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.

Biochemistry-based biorefineries frequently valorize agricultural residues but rarely achieve full carbon utilization, leaving substantial downstream solids and liquids underexploited. This study presents an integrated fermentation-hydrothermal fulvification (HTF) strategy that upgrades grass biomass into lactic acid and artificial humic substances. Acid pretreatment generated 45.1 g/L total sugars and up to 36 g/L lactic acid, while base-pretreated substrates yielded 37.1 g/L of total sugars and 29.7 g/L lactic acid, with lower inhibitor levels. Subsequent HTF under strongly alkaline conditions converted lignin-rich fermentation residues into hydrochars with yields ranging from 21.2 to 45.4 wt.% and produced artificial humic acids up to 10.8 wt.% with elevated carbon contents of 74.5 wt.%. A pronounced decrease in O/C ratio indicates progressive dehydration and condensation reactions. Process liquids reached up to 36.2 g/L total organic carbon and contained organic acids, including a chromatographic peak assigned to lactic acid up to 9.9 g/L, likely formed in situ under alkaline HTF conditions, alongside phenolic compounds up to 1121 mg/L. Spectroscopic and colloidal analyses confirmed partitioning into humic-rich solids and fulvic-like dissolved organics. Humic acid yields from post-fermentation residues remained comparable to standalone HTF of raw grass, indicating that upstream lactic acid production does not compromise downstream humification. By converting the remaining solid residues through HTF into artificial humic substances that do not require further separation, the integrated system supports a waste-minimising biorefinery approach, in which all major fractions are functionally utilised as products while reducing biological risks and potential greenhouse gas emissions associated with untreated residues.

Cassava peel (CP) was valorized through hydrothermal carbonization (HTC) and pyrolysis to address waste management concerns and clean energy demands. The influence of process conditions on the fuel quality, organic-inorganic dynamics, and thermal properties of CP-derived products was investigated. Carbon content (dry ash-free) increased to 69.44% in hydrochars and 89.01% in pyrochars at elevated temperatures. Energy density improved by 45.76% (hydrochars) and 44.65% (pyrochars), while higher heating values rose by 31.40% and 30.87%, respectively, relative to raw biomass. At increasing temperature and residence time, the energy-mass co-benefit index increased while the upgrading energy index declined, indicating improved fuel quality. Combustion and stability indices of both chars correlated strongly with elemental carbon proportion (R2 = 0.90-0.98). Carbon stability increased with increasing conversion intensity, with hydrochars shifting from Class C to B at 240 °C, while pyrochars remained in Class C at 350 °C but reached Class B at ≥ 450 °C. Hydrochars and process liquids produced at 180 °C and 4 h yielded the highest levels of furanic compounds, but levels declined with increasing temperatures. Hydroxyl and C-O groups persisted in all hydrochars and pyrochars (350 °C) but diminished at higher pyrolysis conditions. Scenario estimates suggest that CP-chars could supply 6,631-7,996 GWh annually in coal-fired thermal plants, with lower potential emissions at higher temperatures. The results support CP as a viable feedstock for integrated energy recovery and circular waste management.

This study compares hydrothermal carbonization (HTC), humification (HTH), and fulvification (HTF) of grass biomass to show how increasing alkalinity governs carbon conversion pathways and liquid product formation. Under HTC without alkali addition, carbon conversion was dominated by dehydration and condensation reactions, yielding the highest solid yield (54.10 wt. %) with high carbon content (60.6 wt.%), elevated energy potential (HHV = 25.70 MJ/kg), and the greatest intrinsic thermal stability (T50 = 435 degrees C), while artificial humic acids were not formed and carbon transfer to the liquid phase remained limited (TC = 15.85 g/L; TOC = 15.75 g/L), accompanied by minimal carbon leachability. Moderate alkalinity under HTH reduced solid yield to 44.50 wt% and promoted partial depolymerization and humification, increasing liquid-phase carbon concentrations (TC = 40.47 g/L; TOC = 36.96 g/L) and enabling artificial humic acid formation (2.25 wt.%), while producing hydrochar with favorable surface chemistry for adsorption, reflected by the highest crystal violet uptake (196.28 mg/g). Further increasing alkalinity under HTF shifted carbon partitioning toward the liquid phase, reducing solid yield to 13.18 wt.% while maximizing artificial humic acid formation (8.80 wt.%) and liquid-phase carbon concentrations (TC = 62.15 g/L; TOC = 58.52 g/L); HTF liquid was enriched in lactic acid, characterized by sub-100 nm colloids, the most negative zeta potential (-8.72 mV), and enhanced seed germination up to 95% at 50-fold dilution. Overall, alkalinity is identified as a key parameter directing integrated carbon valorization from energy-dense solids to adsorptionactive humified materials and bioactive liquid products within a circular biomass framework.

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.

AbstractHydrothermal carbonization (HTC) converts wet biomass into hydrochar and a process liquid, but aromatic compounds in the products have been reported as a roadblock for soil applications as they can inhibit germination, plant growth, and soil microbial activity. Here, we compared HTC and hydrothermal humification (HTH) of cow manure digestate while varying the initial alkaline content by adding KOH. HTH converted 37.5 wt% of the feedstock to artificial humic acids (A-HAs) found in both solid and liquid, twice that of HTC. HTH reduced phenolic and furanic aromatic compounds by over 70% in solids and 90% in liquids. The A-HAs in HTH resemble natural humic acids (N-HA), based on FTIR, UV–vis spectra, and CHN and XRD analysis. The HTH liquid possesses 60% higher total organic carbon (TOC) than HTC. Although one-third of TOC can be precipitated as A-HA, a high TOC concentration remains in the liquid, which is shown to be mainly organic acids. Therefore, we also evaluated the HTC and HTH liquids for anaerobic biomethane production, and found that compared to the original cow manure digestate, the HTH liquids increased methane yield by 110.3 to 158.6%, a significant enhancement relative to the 17.2% increase seen with HTC liquid. The strong reduction in organic acids during biogas production from HTH liquid indicates the potential for converting soluble byproducts into methane, while maintaining high A-HAs levels in the solid product. Graphical Abstract

Hydrothermal carbonization (HTC) solid and liquid products may inhibit seed germination, necessitating post-treatment. The hydrothermal humification (HTH) method addresses this drawback by transforming inhibitory compounds, such as aromatics, into artificial humic acids (AHAs) and artificial fulvic acids (AFAs). This study introduces a novel approach by investigating the substitution of the commonly used alkaline agent in HTH, KOH, with hydrated lime to develop cost-effective hydrothermal fertilizers from sugar beet pulp, enriching them with AHAs. It assesses the effects of lime on AHA production and soluble organic compounds compared to KOH. The results indicate that lime significantly reduces furans (from 560 to 3.15 mg/kg DM in solid and from 344 to 3.86 mg/L in process liquid) and boosts sugars and organic acids, especially lactic acid (from 4.70 to 65.82 g/kg DM in solid and from 4.05 to 22.89 mg/L in process liquid), increasing hydrochar yield (68.8% with lime vs. 27.4% with KOH). Despite the lower AHA production with lime compared to KOH (3.47% vs. 15.50%), lime-treated hydrothermal products are abundant in calcium and magnesium, boasting a pH of 7. This property presents a safer and more efficient alternative to hydrothermal fertilizers. The characterization of AHAs aligns with standard and natural humic substances, while lime-assisted HTH products, applied at a level of 0.01% w/w, could significantly enhance wheat growth and nutrient uptake compared to the control group. Importantly, these products show no toxicity on Daphnia magna, underscoring their potential for sustainable agriculture.

Humic substances have an enormous potential for regenerative agriculture to improve soil quality and plant growth. Recently developed technologies called hydrothermal humification enabled the conversion of waste into artificial humic acids, that would allow for sustainable and large-scale applications. However, not much is known about the effect of artificially produced humic acid on the soil microbiome and its effect on drought-exposed soil. Therefore, we studied the effect of drought stress and artificial humic acid on the soil microbiota in sandy soil in a controlled experimental design. Analyses of 16S rDNA amplicon libraries by bioinformatics and statistics revealed that both drought and artificial humic acid application influenced bacterial community composition significantly, but only artificial humic acid affected bacterial diversity. Bacterial families like Pseudomonadaceae, Peptostreptococcaceae and Moraxellaceae enriched under artificial humic acid conditions, suggest an adaptation and selection of the soil bacterial microbiome. Under drought stress, artificial humic acid treatment kept bacterial diversity stable in the changed bacterial community composition. We propose that artificial humic acid application in sandy soil can improve the soil bacterial community, diminish drought stress, favour plant growth-promoting taxa, and bring enormous potential to sequestrate carbon in the soil.

Grasslands play a crucial role in European agriculture and ecology, but are often underutilized due to low-value end-products. The utilisation of late-harvest grass for biochar and heat generation on farm-level is being studied as a potential negative emissions technology. Technical (energy provision and carbon sink), economic (cost vs. benefit), political (regulatory framework) and social (SWOT) perspectives are being evaluated. Technical feasibil-ity has been demonstrated with three different farm-scale technologies and the energetic and carbon-sink poten-tial evaluated. When a continuously operating allothermal unit is evaluated, 35 % of the input biomass energy content can be utilized for heating a farm, in combination with the potential to provide a carbon sink. The cost-benefit analysis shows important monetary savings when including the agronomic value (based on the mar-ket price) of the produced biochar. An assessment of the regulatory framework of biochar production in Germany presents a multitude of regulations applying to such technologies some of which provide a hurdle to navigate and may incur excessive costs for farmers as small-scale biochar producers. A SWOT analysis of a case in Brandenburg, Germany highlights strengths and opportunities, but also obstacles such as lack of infrastructure and regulatory support. This study highlights the need for further development of suitable technology and research on the long-term economic and carbon sink potential of biochar.(c) 2023 Published by Elsevier Ltd on behalf of Institution of Chemical Engineers.

Grass and other herbaceous biomass are abundant, but often under- or not utilized as a renewable resource. Here, the production of biochar from extensive late-harvest grass via multiple thermochemical conversion technologies was investigated at lab and farm scale for use in soil applications. While biochar is a product with highly diverse potential applications, it has a multitude of benefits for agricultural usage as a soil amendment, if the quality adheres to certain limit values of potentially toxic constituents. The results show that the biochar can adhere to all limit values of the European Biochar Certificate (EBC) for utilization in agriculture. Generally, the contents of heavy metals were well below the proposed EBC limits and very low PAH concentrations in the biochar were achieved. The high ash content in the grass of 7.71 wt%db resulted in high nutrient concentrations in the biochar, of benefit in soil applications, but the ash also contains chlorine, nitrogen and sulphur, which presents a challenge for the operation of the thermochemical processes themselves due to corrosion and emission limits. In the farm-scale processes, ash retention ranged from 53.7 wt%db for an autothermal batch process, reaching up to 93.7 wt%db for a batch allothermal process. The release of Cl, N and S was found to differ substantially between processes. Retention ranged from 41.7%, 22.9% and 27.6%, respectively, in a continuous allothermal farm-scale pyrolysis process, to 71.7%, 49.7% and 73.9%, with controlled lab-scale pyrolysis at 450 °C, demonstrating that process optimization may be possible.

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.

This work aims to systematically investigate the influence of process temperature, biomass-to-water ratio, and production scales (laboratory and pilot) on the chemical composition of aqueous and gaseous phases and mass production of chemicals by hydrothermal processing of Açaí (Euterpe oleraceae, Mart.) seeds. The hydrothermal carbonization was carried out at 175, 200, 225, and 250 °C at 2 °C/min and a biomass-to-water ratio of 1:10; at 250 °C at 2 °C/min and biomass-to-water ratios of 1:10, 1:15, and 1:20 in technical scale; and at 200, 225, and 250 °C at 2 °C/min and a biomass-to-water ratio of 1:10 in laboratory scale. The elemental composition (C, H, N, S) in the solid phase was determined to compute the HHV. The chemical composition of the aqueous phase was determined by GC and HPLC and the volumetric composition of the gaseous phase using an infrared gas analyzer. For the experiments in the pilot test scale with a constant biomass-to-water ratio of 1:10, the yields of solid, liquid, and gaseous phases varied between 53.39 and 37.01% (wt.), 46.61 and 59.19% (wt.), and 0.00 and 3.80% (wt.), respectively. The yield of solids shows a smooth exponential decay with temperature, while that of liquid and gaseous phases showed a smooth growth. By varying the biomass-to-water ratios, the yields of solid, liquid, and gaseous reaction products varied between 53.39 and 32.09% (wt.), 46.61 and 67.28% (wt.), and 0.00 and 0.634% (wt.), respectively. The yield of solids decreased exponentially with increasing water-to-biomass ratio, and that of the liquid phase increased in a sigmoid fashion. For a constant biomass-to-water ratio, the concentrations of furfural and HMF decreased drastically with increasing temperature, reaching a minimum at 250 °C, while that of phenols increased. In addition, the concentrations of CH3COOH and total carboxylic acids increased, reaching a maximum concentration at 250 °C. For constant process temperature, the concentrations of aromatics varied smoothly with temperature. The concentrations of furfural, HMF, and catechol decreased with temperature, while that of phenols increased. The concentrations of CH3COOH and total carboxylic acids decreased exponentially with temperature. Finally, for the experiments with varying water-to-biomass ratios, the productions of chemicals (furfural, HMF, phenols, cathecol, and acetic acid) in the aqueous phase is highly dependent on the biomass-to-water ratio. For the experiments at the laboratory scale with a constant biomass-to-water ratio of 1:10, the yields of solids ranged between 55.9 and 51.1% (wt.), showing not only a linear decay with temperature but also a lower degradation grade. The chemical composition of main organic compounds (furfural, HMF, phenols, catechol, and acetic acid) dissolved in the aqueous phase in laboratory-scale study showed the same behavior as those obtained in the pilot-scale study.

The storage and natural drying of wood chips from short rotation coppices (SRC) in open-air piles can be related to high dry matter losses (DML) of more than 20%. Thus it should be researched, whether such loss can energy efficiently be reduced using cold air ventilation (CAV). Respectively, a dedicated channel system for sensor controlled ventilation and drying of wood chips was developed and tested in the drying process of two storage piles of poplar chips (2 x 90 m(3)). The ventilation of the storage piles was facilitated in two consecutive program phases: a cooling program, subsequent to the harvest in the month of March, and a drying program under more favorable weather conditions in the month of April. The characteristically high temperature rise typical for wood chip storage immediately subsequent to storage intake could be limited to an average storage pile temperature of 6.3 degrees C with just 41 blower operation hours due to the cooling program in the month of March. Due to the subsequent drying process in April, the storage pile could be dried further from 51.5% to 11.9% in 196 blower operation hours. The required energy input for the process of CAV, consisting of cooling and drying, amounted to 456 MJ t(-1) (dry matter). At a total demand of electric energy of 5332 MJ per storage pile, a more than six times higher thermal energy advantage of 35,233 MJ was achieved. DML of 11% were measured at the end of wood chip drying using CAV.

The cultivation of fast-growing wood (e.g., poplar, willow or black locust) in short rotation coppices and agroforestry systems presents an opportunity for producing biomass sustainably in the agricultural sector. Cost-efficient agricultural wood production requires the availability of high-performance machinery and methods with which high-quality wood chips can be produced at low cost. It is known from harvesting short rotation coppices in practice that both the wood chip quality and the performance of the harvesting machinery depend on a variety of factors (e.g., harvesting method, weather conditions, tree species). That is why this study examines in detail the influence of the tree species (different varieties of poplar, willow, black locust) and the wood condition (fresh, stored or dried, frozen) on the specific energy demand for comminution in a stationary drum chipper and on the particle size distribution of the wood chips produced. For all the tree species examined, the chipping of dried as well as frozen stems was connected with a significant increase in the specific energy demand for comminution. An increase of 31% has been measured if poplar stems are chipped in frozen conditions (max. 6.31 kWh t−1). Drying led to an increase of 59% for dried willow stems (max. 6.67 kWh t−1). Drying and frost had also an influence on the size and quality of the wood chips, but no globally significant connection could be established for the examined tree varieties.

A process developed at the Leibniz Institute for Agricultural Engineering and Bioeconomy (ATB) for the supply and processing of wet-preserved fiber plants opens up new potential uses for such resources. The processing of industrial hemp into fiber materials and products thereof is undergoing experimental research along the value-added chain from the growing process through to the manufacturing of product samples. The process comprises the direct harvesting of the field-fresh hemp and the subsequent anaerobic storage of the entire plant material. Thus, process risk due to unfavorable weather conditions is prevented in contrast to common dew retting procedures. The effects of the anaerobic storage processes on the properties of the bast part of the plant material are comparable to the results of common retting procedures. Harvest storage, as well as further mechanical processing, leads to different geometrical properties compared to the bast fibers resulting from traditional post harvesting treatment and decortication. The fiber raw material obtained in this way is well suited to the production of fiberboards and the reinforcement of polymer or mineral bonded composites. The objective of this paper is to present recent research results on final products extended by a comprehensive overview of the whole supply chain in order to enable further understanding of the result influencing aspects of prior process steps.

Two hemp varieties have been processed by different process technologies. The resulting fibrous intermediate has been characterized by particle analysis prior the manufacture of fibreboards. The results of comprehensive tests of respective product samples are used to describe the influence of raw material, processing method and target density on selected product properties. It has been shown that the intended respectively realized density of the fibre boards has the greatest influence on their physical and mechanical properties. Comparing values within the same density range both raw material (variety) choice as well as the number of processing steps lead to partially different results. A processing with a disc mill additional to a single step extruding is increasing the ratio of finer particles which applies to one hemp variety to a greater extent than to the other hemp variety. Close relations to respective properties of the fibre boards are identified and presented in the paper.

Grain moisture content is an important factor for the management of harvesting and postharvest operations and for capacity planning in grain harvest, storage and preservation, and a basis for pricing in grain trade. The advantage of rapid and non-destructive on combine moisture content determination is set against the disadvantage of lower measurement accuracy. The objectives of this study are to determine the agreement of on combine grain moisture measurement with laboratory measurement methods, and to assess the suitability of on-combine grain moisture measurement. The appropriateness of on-combine measurement of grain moisture content for the management of harvesting and postharvest operations and capacity planning by maintaining a defined acceptable level of disagreement was also investigated. On-combine moisture measurement (OMC) was compared with two dry-oven methods and two capacitive moisture sensors used in laboratories, in each case for unground and ground grain. Field trials with on-combine moisture measurements and manual sampling were carried out on two farms in Germany in 2014. A total area of 514 ha with 201 manual samples was used for the investigations. The assessment of on-combine moisture measurement indicated that the on combine approach is suitable for quantifying the variability of grain moisture content. The deviation between indirect laboratory methods and on-combine moisture meters was sufficient to determine the allowable total error that agreed with the defined relative error of two percentage points moisture content. In combination with fuzzy classification of grain moisture measurements, the on-combine moisture meters are suitable for process control and capacity planning for grain harvest and preservation. (C) 2017 IAgrE. Published by Elsevier Ltd. All rights reserved.

Restrictions in availability and performance of equipment as well as high cost of harvest equipment for wood from agriculture produced in plantations of short rotation coppices (e.g. poplar, willow or black locust) are still a limiting factors for the further growth of this branch in agriculture. Three different harvest systems - two of them based on modified forage harvester and one mower-chipper - have been investigated during the harvest of poplar and black locust in season 2015/2016 in Germany. Although there are major differences in machine design, requirements to the layout of plantations, maximum harvestable tree size and performance of machines for SRC-harvest, no major differences in the effective material capacity (EMC) between forage harvester based solutions and the mower-chipper (EMC -16 odt h(-1)) could be observed during the test. Wood chips produced with the investigated forage harvesters fulfilled the requirements for chips of class P16 ... P31, but with a higher content of fines (>10%). In contrast, the wood chips produced with the mower-chipper have been much coarser, fulfilling the requirements for chips of class P31 to P45, with a very low content of fines (< 7 % d.b. black locust, < 5% d.b. poplar). All tested harvesters showed reliable operation under practice conditions and are commercially available.