Hydrothermal Carbonization Products Research Articles

Modeling of biogas production from hydrothermal carbonization products in a continuous anaerobic digester.

The coupling between anaerobic digestion and hydrothermal carbonization (HTC) is a promising alternative for sustainable energy production. This study presents a dynamic model tailored for a lab-scale anaerobic digester operating on HTC products, specifically hydrochar and HTC liquor derived from sewage and agro-industrial digestate. Leveraging a modified version of the Anaerobic Model 2 (AM2), our simplified model of four states integrates pH and biomass decay rates into biomass kinetics. Simulation results of the mode were compared with experimental data collected over 164 days from the digester. The obtained results have proven the ability of the proposed model to predict the trend of the biogas production as well as important measured outputs of the bioreactor. The developed model could be used to control and optimize the performance of the digester, which provides potential for bioenergy production from waste streams such as digestate and digestate treated through the HTC process.

Influence of Hydrothermal Carbonization (HTC) Temperature on Hydrochar and Process Liquid for Poultry, Swine, and Dairy Manure

Hydrothermal carbonization (HTC) is a promising technology for wet manure treatment by converting animal manure into valuable fuels, materials, and chemicals. Among other HTC process parameters, the temperature influences HTC products the most. As various animal manures have different compositions, it is not certain how the HTC temperature influences the hydrochar and HTC process liquid. To evaluate the temperature’s effect on HTC, three different manures (poultry, swine, and dairy) were hydrothermally carbonized at three different temperatures (180, 220, and 260 °C), and solid and liquid products were characterized for their morphology, elemental compositions, and ions. The carbon contents of the hydrochar reached as high as 38.98 ± 0.36% and 40.05 ± 0.57% for poultry and swine manure, respectively, when these manures were treated at 260 °C. Ammonium showed an around 30% increase in poultry manure hydrochar with the increase in the HTC temperature. In contrast, in swine manure, it decreased by around 80%, and in dairy manure, the HTC temperature did not have any remarkable effect on the ammonium content. The process liquids from HTC of dairy manure at 220 °C showed the most balanced distribution of different ions, with 4970 ± 673 ppm of sodium, 4354 ± 437 ppm of ammonium, 2766 ± 417 ppm of potassium, 978 ± 82 ppm of magnesium, 953 ± 143 ppm of calcium, 3607 ± 16 ppm of chloride, and 39 ± 7 ppm of phosphate. These results emphasize the manure-specific effects of the HTC temperature on both solid and liquid products, indicating the need for optimized strategies to enhance HTC processes for various types of animal manures.

Recycling food waste to agriculture through hydrothermal carbonization sustains food-energy-water nexus

Recycling underutilized resources from food waste (FW) to agriculture through hydrothermal carbonization (HTC) has been proposed to promote a circular economy (CE) in food-energy-water (FEW) nexus. However, most HTC studies on FW were conducted at laboratory scale, and little is known on the efficacy and feasibility of field application of HTC products from FW, i.e. the aqueous phrase (AP) and solid hydrochar (HC), to support agriculture production. An integrated pilot-scale HTC system was established to investigate practical HTC reaction conditions treating FW. A peak temperature of 180 °C at a residence time of 60 min with 3 times AP recirculation were recommended as optimal HTC conditions to achieve efficient recovery of nutrients, and desirable AP and HC properties for agriculture application. Dilution of the raw AP and composting of the fresh HC are necessary as post-treatments to eliminate potential phytotoxicity. Applying properly diluted AP and the composted HC significantly improved plant growth and nutrient availability in both greenhouse and field trials, which were comparable to commercial chemical fertilizer and soil amendment. The HTC of FW followed with agricultural application of the products yielded net negative carbon emission of −0.28 t CO2e t−1, which was much lower than the other alternatives of FW treatments. Economic profit could be potentially achieved by valorization of the AP as liquid fertilizer and HC as soil amendment. Our study provides solid evidences demonstrating the technical and economic feasibility of recycling FW to agriculture through HTC as a promising CE strategy to sustain the FEW nexus.

Advances in Research and Technology of Hydrothermal Carbonization: Achievements and Future Directions

Hydrothermal carbonization (HTC) has emerged as a pivotal technology in the battle against climate change and fosters circular economies. Operating within a unique reaction environment characterized by water as a solvent and moderate temperatures at self-generated pressures, HTC efficiently converts biomass residues into valuable bio-based products. Despite HTC’s potential—from the management of challenging biomass wastes to the synthesis of advanced carbons and the implementation of biorefineries—it encounters hurdles transitioning from academic exploration to industrial implementation. Gaps persist, from a general comprehension of reaction intricacies to the difficulty of large-scale integration with wastewater treatments, to the management of process water, to the absence of standardized assessment techniques for HTC products. Addressing these challenges demands collaboration to bridge the many scientific sectors touched by HTC. Thus, this article reviews the current state of some hot topics considered crucial for HTC development: It emphasizes the role of HTC as a cornerstone for waste management and biorefineries, highlighting potentialities and challenges for its development. In particular, it surveys fundamental research aspects, delving into reaction pathways, predictive models, analytical techniques, and HTC modifications while exploring HTC’s crucial technological applications and challenges, with a peculiar focus on combined HTC, wastewater integration, and plant energy efficiency.

Influences of reaction parameters and complexation pretreatments on the distribution of phosphorus during hydrothermal carbonization of dewatered sewage sludge

This study investigated the effects of reaction parameters and pretreatments with complexing agents, namely ethylenediaminetetraacetic acid (EDTA), glutamate diacetic acid (GLDA), and citric acid (CA), on the phosphorus contents and forms in the sludge hydrothermal carbonization products. The results showed that reaction temperature had the greatest effect on the distribution and forms of phosphorus in liquid and solid products. High reaction temperatures inhibited the transfer of phosphorus from the solid phase to the liquid phase. Indeed, the proportions of phosphorus in the liquid phases only accounted for 3.56 % at reaction temperature and time of 160 °C and 60 min, respectively. However, this proportion increased to 16.32, 12.62, and 13.15 % following complexation pretreatments with EDTA, GLDA, and CA at 0.1 mol/L, respectively. In addition, the complexation pretreatments enhanced the transfer of phosphorus from the solid phase to the liquid phase. The total phosphorus contents in the liquid phase (TPL) reached 896.46 mg/L. The finding can be explained by the binding of the complexing agents with metal ions, such as Mg, Ca, Al, and Fe, transferring phosphorus originally bound to these metal ions to the liquid phase. In addition, the results demonstrated the effectiveness of the magnesium ammonium phosphate (MAP) crystallization method for recovering phosphorus from the EDTA-pretreated liquid product. X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) analyses showed high purity and crystallinity of the obtained struvite to some extent.

Characterization of Synthetic Humin from Solid Hydrolysate and Biochar from Hydrothermal Carbonization Products of Chicken Feather Waste

Solid hydrolysate and biochar 2:1 are synthetic humus from hydrothermal carbonization of chicken feather waste and contain humin that can be isolated by IHSS method. The recalcitrant humin is obtained in solid form. The yield of isolated humin from biochar 2:1 was 44.5%, and humin from solid hydrolysate was 12.7%. Analysis of humin by FTIR indicated the characteristics of complex functional groups. Based on the XRD and TEM tests, humin is formed from amorphous crystals with <14 nm in size and categorized as a superparamagnetic nanoparticle. The surface morphology of humin from solid hydrolysate is in the form of small spheres attached to larger particles, while humin from biochar 2:1 is smoother and has a larger surface area. This synthetic humin contains the nutrients N, O, Si, Cu, S, Mg, Zn, and K based on the EDX test quantitatively supported by AAS analysis. Characteristics of humin, which contains nutrients, are composed of amorphous crystals with complex functional groups during the hydrothermal carbonization process. Their relatively small heterogeneous molecules are stabilized by hydrophobic interactions and hydrogen bonds to form supramolecular compound associations in hour order. This humin content in synthetic humus is expected to increase its utility as a soil improver.

Life Cycle Assessment of Hydrothermal Carbonization: A Review of Product Valorization Pathways

Hydrothermal carbonization (HTC) has the potential to be a sustainable and environmentally beneficial approach for organic waste treatment. It is likely that HTC product use will dictate the viability of large-scale HTC facilities; therefore, understanding the viability and environmental implications associated with HTC product valorization pathways is critical. The overall goal of this review is to gain an understanding of how HTC product valorization is currently being modeled in life cycle assessment studies, and to use such information to assess current research and/or data needs associated with product valorization. To accomplish this, a review of existing HTC literature was conducted and used to assess the current state of knowledge surrounding the environmental implications of HTC product use. From this review of the literature, it is clear that potential exists for HTC product valorization. To realize this potential in a full-scale application, research gaps and data needs were identified that included a system-level integration to evaluate location-specific information as well as more extensive characterization of the impact of HTC product properties on valorization impacts.

Regulating the distribution of phosphorus in sewage sludge hydrothermal carbonization products by complexation pretreatment

In this study, we investigated the effects of the concentrations of four pretreatment complexing reagents, namely ascorbic acid (AS), citric acid (CA), N, N-bis (carboxymethyl) glutamic acid (GLDA), and ethylenediaminetetraacetic acid (EDTA), on the phosphorus contents and forms in hydrothermally carbonized sludge products. The results showed that among the four complexing reagents, EDTA had the greatest effect on the phosphorus transfer from the solid phase to the liquid phase during the hydrothermal process of the sludge, followed, respectively, by GLDA, CA, and AS. The phosphorus proportion of the liquid phase was 63.96% under hydrothermal process temperature, reaction time, and EDTA concentration of 160 °C, 60 min, and 0.2 mol/L, respectively. The results showed formations of EDTA complexes with Ca, Fe, and Al in the sludge, releasing phosphorus bound to the metal ions into the liquid phase. The highest total phosphorus concentration in the liquid phase was 2533.31 mg/L following the increase in the hydrothermal process temperature from 100 to 160 °C. However, the Fe and Al-EDTA complexes were thermally decomposed after continuously increasing the hydrothermal process temperature to 240 °C, resulting in a readsorption of phosphorus to the solid phase with Fe, Al, and other metals and, consequently, decreasing the phosphorus content to 880.93 mg/L in the liquid phase. The results of this study provide a scientific basis for regulating phosphorus distribution in the solid and liquid phases of hydrothermally carbonized sludge products and effectively recovering phosphorus in the liquid phase.

Hydrothermal carbonization of Typha australis: Influence of stirring rate

According to existing literature, there are no conclusive results on the impact of stirring on hydrothermal carbonization (HTC); some studies report a significant impact on the product's properties, while others indicate no influence. This study investigates the influence of stirring rate on several responses and properties of HTC products, including solid mass yield, solid carbon fraction, surface area, surface functional groups, morphology, and the fate of inorganic elements during HTC. Waste biomass was introduced as a feedstock to a 2 L HTC reactor, where the effects of temperature (180–250 °C), residence time (4–12 h), biomass to water (B/W) ratio (1–10%), and stirring rate (0–130 rpm) were investigated. The findings of this study conclusively indicated that the stirring rate does not influence any of the studied responses or properties of hydrochar under the selected experimental conditions used in this study. Nevertheless, the results indicated that a low-stirring rate (5 RPM) is enough to slightly enhanced the heating-up phase of the HTC reactor. For future research, it is recommended to examine the impact of stirring rate on the HTC of other types of biomass using the methodology developed in this study.

Phosphorus recovery from hydrothermal carbonization of organic waste: a review

AbstractBackgroundThis review sheds light on the topic of phosphorus (P) recovery from hydrothermal carbonization (HTC) of organic waste. The paper focuses on the rising need for securing alternative P sources for the increasing demand, in addition to the development of HTC as a thermochemical technique for waste valorization.ResultsThis article studies the definition of P‐recovery from HTC, while introducing the notion of availability, which is a significant factor for studying the efficiency of P‐recovery. A brief comparison between different treatment techniques for P‐recovery from waste streams is presented, and the advantages of HTC are highlighted among different thermochemical techniques. Furthermore, the mechanisms of P‐transformation during HTC reactions are studied, and the effect of various parameters on P‐destination and recovery is emphasized. Finally, applications of P‐recovery from HTC products on the laboratory and industrial scales are studied to assess the feasibility of the application.ConclusionIn short, the paper offers a detailed insight into the definition, mechanism, and potential feasibility of P‐recovery from HTC of organic wastes within the scopes of resource management, waste valorization, and fertilizer production. Even though HTC for P‐recovery from organic waste has been applied on laboratory and industrial scales, several challenges persist towards optimizing this process. The paper concludes that adopting P‐availability as a criterion for efficiency is necessary to optimize HTC conditions for P‐recovery. Further studies on P‐transformation during later‐stage reactions of HTC are recommended, as well. © 2023 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).

Effect of Biochar and Process Water Derived from the Co-Processed Sewage Sludge and Food Waste on Garden Cress’ Growth and Quality

Very little is known about how products derived from the hydrothermal carbonization (HTC) of municipal waste affect the availability and uptake of nitrogen in plant nutrition. This study examined the effects of 60% sewage sludge and 40% food waste HTC products, i.e., biochar (BC) and process water (PW), as nitrogen sources on garden cress growth and quality. A fertilization program using four nitrogen doses [(control), 9, 12, and 15 kg da−1 N] and BC, PW, chemical nitrogen (CN), and their combinations were used in a pot experiment conducted under greenhouse conditions. The highest nitrogen dose often produced better results in terms of plant growth and quality. Additionally, fertilization with PW+CN and BC+CN at the highest nitrogen dose significantly improved plant height, plant fresh and dry weight, and root dry weight parameters of garden cress over the previous treatments. The highest stem diameter, number of leaves, and plant area values were obtained in the 15 kg da−1 N dose PW+BC application. The vitamin C content in cress decreased with the increasing levels of CN. The highest vitamin C content was obtained with 15 kg N da−1 PW fertilization. BC+PW and CN fertilization applications improved chlorophyll a, b, and the total contents of garden cress leaves. Moreover, the nitrate (NO3) concentration of cress increased with CN doses while it decreased in all BC and PW administrations. The 9, 12, and 15 kg N da−1 doses of PW+CN and the 15 kg N da−1 dose of BC+CN yielded the highest agricultural nitrogen utilization efficiency (ANUE) values. Plant nutrient content was positively affected in all fertilization applications, except for Na and Cl. However, it was determined that BC+CN fertilizer application improved plant nutrient uptake. Surprisingly, PW+CN treatment at the lowest nitrogen dosage resulted in the highest soil organic matter and total nitrogen content. In conclusion, it has been determined that biochar and process water have a synergistic effect with CN to increase plant growth by improving nitrogen efficiency, but their application alone without CN is insufficient to meet the nitrogen requirement.

Energy analysis of olive pomace valorization via hydrothermal carbonization

This research investigates the hydrothermal carbonization (HTC) of olive pomace (OP) while studying the energetic valorization of the hydrochar and by-products produced. Experiments were carried out in accordance with a Doehlert experimental design to optimize two experimental variables: operating temperature (180°C-250 °C) and holding time (0–60 min). Three different process scenarios were examined. They were designed based on new value-added applications for HTC products namely, energy production, agricultural and environmental applications. The first scenario A focuses on the valorization of the HTC liquid phase product. Scenario B introduces residual oil recovery using evaporation and finally in scenario C, the HTC liquid product is treated by wet peroxide oxidation (WO) in view of its discharge in the natural environment. These scenarios were investigated under three process regimes: adiabatic reactor (idealized process), steady state and start-up conditions (the most realistic case). The energy analysis relied on an experimental measurement approach and thermodynamic calculations. Negative and positive values in the energy balance were found for both scenarios A and B, however only positive values were found in scenario C throughout all the process regimes. Ultimately, along with the conceptual scenarios proposed, the influence of the main process parameters (i.e., temperature, holding time) on the performance of each specific application is discussed, which can be exploited to further improve the HTC technology.

Kinetics of hydrothermal carbonization of kitchen waste based on multi-component reaction mechanism

Hydrothermal carbonization (HTC) is a suitable method to pretreat kitchen waste with high moisture content and complex composition. Developing a precise kinetic model can accurately predict the yields of products to obtain better economic benefits in subsequent utilization, such as fuel. This study aimed to propose an HTC kinetic model of kitchen waste by studying the multi-component reaction mechanism. The HTC reactions of multi-component kitchen waste could be summarized as three key reactions: carbonization of carbohydrates, the Maillard reaction, and the amidation reaction. These reactions were reflected in the kinetic model. Moreover, the calculated results indicated the fitting degree reached 0.9995, which accurately simulated the hydrothermal process of kitchen waste. This model illustrated the rate and extent of the reaction between the components. The kinetic results showed that the rate constant of carbonization of carbohydrates was 0.0012, and that of the Maillard reaction and the amidation reaction were 0.0998 and 0.1409, respectively. The amidation reaction competed with the Maillard reaction and dominated the reaction of the constant-temperature stage. This model provided preliminary guidance for regulating and utilizing HTC products from kitchen waste in different institutions and regions.

Hydrothermal carbonization of pulp and paper industry wastewater treatment sludges - characterization and potential use of hydrochars and filtrates

The pulp and paper industry’s mixed sludge represents waste streams with few other means of disposal than incineration. Hydrothermal carbonization (HTC) could be advantageous for the sludge refinement into value-added products, thus complementing the concept of pulp and paper mills as biorefineries. Laboratory HTC was performed on mixed sludge (at 32% and 15% total solids) at temperatures of 210–250 °C for 30 or 120 min, and the characteristics of the HTC products were evaluated for their potential for energy, carbon, and nutrient recovery. The energy content increased from 14.9 MJ/kg in the mixed sludge up to 20.5 MJ/kg in the hydrochars. The produced filtrates had 12–15-fold higher COD and 3–5-fold higher volumetric methane production than untreated sludge filtrates, even though the methane yield against g-COD was lower. The increased value of the hydrochars in terms of energy content and carbon sequestration potential promote HTC deployment in sludge treatment and upgrading.

Co-production of hydrochar, levulinic acid and value-added chemicals by microwave-assisted hydrothermal carbonization of seaweed

Seaweed is considered a third-generation biomass for transport biofuel production with great potential for bioenergy and biorefinery applications. Microwave-assisted hydrothermal carbonization (HTC) offers a conversion route for seaweed valorization to multiple value-added products. However, the HTC products (such as hydrochar and process liquor) are highly dependent on feedstock properties and HTC conditions. This study investigated the valorization of Laminaria digitata to a range of products (primarily including hydrochar, levulinic acid and 5-hydroxymethylfurfural) through microwave-assisted HTC at a range of low temperatures (160, 180 and 200 °C) and levels of dilute acid addition (1, 2 and 4% H2SO4 concentration). The work suggests an optimized process at a temperature of 200 °C with 4% H2SO4, with levulinic acid and 5-hydroxymethylfurfural in the process liquor achieved the highest yields of 12.5% (12.5 g per 100 g dry L. digitata) and 5.8%, respectively. The obtained hydrochar had a higher heating value of 25.5 MJ/kg volatile solids, comparable to lignite coal. At such a condition the total carbon recovery in the produced hydrochar and process liquor accounted for 84% of carbon in the original seaweed. The 200 °C derived hydrochar presented the highest carbon content of 65.4%, but the lowest abundance in oxygen-containing functional groups compared to the hydrochars obtained under other conditions (160 and 180 °C). The economic benefits of the process might be significantly increased if hydrochar was upgraded into activated carbon instead of being used as a solid fuel.

A Review on Sewage Sludge Valorization via Hydrothermal Carbonization and Applications for Circular Economy

In pursuit of establishing a circular economy, a waste-to-energy approach is gaining increasing attention. Valorization of sewage sludge constitutes a critical importance due to generation in high quantities, difficulties in disposal, and associating environmental impacts. Hydrothermal carbonization (HTC) is a relatively recent yet an acclaimed method for sewage sludge management and valorization due to process compliance with sludge characteristics. In this review, research studies are evaluated via categorization of application fields of sludge-derived HTC products such as solid fuel production, gas production, soil remediation, nutrient recovery, water treatment, and energy storage. Research findings are compiled and a network mapping is employed for the visualization of the current situation and correlation in respective fields. The potential of HTC for sewage sludge valorization and future projections concerning available techniques are assessed within the context of circular economy.

Hydrothermal carbonization of forest waste into solid fuel: Mechanism and combustion behavior

The structural characteristics and fuel performance of hydrochars prepared by hydrothermal carbonization (HTC) of forestry waste (FW) were studied. Proximate analysis and ultimate analysis were used to characterize the chemical composition of the samples, scanning electron microscopy and specific surface area analysis were used to characterize the microscopic results of the samples, Fourier transform infrared spectroscopy and Raman spectroscopy were used to characterize the microcrystalline structure, and non-isothermal thermogravimetry was used to characterize the combustion properties of the HTC products. The results show that with the increase of the HTC temperature, the mass yield of hydrochar decreases, and the content of gas products and liquid products increases. With the increase of HTC temperature, the volatile content of hydrochar gradually decreases, and the fixed carbon content gradually increases. The high heating value (HHV) of FW-280 sample is 1.46 times that of the FW. The porosity and specific surface area increase first and then decrease with the increase of the HTC temperature, and reach the maximum value at 240 °C. With the increase of HTC temperature, the IG/IAll value of the sample increased from 0.282 to 0.346, and the order degree of the carbonaceous structure gradually increased. The combustion process of hydrochars can be divided into two stages: volatile matter removal and carbon combustion. FW-280 has better combustion performance due to its higher carbon content and Rmax2 value of 0.002616. Therefore, the comprehensive research on the physicochemical properties and combustion performance of FW hydrochar will facilitate the expansion of the application of FW resources.

Upgrading of flax powder and short fibers into high value-added products

Lignocellulosic materials have great potential to be valorized into new products. Flax by-products such as powder and short fibers are used in the present study to identify plausible potential applications for the products obtained from their hydrothermal treatment. The as-received industrial flax by-products are subjected to hydrothermal carbonization (HTC) in a wide range of severity, an operating parameter combining time and temperature. In this way, the yield and characteristics of the resulting HTC products: hydrochars, carbon quantum dots (CQDs) and organics such as 5-hydroxymethylfurfural (5-HMF) and furfural (FU), are determined. Likewise, pyrolysis of the hydrochars and the starting flax by-products at 900 °C is also carried out, leading to carbon materials with developed surface areas, higher than 950 m2/g, and CO2 capture values of up to 4.8 mmol/g at 1 bar and 0 °C. In the overall process, severities above 4.9 were found to be optimal in terms of higher calorific value (around 27 MJ/kg) of the obtained hydrochars, production of organic products (0.22 and 0.06 g/L of 5-HMF and FU, respectively), photoluminescence quantum yield of the CQDs fraction (4.7%) and CO2 capture (up to 4.8 mmol/g) by the hydrochar-derived carbons.

Hydrothermal carbonization of coffee silverskins

If waste biomass from food processing can be harnessed to create new bioproducts, it will not pollute the environment by its disposal. Hydrothermal carbonization (HTC) has been found to be effective on some types of biomass to produce a solid fuel product and a sugar-rich liquid product. This research investigated the effect of HTC at various temperatures on bioproducts from coffee silverskins, the low-density waste from roasting coffee beans. HTC was performed on coffee silverskins at four different temperatures 180 °C, 200 °C, 230 °C, and 260 °C. Fiber analysis, heats of combustion, and Fourier transform infrared spectroscopy were performed on the untreated and HTC pretreated solid biomass. On the HTC liquid products, pH was found and then sugar monomer concentration determined using high performance liquid chromatography. HTC processing of coffee silverskins increased the energy density of the solid product, with higher temperatures increasing energy density more. The pH of the liquid product was near 4.5 for all experiments. The concentrations of glucose, galactose, and arabinose in the liquid HTC product decreased with higher HTC temperatures. Thus, HTC can convert coffee silverskins into a higher fuel value solid product and a liquid rich in monomeric sugars. Processing temperature affects the solid bioproduct's energy densification and the liquid bioproduct's sugar content. • Hydrothermal carbonization (HTC) can convert coffee silverskins into bioproducts •The solid lignin-rich product can have a fuel value 60% higher than untreated biomass •Higher HTC temperatures produce higher fuel value product but less solubilized sugar •Lower HTC temperatures produce more sugar monomer in the liquid bioproduct

Valorization of hydrothermal carbonization products by anaerobic digestion: Inhibitor identification, biomethanization potential and process intensification

Integrating hydrothermal carbonization (HTC) and anaerobic digestion for biorefinery-oriented full utilization of wet organic wastes is a promising emerging technology. The objectives of this study were to identify the potential inhibitory substances, evaluate the biomethane potential of mixed and aqueous products and explore process intensifying strategies. The results indicated that the high HTC temperature of 240 °C resulted in a significantly low methane yield of 60 ± 5 mL/g COD and a high Short chain fatty acid (SCFAs) accumulation of 4174 ± 76 mg/L. GC-MS analysis showed that the contents of inhibitory pyrazines, pyridines and ketones in aqueous fraction at 240 °C substantially increased from 13.14%, 0.4%, 0.55% at 180 °C to 23.34%, 2.89%, 5.13%, respectively. When the aqueous products obtained from 240 °C-HTC was supplemented or pretreated by carbonaceous material, the methane yields were greatly improved and increased to 1.3-fold and 1.8-fold, respectively. These finding could provide some valuable technical information for HTC based biorefinery of organic waste.