Hydrothermal Carbonization Process Research Articles

Can hydrogen be generated by UV- photodegradation of biomass residues in water media?

The photoinduced processes can be promising routes for hydrogen generation. This study explores hydrogen production through the non-catalyzed photodegradation of various biomass materials, a process that remains largely understudied compared to the catalyzed ones, i.e., photoreforming. Using as precursor almond shell (AS), a lignocellulosic biomass residue, various solid and liquid materials obtained from it were tested as substrates. These materials were obtained through different pretreatment methods including grinding, milling, pyrolysis, and hydrothermal carbonization (HTC), and compared with milled cellulose (MC). Photodegradation tests, conducted in aqueous media under UV light, revealed that hydrogen production strongly depends on the structural and compositional features of the substrates. Among the solid samples, ground almond shell (GAS) and milled cellulose (MC) showed promising hydrogen yields. However, the liquid residue from the HTC process using diluted phosphoric acid (HMAS-L2), which is rich in simple organic acids, stood out, delivering the highest hydrogen production across all the substrates, and reaching an impressive value of 105 μmol of H2 in 5 h of reaction. Attention was also given to the production of other gases, particularly carbon dioxide and methane, as a result of the photodegradation. CO2 production occurred for all the substrates. PMAS (the pyrolyzed milled almond shell) and, specifically, HMAS-L2 generated detectable amounts of CH4 (5 and 22 μmol, respectively).The H2/CO2 ratios reached 0.66 for MC and 0.44 for HMAS-L2, highlighting the interest in evaluating the non-catalyzed biomass photodegradation as a preliminary step for future photoreforming studies. These findings enhance our understanding of biomass-based hydrogen generation and open new avenues for exploring non-catalyzed photoinduced processes.

From Green to Black Gold: Highly Microporous Carbons from Pistachio Shells by a Controlled Physical Activation Process.

Highly microporous carbons with BET surface areas of up to ca. 3300 m2 g-1 and pore volumes of up to 1.6 cm3 g-1 have been successfully synthesized from pistachio shells, a waste whose generation is growing on account of the nutritive value of pistachios and the resilience of this crop to climate change. Such a high pore development has been achieved by a simple and benign CO2 physical activation process assisted by a custom pre-treatment of the biomass. Herein, different approaches have been explored for the transformation into carbon materials with diverse microstructures, mineral matter content and particle size/morphology, tuning therebytheir reactivities towards CO2 and diffusion kinetics and, in this way,pore development. In particular, the most efficient route for the production of highly microporous carbonsinvolves a hydrothermal carbonization process which increases the degree of aromatization and effectively removes the mineral matter, enhancing thereby the efficiency of both carbon production and porosity generation. By increasing the activation temperature, substantial shortening of the operation time can be achieved without compromising pore development. This work provides new integral strategies towards the production of biomass-based, CO2-activated carbons with a focus on optimizing pore structure, minimizing energy consumption and maximizing product yield.

Hydrocoals from waste biomass via catalytic hydrothermal carbonization processing

Hydrocoals from waste biomass via catalytic hydrothermal carbonization processing

Hydrochar and Value-Added Chemical Production Through Hydrothermal Carbonisation of Woody Biomass

This study investigates the optimisation of hydrothermal carbonisation (HTC) parameters for transforming Whitewood biomass into hydrochar, focusing on bioenergy production and valuable chemical extraction as by-products. The optimal carbonisation was achieved at a process temperature of 240 -260 °C, which optimised the higher heating value of the hydrochar to 27-30 kJ/g and ensured a structural integrity similar to lignite coal. Increasing the temperature beyond 260 °C did not significantly enhance the energy content or quality of the hydrochar, establishing 260 °C as the practical upper limit for the HTC process. Residence times between 30 to 60 min were found to have minimal impact on the yield and quality of hydrochar, suggesting significant operational flexibility and the potential to double throughput without increasing energy consumption. The study also revealed that the process water by-product is rich in furan compounds, particularly furfural and hydroxymethyl furfural, with their highest concentration (125 mg/g of feedstock) occurring at 220 °C. The implementation of these findings could facilitate the development of a large-scale HTC facility, significantly reducing reliance on fossil fuels and enhancing economic viability by producing high-energy-density biofuels and high-value chemical by-products.

Comparative Analysis of Optimal Reaction Conditions for Hydrothermal Carbonization and Liquid Hot-Water Processes in the Valorization of Peapods and Coffee Cherry Waste into Platform Chemicals

The management of coffee and peapod waste presents significant environmental challenges, with millions of tons generated annually, leading to disposal issues and resource inefficiencies. Hydrothermal processes offer a promising valorization method, though biomass characteristics significantly influence the resulting products. Biomass characterization revealed distinct profiles for coffee cherry waste (moisture: 10.94%, ashes: 7.79%, volatile matter: 79.91%, fixed carbon: 1.36%, cellulose: 27.6%, hemicellulose: 12.5%, and lignin: 13.7%) and peapods (moisture: 7.77%, ashes: 4.22%, volatile matter: 74.18%, fixed carbon: 13.0%, cellulose: 20.2%, hemicellulose: 17.4%, and lignin: 5.0%). Experiments were conducted in 100 mL and 500 mL hydrothermal reactors with varying conditions for temperature (120–260 °C), time (1–4 h), stirring (none and at 5000 and 8000 rpm), biomass/water ratio (1:5, 1:10, 1:20, and 1:40), particle size (0.5–5 mm), and catalysts (acids and bases). The results showed that peapods produced over 30 times more platform chemicals than coffee. High temperatures (over 180 °C) degraded peapods, whereas coffee yields increased. Both biomasses were influenced similarly by reaction conditions: lower biomass/water ratios, smaller particle sizes, acid catalysts, and no stirring increased yields. Peapods consistently had higher yields than coffee in all conditions. Biochar analysis revealed anthracite from coffee and coal from peapods.

Selective synthesis of oxygenated fuel derivative from microwave assisted acetalization of glycerol: Optimization and mechanistic investigations

Glycerol contains 52 wt% oxygen content, therefore unable to be directly used as fuel due to its poor combustion ability. Thus, the catalytic conversion of glycerol into various oxygen-containing fuel additives is grabbing more attention nowadays. This work provides a novel, sustainable, and eco-friendly method for synthesizing heterogeneous acid carbon catalysts from pearl millet cob (PMC) waste. The hydrothermal carbonization process was carried out at different temperatures to fabricate the series of sulfonated pearl millet cob (SPMC) catalysts. XRD, FT-IR, SEM-EDS, XPS, BET, TGA, and CHNSO analyses were performed to characterize fabricated catalysts. The synthesized catalyst, SPMC-70 (catalyst synthesized at 70 °C temperature), possesses OH, COOH, and SO3H functional groups and a significant total acid density (2.03 mmol/g) with 37 m2/g surface area. The SPMC catalysts were employed for the microwave-assisted acetalization reaction of glycerol with acetone for solketal production. The optimization process was carried out using various reaction parameters, including catalyst dosage (2–6 wt.%), reaction temperature (30–60 °C), glycerol to acetone (GL to AC) molar ratio (1:3–1:9), and reaction time (4–13 min). The SPMC-70 catalyst showed the highest catalytic activity among all the synthesized catalysts and provided 99.11 ± 0.3 % GL conversion with 100 % selectivity of solketal under optimal reaction conditions. Additionally, the recyclability test was performed, and it found that the best catalyst was reusable for up to five reaction cycles. These results showed the effectiveness of carbon-based heterogeneous acid catalysts in deriving a fuel additive, solketal.

Hydrothermal Carbonization of Biomass for Electrochemical Energy Storage: Parameters, Mechanisms, Electrochemical Performance, and the Incorporation of Transition Metal Dichalcogenide Nanoparticles.

Given the pressing climate and sustainability challenges, shifting industrial processes towards environmentally friendly practices is imperative. Among various strategies, the generation of green, flexible materials combined with efficient reutilization of biomass stands out. This review provides a comprehensive analysis of the hydrothermal carbonization (HTC) process as a sustainable approach for developing carbonaceous materials from biomass. Key parameters influencing hydrochar preparation are examined, along with the mechanisms governing hydrochar formation and pore development. Then, this review explores the application of hydrochars in supercapacitors, offering a novel comparative analysis of the electrochemical performance of various biomass-based electrodes, considering parameters such as capacitance, stability, and textural properties. Biomass-based hydrochars emerge as a promising alternative to traditional carbonaceous materials, with potential for further enhancement through the incorporation of extrinsic nanoparticles like graphene, carbon nanotubes, nanodiamonds and metal oxides. Of particular interest is the relatively unexplored use of transition metal dichalcogenides (TMDCs), with preliminary findings demonstrating highly competitive capacitances of up to 360 F/g when combined with hydrochars. This exceptional electrochemical performance, coupled with unique material properties, positions these biomass-based hydrochars interesting candidates to advance the energy industry towards a greener and more sustainable future.

Elevated effect of hydrothermal treatment on phosphorus transition between solid-liquid phase in swine manure

The morphology and composition of phosphorus in biomass wastes are key factors in determining its potential for utilization. However, the morphological distribution and evolutionary mechanism of phosphorus during the hydrothermal conversion of biomass wastes are still unclear. In this study, swine manure was investigated as the research subject, and the changes in its solid-phase organic components, such as lignocellulose, and inorganic constituents, including metals and phosphorus, during the hydrothermal carbonization (HTC) processes were analyzed in relation to hydrothermal reaction severity (LnR0). A significant linear correlation in Phase II was observed between the solid-phase yield of swine manure and the LnR0. The rapid decline in the solid-phase yield during the initial phase (LnR0 < 9.72) was primarily attributed to the hydrolysis of hemicellulose and similar components. Similarly, solid phase phosphorus showed a very significant phase II with the decrease of solid phase yield. In the first stage, inorganic phosphorus and metal ions (calcium ions, magnesium ions) transferred to the liquid phase (LnR0<9.41). When LnR0 > 9.41, and the driving force of inorganic phosphorus and metal ions into solid phase is enhanced. As the LnR0 was further increased, the HTC could fix over 90 % of the total phosphorus content. XANES analysis indicated that hydroxyapatite emerged as the predominant phosphorus fraction in the solid-phase products, comprising more than 60 %, while magnesium ammonium phosphate components also appeared. This research elucidates the underlying mechanisms of component interaction and phosphorus transformation, providing a solid foundation for enhancing the reuse efficiency of phosphorus in wastes.

Exploring Corymbia torelliana hydrochar combustion kinetics through thermogravimetric analysis, peak deconvolution and reaction profile modelling.

This study aims to conduct an applied and innovative investigation to enhance the energy quality of wood residues through hydrothermal carbonization pretreatment. For this purpose, the treatment was carried out at three different temperatures: 180, 220, and 240°C under autogenous pressure. The in natura material and the hydrochars were characterized, and thermogravimetric analyses were performed in an O2 atmosphere with heating rates of 2.5, 5, 10, and 20°Cmin-1. The global activation energy for natura biomass combustion was determined to be 112.49kJ.mol-1. On the other hand, the hydrothermal carbonization process promoted a reduction in this value for the 94.85kJ.mol-1. The conversion function for the in natura biomass was characterized as , order 1, while the hydrochars was 2(1-α) [-ln(1-α)] (1⁄2), Avrami-Erofe'ev I. Triple kinetic parameters were ascertained, and the conversion curves along with their respective derivatives were modeled, exhibiting minimal deviations between theoretical and experimental data. This facilitated the mathematical representation of the reaction processes and allowed for a comprehensive comparison of the results.

Degradation of toxic components in kitchen waste during hydrothermal carbonization process

Hydrothermal carbonization (HTC) is a promising technique for kitchen waste (KW) disposal. However, KW may contain heavy metals (HMs), aflatoxin, nitrites and sulfites, posing risk for hydrochar utilization. In order to clarify the migration of these toxic components during hydrochar formation process, 7 kinds of kitchen wastes were adopted to carry out HTC experiments at 180–240 °C. Concentration detections results showed that Fe, Mn, Cr, Ni, Cu, and Zn contents were relatively high with a range of 30–2500 mg/kg in KW feedstocks. After HTC treatment, Fe, Cr, Cu were mainly (>80 %) enriched in hydrochar, the enrichment factors of Mn, Ni, Zn was almost above 50 %. From the perspective of species and valence distributions, Mn, Fe, Ni, and Zn in hydrochar were below moderate risk level. No aflatoxin was detected in hydrochar, because AFB1 and AFB2 can be completely degraded into organic acids in the HTC environment at 180 °C. Part benzene rings in aflatoxin were reduced and the C-C bonds were further broken, the C-O bonds were oxidized to produce carboxylic acids. Some benzene rings in aflatoxin remained to form organic acids with aromatic structures. NO2− and SO32- ions with strong ecotoxicity were mostly converted into NO3− and SO42- and flowed into the liquid phase. Some NO2− ions were also converted to and ammonia N and pyridine N; some SO32- ions were converted to sulfonic and sulfinic acid organics, which were successively transformed into sulfonyl/sulfinyl and sulfone/sulfoxide organics. The above findings are of great significance for the transformation mechanism of toxic substances in HTC environment and environment-friendly utilization of hydrochar.

Selective electrosorption of heavy metal ions from wastewater with S-doped hierarchical porous carbon derived from waste Camellia oleifera shell

Capacitive deionization (CDI) has garnered significant attention in desalination and the removal of heavy metal ions. The quest for cost-effective and high-performance electrode materials is crucial to advance CDI applications. Herein, we report a sulfur-doped hierarchical porous carbon (SPC) derived from waste camellia oleifera shells via a sustainable hydrothermal carbonization process followed by KOH/ammonium salt activation. The optimized SPC-0.2 exhibits exceptional characteristics, featuring a high specific surface area of 1875 m2 g−1 and substantial sulfur doping at 8.65 %, leading to enhanced specific capacitance (161.3 F g−1) in a 1 M NaCl solution. Under optimal operating conditions (1.2 V, 10 mL min−1, 500 mg L−1 NaCl), the SPC-0.2 electrode achieves a notable desalination capacity of 26.64 mg g−1. In particular, the electrode can selectively remove >99 % of Cr3+ and Cu2+ ions (each 10 mg L−1) in a 100 mg L−1 NaCl solution. This high selectivity is attributed to the formation of sulfides via low adsorption energies between the doped sulfur atoms and the targeted heavy metal ions. Furthermore, the SPC-0.2 electrode demonstrates robust reusability and high efficiency in the actual water body. Collectively, our findings underscore the significant potential of the synthesized SPC as an electrode material for CDI, particularly in the selective capacitive removal of heavy metal ions from wastewater. This work not only contributes to the circular economy by using waste biomass, but also offers a viable solution for environmental remediation.

The role elucidating of EPS in thermal hydrolysis and nitrogen conversion of sewage sludge during hydrothermal carbonization process, and its effect on hydrochar's properties

Hydrothermal carbonization (HTC) was conducted to observe the effect of extracellular polymeric substances (EPS) structure on the nitrogen migration mechanism during the HTC process. The denitrification efficiency of activated sewage sludge (ASS) decreases with an increase in EPS stripping intensity. Loosely and tightly bound extracellular polymers diminish the denitrification effectiveness by inhibiting the hydrolysis of nitrogen-containing organic compounds and protecting the cell structure, respectively. Intracellular nucleic acids and proteins generate stable N-containing species, such as heterocyclic-N and quaternary-N, which are unfavorable for deep denitrification. In general, nitrogen removal is more effective outside the cell than inside. Deep destruction of EPS eliminated a considerable number of N-containing components, and the N/C value of hydrochar at 180 °C without cell membrane protection was 0.06, which dropped to half that of ASS (0.11). This study revealed the influence of EPS structure on nitrogen migration in hydrothermal environment and provided significant insights for the preparation of clean solid fuels.

Optimization of traditional market solid waste conversion process into hydrochar using hydrothermal carbonization technology

Abstract In this study, an analysis was carried out to determine the optimum conditions for the hydrothermal carbonization process of traditional market waste using response surface methodology central composite design. The hydrothermal carbonization process was carried out at temperatures (180, 215, 250°C), process times (30, 60, 90 minutes), and a ratio (waste: water media) of 0,5. The results of response surface analysis show that temperature and process time are parameters that significantly affect the quality of hydrochar. Increasing temperature and process time resulted in a decrease in hydrochar weight from 67,01 to 40,77 grams. Furthermore, there was an increasing heating value of hydrochar from 18,87 to 30,5 MJ/Kg. The optimization formulation of the hydrothermal carbonization process of traditional market waste was obtained at a temperature of 181,133°C and a process time of 30 minutes with a prediction value of weight and heating value obtained, namely 61,39 grams and 23 MJ/Kg.

Investigation of co-combustion characteristics and kinetics of low-ranked coal and hydrochar derived from cow manure

CO2 emission should be reduced by the effective utilization of low-ranked coal in a coal-based power plant based on co-combustion of coal and biomass. This study investigated the co-combustion behavior of lignite and cow manure using three different kinds of samples: raw lignite coal blended with cow manure (CM-L), raw lignite coal blended with hydrochar derived from cow manure (HCM-L), and co-hydrothermal carbonization (Co-HTC) of lignite coal and cow manure (Co-HCML) using thermogravimetric analysis and a hydrothermal carbonization (HTC) temperature of 200 °C for 60 min. The kinetic parameters were calculated and analyzed using the Flynn-Wall-Ozawa and Kissinger-Akahira-Sunose methods. The combustion characteristics were studied of the various kinds of hydrochar mixed with lignite coal. The results showed that the low-ranked coal improved the fuel properties by increasing carbon content and decreasing sulfur through the HTC processes. The activation energy of Co-HCML was the lowest, which is preferable, and therefore it was recommended as the promising process.

Hydrothermal carbonization of Chinese medicine residue from licorice: Effects of pore and chemical structures on chromium migration

The Chinese medicine residue (CMR) is composed of wet substances, so using hydrothermal carbonization (HTC) to recover renewable energy from the residue is a suitable treatment method. Chromium (Cr), a kind of heavy metal element, is enriched in hydrochar and severely restricts its effective utilization. An in-depth analysis of the migration path and mechanism of Cr in hydrochar is helpful in promoting energy utilization for CMR. Here, licorice, a significant Chinese medicine, was selected as the example to analyze the evolutions of its pore and chemical structures and their effects on the migration mechanism of Cr during the HTC process. The products obtained under various HTC conditions were analyzed using nitrogen adsorption, FTIR, and 13C NMR. The results show that, considering reaction time and relevant reactions as the primary factors during the HTC process, the migration pathway of Cr in hydrochar undergoes two stages, and they are the accompanying migration stage and the recovery aggregation stage. Active adsorption sites for Cr may exist within the pore structure of hydrochar. In the HTC process, hydrolysis, decarboxylation, and decarbonylation reactions are the direct drivers of Cr migration, while aromatization is the underlying cause of Cr recovery and aggregation. It is hypothesized that Cr catalyzes the acetylene cyclotrimerization reaction, thereby promoting the formation of aromatic structures in hydrochar and integrating into the hydrochar carbon skeleton.

Low-energy thermo-chemical conversion processes of municipal wet waste

Hydrothermal carbonization (HTC) is a low-energy thermochemical process that converts wet biomass into a carbon-rich solid, commonly called hydrochar, for use in a variety of areas, such as soil amendment, biofuels or to produce carbon-based materials. The purpose of this paper is to increase knowledge for the economic valorization of municipal wet waste, considered as a raw material to obtain high value-added products through an HTC process and an additional chemical activation procedure. In the first part of the work, a 4.5-liter batch reactor was designed, built, and used in the HTC experimental campaign by varying the main process parameters, namely reaction time, amount and type of organic waste (e.g. vegetables, fruits, bread, pasta), water concentration, temperature and pressure. In addition, some experiments were conducted by applying the steam explosion technique at the end of the HTC process. The HTC results showed that in biomass with high water content, increasing residence time decreases the hydrochar yield. Considering a dry heterogeneous waste with high carbon content, the yields at the end of the process are much higher. In the second part of this work, the hydrochar samples were treated with a high-temperature activation process based on the use of KOH, obtaining activated carbon. Particularly, the best results were achieved by using high KOH: hydrochar ratios, resulting in high-quality activated carbons with good porosity and a high surface area of 2890 m2/g. Finally, an energy analysis was carried out to evaluate how to make the whole process cost-effective.

Microplastics in Sewage Sludge: Worldwide Presence in Biosolids, Environmental Impact, Identification Methods and Possible Routes of Degradation, Including the Hydrothermal Carbonization Process

Biomass-to-biofuel conversion represents a critical component of the global transition to renewable energy. One of the most accessible types of biomass is sewage sludge (SS). This by-product from wastewater treatment plants (WWTPs) contains microplastics (MPs) originating from household, industrial and urban runoff sources. Due to their small size (&lt;5 mm) and persistence, MPs present a challenge when they are removed from sewage systems, where they mainly accumulate (~90%). The presence of MPs in SS poses environmental risks when biosolids are applied as fertilizer in agriculture or incinerated for the purpose of energy production. The key problem is the efficient and reliable identification and reduction of MPs in sewage systems, due to the lack of standardized procedures. The reduction methods for MPs might involve physical, chemical, biological, and hydrothermal approaches, including hydrothermal carbonization (HTC). The HTC of SS produces hydrochar (HC), a solid biofuel, and presents a cutting-edge approach that simultaneously addresses secondary microplastic pollution and renewable biomass-derived energy production. In this article, we review briefly the MPs content in biosolids from different countries, and present HTC as a promising method for their removal from SS. In conclusion, HTC (i) effectively reduces the abundance of MPs in biosolids, (ii) produces an improved solid source of energy, and (iii) contributes to circular SS management.

Upcycling drinking bottle waste to intercalated 2D-0D carbon architectures and its supercapacitor applications

Despite its many benefits to our modern life, plastic contributes a large volume of solid waste that increasingly threatens our environment and health. Through a hydrothermal depolymerization and carbonization process that involves nitric acid and ethanol, drinking bottles that are made of polyethylene terephthalate are successfully converted into carbon quantum dots (CDs) and thin carbon nanosheets simultaneously with the former intercalated between layers of the latter to form a unique ball-sheet architecture. When used as electrode material, the stacking carbon nanosheets in this plastic-derived, ball-sheet carbon (PBSC) structure create a conductive network to allow rapid transport of ions and electrons while the well-dispersed CDs offer a large surface area and numerous sites to host them. The supercapacitors made of these PBSC electrodes exhibit double-layer capacitor behaviors with a specific capacity reaching 237 F/g at a charge rate of 1 A/g and excellent cycling stability. Our efforts offer a new route to upcycle plastic waste as valuable energy storage materials, which may help boost its recycling and the sustainable deployment of various clean energy resources.

Preparation of Supercapacitor Carbon Electrode Materials by Low-Temperature Carbonization of High-Nitrogen-Doped Raw Materials from Food Waste.

To address the problem of the low nitrogen (N) content of carbon materials prepared through the direct carbonization of food waste, soybean meal and egg whites with high N contents were selected to carry out carbonization experiments on food waste. At 220 °C, the effects of hydrothermal carbonization and microwave carbonization on the properties of supercapacitor electrode materials were investigated. The results show that food waste doped with soybean meal and egg whites could achieve good N doping. At a current density of 1 A·g-1, the specific capacitance of the doped carbon prepared by hydrothermal doping is as high as 220.00 F·g-1, which is much greater than that of the raw material prepared through the hydrothermal carbonization of food waste alone, indicating that the hydrothermal carbonization reactions of soybean meal, egg white, and food waste promote the electrochemical properties of the prepared carbon materials well. However, when a variety of raw materials are mixed for pyrolysis carbonization, different raw materials cannot be fully mixed in the pyrolysis process, and under the etching action of potassium hydroxide, severe local etching and local nonetching occur, resulting in a severe increase in the pore size distribution and deterioration of the electrochemical performance of the prepared carbon materials. At a current density of 1 A·g-1, the specific capacitance of these prepared carbon materials is 157.70 F·g-1, whereas it is only 62.00 F·g-1 at a high current density of 20 A·g-1. Therefore, this study suggests that the hydrothermal carbonization process is superior to the microwave pyrolysis carbonization process for preparing supercapacitor electrode materials with multiple samples doped with each other.

Hydrothermal Carbonization of Residual Biomass from Agricultural and Agro-Industrial Sector

Hydrothermal carbonization (HTC) is a promising method for the conversion of agricultural and agro-industrial residues into valuable products. HTC processes biomass through chemical reactions that produce hydrochar, a carbon-rich solid similar to lignite. Unlike other thermochemical processes, HTC can handle high-moisture biomass without pre-drying. This article evaluates the efficiency of HTC on wood chips, wheat straw, and grape pomace, examining their chemical and structural characteristics and critical operational parameters such as the temperature, pressure, biomass/water ratio, and reaction time. The obtained results highlight that the two key process parameters are the temperature and the ratio between the solid biomass and liquid phase. Increasing the first parameter increases the energy content by 20% and increases the carbon concentration by up to 50%, while reducing the oxygen content by 30% in the hydrochar. Varying the second parameter leads to the alternating reduction of the ash content but simultaneously reduces the energy content. The reaction time seems to have a limited influence on the quality parameters of the biochar produced. Lastly, HTC appears to successfully enhance the overall quality of widely available agricultural wastes, such as grape pomace.