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Burning agricultural biomass in the field significantly contributes to air pollution, particularly in the Indian context, where numerous cities have consistently ranked among the world's most polluted over the past few decades. The investigation endeavors to examine the potential utilization of cotton stalks as an environmentally friendly and sustainable energy source. During the investigation, biochar was generated through pyrolysis at temperatures of 300, 500, and 700 ˚C for 4 h, while hydrochars were produced via hydrothermal carbonization (HTC) at 180, 210, and 240 ˚C for the same duration. The findings revealed that hydrochar exhibited higher mass and energy yields, with mass yields of 60 ± 7% compared to 41 ± 10% for biochar, and energy yields of 87 ± 1% compared to 63 ± 5% for biochar. Elemental analysis results indicated an increase in carbon percentage with rising process temperatures, with carbon content increasing from 59% at 300 ˚C to 78% at 700 ˚C for pyrolysis, and from 49% at 180 ˚C to 63% at 240 ˚C for HTC. The biochar synthesized at 700 ˚C demonstrated the highest measured high heating value (HHVm) of 29.83 MJ/kg, whereas for HTC, the HHVm of 25.88 MJ/kg was reported for hydrochar synthesized at 240 ˚C. From the computed thermal kinetic parameters, it is evident that the biochars are more thermally stable than hydrochars and raw cotton. According to the Van Krevelen diagram, both biochar and hydrochar products exhibited improved fuel properties. The cumulative evidence suggests a ground-breaking potential for utilizing these char products as sustainable solid fuel alternatives. [ABSTRACT FROM AUTHOR]

To effectively remove lead (Pb(II)) and bisphenol A (BPA) from wastewater, polyvinyl chloride modified magnetic hydrochar (PVC-AMHC) was synthesized through co-hydrothermal carbonization of polyvinyl chloride and corn straw, and subsequently activated using NaOH. Characterization demonstrated that both PVC and NaOH activation increased the content of oxygen-containing functional groups, and Fe3O4 was successfully loaded onto the material surface. Furthermore, PVC-AMHC displayed remarkable uptake capacity with the maximum uptake amount of Pb(II) (217.53 mg/g) and BPA (185.53 mg/g) at 130 and 30 min, respectively, under a wide pH range. Additionally, PVC-AMHC possessed high tolerance to different interference cations and maintained excellent adsorption performance during four regeneration cycles. The thermodynamic analysis suggested that the absorption processes of Pb(II) and BPA by PVC-MHC were spontaneous (-ΔG0) with an endothermic characteristic (+ΔH0). Adsorption mechanisms of Pb(II) on PVC-AMHC included complexation, electrostatic attraction, and pore filling, and those of BPA were mainly associated with hydrogen bonding and pore filling. In conclusion, PVC-AMHC was an environmentally friendly adsorbent with effectively simultaneous removal of Pb(II) and BPA from wastewater. Highlights: • PVC-AMHC is prepared via co-hydrothermal carbonization of polyvinyl chloride and corn straw, and activated by NaOH. • PVC modification and NaOH activation promote the increase of oxygen-containing functional groups of PVC-AMHC. • PVC-AMHC has excellent regeneration property and anti-interference ability to various co-existing ions. [ABSTRACT FROM AUTHOR]

Anaerobic digestion of livestock and poultry waste has been confined to the low efficiency and the accumulation of harmful heavy metals. An effective way can be expected for the nanomaterials or biochar-based materials rich in the trace element selenium (Se). Particularly, selenium nanoparticles (SeNPs) have attracted much more interests in recent years, due to their low toxicity, high biocompatibility, and excellent physicochemical properties. Therefore, the SeNPs have been widely used in the various fields, such as environmental remediation, agricultural production, clinical medicine, and chemical manufacturing. Generally, the SeNPs can be synthesized by different approaches (e.g. biological, physical, and chemical ones). This study aims to explore the effects of hydrochar-based nano selenium on methane production and arsenic removal from mesophilic and thermophilic anaerobic digestion of swine manure. The Bacillus subtilis subspecies stercoris strain XP from our laboratory was added into the preparation of bio-nano selenium. Bio-nano selenium and garden wastes (i.e., bark, branches, and wood chips of arboreal trees) were applied to prepare the hydrochar-based nano selenium (SeHC) through hydrothermal carbonization. And then the physicochemical properties of SeHC were further analyzed to facilitate the subsequent applications. Scanning electron microscopy (SEM), mapping imaging, and energy-dispersive X-ray spectroscopy (EDX) were applied to characterize the resulting materials. Batch experiments of anaerobic digestion were carried out to verify the preparation. Swine manure containing arsenic (4.43 mg/kg) was taken as the research object. The SeHC was also added for the reinforcement. Three treatment groups were also applied, including hydrochar (HC), bio-nano selenium (Se), and SeHC. A systematic investigation was implemented to explore the effects of different treatments on methane production of swine manure and the removal rate of arsenic under mesophilic (37°C) and thermophilic (44°C) anaerobic digestions. Meanwhile, the treatment group without any addition of hydrochar or selenium was considered as the control (CK). The results showed that the SeHC shared a multi-dimensional spatial structure, where the spherical nano-selenium particles with a diameter of 100~200 nm were successfully loaded on the surface of SeHC. The BET (Brunauer-Emmett-Teller) surface area of SeHC was significantly (P<0.05) enhanced by 15.1%, compared with the HC without selenium modification. Fourier Transform Infrared Spectroscopy (FT-IR) indicated that much many more types of surface functional groups (e.g. N-H, C=O, C-O, and C-X) were found in the SeHC. Moreover, the Gompertz model fitting showed that the thermophilic fermentation coupled with SeHC treatment group was more conducive to the anaerobic methanization. In terms of the mesophilic and thermophilic anaerobic conditions, the final cumulative methane production (P’) and the maximum methane production rate (Rm) of the SeHC treatment group were significantly promoted by 39.37%, 11.70%, 72.20%, and 75.54%, respectively, compared with the CK group. Meanwhile, the treatment of SeHC shared the better efficiency in the removal of arsenic under anaerobic digestion. The removal rate was ranked in the descending order of the SeHC, Se, HC, CK. Specifically, the maximum removal rate was 5.3% and 10.7% in the mesophilic and thermophilic digestion, respectively. In summary, the SeHC coupled with the thermophilic anaerobic digestion can be expected to improve the anaerobic digestion for the rapid removal of harmful substances, such as arsenic. The findings can also provide a theoretical reference to develop the hydrochar-based nano selenium in the environmental and bioenergy production. [ABSTRACT FROM AUTHOR]

In this study, we selected walnut shell-derived pristine HC (pHC) and two modified derivatives obtained by oxidative and alkali treatments (designated mHC-O and mHC-A, respectively) to investigate the passivation performance of Pb(II) in contaminated soil. The yields of mHC-A and mHC-O were 70.58% and 95.38%, respectively, after posttreatment. According to the XPS, FTIR, and acidity titration results, the amounts of the three major OCGs (i.e. C−O, C=O, and O−C=O) all increased after H2O2 oxidation. Moreover, chemical modification fundamentally changed the structural characteristics of pHC. DTPA extraction tests indicated that the extractable Pb content after 30 days of incubation decreased by 13.60%, 19.32% and 14.53% at 7% (w/w) doses of HC, mHC-O and mHC-A, respectively, compared to that of the control. Furthermore, mHC-O was superior to pHC and mHC-A in terms of Pb passivation efficiency, which was consistent with the results of BCR sequential extraction and leaching tests using three root exudates. For mHC-O at the 7% dose, the contents of bioavailable Pb in the contaminated soil were 19.85 and 8.83 mg/kg based on DTPA leaching and BCR analysis, respectively, while they were 0.616, 0.564 and 0.07 mg/kg in the root exudate leaching tests of Ophiopogon japonicus, radish and spinach, respectively, indicating that the root exudate leaching method lowered the bioavailable Pb content compared to the DTPA and BCR methods. Overall, Oxidation posttreatment with HC could improve the passivation of Pb in contaminated soils. [ABSTRACT FROM AUTHOR]

Unscientific disposal of diaper waste (DW) creates a major environmental issue. Majority of DW containing cellulose, super absorbable polymer, polyethylene, and polypropylene ends up in the landfills where it may take around 400–600 years for decomposition on its own. Hydrothermal pre-treatment (HPT) is an emerging process to transform the moisturized organic waste into the value-added products. In the present study, the HPT of DW was carried out in a 2 L high pressure reactor at 200 °C for 1 h duration. The runs were performed with a diaper soaked either in tap water (1.5 L and 1 L) or synthetic urine. The hydrochar (HC) and process wastewater (PW) obtained after HPT were subjected to detailed characterization. Due to high energy content in the HC samples (lower calorific value = 22.2–24.3 MJ/kg), these are suggested to be used as co-fuel. Out of the three HC samples, the solid sample obtained after HPT of the simulated DW showed superior energy related parameters such as energy densification, energy retention efficiency and normalized energy yield. A comparative energy assessment predicted the HPT of DW followed by incineration of the HC as more energy efficient treatment option compared to the direct incineration of DW. However, the PW contained high organic load and low biodegradability. Hence, the stream needs further treatment and characterization to identify and recover the value-added chemicals. Statement of Novelty: The diaper waste is continuously increasing globally. Due to its bulky nature, it occupies large volumes landfill sites. Since diaper waste contains significant amount of moisture, an attempt was made to study the performance of hydrothermal pre-treatment of diaper waste. After the pre-treatment, solid hydrochar and process wastewater were produced. In the present work, both the streams were characterized for their physico-chemical properties. Moreover, the potential of hydrochar for energy recovery was also assessed. The study will be useful to the researchers working on diaper waste disposal and hydrothermal treatment. Highlights: HPT of DW at 200 °C for 1 h produced hydrochar (HC with good heating value). Major reactions during HPT were dehydration, decarboxylation and aromatization. FTIR of the HC samples revealed several functional groups at their surface. Process wastewater had high organic load but low biodegradability. HPT of DW followed by incineration of HC showed better energy efficiency. [ABSTRACT FROM AUTHOR]

WATER pollution possesses a potential threat to the surrounding ecosystem. Thus, the current study investigates the efficiency of using two safe organic products, named hydrochar and Ndoped hydrocar for removal of Pb(II) from contaminated waters. To attain this aim, sugarcane bagasse was collected then pyrolyzed (+/-NH3 ) in an electric furnace at 200 ̊C for 24 h. Thereafter, the efficiency of each organic product for removal of Pb(II) from a water artificially polluted with Pb(II) (55 mg Pb L -1 ) was tested individually. These hydrochars were added at a rate of 0.25g to purify 500 mL of contaminated water. Throughout the experimental period, water samples were collected periodically at 13 time periods starting from the zero time up to 360 min of contact with 30 min time intervals. Key results indicate that application of hydrochar remarkably diminished soluble Pb(II) concentrations. In this concern, Pb(II) sorption occurred from the beginning of contact with experiment up to 150 min of contact, recording approximately 70% Pb(II) removal efficiency. Thereafter significant increases in soluble Pb(II) occurred, which accounted for about 50% of the sorbed Pb(II) amount. On the other hand, N-doped hydrochar lessened considerably Pb sorption (≈3 folds) and, at the same time, accelerated its desorption. Kinetics of Pb(II) desorption by using both types of hydrochars followed the inverse third-order model. These results supported our main hypothesis, while raises doubts about the feasibility of using hydrochars for successful decontamination of waters polluted with Pb(II). Future perspectives are needed to find out better modifications of hydrochar for effective removal of contaminants from wastewaters and investigate the mechanisms beyond their modes of action. [ABSTRACT FROM AUTHOR]

Hydrochar (HC), a carbon (C)-rich solid material produced using a hydrothermal technique at relatively low temperatures and pressures, has gained little attention regarding its use as a nanocatalyst in multiple wastewater treatment technologies. These HC-based nanocatalysts, catalyst support materials, and nano-adsorbents have the advantage of being cost-effective and chemically stable, having a porous structure, semiconductive properties, and oxygen (O)-rich surface functionality. Laboratory-scale trials that have successfully used HC catalysts to accelerate the kinetics of advanced oxidation processes (AOPs) (photocatalysis, electrochemical oxidation, Fenton catalysis) are here reviewed in depth, with a special focus on the mechanisms involved. The potential of HC catalysts in energy and valuables recovery using anaerobic digestion, bioelectrochemical systems, metal air batteries, transesterification, isomerization, and reforming processes are highlighted. In addition, the synthesis of HC from waste biomass (a zero-cost C precursor) would reduce the cost of expensive electrocatalysts, reduce greenhouse gas (GHG) emissions, ensure C capture, offer a low-C economy with less of a C footprint, and enhance environmental sustainability. This review provides a unique and comprehensive sustainability related perspective on HC and HC-based nanocatalysts that can be used to positively impact the United Nations' Sustainable Development Goals (SDGs), especially SDGs 3, 6, 7, 11, and 13. Finally, a circular economy approach that includes HC and HC catalyst use in wastewater treatment and waste management systems is discussed, along with future perspectives and challenges. [ABSTRACT FROM AUTHOR]

Hydrothermal carbonization (HTC) is recognised as a low temperature and efficient method for the conversion of biomass to solid biofuel. In this study, the effect of process temperature and biomass-to-water ratio (B/W) on the fuel properties of hydrochar produced from wood shavings was investigated. HTC was conducted in an autoclave using reaction temperature of 230 °C and 260 °C for 20 minutes with B/W ratio of 0.11 to 0.43. The produced hydrochars were characterised by the mass yield (MY), higher heating value (HHV), proximate and ultimate properties. The results showed that the properties of the hydrochars improved with increasing process temperature and B/W ratio. The higher heating value (HHV) increased to 26.74 MJ/kg as the severity of the reaction was increased to the process temperature of 260 °C. Also, the atomic H/C and O/C ratios of hydrochars carbonised at 230 °C and 260 °C were closed to the regions of a peat and lignite on the plotted van Krevelen diagram. Hence, the produced hydrochar has a promising potential as a sustainable solid biofuel for energy application.

This work investigates the performance of a Microbial Fuel Cell (MFC) for Acid Mine Drainage (AMD) treatment using bare and hydrochar-doped carbon felt (CF) anodes. Hydrochar was synthesized through hydrothermal carbonization of Spergularia rubra, followed by activation at 500 °C, resulting in improved O/C and H/C ratios of 0.26 and 0.78, respectively. The study reveals that doping CF anodes with non-activated and activated hydrochar significantly enhances copper recovery and electricity generation. The highest copper recovery rate of 16.0 mg/L h−1 was achieved with activated hydrochar-doped CF (CFaH) anodes, followed by 10.6 mg/L h−1 with non-activated hydrochar-doped CF (CFnaH) anodes, and 7.1 mg/L h−1 with bare CF anodes. Hydrochar doping also improved the maximum current density to 0.21 mA cm−2 compared to 0.16 mA cm−2 with bare CF anodes. These results demonstrate the potential of hydrochar-doped CF anodes for efficient metal and energy recovery from AMD, offering a sustainable and energy-efficient alternative to conventional methods. [ABSTRACT FROM AUTHOR]

[Display omitted] • The modification of lignocellulosic-biomass offers a strategy to tailor HTC's surface. • Lignin-derived molecules facilitate the sulfonation mechanism of the HTCs using H 2 SO 4. • Cellulose is vital to the development of carbon–oxygen containing groups on the HTCs. • The –SO 3 H groups enhance the catalytic efficiency of the HTCs in solketal production. The development of strategies targeting the deployment of renewable platforms has consistently garnered global attention, including lignocellulosic-derived methods for the production of hydrochars. Such materials have a versatile application repertoire due to their distinctive surface features. Despite numerous attempts to enhance the surface acidity of lignocellulosic-based hydrochars for catalytic purposes by incorporating sulfur-oxygen and carbon–oxygen functional groups, the specific contributions of each lignocellulosic component to the development of these groups remains unclear. This study elucidates the roles of lignin and cellulose in the formation of −SO 3 H and carbon–oxygen functional groups on the surface of hydrochars. This was achieved by significantly altering the cellulose-to-lignin molar ratio in the herein selected feedstock before subjecting it to the H 2 SO 4 -assisted hydrothermal carbonization process. The findings demonstrated that intermediate phenolic compounds – generated through the depolymerization and hydrolysis of lignin – are highly susceptible to sulfonation, leading to increased functionalization yields with −SO 3 H groups. Conversely, cellulosic-derived furanic intermediates (mainly furfural and 5-hydroxymethylfurfural) enhance the population of carbon–oxygen functional groups, varying in type, nature, and acid strength. The acidic surface features of the hydrochars were successfully validated in the solvent-free acetalization of glycerol with acetone. The concentration of −SO 3 H groups significantly boosted the catalytic performance of the material, achieving nearly full selective conversion of glycerol to solketal within 40 min of reaction, with a turnover frequency as high as 228 h−1 and satisfactory reusability. Therefore, this investigation reveals that lignin primarily facilitates the one-step sulfonation process, while cellulose exclusively contributes to the evolution of carbon–oxygen functionalities on the hydrochars. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hydrochar was first treated by ball milling method as a convenient way. • BM-HC exhibited a superior combined MB removal rate of 95.22 % of MB in 30 min. • Ball milling can produce more furan structure and promote visible light absorption. • Possible removal mechanism and degradation pathway of MB was proposed. • Degradation intermediates of MB had a significant reduction in biotoxicity. In this study, hydrochar (HC) was firstly treated by ball milling for methylene blue (MB) removal through combined adsorption-photodegradation. The ball-milled bamboo hydrochar (BM-HC) exhibited a maximum adsorption capacity of 49.522 mg/g and a synergistic adsorption-photodegradation removal rate of 95.22% within 30 min, which was superior to those of pristine HC (20.530 mg/g, 79.47%). Compared with HC, BM-HC had smaller particle size, increased quantities of polyfuran rings, enhanced adsorption of visible light, which were favorable for the enhancement of adsorption capacity and photodegradation rate. The effect of the catalyst dosage, MB concentration, water matrix, pH, coexisting ions on MB photodegradation were examined. The possible synergistic adsorption and photodegradation mechanism of MB was illustrated. The foremost active specie in the synergistic removal of MB was h+. In addition, the possible degradation pathways of MB were proposed depending on the intermediates detected by Liquid chromatography-mass spectrometry (LC-MS), and the biotoxicity of MB and its intermediates was evaluated by Ecological Structure-Activity Relationship (ECOSAR) program. This work confirms that ball-milled hydrochar could be used as a potential catalyst for pollutants removal in water via synergistic adsorption and photocatalysis. [ABSTRACT FROM AUTHOR]

[Display omitted] • Effective dual-activator modification method for hydrochar was developed. • H 3 PO 4 synergistically promoted K 2 CO 3 activation of hydrochar for high adsorption capacity. • Modified hydrochar has high specific surface area and adsorption efficiency to CBZ. • Prepared hydrochar shows great potential for practical applications in water treatment. The decontamination of trace micropollutants from water environments is a widely concerned issue, and developing green and efficient adsorbent serves as an effective solution. In this study, using dual-activator modification method, an efficient hydrochar adsorbent was prepared through a two-step sequential process combining H 3 PO 4 hydrothermal treatment with K 2 CO 3 pyrolysis activation for carbamazepine (CBZ) adsorption removal. The results indicated that H 3 PO 4 facilitated the K 2 CO 3 activation process. The prepared hydrochar exhibited excellent adsorption properties due to its high specific surface area (1265.08 m2·g−1) and aromatic porous mesh structure, with the maximum and dynamic adsorption capacity for CBZ of 376.11 and 296.98 mg·g−1, respectively. The adsorption mechanism primarily involved pore-filling effects, π-π electron-donor–acceptor (EDA) interactions and hydrophobic interactions. Additionally, the obtained hydrochar material showed high adsorption efficiency for various pollutants and performed well in actual water samples. This study may provide theoretical and technical support for the development and application of high-efficiency hydrochar-based adsorbents. [ABSTRACT FROM AUTHOR]

• Molecular fractionation of HDOM at Fe oxyhydroxides-water interface was investigated. • High Mw, O-rich, aromatic compounds were preferentially absorbed by Fe oxyhydroxides. • Toxicogenomics-based assay was used to evaluate the genotoxicity evolution of HDOM. • Oxidative, membrane, and DNA stresses were primary responses upon exposure to HDOM. • Interface fractionation reduced genotoxicity of HDOM in oxidative and DNA stresses. Adsorption fractionation of dissolved organic matter (DOM) induced by soil minerals is a common geochemical process, which has been widely documented on natural DOM. Hydrochar is a promising functional material in soil remediation but can continuously release abundant endogenic DOM with potential biotoxicity. However, adsorption fractionation at molecular level and its influence on toxicity evolution of hydrochar-derived DOM (HDOM) at genetic level at the soil-water interface remain poorly understood. Herein, we investigated the molecular fractionation of HDOM on three typical soil iron minerals (i.e., ferrihydrite, goethite, and hematite). Results from ultrahigh-resolution mass spectrum showed that HDOM molecules with high molecular weight and high contents of unsaturated oxidized or aromatic structures (e.g., unsaturated phenolic compounds, polyphenols, and organic acids) were preferentially absorbed by iron oxyhydroxides, while aliphatic molecules and poorly oxygenated compounds (e.g., hydrocarbon, phenols, and alcohols) were retained in aqueous phase. Furthermore, we quantitatively evaluated their genotoxicity variation using a toxicogenomics assay using green fluorescence protein-fused whole-cell array, and results showed that oxidative, protein, membrane, and DNA stresses were primary responses upon exposure to original HDOM. Interface fractionation induced by iron oxyhydroxides significantly reduced genotoxicity of HDOM, especially for oxidative, membrane and DNA stresses. Overall, the selective absorption of HDOM molecules by iron oxyhydroxides shifted its biotoxicity, which might change the ecological effects of hydrochar amendment, e.g., microbial community structure, environmental pollutant transformation, and even the ecological function of terrestrial and aquatic ecosystems. These findings would contribute to unraveling the environmental geochemistry process of HDOM in the natural soil-water interface and provide a new insight into the biotoxicity of hydrochar usage to terrestrial and aquatic environments. [Display omitted] [ABSTRACT FROM AUTHOR]

Char materials (e.g., hydrochar) can enhance carbon sequestration, improve soil quality and modulate soil microbial communities to recuperate soil health. However, little is known about the soil organic carbon (SOC) content, as well as the microbial communities and co-occurrence networks in response to hydrochar amendment in an inshore saline soil. Here, the effect of Sesbania cannabina (a halophyte) straw derived hydrochar (SHC) amendment on SOC and labile organic carbon (LOC) fractions and the potential associations among SOC content change, soil C-cycling enzyme activities and microbial communities were illustrated using a pot experiment. SHC effectively improved the contents of SOC and LOC, particularly particulate organic carbon (POC), and stimulated the activities of C-cycling enzymes. Furthermore, SHC induced shift in microbial community compositions and co-occurrence networks, result in decrease in relative abundance of Actinobacteriota and its corresponding ecological cluster, which may favor SOC accumulation. Functional annotation of prokaryotic taxa (FAPROTAX) analysis also revealed a decrease in microbial ecological function related to carbon degradation. These findings provided a deeper insight about the hydrochar-induced SOC enhancement and suggested an efficient approach to improve C sequestration and improve soil health in the coastal salt-affected soil. [Display omitted] • SHC significantly increased SOC content and enzyme activities related to C cycling, modified microbial communities. • SHC decreased ecological cluster composed of Actinobacteriota, which may favor SOC accumulation. • Amendment with hydrochar in coastal salt-affected could enhance C sequestration and soil health. [ABSTRACT FROM AUTHOR]

To address the issues of formaldehyde emission, mildew, and easy combustion of traditional wood adhesives, this paper, for the first time, reported formaldehyde-free plywood bio-adhesives using carbonaceous material (hydrochar) generated from hydrothermal carbonization (HTC) of glucose with or without acrylic acid (AA) and acrylamide (AM). The highest wet shear strength of bio-adhesives (BD-G/AA-180) was 1.32 MPa, which meets the Chinese national standard GB/T 9846-2015 (≥0.7 MPa). It was found that functional groups (–NH 2 and –COOH) were abundant on the surface of hydrochar from co-HTC of glucose with AM or AA. The formation of covalent bonds (between components of bio-adhesives; between bio-adhesives and wood) via dehydration or esterification reaction was a key factor in improving wet shear strength during hot-press treatment. Unlike bio-adhesives developed from polysaccharides and proteins, these hydrochar carbonaceous material-derived bio-adhesives had excellent anti-mildew properties and flame resistance with help from ammonium polyphosphate. This work paves a new road to prepare green formaldehyde-free plywood bio-adhesives. [Display omitted] • Use of glucose hydrochar to prepare bio-adhesives was reported for the first time. • Covalent bonds via dehydration or esterification were key to wet shear strength. • Functional groups on the surface of hydrochar improved bio-adhesive performance. • Hydrochar-based bio-adhesives had excellent anti-mildew properties. [ABSTRACT FROM AUTHOR]

[Display omitted] • Co-HTC significantly improved the hydrochar quality as a solid fuel. • Co-HTC increased the fixed carbon but decreased the ash contents in the hydrochar. • Both HHV and fuel ratio increased as the proportions of rice straw increased. • The hydrochar combustibility index increased by 30% to 419% with co-HTC. • The synergistic effect of co-HTC is more significant at 180 °C and 220 °C. This study assessed the effects of mass mixing ratio and hydrothermal temperature on the co-hydrothermal carbonization (co-HTC) of sewage sludge and rice straw regarding the yield, chemical composition, fuel properties, surface functional groups, and combustion behavior of the hydrochar. The co-HTC increased the hydrochar yield at 180 °C but decreased it at 220 and 260 °C. The co-HTC increased the hydrochar organic matter contents, higher heating values, fuel ratios, and combustion behavior (combustibility index) by 16 % to 63 %, 15 % to 85 %, 51 % to 321 %, and 30 % to 419 %, respectively. The co-HTC also enhanced the formation of oxygen-containing functional groups on the hydrochar surface. The synergistic and anti-synergistic effects of the co-HTC were more positive at 180 and 220 °C but more negative at 260 °C. The co-HTC of municipal sludge and rice straw is promising in converting waste materials into high-quality hydrochar as a clean solid fuel. [ABSTRACT FROM AUTHOR]

The environmental challenges associated with food production can be addressed via the thermochemical upcycling of agro-industrial biomass. Two such methods, hydrothermal carbonization (HTC) and pyrolysis, can be coupled to first reduce the water content of wet biomass wastes by producing a hydrochar (HC) via HTC and then a bio-oil via pyrolysis of the HC. However, HTC of biomass results in the formation of secondary char (SC), an amorphous tar-like mixture resulting from organic compounds released into the aqueous phase that adsorb, recondense and polymerize on the parent biomass. This study investigated how HTC temperature impacts the formation of SC from apple pomace and the SC's subsequent impact on fast pyrolysis products. HCs were produced at temperatures of 175°C, 200°C, and 250°C. Lower HTC temperatures favor the formation of biorefinery platform chemicals such as 5-hydroxymethylfurfural and levulinic acid, while higher temperatures result in increased lignin degradation products (i.e., phenolics). HCs were subjected to fast pyrolysis before and after SC extraction in two analytical pyrolysis instruments. Fast pyrolysis of HC produced compounds similar to those found in SC, but with variations in CO and CO 2 emissions. The combination of SC extraction and fast pyrolysis demonstrates promise for recovering value-added compounds from agro-industrial waste biomass while retaining a solid char for fuel and carbon management. • Identified products of hydrochar fast pyrolysis using py-GC-MS/FID/TCD and py-MBMS. • Secondary char (SC) inhibits pyrolytic reactions on surface of hydrochar. • Char post-SC extraction had increased surface area, more pyrolytic reactions. • SC contains value-added compounds like 5-hydroxymethylfurfural and levulinic acid. [ABSTRACT FROM AUTHOR]

Bioplastics possess the potential to foster a sustainable circular plastic economy, but their end-of-life is still challenging. To sustainably overcome this problem, this work proposes the hydrothermal carbonization (HTC) of residual bioplastics as an alternative green path. The focus is on cellulose acetate - a bioplastic used for eyewear, cigarette filters and other applications - showing the proof of concept and the chemistry behind the conversion, including a reaction kinetics model. HTC of pure and commercial cellulose acetates was assessed under various operating conditions (180-250 °C and 0-6 h), with analyses on the solid and liquid products. Results show the peculiar behavior of these substrates under HTC. At 190-210 °C, the materials almost completely dissolve into the liquid phase, forming 5-hydroxymethylfurfural and organic acids. Above 220 °C, intermediates repolymerize into carbon-rich microspheres (secondary char), achieving solid yields up to 23 %, while itaconic and citric acid form. A comparison with pure substrates and additives demonstrates that the amounts of acetyl groups and derivatives of the plasticizers are crucial in catalyzing HTC reactions, creating a unique environment capable of leading to a total rearrangement of cellulose acetates. HTC can thus represent a cornerstone in establishing a biorefinery for residual cellulose acetate., (© 2024 The Authors. ChemSusChem published by Wiley-VCH GmbH.)