Biomass, Volume 6, Issue 2 (April 2026) – 15 articles

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. Full article

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. Full article

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 (S_BET = 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. Full article

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. Full article

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. Full article

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. Full article

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. Full article

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. Full article

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. Full article

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. Full article

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. Full article

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%). Full article

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 (t_1/2 = 8.82 ± 0.34 and D = 29.32 ± 1.13 h) and β-glucosidase (t_1/2 = 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. Full article

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. Full article

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. Full article