Woody biomass crops are increasingly considered a promising alternative to conventional agricultural systems due to their potential for sustained carbon sequestration under accelerating climate change. Optimizing management practices in such systems is therefore critical to enhance biomass production and carbon storage. In this study, we investigated how management influences biomass allocation in four poplar plots differing in planting density, variety, and harvest-rotation design during their 6th and 7th year of growth. Biomass stocks were quantified for crown, stem, coarse roots, and fine roots. Management effects were most pronounced in aboveground biomass, whereas belowground responses were less consistent. The highest aboveground biomass was observed in the high-density system within the first rotation (MxHD1), reaching 55.32 Mg ha-1 in 2024 and 94.91 Mg ha-1 in 2025. Belowground biomass ranged from 8.12 to 18.35 Mg ha-1 across plots and years. The root:shoot ratio declined with increasing shoot basal diameter and was highest in the year following harvest. Based on these data, we developed general and management-specific allometric models to predict aboveground and belowground biomass from diameter at breast height. Including management factors improved prediction accuracy, supporting more precise quantification of biomass allocation under different cultivation strategies.

Peatlands are essential long-term carbon sinks, yet continued peat extraction for horticulture contributes to greenhouse gas emissions and ecosystem degradation. Here, we introduce artificial peat, a peat-formation-inspired material produced by selectively mimicking natural humification pathways under controlled alkaline conditions. Unlike conventional biomass conversion processes that aim for complete degradation, carbonization, or simple constituent replacement, this approach promotes controlled partial transformation of lignocellulosic biomass into artificial humic substances while preserving a stabilized fibrous framework. Batch and continuous processing routes operated under mild conditions (≤120 °C) using widely available feedstocks, including paludiculture biomass, wood residues, leaves, and agricultural by-products. Artificial humic acid yields ranged from 6.9 to 42.3 wt% in batch systems. Across both processing modes, carbohydrate fractions decreased and lignin underwent partial depolymerization followed by condensation into humified macromolecular structures, accompanied by a marked reduction of readily oxidizable organic matter. Multimodal analyses (elemental composition, Van Krevelen evolution, FTIR, microscopy/EDX, and oxidative thermogravimetry) revealed a transition toward oxygen-rich, condensed architectures with enhanced oxidative stability relative to raw biomass. The applied thermal–alkaline conditions are expected to promote hygienization and seed inactivation, while the conversion of labile biomass components into humic substances suggests improved chemical and potential biological stability. Produced within minutes rather than millennia, artificial peat combines humic functionality with preserved structural integrity, establishing a scalable and resource-efficient alternative to natural peat for sustainable growing media and carbon stabilization applications.

The safe storage of renewable biomass in piles poses a significant challenge. Low-temperature oxidation, water evaporation or condensation, and the metabolic processes of microorganisms occur simultaneously within openair biomass piles, leading to intense self-heating. Drawing on our knowledge of Computational Fluid Dynamics (CFD) simulation, we successfully integrated the three mechanisms of biomass pile heating in the present work. This study examined moisture migration and temperature changes in a woodchip storage pile over a simulated 3month period. We focused on enhancing the mathematical model of water migration, developing a method sensitive to environmental humidity, and adding a correction factor to match the experimentally measured water migration rate. Based on the above simulation framework, this study investigated the effects of changes in pile height, particle diameter, ambient humidity, and temperature on self-heating. Finally, a preliminary investigation was conducted on the safety margins that can prevent spontaneous ignition of woodchip storage piles under certain extreme weather conditions. The results indicate that during the self-heating process of a woodchip storage pile, the highest temperature inside the pile differs from the experimental record by only 3 to 4 degrees C, and the duration of the elevated temperature differs by about 2 days. When the correction factor phi is 0.5, the moisture migration process within the pile better matches the experimental data. The dry matter loss of the biomass is approximately 11 %, slightly higher than the 9 % in the experimental record. Reducing the pile height, increasing particle size, and maintaining lower ambient temperature and humidity are all beneficial for safe storage. Finally, a safety margin to prevent woodchip pile spontaneous ignition is proposed: when the pile height is 6 m, the particle size should not be less than 3 cm; when the stack height is 3.5 m, the particle size should not be less than 2 cm. This long-term simulation of biomass storage piles provides significant input for the safety of biomass storage, as it accurately predicts temperature variation and moisture migration.

On agricultural soils, short rotation coppices (SRC) can be an efficient alternative for long-term carbon fixation in roots compared to conventional land-uses. Previous studies on root biomass focused mainly on fine roots or topsoil layers, but a comprehensive assessment requires accounting for total root biomass across both topsoil and subsoil. Three plots of a poplar SRC with rotation length of 2, 4 and 16 years (SRC2, SRC4 and SRC16) were studied to assess total root biomass (finer <7 cm and coarser >7 cm), its distribution down to 1 m depth, and the root decomposition rates 12 and 24 months after re-conversion. The objective of this study was to quantify the relevance and persistence of carbon stocks from SRC root biomass after re-conversion. Total root biomass was 66.53 Mg ha(-1) (SRC16), 37.90 Mg ha(-1) (SRC4) and 30.24 Mg ha(-1) (SRC2), which equals 23.13 Mg C ha(-1) (SRC16), 15.49 Mg C ha(-1) (SRC4) and 12.39 Mg C ha(-1) (SRC2). Most biomass was stored in roots <7 cm, but coarser root residues were still relevant with 12.90 Mg ha(-1) (SRC16), 2.11 Mg ha(-1) (SRC4), and 3.31 Mg ha(-1) (SRC2), especially for the longest rotation. Fifty percent of the subsoil-C stayed stable within 24 months. The observed decrease in decay rate, shows the mid-to long-term effect of carbon storage even after re-cultivation. Coarser roots were more resilient to mineralization than finer roots due to a smaller relative reactive surface and a higher C:N ratio. In conclusion, not only aboveground SRC yield contributes the SRC carbon sink effect, but also belowground biomass, which can be seen by comparison with root studies from forests and grasslands.

Rewetting of peatlands requires the development of new biomass utilization pathways. The supply of strategic elements with key importance for the development of priority technologies, such as germanium (Ge), silicon (Si) and rare earth elements, from fenland plants is one option. To provide a first estimation of the potential, concentrations of strategic elements were determined in nine biomass samples covering typical fenland vegetation in northeast Germany. Subsequently, a simplified estimation of potential revenue from strategic element recovery was made. The analysed plant species can be classified as high or intermediate Si plant accumulators with highest contents of more than 16.0 g Si kg −1 dry mass (DM) in sedges and common reeds. Ge concentrations were lower with reed canary grass containing the highest amounts of 465.3 µg Ge kg −1 DM. Simultaneous acquisition of Ge and Si could provide higher total element yields and revenues of up to 500 $ ha −1 . In contrast, the potentials for supplying rare earth elements appeared to be very low, with common reed containing the highest sum of rare earth elements of 437.4 µg kg −1 DM. Biomass from rewetted fenlands is capable of accumulating strategic elements. More knowledge is required to understand the factors affecting their accumulation.

Integrated biorefineries play a transformative role in sustainable development by converting biomass and biogenic residues into high-value products while minimizing waste, emissions, and resource inefficiencies. This review explores innovations in biorefinery processes, emphasizing the synergy between thermochemical, biochemical, and biological technologies such as pyrolysis, fermentation, anaerobic digestion, hydrothermal carbonization, and algae and insect systems. Recent advancements, including hydrothermal humification and fulvification, enhance nutrient recovery, carbon sequestration, and near-zero waste production by generating artificial humic substances. Smart integrated biorefineries and the sustainable and circular bioeconomy systems are introduced as frameworks that promote synergy, interconnectivity, and resource optimization. These concepts emphasize that biomass valorization should be maximized before its final use. Biochar plays a multifaceted role beyond carbon sequestration. Rather than premature burial, it can be derived from fermented residues for lactic acid production or used to enhance fermentation and methane yields in anaerobic digestion. Additionally, nutrient-loaded biochar serves as a slow-release fertilizer, mitigating runoff, and GHG emissions. Meanwhile, heat from biochar production can generate electricity, and CO₂ emissions can support algae cultivation. Bio-oil, another byproduct, can be upgraded into platform chemicals, forming a closed-loop system that optimizes biomass utilization and minimizes environmental impact. Conventional biomass treatment methods, such as incineration, combustion, and composting, waste valuable resources and contribute to environmental degradation. Instead, a closed-loop, self-optimizing approach ensures full biomass utilization while addressing planetary boundaries. By integrating machine learning, digital twins, and decision-support systems, smart integrated biorefineries enhance resource efficiency, adapt to market demands, and accelerate the transition to a low-carbon, resource-efficient future.

The breeding of willows with specific material and growth properties for textile timber construction is at the center of research. The high-value utilization of willow as a raw material to produce willow wood thread and willow wood textiles, for applications in architecture, product design, the timber and textile industry, represents a process technological innovation. In coupled usage, salicylates are extracted from the willow bark for medicine and cosmetics. For timber construction, whose demand is continuously increasing due to its excellent ecological balance and natural lightweight properties, willow wood thread is a disruptor, upon which the benefits of lighter, stronger, more aesthetic textile components could be combined with the advantages of wood. Automated weaving and braiding, robotic manufacturing, and additive manufacturing processes represent completely new processing forms for wood, offering new design and construction possibilities. Controlling the naturally grown, physical, and aesthetic properties of the willow wood thread already during cultivation is a novelty. Through hybridization of various willow species, breeding, and selection, varieties with specific growth characteristics have been developed, significantly improving the production of solid willow wood thread. Criteria included morphological features such as shoot length, shoot number, side shoots, verticality, torsion degree, diameter-length ratio, pith content, processability on textile machines and in robotic manufacturing, visual quality, and yield. Through cultivation in agroforestry systems, competition with food crops and log wood is minimized, and the diversification of agricultural yields as a renewable resource with positive microclimatic and soil-improving properties, as well as the increase in biodiversity in the cultural landscape, is achieved.

Organic livestock farming requires all resource input to be organic as well. Competition for raw materials as bedding increases the demand for alternative bedding materials. The production of absorbent fibre pellets from underutilized lignocellulosic plant material is therefore a research area that needs further attention. Precise research on processing methods and absorbent quantity is essential for the development of sustainable, high- quality absorbent bedding pellets. Twin-screw extruded fibre from eight different raw materials were processed into absorbent pellets. These pellets were investigated for physical properties including absorbency, mechanical durability, particle-size distribution and bulk density in accordance with relevant standards. Due to the absence of a standardised method for assessing absorbency, a testing method was devised. This involved submerging the produced pellets in deionized water for durations of 30 s, 300 s, and 1200 s. This research analysed various raw materials for suitability in absorbent pellet production. Poplar pellets performed good in absorbency (130 %, 172 %, 194 % respectively) and mechanical durability (95 %). As a result, larger quantities of absorbent pellets could be produced from poplar if needed since poplar wood chips are of higher availability due to existing short rotation coppices. This article emphasised producing absorbent bedding pellets, prioritising, using twin-screw extruded lignocellulosic fibre, revealing significant raw material influence on absorption properties.

Biomass degradation by microorganisms may cause major losses during the storage of wood chips for energy production. Poplar wood chips from short rotation coppices are especially prone to degradation with dry matter losses (DML) of up to 25% within a storage period, emphasizing the need for countermeasures. Therefore, we investigated the potential of the addition of alkaline Ca(OH)2 to the wet biomass of poplar wood chips and hypothesised that the establishment of an alkaline environment would reduce the activity of fungi, the primary wood degraders. Three industrial-scale piles (250 m3) with 0, 1.5 and 3% Ca(OH)2 were installed in Gussing, Austria and for four months (April-August 2019) the pile temperature, pH, moisture content, gas evolution (O2, CO2, H2, H2S, CH4) as well as DML were monitored. Ca(OH)2 altered the physicochemical properties of the wood chips but did not prevent biomass losses. However, as compared to literature, the DML were, compared to earlier investigations, also low in the control. In addition, cultivation methods were performed to evaluate the diversity of thermophilic microbes throughout the storage. Numerous filamentous fungi belonging to the phyla Ascomycota and Mucoromycota were isolated, being Rhizomucor pusillus, Aspergillus fumigatus, Thermomyces lanuginosa and Thermoascus aurantiacus the dominant species. Only minor differences in the fungal composition were detected as a result of Ca(OH)2 addition. Instead, clear shifts in colony forming units (CFUs) were detected as a function of progressing storage time, with a decrease of the number of propagules after four months.

Producing durable and efficient solid biofuels should be an important consideration in Nigeria's present economy due to the numerous advantages associated with it. It offers the benefit of energy generation, particularly in rural areas, and could potentially replace fossil fuels. However, the adoption and production of solid biofuels at commercial scale in Nigeria is limited by some challenges, including the lack of a developed supply chain structure, inadequate facilities, and air pollution. The present study summarizes the types of solid biofuel production technologies deployed in Nigeria as well as the biomass feedstock utilized in the production of fuel briquettes and pellets. While opportunities exist in the gasification of biomass in Nigeria, direct combustion is a readily applicable fuel conversion process that can be utilized to generate electricity from solid biofuel. The major challenges surrounding the full adoption of solid biofuel production and utilization in Nigeria are highlighted. Among others, promotion of clean energy alternatives, investments and financial incentives, sustainable renewable energy policy and energy transition plan, and legislative backing are identified as factors that could accelerate the commercial production and adoption of solid biofuel in Nigeria.

Biomass has a high potential to contribute towards resolving the energy deficit. Processing biomass into solid fuels enhances its use in various bioenergy conversion technologies. The quality of densified biomass depends on several variables. The investigation of the effect of densification parameters on briquette quality is necessary for process optimization. This study investigates the influence of die temperature (100, 120, 140 °C) and feeding speed (2.4, 2.9, 3.3 mm s−1) on the quality of briquettes produced from poplar using a hydraulic biomass briquetting machine. The density of the briquettes ranged between 746.7 and 916.8 kg m−3, the mechanical durability ranged from 97.4 to 98.4%, and the water resistance index was between 91.6 and 96.1%. The results show that the temperature was statistically significant (p < 0.05) on the density, mechanical durability and water resistance of biomass briquettes. The feeding speed was statistically significant (p < 0.05) on the density and water resistance. The interaction of temperature and feeding speed was statistically significant (p < 0.05) on all properties considered. The results obtained in this study are useful for optimizing the quality of briquettes produced using the hydraulic piston press.

Studies on the use of biomass from short rotation coppices for briquette production as a sustainable biofuel have been scarce in the literature. This study investigated the effects of two process variables, hammer mill screen size at three levels (5.3, 10.3, and 25.4 mm) and moisture content at three levels (13.6, 19, and 25% (w.b.)), on the properties of briquettes from poplar Max-4 trees. The whole tree was divided into two fractions, the crown and the stem, and briquettes were produced from them. The effects of the variables on compressed density, relaxed density, relaxation ratio, and the shatter index of the briquettes were analyzed. The results showed that the combined interaction of the variables had no significant effects (p > 0.05) on the compressed density, relaxed density, and relaxation ratio of the briquettes. However, hammer mill screen size and moisture content both significantly influenced the shatter index irrespective of the tree fraction (p < 0.05). Hammer mill screen sizes of 5.3 and 10.3 mm at moisture contents of 13.6 and 19% (w.b.) resulted in good quality briquettes across the properties investigated for both the crown and stem poplar tree fractions. This study shows that high-quality briquettes can be produced from poplar Max-4 woody biomass.

Storage of woody biomass in large wood chip piles is unavoidable for biotechnological applications, but comes along with considerable biomass-, energy- and thus, economic losses due to exothermic reactions and microbial degradation. The homogeneous amendment of the storage piles with an alkaline stabilization agent, calcium hydroxide (Ca(OH)2), was found to decrease dry matter loss in Picea abies; for Populus canadensis piles the effects cannot clearly be deduced. Here we investigated the bacterial and fungal communities of industrial-scale wood chip piles (250 m3) of these two different tree species and related them to physicochemical conditions and enzymatic activities after 35 and 120 d, representing short- and long-term storage of the wood chips, respectively. Coming from different wood types (hard vs. softwood), we expected the communities to converge over time, due to similar storage conditions. Despite pH posing selective pressure, we expected a minor Ca(OH)2 effect as already known from previous studies. We found that the effectiveness of Ca(OH)2 addition depended on the wood type that determined both the native microbial seeding community and temperature pattern of all piles, thereby exerting selective forces of differing strength. Generally, a thermophilic community consisting of single fungal and variable bacterial taxa were identified. As expected, the microbial communities from P. abies and P. canadensis converged over time. Biomass loss was connected to C-cycle related enzymatic activities and to the abundance and composition of fungal communities. Chaetomium sp. was identified as potential key taxon determining biomass degradation under the given storage conditions.

Biomass from agriculture is a promising alternative fuel due to its carbon-neutral feature. However, raw biomass does not have properties required for its direct utilization for energy generation. Torrefaction is considered as a pretreatment method to improve the properties of biomass for energy applications. This study was aimed at investigating the effects of torrefaction temperature and residence time on some physical and chemical properties of torrefied corncobs. Therefore, a fixed-bed torrefaction reactor was developed and used in the torrefaction of corncobs. The torrefaction process parameters investigated were the torrefaction temperature (200, 240, and 280 °C) and the residence time (30, 60, and 90 min). The effects of these parameters on the mass loss, grindability, chemical composition, and calorific value of biomass were investigated. It was shown that the mass loss increased with increasing torrefaction temperature and residence time. The grinding throughput of the biomass was improved by increasing both the torrefaction temperature and the residence time. Torrefaction at higher temperatures and longer residence times had greater effects on the reduction in particle size of the milled corncobs. The calorific value was highest at a torrefaction temperature of 280 °C and a residence time of 90 min. The energy yield for all treatments ranged between 92.8 and 99.2%. The results obtained in this study could be useful in the operation and design of torrefaction reactors. They also provided insight into parameters to be investigated for optimization of the torrefaction reactor.

For sustainable agriculture, the contentious input of peat in growing media needs to be replaced by a substitute with the best possible water-holding capacity (WHC). Wood from fast growing poplar trees, cultivated in short rotation coppices (SRC), is a suitable alternative if it is processed correctly in a twin-screw extruder. The processing parameters, such as the aperture setting of the extruder, moisture content, and specific energy demand (SED), during twin-screw extrusion, as well as their influence on fibre properties such as WHC and particle size distribution, are investigated. SRC-poplar wood chips from clone Max3 are the raw material used for this research. As a result, the best volume-based WHC (75%) at −1 kPa suction tension was achieved for dry extruded wood chip fibre at an aperture setting of 15 mm and an SED of 340 kWh*t−1. The smallest SED of 140 kWh*t−1 was measured at apertures of 35 mm and 40 mm, which resulted in a volume-based WHC of approximately 30% and a dry matter mass flow during processing of 0.289 t*h−1 (40 mm). The particle size distribution of semi-dry wood chips has the highest fine fraction as well as the smallest coarse fraction. Conclusively, poplar wood can be processed fresh and dry into fibre at an acceptable SED, which results in an acceptable WHC.

The aim of this work was to improve the understanding of dry matter losses (DML) that occur in wood chips during the initial phase of storage in outdoor piles. For this purpose, a laboratory scale storage chamber was developed and investigated regarding its ability to recreate the conditions that chips undergo during the initial phase of outdoor storage. Three trials with poplar Max-4 (Populus maximowiczii Henry × Populus nigra L.) chips were performed for 6–10 weeks in the storage chamber under controlled temperature and assisted humidity. Two different set-ups were investigated to maintain a high relative humidity (RH) inside the storage chamber; one using water containers, and one assisted with a humidifier. Moisture content (MC) and DML of the chips were measured at different storage times to evaluate their storage behaviour in the chamber. Additionally, microbiological analyses of the culturable fraction of saproxylic microbiota were performed, with a focus on mesophilic fungi, but discriminating also xerophilic fungi, and mesophilic bacteria, with focus on actinobacteria, in two trials, to gain a view on the poplar wood chip-inhabiting microorganisms as a function of storage conditions (moisture, temperature) and time. Results show that DML up to 8.8–13.7% occurred in the chips within 6–10 storage weeks. The maximum DML were reached in the trial using the humidifier, which seemed a suitable technique to keep a high RH in the testing chamber, and thus, to analyse the wood chips in conditions comparable to those in outdoor piles during the initial storage phase.

The adverse effect of the use of fossil fuels on the environment and public health has given rise to a sustained renewable energy research and development. An important component of global renewable energy mix is the use of loose biomass, including agricultural and forestry residues, to produce solid fuels in the form of briquettes. Briquettes play a significant role in bioenergy mix in developing and developed countries. The production of biomass briquettes often entails the collection, transportation, storage, processing, and compaction of loose biomass that meet specific quality parameters. The densification process often involves the addition of binders to improve the cohesive strength of the briquette material. This paper surveys recent literature from 2012 to 2021 to establish the current state of research on the use of binders in briquette production; and reviews current parameters used in assessing the quality of biomass briquettes with focus on mechanical and handling properties. While a number of quality parameters were identified, their assessment methodologies varied widely in the literature, thus necessitating standardization for comparability purposes. The review also includes factors affecting the wide production and adoption of biomass briquettes in most developing economies and proposes ways of overcoming the bottlenecks.

One of the most challenging aspects of using wood chips as renewable energy source is the loss of biomass related to storage. Therefore, we installed three outdoor industrial-scale piles (250 m(3)) of poplar wood chips and monitored the bacterial and fungal communities by next-generation sequencing over a storage period of 120 d. Two of the three piles were supplemented with calcium dihydroxide (Ca(OH)(2)) (1.5%, 3% w/w) in order to test its potential as alkaline stabilization agent to preserve woody biomass during storage. Shifts in the microbial community composition occurred almost entirely in the beginning of the storage experiment, which we attribute to the temperature rise of up to 60 degrees C within the first week of storage. Later, however, we found little changes. Independent of Ca(OH)(2) concentration, a consortium of lignocellulolytic and thermotolerant microorganisms dominated the stored wood chip microbiota emphasizing their role as key players during wood decomposition. Although the addition of Ca(OH)(2) altered the physicochemical properties of wood chips, it did not prevent loss of biomass. Especially the pH was increased in Ca(OH)(2) treated piles. However, only minor differences in the microbial communities' composition were detected following Ca(OH)(2) addition, highlighting the microbes tolerance towards and adaptation to changing environmental conditions.

Peat is a highly contentious input in agriculture. Replacing or reducing peat by substitution with lignocellulosic biomass processed into fibre by twin-screw-extrusion could contribute to more sustainable agriculture with regard to horticultural production. Therefore, plant wastes including pruning from Olea europaea L. and Vitis spp. L., residues from perennial herbs like Salvia spp. L., Populus spp. L. and forest biomass were processed to fibre for peat replacement with a biomass extruder. The water-holding-capacity (WHC), particle-size-distribution and other physical fibre characteristics were determined and compared to peat. The specific energy demand during extrusion was measured for aperture settings from 6–40 mm. No fibre reached the 82% WHC of peat. At the setting of 20 mm of all materials investigated, Salvia performed best with a WHC of 53% and moderate specific energy demand (167 kWh tDM−1) followed by Olea europaea with a WHC of 43% and a low energy demand (93 kWh tDM−1). For Populus, opening the aperture from 20–40 mm decreased energy demand by 41% and WHC by 27%. The drying of biomass for storage and remoistening during extrusion increased the specific energy demand. Despite a lower WHC than peat, all investigated materials are suitable to replace peat in growing media regarding their physical properties.