Biomass, Volume 5, Issue 2 (June 2025) – 18 articles

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. Full article

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 (Fe_tot), total Arsenic (As_tot), and total Chromium (Cr_tot) 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 (pH_pzc). 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 (S_BET) 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 Fe_tot. 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. Full article

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. Full article

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. Full article

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. Full article

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. Full article

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 g_H2/kg_Feed to 35.7 g_H2/kg_Feed. 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. Full article

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. Full article

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. Full article

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. Full article

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). Full article

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 Full article

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. Full article

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 MW_th 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. Full article

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. Full article

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. Full article

The aim of this study is the quantitative and qualitative characterization of food waste from the restaurant sector in Riobamba, Ecuador as part of circular economy efforts. A weekly analysis of waste generation data collected from 13 participating restaurants showed that the average daily food waste generated was 18.48 kg/restaurant/day. The highest percentage (55%) was produced by organic waste, which was primarily composed of waste from vegetables. Plastics represented most of the recyclable waste (21%), and 24% of the waste was disposable. With a low dry matter content of 24.33 ± 5.12% and an average moisture level of 75.68 ± 5.12%, the high organic content indicates its potential for value-adding through biological recycling processes like anaerobic digestion and composting. Fruit and vegetable waste had high moisture levels (80.3 ± 2.54% and 81.2 ± 2.75%, respectively), which made them perfect for composting and biogas production. However, the moisture and dry matter contents differed greatly amongst the waste categories. The increased dry matter concentration of animal protein waste (54.5 ± 4.30%) indicated that it may be converted into products with added value, such as animal meal and oils. Plant protein waste needs to be processed quickly to avoid spoiling because of its extraordinarily high moisture content (95.7 ± 3.20%) and low dry matter (4.3 ± 3.20%). The findings underscore the necessity for focused measures, such as composting, anaerobic digestion, and enhanced recycling, to optimize resource recovery and mitigate environmental consequences. Full article

Pineapple (Ananas comosus) is one of the most economically important fruit cultivars in South Africa. The fruit is locally consumed, processed into various industrial products or exported to foreign markets. Approximately 115,106 metric tons of pineapple fruit are harvested in South Africa. The pineapple value chain generates significant amounts of waste, in the form of pomace, peel, crown, stem, core and base. If not properly treated, pineapple waste (PAW) could have a profound detrimental impact on the environment. This calls for advanced technological platforms to transform PAW into useful bio-based products. A biorefinery is a potent strategy to convert PAW into multiple food and non-food products while effectively disposing of the waste. The objective of this review is to explore possible pathways for the valorization of PAW into energy and material products in a biorefinery. The paper looks at 10 products including biogas, biohythane, bioethanol, biobutanol, biohydrogen, pyrolytic products, single-cell proteins, animal feed, vermicompost and bioactive compounds. Several platforms (i.e., biochemical, chemical, physical and thermochemical) are available to convert PAW into valuable goods. Amongst them, the biochemical route appears to be the most favorable option for the valorization of PAW. Anaerobic digestion and fermentation are well-established biochemical technologies for PAW valorization. These methods are simple, low-cost, eco-friendly and sustainable. The focal point of emerging research is the enhanced efficacy of biorefinery platforms. The commercialization of PAW biorefining is a potential gamechanger that could revitalize the entire South African economy. Full article