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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 9.41, 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.

In this work, alternative process chains for sewage sludge treatment by hydrothermal carbonization (HTC) and pyrolysis and the subsequent utilization of biochar and hydrochar were investigated by means of a comparative life cycle assessment (LCA). The mono-incineration of sewage sludge was defined as the benchmark process, being the main valorization route in several countries. The results revealed an advantage for HTC compared to pyrolysis and mono-incineration in most environmental impact categories, thanks to the higher char yield and the lower energy request. The global warming potential (GWP) of using hydrochar ranged from −71.4 to 7.7 g CO2-eq. kg−1 sewage sludge. However, the direct material application of the hydrochar in agriculture showed an increased toxicity potential, so that an energy utilization appears to be more environmentally friendly. For the pyrolysis route, a slightly higher energy demand and thus a higher environmental impact was determined, whereby GWP was between −11.7 to 9.1 g CO2-eq. kg−1 sewage sludge. The direct material application of the biochar in agriculture also showed low toxicity potentials while achieving nutrient recycling for phosphorus and a long-term carbon sequestration potential. Overall, ecological advantages were demonstrated for both thermochemical processes, making pyrolysis and HTC promising alternatives for sustainable sludge management.

Hydrothermal carbonization (HTC) is widely recognized as a promising approach for enhancing the fuel properties of agricultural waste. This study investigated the HTC characteristics of corn stalks, focusing on the effect of secondary char (SC) on the fuel properties and pyrolysis behaviors of hydrochars at different temperature and liquid-solid ratio (LSR). Results showed that lower LSR increased the carbon content and higher heating value of hydrochars. Higher temperature strengthened the effect of LSR. At 240 °C, hydrochar yield decreased from 58.56 % to 45.59 % as the LSR increased. The higher LSR enhanced hydrolysis and promoted the transfer of organic components to aqueous phase, thereby facilitating SC formation with a content as high as 12.10 %. The increase in SC was accompanied by larger carbon microspheres and greater deposition coverage, resulting in reduced specific surface area and elevated oxygen-containing functional groups. The covering of SC strengthened the pyrolysis-like reaction of primary char (PC) during HTC (limited by contact with water). These changes influenced subsequent pyrolysis behavior, with PC tending to produce phenols at low LSR but aromatic hydrocarbons at high LSR. This work could enhance the understanding of SC and provide a practical approach combining HTC and extraction to regulate bio-oil preparation by pyrolysis.

The rise in the population and rapid industrialization has resulted in a rise in the global energy consumption. In order to minimize the load on the conventional energy sources, various studies are being conducted for the production of biofuels by hydrothermal operations. Unlike conventional processes of biofuel production, wet biomass can be directly utilised without drying in turn reducing the energy consumption. Feedstocks such as agricultural residue, forest residue, energy crops, algae, sludge, litter and food waste can be utilised for the production of biofuels. The operation intensities (temperature and pressure) can be varied from pressurized hot water to supercritical water. Hydrothermal operations depending on the operating parameters are further subcategorised into four types namely wet torrefaction (WT), hydrothermal carbonization (HTC), hydrothermal liquefaction (HTL) and hydrothermal gasification (HTG). Even though the operating conditions of wet torrefaction and hydrothermal carbonization lie in similar categories, the difference is clearly visible in the level of carbonization. Due to the wide range of operating temperature and pressure, mainly three different products are produced through hydrothermal operations. The temperature range for wet torrefaction can be limited between 150 and 220 °C, whereas the HTC process can be between 200 and 260 °C. At higher temperatures (260 – 370 °C) in hydrothermal liquefaction (HTL), increased isomerization, depolymerization and repolymerization of organic compounds within the biomass occurred, causing liquid product (bio-oil) to be formed as the major product. Hydrothermal gasification can be further subcategorised into three types: namely aqueous phase refining, near critical water gasification and supercritical water gasification (SCWG). This paper has reviewed different hydrothermal operations based on biofuel production from different biomass.

Cattail leaves (CL) have been used as a carbon source to synthesize nanoporous carbon (NPC) support with high surface area (SBET = 2002.12 m2g−1) via hydrothermal carbonization and potassium hydroxide (KOH) activation. The studied catalysts, including monometallic Pd/NPC and Ni/NPC, and bimetallic PdNi/NPC, were synthesized and characterized by using several techniques (e.g., scanning electron microscopy, transmission electron microscopy, nitrogen sorption, Fourier transform infrared spectroscopy, thermogravimetric analysis, and X-ray diffraction). Their catalytic activity toward partial hydrogenation of palm biodiesel to H-FAME was tested, and the liquid product composition, cloud point, and oxidation stability were determined. The studied catalysts have a high porosity with the SBET of approximately 2037.34–2187.96 m2g−1 led to excellent metal dispersion. Although Ni did not show high catalytic activity compared to Pd, Ni incorporated with Pd as PdNi/NPC catalyst significantly increased the cis-C18:1 selectivity and prevented the catalytic deactivation during the partial hydrogenation. The oxidation stability of palm biodiesel feedstock was increased from 13.69 to 17.12 h while the cloud points adversely increased by only 3 degrees from 12 to 15 °C (still lower than 16 °C of the Thai industrial recommendation) with bimetallic PdNi/NPC catalyst. The main benefit of bimetallic PdNi/NPC over monometallic Pd/NPC and Ni/NPC is shown through not only higher C18:2 conversion but also much higher cis-to-trans ratio of C18:1 resulting in higher oxidation stability with acceptable compromise on the cloud point increasing. Consequently, the produced palm H-FAME can be used at a high blend ratio.

Nanoporous carbon (NPC) has gained significant attention in wastewater treatment due to its effectiveness. The adsorption process, known for its simplicity, stability, and cost-effectiveness, is widely recognized as an efficient method for removing carbamazepine (CBZ) residues accumulate in the environment. However, the application of NPC is often hindered by challenges in the regeneration process after use, as well as issues related to large surface area, pore size, and functional groups. Fortunately, the samples in this study not only maintained their adsorption efficiency but also demonstrated the ability to be regenerated multiple times. Herein brewery waste was subjected to hydrothermal treatment at 200 °C for 1 h and followed by KOH and NaCl activation with different KOH:NaCl (w/w) ratios of 5:0, 4:1, 3:2, 1:1, 2:3, 1:4, and 0:5 to optimize the properties of malt husk derived nanoporous carbon (NPC). The optimal condition KOH:NaCl ratio of 1:1 had a maximum specific surface area of 906 m2/g with a total pore volume of 0.252 cm3/g. According to the adsorption test, the CBZ adsorption isotherm was well-fitted to the Langmuir model (R2 = 0.976) kinetic data were consistent with the pseudo-second-order model (R2 = 0.995). This suggests that the adsorption mechanism involves monolayer adsorption and chemisorption interaction. The Gibbs free energy and enthalpy of CBZ adsorption by NPC were found to be spontaneous and endothermic. The regeneration test revealed a 95.35% decrease in the adsorption capacity of NPC after 5 repeated cycles. Consequently, the study suggests a potential application of nanoporous carbon from MH as an alternative adsorbent for removing carbamazepine in wastewater.

Recently, it has been critical to effectively remove oxytetracycline (OTC) from aquaculture wastewater before releasing into the environment. The adsorption process is recognized as an efficient pathway for removing OTC since it is a simple, stable, and cost-effective method. This study aims to develop nanoporous carbon entirely from shrimp waste (SW) via hydrothermal carbonization assisted with KOH activation. Existing KOH significantly increases the porosity of SW nanoporous carbon. The optimal SW porous carbon was obtained using 5 wt%KOH for activation, which had the largest surface area of 679.51 m2/g with the total pore volume of 0.458 cm3/g. Moreover, the SW porous carbon with the highest porosity was selected for the OTC adsorption. The Langmuir isotherm model and the pseudo-second-order kinetic model match the experimental data, implying that the adsorption mechanism is mono-layered adsorption due to micropores by chemisorption interaction. The adsorption capacity significantly improved by increasing the dosage of SW nanoporous carbon. The SW nanoporous carbon adsorption for OTC is primarily regulated by pore filling affected by hydrogen bonding, and π-π* interaction also plays a significant role. The SW nanoporous carbon showed an efficient OTC adsorption after 5 regeneration cycles. This work demonstrates biomass waste recycling and emphasizes the potential of aquatic food processing waste-derived nanoporous carbon for antibiotic adsorption.

In this study, CO2 capture using Hydrochar adsorbents synthesized from Cigarette Filter, specifically H-208 and HA-204, was rigorously investigated. Optimization using RSM was applied to fit a quadratic model to the data with F-value of 184.95 and R2 of 0.9847. H-208 and HA-204 display maximum CO2 adsorption capacities of 1028.35 mg/g and 1003.35 mg/g, respectively, at 9 bar and 25 °C. Isotherm studies ranked Freundlich and Sips models as effective descriptors, highlighting differences in adsorption behavior between HCs synthesized at different conditions. Kinetic modeling identified the Elovich model as suitable for predicting time-dependent CO2 adsorption. Thermodynamic analysis revealed differences in adsorbent affinity and spontaneity between HCs, with higher enthalpy values for H-208 indicating stronger adsorbent-adsorbate interactions. ΔH° values of −61.863 kJ/mol for H-208 and -47.442 kJ/mol for HA-204, signifying an exothermic adsorption process. The CO2 adsorption mechanism involves physical and chemical processes influenced by the polar structure, surface area, and functional groups of HCs. The effect of HCl on CO2 adsorption is insignificant, and the use of HCl only reduces the synthesis time. Adsorbent reusability tests showed minor capacity declines over multiple cycles, indicating their potential in environmental remediation and industrial gas separation processes.

Thermochemical conversion technologies are emerging as preferred resource recovery practices for managing animal manure in agricultural regions. Although the implementation of such technologies has been previously studied, difficulties exist in maintaining balance between high rate of resource recovery and low environmental, economic, and social impacts, particularly in rural regions with limited resources. We developed a data-driven framework by integrating machine learning with life cycle thinking that can be used as an open-source tool to help overcome these barriers. The framework was applied to compare two emerging technologies: pyrolysis versus hydrothermal carbonization for managing the excess poultry litter in a rural agricultural region. Among different machine learning models, random forest regression was the most successful to predict resource recovery of both technologies. Next, sustainability analysis indicated that the environmental (global warming), economic (annual worth), and social (system intrusiveness) impacts of pyrolysis was lower than hydrothermal carbonization. Finally, the framework revealed that implementation of pyrolysis at 600 °C for 1 h with the heating rate of 20 °C/min would result in the highest rate of resource recovery that corresponded to the lowest impacts. These results can be helpful in providing operational conditions for implementing emerging resource recovery technologies in rural agricultural regions.

Oil palm trunk (OPT) is a solid residue discharged from palm-oil upstream industry, with high potential as a feedstock for solid fuel production. However, its high moisture content and low energy density causes the limitation of utilization. In this research, hydrothermal carbonization (HTC) was applied to upgrade OPT. Effect of different reaction temperature and residence time on thermal characteristics and combustion behaviors of hydrochar obtained from HTC were investigated. OPT gradually converted into hydrochar with higher carbon content and heating values. The proximate and ultimate analyses indicated that fuel properties of hydrochars enhanced by increasing HTC temperature and residence time. The high heating values (HHV) increased by 7.18% at 180 °C, 30 min and reached up to 48% at 240 °C, 60 min. Meanwhile, combustion behaviors of hydrochars based on thermogravimetric analysis (TGA) were examined. The results showed that hydrochars had a higher ignition temperature than that of the raw OPT, leading to a more stable combustion. Furthermore, slagging and fouling problems were greatly minimized owing to the removal of a significant portion of alkaline remained in OPT, especially potassium (66% removal) and calcium (48% removal). The results revealed that OPT is of great potential as a solid fuel employing HTC process.

Excessive phosphorus load to surface water is undesirable since it can cause eutrophication. In this study, three different pyrolyzed hydrochars from corn stover were synthesized by applying hydrothermal carbonization (HTC) at 260 °C and then eventual pyrolysis at 400°, 600°, and 800 °C, respectively, and finally were used for phosphorus removal from aqueous solution. By linking the physicochemical properties of these pyrolyzed hydrochars investigated here, we tried to comprehend the effect of HTC and pyrolysis temperature on the hydrochar structure and phosphorus adsorption. Results show that high pyrolysis temperatures (600 °C and 800 °C) enhanced the hydrochar's phosphorus adsorption compared to low pyrolysis temperature (400 °C). HTC260P800 type hydrochar showed a fast phosphorus adsorption kinetics, while the HTC260P600 showed an overall high adsorption capacity, with the maximum phosphate adsorption capacity of 5090 mg/kg calculated using isotherm model. Three different adsorption isotherm models (Langmuir, Fruendlich, and Redlich-Peterson) were used to fit the isotherm data; among them, the Redlich-Peterson isotherm model fit the data best for all three hydrochars. pH was found to be a critical factor in terms of phosphorus removal, and the optimum pH was found to be 5, probably due to the enhanced electrostatic interaction between positively charged hydrochar and negatively charged phosphate ions. The desorption experiment showed that a small fraction of the adsorbed phosphate (15.6 % to 24.4 %) was released from the spent hydrochar samples, which might be due to the strong attachment of phosphate ions to the sorption sites. Reusing the spent pyrolyzed hydrochar showed lower phosphate adsorption capacity than the fresh ones, ranging from 423 mg/kg to 903 mg/kg.

In this research, organic waste was subjected to hydrothermal carbonization (HTC) using faecal sludge as the water source. HTC is a sustainable method for converting organic waste into valuable hydrochar. However, the use of portable water as a reaction medium in HTC is environmentally unsustainable and increases operational costs. The aim of this study was to optimize HTC operating parameters such as residence time, temperature, and biomass to water (BTW) ratio for maximizing both higher heating value (HHV) and hydrochar yield and also to determine the effects of these operating parameters on the hydrochar properties. This study utilized a Box Behnken design within the response surface methodology to identify optimal HTC conditions. Temperature was varied between 180 and 250 °C, residence time between 30 min and 120 min, and BTW ratio between 1 and 10. Volatile matter percentage was reduced in the hydrochar compared to that of the feedstock. A progressive rise in carbon percentage and a decline in oxygen percentage were observed with increasing temperatures. Temperature and residence time were the most significant factors affecting HHV, on the other hand, temperature and BTW ratio were the most significant factors that affected hydrochar yield. Numerical optimization of the factors revealed that a maximum HHV of 28.409 MJ/kg was obtained at 250 °C, 116 min, and a 1:9 BTW ratio, while an ideal hydrochar yield of 57.491% was obtained at 242 °C, 95 min and a BTW ratio of 1:9. This study highlights the environmental sustainability of utilizing faecal sludge as a water source in HTC, presenting a promising possibility for transforming organic waste into valuable hydrochar while addressing concerns related to water use.

The significant rise in plastic consumption and waste generation, coupled with the urgent need for sustainable energy solutions, has led to innovative research seeking to convert plastic waste into valuable resources. This review focuses on the application of hydrothermal carbonization as a promising technique for transforming plastic waste into valuable products. It highlights the suitability of hydrothermal carbonization for plastic waste conversion, and presents recent reports showing promising results, prospects, and a range of potential hydrochar applications, including solid recovered fuels, catalysts, direct carbon fuel cells and supercapacitors. This review further presents the challenges in utilizing plastic hydrochar across different applications, which include feedstock variability, contamination, scalability, material properties, and environmental considerations. The need for optimized synthesis methods, stable performance, and long-term sustainability is also emphasized. The critical evaluation of the applications of hydrothermal carbonization can contribute to advancing sustainable waste management and renewable energy production.

The production of gel from Aloe vera plants is an emerging industry, however the residual leaves are considered waste and are not utilized. The purpose of this work was to prepare hydrochars from Aloe vera leaves under different conditions, and determine the fate of macro- and micronutrients in the solid products, in view of developing a novel biofertilizer. In this framework, distilled water, citric acid and potassium hydroxide solutions were used as feedwaters and the experiments were performed at the temperatures of 180 and 220 °C and treatment times of 1 – 8 h. All obtained hydrochars had increased Ca and P contents compared to the feedstock, whereas the highest Ca and P concentration of 10.4% and 7382 mg kg−1, respectively, were achieved under alkaline conditions after 8 h of treatment. Citric acid promoted carbonization, achieving H/C = 1.11, O/C = 0.34 of the hydrochar obtained at 220 °C after 8 h of treatment. The use of KOH counterbalanced the production of acids from the degradation of the biomass, thus restricting the carbonization progress. The metals K, Fe, Cu and Mg showed high solubilization tendencies, however their concentrations on the hydrochars increased beyond the 4 h treatments due to precipitation and re-sorption phenomena. The N content in the hydrochars ranged between 0.56 – 1.12%, increasing with temperature and time due to the formation and precipitation of pyridine, pyrroline and pyrrolidine derivatives. Overall, due to the high ash content, low pH and increased Ca and P concentrations, the hydrochars may be suitable as substrates for the development of bio-fertilizers purposed for alkaline soils.

Hydrothermal carbonization is an innovative method of sewage sludge disposal. The solid product hydrochar (c.a.10%), may be converted to a fuel or fertilizer. Gaseous products (less than 10%) are mainly CO2 and nitrogen, but c.a. 80% of post-processing liquid presents as a challenging issue due to its high toxicity. Therefore, the main aim of this study was to determine the potentiality of hydrochars derived from sewage sludge as a fuel, at two temperatures: 200 and 220 °C, and 2 h of residence time, and successfully utilize the filtrates after the implementation of an adequate purification process. The results of hydrochars depicted better energy properties and dewaterability than in the case of raw sewage sludge, including improved chemical composition, a higher fixed carbon content and fuel ratio, and it also gained more effective filtration. The comprehensive analysis of the Thermal Analysis data proved that hydrochar can be combusted, but based on X-ray Fluorescence data a high tendency to slagging and contamination is expected. The highly toxic processing liquids indicated a great need for an appropriate treatment. Accordingly, distillation and the preliminary study of wet oxidation processes were applied. In both methods the chemical oxygen demand, an indicator of organic pollution, was significantly reduced.

The utilization of biomass and bio-waste, particularly through hydrothermal processes, has shown promise as a technology for converting these materials into valuable products. While most research has traditionally focused on the solid and liquid byproducts of these hydrothermal treatments, the gaseous phase has often been overlooked. This study specifically investigates the conversion of off-gases produced during hydrothermal carbonation (HTC) into synthetic natural gas, offering a readily marketable product with economic potential. Although the methanation of conventional flue gases has been extensively studied, dealing with non-standard off-gases from processes like HTC presents challenges due to the presence of minor impurities like CO and CH4. This novel research seeks to experimentally evaluate the methanation of HTC off-gases using nickel-based catalysts and analyze how these impurities affect the catalytic performance. The studied catalysts include nickel supported by ceria and alumina, as well as alumina supported nickel-cobalt systems. The results demonstrate that these catalysts exhibit high CO2 conversion and CH4 selectivity under ideal gas conditions. However, when real gas compositions with impurities are considered, CO2 conversion decreases at lower temperatures (ca. 20% lower conversion for real gas vs. ideal), probably due to side reactions such as CH4 cracking. This difference becomes less pronounced at higher temperatures. Nevertheless, the catalysts perform satisfactorily, especially at temperatures exceeding 350 °C. In conclusion, this study sheds light on the methanation of HTC off-gases and underscores the significance of understanding how impurities in real gases impact the process, providing potential directions for future research.

Reducing CO2 emissions from cement production can be achieved by incorporating carbonaceous materials as partial replacements for traditional cement. However, the effects of these particles on cement composites are not fully understood. This study explores the potential of hydrothermally carbonized nanospheres (HCN) obtained through green synthesis from discarded pomegranate peel as a partial replacement for cement. HCN were added to cement using two mixing techniques: dry mixing and wet mixing in four dosages: 0.1 %, 0.25 %, 0.5 %, and 1 % by weight, replacing cement. The study investigated the impact of both HCN dosages and mixing techniques on the 7- and 28-day properties of the cement composites. Workability improved for all samples while density decreased upto 6.67 % after 7 days and upto ≅ 5 % after 28 days. Wet-mixed samples showed significant increases in flexural strength after 7 days, with the HCN0.1 %W sample showing a 37.18 % increase, while the dry-mixed HCN1 %D sample showed a 25.34 % increase. There was a reduction in compressive strength for all samples, but it remained within a comparable range, with a significant increase from 7 to 28 days, reaching up to 70.93 % for the HCN0.5 %W sample. Overall, HCN has the potential to significantly affect the properties of cement composites even at very low doses, however, it should be properly optimized to enhance the properties of the cement composite as well as contribute to sustainability.

An efficient carbon material was prepared using hydrothermal carbonization of birch-wood chips in the water under elevated pressure, subsequent chemical activation, and doping with nitrogen. The obtained catalyst had a large specific surface area of 2431 m2 g−1 and a high nitrogen content of 4.60 at.%. Most of the nitrogen was in the pyridinic-N (57.61 at.%) form. The synthesized material exhibits excellent electro-catalytic activity for the oxygen reduction reaction with an onset potential of 0.9 V versus the reversible hydrogen electrode, showing the 4e− electrons transfer path in 0.1 M KOH solution.

Hydrothermal carbonization (HTC) has been established as one of the most promising techniques for producing biofuels from high moisture containing organic samples such as, biomass. However, limited progress is observed in terms of the kinetic modeling of this process. Existing kinetic models involve mechanistic and experimental shortcomings due to the nature of the non-isothermal and isothermal subsequent steps involved in the process. To address these limitations, a distributed activation energy model (DAEM) was applied to predict HTC kinetics of lignocellulosic biomass. The DAEM considered the non-isothermal temperature profile of the reactor to account for the considerable devolatilization taking place during the transient step of heating. A micro-kinetic reactor was fabricated to facilitate kinetic experiments to estimate the DAEM parameters- mean activation energy, standard deviation, and pre-exponential factor. These parameters were found to be 96.03 kJ mol−1, 3 kJ mol−1, and 5 × 108 s − 1 respectively, based on experiments at final HTC temperatures of 190 °C and 210 °C for lignocellulosic biomass. Furthermore, the parameters were used to accurately predict HTC kinetics at 230 °C using the estimated parameters at 190 °C and 210 °C. The obtained results would be valuable inputs for reactor design and large-scale simulations for HTC of lignocellulosic biomass.

Anaerobic digestion presents a viable approach for managing biodegradable waste. However, the process generates a significant amount of digestate, which, if not appropriately managed, can contribute to eutrophication and salinization. This research explores the integration of hydrothermal carbonization (HTC) and pyrolysis as a potential solution for digestate management, emphasizing volume reduction and energy recovery. The study specifically focuses on the production of biochar from agricultural waste digestate (AWD) in an energy-efficient manner. Utilizing HTC as a pretreatment was found to enhance the heating value of both the AWD and the subsequent pyrolytic char, and it also improved the carbonization degree of the resulting char. Energy balance analysis revealed that the pyrolysis of AWD shifted from an endothermic to an exothermic reaction upon HTC pretreatment. This transition decreased the reaction's energy absorption from 41.1 to 1557.6 MJ to an energy release of 685.1 to 960.6 MJ per ton of digestate, thereby optimizing energy consumption in digestate management. Additionally, it was noted that using acetone as a solvent in gas chromatography for biooil samples with high ammonia content led to the formation of diacetonamine, an outcome that is deemed undesirable.

Carbocatalysts doped with heteroatoms such as nitrogen or sulphur have been reported to be useful in persulfate-based advanced oxidation processes for organic pollutant removal. However, there is limited research on the effect of doping with phosphorus atoms on degradation performance. In this work, a new nitrogen and phosphorus-doped carbocatalyst (N, P-HC) was designed using hydrothermal carbonization followed by pyrolysis at 700 °C, with olive pomace as a carbon source, to degrade organic pollutants in the presence of peroxydisulfate (PDS). Experimental results showed that N, P-HC, with its large specific surface area (871.73 m2.g−1), high content of N-pyridinic and N-pyrrolic groups, and the presence of P-O-C and O-P-C bonds, exhibited high degradation performance (98% degradation of Rhodamine B (RhB) in 40 min, with an apparent rate constant (kapp) of 0.055 min−1 and an excellent turnover frequency (TOF) of 0.275 min−1). Quenching study and EPR analysis revealed that singlet oxygen generation (1O2) and direct electron transfer were the main reaction pathways for the non-radical pathway in the degradation of RhB. The improved catalytic efficiency in the N, P-HC/PDS/RhB system can be attributed to the synergistic effect between N and P atoms in the graphitic structure of the carbocatalyst, its high surface area, and the presence of oxygenated functional groups on the surface of the N, P-HC. The used N, P-HC carbocatalyst can also be efficiently recovered by heat treatment at 500 °C. Overall, this study presents a simple and environmentally friendly method for synthesizing a high-performance N, P co-doped olive pomace-based carbocatalyst for water decontamination through PS-AOPs processes.

This study investigated the hydrochar-based porous carbon prepared by combining the technical route of hydrothermal carbonization (HTC) + chemical activation. The hydrochar morphology was adjusted by changing the activation reaction conditions and adding metal salts. Experiments showed that the activation of KHCO3 significantly increased the specific surface area and pore size of the hydrochar. Besides, oxygen-rich groups on the surface of the activated hydrochar interacted with heavy metal ions to achieve efficient adsorption. The activated hydrothermal carbon adsorption capacity for Pb2+ and Cd2+ ions reached 289 and 186 mg/g, respectively. The adsorption mechanism study indicated that the adsorption of Pb2+ and Cd2+ was related to electrostatic attraction, ion exchange, and complexation reactions. The “HTC + chemical activation” technology was environmentally friendly and effectively implemented antibiotic residues. Carbon materials with high adsorption capacity can be prepared so that biomass resources can be utilized with excessive value, as a consequence presenting technical assistance for the comprehensive disposal of organic waste in the pharmaceutical industry and establishing a green and clean production system.

Active packaging is essential for reducing food quality loss and ensuring consumer safety. Recently, carbon dots, synthesized from agricultural bio-wastes, have been used as active nanofillers. Mango peels, generally discarded as waste, can serve as potential precursor for synthesis of carbon dots. Mango peel carbon dots (MPCD) were prepared and characterized. Characteristics of active film based on chitosan (CS)/fish gelatin (FG) blend incorporated with MPCD at different concentrations (1, 3, and 5 wt%) were investigated. MPCD with augmenting concentrations enhanced mechanical properties of CS/FG film. Film containing 5 % MPCD had 15 % higher tensile strength than the control (without MPCD). The film containing MPCD showed the improved antioxidant activity, antimicrobial and UV barrier properties. The pouch (5 × 5 cm 2 ) made from film added with 5 % MPCD via heat sealing was used for packaging minced pork. Minced pork packed in the pouch showed lower bacterial growth (below 6 log CFU/g) and chemical changes than that packed in polyethylene pouch during 15 days of storage at 4 °C. Therefore, the conversion of mango peel into valuable carbon dots promotes a zero-waste sustainable approach in line with the biocircular economy. Active pouch could be employed as novel biodegradable active and green packaging for the food industry., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Graphite carbon (G) @ silver (Ag) @ porous silicon Bragg mirror (PSB) composite SERS substrate was successfully synthesized using electrochemical etching (ec) and hydrothermal carbonization (HTC) techniques with silver nitrate as the source of silver and glucose as the source of carbon. The PSB was used as a functional scaffold for the synthesis of graphite-carbon and silver composite nanoparticles (G@AgNPs) on its surface, thereby combining SERS activity and antioxidant properties. To our knowledge, this is the first time that G@AgNPs has been synthesized on the PSB using glucose as a carbon source. The synthesized G@Ag@PSB was utilized as a SERS platform for the detection of gallic acid (GA). Test results demonstrated that the substrate exhibited a remarkable SERS enhancement capability for GA, with the enhancement factor (EF) reaching 2 × 10 5 . The reproducibility of the SERS spectral signal was excellent, with a relative standard deviation (RSD) of 7.5 %. The sensitivity test results showed that the linear range of GA detection based on G@Ag@PSB composite SERS substrate was 2 × 10 -3 -2 × 10 -12 M. The relationship between GA concentration and SERS signal intensity exhibited a strong linear correlation, with a linear correlation coefficient (R 2 ) of 0.97634. Moreover, even with an extended storage period, only a marginal decline in the signal intensity of GA on the substrate was observed. The results of this study demonstrate that the prepared G@Ag@PSB composite SERS substrate had good potential application performance as a low-cost SERS detection platform suitable for commercial use. In addition, this advance facilitates the further exploration of more nanomaterials with ultra-high sensitivity in SERS technology., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier B.V.)

Carbon quantum dots (CQDs) are receiving increasing attention due to their tunable redox activity, abundant surface functional groups, and excellent aqueous dispersion. However, their low quantum yield remains a significant impediment to their synthesis and practical application. In the present work, cellulose nanocrystals (CNCs) were utilized as precursors for the optimized hydrothermal synthesis of CQDs. Subsequently, the synthesized CQDs were electrodeposited onto a carbon-coated surface. The influence of hydrothermal temperature and time on the quantum yield and electrochemical properties of CQDs was systematically explored. The successfully synthesized CQDs exhibited an average particle size of approximately 5 nm. The quantum yield was enhanced from 14.35 % to 23.7 % as the hydrothermal temperature increased from 180 °C to 230 °C. Additionally, the electrochemical properties of the composite films were investigated. Electrochemical assessments demonstrated an increase in specific capacitance from 60.4 mF·cm -2 to 65.2 mF·cm -2 with an elevation in temperature from 180 °C to 210 °C. Remarkably, the CQDs displayed higher energy density (8.819 mWh·cm -2 ) and power density (1800 mW·cm -2 ) at 210 °C for 8 h. This work offers a scalable approach for the efficient production of high-performance CQDs, showcasing their substantial potential for supercapacitor applications., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

This work explores the effects of amending a loamy sand soil with hydrochars having different physicochemcial characteristics. The effects of different hydrochars on emissions of the greenhouse gases nitrous oxide (N2O) and carbon dioxide (CO2) were investigated together with the relationship between the hydrochar's mineral nitrogen content and the soil microbial biomass. Soil samples were amended with eleven different hydrochars and feedstocks having different carbon and nitrogen contents at application rates of 5 t ha−1 and 25 t ha−1. Microbial immobilization was the main mineral nitrogen sink in soil following hydrochar application. Moreover, the processing conditions applied during hydrochar production (i.e., the pyrolysis temperature and residence time) had significant effects on N2O and CO2 emissions: treatment with incubated hydrochars yielded significantly lower N2O emissions than treatment with non-carbonized feedstocks, particularly at the highest level of hydrochar application (25 t ha−1). Further analysis revealed that increasing the process temperature and residence time during hdyrochar production significantly increased the final product's total organic carbon content but reduced its content of hot water extractable carbon. Hydrochars produced with higher process temperatures and longer residence times therefore yielded lower CO2 emissions during a 44-day incubation experiment than raw feedstocks or hydrochars produced under less severe conditions. Hydrochars formed from sewage sludge at high process temperatures and with long residence times are thus promising soil additives for reducing GHG emissions.

We hypothesized that the morphology of the hydrochar from hydrothermal carbonization of glucose would be affected by Fe2+; and indeed, with such ions, large pieces of hydrochar formed that comprised aggregated spherical particles and blue and thin films. Thin carbonized films formed at the bottom of the autoclave liners or on TeflonTM tape used as a template. Free-standing films could be prepared by stretching the TeflonTM tape after the synthesis. The carbonized films that formed at the bottom of the autoclave adhered to spherical hydrochar particles. The blueness was ascribed to thin-film interference under white-light irradiation and related to the film thickness, which was about 200 nm. Analysis of transmission electron microscopy (TEM) images showed that the films consisted of a layered amorphous carbon. The amorphous and thin films were more carbonized than the amorphous carbon of the TEM grid, as derived via electron energy loss spectroscopy (EELS). Additional analysis of one of the thin films by X-ray photoelectron spectral analysis showed a higher carbon fraction than for bulk hydrochar, supporting the EELS analysis. We believe that the synthesis of thin films of hydrochar can open up new colloidal processing pathways, which could be useful in the preparation of carbon-based materials and alike.

In this work, simulated food waste (15% white bread, 15% palm dates (without seeds), 5% boiled egg (without shells), 20% spent tea leaves, 20% spent coffee ground, and 25% banana peel in parts weight) was subjected to hydrothermal carbonization (HTC) at 180, 200 and 220 °C for 120 min. The mass yield and energy yield of the resultant hydrochars viz. HTC180, HTC200, and HTC220 were 69.46, 68.50, 65.35% and 88.91, 87.68, 84.30%, respectively. Among the hydrochars produced, HTC220 had the highest heating value (HHV: 23.61 MJ/kg), while the food waste had a HHV of 18.17 MJ/kg. Activation energy for the combustion of food waste and HTC220 was determined by modelling the thermogravimetric data using the Arrhenius equation and was found to be in the range of 29.98 to 33.51 kJ/mol and 16.52 to 25.47 kJ/mol, respectively. The densification ratio for the three hydrochar samples varied slightly (1.28–1.29). The results indicate that the hydrochar produced from food waste could be a potential to substitute coal combustion.

Industrial wastewater effluent containing dyes and hazardous waste, such as olive waste, pose serious threat to health and environment. This work investigated the removal of azo and non-azo dyes from a single and binary aqueous system using hydrochar produced from hazardous olive waste using hydrothermal carbonization (HTC). Optimisation suggested hydrochar obtained at 250°C (HC-9) exhibited best physiochemical, structural properties and around 300% increase in carboxylic and carbonyl groups indicated by nuclear magnetic resonance spectroscopy. HC-9 removed ∼100% of Methylene blue and Congo red in single (120 and 180 min) and binary system (60 min), respectively. Ex situ X-ray photon electron spectroscopy and surface area analysis after adsorption suggested chemisorption supported by pseudo-second order reaction, Langmuir, and Redlich-Peterson model. HC-9 exhibited around 80% reusability in three adsorption cycles. Thus, better working efficiency of our hydrochar in the complex wastewater make it a potential candidate to be employed in commercial plants.

Treatment of swine manure by hydrothermal carbonization (HTC) with the aid of different surfactants was first explored in this study. PEG 400 (polyethylene glycol 400) and Tween 80 facilitated the formation of bio-oil. SLS (sodium lignosulfonate) and SDS (sodium dodecyl sulfate) promoted the formation of water-soluble matters/gases. Span 80 enhanced the formation of hydrochar, which resulted in a 50.19 % mass yield, 92.39 % energy yield, and a caloric value of 28.68 MJ/kg. The hydrochar obtained with Span 80 presented a similar combustion performance to raw swine manure and the best pyrolysis performance. The use of Span 80 promoted the transfer of degradation products to hydrochar, especially hydrophobic ester and ketone compounds. Notedly, Span 80 suppressed the synthesis of PAHs during the HTC process, which was reduced to 0.92 mg/kg. Furthermore, the hydrochar produced with Span 80 contained lower contents of heavy metals. On the whole, Span 80 has shown great potential in enhancing the HTC of swine manure. The acting mechanisms of surfactants in the HTC of swine manure included adsorption, dispersion, and electrostatics repulsion., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Hydrothermal carbonization (HTC) of single plastic polymers such as polyethylene terephthalate (PET) and polystyrene (PS) has not yet been explored on a large scale, particularly their thermal behavior, chemical transformations under subcritical conditions, and the energy properties of the resultant hydrochar. This study investigated these aspects by employing techniques, such as thermogravimetric analysis (TGA), Fourier transformed infrared spectroscopy (FTIR), elemental and calorific analysis. The results show that PET hydrochar has a superior energy densification (1.37) and energy yield (89 %) compared to PS hydrochar (1.13, 54 %). Hydrothermal carbonization modifies the chemical structure of the polymers by increasing the number of carbonyl groups (CO) in PET and forming new ones in PS, and by enhancing hydroxyl groups (OH) in PET while retaining them in PS. Both materials preserve their aromatic and aliphatic structures, with the introduction of alkenes groups (CC) in the PET hydrochar. PET hydrochar begins to decompose at lower temperatures (150-270 °C) than PS hydrochar (242-283 °C) but reaches higher peak temperatures (420-585 °C vs. 390-470 °C), with both types achieving similar burnout temperatures (650-800 °C). PET hydrochar recorded a higher activation energy (121-126 kJ/mol) than PS hydrochar (67-74 kJ/mol) with the Mampel first-order reaction model as the best fit., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

In this study, Ethinylestradiol was removed from aqueous solution (maximum removal 83.1%) by hydrothermally carbonized and steam activated carbon adsorbent prepared from palm kernel shells. The effects of varying adsorbent mass, pH, temperature and concentration of Ethinylestradiol on adsorption were studied. It was found that pseudo second order kinetic model is able to describe well the adsorption of Ethinylestradiol. Thermodynamic studies showed that the adsorption process was mainly chemisorption as the calculated activation energy for adsorption was 60.4 KJmol−1. Adsorption was considered to take place between the functional groups on the adsorbent and those on the Ethinylestradiol molecule. The characterization showed that adsorbent was mesoporous with specific surface area of 320 m2g−1, it had several oxygen-containing functional groups, and defects in its graphitic structure (ID/IG ratio ∼ 2.2).Novelty statement: High carbonization temperatures (300°C - 600°C) followed by high-temperature steam activation (600°C - 1000°C) have been used to prepare carbon adsorbents over the past decades. In this work, the novelty lies on lower processing temperatures. Hydrothermal carbonization realized at 200°C and following steam activation at 500°C will produce an efficient carbon adsorbent, which is shown in this study. The lower carbonization-activation temperatures produce adsorbents with higher amount of functional groups beneficial to adsorption, and decreases energy costs of the production.

Using aquatic biomass as a solid fuel is limited by its low energy density, low lignin content and high moisture content. This study investigated upgrading aquatic biomass as a solid fuel using hydrothermal carbonization with temperatures in the moderate temperatures range for a reaction time of 30 min. Thermogravimetric analysis (TGA) tests were used to study the combustion behavior of the raw aquatic biomass and its derived hydrochar during the combustion process. Chemical composition analysis indicated that compared to the raw aquatic biomass, the fuel quality of the derived hydrochar had been improved by increasing the carbon contents with a substantial decrease in the volatile matter and ash content. Furthermore, higher fuel quality of the derived hydrochar was observed with increasing hydrothermal temperature. Similarly, based on the TGA test, the hydrochars had increased ignition temperatures, higher combustion temperatures and higher burnout temperatures compared to the raw aquatic biomass. The combustion characteristic index values for all hydrochar samples derived from water hyacinth and cattail leaves were appropriate for combustion.

Rapid population growth and urbanization have led to the generation of huge quantities of municipal solid waste (MSW) in urban areas. The organic fraction of municipal solid waste (OFMSW) represents up to 57 % of the municipal waste generated globally. In the context of accomplishing a bio-based circular economy, resource recovery from OFMSW has become a necessity. This study describes the different technologies that are practically used to recover valuable resources (e.g., bio-oil, biochar, biomethane) from OFMSW, such as anaerobic digestion, composting, hydrothermal carbonization, pyrolysis and landfilling. However, for the successful implementation of these technologies under the local conditions, it is a pre-requisite that these technologies also meet the regulatory requirements and get support and commitment from the national and local governments.

The organic matter molecular mechanism by which combined hydrothermal carbonization (co-HTC) of municipal sludge (MS) and agricultural wastes (rice husk, spent mushroom substrate, and wheat straw) reduces the inhibitory effects of aqueous phase (AP) products on pak choi (Brassica campestris L.) growth compared to HTC of MS alone is not clear. Fourier-transform ion cyclotron resonance mass spectrometry was used to characterize the differences in organic matter at the molecular level between AP from MS HTC alone (AP-MS) and AP from co-HTC of MS and agricultural waste (co-Aps). The results showed that N-bearing molecules of AP-MS and co-Aps account for 70.6 % and 54.2 %-64.1 % of all molecules, respectively. Lignins were present in the highest proportion (56.3 %-78.5 %) in all APs, followed by proteins and lipids. The dry weight of co-APs hydroponically grown pak choi was 31.6 %-47.6 % higher than that of the AP-MS. Molecules that were poorly saturated and with low aromaticity were preferentially consumed during hydroponic treatment. Molecules present before and after hydroponics were defined as resistant molecules; molecules present before hydroponics but absent after hydroponics were defined as removed molecules; and molecules absent before hydroponics but present after hydroponics were defined as produced molecules. Large lignin molecules were broken down into more unsaturated molecules, but lignins were the most commonly resistant, removed, and produced molecules. Correlation analysis revealed that N- or S-bearing molecules were phytotoxic in the AP. Tannins positively influenced the growth of pak choi. These results provide new insights into potential implementation strategies for liquid fertilizers produced from AP arising from HTC of MS and agricultural wastes., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

This study employed hydrothermal carbonization (HTC) in conjunction with ZnCl 2 activation and pyrolysis to produce biochar from one traditional Chinese medicine astragali radix (AR) residue. The resultant biochar was evaluated as a sustainable adsorbent for tetracycline (TC) elimination from water. The adsorption performance of TC on two micropore-rich AR biochars, AR@ZnCl 2 (1370 m 2  g -1 ) and HAR@ZnCl 2 (1896 m 2  g -1 ), was comprehensively evaluated using adsorption isotherms, kinetics, and thermodynamics. By virtue of pore diffusion, π-π interaction, electrostatic attraction, and hydrogen bonding, the prepared AR biochar showed exceptional adsorption properties for TC. Notably, the maximum adsorption capacity (930.3 mg g -1 ) of TC on HAR@ZnCl 2 can be achieved when the adsorbent dosage is 0.5 g L -1 and C 0 is 500 mg L -1  at 323 K. The TC adsorption on HAR@ZnCl 2 took place spontaneously. Furthermore, the impact of competitive ions behavior is insignificant when coexisting ion concentrations fall within the 10-100 mg L -1 range. Additionally, the produced biochar illustrated good economic benefits, with a payback of 701 $ t -1 . More importantly, even after ten cycles, HAR@ZnCl 2 still presented great TC removal efficiency (above 77%), suggesting a good application prosperity. In summary, the effectiveness and sustainability of AR biochar, a biowaste-derived product, were demonstrated in its ability to remove antibiotics from water, showing great potential in wastewater treatment application., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Inc.)

Recycling of aqueous phase (AP) as a by-product after hydrothermal carbonization (HTC) of sewage sludge (SS) has been of interest. The combination of magnesium ammonium phosphate (MAP) or the so-called struvite crystallization and aqueous phase (AP) recirculation has great potential for resource recovery and hydrochar enhancement. In this study, both the aqueous phase of HTC after MAP recovery of NH 4 + -N (AP-MAP) and the untreated aqueous phase of HTC (AP-HTC) were reused for HTC of fresh SS, and both aqueous phases were recycled four times. The effects of the two AP cycles on the properties of AP and hydrochar at 200, 230, and 260 °C were studied, and the effect of temperature on the two AP cycles was similar. The hydrochar produced by the AP-MAP cycle had lower nitrogen content than that of the AP-HTC cycle due to the low ammonia nitrogen (NH 4 + -N) content, and the combustion performance was improved. MAP recovery reduces the accumulation of NH 4 + -N in the AP cycle and MAP is also a high-quality fertilizer. Therefore, the combination of MAP recovery and AP recycling provides a feasible technical approach for resource utilization, eutrophic AP treatment, and production of high-quality hydrochar in the HTC process of SS., Competing Interests: Declaration of competing interest We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted., (Copyright © 2024. Published by Elsevier B.V.)

Livestock manure is often contaminated with heavy metals (HMs) and HM resistance genes (HMRGs), which pollute the environment. In this study, we aimed to investigate the effects of the aqueous phase (AP) produced by hydrothermal carbonization (HTC) of sewage sludge (SS) alone and the AP produced by co-HTC of rice husk (RH) and SS (RH-SS) on humification, HM bioavailability, and HMRGs during chicken manure composting. RH-SS and SS increased the humic acid content of the compost products by 18.3 % and 9.7 %, respectively, and significantly increased the humification index (P < 0.05) compared to the CK (addition of tap water). The passivation of HMs (Zn, Cu, As, Pb, and Cr) increased by 12.17-23.36 % and 9.74-15.95 % for RH-SS and SS, respectively, compared with that for CK. RH-SS and SS reduced the HMRG abundance in composted products by 22.29 % and 15.07 %, respectively. The partial least squares path modeling results showed that SS and RH-SS promoted compost humification while simultaneously altering the bacterial community and reducing the bioavailability of metals and host abundance of HMRGs, which has a direct inhibitory effect on the production and distribution of HMRGs. These findings support a new strategy to reduce the environmental risk of HMs and HMRGs in livestock manure utilization., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Hydrothermal carbonization process water (HTPW) has been utilized as a substitute for chemical fertilizers in agricultural applications. However, the input of HTPW into paddy water, particularly the significant proportion of dissolved organic matter (DOM) in HTPW (DOM-HTPW), directly engages in photochemical transformations, a phenomenon often overlooked. This study observed a consistent decrease in humification (SUVA 280 , 7.7-53.9%) and aromaticity (SUVA 254 , 6.1-40.0%) of DOM-HTPW after irradiation. The primary active photobleaching components of DOM-HTPW varied depending on the feedstock, such as protein for chicken manure DOM-HTPW and lignin for rice straw DOM-HTPW. The photochemical activity of DOM-HTPW was augmented by its lower molecular weight and higher hydrophilic composition, particularly evident in chicken manure DOM-HTPW, which exhibited higher generation rates for 1 O 2 (35.1-37.1%), 3 DOM* (32.8-43.9%), and O 2 •- (28.6-48.8%) as measured by molecular probes. DOM-HTPW effectively facilitated the phototransformation of tetracycline, with the contribution of O 2 •- being more significant than 3 DOM* and 1 O 2 . These findings shed new light on the understanding the photochemical processes of DOM-HTPW as exogenous DOM and the interconnected fate of contaminants in aquatic environments., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Hydrothermal carbonization may be a sustainable sanitary treatment for wet organic waste including human excreta. Human-excreta-derived hydrochar properties differ from those of typical wet biomass due to the formation of a biocrude-like phase at low reaction temperatures. This study characterized the importance of this phase in terms of hydrochar combustion properties and potential agricultural use. Hydrothermal carbonization of raw human excreta was undertaken at 180, 210, and 240 °C, after which the biocrude phase was extracted with dichloromethane. Physicochemical properties, surface-area parameters, combustion profiles, and gas emissions of non-extracted hydrochar, biocrude, and extracted hydrochar were compared. The potential agricultural use of extracted hydrochar was assessed in germination experiments. Biocrude comprised up to 49.5% of hydrochar mass with a calorific value of >60% that of extracted hydrochar. Biocrude combustion properties were better than those of hydrochar, before and after extraction as demonstrated by higher combustion index value (S i ). The extracted hydrochar surface area (34.7 m 2  g -1 ) was greater than that of non-extracted hydrochar (<2 m 2  g -1 ), and seeds germinated more readily due to the lower phytotoxin content. Most macro and micronutrients required for plant growth were retained in the extracted hydrochar. The extraction of biocrude from human-excreta-derived hydrochar not only provided a higher-quality fuel with enhanced combustion properties but also improved hydrochar characteristics, suggesting its potential as a soil additive for enhanced plant growth., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Hydrothermal carbonization (HTC) is a promising alternative to transform biomass waste into a solid carbonaceous material (hydrochar) and a process water with potential for material and energy recovery. In this study, two alternatives for process water treatment by conventional and acid-assisted HTC of swine manure are discussed. Process water from conventional HTC at 180 °C showed high biodegradability (55% COD removal) and methane production (∼290 mL STP CH 4 g -1 COD added ) and the treatment in an upflow anaerobic sludge blanket reactor allowed obtaining a high methane production yield (1.3 L CH 4 L -1 d -1 ) and COD removal (∼70%). The analysis of the microbiota showed a high concentration of Synergistota and Firmicutes phyla, with high degradation of organic nitrogen-containing organic compounds. Acid-assisted HTC proved to be a viable option for nutrient recovery (migration of 83% of the P to the process water), which allowed obtaining a solid salt by chemical precipitation with Mg(OH) 2 (NPK of 4/4/0.4) and MgCl 2 (NPK 8/17/0.5), with a negligible content of heavy metals. The characteristics of the precipitated solid complied with the requirements of European Regulation (2019)/1009 for fertilizers and amendments in agricultural soils, being a suitable alternative for the recycling of nutrients from wastes., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

Phosphorus (P) loss caused by the irrational use of manure organic fertilizer has become a worldwide environmental problem, which has caused a potential threat to water safety and intensified agricultural non-point source pollution. Hydrothermal carbonization is method with a low-energy consumption and high efficiency to deal with environmental problems. Application of pig manure-derived hydrochar (PMH) to soil exhibited potential of sustainable development compared with the pristine pig manure (PM). However, the effects of PMH on the distribution of P among the fractions/forms and the interaction between microorganisms and P forms and its relevance to the potential loss of P in paddy fields has not been clarified. Therefore, in this study, a soil column experiment was conducted using the untreated soil (control), and the PM, PMH1 (PMH derived at 180 °C), and PMH2 (PMH derived at 260 °C) treated soils (at the dose of 0.05 %) and rice was cultivated to investigate the effects of PM and PMH on the P fractions, mobilization, ad potential loss via the induced changes on soil microbial community after a complete growing season of rice. The trend of P utilization was evaluated by P speciation via continuous extraction and 31 P NMR. The addition of PMH reduced the proportion of residual P in soil by 23.8-26.3 %, and increased the proportion of HCl-P and orthophosphate by 116.2-158.6 % and 6.1-6.8 % compared to PM. The abundance of gcd gene developed after the application of PMH2, which enhanced the mobile forms of soil P utilization via secreting gluconic acid. The network diagram analysis concluded that the changes in various P forms were mainly related to Proteobacteria, Bacteroides, Firmicutes and Acidobacteria. The results illustrated that PMH mitigate the potential risk of P loss more than PM by altering P fractions and affecting soil microbial community., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Hydrothermal carbonization (HTC) is considered a promising technology for biomass waste management without pre-drying. This study explores the potential for swine manure management by comparing batch and continuous processes, emphasizing the benefits of the continuous mode, particularly for its potential full-scale application. The continuous process at low temperature (180 °C) resulted in a hydrochar with a lower degree of carbonization compared to the batch process, but similar characteristics were found in both hydrochars at higher operating temperatures (230-250 °C), such as C content (∼ 52 wt%), fixed carbon (∼ 24 wt%) and higher calorific value (21 MJ kg -1 ). Thermogravimetric and combustion analyses showed that hydrochars exhibited characteristics suitable as solid biofuels for industrial use. The process water showed a high content of organic matter as soluble chemical oxygen demand (7-22 g L -1 ) and total organic carbon (4-10 g L -1 ), although a high amount of refractory species such as N- and O-containing long aromatic compounds were detected in the process water from the batch process, while the process water from the continuous process presented more easily biodegradable compounds such as acids and alcohols, among others. The longer time required to reach operating temperature in the case of the batch system (longer heating time to reach operating temperature) resulted in lower H/C and O/C ratios compared to hydrochar from the continuous process. This indicates that the dehydration and decarboxylation reactions of the feedstock play a more important role in the batch process. This study shows the efficiency of the continuous process to obtain carbonaceous materials suitable for use as biofuel, providing a solution for swine manure management., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)

Converting industrial sludge into catalytic materials for water purification is a promising approach to simultaneously realize effective disposal of sludge and resource of water. However, manipulating the high efficiency remains a huge challenge due to the difficulty in the active sites control of the sludge. Herein, we proposed a constitutive modulation strategy by the combination of hydrothermal and pyrolysis (HTP) for the fabrication of defects-assistant Fe containing sludge-derived carbon catalysts on upgrading performance in peroxymonosulfate (PMS) activation for pollutant degradation. Adjustable defects on dyeing sludge-derived carbon catalysts (DSCC) were achieved by introducing oxygen or nitrogen functional precursors (hydroquinone or p-phenylenediamine) during hydrothermal processes and by further pyrolysis, where O was detrimental while N was beneficial to defect generation. Compared to the DSCC with less defects (DHSC-O), the defect-rich sample (DHSC-2N) exhibited superior catalytic performance of PMS activation for bisphenol A (BPA) elimination (k = 0.45 min -1 , 2.52 times of DHSC-O), as well as 81.4% total organic carbon (TOC) removal. Meanwhile, the degradation capacity was verified in wide pH range (2.1-8.1) and various aqueous matrices, reflecting the excellent adaptability and anti-interference performance. Furthermore, the continuous-flow experiments on industrial wastewater showed synchronous BPA and chemical oxygen demand (COD) removal, implying great potential for practical application. Solid electron paramagnetic resonance (EPR) and 57 Fe Mösssbauer spectra analysis indicated that the defects acted as secondary active sites for Fe sites, which were beneficial to accelerating the electron transfer process. The only Fe active sites preferred the radical pathway. The controllable reaction tendency provides possibilities for the on-demand design of sludge-based catalysts to meet the requirements of practical wastewater treatment under Fenton-like reaction., Competing Interests: Declaration of competing interest The authors declare no competing financial interest., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Polyvinyl chloride (PVC) waste plastic is a typical solid waste. In this paper, the dechlorination and carbonization behavior of PVC in ethanol-water/water system under different process parameters (temperature, residence time, solid-liquid ratio) was studied, and hydrothermal carbon was characterized by SEM, elemental analysis, TG-DTG, XPS, Py-GC/MS. The results show that temperature is the key to the hydrothermal dechlorination of PVC, and the dechlorination efficiency of PVC is the highest by parameter optimization (220°C-90 min-10% S/D-80% E/D), which can reach 96.33 %. With the removal of Cl, the surface of the PVC matrix changed from full and smooth flocculent to honeycomb with uniform pore size distribution. Thermogravimetric analysis shows that the combustion of hydrochar can be divided into three stages: HCl precipitation and volatile combustion, semi-coke and coke combustion, and fixed carbon combustion. The combustion parameters and kinetic parameters of hydrochar were measured, and it was found that the hydrothermal carbonization of PVC at higher temperatures and ethanol-water ratio could improve the combustion performance of hydrochar. The highest calorific value can reach 36.68 MJ/mol. Py-GC/MS analyzed the distribution of the pyrolysis products, and alkylbenzene and aliphatic were the main products of pyrolysis. The structural analysis of hydrochar showed that C-C and CC accounted for the largest proportion, accompanied by a small amount of C-O and CO and trace C-Cl. The possible reaction mechanism of the hydrothermal carbonization of PVC was analyzed based on the distribution of functional groups and compound composition. This work provides an effective and sustainable method for the recycling of refractory chlorinated plastics., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Hydrothermal carbonization (HTC) was used to convert macrophyte Potamogeton lucens into solid biofuel-hydrochar. HTC was carried out in a high pressure reactor with and without chemical additives under subcritical temperatures (240–320 °C), residence times (10–40 min) and biomass to water dilution ratios varying from 1:4 to 1:12. Hydrochar produced in HTC with chemical additives viz. KOH, Na2CO3 and acetic acid had improvement in higher heating value (HHV) and energy density (Ed) in comparison to non-additive HTC from level of sub-bituminous coal to bituminous coal. As reflected by Van Krevelen diagram, HTC with additives had also improvement in H/C and O/C atomic ratios. Enhancement in HHV by utilization of additives followed order; acetic acid > Na2CO3 > KOH. Hydrochar yield of 39% obtained in non additive process decreased to 36% (both with KOH, Na2CO3) and 37% (with acetic acid). However at same time Ed was enhanced from a value of 1.69 in non-additive HTC to 1.72, 1.76 and 1.84 with KOH, Na2CO3 and acetic acid respectively. The hydrochar produced has thus huge potential to serve as an alternate fuel. The study also expresses yield (Y), HHV, Ed and energy yield (Ey) in terms of temperature, residence time and biomass to water dilution ratio by linear and nonlinear laws.

Herein, a novel N, S co-doped porous carbon (S5C5-AC) for Cr(VI) removal was prepared by co-hydrothermal carbonization (HTC) of sewage sludge (SS) and low-rank coal (LC) combining with KOH modification. The results showed that S5C5-AC had excellent adsorption performance on Cr(VI), and lower pH value, higher initial concentration and longer contact time were beneficial for Cr(VI) adsorption. The adsorption kinetics and isotherms revealed that Cr(VI) adsorption by S5C5-AC was homogeneous and dominated by chemisorption. The adsorption isotherm showed that the maximum equilibrium adsorption capacity of S5C5-AC for Cr(VI) was 382.04 mg/g at 25 °C. Furthermore, the results showed that the main mechanisms for Cr(VI) removal were the pore filling, electrostatic interaction and reduction. Moreover, the electron transfer mechanism during the adsorption and reduction process was further explored at the molecular and electronic levels by density functional theory (DFT) and front orbital theory (FOT) simulations. The analysis of DFT and FOT indicated that the synergistic effect between S and N functional groups was exhibited during the Cr(VI) removal process. Considering the existence of synergistic effects between N and S functional groups during adsorption, the S and N content and form were modified collaboratively. Increasing the relative content of pyrrolic N may be the most effective pathway for improving removal performance. Besides that, S5C5-AC exhibited excellent adsorption capacity over a high coexisting ion concentration range and various actual water bodies and regeneration performance, which indicated that S5C5-AC had promising potential for the remediation of wastewater in industrial applications., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)