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Magnetic biochar (MBC) has drawn great attention as a versatile catalyst for advanced oxidation elimination of pollutants from aqueous solution with synergy of iron species and carbon matrix. Herein, an MBC was manufactured by oxidative hydrothermal carbonization employing potassium ferrate as precursor and internal oxidant for Fenton-like degradation of phenols in aqueous solution. This unique oxidative hydrothermal carbonization allowed multiple iron species to be introduced with persistent free radicals (PFRs), providing diverse catalysis sites for activating H 2 O 2 into reactive oxygen species (ROSs) for efficient degradation of phenols. Moreover, graphite structure was generated with abundant oxygen functional groups, benefiting to accelerating Fe3+/Fe2+ cycle by electron shuttle and transfer. The catalysis degradation efficiency was up to 99.74 % with 44.4 % of total organic carbon (TOC) removal rate for 75 mg L−1 of phenol using 0.2 g L−1 MBC dosage. Satisfactory recyclability was achieved for the MBC as the catalysis degradation efficiency slightly decreased from 99.74 % to 87.95 % after five times recycling. Moreover, the MBC catalysis system exhibited extensive applicability in real water matrices and for degradation of different phenols with high efficiency. Serving as a demonstration of oxidized magnetic biochar for efficient Fenton-like degradation of phenols, this work highlighted the great potential of oxidative hydrothermal carbonization in preparation of high performance magnetic biochar. [Display omitted] • Multiple catalysis sites were introduced for activating H 2 O 2 into diverse ROSs. • Diverse active redox sites facilitated Fe3+/Fe2+ cycle. • Iron oxides and carbon matrix simultaneously boosted the Fenton-like degradation. • High catalytic activity was achieved with superior recyclability. • Adsorption of degradation intermediates also contributed to removal of TOC. [ABSTRACT FROM AUTHOR]

Hydrothermal carbonization (HTC) of untreated sewage sludge with high water content was evaluated as an alternative to usual wastewater treatment. This bold approach allowed bioproducts useful as biofuel and nutrient sources to be obtained directly from raw sludge. HTC experiments were performed in a scalable arrangement composed of a 10-liter high-pressure reactor. The influence of the experimental conditions, including temperature (180–220°C), reaction time (60–120 min), and pH (6.5–12.0), was evaluated on nutrients and heavy metal distribution through the liquid phase by a 23 central composite design with a triple central point. The bioproducts were characterized by a set of six analytical techniques, and the results were refined by statistical procedures (Principal Component Analysis, Response Surface Methodology, and Sensitivity Analysis). pH is a variable that impacts bioproducts' characteristics, making it a guiding factor for application. Basic pH promotes transfer of components from solid to liquid phase, while natural pH favors the heating value of hydrochars. Liquid phase is a carbon- and nitrogen-rich source that can be useful for plant nutrition, mainly due to the increase of ammonia nitrogen from 20.6 to 51.7 wt% under pH 6.5, and an expressive decrease of chemical oxygen demand from 32 to 6–16 mgO 2 L−1. The hydrochar is a renewable solid fuel, reaching up to 12.43 MJ kg−1 under pH 6.5; the basic pH favored an increase in the O/C ratio and lower HHV values. HTC of primary sewage sludge can replace steps of a conventional treatment station and promotes treated wastewater reuse. [Display omitted] • HTC technology of raw sewage sludge was evaluated in a 10-liter high-pressure reactor. • The liquid phase is a source of water and nitrogen with potential for plant nutrition. • Results reinforce waste management and expands the waste-to-energy concept. • This approach can replace one or more steps in a conventional WWTP. [ABSTRACT FROM AUTHOR]

The exploration of catalyst preparation techniques that incorporate environmental-friendly methodologies has consistently been the focus of scientific inquiry within the field of green synthesis of oxygen-containing organic chemicals. Herein, a metal-free hydrothermal carbonation carbon (HTCC) has been prepared utilizing cyanobacterial biomass produced during a water bloom in a freshwater lake. The HTCC produced is capable of performing photocatalytic selective oxidation of cyclohexane to cyclohexanol and cyclohexanone (KA oil) under ambient conditions. The use of cyanobacterial biomass allows for the efficient preparation of HTCC, which exhibits a conversion rate of cyclohexane that is 4.1 times of HTCC prepared with alternative carbon sources (glucose). The selectivity to KA oil over the samples are almost 100 %. Characterizations and analysis reveal that cyanobacteria can lead to self-doping of nitrogen and hydrophobicity of the resulting HTCC, while sulfuric acid etching endow it with more photoactive sp2 hybridized structure units that contribute to a higher photogenerated carrier separation efficiency. The suitable band structure enables the cyanobacterial HTCC to produce superoxide radicals to oxidize cyclohexane. These findings are of great significance for the development of eco-friendly photocatalysts and the utilization of biomass resources. [Display omitted] • Cyanobacterial waste biomass derived hydrothermal carbonization carbon (HTCC). • Photocatalytic aerobic oxidation of cyclohexane at room temperature with air. • Nearly 100 % selectivity of cyclohexanol and cyclohexanone (KA oil). [ABSTRACT FROM AUTHOR]

Hydrothermal carbonization is a widely recognized process for converting biomass into biomass charcoal, aimed at reducing and replacing the use of natural resources while also mitigating CO 2 emissions responsible for global warming. However, the complexity of the hydrothermal carbonization process presents challenges in elucidating the interplay of different features. Thus, this study employs extreme gradient boosting machine learning algorithm to predict the values of six target outputs namely; yield, calorific value, ash, carbon, hydrogen, and oxygen content of hydrochar. Notably, the study leverages a rich dataset comprising over 1000 data points and 16 input features. The results indicate high correlations, with R2 ranging from 0.84 to 0.97. Furthermore, the study investigates the impact of input features on all six outputs through the application of Shapley values and SHAP dependence plot techniques, highlighting its novelty and contribution to the field. • Machine learning model predicted six outputs for hydrothermal carbonization. • XGB model offered high accuracy with R2 of 0.84–0.97 using 16 input features. • Shapley values and SHAP dependence plot offered insight into HTC of biomass. [ABSTRACT FROM AUTHOR]

Heavy metal pollution is a severe environmental challenge, posing significant threats to ecosystems and human health. Heavy metals like cadmium, lead, and mercury can disrupt food chains and degrade soil and water quality at high concentrations, impacting ecological balance. For human health, heavy metal pollution can cause chronic poisoning and increase cancer risks. Thus, developing rapid and sensitive detection techniques for heavy metal ions is crucial. Electrochemical techniques, compared to traditional methods, offer high selectivity, fast analysis, simplicity, and cost-effectiveness. Biomass-derived carbon material-modified electrodes, with their low cost and high sensitivity, are widely applied in heavy metal ion detection. This review summarizes three primary green synthesis methods for carbon materials: hydrothermal carbonization, pyrolytic carbonization, and sol-gel synthesis. It explores how factors in green synthesis influence the structure and performance of biomass carbon in detecting heavy metal ions, guiding the development of rapid, highly sensitive, and selective electrochemical detection techniques. [Display omitted] • Summarizes three eco-friendly, cost-effective methods for metal ion detection. • Green-synthesized biomass carbon significantly boosts metal ion detection sensitivity. • Doping and composites enhance biomass carbon performance in sensing applications. • Discusses real-world uses and future trends in large-scale, eco-friendly production. [ABSTRACT FROM AUTHOR]

Rational utilization of waste biomass is an important renewable energy alternative to address environmental issues caused by fossil fuels and climate change. Hydrothermal carbonization can improve the quality of municipal sewage sludge (SS) fuel by reducing water content, removing chlorine, and increasing energy density. This paper proposes an in-situ steam gasification method for syngas production. The influences of original water vapor content of hydrochar (0–30 %); hydrothermal conditions including severity factor (SF), fungus–bran mixing ratio (FBMR), and the proportion of citric acid mixed promoting agent (CAPA); and gasification temperature (700–900°C) on the composition of syngas. The effects of pure hydrochar gasification and mixed gasification on syngas composition were examined. Response surface methodology was used to optimize and maximize the higher heating value (HHV) of syngas. In addition, life cycle assessment was used to evaluate the environmental impact of the wet hydrochar gasification process. The vapor atmosphere generated automatically by heating wet hydrochar promoted steam reforming and water-gas shift reactions, driving them towards hydrogen production. Excess steam consumed a large amount of energy, leading to decreased reactor temperature, which in turn reduced gasification reaction activity and production of various gas components. As the SF increased, the syngas yield tended to decrease and the gasification reaction index decreased. Conversely, as the FBMR increased, the contents of all syngas components increased, along with the gasification reaction index. Additionally, as the gasification temperature increased, the HHV of the syngas increased. The quality of the syngas produced by mixed gasification was significantly better than that produced by pure hydrochar gasification. Compared to the syngas from the gasification of dry SS hydrochar, the HHV of the syngas from wet SS hydrochar increased by 4.4 %. At optimal conditions of SF 0.1, FBMR 20 %, and CAPA 20 %, the HHV of the syngas from wet hydrochar gasification increased by 28.1 %. Under these optimal conditions generated the highest quality syngas; at a gasification temperature of 900℃, the environmental impact was minimal. The lower quality of syngas and economic costs of drying hydrochar are considered disadvantages of traditional dry hydrochar gasification. However, the high-quality syngas produced from wet hydrochar in this study addressed these issues, laying a solid foundation for future industrial scale applications. [Display omitted] • The effect of moisture content of hydrochar on gasification behavior was studied. • The gasification effect of mixed raw materials is better than that of co-hydrochar. • The response surface optimization results in higher HHV of syngas. • The life cycle assessment evaluates the environmental impact of the process. [ABSTRACT FROM AUTHOR]

Crop straw containing abundant carbohydrates and metals is regarded as an ideal precursor for preparing hydrothermal carbonization carbon (HTCC)-based photocatalysts, but the inherent role of native metals on the photocatalytic performance of HTCC remains unclear. Herein, HTCC derived from corn straw (HTCS) catalyzed by native trace metals was prepared by a green hydrothermal process for photocatalytic removal of antibiotics. Sulfamethoxazole (SMX) degradation kinetic constant (k) over HTCS was 5.4 times that of g-C 3 N 4. The results showed the native Ca (0.56%), Mn (0.023%) and Fe (0.055%) in corn straw should catalyze the formation of HTCS, and then promote the photocatalytic SMX removal over HTCS. Pure carbohydrate experiments certified that the Mn and Ca additions could modify the structure of HTCC. More surface C O formation and furan rings polymerization originated by Ca and Mn catalysis in hydrothermal process. Surface C O provided electron-deficient connection sites for SMX to form HTCS-SMX complex, and then complex was excited under visible light illumination to transfer electrons from SMX's HOMO to CB of HTCS. Ploymerized furan rings promoted electron transfer in the process. This work provides a green conversion way from waste (agriculture residue) to treasure (efficient carbon-based materials) for water purification. [Display omitted] • The promotion role of native trace metals (Ca, Fe and Mn) on photocatalytic performance was discovered. • The HTCS exhibited attractive performance for photocatalytic degradation of SMX. • The native Ca and Mn catalyzed the hydrothermal carbonization and promoted formation of O and polymerized furan rings. • This work provides a green conversion way from agriculture residues to efficient carbon based materials for water purification. [ABSTRACT FROM AUTHOR]

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

Hydrothermal carbonization (HTC) of polyvinyl chloride (PVC) to produce high-value-added hydrochars as a solid fuel alternative can play a pivotal role in carbon sequestration and energy supply. However, there is unclear for the interaction mechanism and combustion performance of co-hydrochars derived from PVC waste and biomass. In this study, waste PVC mats (PVCM) mixed with wheat straw (WS) were as feedstocks to prepare the co-hydrochars by the acid-catalyzed co-HTC at different hydrothermal temperatures and mass ratios. The presence of WS enhanced the PVCM substitution and prevented the condensation of the PVCM-derived hydrochar aggregation. In turn, PVCM played a stimulative role in the WS decomposition. Meanwhile, the interactions were improved sufficiently in the acidic mediums. The fuel properties and combustion behavior of co-hydrochars were elevated by valid interactions between PVCM and WS. The co-hydrochar obtained using co-HTC at a mass ratio of 1:1 under 240 °C (HC-240–1:1) exhibited the optimal higher heating value (32.72 MJ/kg), splendid dechlorination efficiency (97.41%) as well as worthy fuel ratio (0.89). The combustion process of HC-240–1:1 was more facile and consistent as a result of the elevated ignition and burnout temperatures along with reduced activation energies. Furthermore, the liquid phase products were recycled to assess the reusability. The process water expedited the process of co-HTC, which was confirmed by the improved HHV (32.72 MJ/kg to 39.71 MJ/kg) and mass yield (30.73% to 32.44%). The strategy of PVC waste mixed with biomass through the acid-catalyzed co-HTC was considered a promising way to produce environmentally friendly solid fuels, providing some theoretical basis for the commercialization of co-HTC. [Display omitted] • PVC mats and wheat straw upgraded to solid fuel via acid-catalyzed co-HTC. • The interaction mechanism between feedstocks to form co-hydrochar was proposed. • Impurities in PVC mats impacted the combustion behavior of co-hydrochars. • Process water recycling strategy enhanced environmental benefits. [ABSTRACT FROM AUTHOR]

A novel approach for porous carbon fabrication from microalgae is presented for efficient CO 2 capture. Microalgae-derived hydrochar is produced through deep eutectic solvent-assisted hydrothermal carbonization (DES-HTC), followed by chemical activation to obtain N, O dual-doped ultra-microporous carbon. The finalized carbon exhibited high nitrogen content (3.92%), oxygen content (21.46%), and ultra-micropore volume (0.25 cm3/g). Subsequently, it exhibited excellent CO 2 adsorption capacity (4.37 mmol/g) and CO 2 /N 2 selectivity (32) at 25 °C and 1 bar. Equilibrium and in-situ FTIR spectra of CO 2 adsorption substantiated that the synergy between the abundant oxygen and nitrogen functional groups and the ample ultra-micropores significantly enhanced the capacity. Characterization of hydrochar indicated that the addition of DES during HTC effectively accelerated the Maillard reaction, facilitating the insertion of nitrogen and oxygen atoms into the carbon matrix and reducing their loss in subsequent chemical activation. Furthermore, DES was found to increase thermally unstable oxygen functional groups during HTC, promoting in ultra-micropore formation during activation. These findings provide a framework for advancing microalgae-based carbon materials in CO 2 capture applications. [Display omitted] • DES-HTC produced N, O dual-doped carbon from microalgae for CO 2 capture. • Excellent CO 2 adsorption performance due to high N, O content, ultra-micropore. • Characterization of hydrochar revealed N, O insertion during DES-HTC. • DES-HTC promoted ultra-micropore formation during chemical activation. • Microalgae-derived porous carbon has potential for sustainable carbon capture. [ABSTRACT FROM AUTHOR]

Carbon quantum dots (CQDs) are highly promising fluorescent nanomaterials with a wide range of applications. This study presented a novel, clean, hydrothermal carbonization (HTC) method for synthesizing fluorescent CQDs from sludge. A response surface design method was employed to optimize synthesis conditions, resulting in CQDs with excellent fluorescence properties. They were excited at 320 nm and emitted blue fluorescence at 450 nm under UV light. A mechanism for the formation of CQDs from sludge during HTC was proposed and revealed that the CQDs had an aromatic polymer structure with abundant oxygen-containing groups. X-ray photoelectron spectroscopy confirmed N and Fe doping of CQDs, which significantly improved their fluorescence properties. Additionally, a fluorescence quenching analysis showed that the CQDs selectively detected Pb2+ in the aqueous phase, indicating their potential application in Pb2+ detection. The photoinduced electron transfer (PET) arising from amino groups and other reductive functional groups has been shown to align with the quenching mechanism during the detection of Pb2+ by CQDs. This study provided a cost-effective and scalable approach that could be used to produce CQDs for the in situ detection of Pb2+ in wastewater. [Display omitted] • CQDS was extracted as a by-product of sludge HTC. • Aromatic polymer structure of CQDs derived from hydrolysis products of sludge. • CQDs effectively doped with N and Fe to selectively detect Pb2+ in wastewater. • The quenching mechanism was analyzed by FT-ICR MS. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The organic fraction of municipal solid waste was converted into advanced hydrochar. • Phytotoxic property of hydrochar was eliminated by thermal treatment below 300 °C. • Advanced hydrochar is produced in a zero waste process. • Undesired compounds are valorized directly providing energy for the process. • Gas chromatography allows fast, rough evaluation of the phytotoxicity of hydrochar. Abstract Unlike biochars, hydrochars often have initial phytotoxic effects that prevent their being directly applied to soil, an undesirable property thought to be due to the volatile organic compounds they contain. Thermal treatment in the 200–600 °C temperature range was proposed for mitigation purposes and it was shown that at a temperature of 275 °C phytotoxicity is eliminated from the carbonaceous solids. The phytotoxic property was "recovered" or maintained in the separated liquid, which can be used to generate heat in the HTC process, thereby achieving the safe disposal of harmful compounds at no additional cost. The post-treatment unlocks the potential of transforming the organic fraction of municipal solid waste into a soil amendment product in a zero-waste process. The absence of phytotoxicity was confirmed by the Zucconi method on seed germination. A gas-chromatographic method was also developed, based on the quantification of the total amount of substances detected by desorption, for a rough but quick estimation of hydrochar phytotoxicity. It was shown that the absence of these volatile compounds is in line with the absence of phytotoxicity as evaluated by the Zucconi method. [ABSTRACT FROM AUTHOR]

Abstract Peatlands represent a valuable global carbon store and are critical for preserving biodiversity. In order to reduce peat mining a significant effort is made to search for substitutes of peat in its different uses. Organic products obtained by hydrothermal carbonization processes could fully or partially replace peat in growing media if they possess some suitable properties. The study focused on the properties of a hydrochar produced from wheat (HTC) and included its chemical characterization and stability estimates using microbial respiration and nitrogen mineralization essays. As inhibition to seed germination could significantly restrict the eventual use of HTC in growing media, a number of seed germination trials were carried out to reveal the magnitude of phytotoxicity in relation to sphagnum peat and biochar and the effect that some simple and low-cost pre-conditioning treatments have on the rate of germination. This rate was greatly increased by simply wetting the material a few days prior to use or by mixing it with compost. It was shown that the positive effect on seedling emergence should be attributed, at least partly, to the degradation by microorganisms of toxic substances presumably produced during carbonization. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Carbon-supported Fe catalysts from sewage sludge were used for CWPO of BmimAc. • Catalyst prepared by chemical activation showed high porosity and Fe dispersion. • Catalyst synthetized by hydrothermal carbonization showed low activity. • Chemical activated catalyst was active and stable with negligible Fe leaching. Abstract The stability of two carbon-supported Fe catalysts in the catalytic wet peroxide oxidation (CWPO) of 1-Butyl-3-methylimidazolium acetate (BmimAc) was examined. One catalyst (Fe/AS) was obtained by chemical activation of dried sewage sludge with iron chloride at a FeCl 3 :sewage sludge mass ratio of 3 and the other (Fe/HTCS) by hydrothermal carbonization of the sludge in the presence of FeCl 3 at a mass ratio of also 3. Fe/AS catalyst exhibited a well-developed porosity, whereas Fe/HTCS one did not show porosity. The carbon content was high in both catalysts, with a total Fe content of 5.2 and 6.6% (w/w) for Fe/AS and Fe/HTCS catalysts, respectively. An aditional Fe catalyst prepared by incipient wetness impregnation on a commercial active carbon support (Fe/AC) was used for comparison with the previous two. All catalysts were active in experiments of H 2 O 2 decomposition and long-term CWPO runs (0.133 kg Fe h mol BmimAc –1 at 80 °C). Whereas Fe/AC catalyst lost activity largely due to Fe leaching (90% of Fe Bulk), Fe/AS and Fe/HTCS catalysts exhibited virtually no Fe leaching and hence fairly good stability. Fe/AS catalyst, which afforded complete removal of Bmim+ and TOC conversion values around 30%, proved the most efficient catalyst. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Green waste was hydrothermally treated and process water was reused up to 11 times. • Recirculation increased char yield by 4–10 wt% at 180 and 220 °C, respectively. • Recirculation increased the energy yield from 70 to 90% at 220 °C. • In contrast to 220 °C, accumulated acids reached a maximum concentration at 180 °C. • The proportion of detected organic acids on TOC increased by recirculation. Abstract Hydrothermal carbonization (HTC) is a promising conversion technology for wet biogenic waste material. However, after HTC the process water (PW) is highly enriched with organics. By reutilization of PW, the amount of contaminated waste water can be strongly reduced. However, temperature influence on hydrochar and PW composition during PW recirculation was not examined yet. Therefore, municipal green waste (MGW) was hydrothermally treated at 180 and 220 °C. The PW after HTC was fully reused up to 11 times. Results showed that hydrochar mass yield increases with progressing PW recirculation. Higher temperatures strengthen this effect. However, the higher heating value was not affected by recirculation process. PW analysis showed an accumulation of total organic carbon (TOC), chemical oxygen demand (COD), and organic acids. Most enriched and detected acids are acetic, formic, lactic and propionic acid. Only for formic acid, higher temperatures reduced the accumulation potential. The proportion of detected organic acids on TOC increased and could indicate a degradation of complex organic compounds. Detected phenols accumulated and increased by the factor of 5 at 220 °C. Finally, accumulation kinetics were calculated and showed in good approximation a first order behavior. Over all HTC recirculation steps, no PW had to be disposed. [ABSTRACT FROM AUTHOR]

This study examined the influence of process variables on the hydrochar production from wet biomasses and compared the agronomic value of hydrochars with that of the biochars produced by dry carbonization. Response surface methodology was used to investigate the effect of each three process variables (temperature, biomass:water ratio and reaction time) in hydrothermal carbonization (HTC) as well as their combined interactive effect on the mass yield and stable-C content of hydrochars. The results showed that the temperature and reaction time were significant factors affecting the stable-C content in HTC of the orange pomace, whereas the effect of all process variables is evident on stable-C content in HTC of grape pomace. For orange pomace, the effect of interaction between temperature and reaction time on mass yield was significant. However, in case of grape pomace, there existed no interaction effect between process variables on stable-C and mass yield. Findings from this work showed that char properties related to soil amendment are essentially determined by the type of carbonization process. Compared to the biochars produced by dry carbonization, the hydrochars had higher CEC and lower EC but more acidic pH values and lower stable-C content. Although chars have almost similar nitrogen content, the amount of water soluble nitrogen compounds in biochars were found to be significantly higher compared to the hydrochars. This result suggests that N-containing structures in the biomasses during HTC process were probably condensed to form N-heterocyclic aromatic structures, while much of nitrogen in biochars was present as available nitrate and amine N. [ABSTRACT FROM AUTHOR]

In the recent years, special focus has been given to the issues related to the management of biomass conversion systems by-products. In the view of transforming those products, mostly treated today as wastes, in valuable products, different valorization pathways can be considered. As an example, considerable attention has been devoted to the potential use of carbon-rich materials such as soil amendments and for long term carbon storage. These materials, produced by biomass thermochemical conversion are known as biochars. Several processes, from pyrolysis to gasification and hydrothermal carbonization, are today available for biochar production although characterized by relatively high costs. To overcome this restraint, an option is represented by the achievement of further economic benefits by extending its value chain. Coupling thermochemical processes to Anaerobic Digestion is thus an emerging field of research aimed at expanding usable feedstock with biologically recalcitrant substrates, such as paper, woody materials etc. Biochar in fact may promote the biomethane production, by acting both as support for bacteria colonies, conductor for electron transfer among species, sorbent for indirect inhibitors, and reactant in biochars labile carbon methanization. Thus, system integration of biogas and biochar is promising taking advantage of several profitable synergies. The aim of the paper is to review biochar characteristics and study early applications so far demonstrated and carried out, for the use of biochar in the anaerobic digestion processes. [ABSTRACT FROM AUTHOR]

Hydrothermal carbonization (HTC) has been a promising treatment technology of heavy metal-enriched hyperaccumulator biomass to produce superior hydrochar adsorbent for contamination removal from the wastewater. However, a high amount of heavy metal in derived hydrochar limits its further application. In this study, the effect of reaction temperature (180–270 ℃) and medium pH during HTC on heavy metal contents, speciation and leaching risk of hydrochar from the hyperaccumulator biomass Sedum alfredii Hance was investigated to assess its environmental risk. HTC at a low reaction temperature and acid addition facilitated the removal of Zn/Cd/Pb from the solid phase, meanwhile the addition of acid favored the immobilization of Zn/Cd/Pb and lowered the potential leaching risk of Zn/Cd/Pb. Hydrochar prepared from HTC at 240 °C and pH = 2 had lower heavy metal content and lower releasing risk, followed by KOH modification to obtain high adsorption performance. The modified hydrohcar (KSAB) were characterized by SEM, XRD, BET, Boehm titration and FT-IR, and showed that the surface specific surface area and pore structure were optimized and OFGs of hydrochar were improved significantly after KOH treatment. Adsorption experiments showed that the Cd(II) adsorption process onto KSAB well accorded with pseudo-second-order kinetics and Langmuir isotherms. The maximum Cd(II) adsorption capacity of KSAB was 25.69 mg/g, which was 17 times compared to that of pristine hydrochar. Microstructure characteristics and mechanism analysis further suggested that electrostatic interactions, surface complexation, cation-π and ion exchange were the main Cd(II) removal mechanisms of KOH-modified hydrochar. Therefore, hydrochar derived from hyperaccumulator biomass can be used as a highly efficient absorbent to remove Cd(II) from wastewater after KOH modification. [Display omitted] • Low temperature and acid-medium during HTC process facilitated Zn/Cd/Pb removal from hydrochar. • Acid-mediated HTC process favored HMs stability and reduced HMs leaching risk in hydrochar. • KOH modification increased oxygen functional groups on hydrochar surfaces. • The adsorption process was mainly controlled by chemisorption mechanism. [ABSTRACT FROM AUTHOR]

The addition of corn straw (CS) to sewage sludge (SS) for co-hydrothermal carbonization (co-HTC) can increase the importance of hydrochar as an alternative to fossil fuels. This study aims to achieve a synergistic, proper, and innovative treatment of SS and CS through combined HTC and gasification. Therefore, the physicochemical properties of co-hydrochar samples prepared at different HTC temperatures and CS ratios were investigated, and the CO 2 gasification performances at these conditions were also analyzed. The results showed that the hydrochar exhibited a substantial increase in specific surface area (SSA) and a decrease in the oxygen-to-carbon and hydrogen-to-carbon ratios compared to the feedstock. This suggests that HTC has the potential to improve fuel quality. Specifically, the SSA of the hydrochar was found to be 1.1–3.6 times higher than that of the feedstock. The reduction of the C O group in the co-hydrochar indicated the occurrence of the Maillard reaction during the co-HTC process. The content of alkali and alkaline earth metals in the co-hydrochar was high at the CS ratios of 25% and 50%. Owing to the addition of CS, the content of heavy metals in the co-hydrochar decreased, reducing the risks of environmental hazards caused by the utilization of hydrochar. The synergistic effect of hydrochar on the gasification performance increased with the CS content. The cold gas efficiency reached the highest value of 90.93% at the reaction temperature of 260 ℃ and CS mixing ratio of 25%. The results of this study indicate that the co-HTC process of SS and CS, combined with the gasification technology, is a promising method that can be used to optimize sewage treatment while minimizing the associated environmental risks. [Display omitted] • A resourceful treatment of sewage sludge and corn straw (CS) was achieved. • Hydrothermal carbonization (HTC) and gasification processes were applied. • Hydrochars produced at different HTC temperatures and CS ratios were analyzed. • HTC reduced the O:C and H:C ratios in the feedstock. • HTC improved the coalification of the fuel. [ABSTRACT FROM AUTHOR]

Hydrothermal carbonization (HTC) is a promising technology for sewage sludge (SSL) utilization. However, the yield and performance of hydrochar need to be further improved produced when SSL is used as a feedstock must be improved further. Herein, a process combining physicochemical pretreatment, namely, Fenton oxidation (FO) and HTC was developed for SSL utilization. Moderate oxidation was found to improve the yield and performance of the produced hydrochar. The product distribution, yield, and properties of the hydrochar produced using the proposed combined process were compared with those of the hydrochar produced via direct HTC treatment. The pretreatment affected the surface structure and organic composition of SSL and promoted the carbonization of the intermediate products. Thus, compared with the yield of hydrochar (50.7 %) obtained via the direct HTC treatment, the yield of the hydrochar obtained using the combined process increased to 55.0–65.2 % (depending on the pretreatment condition). Hydrochar properties were enhanced using the combined process, and the energy density of hydrochar slightly decreased after pretreatment (1.2–13.1 %); however, the energy yields increased by 0.6–30.1 % due to the enhanced hydrochar yield. The carbonization degree of hydrochar improved, the carbon in the feedstock distributed to the hydrochar increased from 33.40 % to 46.09 %. Moreover, the hydrochar showed more distinct pore channels, slightly improving its combustion activity. This study shows the efficacy of the combined pretreatment–HTC process and provides an experimental basis for the combined hydrothermal treatment of SSL. [Display omitted] • A process combine Fenton oxidation & hydrothermal carbonization was proposed. • Fenton oxidation regulates the yield and properties of hydrochar downstream. • The impact of pretreatment regulation is related to FO parameters. • Moderate oxidation of feedstock is conducive to improve its hydrothermal reactivity. [ABSTRACT FROM AUTHOR]

In this work, spherical activated carbons (SACs) were synthesized from spherical carbons (SCs) obtained by hydrothermal carbonization treatment of sucrose and subsequent CO 2 activation. The effects of SC synthesis conditions (temperature, time and sucrose concentration) on the BET surface area ( S BET ) values of obtained SACs were investigated and optimized by response surface methodology (RSM) based on central composite rotatable (CCR) design. The optimum conditions were found to be: temperature of 194 °C, hydrothermal carbonization time of 1197 min and 0.85 mol L −1 sucrose concentration. The optimization performed by CCR in conjunction with RSM allowed obtaining SAC with high surface area by performing only one experiment, saving time, energy and precursor. We have demonstrated that it is not necessary to perform the hydrothermal carbonization above 24 h, often adopted in similar studies, since the temperature and sucrose concentration have greater influence in the SAC area. The characterization of spherical activated carbon obtained in the optimized conditions (SAC op ) was carried out by scanning electron microscopy, N 2 physisorption, Fourier transform infrared spectroscopy, X-ray diffraction, Raman spectroscopy and thermogravimetric analysis. The SAC op showed spheres with an average diameter of 3.0 μm, S BET of 1012 m 2  g −1 , hydrophilic surface, amorphous structure and good thermal stability. [ABSTRACT FROM AUTHOR]

Highly efficient heavy metal adsorption was achieved using carbon microspheres (CMs) functionalized with boronic acid (B-CMs). The adsorbent B-CMs were prepared by hydrothermal carbonization of xylose and subsequent functionalization. They had a nonporous structure with a surface area of 76.1 m 2 /g and the presence of boronic acids on their surface was confirmed using Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. The distribution of boronic acid on the surface of the B-CMs was analyzed using energy-dispersive X-ray spectroscopy. The adsorption kinetics for Cu(II), Ni(II), and Cr(VI) ions best fitted a pseudo-second-order model, while the adsorption isotherms best fitted the Freundlich model, with Ni(II) showing the highest adsorption capacity. The adsorption capacity for these three metal ions decreased by less than 10% and 15–25% after one and three uses, respectively. Thus, considering that the B-CMs showed high adsorption capacities and were derived from agricultural waste (xylose) by a simple hydrothermal process, they seem highly suited for use as efficient and environment-friendly heavy metal adsorbents. [ABSTRACT FROM AUTHOR]

The coffee husk was used as precursor of hydrochar and chemometrics tools were applied to optimize the experimental conditions in order to obtain hydrochar with well-development surface area. The central composite rotatable design was employed and the optimization of parameters (temperature, time and water:precursor ratio) was performed from Response Surface Methodology (RSM). The analysis of variance showed that significant effects were: temperature and time. The optimal condition was found to be: temperature of 210 °C, time of 243 min, and water:precursor ratio of (3.4:1), resulting in a hydrochar (HC op ) with BET surface area value ( S BET ) of 31.3 m 2 g −1 . The HC op was properly characterized and applied in adsorption studies of methylene blue (MB) dye. The adsorption studies showed that the Elovich kinetic model and Langmuir isotherm model were that better described the experimental data. The monolayer adsorption maximum capacity of HC op was estimated to be 34.85 mg g −1 . Additionally, the thermodynamic study showed that adsorption occurs via spontaneous and endothermic process. [ABSTRACT FROM AUTHOR]

A novel carbonaceous composite material containing red mud and sucrose based carbon spheres, named as RM@C composite, has been prepared via one-step hydrothermal carbonization (HTC) process. The prepared RM@C composite is an environmentally friendly material because it utilized the red mud, a waste emerged from aluminium manufacturing, and sucrose, a renewable carbon precursor, in the one-step HTC process. After characterization of the composite material by XRD, FT-IR, TGA and SEM-EDX techniques, and specific surface area, pore size distribution and pH of zero point of charge (pHzpc) measurements, its batch adsorption performance was examined on the methylene blue in aqueous solution. The effective adsorption was achieved at pH ≥ 11. At pH 11, the adsorption performance of RM@C was superior to both red mud and naked carbon spheres. Kinetic analysis revealed that adsorption equilibrium is attained in 60 min and it is governed by the pseudo-second-order kinetic model together with intra-particle diffusion model. On the basis of isotherm analysis, Langmuir isotherm model better expressed the experimental data than Freundlich model. The Langmuir adsorption capacity of the composite material toward methylene blue was determined as 76.92 mg/g. The adsorption of methylene blue gradually decreased with increasing the ionic strength of the solution. The RM@C composite can be reused at least five cycles of adsorption-desorption without significant changes in the adsorption efficiency. [ABSTRACT FROM AUTHOR]

Carbonaceous material containing sulfonate groups as solid acid catalyst was generated by one-step mild hydrothermal carbonization of glucose. The process took place in the presence of hydroxyethylsulfonic acid at 180 °C for 4 h. The obtained sulfonated carbon (C-SO 3 H) was microsphere with diameter size of 50–100 micrometer. The sulfonate groups were further attached on the surface of the carbonaceous materials. The catalytic esterification of waste cooking oil (WCO) with methanol could be easily achieved by using C-SO 3 H. Free fatty acids (FFAs) in WCO could be decreased up to 93.4% at 60 °C for 3 h. The biodiesel yield was achieved about 87% within 1 h at 60 °C by transesterification using 1% NaOH (w/w) as catalyst. The C-SO 3 H was demonstrated to have good stability with only 7% decrease in FFAs conversion after 5 repeat uses. The sulfonated carbon-based solid acid catalyst was thus designed to be an active, stable and reusable solid acid as an environmentally benign replacement for homogeneous catalyst. [ABSTRACT FROM AUTHOR]

The aim of the work was to check the possibility of obtaining a biocomposite with magnetic properties capable of removing cadmium ions from aqueous solutions. The biocomposite consists of hydrochar obtained by hydrothermal carbonization of raffia fibers, Lindnera jadinii yeast and Fe 3 O 4 nanoparticles. The obtained biocomposite was characterized by SEM, FTIR, VSM, XRD, TGA and BET analysis. The study examined the effect of sorption time, initial concentration of cadmium ions, temperature, the pH ZPC and the reusability of the biocomposite. Based on the obtained results, non-linear equilibrium and kinetic models were selected. The equilibrium model with the highest matching factor describing the sorption of Cd(II) by the bionanocomposite was the Temkin isotherm model R2 = 0.9960 and ARE = 2.06%, while the kinetic model with the best fit was the Elovich model R2 = 0.9928 and ARE = 5.44%. The results showed that the maximum Cd(II) adsorption capacity of the biocomposite was equal to 16.34 mg/g at 25 °C and increased with increasing temperature up to 26.22 mg/g at 40 °C. The performed Cd desorption tests showed a significant efficiency of the biocomposite for five successive cycles of the sorption-desorption process with the use of HNO 3 , obtaining a leaching degree of 96–98.8%. The conducted research provides new data on the use of composites obtained from biomass, microorganisms and Fe 3 O 4 in the bioremediation of heavy metals from water media and proves the effectiveness of removal and potential use in real environmental conditions of the biocomposite due to its easy recovery from contaminated aqueous solutions. • A biocomposite with magnetic properties was obtained. • The obtained biocomposite was characterized. • The removal of Cd ions by the biocomposite was carried out. • The effect of parameters on the sorption process was determined. [ABSTRACT FROM AUTHOR]

Seeking continuous treatment of downstream wastewater is a desperate requirement for the scale-up of hydrothermal technology. In this study, a novel multistage anaerobic hythane reactor (MAHR), which was constructed with an internal downflow biofilter bed and an external up-flow sludge bed, was used to dispose of hydrothermal carbonation wastewater (HTCWW), a by-product of the hydrochar preparation process of microalgae. To verify the performance of MAHR for the actual complex wastewater treatment, a conventional up-flow anaerobic sludge bed reactor (UASB) was used as a comparison. The two reactors were both operated independently in parallel with a hydraulic retention time (HRT) of 12 h and an organic load rate (OLR) of 20 g SCOD/L/d. Both MAHR and UASB achieved 84% COD removal rate and 7.0 ± 0.6 and 5.5 ± 0.3 L/L/d of methane production rate, respectively, when the proportion of HTCWW was increased to 100% of the original wastewater. Specifically, the hythane-producing area (M H) of MAHR was gradually transformed into methane producing area in the process of feeding HTCWW. High-performance liquid chromatography (HPLC) analysis revealed that more small molecule compounds including organic acids and inhibitors were degraded in MAHR. Fourier transform ion cyclone resonance mass spectrometry (FT-ICR MS) analysis demonstrated that more soluble proteins and lipids were degraded to some extent, while the lignin and condensed aromatic compounds increased especially in UASB. A dramatic change was observed in the dominating microbial communities in MAHR and UASB from the Streptococcaceae associated with carbohydrates degradation to the Renkenellaceae involved in both proteins and carbohydrates degradation. At the archaeal level, hydrogenotrophic methanogens replaced acetoclastic methanogens. Redundancy analysis (RDA) further verified the relationship between dominant functional communities and the anaerobic digestion performance of the reactors. The above results indicate that MAHR is a promising configuration for the anaerobic valorization of hydrothermal wastewater. [Display omitted] • Hydrothermal wastewater reshapes function of novel MAHR and its microbial structure. • MAHR had higher methane than UASB during continuous AD of hydrothermal wastewater. • More organic compounds were degraded in MAHR than UASB measured by HPLC and FT-ICR MS. • Family Renkenellaceae was dominated in MAHR and UASB after domestication by HTCWW. • Hydrogenotrophic methanogens replaced the acetoclastic methanogens in two reactors. [ABSTRACT FROM AUTHOR]

Hydrothermal carbonization (HTC) has demonstrated high potential for livestock manure management. However, reducing the potential risk of residual heavy metals is still challenging. In this study, poultry manure (PM) was hydrothermally carbonized to investigate the impacts of HTC temperature and ethylenediaminetetraacetic acid (EDTA) on the evolution of nutrients (i.e., N, P, K, Na, Ca, and Mg), heavy metals (Cu and Zn), and the properties of hydrochars and process water through HTC. Results indicated that HTC temperature was a critical factor that regulated hydrochar and process water properties and the fates of nutrients and heavy metals, while EDTA mainly affected metal distribution through HTC. A high proportion of C, N, and P was reclaimed in the solid phases, making hydrochar an optimal organic fertilizer with high fertility (N + K 2 O +P 2 O 5 > 5%). However, N and P in hydrochars were low in availabilities. Through HTC, Ca, Mg, Cu, and Zn were concentrated in hydrochars, but Na and K were mainly distributed in the process water. A rising HTC temperature elevated the proportion of Zn in hydrochars, while it had limited impacts on Na, K, and Ca distribution. By comparison, EDTA facilitated the release of Cu, Mg, and Zn into the process water. Furthermore, EDTA involvement reduced the potential risk of Cu and Zn in hydrochars. Our findings highlighted the sound impacts of EDTA on risk reduction and nutrient recovery from livestock manure through HTC, and would provide references for livestock manure management for sustainable agriculture. [Display omitted] • PM derived hydrochar showed high fertility with abundant N and P. • EDTA impacts metals distribution between hydrochars and process water. • Species-specific metal distribution in solid and liquid phase was observed during HTC. • EDTA enhanced HTC reduced the potential risks of Cu and Zn in PM derived hydrochars. [ABSTRACT FROM AUTHOR]

In situ electrochemical disinfection via H 2 O 2 through two-electron molecular oxygen reduction reaction (2e-ORR) represents a promising strategy for sustainable disinfection. However, its disinfection performance is largely confined by its low selectivity/reactivity towards two-electron oxygen reduction reaction (2e-ORR) for H 2 O 2 production. To tackle this, carbon spheres modified tubular titanium air diffusion cathode (CS@TTC) was developed. It intended to improve interfacial structures for high H 2 O 2 production through a facile hydrothermal carbonation approach. Evolution of morphology and chemical nature of carbon spheres have been systemically investigated under diverse hydrothermal temperature, hydrothermal time and pyrolysis temperature·H 2 O 2 accumulation has improved 6.59-fold at CS@TTC compared to the raw base TTC. Both chemical nature of carbon sphere and a superior oxygen mass transfer (0.0284 s−1) were responsible for this enhancement. Besides, CS@TTC cathode was used in the electrochemical system for disinfection performance, in which 6.42 log of E. coli was deactivated after 120 min. Hence, this study gives an insight into that the H 2 O 2 -based electrochemical disinfection is promising to be a next-generation process. [Display omitted] [ABSTRACT FROM AUTHOR]

Herein, the valorization of vegetable and fruit waste was assessed via hydrothermal carbonization (HTC) and anaerobic digestion (AD) in terms of product characterization and energy requirements. HTC was conducted at reaction temperatures between 150 ºC and 190 ºC, and residence times between 20 min and 40 min. The increase in the process severity resulted in hydrochars with higher carbon contents and higher energy densification ratios. AD was performed in two different ways. i.e., batch and semi-continuous reactions. From the batch experiments a methane yield of 300 L CH 4 /kg VS was obtained, while for the semi-continuous, the average specific methane production estimated (for HRTs from 75 to 50 days) was 213 ± 32 L CH 4 /kg VS. To estimate the energy requirements, mass and energy balances were performed considering the basic stages of each process to obtain a suitable biofuel material. In this sense, it was concluded that for this specific waste, AD was a more suitable process with a positive energy net balance. On the contrary, HTC presented a negative energy net balance being required 1.29 MJ/kg of fresh food waste. A combined HTC-AD treatment may be an efficient method to take advantage of both technologies leading to higher energy efficiencies and other valuable products. [Display omitted] • A carbon-rich solid product is obtained from HTC of fruit and vegetable waste. • The higher the severity of the HTC, the better the fuel properties of the hydrochars. • The energy recovered by HTC is higher than that of AD (923 MJ vs. 867.1 MJ). • Batch and semi-continuous anaerobic digestion experiments were performed. • AD presented a positive energy balance, while HTC showed negative outputs. [ABSTRACT FROM AUTHOR]

Porous-activated biochars with abundant pores have great potential for the treatment of volatile organic compounds (VOCs). However, the lack of cost-effective pore-modulation methods for these materials has hindered their feasibility for large-scale use as adsorbents. In this study, hydrothermal carbonization (HTC) of glucose, the basic unit of cellulose, was investigated, and the pore structure of the obtained hydrochar was precisely determined by controlling the main factors of the hydrothermal process. Orthogonal experiments were conducted to determine the most suitable conditions for a hierarchical porous structure, and the water ratio was considered the main regulating factor. The range of possible carbon precursors was extended to all biomasses by proposing an innovative model to explain the formation of pore structures during the conversion of basic biomass components to biochar in the HTC process. The results revealed that the water ratio significantly affected the decomposition and carbonization of biomass in HTC, which further affected the microdomain unit size and, thus, the biochar pore structure. Further, the graded porous structure substantially enhanced the biochar adsorption capacity. HTC was found to have a greater potential for practical applications, as it presented a substantially higher yield, compared to direct carbonization processes. Overall, this work provides guidance and an effective reference for the pore size adjustment of porous-activated biochar developed for the adsorption of pollutants. [Display omitted] • Biomass hydrothermal process was explained using glucose as model. • Formation of biochar pores was investigated based on microdomain structure model. • Variation of water ratio has modulatory effects on biochar porosity. • Activated hydrochar has better yield and economy than pyrolytic carbon. [ABSTRACT FROM AUTHOR]

Scientific disposal of sewage sludge (SS) is a tedious task worldwide. Landfilling of the SS after centrifugation may have serious adverse impacts on the environment. The present study investigated efficacy of hydrothermal carbonization (HTC) as pretreatment for the centrifuged sewage sludge with an aim to improve resource recovery. In this study, both solid and liquid fractions recovered after the HTC were subjected to the detailed analysis for examining the opportunities for recovery of value-added chemicals and biogas. The HTC conditions were optimized using design of experiments (DOE) approach. The runs were performed in a high-pressure reactor at 160–240 °C temperatures and total pressures of 6.1–34.2 kg/cm2 for 1–3 h duration without supply of air. The optimum HTC temperature and duration were found to be 200 °C and 1 h, respectively. Under these conditions, the dried hydrochar (HC) had higher heating value of ~13 MJ/kg. Its properties were found similar to that of the sub-bituminous coal based on the atomic ratio of elements. The HTC pretreatment resulted in substantial reduction in carbon and oxygen due to decarboxylation, dehydration and oxidation (due to oxygen present in reactor headspace) reactions. The process wastewater (PWW) recovered after HTC at the optimum conditions had high concentration of the recoverable value-added compounds such as humic acid (HA) and PO 4 3--P (concentration = 20 g/l and ~0.5 g/l, respectively). Moreover, significant quantity of biogas could be generated from the PWW. Hence, hydrothermal pretreatment can be considered a potential option for SS valorization. [Display omitted] • HTC of centrifuged SS showed good recovery potential at 200 °C temperature. • Distribution of C and N in solid, liquid and gaseous phase was obtained. • More than 220 ml/g sCOD biogas production was observed from process wastewater. • EEM spectra showed high concentration of HA and FA after HTC at 200 °C temperature. • Using HTC pretreatment, recovery of non-renewable PO 4 3--P may also be possible. [ABSTRACT FROM AUTHOR]

This work targets to study the influence of PW recirculation on hydrochars at 180, 220, and 260 ℃. Rice husk was hydrothermal carbonized for 1 h and PW was cycled 5 times. The results showed that PW recirculation improved the mass yield and energy recovery efficiency (ERE) of hydrochars. With the increase of temperature, the mass yield of hydrochars decreased and ERE increased first and then decreased. PW recirculation promoted the increase of carbon content at 180 and 220 ℃. When the temperature increased, the carbon content increased, while the hydrogen and oxygen content decreased. The high heating value (HHV) increased with the increase of PW recirculation and temperature. At 180 and 220 ℃, the fixed carbon increased with the increase of PW recirculation and temperature. SEM analysis showed that PW recirculation promoted the formation of carbon microspheres. At 260 ℃, carbon microsphere fusion occurred. After recirculation, the ignition temperature and burning temperature of hydrochars decreased. The aromatic vibration (C C) intensified after the PW recirculation, indicating the occurrence of aromatization and polymerization. Overall, PW recirculation could improve the hydrothermal carbonization process to a certain extent. [Display omitted] • PW recirculation could promote the formation of hydrochars at 180, 220, and 260 ℃. • The MY of hydrochars increased by 3.98% (180 ℃), 8.11% (220 ℃) and 4.44% (260 ℃). • The ERE of hydrochars increased by 13.18% (180 ℃), 18.58% (220 ℃) and 19.62% (260 ℃). • Compared with 180 ℃ and 260 ℃, 220 ℃ was a more suitable temperature for HTC. • PW recirculation could promote the formation of microparticles on surfaces of hydrochars. [ABSTRACT FROM AUTHOR]

In order to prepare low nitrogen content hydrochar, deep eutectic solvents (DES) have been utilized as a green solvent to remove nitrogen from sewage sludge (SS) during the hydrothermal carbonization (HTC) processing. Compared to without DES, the maximum removal efficiency of nitrogen in hydrochar can increase as high as 69.49% at 210 oC when choline chloride and oxalic acid are employed as DES. Results demonstrate that different DES systems possess different capability to remove nitrogen, and DES offers the advantages to degrade floc structure of SS, thus inhibiting Maillard reaction during the HTC. It is revealed that organic matter releasing from floc structure within SS, low polysaccharide content, as well as fast caramelization under basic condition are vital factors to retard Maillard reaction to obtain low nitrogen content hydrochar from SS. In addition, the possible removal pathways are also analyzed and proposed in this investigation. [Display omitted] • DES could dissolve proteins during the HTC of SS. • Disruption of floc structure of SS was key to inhibit Maillard reaction. • DES(CO) has a stronger capability than DES(CU) to disrup the floc structure of SS. • DES(CO) promoted hydrolysis of organic matter and increased carbonization degree of biochar. [ABSTRACT FROM AUTHOR]

The potential for applying renewable resources to a fermentative lactic acid purification process has been investigated. The adsorption behavior of lactate and 10 inorganic ions onto 12 different types of sorbents was investigated. The performance of six different renewable bio-based sorbents (willow, poplar, their hydrothermally carbonized forms (HTC-willow and HTC-poplar), alginate and chitosan) were studied and compared with five common fossil-based polymers and one charcoal sorbent. The ion adsorption capacities and breakthrough curves of the different sorbents were investigated in column experiments. Moreover, impacts of the presence of individual ions on the breakthrough curves were investigated by the application of an aqueous lactic acid solution and a sodium lactate fermentation broth. The lactate capacities of the biosorbents (>140 mg g −1 ) were at least threefold higher than those of the conventional sorbents (<40 mg g −1 ). Furthermore, the HTC conversion allowed for a 60% increase in the lactate adsorption capacity. [ABSTRACT FROM AUTHOR]

Hydrothermal carbonization (HTC) is highly acknowledged for its ability to convert wet food waste into high calorific value hydrochar at a fast rate. However, the liquid by-product from the process, named HTC wastewater, contains high level of chemical oxygen demand (COD) of 40,000–55,000 mg/L. This HTC wastewater can greatly pollute the environment if it was released without a proper treatment, and hinder the industrial application of HTC technology. In this study, hydrochar was produced via HTC process at 250 °C, and KOH activation was employed to further improve the physical structure of the hydrochar to prepare activated carbon (AC). The obtained AC had the mesoporous structure with specific surface area of 1807.42 m2/g. The AC was used to catalyze persulfate (PS) oxidation for the degradation of HTC wastewater. The experiment of catalytic persulfate degradation of HTC wastewater was designed by the central composite design (CCD) method, and optimized by using response surface method (RSM). The experimental results were statistically discussed by the analysis of variance (ANOVA). The optimal condition determined by CCD model was PS dosage = 6.20 mmol, temperature = 32.47 °C, and pH value = 3.69, achieving a COD removal efficiency of 78.94%. The hydrochar catalyzed persulfate degradation of HTC wastewater caused a great reduction of its pollution degree, which can be a promising pretreatment for HTC wastewater with minimal effort and cost. [Display omitted] ● Food waste was converted into activated carbon via HTC procedure followed by KOH-activation. ● AC can efficiently catalyze PS to produce oxidative radicals. ● CCD model was applied to optimized AC catalyzed PS oxidation. ● A COD removal efficiency of 78.94% for HTC wastewater was achieved. [ABSTRACT FROM AUTHOR]

The hydrothermal carbonization (HTC) process has been found to consistently improve biomass fuel characteristics by raising the higher heating value (HHV) of the hydrochar as process severity is increased. However, this is usually associated with a decrease in the solid yield (SY) of hydrochar, making it difficult to determine the optimal operating conditions to obtain the highest energy yield (EY), which combines the two parameters. In this study, a graph-based genetic programming (GP) method was used for developing correlations to predict HHV, SY, and EY for hydrochars based on published values from 42 biomasses and a broad range of HTC experimental systems and operating conditions, i.e., 5 ≤ holding time (min) ≤ 2208, 120 ≤ temperature (°C) ≤ 300, and 0. 0096 ≤ biomass to water ratio ≤ 0.5. In addition, experiments were carried out with 5 pomaces at 4 temperatures and two reactor scales, 1 L and 18.75 L. The correlations were evaluated using this experimental data set in order to estimate prediction errors in similar experimental systems. The use of the correlations to predict HTC conditions to achieve the maximum EY is demonstrated for three common feedstocks, wheat straw, sewage sludge, and a fruit pomace. The prediction was confirmed experimentally with pomace at the optimized HTC conditions; we observed 6.9 % error between the measured and predicted EY %. The results show that the correlations can be used to predict the optimal operating conditions to produce hydrochar with the desired fuel characteristics with a minimum of actual HTC runs. [Display omitted] • Correlations to predict hydrochar heating value and solid yield based on genetic programming. • Optimize HTC conditions for the highest energy yield with these correlations. • Use algorithm to predict energy yield with high accuracy without performing HTC runs. • Assess the feasibility of using HTC to convert wide variety of biomasses to fuel. [ABSTRACT FROM AUTHOR]

The treatment of sewage sludge (SS) presents challenges in terms of the effective simultaneous immobilization of heavy metals (HMs). This study analyzed the heavy metal migration behavior and fuel characteristics of hydrochar generated by co-hydrothermal carbonization (co-HTC) of SS and water hyacinth (WH) under the addition of attapulgite. The results showed that the co-HTC treatment facilitated the conversion of Cu, Cr, and Ni from the bioavailable fraction to the relatively stable fraction, with little effect on Mn and Pb. At 20% attapulgite of co-HTC, not only did the total concentration of HMs decreased significantly but the bioavailability of all measured metals decreased, reducing the potential ecological risk of the hydrochars. Moreover, the fuel ratio of co-HTC hydrochars was found to be improved (0.03─0.29), and an increase in the higher heating values (3.16─12.44 MJ/kg) compared to hydrochar from SS. The results of TG, FTIR spectra, and kinetic analysis further indicate that co-HTC promotes the aromaticity of the hydrochars and improves the fuel grade. From the perspectives of HMs immobilization and clean fuel production, co-HTC with SS and WH and the addition of attapulgite is an effective SS treatment method. [Display omitted] • Co-HTC of SS and WH reduced the leaching toxicity of Cr, Ni, and Cu. • The content of (F1 +F2) in hydrochar with 20% attapulgite was the least. • The co-HTC of SS and WH increased the HHV of the hydrochar to 12.44 MJ/kg. • The activation energy of the hydrochar was the lowest at SS: WH= 7:3. [ABSTRACT FROM AUTHOR]

Higher heating value (HHV) is an important property of fuels because it can be used to calculate their required quantity for generating heat in thermal processes. In this work, the HHV of sugarcane leaf and giant leucaena wood after treatment via hydrothermal carbonization (HTC) under various conditions were measured. The HTC was performed with biomass to water weight ratio of 1:0–1:25, 156–273 °C for 9.5–110 min. The empirical correlations based on ultimate and proximate analysis were proposed for predicting HHV of sugarcane leaf and giant leucaena wood during the HTC process. The multiple linear and nonlinear regression methods were used to develop the correlation. The nonlinear correlation was better than the linear correlation for predicting HHV of hydrochar based on ultimate analysis, while the linear correlation was better than the nonlinear equation for predicting HHV of hydrochar based on proximate analysis. Types of biomass feedstock, HTC operating conditions, compositions of hydrochar and scopes of ultimate and proximate variable affected to the accuracy for using the HHV correlation prediction. The aim of creating the correlation was to accurately predict the HHV of hydrochar obtained at different HTC conditions by using ultimate and proximate analysis data, saving experimental costs, and providing a theoretical basis for modeling hydrochar combustion and hydrothermal carbonization processes. [Display omitted] • HHV equations of hydrochar from sugarcane leaf and giant leucaena were developed. • Hydrochar was derived from various conditions of HTC process designed using DOE. • HHV prediction models were developed based on ultimate and proximate compositions. • The developed HHV equations were more accurate than the previous correlations. [ABSTRACT FROM AUTHOR]

In recent times, synthesis of valuable carbon materials via hydrothermal carbonization technique using biomass precursors for various applications has received revived interest in view of energy efficiency and sustainability. In present work, low-cost carbon material was synthesized using Mesua ferrea L. seed cake through hydrothermal carbonization method. The material was characterized using various techniques and its CO 2 capture performance was investigated through a dynamic column breakthrough measurements. The sorbent exhibited a fresh adsorption capacity of 2.63 mmol g −1 at 30 °C under a total pressure of 1 bar. Both textural properties and surface chemistry influence the CO 2 dynamic adsorption. The sorbent maintained an average working capacity of ∼ 2.47 mmol g −1 during eight cycles of adsorption-desorption. The experimental data can be adequately described by Yoon-Nelson kinetic model. The adsorption kinetic mechanism is further explained by applying intraparticle diffusion model to the experimental data. [ABSTRACT FROM AUTHOR]

Carbonaceous adsorbents were prepared from hydrothermal carbonization of cellulose followed by chemical activation under various conditions. The effect of the surface chemistry of the prepared adsorbents on the adsorption of ionic liquids (ILs) with various chemical structures was investigated. Here, the adsorption of hydrophobic ILs from aqueous streams was enhanced by increasing the activation temperature thus reducing the number of oxygenated groups on the surface of the carbonaceous adsorbent. In addition, the adsorption capacity of hydrophilic ILs on carbon materials was increased by increasing the KOH/HC weight ratio used for activation. For the prepared carbon material adsorbents, the adsorption capacities of imidazolium-based ILs, with different anions, onto the adsorbent increased with increasing hydrophobicity of the IL anions in the following order Cl − < TFA − < [BF 4 ] − < OTf − < [PF 6 ] − < NTf 2 − . Therefore, the adsorption capacities of carbon materials for ILs can be tailored through alteration of their surface chemistry by changing activation conditions. [ABSTRACT FROM AUTHOR]