Hydrothermal Carbonization Research Articles

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.

Current and emerging waste-to-energy technologies: A comparative study with multi-criteria decision analysis

In response to the rise in waste crisis and the possibility of energy utilization from waste, there has been increasing interest in waste-to-energy (WtE) conversion technologies, which requires intense scientific attention. There are diverse WtE technologies that apply to different waste types and require multidisciplinary decision support. The paper applies a Multi-criteria Decision Analysis (MCDA) tool to compare their economic, technological, socio-cultural, and environmental aspects to help identify the most promising choice. The comparison used in this study concerns four widely used technologies: Incineration (INC), Anaerobic Digestion (AD), Gasification (GAS), and Pyrolysis (PYR), and one emerging WtE conversion technology, Hydro-thermal Carbonization (HTC). The Comparison criteria are divided into four main criteria and fifteen sub-criteria. The Analytical Hierarchy Process (AHP) model was implemented using ’SuperDecisions’ software to make pairwise comparisons of identified criteria and to rank the WtE technology alternatives. Thirty-two international studies were shortlisted to gather data and provide input into the AHP model. The results show that the environmental factors are prioritized with a priority vector of 0.56. Further, the study concludes that the most suitable WtE technology, based on chosen parameters, is AD, followed by HTC, INC, and PYR with the priority vectors of 0.348, 0.201, 0.162, and 0.148, respectively, provided applicability. The emerging technology, HTC, is found to be the second most suitable technology. Further, the results represent the hierarchy structure arranged so that the main components are divided into sub-components with alternatives at the structure’s base, and the ’SuperDecisions’ model based on this hierarchy can be used in the future to find suitable WtE technology for a specific city with the necessary input for identified main and sub-criteria. This research not only provides a structured comparison of WtE technologies but also offers a scalable AHP framework that can be adapted for specific municipal contexts in future studies. By addressing the diverse needs of decision-makers across different regions, our model contributes to a more nuanced understanding of WtE technology selection and lays the groundwork for incorporating local policies and regulations in subsequent research phases.

Hydrochar from co-hydrothermal carbonization of sewage sludge and sunflower stover: Synergistic effects and combustion characteristics

This study carried out co-hydrothermal carbonization (Co-HTC) on sewage sludge (SS) and sunflower straw (SFS) at various ratios (1:0, 3:1, 1:1, 1:3, 0:1) to prepare hydrochar. The raw samples and produced hydrochar were characterized using ultimate analysis, proximate analysis, Brunauer-Emmett-Teller (BET), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The potential synergistic impact during the reaction process were analyzed. As the SFS ratio increased, the fuel ratio of hydrothermal carbons rose from 0.29 to 0.37, while the higher heating value (HHV) improved from 7.44 (MJ/kg) to 20.86 (MJ/kg). The co-hydrothermal synergistic effect resulted in enhanced the hydrochar yield, energy yield, carbon sequestration rate and organic retention rate. Compared to raw sample, the surface of hydrochar exhibits a rougher and more fragmented structure, with an increased number of microspheres and micropores, resulted in an increased specific surface area. Thermogravimetric analysis (TGA) demonstrated that, in comparison to HTC of sludge alone, the Co-HTC of SS with SFS enhances the ignition temperature and delays the completion of combustion. Therefore, Co-HTC with SFS is an effective method for converting SS into clean solid fuel for energy applications.

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.

Deep‐eutectic‐solvent‐assisted hydrothermal carbonization of sewage sludge for green wood bioadhesive production

AbstractThis study reports the use of deep‐eutectic‐solvent‐ (DES‐) assisted hydrothermal carbonization (HTC) to disrupt the floc structure of sewage sludge (SS) for deep carbonization, with the resulting hydrochars employed in the preparation of formaldehyde‐free plywood bioadhesives. Sewage‐sludge‐based bioadhesive exhibits an excellent wet shear strength, complying with the requirements of Chinese national standard GB/T 9846–2015 (≥0.7 MPa). The molecular weight of proteins and the formation of covalent bonds via dehydration have a notable role in improving adhesive performance (wet shear strength). The Maillard reaction is a key reaction during HTC to destroy the secondary structure of proteins, resulting in the release of more OH and NH2. The main reaction during hot‐press treatment is dehydration. High ash content in bioadhesives improves flame resistance potential, particularly on addition of DES. A plausible mechanism is proposed for this. This work provides a new method for the valorization of SS‐derived hydrochars and contributes to the development of greener formaldehyde‐free wood bioadhesives.

Hydrogen spillover on Ni@Graphene enables robust and efficient catalytic hydrogenation of aqueous levulinic acid to γ-valerolactone

Hydrogenation of biomass-derived aqueous levulinic acid (LA) to produce γ-valerolactone (GVL) is a promising approach from biomass to sustainable platform chemicals. However, the practical application of this method is limited because aqueous LA is highly corrosive to metal-based hydrogenation catalyst in high-temperature hydrothermal environments. Herein, we encapsulated metallic Ni0 particles with a few layers of graphene using a hydrothermal carbon coating method to obtain Ni@FLG-600 catalyst, which exhibited efficient catalytic activity and excellent cycling stability for the hydrogenation of aqueous LA to GVL. The defect-rich graphene shell prevents the Ni0 from acid corrosion meanwhile selectively permits the passage of small H2 molecules. The resulted active H* on Ni0 spills over to the outer surface of graphene shell and reacts with LA. Remarkably, the amount of H* on graphene shell can be the descriptor of activity. This finding presents a new strategy for the fabrication of acid-resistant catalysts for aqueous biomass hydrogenation.

Hydrothermal carbonization of coking sludge: Migration behavior of heavy metals and magnetic separation performance of hydrochar

This study comprehensively investigated the migration behavior and environmental risk of heavy metals (HMs) during the hydrothermal carbonization (HTC) of coking sludge (CS). The results indicated that over 90 % of HMs accumulated in the coking sludge hydrochar (CHC). The decomposition and loss of organic matter led to an increased concentration of HMs with rising temperatures. However, HTC also facilitated the transformation of HMs from bioavailable fractions to more stable fractions. Higher hydrothermal temperatures positively influenced the control of HMs' environmental risks. Ecological risk assessments revealed that the Potential Ecological Risk Index (RI) values of HMs in CHC decreased from 631.15 to 134.23, reaching considerate risk levels. Risk assessment codes indicated that, except for Mn, other HMs were reduced to no risk or low risk after hydrothermal treatment. Furthermore, the magnetic separation performance of CHC was explored, and its practical value was validated using a semi-continuous adsorption-separation device. The results showed that CHC achieved removal rates of 80.41–87.15 % for Congo red (CR) and tetracycline (TC), maintaining stability in various complex water environments. The CHC was rapidly separated after adsorption with a simple magnetic field, achieving a separation and recovery rate of over 80 %. These findings provided theoretical support for the stabilization of HMs in CS and the resource utilization of hydrochar in water treatment applications.

Use of carbon-encapsulated zero-valent iron nanoparticles from waste biomass to hydrogen sulphide wet removal.

This study evaluates the use of carbon-encapsulated zero-valent iron nanoparticles for biogas upgrading in wet systems. The nanoparticles were produced by hydrothermal carbonization, using olive mill waste (OMW) or microalgae as carbon sources. The solids were characterized to investigate the specific surface area, total and zero-valent iron content, pHPZC and chemical and crystalline composition. Their adsorption performance towards hydrogen sulphide (H2S) was tested by treating two types of synthetic biogas with and without CO2. In both cases, the starting H2S concentration was approximately 60 ppm and the experiments lasted until the complete saturation of the nanoparticles. Optimal Fe/C ratios of 0.05 for OMW nanoparticles and 0.2 for microalgae nanoparticles demonstrated H2S-specific adsorption capacities of 9.66 and 9.55 , respectively, in a synthetic biogas without CO2. The addition of CO2 in biogas reduced adsorption, possibly due to system acidification. X-ray photoelectron spectroscopy analysis revealed surface compounds on the surface of the spent nanoparticles, including disulphides, polysulphides and sulphate. The saturated adsorbents were effectively regenerated with air, leading to the oxidation of sulphur species and desorption. The regeneration allowed a total adsorption capacity of 53.25 and 34.14 , after 10 consecutive cycles of adsorption/regeneration with a single batch of olive mill and microalgae nanoparticles, respectively.

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.

Removal of methylene blue by hydrochar modified from hydrothermal carbonization technique

Removal of methylene blue by hydrochar modified from hydrothermal carbonization technique

Hydrothermal carbonization of Azolla biomass for derived carbon as potential sustainable materials for efficient photosynthesis in agricultural plants and as electrochemical electrode materials

Hydrothermal carbonization of Azolla biomass for derived carbon as potential sustainable materials for efficient photosynthesis in agricultural plants and as electrochemical electrode materials

Correction to: Pyrolysis or hydrothermal carbonisation for anaerobic-digested sewage sludge? A comparison of pyrochar and hydrochar stucture and stability

Correction to: Pyrolysis or hydrothermal carbonisation for anaerobic-digested sewage sludge? A comparison of pyrochar and hydrochar stucture and stability

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.

Production of hydrochar from the hydrothermal carbonisation of food waste feedstock for use as an adsorbent in removal of heavy metals from water

AbstractIn this research, discarded butternut peels were converted into hydrochar products through hydrothermal carbonisation (HTC), with adjustments made to the temperature (ranging from 180 to 260℃) and residence time (spanning 45–180 min). The findings indicated that both the temperature and time of carbonisation significantly influenced the yield of hydrochar (HC), as well as its physiochemical and structural properties. Higher temperatures and prolonged residence time led to decreased yield, elevated fixed carbon content and an increased fuel ratio. Furthermore, raising the process conditions increased HHV and reduced the oxygen-containing functional groups. The HC yield dropped from 28.75 to 17.58% with increased carbonisation temperature and time. The findings of this study also suggest that modified hydrochar is a promising material for removing heavy metals from wastewater. It is a relatively low-cost and abundant material that can be produced from various biomass feedstocks, including food waste. In addition, it is a sustainable and environmentally friendly option for wastewater treatment. Hydrochar-based systems offer several advantages over traditional methods of heavy metal removal, such as chemical precipitation and ion exchange. The unique physicochemical characteristics of hydrochar, including its porous structure and oxygen-rich functional groups, offer a high surface area and more binding sites for heavy metal ions. By changing the physicochemical properties of hydrochar with chemicals like phosphoric acid, it is possible to increase its adsorption capacity. The Freundlich isotherm was the best fit for the adsorption data for all three metal ions (Pb2+, Cu2+ and Cd2+), indicating that the adsorption process is multilayer and heterogeneous.

A CASE STUDY OF IMPLEMENTATION OF CIRCULAR ECONOMY PRINCIPLES TO WASTE MANAGEMENT: INTEGRATED TREATMENT OF CHEESE WHEY AND HI-TECH WASTE

In a global context characterized by severe environmental problems and increasing resource scarcity, waste represents both a challenge and an opportunity. This study aims to demonstrate with a real case the potential for optimizing the waste valorization action attainable through the synergic application of different treatments to residues of equally different nature and origin. In particular, bio-chemical (dark fermentation), chemical-physical (selective leaching) and thermo-chemical (hydrothermal carbonization) treatments were applied for the integrated valorization of whey from sheep cheese production and Hi-Tech waste (discarded electrical and electronic equipment). The treatments were applied at a laboratory scale on real samples of these residues. The organic acids used for selective leaching of valuable metals from Hi-Tech waste were obtained by dark fermentation of the cheese whey, while hydrothermal carbonization was used to convert the waste from previous stages into hydrochar feasible as solid fuel or soil improver. The dark fermentation tests have highlighted the possibility of recovering ≈ 100 g of organic acids from 1 L of whey; furthermore, it is also possible to recover bio-hydrogen depending on the operating conditions applied and the type of targeted organic acids. The leaching tests have demonstrated how the organic acids from whey fermentation have selective and quantitative mobilization capacities comparable to those of the same acids available on the market. The carbonization tests produced carbon-enriched hydrochar with promising fuel properties, as well as process waters suitable for anaerobic digestion with methane production. The results of the project led to the filing of an international patent.

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.

Effect of HTC and Water-Leaching of Low-Grade Biomasses on the Release Behavior of Inorganic Constituents in a Calcium Looping Gasification Process at 650 °C.

The release of alkali metals (K, Na) and nonmetals (S, Cl) during a calcium looping (CaL) gasification process of waste derived-hydrochars, water-leached samples, and CaO-biomass blends was investigated. Special attention was paid to biomasses that are not particularly promising for gasification requirements but have a large occurrence in Europe, including Grape Bagasse, Organic Fraction of Municipal Solid Waste (OFMSW), Green Waste, and Out-of-use woods from construction debris and discarded furniture. The release experiments were performed at 650 °C in a flow channel reactor to investigate the behavior of inorganic trace substances. Hot-gas analysis was performed by Molecular Beam Mass Spectrometry (MBMS). Thermodynamic equilibrium calculations via FactSage indicate H2S, carbonyl sulfide (COS), KCl, NaCl, and HCl as the main inorganic impurities. Thus, the focus of the experiments was placed on these species. It was found that the concentrations of trace elements released during gasification at 650 °C, such as H2S, SO2, KCl, and NaCl, are hardly affected by intense water-leaching. In contrast, carbonaceous materials from hydrothermal carbonization exhibit a higher concentration of trace potassium substances (K, KCl, and K2Cl+). When biomass samples are combined with CaO, the total amount of inorganic trace compounds (K, Na, and S compounds) in the resulting syngas could be decreased.

Utilization of papermaking black liquor as liquid phase for hydrothermal carbonization of corn stalks: The unique role of alkali for production of hydrochar

Papermaking black liquor (BL) contains a large amount of organic matter, alkali, and salt, which has high value in industrial and agricultural production. In the present paper, hydrothermal carbonization (HTC) technology has been employed to deal with BL and corn stalk (CS) under various conditions. A variety of analytical technologies, including Fourier Transform Infrared Spectrometer, X-Ray Diffraction, element analyzer, comprehensive thermal analyzer, scanning electron microscope, chromatography/mass spectrometry, TOC analyzer, and density functional theory (DFT), were used to characterize the physicochemical properties of hydrochar and aqueous phase product. The effects of experimental parameters (temperature, solid-liquid ratio, and time) on the HTC of BL and CS were systematically investigated. The higher energy yield and densification of hydrochar prepared by our HTC technology were obtained at 260 ℃ in 30 min with a solid-liquid ratio of 1:3. Mechanism study indicates that NaOH, which comes from the original BL, could effectively facilitate the cleavage of β–O–4 bond in lignin and β–1–4 glycosidic bond in cellulose and hemicellulose molecules. Hemicellulose and cellulose are more susceptible to degradation relevant to the lignin in the presence of NaOH. Elementary analysis shows that the dosage of BL is important for improving energy densification of hydrochar. The combustion characteristics show that hydrochar presents a thermochemical behavior, which is close to bituminous coal. Owing to hydroxyl ion in NaOH ion pair was consumed in the series of dehydrogenation reactions, pH of HTC aqueous phase product significantly decreases from 11 to 13 in original BL to 4.8–5. Such results indicate that a completely change for the components of BL could be obtained by our HTC technology, which provide a novel idea for the treatment of Papermaking BL without concentration.