. The specific surface areas and the micropore volumes were slightly affected by the treatments, with microwave alone or combined with ultrasound having the strongest effect. The number of acid sites increased, and the relative number of strong sites decreased with the treatments. The relative amount of Bronsted to Lewis sites was increased by ultrasound and decreased by microwave, alone or combined. These catalysts decreased oxygenated products and increased BTEX production during tamarind pulp pyrolysis. Product distribution was similar for all cases, meaning that HZSM-5 with the following characteristics is a selective catalyst for BTEX in tamarind pulp pyrolysis: specific surface area = 310–347 m2/g; micropore volume = 0.099–0.105 cm3 g−1; acidity = 327 to 571 µmol NH3 gcat−1; and ratio of Bronsted to Lewis acid sites = 0.034 to 0.044.

Biomass doi: 10.3390/biomass6010004

Authors: Daniel Ignacio Travieso Fernández Christian Jeremi Coronado Rodriguez Einara Blanco Machín Daniel Travieso Pedroso João Andrade de Carvalho Júnior

Brazil possesses a large bioenergy resource, embedded in agro-industrial, livestock, and urban residues; this study quantifies its technical magnitude and associated energy value. An assessment was conducted by substrate, combining official statistics with literature-based yields and recovery factors. Biogas volumes were converted into biomethane using representative upgrading efficiencies, and thermal and electrical equivalents were derived from standard lower heating values and conversion efficiencies. Uncertainty bounds reflect the variability of feedstock yields and process performance. The national technical potential is estimated at roughly 80–85 billion Nm3/year of biogas, corresponding to ~43–45 billion Nm3/year of biomethane and around 168–174 TWh/year of electricity. Contributions are led by the sugar–energy complex (~one-third), followed by livestock and other agro-industrial residues (~one-third), while urban sanitation supplies ~8–10%. Potentials are concentrated in the Southeast, Center-West, and South, and current production represents only ~2–3% of the assessed potential. The findings indicate that realizing this potential requires targeted measure standardization for grid injection, support for pretreatment and co-digestion, access to credit, and alignment with instruments such as RenovaBio and “Metano Zero” to unlock significant methane-mitigation, air-quality, and decentralized energy-security benefits.

Biomass doi: 10.3390/biomass6010003

Authors: Diana Litzajaya García-Ruiz Dylan Sinhue Valencia-Delgado Salvador Moisés Hernández-Ocaña Luis Fernando Ortega-Varela Lada Domratcheva-Lvova Fermín Morales-Troyo Yadira Solana-Reyes Carmen Judith Gutiérrez-García

The valorization of agro-industrial waste could be a strategy to improve organic waste management. The production of activated carbon (AC) is a path to use for this waste, with the aim of reducing its negative effects. AC is characterized by a high internal surface area, chemical stability, and oxygen-containing functional groups in its structure. This work is focused on the valorization of agro-industrial waste such as pineapple peel and coconut shells. These are made up of sucrose, glucose, fructose, and other essential nutrients, as well as cellulose, hemicellulose, and lignin. Activated Carbon was obtained with slow pyrolysis at 400 °C, for 4 h in a stainless-steel tubular reactor with physical activation. The obtained samples were analyzed using SEM, TGA, FTIR, and BET to verify the morphology, thermal degradation, functional groups and pores ratio of the AC, highlighting the presence of materials pore >10 µm. The TGA residual materials gave 16.3% of pineapple peel AC ashes and 0.2% of coconut AC. A C=C, C-HX, CO, and OH stretching were observed in 400–4000 cm−1. The peak intensity decreased once the biodiesel was treated with AC, because the traces of water and functional groups interacted actively, resulting a high content of bases. Activated carbon was used for dry cleaning of the obtained biodiesel from residual oil, which was effective in reducing pH and moisture levels in the biodiesel samples. Pore distribution was determined by BET, 5.6 nm for pineapple peel and 39.8243 nm for coconut shells. The obtained activated carbon offers a sustainable alternative to traditional carbon sources and contributes to the circular economy by recycling waste biomass.

Biomass doi: 10.3390/biomass6010002

Authors: Sergio Medina Ullrich Stahl Fernando Gómez Angela N. García Antonio Marcilla

Waste valorization is a necessary activity for the development of the circular economy. Pyrolysis as a waste valorization pathway has been extensively studied, as it allows for obtaining different fractions with diverse and valuable applications. The joint analysis of results generated by thermogravimetry (TGA) and analytical pyrolysis (Py-GC/MS) allows for the characterization of waste materials and the assessment of their potential as sources of energy, value-added chemicals and biochar, as well as providing awareness for avoiding potential harmful emissions if the process is performed without proper control or management. In the present study, these techniques were employed on three greenhouse plant residues (broccoli, tomato, and zucchini). Analytical pyrolysis was conducted at eight temperatures ranging from 100 to 800 °C, investigating the evolution of compounds grouped by their functional groups, as well as the predominant compounds of each biomass. It was concluded that the decomposition of biomass initiates between 300–400 °C, with the highest generation of volatiles occurring around 500–600 °C, where pyrolytic compounds span a wide range of molecular weights. The production of organic acids, ketones, alcohols, and furan derivatives peaks around 500 °C, whereas alkanes, alkenes, benzene derivatives, phenols, pyrroles, pyridines, and other nitrogenous compounds increase with temperature up to 700–800 °C. The broccoli biomass exhibited a higher yield of alcohols and furan derivatives, while zucchini and tomato plants, compared to broccoli, were notable for their nitrogen-containing groups (pyridines, pyrroles, and other nitrogenous compounds).

Biomass doi: 10.3390/biomass6010001

Authors: Sergio A. Coronado-Contreras Zaira G. Ibarra-Manzanares Alma D. Casas-Rodríguez Álvaro Javier Pastrana-Pastrana Leonardo Sepúlveda Raúl Rodríguez-Herrera

This review examines how the integration of circular bioeconomy principles with digital technologies can drive climate change mitigation, improve resource efficiency, and facilitate sustainable biorefinery development. This highlights the urgent need to transition away from fossil fuels and introduces the bio-circular economy as a regenerative model focused on biomass valorization, reuse, recycling, and biodegradability. This study compares linear, circular, and bio-circular approaches and analyzes key policy frameworks in Europe, Latin America, and Asia linked to several UN Sustainable Development Goals. A central focus is the role of digitalization, particularly artificial intelligence (AI), the Internet of Things (IoT), and blockchain. Examples include AI-based biomass yield prediction and biorefinery optimization, IoT-enabled real-time monitoring of material and energy flows, and blockchain technology for supply chain traceability and transparency. Applications in agricultural waste valorization, bioplastics, bioenergy, and nutraceutical extraction are also discussed in this review. Sustainability tools, such as automated life-cycle assessment (LCA) and Industry 4.0 integration, are outlined. Finally, future perspectives emphasize autonomous smart biorefineries, biotechnology–nanotechnology convergence, and international collaboration supported by open data platforms.

Biomass doi: 10.3390/biomass5040082

Authors: Laura Daniela López-Itas David Gómez-Ríos Howard Ramírez-Malule

The aviation industry faces increasing pressure to reduce its environmental impact and achieve net-zero emissions by 2050. In this context, sustainable aviation fuels (SAF) have emerged as a critical alternative to conventional jet fuels. This study provides a comprehensive analysis of SAF technologies from a chemical engineering perspective, highlighting key production routes, technological maturity levels, and implementation challenges. A bibliometric analysis using the Scopus database and VOSviewer software was conducted to identify research trends and thematic clusters in SAF literature. The analysis reveals a growing interest in advanced biofuels and physicochemical conversion technologies, particularly those supported by catalytic and thermochemical processes. Certified and emerging SAF pathways were examined with respect to their process efficiency, feedstock availability, and scalability. Additionally, the study explores the potential of Latin America as a strategic region for SAF development, considering its abundant biomass resources and ongoing pilot projects. This critical and holistic analysis aims to support researchers, engineers, and policymakers in understanding the current state and future directions of SAF technologies within the framework of chemical process design and optimization. Overall, Hydroprocessed Esters and Fatty Acids Synthetic Paraffinic Kerosene (HEFA-SPK) and Fischer–Tropsch Synthetic Paraffinic Kerosene (FT-SPK) are identified as the most mature and widely deployed SAF production routes, whereas Alcohol to Jet (ATJ), Synthesized Iso-Paraffins (SIP), and Direct Sugar to Hydrocarbons (DSHC) remain at earlier technological stages despite their long-term potential for feedstock diversification and reduced environmental impacts. The analysis also underscores Latin America, where abundant biomass resources, consolidated agro-industrial systems, and emerging SAF research initiatives create favorable conditions for future development and deployment.

Biomass doi: 10.3390/biomass5040081

Authors: João Otávio Ferraro Kishima Mayara Thamela Pessoa Paiva Maria Eduarda Matos Cassiano Avacir Casanova Andrello Suzana Mali

Climate change and the impacts related to nonbiodegradable synthetic materials highlight the need for sustainable alternatives. Biopolymers from renewable sources show great potential for producing hydrogels, which are three-dimensionally crosslinked materials with high water absorption. In this work, super-absorbent biodegradable hydrogels were produced via single-step reactive extrusion using mixtures of starch, gelatin, cellulose, and xanthan gum, with glycerol as a plasticizer, and citric acid as a crosslinking agent. Pelleted hydrogels were obtained with water absorption between 290% and 363%. Reactive extrusion promoted the formation of new ester and amide bonds, confirmed by FT-IR. Citric acid was effective as a crosslinker, and higher citric acid content (3%) produced samples with greater swelling, supported by the porous internal structure observed. Preliminary agricultural tests showed that the formulation with the highest citric acid content, when added to soil at 5%, significantly increased water-holding capacity and resulted in the highest germination rate of maize seeds. Overall, the extrusion process proved efficient, scalable, and environmentally friendly for producing biodegradable hydrogels for agricultural applications.

Biomass doi: 10.3390/biomass5040080

Authors: Plamen Saraliev Nikolay Kolev Desislava Vlahova-Vangelova Stefan Dragoev Desislav Balev

Egg products are a convenient and safe form of eggs, possessing valuable nutritional and functional properties. The egg processing industry is responsible for the enormous amounts of biomass in the form of animal by-products (ABPs). According to EU legislation, the ABPs are under strict control from the formation to the disposal of biomass, as they carry a risk to the ecosystem and public health. For this reason, restrictions have been introduced on their use after disposal, ranging from bioactive applications in medical, cosmetic, and pharmaceutical products, as well as feed. The shells are subject to special conditions for processing and use. The by-products of egg breaking are divided into solid (eggshells and eggshell membranes) and liquid (technical albumen) by-products. The biological value is determined by the composition, which varies significantly across the by-products. In the context of the circular economy, all egg by-products contain valuable substances that can be used in food and non-food industries. First, eggshells are the leading by-product, composing 95% of the inorganic substance calcium carbonate, which, after processing, can be used in agriculture, food and feed industries, and medicine. Second, there is a liquid by-product containing proteins from the egg white and a small part of fats from the yolk. Literature data on this by-product are scarce, but there is information about its use as a feed additive, while the extracted and purified proteins can be useful in pharmacy. Egg membranes constitute only 1% of the egg mass, but humanity has long known about the benefits of collagen, keratin, and glycosaminoglycans, including hyaluronic acid, which compose this material. The processed membranes can be used as a food additive, in cosmetics, medicine, or pharmacy, just like other egg by-products mentioned above. This literature review focuses on the possible methods and techniques for processing by-products and their potential application. The literature sources in this review have been selected according to their scientific and practical applicability. The utilization of these by-products not only reduces the impact on the environment but also facilitates the creation of value-added materials.

Biomass doi: 10.3390/biomass5040079

Authors: Renan Coghi Rogeri Katarzyna Stolecka-Antczak Priscila da Silva Maradini Priscila Rosseto Camiloti Andrzej Rusin Lucas Tadeu Fuess

Anaerobic digestion of sugarcane vinasse is integral to enhancing ethanol distilleries’ environmental and energy performance by converting organic waste into biogas; however, the flammable and toxic nature of biogas has led to significant safety concerns, particularly in anaerobic bioreactors where biogas is produced and stored. This study provides a comparative risk assessment of different anaerobic reactor configurations—a covered lagoon biodigester (CLB), a continuous stirred-tank reactor (CSTR), an upflow anaerobic sludge blanket reactor (UASB), and an anaerobic structured-bed reactor (AnSTBR)—processing vinasse, focusing on fire, explosion, and hydrogen sulfide (H2S) toxicity hazards. Jet fire scenarios posed the most severe threat, with fatal outcomes extending up to 66 m, while the fireball scenario exhibited no lethal range. The risks to human life from explosions were minimal (1.2%). H2S toxicity was identified as the most critical consequence, with particularly severe impacts in CLB systems, where the hazardous zone was up to 20 times larger than in AnSTBR. Therefore, the design of anaerobic bioreactors for vinasse treatment must primarily address the risks associated with H2S-rich biogas, as reactor configuration plays a key role in mitigating or amplifying these hazards—high-rate systems such as AnSTBR and UASB demonstrating safer profiles due to their compact design and lower gas storage volumes.

Biomass doi: 10.3390/biomass5040078

Authors: Nayanna Shayra Silva Taveira Daniel Silveira Serra Morsyleide de Freitas Rosa Rubens Sonsol Gondim Mona Lisa Moura De Oliveira Matheus de Oliveira Barros Men de sá Moreira de Souza Filho Adriano Lincoln Albuquerque Mattos Selene Maia de Morais Maria Cléa Brito Figuêredo

Green coconut husk is an abundant and underutilized agro-industrial residue in Brazil, contributing significantly to landfill overload. This study investigates the pyrolysis of pellets derived from this biomass as a technological alternative for its valorization, focusing on the integrated characterization of the three resulting products. Pellets were subjected to pyrolysis in a fixed-bed reactor under two distinct conditions: at 400 °C to maximize biochar production, and at 600 °C to enhance gas generation. The raw material and resulting solid, liquid, and gaseous fractions were characterized using physicochemical, thermal, morphological, and chromatographic analyses. Pyrolysis at 400 °C yielded biochar with high fixed carbon content (67.03%) and elevated heating value (27.80 MJ/kg), suitable for soil amendment and carbon sequestration. At 600 °C, the non-condensable gas exhibited a higher hydrogen concentration (35.84%) and an H2/CO ratio of 1.84, favorable for chemical synthesis applications. Notably, palletization resulted in a significant bio-oil and gas yield even under 400 °C. The bio-oil underwent chemical upgrading, which significantly increased the phenolic content and raised its heating value to 20.40 MJ/kg. Additionally, combustion tests revealed that the gas produced emitted lower levels of NOx compared to natural gas.

Biomass doi: 10.3390/biomass5040077

Authors: Stiven J. Sofán-Germán Fabio L. Acuña-Izquierdo Jesús D. Rhenals-Julio Karen P. Cacua Madero Jorge M. Mendoza-Fandiño

This study provides a comparative thermochemical analysis of coconut husk, rice husk and mineral coal, assessing their potential for use in sustainable energy applications. Standardised proximate and ultimate analyses, thermogravimetric (TGA/DTG) evaluations and combustibility index measurements were performed under identical laboratory conditions to ensure consistent comparisons could be made. Coconut husk exhibited the lowest ignition temperature (320.88 °C) and the highest combustibility index (2.385). This indicates its suitability for rapid combustion and biochar production. Its low ash and sulphur content enhances its environmental performance. Rice husk demonstrated moderate thermal behaviour and a high ash yield owing to its elevated silica content, suggesting greater potential for non-energy applications, such as silica recovery and advanced materials production. Mineral coal displayed the highest carbon content and calorific value (24.38 MJ/kg), reflecting high energy density, but also a considerable sulphur content that raises environmental concerns. Unlike many studies that address these materials separately, this work provides a direct, side-by-side comparison under controlled conditions. This offers practical insights for selecting materials in energy systems. The results reinforce the potential of agro-industrial residues in cleaner energy strategies, while emphasising the need for emission control measures when using fossil fuels.

Biomass doi: 10.3390/biomass5040076

Authors: Rubén Gonsálvez-Álvarez Encarnación Martínez-Sabater María Ángeles Bustamante Mario Piccioli José A. Saez-Tovar Luciano Orden Concepción Paredes Raúl Moral Frutos C. Marhuenda-Egea

Composting is an effective biotechnological process for transforming agro-industrial residues into stabilized and nutrient-rich organic amendments. However, the molecular mechanisms underlying organic matter transformation remain poorly resolved. In this study, a mixture of winery by-products and poultry manure was composted under controlled aeration and monitored through high-field 1H NMR spectroscopy of the water-extractable organic matter (WEOM), followed by interval-based chemometric analysis. The NMR spectra revealed distinct compositional trends, including the rapid depletion of amino acids and carbohydrates, the transient accumulation of low-molecular-weight organic acids, and the gradual enrichment in aromatic and phenolic compounds associated with humification processes. Chemometric modeling using Partial Least Squares (PLS) regression and its interval variants (iPLS and biPLS) enabled accurate prediction of composting time (r ≈ 0.95) and identification of diagnostic spectral intervals corresponding to key metabolites. These findings demonstrate the capability of NMR-based molecular profiling, combined with multivariate modeling, to elucidate the biochemical pathways of composting and to provide quantitative indicators of compost stability and maturity.

Biomass doi: 10.3390/biomass5040075

Authors: Andrei M. Egorin Svetlana A. Novikova Igor D. Priymak Yulia O. Privar Anastasia V. Brikmans Daria Kh. Shlyk Andrei M. Gilev Olga V. Nesterova

This study investigated the potential of a commercially available birch biochar, previously used as a soil amendment, for the adsorption of Pb2+ ions from aqueous solutions. For the first time, direct potentiometry with a lead ion-selective electrode was used for continuous in situ real-time monitoring of the adsorption process. The biochar demonstrated a maximum adsorption capacity of 14.21 mg/g (Langmuir model) and a high affinity for Pb2+. Kinetic analysis revealed a two-stage process limited by intraparticle diffusion. A significant decrease in pH and power-law dependencies between the adsorption parameters and the liquid/solid ratio confirmed ion exchange as the primary mechanism. Additionally, the biochar’s surface characteristics and accessibility for large molecules were evaluated by methylene blue adsorption, yielding a specific surface area of 4.0–6.6 m2/g. This value, being an order of magnitude lower than the BET surface area, highlighted the microporous nature of the biochar and its limited accessibility for bulky organic cations, providing crucial context for interpreting the lead adsorption mechanisms. The biochar effectively reduced the lead concentration to levels meeting the standards for irrigation water, demonstrating its dual application not only as an amendment but also as an effective and stable sorbent for water purification, while direct potentiometry proved to be a promising method for studying such processes.

Biomass doi: 10.3390/biomass5040074

Authors: Elisa Basika Allan J. Komakech Simon S. Kizito Richard D. Lee Therese Schwarzböck

This research explores the effects of milling on fecal sludge (FS) biochar with an emphasis on milling time (5, 10, and 15 min) and ball-to-powder ratio (BPR) (4.533 g/g, 9.067 g/g, and 10.5 g/g). FS biochar was prepared through slow co-pyrolysis of a 50:50 mixture (by weight) of fecal sludge and rice husk powder at 550 °C. The resultant FS biochar with good qualities was subjected to methylene blue (MB) dye adsorption at varying FS biochar weights (0.05 g, 0.1 g, and 0.15 g) and adsorption durations. The BSA peaked at 50 m2/g for a BPR of 10.5 g/g and a milling duration of 10 min. Prolonged milling (15 min) led to structural degradation and reduced BET surface area (BSA). The pore volume peaked at a BPR of 9.067 g/g for shorter milling times and 10.5 g/g for extended milling. The SEM revealed that a milling time of 10 min at a BPR of 9.067 g/g provided the best balance between particle size reduction and uniform morphology, minimizing agglomeration. MB adsorption revealed that FS biochar milled for 10 min and 9.067 g/g BPR demonstrated the best properties. These findings highlight the potential of FS biochar for applications in environmental remediation and agricultural fields, contributing to resource recovery from FS.

Biomass doi: 10.3390/biomass5040073

Authors: Jéssica Justicia Claudia Cervigón Francisco Heras

Aqueous phase reforming has been posed as a promising technology for renewable hydrogen production in the framework of the transition to a sustainable energy economy. Since the use of chemical compounds as process feedstock has proven to be one of the major constraints to its potential scalability, several cost-free residual biomasses have been investigated as alternative substrates. This also allows for the recovery of residues, offsetting the significant costs of waste management through conventional treatment. In recent years, different wastes from the food processing industry such as brewery, fish canning, dairy industries, fruit juice extraction, and corn production wastewaters, have taken the attention of scientific community due to their composition, favorable to this process, and its high-water content. However, few and heterogeneous results can be found within the literature, suggesting that the research into this application is now at a stage of development which will require further investigation. Therefore, this work is focused on compiling and discussing the reported studies, aiming to present a critical reflection on the potential of aqueous phase reforming as a means for the valorization of this kind of residue.

Biomass doi: 10.3390/biomass5040072

Authors: Verónica Córdoba Gianluca Ottolina

Anaerobic co-digestion of agro-industrial and municipal biowastes can enhance methane production, but the optimal mixture depends on nonlinear interactions among substrates. This study evaluated swine wastewater (SW), cheese whey (CW), and the organic fraction of municipal solid waste (OFMSW) under mesophilic batch conditions to quantify composition–response relationships and identify a robust operating window. A restricted simplex-centroid mixture design was tested; linear, quadratic, and special cubic models were fitted and evaluated using ANOVA, diagnostic plots, and optimization with desirability mapping. Cumulative methane yield (CMY) ranged between 251 and 295 NmL CH4 g VS−1 in the mixtures, outperforming SW as single component. All mixtures maintained neutral pH and moderate alkalinity ratios. The special cubic model provided the best performance (high R2 and R2pred) and revealed significant ternary interaction. The optimization indicated a composition near 63% SW, 10% CW, and 27% OFMSW with a predicted CMY of 300 NmL CH4 g VS−1; a high-performance band (desirability 0.90–1.00; corresponding to CMY ≥ 294.8) defined a robust window of ~60–66% SW, 6–20% CW, and 20–31% OFMSW. Overall, balanced ternary co-digestion showed synergistic effects beyond additive expectations, and the response surface model based on mixture design proved effective in capturing interactions and providing flexible guidance for practical implementation.

Biomass doi: 10.3390/biomass5040071

Authors: Vivian Lima dos Santos Luiz Carlos Lobato dos Santos George Simonelli

The growing demand for energy and the environmental impacts of fossil fuels have driven the search for sustainable alternatives such as biodiesel. Castor oil stands out as a promising non-edible feedstock but requires optimization strategies to overcome challenges in its conversion to biodiesel. This study developed a predictive model to determine the optimal parameters for homogeneous alkaline or acid transesterification of castor oil, aiming to maximize fatty acid methyl ester (FAME) yield. A dataset of 406 operating conditions from the literature was used to train and evaluate six models: Multilayer Perceptron with logistic sigmoid activation (MLP-logsig), hyperbolic tangent activation (MLP-tansig), Radial Basis Function network (RBF), hybrid RBF + MLP, Random Forest (RF), and Adaptive Neuro-Fuzzy Inference System (ANFIS). The MLP-tansig achieved the best performance in training, validation, and testing (R > 0.98). However, when combined with a Genetic Algorithm (GA), it generated infeasible parameters. Conversely, the RBF + GA combination yielded results consistent with the literature: molar ratio 19.35:1, alkaline catalyst 1.13% w/w, temperature 50 °C, reaction time 70 min, and stirring speed 548.32 rpm, achieving 100% FAME yield. This approach reduces the need for extensive experimental testing, offering a cost- and time-efficient solution for optimizing biodiesel production.

Biomass doi: 10.3390/biomass5040070

Authors: Sabina Alexandra Nicolae

Driven by global economic growth and the rapid advancement of emerging technologies, the escalating demand for fossil fuels and hazardous chemicals has intensified, contributing to severe environmental degradation and widespread pollution. Hence, the demand for sustainable, eco-friendly solutions has become more urgent than ever. Since the industrial revolution, the atmospheric concentration of CO2 has been on the rise, with reports suggesting a significant increase by 2080. To overcome this, more and more sustainable materials have been proposed as efficient adsorbents for CO2. Biomass represents a green and sustainable platform for the production of materials with applications in various areas. Considering its non-toxic character, abundance, and low cost, biomass is frequently used as carbon feedstock. This paper focuses on the usage of biomass for the synthesis of efficient CO2 adsorbents. This study addresses the influence of biomass composition on final uptake performance, offering a better insight into the role of each feedstock component in shaping the properties of the final material. In addition, the advantages and disadvantages of the carbon synthesis routes are presented, accompanied by various examples of materials and their performances. Overall, the current work focuses on multiple cases of biomass-derived carbons for CO2 adsorption, covering aspects from synthesis to performance evaluation, while highlighting the current findings and existing challenges.

Biomass doi: 10.3390/biomass5040069

Authors: Sahar Abbas Idirissia Janati Idrissi Siham Rouas Mohammed Dehhaoui Taha El Kamli Fouad Mokrini El Mehdi Bouchtaoui Noureddine Ouazzani

The diverse phytochemical profile of olive leaves makes them an attractive feedstock for biomass utilization. The main objective of this study was to evaluate the phenolic content and antioxidant activity (AOA) of olive leaf extracts from four varieties cultivated in the Meknes region (Morocco) across two major collection periods: olive harvest (November) and pruning season (March). This study particularly focused on assessing how variety and season affect total phenolic compounds (TPC), ortho-diphenols (ODPC), total flavonoid content (TFC), and antioxidant activity (AOA). The results revealed that olive leaves collected in November exhibited the highest levels of TPC, ODPC, and AOA, while those from March were richer in TFC. Among the studied cultivars, Koroneiki showed the highest TPC and extraction yields in both November (72.08 ± 0.83 mg GAE/g DM; 42.61 ± 6.51%) and March (46.38 ± 0.83 mg GAE/g DM; 41.00 ± 1.84%). In contrast, Picual leaves displayed the highest antioxidant activity across both periods. The mineral profile of November leaves exhibited varietal specificities and a negative correlation between TPC and most nutrients except Fe, Cu, and Mn. These findings underscore the substantial impact of seasonal variation and cultivar differences on biochemicals, AOA, and minerals, and must be carefully considered for further valorization.

Biomass doi: 10.3390/biomass5040068

Authors: Sergio Arango-Osorio Carlos Alejandro Zuluaga-Toro Idi Amín Isaac-Millán Antonio Arango-Castaño Oscar Vasco-Echeverri

Anaerobic digestion is a sustainable approach for waste treatment and renewable biogas production. A key parameter for large-scale applications is the Biochemical Methane Potential (BMP), which enables methane yield estimation and facilitates process scale-up. This study introduces an automated, low-cost prototype for BMP testing, comprising three 2-L reactors with provisions for future expansion. Control and data acquisition are carried out by low-cost embedded systems integrated with sensors for pressure, temperature, pH, and biogas flow. The system was evaluated using a mixture of pig manure and sludge from a local wastewater treatment plant. Real-time monitoring of temperature, pH, and biogas production was achieved. The heat exchanger, designed through transient energy balance modeling, increased the reactor temperature from 20 °C (lab temp.) to 38 °C in 400 s. Overall, the prototype demonstrated reliable performance, achieving rapid heating, stable monitoring, and precise biogas flow quantification through both displacement and pressure methods.

Biomass doi: 10.3390/biomass5040067

Authors: Dimitra Karageorgou Petros Katapodis

An intracellular α-glucosidase was isolated and purified from a Pseudanabaena sp. cyanobacterial strain. Before the enzyme purification, the optimal cultural conditions were determined. Optimal culture conditions (15 g/L maltose, 2 g/L yeast extract, 23 ± 1 °C) yielded 3.3 g/L of biomass and 2186 U/L of α-glucosidase in a lab-scale bioreactor. The purified enzyme displayed a molecular mass of 52 kDa with optimum activity at 40 °C and pH 7.0, and maintained stability within an acidic and neutral range of pH 4.0 to 7.0. Enzyme activity was affected by both the concentration and interaction time of the metal ions and chelator. Kinetic constants of Km, Vmax, and kcat for the hydrolysis of pNPG were determined as 2.0 Mm, 2.9 μmol min−1, and 14.86 min−1, respectively. The activation energy (Ea) was 24.2 kJ mol−1 and the thermodynamic parameters of enthalpy (ΔH*), entropy (ΔS*) of activation, Gibbs free energy (ΔG*), free energy of substrate binding (ΔG*E-S), and transition state formation (ΔG*Ε-Τ) were 21.6, −116, 57.8, −22.2, and −41.2 kJ mol−1, respectively. Moreover, the thermodynamic parameters for thermal inactivation of the enzyme were ΔH*= 131 kJ mol−1, 105 ≤ ΔS* ≤ 108 kJ mol−1, and 96 ≤ ΔG* ≤ 98 kJ mol−1, while the thermal inactivation energy (E(a)d) was determined to be 133 kJ mol−1. This is the first detailed investigation concerning the characterization of α-glucosidase derived from cyanobacteria. The presented enzymatic characteristics provide a valuable predictive model for identifying suitable applications.

Biomass doi: 10.3390/biomass5040066

Authors: Francisco Gerhardt Magro Alan Rempel Christian Oliveira Reinehr Luciane Maria Colla

The search for sustainable development has led several production processes to adopt biorefineries. We evaluated the cultivation of Spirulina platensis and Scenedesmus obliquus in consortium (50/50%), with the addition of effluent of the anaerobic digestion (AD) of cattle waste, in fed-batch mode, to obtain biomass in 10 L raceways. Subsequently, cultivation was carried out at pilot scale in a 100 L raceway. Zarrouk medium (20%) was used, with the addition of 10% (v/v) of effluent in the fed-batch process. The biomasses were characterized to evaluate their application. In 10 L raceways, higher biomass concentrations were obtained in the cultivation of Spirulina with the addition of effluent, or with the microalgae consortia without the addition of effluent (around 1 g/L). The addition of the effluent reduced the carbohydrate content and increased the protein content during the cultivation. Scale-up (100 L raceways) with Spirulina showed similar results to those obtained in the 10 L raceways, with removals of 48%, 88% and 11% for COD, nitrogen and total phosphorus, respectively. The cultivation of microalgae in consortium and Spirulina can be used in the post-treatment of effluent of AD, allowing the production of biomass for different applications.

Biomass doi: 10.3390/biomass5040065

Authors: Samuel C. Oliveira Rafael H. Gonçalves Ivan Ilich Kerbauy Veloso

In this study, a mathematical model was proposed for a continuous, multistage, industrial-scale alcoholic fermentation process, comprising four vats in series with volumes equal to 600 m3, with separation, acid treatment, and cell recycling from the fourth to the first vat. The system was operated daily under variable volumetric flow rates and substrate concentrations in the feed stream, i.e., F0 = 93–127 m3/h and S0 = 210–238 g/L. The mathematical model consisted of mass balance equations for cells, substrate, and product in the vats, the separator, and the acid treatment unit. An unsegregated and unstructured approach was used to describe the microbial population, with the kinetics of cell growth, substrate consumption, and product formation represented by equations generally adopted for alcoholic fermentation. The model parameters were estimated by nonlinear regression, providing typical values for alcoholic fermentation. Model predictions agreed well with both the experimental data used in the parameter estimation step and those used in the model validation step.

Biomass doi: 10.3390/biomass5040064

Authors: Hálisson Lucas Ribeiro Matheus de Oliveira Barros Adriano Lincoln Albuquerque Mattos Morsyleide de Freitas Rosa Men de Sá Moreira de Souza Filho Henriette Monteiro Cordeiro de Azeredo

Starch is a promising alternative to petroleum-based polymers due to its biodegradability and renewable nature. However, its widespread use in non-food applications raises ethical concerns. Mango kernels, a major byproduct of mango processing, represent an abundant yet underutilized starch source. However, conventional starch extraction requires costly purification steps with significant environmental impact. This study explores the development of extruded biocomposites, using corn starch and mango kernel flour (MKF) as a more sustainable alternative. The influence of lignin, extractives, amylose, and amylopectin content on the material properties was assessed. MKF was obtained by removing both tegument and endocarp from the mango kernels, grinding them in a colloidal mill, and finally drying the ground kernels. The resulting flour was blended with corn starch, processed in an internal mixer, and injection-molded. The composites were characterized through mechanical testing, water absorption analysis, colorimetry, and UV absorption assays. Notably, the composite containing ~20% MKF exhibited mechanical properties comparable to commercial polyethylene (PE-PB 208), with a tensile strength of 9.53 MPa and a Young’s modulus of 241.41 MPa. Additionally, MKF enhanced UVA protection. These findings suggest that mango kernel flour can partially replace starch in the production of injection-molded biopolymers, offering a more sustainable approach to biodegradable plastic development.

Biomass doi: 10.3390/biomass5040063

Authors: Sajad Ebrahimi Joseph Szmerekovsky

Achieving decarbonization targets in the aviation sector requires transformative approaches to sustainable aviation fuel (SAF) production. In this pursuit, feedstock innovation has emerged as a critical challenge. This research uses the U.S. SAF Grand Challenge as a case study, focusing on its feedstock innovation workstream, to investigate how Industry 4.0 technologies can fulfill that workstream’s objectives. An integrative literature review, drawing on academic, industry, and policy sources, is used to evaluate the Technology Readiness Levels (TRLs) of Industry 4.0 technology applications across the SAF biomass supply chain. The analysis identifies several key technologies as essential for improving yield prediction, optimizing resource allocation, and linking stochastic models to techno-economic analyses (TEAs): IoT-enabled sensor networks, probabilistic/precision forecasting, and automated quality monitoring. Results reveal an uneven maturity landscape, with some applications demonstrating near-commercial readiness, while others remain in early research or pilot stages, particularly in areas such as logistics, interoperability, and forecasting. The study contributes a structured TRL-based assessment that not only maps maturity but also highlights critical gaps and corresponding policy implications, including data governance, standardization frameworks, and cross-sector collaboration. By aligning digital innovation pathways with SAF deployment priorities, the findings offer both theoretical insights and practical guidance for advancing sustainable aviation fuel adoption and accelerating progress toward net-zero aviation.

Biomass doi: 10.3390/biomass5040062

Authors: Malvin Moyo Vusumzi Emmanuel Pakade

We investigated the application of an adsorbent fabricated from satsuma mandarin peel biomass using coating with poly(glycidyl methacrylate) followed by sequential treatment with hydroxylamine and hydrochloric acid for the remediation of hexavalent chromium-polluted water. The adsorbent was characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). Batch adsorption experiments were conducted wherein initial solution pH, initial chromium concentration, contact time, and temperature were varied. The adsorption equilibrium experimental data were well simulated by the Langmuir and Jovanovic models, pointing toward the formation of a monolayer of adsorbed chromium ions. The total chromium adsorption capacity of the functionalized satsuma mandarin peel adsorbent reached 219.28 mg g−1 at initial pH 1.4 and 60 °C, markedly higher than 110.23 mg g−1 at 30 °C. Where Cr(VI) was the sole chromium oxidation state in the initial solutions synthesized from potassium dichromate, the presence of Cr(III) ions in the final solutions confirmed Cr(VI) reduction. The results of this study show that the functionalized satsuma mandarin peel biomass is a potential candidate for use in the removal of hexavalent chromium from aqueous solution through reduction-coupled adsorption.

Biomass doi: 10.3390/biomass5040060

Authors: Alan Moura Feio Giulian César da Silva Sá Alexandre Orsato Karoline Leite Lucas Mariano Siqueira Pimentel Joane de Almeida Alves Glenda Soares Gomes Evelly Oliveira Ramos Cristina M. Quintella Sinara Pereira Fragoso José Augusto Pires Bitencourt Emilly Cruz da Silva Sidnei Cerqueira dos Santos

Processing economically and socio-culturally significant Amazonian fruits—andiroba (Carapa guianensis Aubl.), açai (Euterpe oleracea Mart.), and babassu (Attalea speciosa Mart. ex Spreng.)—generates substantial biomass waste, posing critical environmental and waste management challenges. This study explored the valorization of these abundant residual biomasses as sustainable feedstocks for biosurfactant production by bacterium Pseudomonas aeruginosa P23G-02, while simultaneously profiling their nutritional value and broader implications for a circular bioeconomy. Through liquid fermentation, biosurfactants were produced at an approximate yield of 6 mg/mL. The isolated biosurfactants exhibited favorable properties, including emulsification indices of around 60% and surface tension reduction to below 30 mN/m, with the andiroba-derived biosurfactant identified as a rhamnolipid type. Nutritional profiling of the residues revealed significant energy values, reaching up to 656 kcal/100 g, with açai and babassu residues being carbohydrate-rich (exceeding 80%), and andiroba residues exhibiting a high lipid profile (up to 57%). These distinct compositions critically influenced biosurfactant yield. These findings underscore the viability of Amazonian fruit biomass as valuable resources for developing eco-friendly bioproducts and innovative waste management solutions. While highlighting a promising pathway for circular bioeconomy development, future research should address biosafety and explore alternative microbial hosts for applications in sensitive sectors such as food and nutrition.

Biomass doi: 10.3390/biomass5040061

Authors: Renu Geetha Bai Salini Chandrasekharan Nair Liina Joller-Vahter Timo Kikas

The rapid growth of the human population and industrialization has intensified anthropogenic activities, leading to the release of various toxic chemicals into the environment, triggering significant risks to human health and ecosystem stability. One sustainable solution to remove toxic chemicals from various environmental matrices, such as water, air, and soil, is bioremediation, an approach utilizing biological agents. Microalgae, as the primary producers of the aquatic environment, offer a versatile bioremediation platform, where their metabolic processes break down and convert pollutants into less harmful substances, thereby mitigating the negative ecological impact. Besides the CO2 sequestration potential, microalgae are a source of renewable energy and numerous high-value biomolecules. Additionally, microalgae can mitigate various toxic chemicals through biosorption, bioaccumulation, and biodegradation. These remediation strategies propose a sustainable and eco-friendly approach to address environmental pollution. This review evaluates the microalgal mitigation of major environmental contaminants—heavy metals, pharmaceuticals and personal care products (PPCPs), persistent organic pollutants (POPs), flue gases, microplastics, and nanoplastics—linking specific microalgae removal mechanisms to pollutant-induced cellular responses. Each section explicitly addresses the effects of these pollutants on microalgae, microalgal bioremediation potential, bioaccumulation process, the risks of trophic transfer, and biomagnification in the food web. Herein, we highlight the current status of the microalgae-based bioremediation prospects, pollutant-induced microalgal toxicity, bioaccumulation, and consequential biomagnification. The novelty of this review lies in integrating biomagnification risks with the bioremediation potential of microalgae, providing a comprehensive perspective not yet addressed in the existing literature. Finally, we identify major research gaps and outline prospective strategies to optimize microalgal bioremediation while minimizing the unintended trophic transfer risks.

Biomass doi: 10.3390/biomass5040059

Authors: Sunyong Park Seon Yeop Kim Kwang Cheol Oh Seok Jun Kim Padam Prasad Paudel Do Su Park Kyeong Sik Kang Sun Hwa Ryu Dae Hyun Kim

Agricultural residues such as maize byproducts and discarded cocopeat substrates are abundant but underutilised biomass resources. Improving their fuel quality requires densification, such as pelletisation, combined with thermochemical upgrading. In this study, pellets were prepared by blending cocopeat and maize residues at weight ratios of 9:1, 7:3, and 5:5, followed by torrefaction at 220, 250, and 280 °C. Their fuel characteristics were evaluated through mass yield, elemental and proximate analyses, chemical composition, calorific value, combustion indices, and grindability. Results showed that increasing maize residue content reduced ash and fuel ratio but increased volatile matter, while cocopeat-rich pellets provided higher fixed carbon and lignin contents, improving thermal stability. Torrefaction significantly enhanced calorific value (up to 21.83 MJ/kg) and grindability, while increasing aromaticity. However, higher torrefaction severity decreased the combustibility index but improved volatile ignitability, indicating a trade-off between ignition behaviour and stable combustion. An optimal balance was observed at 250 °C, where energy yield and combustion performance were maximised. This study demonstrates the feasibility of valorising discarded cocopeat substrates, blended with maize residues, into renewable solid fuels, and provides practical guidance for optimising blending ratios and torrefaction conditions in waste-to-energy applications.

Biomass doi: 10.3390/biomass5040058

Authors: Natalija Cudecka-Purina Dace Arina Inara Teibe Ruta Bendere Zanda Melnalksne Liene Jakobsone Zane Ruperta

The transition to a circular economy requires effective food waste (FW) collection and recycling systems. This study aims to evaluate general public attitudes, behaviours, and systemic challenges related to FW sorting in Latvia, in light of the recent mandate for separate biowaste collection. The study covers two important sections—assessment of the amount of FW generated in primary production sectors, and a pilot case study of biodegradable waste sorting in selected households in Latvia. A mixed-methods approach was used, combining a nationwide survey of 458 entities involved in primary food production and 115 households, followed by 99 households with backyards voluntarily participating in a pilot case study to evaluate their BW management practices. The research findings reveal that there is a need to establish a precise/specific framework for the evaluation of FW for each sector; the development of appropriate coefficients would facilitate the process of estimating waste generated by primary production in the future. Research findings revealed that inhabitants are interested in home composting; however, the implementation of home composting requires active support from project implementers, including increasing environmental awareness and providing financial incentives. These results offer practical insights for municipalities and national stakeholders aiming to increase biowaste collection rates and support country-level broader sustainability goals. The research results have practical application with the possibility to replicate the best practices and recommendations to other countries or regions within the EU and beyond.

Biomass doi: 10.3390/biomass5030057

Authors: Hoe-Gil Lee Zachary Dulany

Biomass energy transforms waste into biofuels and supports water purification. This study examines enhanced hydrogen production via dark fermentation, tracking volatile fatty acids (VFAs), chemical oxygen demand (COD), carbohydrates, and hydraulic retention time (HRT) to optimize biogas yield and quality. Investigations into acidogenesis and acetogenesis explore methods for breaking down long-chain VFAs into short-chain VFAs, which are critical for efficient hydrogen generation. Testing and analysis of VFAs, carbonates, COD, and HRT provide insights into bacterial activity that drives hydrogen production. The main VFAs produced were acetic, propionic, and butyric acids. DF1 and DF2 primarily generated acetic acid, consistent with cheese whey (CW)-based fermentations. DF1.1, using 5× diluted CW and a 30:70 inoculum-to-substrate ratio (I2SR), exhibited elevated butyric acid levels, similar to those observed with food waste. The first dark fermentation process (DF1) initially showed effective carbohydrate metabolism but later experienced spikes in succinic and lactic acids, which reduced hydrogen production. In contrast, the second dark fermentation process (DF2) maintained low lactic acid levels and increased acetate concentrations, indicating improved system performance. DF1.1 also demonstrated stable VFA production and lactic acid reduction. Greater CW dilution, higher initial pH, and increased HRT were key factors in minimizing acidification and enhancing hydrogen-producing pathways.

Biomass doi: 10.3390/biomass5030056

Authors: Felix Melcher Max Schneider Michael Paper Marion Ringel Daniel Garbe Thomas Brück

There is an increasing industrial demand for sustainable resources for lipid-based biofuels and platform chemical production. A promising, CO2-efficient resource is autotrophically cultivated microalgae, either for direct single-cell oil (SCO) production or as a biomass substrate for fermentative SCO production via organisms like yeasts. Regarding the latter, chemical biomass hydrolysis typically results in high sugar yield and high salt concentrations due to the required neutralization prior to fermentation. In contrast, enzymatic hydrolysis is often lacking in mass efficiency. In this study, the enzymatic hydrolysis of both nutrient-replete and lipid-rich autotrophic Microchloropsis salina biomass was optimized, testing different pre-treatments and enzyme activities. Hereby, the protease treatment to weaken the cell wall integrity and the dosing of the Cellic CTec3 was identified to have the highest effect on hydrolysis efficiency. Sugar yields of 63% (nutrient-replete) and almost 100% (lipid-rich) could be achieved. The process was successfully scaled-up in mini bioreactors at a 250 mL scale. The resulting hydrolysate of the lipid-rich biomass was tested as a substrate of the oleaginous yeast Cutaneotrichosporon oleaginosus in a consumption-based acetic acid fed-batch setup. It outperformed both the model substrate and the glucose control, demonstrating the high potential of the hydrolysate as feedstock for yeast oil production. The presented sequential and circular SCO-producing value chain highlights the potential for mass- and space–time-efficient biofuel production, combining the autotrophic cultivation of oleaginous algae with decoupled yeast oil fermentation for the first time.

Biomass doi: 10.3390/biomass5030055

Authors: Jawaher Al Balushi Shamail Al Saadi Mitra Ahanchi Manar Al Attar Tahereh Jafary Muna Al Hinai Anteneh Mesfin Yeneneh J. Sadhik Basha

Spent coffee grounds (SCGs), a globally abundant by-product of the coffee industry, represent a significant source of lignocellulosic biomass with considerable valorization potential. Rich in organic compounds, lipids, and antioxidants, SCGs are increasingly recognized as a sustainable feedstock for energy, materials, and environmental applications within a circular bioeconomy framework. This review critically examines recent advances in SCG valorization via thermochemical, biochemical, and material-based pathways. The review focuses on the conversion of SCGs into biofuels (biodiesel, bioethanol, biogas, and bio-oil), activated carbon for water and air purification, biodegradable polymers, and soil-enhancing amendments. Comparative analyses of process conditions, product yields, and techno-economic feasibility are provided through summarized tables. Although laboratory-scale studies demonstrate promising outcomes, challenges persist in terms of process scalability, environmental impacts, feedstock variability, and lack of regulatory standardization. Furthermore, comprehensive life cycle assessments and policy integration remain underdeveloped. By merging all findings, this review identifies key knowledge gaps and outlines strategic directions for future research, including the development of integrated valorization platforms, hybrid conversion systems, and industrial-scale implementation. The findings support the role of SCG valorization in advancing sustainable resource management and contribute directly to the achievement of multiple Sustainable Development Goals.

Biomass doi: 10.3390/biomass5030054

Authors: Elahe Parvari Devinder Mahajan Elizabeth L. Hewitt

Biomass pyrolysis is a thermochemical process that breaks down organic matter in the absence of oxygen, offering a sustainable route for converting biomass into bio-oil, biochar, and syngas. This review provides a comprehensive overview of pyrolysis, focusing on its fundamental principles, modes, and its applications across different industries. It covers major pyrolysis types and explores the reactors used in these processes and how key parameters, such as temperature, heating rate, and residence time, impact the distribution and quality of pyrolysis products. Special attention is given to bio-oil upgrading methods, including catalytic and non-catalytic processes, and how they affect fuel quality. The study also presents techno-economic assessments of various pathways, identifying cost-effective configurations like pyrolysis combined with hydrotreatment and heat integration. Despite encouraging advancements, scaling up bio-oil technologies continues to face significant challenges, primarily due to cost competitiveness and variability in feedstock supply. This review emphasizes the critical need for continued innovation in reactor design, catalyst efficiency, and integrated process optimization, alongside supportive policy frameworks and strategic investments to accelerate commercial deployment. Finally, this review aims to help researchers, engineers, and policymakers work together to advance pyrolysis technology as a practical solution for producing low-carbon fuels and chemicals.

Biomass doi: 10.3390/biomass5030053

Authors: Bojórquez-Quintal Emanuel Maccioni Oliviero Zaza Fabio Procacci Silvia Gagliardi Serena Bacchetta Loretta

The coffee cherry processing produces various waste products, such as coffee husks, which are a valuable source of pectin and phenolic acids that can be used as high-value biomolecules in human and animal food, cosmetics, and pharmaceutical production chains. This study aims to optimize the eco-friendly extraction of polysaccharides, as pectin, and phenolic compounds from coffee peel using response surface methodology (RSM). This model was used to evaluate the extraction variables (temperature, time, pH, ionic strength, ultrasonic frequency, particle size, and solid/liquid ratio in water) to identify the critical factors. All responses were fitted to the RSM model, which revealed high estimation capabilities. Ionic strength and temperature were found to be critical process variables for pectin extraction, while the main factors responsible for phenolic extraction were ultrasonic frequency, pH, and solid/liquid ratio. Therefore, the operating conditions to optimize the extraction of both pectin and phenolic compounds were 80 °C, ultrasonic frequency 60 kHz, solid/liquid ratio 1:20, using pH 2 or 12 in the case of pectin or polyphenols, respectively. Direct Analysis in Real Time Mass Spectrometry (DART-MS) and Fourier-Transform Infrared Spectroscopy–Attenuated Total Reflectance (FTIR-ATR) analyses were performed to evaluate the chemical profile of the extracts and pectin. The recycling of coffee husk waste into bioproducts in view of the circular economy contributes to minimizing the impact on the environment and to generating additional income for coffee growers.

Biomass doi: 10.3390/biomass5030052

Authors: Sourabh Chakraborty Nazlim Aktay Fikret Muge Alptekin Melih Soner Celiktas Nurhan Turgut Dunford

Porous carbon from renewable resources like biomass is a key material utilized in many applications ranging from environmental remediation to energy storage. There are limited reports in the literature on the effects of biomass pretreatment, production process parameters, and downstream processing on the final product properties. This is the first study aimed at closing the latter research gap. Six different types of underutilized biomass were examined: eastern red cedar wood, pecan shells, hazelnut shells, algal biomass, miscanthus, and sludge produced at municipal wastewater treatment facilities. Although pretreatment of biomass with KOH or ZnCl2 enhanced formation of micro- and mesopores, carbon yield was lower (15.3–32.5%) than that obtained via non-catalytic pyrolysis (28.3–48%). An optimization study performed using response surface methodology and cedar wood has shown the significant effects (p < 0.05) of temperature and catalyst/biomass ratio on total BET pore volume and surface area. Additionally, catalyst/biomass ratio had a significant effect on the crystal structure and pore size distribution in the carbon produced by pyrolysis. Hence, optimization of process temperature, hold time, and activation ratio is capable of yielding porous carbon from cedar wood pyrolysis with desirable properties.

Biomass doi: 10.3390/biomass5030051

Authors: Nora Estela Ponce-Fernández Leticia Casas-Godoy Rebeca Astorga-Trejo Cuauhtémoc Reyes-Moreno Claudia Castro-Martínez

Corn residues are an abundant and low-cost lignocellulosic feedstock that provides a renewable carbon platform for the production of biofuels, bioplastics, and high-value aromatic volatile compounds (AVCs). Isoamyl alcohol, an important AVC, has applications in the food, cosmetics, and biofuel industries. This study evaluated the bioconversion of corn cob acid hydrolysates by Meyerozyma guilliermondii into isoamyl alcohol and ethanol. Corn cob was selected as feedstock due to its high hemicellulose content. A Box–Behnken (BBD) design was used to optimize phosphoric acid hydrolysis. The optimal treatment (2.49% v/v H3PO4, 130 °C, 120 min, 1 mm particle size) generated 19.79 g L−1 xylose with 2.74 g L−1 acetic acid. Then, agitation speed and nitrogen concentration were optimized via a central composite design (CCD) in synthetic and hydrolysate-based media fermentations. Isoamyl alcohol specific yield after 48 h of fermentation was higher in hydrolysate medium (12.08 ± 0.67 mg·g−1) than in synthetic medium (8.274 ± 0.83 mg·g−1). Free amino nitrogen (FAN) and intracellular protein analyses revealed higher nitrogen consumption in synthetic media fermentation and greater biomass production in acid hydrolysate media. In addition to isoamyl alcohol (33 mg·L−1), and ethanol (10.18 g·L−1), 1-butanol (61.2 mg·L−1), 1-propanol (13.25 mg·L−1), and acetaldehyde (14.88 mg·L−1) were produced. These results demonstrate the potential of M. guilliermondii to convert corn cob into value-added products.

Biomass doi: 10.3390/biomass5030050

Authors: Ilias Diamantis Spyridon Stamatiadis Eirini-Maria Melanouri Seraphim Papanikolaou Panagiota Diamantopoulou

Olive mill wastewater (OMW) is a phenol-rich effluent with high organic load, posing significant environmental disposal challenges in the Mediterranean countries. This study evaluated the bioremediation and valorization potential of OMW by eleven edible and/or medicinal fungal strains (Agrocybe cylindracea, Lentinula edodes, Pleurotus sapidus, Pleurotus sajor-caju, Flammulina velutipes, Ganoderma adspersum, Tuber aestivum and Tuber mesentericum). Firstly, screening for mycelial growth on agar media with commercial glucose and OMW (concentrations from 0 to 50%, v/v) revealed a strain-specific tolerance to phenolic toxicity. Although all tested strains could grow on OMW-based media, G. adspersum, T. mesentericum and T. aestivum presented the highest mycelial growth rates (Kr), exceeding 10 mm/day at elevated OMW levels (50%, v/v). Based on screening outcomes, seven strains were selected for further evaluation under static liquid fermentations in media with 15 and 35% (v/v) OMW. Growth kinetics, substrate consumption, phenolic removal, decolorization capacity, intracellular polysaccharide (IPS) and total lipid content were assessed. Tuber spp. and G. adspersum exhibited the highest tolerance to phenolic compounds, producing biomass exceeding 15 g/L at 35%, v/v OMW. Maximum IPS production reached up to 46.23% (w/w), while lipid content exceeded 15% (w/w) of dry biomass in F. velutipes and T. mesentericum, indicating an oleaginous microorganism-like behavior. Phenolic removal surpassed 80% in most cases, demonstrating efficient enzymatic degradation. Decolorization efficiency varied between strains, but remained above 70% for L. edodes, G. adspersum and F. velutipes. These findings highlight the potential of edible and/or medicinal fungi to simultaneously detoxify OMW and produce biomass and high-value metabolites, supporting a sustainable, low-cost agro-industrial waste management aligning with circular bioeconomy principles.

Biomass doi: 10.3390/biomass5030049

Authors: Pedro C. B. Fernandes Joaquim Silva

The brewing industry generates vast amounts of by-products of biotic and abiotic nature that require proper handling to reduce their environmental footprint annually. Simultaneously, and in alignment with the current circular economy dynamics, there is a growing trend towards the valorization of such by-products, through upcycling and/or repurposing. Biotic by-products are a low-cost source of valuable compounds, such as proteins, carbohydrates, lipids and phenolic compounds, which, with adequate recovery methods, can be used in various industries, e.g., agro-food and pharma, among others, where their bioactive and physical-chemical properties can be harnessed effectively. Abiotic by-products are increasingly valorized through pathways that prioritize material recovery and functional reuse. This work aims to address the most relevant by-products from brewing by providing a broad perspective that abridges their sources alongside the manufacturing chain, the composition of the different by-products, and current and foreseen handling and valorization strategies.

Biomass doi: 10.3390/biomass5030048

Authors: Maria-Ioanna Togantzi Martha Mantiniotou Dimitrios Kalompatsios Vassilis Athanasiadis Ioannis Giovanoudis Stavros I. Lalas

Every year, a substantial amount of food is discarded globally. A significant portion of this waste is composed of fruit by-products or fruits that do not meet consumer standards. Apples rank as the third most extensively produced fruit crop globally, generating substantial waste. This study examined apples that did not meet food industry standards and were destined for disposal. The objective was to recover bioactive compounds from their juice using Cloud Point Extraction (CPE). Like other extraction methods, CPE isolates target compounds from the sample, enhancing recovery yield. A primary advantage of CPE is that it operates without requiring specialized equipment or hazardous reagents. Additional benefits include efficacy, simplicity, safety, and speed. Furthermore, a food-grade surfactant, lecithin, was used to encapsulate bioactive compounds, ensuring non-toxicity for both humans and the environment. After three CPE steps, we recovered 95.95% of the total polyphenols from second-grade apple juice (initial TPC: 540.36 mg GAE/L). The findings highlight CPE’s effectiveness for polyphenol extraction and for producing antioxidant-rich extracts. These extracts may be utilized as nutritional supplements, feed additives, and for nutraceutical or medicinal applications.

Biomass doi: 10.3390/biomass5030047

Authors: Flora Tsvetanova Greta Naydenova Stanislava Boyadzhieva

Sunflower seed hulls and meal are among the most abundant by-products of the food industry. They are an example of waste and, at the same time, a plentiful biomass that cannot be utilized directly in human and animal diets due to their hard digestibility and low nutritional value. Besides their main compounds—carbohydrates, lipids, and proteins—they possess valuable constituents such as vitamins, minerals, and especially phenolics that contribute to their antioxidant capacity. Numerous benefits can be retrieved from such by-products. Since sunflower meal and seed hulls are cheap renewable sources of beneficial substances, their potential in relation to the improvement in our daily life needs to be studied. This is the reason why, in recent years, there has been such a serious interest in their utilization and valorization towards the concept of a circular bio-based economy and process sustainability. This review aims to trace the potential applications and implementation of sunflower meal and hulls in the different fields of industry and environmental protection strategies.

Biomass doi: 10.3390/biomass5030046

Authors: Paula Gómez-Contreras Maite Cháfer Amparo Chiralt Chelo González-Martínez

Development of biodegradable packaging materials and valorization of agri-food waste are necessary to produce more sustainable materials while reducing the environmental impact. Starch-based biocomposite films reinforced with beer bagasse fractions with different purification degrees were developed and characterized in structural, mechanical, thermal and optical properties. To this aim, 5% and 10% (w/w) of either beer bagasse (BB) or its lignocellulosic-rich fibers (LF), obtained by subcritical water extraction at temperatures between 110 and 170 °C, were incorporated into starch matrices. Elastic modulus and tensile strength values increased by up to eight-fold and 2.5-fold, respectively, compared to the control film. The incorporation of BB or LF significantly enhanced the mechanical resistance of the films. In general, the increment in the filler:polymer ratio significantly increased the EM values (p < 0.05), while decreasing the stretchability of the films around 80–85%, regardless of the type of filler. This effect suggests a good interfacial adhesion between the fillers and the polymeric matrix, as observed by FESEM. The biocomposite films exhibited a dark reddish appearance, reduced transparency, light blocking barrier capacity and remarkable antioxidant activity due to the presence of phenolic compounds in the fibers. The water vapor and oxygen barrier properties were better preserved when using the more purified LF obtained at 170 °C. Overall, starch films reinforced with beer bagasse fractions showed strong potential for the development of biodegradable food packaging materials.

Biomass doi: 10.3390/biomass5030045

Authors: Fidel Vallejo Diana Yánez Luis Díaz-Robles Marcelo Oyaneder Serguei Alejandro-Martín Rasa Zalakeviciute Tamara Romero

This study optimizes the production of activated carbons from hydrothermally carbonized (HTC) biomass using potassium hydroxide (KOH) and phosphoric acid (H3PO4) as activating agents. A 23 factorial experimental design evaluated the effects of agent-to-precursor ratio, dry impregnation time, and activation duration on mass yield and iodine adsorption capacity. KOH-activated carbons achieved superior iodine numbers (up to 1289 mg/g) but lower mass yields (18–35%), reflecting enhanced porosity at the cost of material loss. Conversely, H3PO4 activation yielded higher mass retention (up to 54.86%) with moderate iodine numbers (up to 1117.3 mg/g), balancing porosity and yield. HTC pretreatment at 190 °C reduced the ash content, thereby enhancing the stability of hydrochar. These findings highlight the trade-offs between adsorption performance and process efficiency, with KOH suited for high-porosity applications (e.g., water purification) and H3PO4 for industrial scalability. The study advances biomass waste valorization, aligning with circular economy principles and offering sustainable solutions for environmental and industrial applications, such as water purification and energy storage.

Biomass doi: 10.3390/biomass5030044

Authors: Óscar González-Prieto Luis Ortiz Torres María Esther Costas Costas

The feasibility of utilizing biochar as a static floating material for agricultural applications was researched to prevent evaporation from open water static storage systems or as a floating barrier in slurry pits, for instance. Five types of biochar were created from chips, bark, and pellets of pine and residues from two acacia species using a pyrolysis time between 60 and 120 min and mean temperatures between 380 and 690 °C in a simple double-chamber reactor. Biomass and biochar were characterized for their main properties: bulk density, moisture content, volatile matter, ash content, fixed carbon, and pH. Biochar was also evaluated through a basic floatability test over 27 days (648 h) in distilled water. The highest fixed carbon content was observed in pine bark biochar (69.5%), followed by the pine pellets (67.4%) and pine chips (63.4%). Despite their high carbon content, the pellets exhibited a low floatability level, whereas pine bark biochar showed superior static floatage times, together with chip and ground chip biochar. These results suggest that biochar produced from bark and wood chips may be suitable for application as floatability material in water or slurry management systems. These results warrant further research into the static floating of biochar.

Biomass doi: 10.3390/biomass5030043

Authors: Emilly Silva Yonny Lopez Juarez Paes Fernanda Maffioletti Gabrielly Souza Fabricio Gonçalves

This research aimed to evaluate the biological resistance to xylophagous organisms and the dimensional stability related to water absorption in plastic wood panels manufactured by compression molding and produced with pine wood and recycled thermoplastics. The wood–plastic composites (WPCs) were prepared from 50% pine sawdust and 50% recycled plastics (polyethylene terephthalate-PET, high-density polyethylene-HDPE, and polypropylene-PP). The thickness swelling test was carried out by immersing of the WPC samples in water at room temperature (25–30 °C) and evaluating the total change in WPC thickness after 1500 h (≈9 weeks or two months). In addition, the coefficient of initial swelling was evaluated to verify the variability of the swelling. For the biological resistance evaluation of the WPCs, tests were carried out with soil or arboreal termites (Nasutitermes corniger) and drywood termites (Cryptotermes brevis). The WPC loss of mass and termite mortality were evaluated. The use of PP promoted the best response to thickness swelling. The simple mathematical model adopted offers real predictions to evaluate the thickness of the swelling of the compounds in a given time. For some variables there were no statistical differences. It was shown that treatment 3 (T3) presented visual damage values between 0.4 for drywood termites and 9.4 for soil termites, in addition to 26% termite mortality, represented by the lowest survival time of 12 days. The developed treatments have resistance to termite attacks; these properties can be an important starting point for its use on a larger scale by the panel industries.

Biomass doi: 10.3390/biomass5030042

Authors: Joshua M. Henkin Kalidas Mainali Brajendra K. Sharma Madhav P. Yadav Helen Ngo Majher I. Sarker

Beer production produces significant amounts of brewers’ spent grain (BSG), a lignocellulosic by-product with important environmental and economic impacts. Despite its high moisture content and rapid microbial breakdown, BSG has a stable, nutrient-rich composition, especially high in protein, fiber, and polyphenolic compounds. While its perishability limits direct use in food systems, BSG is often repurposed as livestock feed. Recent advances in bioprocessing and extraction technologies have expanded their use across different sectors. This review explores the composition of crude BSG and evaluates innovative valorization methods, including recovering bioactive compounds with pharmaceutical and nutraceutical value, and converting them into biofuels such as biogas, biodiesel, and bioethanol. Special focus is given to methods involving enzymatic hydrolysis, fermentation, and chemical extraction to isolate proteins, peptides, amino acids, sugars, and polyphenols. By analyzing emerging applications and industrial scalability challenges, this review highlights BSG’s growing role within circular economy models and its potential to promote sustainable innovations in both the brewing industry and the wider bioeconomy.

Biomass doi: 10.3390/biomass5030041

Authors: Gianluca Ottolina Federica Zaccheria Jacopo Paini

This review examines sustainable cascading biorefinery strategies for the green alga Ulva, which is globally prevalent in eutrophic marine waters and often forms extensive “green tides.” These blooms cause substantial environmental and economic damage to coastal communities. The primary target products within an Ulva biorefinery typically encompass salts, lipids, proteins, cellulose, and ulvan. Each of these components possesses unique properties and diverse applications, contributing to the economic robustness of the biorefinery. Salts can be repurposed for agricultural or even human consumption. Lipids offer high-value applications in nutraceuticals and animal feed. Proteins present significant potential as plant-based nutritional supplements. Cellulose can be transformed into various advanced materials. Finally, ulvan, a polyanionic oligosaccharide unique to Ulva, holds promise due to its distinct properties, particularly in the biomedical field. Furthermore, state-of-the-art chemical modifications of ulvan are presented with the aim of tailoring its properties and broadening its potential applications. Future research should prioritize optimizing these integrated extraction and fractionation processes. Furthermore, a multi-product biorefining approach, integrated with robust Life Cycle Assessment studies, is vital for transforming this environmental challenge into a significant opportunity for sustainable resource valorization and economic growth.

Biomass doi: 10.3390/biomass5030040

Authors: Megananda Eka Wahyu Damayanti Damayanti Ho Shing Wu

This study explored the production and activation of biochar from rice straw residue for dye adsorption applications. Rice straw, a widely available but underutilized biomass, was processed to isolate lignin and generate biochar through pyrolysis at 450 °C and 550 °C. Activation using chemical agents (e.g., KOH and NaOH) was performed to enhance surface area and porosity. Among the tested conditions, KOH activation at a char-to-agent ratio of 1:3 produced activated carbon at 800 °C with the highest BET surface area (835.2 m2/g), and high fixed carbon (44.4%) after HCl washing. Thermogravimetric analysis was used to investigate pyrolysis kinetics, with activation energies determined using the Kissinger, Flynn–Wall–Ozawa, and Kissinger–Akahira–Sunose models. The brown solid showed a higher activation energy (264 kJ/mol) compared to isolated lignin (194 kJ/mol), indicating that more energy is required for decomposition. The AC was evaluated for the adsorption of methylene blue (MB) and methyl orange (MO) from aqueous solutions. Both dyes followed the Langmuir isotherm model, indicating that monolayer adsorption occurred. The maximum adsorption capacities reached 222 mg/g for MB and 244 mg/g for MO at 303 K, with higher values at elevated temperatures. Adsorption followed a pseudo-second-order kinetic model and was governed by a physisorption mechanism, as supported by thermodynamic analysis (ΔH < 20 kJ/mol and Ea < 40 kJ/mol). These findings demonstrate that KOH-activated biochar from rice straw residue is a high-performance, low-cost adsorbent for dye removal, contributing to sustainable biomass utilization and wastewater treatment.

Biomass doi: 10.3390/biomass5030039

Authors: Helitha Nilmalgoda Jayashan Bandara Isuru Wijethunga Asanga Ampitiyawatta Kaveenga Koswattage

This study investigates biochar-enriched organic fertilizers made from bagasse, ash, spent wash, and cane tops, assessing their impact on corn growth over 45 days. A randomized complete block design with three replicates was used, testing six formulations with biochar levels at 0%, 10%, and 20%, along with soil-only and commercial fertilizer controls. Treatments T5 (bagasse + ash + spent wash + cane tops), T11 (T5 + 10% biochar), and T17 (T5 + 20% biochar) showed the best results for plant height, leaf development, and biomass production, with T17 performing the best for growth, biomass, and girth. The biochar in T17 had a pH of 9.37 ± 0.16, 18.00 ± 1.25% ash content, and a surface area of 144.58 m2/g. Nutrient analysis of the compost showed 2.85% potassium, 1.12% phosphorus, 1.85% nitrogen, 4.1% calcium, 0.23% magnesium, and 130 mg/kg zinc. The elemental composition was 68.50% carbon, 4.50% hydrogen, 6.00% nitrogen, and 25.30% oxygen, with 85.00% total organic carbon (TOC). This study concludes that T17 is the most effective formulation, offering both environmental and financial benefits, with composting potentially generating $11.16 million in profit, compared to the $19.32 million spent annually on waste management in Sri Lanka’s sugar industry.

Biomass doi: 10.3390/biomass5030038

Authors: Dimitris P. Makris

Biomass was launched in 2021, aiming at providing an open access reservoir of knowledge pertaining to the field of biomass and its harnessing [...]

Biomass doi: 10.3390/biomass5030037

Authors: Gitanjali Jothiprakash Prabha Balasubramaniam Senthilarasu Sundaram Desikan Ramesh

Biomass gasification is an effective process for converting organic wastes into syngas. Syngas is a biofuel that possesses several potential applications in the energy sector. However, the major bottleneck for the commercialization of this technology is tar production in biomass gasification, which affects gasifier performance and syngas yield/quality. Tar can be destructed by adopting in situ or ex situ modes of utilizing catalysts in biomass gasification. The added advantage of tar reduction is enhanced syngas energy content. Despite their advantages, catalysts face challenges such as high costs, declining performance over time, and difficulties in regeneration and recycling. Deactivation can also occur due to poisoning, fouling, and carbon buildup. While some natural materials have been tested as alternative materials, the financial sustainability and affordability of catalysts remain crucial for large-scale syngas production. This paper offers an overview of tar reduction strategies and the role of various catalysts in the gasification process and future perspectives on catalyst development for biomass gasification.

Biomass doi: 10.3390/biomass5020036

Authors: Telma Moreira Maria Margarida Mateus Luís C. Duarte Maria Joana Neiva Correia

Biomass liquefaction is a promising thermochemical route to convert lignocellulosic residues into bio-oil. This study evaluates the liquefaction behavior of 13 biomasses with varying particle sizes (0.3–2.0 mm) and moisture contents (5–11%) under mild solvolysis conditions. High-performance liquid chromatography (HPLC-RID) and thermogravimetric analysis (TGA) were used to characterize bio-oil composition and biomass properties, respectively. Maximum conversion (72%) was achieved for Miscanthus, while Ulva lactuca reached only 23% due to its low carbohydrate content. Hemicellulose-rich feedstocks showed higher yields, whereas high lignin content generally reduced conversion. Furfural was the main compound identified in the aqueous phase (up to 51 g/L), reflecting extensive pentose degradation. Laboratory and industrial-scale liquefaction of cork and eucalyptus revealed scale-dependent differences. Industrial cork bio-oil showed increased xylose (0.70 g/L) and furfural (0.40 g/L), while industrial eucalyptus exhibited elevated levels of acetic (0.46 g/L) and formic acids (0.71 g/L), indicating enhanced deacetylation and demethoxylation reactions. These findings offer valuable insights for optimizing feedstock selection and process conditions in biomass liquefaction. The valorization of lignocellulosic residues into bio-oil contributes to the development of scalable, low-carbon technologies aligned with circular economy principles and bio-based industrial strategies.

Biomass doi: 10.3390/biomass5020035

Authors: Patrícia D. Barata Alexandra I. Costa Sónia Martins Magda C. Semedo Bruno G. Antunes José V. Prata

Tomato waste (TW) was employed as a sustainable source for the synthesis of fluorescent carbon dots (CDs) via a microwave-assisted hydrothermal carbonization (Mw-HTC) method, aiming at its valorization. Several amines were used as nitrogen additives to enhance the fluorescence quantum yield (QY) of CDs, and a set of reaction conditions, including additive/TW mass ratio (0.04–0.32), dwell time (15–60 min), and temperature (200–230 °C) of the HTC process, were scrutinized. The structural analysis of the tomato waste carbon dots (TWCDs) was undertaken by FTIR and 1H NMR techniques, revealing their most relevant features. In solid state, transmission electron microscopy (TEM) analysis showed the presence of nearly spherical nanoparticles with an average lateral size of 8.1 nm. Likewise, the topographical assessment by atomic force microscopy (AFM) also indicated particles’ heights between 3 and 10 nm. Their photophysical properties, revealed by UV–Vis, steady-state, and time-resolved fluorescence spectroscopies, are fully discussed. Higher photoluminescent quantum yields (up to 0.08) were attained when the biomass residues were mixed with organic aliphatic amines during the Mw-HTC process. Emission tunability is a characteristic feature of these CDs, which display an intensity average fluorescence lifetime of 8 ns. The new TWCDs demonstrated good antioxidant properties by the ABTS radical cation method (75% inhibition at TWCDs’ concentration of 5 mg/mL), which proved to be related to the dwell time used in the CDs synthesis. Moreover, the synthesized TWCDs suppressed the growth of Escherichia coli and Staphylococcus aureus at concentrations higher than 2000 μg/mL, encouraging future antibacterial applications.

Biomass doi: 10.3390/biomass5020034

Authors: Luiz Eduardo Nochi Castro William Gustavo Sganzerla Larissa Resende Matheus Vanessa Cosme Ferreira Mauricio Ariel Rostagno Tania Forster-Carneiro

This study investigates the competitive dynamics of reducing sugar production and degradation during the subcritical water processing (SWP) of lyophilized grape pomace (LGP), with the goal of optimizing sugar yield. Under the SWP conditions tested (150 °C, 150 bar, pH 7, S/F of 30 g water g−1 LGP, and a flow rate of 5 mL min−1), we achieved a reducing sugar yield of 296.0 mg sugars g−1 LGP, effectively balancing sugar production and degradation. Sugar yield decreased as the temperature increased from 150 °C to 210 °C, due to the degradation of monosaccharides into by-products like furfural and 5-HMF. A first-order reaction model was developed to better understand the kinetic competition between sugar formation and degradation at varying temperatures. The highest sugar yield occurred at 150 °C, where sugar production was maximized, and degradation was minimized. These findings offer valuable insights for subcritical water processing in the valorization of LGP into fermentable sugars while minimizing the formation of undesirable by-products.

Biomass doi: 10.3390/biomass5020033

Authors: Velyana Georgieva Lenia Gonsalvesh Sonia Mileva Mariyana Hamanova Hyusein Yemendzhiev

This study investigates the potential of biochars derived from agricultural waste biomass for the removal of heavy metal ions from aqueous solutions. Biochars were produced via slow pyrolysis at 793 K using almond shells (AS), walnut shells (WS), pistachio shells (PS), and rice husks (RH) as feedstocks. The physicochemical properties and adsorption performance of the resulting materials were evaluated with respect to Cd(II), Mn(II), Co(II), Ni(II), Zn(II), total Iron (Fetot), total Arsenic (Astot), and total Chromium (Crtot) in model solutions. Surface morphology, porosity, and surface chemistry of the biochars were characterized by scanning electron microscopy (SEM), nitrogen adsorption at 77 K (for specific surface area and pore structure), Fourier-transform infrared spectroscopy (FTIR), and determination of the point of zero charge (pHpzc). Based on their textural properties, biochars derived from WS, PS, and AS were classified as predominantly microporous, while RH-derived biochar exhibited mesoporous characteristics. The highest Brunauer–Emmett–Teller (SBET) surface area was recorded for PS biochar, while RH biochar showed the lowest. The pistachio shell biochar exhibited the highest specific surface area (440 m2/g), while the rice husk biochar was predominantly mesoporous. Batch adsorption experiments were conducted at 25 °C, with an adsorbent dose of 3 g/L and a contact time of 24 h. The experiments in multicomponent systems revealed removal efficiencies exceeding 87% for all tested metals, with maximum values reaching 99.9% for Cd(II) and 97.5% for Fetot. The study highlights strong correlations between physicochemical properties and sorption performance, demonstrating the suitability of these biochars as low-cost sorbents for complex water treatment applications.

Biomass doi: 10.3390/biomass5020032

Authors: Sara Mrhari Derdag Naaila Ouazzani

In response to significant environmental challenges, biochar has garnered attention for its applications across diverse fields. Characterized by high carbon content resulting from the thermal degradation of biomass, biochar offers a sustainable strategy for waste valorization and environmental remediation. This paper offers a comprehensive overview of biochar production from residual biomass, emphasizing feedstock selection, conversion pathways, material properties, and application potential. Key production techniques, including pyrolysis, gasification, and hydrothermal carbonization, are critically evaluated based on operational conditions, energy efficiency, product yield, and environmental implications. The functional performance of biochar is further discussed in the context of soil enhancement, wastewater treatment, renewable energy generation, and catalytic processes, such as biohydrogen production. By transforming waste into value-added products, biochar technology supports circular economy principles and promotes resource recovery. Ongoing research aimed at optimizing production processes and understanding application-specific mechanisms is crucial to fully realizing the environmental potential of biochar.

Biomass doi: 10.3390/biomass5020031

Authors: Filip Brleković Katarina Mužina Tatjana Haramina Stanislav Kurajica

The objective of this study was to explore the potential of creating advanced insulating biocomposites using waste almond and hazelnut shells as particulate fillers, combined with a geopolymer binder, to develop sustainable materials with minimal environmental impact. Optimal conditions for the preparation of biocomposites were determined by measuring the compressive strengths. The aforementioned optimal conditions included a geopolymer to waste nutshell mass ratio of 2, room-temperature curing, and the use of metakaolin geopolymers activated with potassium solutions. Notably, the highest compressive strengths of 4.1 MPa for hazelnut shells biocomposite and 6.4 MPa for almond shells biocomposite were obtained with milk of lime pretreatment at 80 °C for 1 h. Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX) and Fourier transform infrared spectroscopy (FTIR) analyses revealed better adhesion, as well as improved geopolymer gel polymerization. Furthermore, thermal conductivity and diffusivity measurements demonstrated values characteristic of insulating materials, reinforcing their potential for eco-friendly construction applications.

Biomass doi: 10.3390/biomass5020030

Authors: Ranjani Siriwardane Jarrett Riley Chris Atallah Michael Bobek

A thermodynamic integrated process assessment and experimental evaluation of the conversion of woody biomass to H2 using chemical looping approaches were explored in this work. Both a two- and three-reactor approach were evaluated for effectiveness with a CaFe2O4 oxygen carrier (OC). Experimental test campaigns consisted of semi-batch operations where a single reactor was loaded with a batch charge of the OC and fuel. Multi-reactor approaches were experimentally simulated by switching the gas atmosphere around the batch charge of the OC. The experiments showed that woody biomass was capable of reducing CaFe2O4, enabling the production of H2 from steam oxidation. High steam conversion rates to H2 of >75% were demonstrated. Reduced CaFe2O4 catalyzed tar cracking, multi-cycle tests showed stable reactivity, and sub-pilot-scale tests showed improved reactivity and H2 yield, accompanied by improved attrition resistance after over 30 cycles. The three-reactor configuration showed the highest potential for H2 yield between the case studies, while the two-reactor configuration had the lowest auxiliary feed requirement. Both approaches showed increased yields and lower utilities than the baseline steam gasification technology.

Biomass doi: 10.3390/biomass5020029

Authors: Joao Carlos Alves Macedo Maryam Shirinkar Richard Landers André Henrique Rosa

The transition from fossil resources to renewable raw materials derived from lignocellulosic waste is crucial for economic and environmental sustainability. Advancing toward a bio-based economy necessitates the development of innovative heterogeneous catalysts. This study explores the use of modified sugarcane bagasse biochar, embedded with ruthenium and iron particles, as a green catalyst for converting levulinic acid (LA) to γ-valerolactone (GVL). The efficiency of both raw and modified biochar in the LA to GVL conversion process, utilizing formic acid (FA) exclusively as the hydrogen source, was systematically assessed through characterization techniques, including XRD, TGA, XPS, and SEM/EDS. The gelification method using alginate enhanced the ruthenium and iron content on the surface of the biochar. The results demonstrate that the modified material has significant potential for efficient LA-to-GVL conversion, achieving a yield of 73.0 ± 9.2% under optimized conditions (0.5 g of BC500Fe/3%Ru at 180 °C for 3 h, with 4 mmol LA, 8 mmol FA, and 10 mL of water). Iron on the biochar surface facilitated the formation of adsorption sites for LA, supporting the notion of this novel catalyst for LA conversion in an aqueous medium in the presence of FA. This research underscores the potential of this green catalyst in advancing sustainable biomass conversion and contributes to the ongoing shift towards a bio-based economy.

Biomass doi: 10.3390/biomass5020028

Authors: Wolfgang Gebhard Sebastian Zant Johannes Neidel Andreas Apfelbacher Robert Daschner

Sustainably produced hydrogen has the potential to substitute fossil fuels and significantly reduce CO2 emissions. Fraunhofer UMSICHT develops a new thermochemical conversion technology to gasify ash-rich biogenic residues and waste materials that are difficult to treat with conventional gasifiers, enabling their conversion into higher-quality energy carriers such as hydrogen and syngas. Ash-rich feedstocks are difficult to convert in conventional gasification methods, as they tend to agglomerate and form slag, leading to blockages in the reactor and process disturbances. In this experimental study, hydrogen-rich syngas is produced from biogenic residual and waste materials (sewage sludge) using the Enhanced Carbon-To-X-Output (EXO) process. The EXO process is a three-stage thermochemical conversion process that consists of a combination of multi-stage gasification and a subsequent reforming step. The influence of temperature in the reforming step on the gas composition and hydrogen yield is systematically investigated. The reformer temperature of the process is gradually increased from 500 °C to 900 °C. The feedstock throughput of the pilot plant is approximately 10 kg/h. The results demonstrate that the temperature of the reforming step has a significant impact on the composition and yield of syngas as well as the hydrogen yield. By increasing the reformer temperature, the syngas yield could be enhanced. The hydrogen yield increased from 15.7 gH2/kgFeed to 35.7 gH2/kgFeed. The hydrogen content in the syngas significantly increased from 23.6 vol.% to 39 vol.%. The produced syngas can be effectively utilized for sustainable hydrogen production, as a feedstock for subsequent syntheses, or for power and heat generation.

Biomass doi: 10.3390/biomass5020027

Authors: Shuhan Xiao Yang Yang

Achieving efficient electrocatalytic oxidation of cellulose-derived biomass is a pivotal strategy for advancing bioenergy utilization and achieving carbon neutrality. This study addresses the challenges of low conversion efficiency caused by cellulose’s high crystallinity and excessive energy consumption in conventional processes by proposing a novel integrated system combining solid heteropoly acid catalytic pretreatment and electrocatalytic oxidation. By preparing the (C16TA)H2PW solid acid catalyst, we successfully achieved hydrolysis of microcrystalline cellulose under 180 °C for 60 min, attaining a glucose yield of 40.1%. Furthermore, a non-noble metal electrocatalyst system based on foam copper (CuF) was developed, with the Co3O4/CuF electrode material demonstrating a Faradaic efficiency of 85.3% for formate production at 1.66 V (vs. RHE) in 1 mol L−1 KOH electrolyte containing the pretreated cellulose mixture, accompanied by a partial current density of 153.2 mA cm−2. The mechanism study indicates that hydroxyl radical-mediated C-C bond selective cleavage dominates the formate generation. This integrated system overcomes the limitations of poor catalyst stability and low product selectivity in biomass conversion, offering a sustainable strategy for green manufacturing of high-value chemicals from cellulose.

Biomass doi: 10.3390/biomass5020026

Authors: Vijitha Amalapridman Peter A. Ofori Lord Abbey

Concerns about sustainable energy sources arise due to the non-renewable nature of petroleum. Escalating demand for fossil fuels and price inflation negatively impact the energy security and economy of a country. The generation and usage of biofuel could be suggested as a sustainable alternative to fossil fuels. Several studies have investigated the potential of using edible crops for biofuel production. However, the usage of algae as suitable feedstock is currently being promoted due to its ability to withstand adverse environmental conditions, capacity to generate more oil per area, and potential to mitigate energy crises and climate change with no detrimental impact on the environment and food supply. Furthermore, the biorefinery approach in algae-based biofuel production controls the economy of algal cultivation. Hence, this article critically reviews different cultivation systems of algae with critical parameters including harvesting methods, intended algae-based biofuels with relevant processing techniques, other applications of valorized algal biomass, merits and demerits, and limitations and challenges in algae-based biofuel production.

Biomass doi: 10.3390/biomass5020025

Authors: Francisco Martínez-Ruiz Gabriela Andrade-Bustamante Ramón Holguín-Peña Prabhaharan Renganathan Lira Gaysina Natalia Sukhanova Edgar Puente

The projected global population is expected to reach 9.7 billion by 2050, necessitating a significant increase in food production. Malnutrition remains a global health challenge that contributes to over 3.5 million deaths annually and accounts for 45% of all child mortalities. Microalgae, including cyanobacteria, are a promising solution because of their rich composition of bioactive compounds such as polyunsaturated fatty acids, carotenoids, proteins, vitamins, and minerals. These biomolecules provide various health benefits, including antioxidant, antidiabetic, anticancer, anti-inflammatory, and cardioprotective properties, making microalgal biomass a valuable ingredient in functional food formulations. However, the large-scale adoption of microalgae for food production faces several challenges, including species-specific variations in biochemical composition, inconsistencies in biomass yield, structural alterations during extraction and purification, sensory issues, and bioprocessing inefficiencies. Furthermore, regulatory challenges and concerns regarding bioavailability and safety continue to limit their widespread acceptance. Despite these limitations, microalgal bioactives have significant potential for the development of next-generation nutraceuticals and functional foods. This review examines the bioactive compounds found in microalgae, detailing their biological activities and functional applications in the food industry. Additionally, it explores the key challenges preventing their integration into food products and proposes strategies to overcome these challenges, ultimately facilitating the commercialization of microalgae as a sustainable and health-promoting food source.

Biomass doi: 10.3390/biomass5020024

Authors: Filipe M. M. Cordeiro Salomé G. Bedoya Daniel A. P. Santos Rebeca S. Santos Thomas V. M. Bacelar Filipe S. Buarque George Simonelli Ana C. M. Silva Álvaro S. Lima

High-value-added biomolecules such as phenolic compounds and flavonoids from secondary metabolism and macromolecules such as sugars are the main constituents of several plants. Thus, this work aims to optimize the extraction of these biomolecules present in the pods of Cassia grandis L.f. Initially, the effect of choline-based ionic liquids—ILs (choline chloride [Ch]Cl, dihydrogen citrate [Ch][DHC], and bitartrate [Ch][BIT]) as extracting agents for phenolic compounds and flavonoids was evaluated based on their efficiency and selectivity. Then, a 23 full factorial design with six central points was performed using the IL concentration, the solid–liquid ratio, and the temperature as independent variables. The extract obtained in the best condition was subjected to pervaporation, after which the concentrates and the crude extract were used to determine the physical properties (density, viscosity, and refractive index). The hydrophobic–hydrophilic balance of the extracting agent and the biomolecules are the extraction process’s driving force. The best extraction condition was formed by [Ch][DHC] at 15 wt%, with a solid–liquid ratio of 1:15, at 45 °C for 30 min, resulting in 153.71 ± 5.81 mg·g−1 of reducing sugars; 483.51 ± 13.10 mg·g−1 of total sugars; 11.79 ± 0.54 mg·g−1 of flavonoids; and 38.10 ± 2.90 mg·g−1 of total phenolic compounds. All the physical properties of the biomolecules are temperature-dependent; for density and refractive index, a linear correlation is observed, while for viscosity, the correlation is exponential. Increasing the temperature decreases all properties, and the extract concentration for 8× presents the highest values of density (1.283 g·cm−3), viscosity (9224 mPa·s), and refractive index (1.467).

Biomass doi: 10.3390/biomass5020023

Authors: Tor Ivan Simonsen Demi Tristan Djajadi Sune Tjalfe Thomsen

Lignin-rich residues from lignocellulosic biorefineries remain underutilized, limiting their economic viability. This study demonstrates how modifying hydrothermal pretreatments with temperatures and additives enhances the lignin-rich residue’s solubility in alcohol, a key step toward its valorization in biofuel and material applications. Effective carbohydrate removal greatly enhanced the residue’s alcohol solubility, supporting both saccharification and lignin utilization. Notably, a 5% hydrogen peroxide treatment doubled the residue’s alcohol solubility, reaching ~40%, while maintaining similar saccharification yields. Low concentrations of surfactants and oxidizers enhanced the alcohol solubility independently of the saccharification yield, while alkali improved both. These findings highlight that minor pretreatment adjustments, such as low-concentration additives, can optimize lignin’s utilization in biorefineries, while maintaining a high carbohydrate conversion

Biomass doi: 10.3390/biomass5020022

Authors: Mourad Ouhammou Abdellah Mourak Aziz Ait-Karra Jaouad Abderrahim Najat Elhadiri Mostafa Mahrouz

This study investigates the extraction, isolation, and chemical modification of cellulose from coffee ground residues using TEMPO-NaBr-NaClO oxidation. These residues represent a promising renewable source of cellulose, which is obtained after the removal of impurities such as lignin (24%), hemicellulose (42%), and other compounds. The TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical)-catalyzed oxidation selectively converts primary hydroxyl groups into carboxylate groups (-COOH) under mild conditions in aqueous media, achieving an oxidation yield of up to 67%. Structural and morphological analyses, including scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and X-ray diffraction (XRD), confirm the successful chemical modification of the cellulose. The results indicate a reduction in crystallinity index from native cellulose (80%) to oxidized cellulose (65%), reflecting partial disruption of the microfibril structure and the introduction of new chemical functionalities. FTIR analysis reveals the appearance of characteristic carboxylate bands, confirming the conversion of hydroxyl groups into carboxyl groups. Energy-dispersive X-ray (EDX) analysis further highlights a significant increase in oxygen content, indicating the efficiency of the oxidation process. The TEMPO-oxidized cellulose is water-soluble, enabling the production of valuable polyelectrolytes and intermediates. These chemical modifications improve the cellulose’s reactivity, broadening its potential applications in various fields, including biocomposites, sustainable packaging materials, and functional films. This work demonstrates the feasibility of utilizing coffee ground residues as a renewable, eco-friendly source of modified cellulose for high-value applications.

Biomass doi: 10.3390/biomass5020021

Authors: Marcel Dossow Vahid Shadravan Weiss Naim Sebastian Fendt David Harris Hartmut Spliethoff

This study assesses Queensland’s sugar industry potential for sustainable aviation fuel (SAF) production via biomass-to-liquids (BtL) processes. Using surplus sugarcane bagasse, preliminary estimates suggest that individual mills could support 60–130 MWth gasifiers, while clustered approaches enable larger capacities. Annual BtL syncrude production could reach 440 mL, increasing to ~1000 mL with additional feedstocks. These findings highlight both the industrial-scale viability of SAF production and the logistical and engineering challenges that must be addressed to align with Australia’s renewable energy and fuel security goals.

Biomass doi: 10.3390/biomass5020020

Authors: Leonel J. R. Nunes

Stochastic models can be used for predicting the availability of residual woody forest biomass, considering the variability and uncertainty associated with climatic, operational, and economic factors. These models, such as ARIMA, GARCH, state transition models, and Monte Carlo simulations, are widely used to capture seasonal patterns, dynamic variations, and complex uncertainties. Their application supports critical decisions in forest and energy operations planning. The implementation of the models was carried out in Python, using specialized packages such as Statsmodels for ARIMA, Arch for GARCH, and PyMC3 for state transition models. Probabilistic calculations were performed with Numpy and Scipy, while Matplotlib and Seaborn were used for data visualization. Hypothetical data simulating real-world scenarios were analyzed, divided into training and testing sets, with cross-validation and metrics such as RMSE, MAPE, and R2. ARIMA demonstrated high accuracy in capturing seasonality, while GARCH effectively modeled volatility. Monte Carlo simulations provided the most reliable forecasts, capturing uncertainties across multiple scenarios. The models excelled in predicting periods of high biomass availability with robust projections. The results confirm the efficacy of stochastic models in predicting residual biomass, with a positive impact on sustainable planning. However, challenges such as data dependency and computational resources still need to be addressed, pointing to directions for future research and methodological improvements.

Biomass doi: 10.3390/biomass5020019

Authors: Arnulfo Domínguez-Hernández Alejandra Juárez-Velázquez Elisa Domínguez-Hernández Rosalba Zepeda-Bautista Claudia Hernández-Aguilar Martha Domínguez-Hernández

Sustainable agricultural practices are essential to address global food security challenges while minimizing environmental impacts. This study aimed to evaluate integrated farming systems with varying levels of integration (from lower to higher)—maize monoculture + livestock (MM), maize + cover crop + mixed prairie + livestock (MCP), and maize + red clover + mixed prairie + livestock (MRP)—to assess their contributions to circularity and sustainability. The research examined biomass and protein production, nutrient cycling, energy use, food needs covered, and workload over two cropping cycles. The findings revealed that highly integrated systems (MRP and MCP) significantly enhance biomass production, energy efficiency, and nutrient recycling compared to the MM system (p < 0.05). MRP produced 4 times more biomass than MM (9.4 t ha−1), while MCP achieved a 0.99 Nitrogen Recycling Index compared with 0.38 in MM, underscoring the benefits of grazing and increasing agrobiodiversity. Integrated systems also improved soil health (+17.4% organic matter in MRP and MCP, +91.5% nitrogen in MCP), reduced dependency on synthetic inputs, and boosted protein production (animal-derived protein in MRP and MCP = 395.4 kg, MM = 73.7 kg), thus meeting food needs for large populations. However, they required increased labor and technical expertise, presenting adoption barriers for smallholders. The synergy between agroecological practices and circularity offers a pathway to sustainable intensification, fostering economic, environmental, and social resilience. In this way, the results highlighted the potential of integrated farming systems to transform agricultural systems.