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Wet distillers grains, as a waste biomass with a large annual output, pose a threat to the environment and food industry. Herein, artificial humic acid (AHA) was first produced from wet distillers grains in a dual-stage microwave-assisted hydrothermal process. The influence of temperature on AHA's characteristics was investigated and compared with natural humic acid (NHA) and standard humic acid (SHA). A high yield of AHA at 20.6% was obtained at 200 °C with a total reaction time of 1 h, which is 1.8–3.1 times that obtained in traditional single-stage hydrothermal process. Increasing the reaction temperature induced the formation of phenolic hydroxyl in AHA. AHA was rich in aromaticity and carboxylic acid structure, showing similar spectral characteristics to NHA. The distribution of molecular weight of AHA was mostly 5797 Da, which decreased by 15% compared to SHA. The optimal concentration of AHA to promote seedling growth was 0.2 g/L, and the root length was 2.0 times that of the control. The microwave hydrothermal process is a facile and efficient approach to preparing AHA from waste biomass with high moisture content. [Display omitted] • AHA was first produced from wet distillers grains in a dual-stage microwave HTC. • The highest yield of AHA at 20.6% was obtained at 200 °C for 1 h in the HTC. • AHA showed higher aromaticity and carboxylic acid content than natural humic acid. • Molecular weight of AHA was mostly 5797 Da, which is 15% lower than that of SHA. • 0.2 g/L of AHA increased the seedling root length to 2.0 times that of the control. [ABSTRACT FROM AUTHOR]

Dechlorination of waste PVC (WPVC) by hydrothermal treatment (HTT) is a potential technology for upcycling WPVC in order to create non-toxic products. Literature suggests that acids can improve the HTT process, however, acid is expensive and also results in wastewater. Instead, the acidic process fluid (PF) of hydrothermal carbonization (HTC) of orange peel was utilized in this study to enhance the dechlorination of WPVC during HTT. Acidic HTT (AHTT) experiments were carried out utilizing a batch reactor at 300–350 °C, and 0.25–4 h. The finding demonstrated that the dechlorination efficiency (DE) is high, which indicates AHTT can considerably eliminate chlorine from WPVC and relocate to the aqueous phase. The maximum DE of 97.57 wt% was obtained at 350 °C and 1 h. The AHTT temperature had a considerable impact on the WPVC conversion since the solid yield decreases from 56.88 % at 300 °C to 49.85 % at 350 °C. Moreover, AHTT char and crude oil contain low chloride and considerably more C and H, leading to a considerably higher heating value (HHV). The HHV increased from 23.48 to 33.07 MJ/kg when the AHTT time was raised from 0.25 to 4 h at 350 °C, indicating that the AHTT time has a beneficial effect on the HHV. The majority fraction of crude oil evaporated in the boiling range of lighter fuels include gasoline, kerosene, and diesel (57.58–83.09 wt%). Furthermore, when the AHTT temperature was raised from 300 to 350 °C at 1 h, the HHV of crude oils increased from 26.11 to 33.84 MJ/kg. Crude oils derived from AHTT primarily consisted of phenolic (50.47–75.39 wt%), ketone (20.1–36.34 wt%), and hydrocarbon (1.08–7.93 wt%) constituents. In summary, the results indicated that AHTT is a method for upcycling WPVC to clean fuel. [Display omitted] • Acidic process fluid improves dechlorination of waste PVC through AHTT. • AHTT's char has higher ignition temperature and lower burnout temperature. • The char has low slagging, fouling and alkali indexes, and chlorine content. • The HHV of the AHTT's crude oil are between 26.11 and 34.6 MJ/kg. [ABSTRACT FROM AUTHOR]

Nuclear energy is playing an increasingly important role on the earth, but the nuclear plants leaves a legacy of radioactive waste pollution, especially uranium-containing pollution. Straw biochar with wide sources, large output, low cost, and easy availability, has emerged as a promising material for uranium extraction from radioactive wastewater, but the natural biomass with suboptimal structure and low content of functional groups limits the efficiency. In this work, microbial etch was first came up to regulate the biochar's structure and function. The surface of the biochar becomes rougher and more microporous, and the mineral contents (Ca, P) indirectly increased by microbial etch. The biochar was modified by calcium phosphate and exhibited a remarkable uranium extraction capacity of 590.8 mg g−1 (fitted value). This work provides a cost-effective and sustainable method for preparing functionalized biochar via microbial etch, which has potential for application to uranium extraction from radioactive wastewater. [Display omitted] • Microbial etch process constructed a large amount of Ca sites in the cotton straw. • Microbial etch facilitated the formation of calcium phosphate on the hydrothermal biochar. • The adsorption capacity of CCS-P for U(VI) was 590.8 mg g−1. • Microbial etch is a novel method for the production of high-performance uranium adsorbent. [ABSTRACT FROM AUTHOR]

As an effort to tackle some of the most pressing ecological issues we are currently experiencing, there has been an increasing interest in employing biomass-derived char products in various disciplines. Thermal combustion of biomass results in biochar production, which is a remarkably rich source of carbon. Not only does the biochar obtained by the thermochemical breakdown of biomass lower the quantity of carbon released into the environment, but it also serves as an eco-friendly substitute for activated carbon (AC) and further carbon-containing products. An overview of using biochar to remove toxic pollutants is the main subject of this article. Several techniques for producing biochar have been explored. The most popular processes for producing biochar are hydrothermal carbonization, gasification and pyrolysis. Carbonaceous materials, alkali, acid and steam are all capable of altering biochar. Depending on the environmental domains of applications, several modification techniques are chosen. The current findings on characterization and potential applications of biochar are compiled in this survey. Comprehensive discussion is given on the fundamentals regarding the formation of biochar. Process variables influencing the yield of biochar have been summarized. Several biochars' adsorption capabilities for expulsion pollutants under various operating circumstances are compiled. In the domain of developing biochar, a few suggestions for future study have been given. [Display omitted] • This survey looked into the production of biochar using various techniques. • Process variables that affect the yield of biochar were emphasized. • This article briefly describes the biochar synthesis mechanism. • Biochar application for the evacuation of organic and inorganic pollutants was briefed. • Synthesis and application of magnetic biochar was summarized. [ABSTRACT FROM AUTHOR]

Carbon-encapsulated iron oxide nanoparticles (CE-nFe) have been obtained from an industrial waste (oil mill wastewater-OMW, as a carbonaceous source), and using iron sulfate as metallic precursor. In an initial step, the hydrochar obtained has been thermally activated under an inert atmosphere at three different temperatures (600 °C, 800 °C and 1000 °C). The thermal treatment promotes the development of core-shell nanoparticles, with an inner core of α-Fe/Fe 3 O 4 , surrounded by a well-defined graphite shell. Temperatures above 800 °C are needed to promote the graphitization of the carbonaceous species, a process promoted by iron nanoparticles through the dissolution, diffusion and growth of the carbon nanostructures on the outer shell. Breakthrough column tests show that CE-nFe exhibit an exceptional performance for H 2 S removal with a breakthrough capacity larger than 0.5–0.6 g H 2 S/g catalyst after 3 days experiment. Experimental results anticipate the crucial role of humidity and oxygen in the adsorption/catalytic performance. Compared to some commercial samples, these results constitute a three-fold increase in the catalytic performance under similar experimental conditions. [Display omitted] • Oil mill wastewater has been transformed into added value catalysts for H2S removal. • Well-designed Fe-based core-shell nanoparticles have been successfully prepared. • These composites exhibit an exceptional performance for H2S removal. [ABSTRACT FROM AUTHOR]

Sustainable, efficient, and environmentally friendly ways to tailor the carbonaceous materials from bio sources with desired functionalities remain a challenge around the world. In this study, we represent a novel approach to synthesize carbon hybrid material based on Zinc Oxide/carbon (ZnO/C) hybrid systems by catalytic hydrothermal process via crosslinking reaction through nucleation and growth of ZnO particles at the functional groups of oxidized carbon material. This research explored the volarization of Condensed Corn Distillers Soluble (CDS) as a carbon precursor to synthesize biobased carbon spheres. Surface modification of the produced carbon spheres took place using zinc chloride (ZnCl 2) during hydrothermal carbonization (HTC). Zinc chloride (ZnCl 2) was used to function as a catalyst during HTC and functioned as a ZnO source to synthesize (ZnO/C) hybrid systems. Design Expert software v13 was used to design the hydrothermal carbonization (HTC) experiments and response surface methodology was used to find the optimized conditions for the preparation of carbon hybrid systems. The hydrothermal synthesis process introduced 3D stone like zinc oxide particles onto the carbon matrix. These particles were self-assembled onto the carbon framework to produce carbon hybrid systems with unique physical, chemical, structural and functional properties. Herein, the obtained carbon hybrid systems (ZnO/C) were investigated and discussed in detail. ZnO/C hybrid systems were analyzed for surface morphology using scanning electron microscopy (SEM) that presented a 3D spherical interconnected phase and XRD analyses were used for phase crystallinity that showed new crystalline phases such as hopeite and zincite after the ZnCl 2 incorporation. Surface functional groups were also analyzed by FTIR and results confirmed the presence of hydrophilic groups such as –OH, C C, and COOH on the surface of ZnO/C hybrid carbon systems. This study provided the insightful guidance for tailoring novel design of multifunctional carbon material as an adsorbent/catalyst for various applications of sustainable remediation. [Display omitted] • A novel approach to design carbonaceous materials has been described. • Zinc Oxide/Carbon hybrid systems are developed from industrial waste. • Effect of zinc chloride during hydrothermal carbonization has been investigated. • The synthesized hybrid carbon material has the capability for environmentally sustainable remediation. [ABSTRACT FROM AUTHOR]

Hydrothermal carbonization was applied to taro peel wastes to produce hydrochars using a facile and environmentally friendly process. Four different entities were prepared: hydrochar (TPh), phosphoric-activated hydrochar (P-TPh), and silver@hydrochars (Ag@TPh, Ag@P-TPh). The elemental compositions of the single and composite hydrochars were confirmed by EDX. Among the produced hydrochars, the morphology of the Ag@hydrochar composites demonstrated more wrinkled structure, and Ag nanoparticles decorated the surface. The optimal experimental conditions for levofloxacin adsorption were determined to be a contact time of 45 min, hydrochar dose of 0.15 g L−1, and pH of 7. The best adsorption performances were assigned to Ag@hydrochars. Two machine learning models were applied to predict the levofloxacin adsorption efficiency of the Ag@hydrochars. A central composite design (CCD) and a 3-10-1 artificial neural network (ANN) model were developed to estimate the removal performance of levofloxacin using Levenberg-Marquardt backpropagation algorithm based on correlation and error analysis of the adopted training functions. Furthermore, the ANN sensitivity analysis revealed the order of the relative importance variable as initial concentration> hydrochar dose> pH. The predicted values of the CCD and ANN models fitted the experimental results with R2> 0.989. Therefore, the applied models were effective in predicting levofloxacin removal under different operating conditions. This work provides an open option for the sustainable management of food industry wastes and the possibility of waste valorization to effective hydrochar composites to be applied in water treatment processes. [Display omitted] • Taro peels (Food waste) derived single and nano-composite hydrochars were synthesized. • Ag@hydrochars with/without acid activation were the optimum nano-composite hydrochars. • Ag@hydrochars were successfully removed levofloxacin from water. • Two machine learning models were selected to optimize the removal of levofloxacin. • 3-10-1 ANN structure was trained with 3 inputs, 10 hidden layers, 1 output. [ABSTRACT FROM AUTHOR]

Hydrothermal carbonization (HTC) is an emerging technology for treating sewage sludge. However, the resulting HTC process water is heavily contaminated with various carbonaceous and nitrogenous components, some of them being non-biodegradable. To implement HTC as a full-scale treatment alternative for sewage sludge, effective concepts for treating process water are crucial. This study focuses on the electrochemical oxidation (EO) using a boron-doped diamond electrode to treat one HTC process waters with different pretreatments: (i) without pretreatment, (ii) biologically pretreated with chemical oxygen demand (COD) removal, (iii) biologically pretreated with nitrification and denitrification. The EO removed COD of all HTC process waters by over 97%, but as COD concentrations decreased, the instantaneous current efficiency (ICE) dropped below 5% and energy consumption increased. The organically bound and refractory nitrogen was completely mineralized and converted to mainly NO 3 –N. After EO of process waters without nitrification/denitrification, nitrogen was present as NO 3 –N with up to 730 mg/L and NH 4 –N with up to 1813 mg/L. Such high ammonium concentrations treatment could be interesting for nitrogen recovery. In addition, the toxicity towards Vibrio fischeri could be reduced to a large extent. The findings suggest that EO after a biological step with COD removal is a viable solution for HTC process water treatment. [Display omitted] • EO successfully reduced refractory organic matter in HTC process water • EO significantly reduced the toxicity of the process waters • Biological pre-treatment was crucial for the effectiveness of EO • High ammonium concentrations allow for the recovery of nitrogen after EO [ABSTRACT FROM AUTHOR]

In this study, the chemical structures, fuel characteristic, and formation mechanism of hydrochar during hydrothermal carbonization (HTC) at 150–270 °C for 0–120 min were investigated using coking sludge (CS) as the feedstock. The results showed that the yield decreased from 96.86 to 60.98%, whereas the carbonization rate increased from 6.74 to 93.41% at 270 °C. More stable structures with aromatic and N-heterocycles rings were formed through hydrolysis and polymerization. The H/C and O/C ratio decreased from 1.75 to 0.60 to 1.04 and 0.09, and the combustion stability index (H f) decreased from 0.86 to 0.60 °C.103, and the flammability index (S) increased from 24.16 to 26.42 %/(min2 °C3) 10−8, indicating an improvement of fuel performance. A kinetic model to describe the conversion of organic components of CS was developed to elucidate the formation mechanism of hydrochar combined with the change of water-soluble intermediates (SM). The solid-solid conversion reaction of protein and humus components was the predominant hydrochar formation pathway, with an activation energy (Ea) of 26.06 kJ/mol. The polymerization of aromatic compounds slightly participated in the hydrochar formation, with an Ea of 86.12 kJ/mol. The water-soluble intermediates mostly transformed into inorganic substances (IS) through decarboxylation, deamination, or decomposition reaction, with an Ea of 5.73 kJ/mol. This study provided insights for understanding the formation of hydrochar from CS through HTC, which is vital for controlling the polymerization of intermediates and solid-solid conversion to enhance the carbonization efficiency. [Display omitted] • CS converted into CHC with aromatic and N-heterocyclic structures. • Higher temperature and longer time were conducive to the formation of CHC. • The fuel performance of CHC was improved and reaches optimum at 210 °C. • A kinetic model of HTC based on organic components in CS was proposed. • The solid-solid reaction of Protein and humus dominates the CHC formation. [ABSTRACT FROM AUTHOR]

Biochar (BC) and hydrochar (HC) are solid by-products obtained from various types of biomasses through the processes of pyrolysis and hydrothermal carbonization, respectively. Both BC and HC represent a sustainable solution for carbon sequestration and can be used as soil amendments or sorbents for organic and inorganic pollutants. However, the properties of BC and HC largely depend on feedstock and production parameters, which significantly affect their proper use. A detailed characterization of these materials is therefore needed to assess their suitability for environmental and/or agricultural applications. In this work, two BC samples and two HC samples were characterized with a multianalytical approach, including total reflection X-ray fluorescence (TXRF) spectroscopy, scanning electron microscopy (SEM), Fourier-transform infrared (FT-IR) spectroscopy, thermogravimetric analyses (TG), and pyrolysis coupled to gas chromatography and mass spectrometry (Py-GC/MS). By comparing BC and HC data, HC showed a higher content of mineral elements, including important plant nutrients and potentially toxic elements. HC produced from solid urban wastes contained also some potentially toxic organic molecules, like chlorinated aromatic compounds. BC samples were characterized by a higher porosity and hydrophobicity than HC, thus being potentially more suitable for the sorption of organic pollutants. HC samples showed a higher content of cellulose and hemicellulose, resulting in a more hydrophilic but less thermally stable material than BC. In conclusion, both BC and HC have interesting properties for environmental and agricultural applications but careful selection of feedstock is needed, especially for HC production. • BC and HC have different properties depending on feedstock and production process. • BC and HC samples were studied by TXRF, FT-IR, SEM, TG, Py-GC/MS. • BC samples showed a higher pH, porosity and hydrophobicity compared to HC. • HC showed a higher content of mineral elements and potentially toxic substances. • Both BC and HC can be used as sorbents or soil amendments. [ABSTRACT FROM AUTHOR]

Hydrothermal carbonization of biogas slurry and animal manure into hydrochar could enhance waste recycling waste and minimize ammonia (NH 3) volatilization from paddy fields. In this study, cattle manure-derived hydrochar prepared in the presence of Milli-Q water (CMWH) and biogas slurry (CMBSH), and biogas slurry-based hydrochar embedded with zeolite (ZHC) were applied to rice-paddy soil. The results demonstrated that CMBSH and ZHC treatments could significantly mitigate the cumulative NH 3 volatilization and yield-scale NH 3 volatilization by 27.9–45.2% and 28.5−45.4%, respectively, compared to the control group (without hydrochar addition), and significantly correlated with pH and ammonium–nitrogen (NH 4 +–N) concentration in floodwater. Nitrogen (N) loss via NH 3 volatilization in the control group accounted for 24.9% of the applied N fertilizer, whereas CMBSH- and ZHC-amended treatments accounted for 13.6−17.9% of N in applied fertilizer. The reduced N loss improved soil N retention and availability for rice; consequently, grain N content significantly increased by 6.5–14.9% and N-use efficiency increased by 6.4–16.0% (P < 0.05), respectively. Based on linear fitting results, NH 3 volatilization mitigation resulted from lower pH and NH 4 +–N concentration in floodwater that resulted from the acidic property and specific surface area of hydrochar treatments. Moreover, NH 3 -oxidizing archaea abundance in hydrochar-treated soil decreased by 40.9–46.9% in response to CMBSH and ZHC treatments, potentially suppressing NH 4 +–N transformation into nitrate and improving soil NH 4 +–N retention capacity. To date, this study applied biogas slurry-based hydrochar into paddy soil for the first time and demonstrated that ZHC significantly mitigated NH 3 and increased N content. Overall, this study proposes an environmental-friendly strategy to recycle the wastes, biogas slurry, to the paddy fields to mitigate NH 3 volatilization and increase grain yield of rice. [Display omitted] • Biogas slurry and manure were transformed into hydrochar as one soil conditioner. • Biogas-slurry-hydrochars mitigated NH 3 volatilization by 27.9–45.2%. • NH 3 mitigation by hydrochars contributed to improve soil N retention and grain N. [ABSTRACT FROM AUTHOR]

The popularization of large-scale biogas project makes the disposal of fermentative residue an urgent issue to be solved. Hydrothermal carbonization (HTC) technology is suitable for treating wet biomass to produce carbonaceous materials. In this study, the solid residue from the two-phase anaerobic digestion (AD) was hydrothermally converted in the range of 180–240 °C, and the hydrochar and aqueous components were characterized for subsequent utilization. The heating values of hydrochar were indicated to be increased by 14.2% and 16.6% at 210 °C and 240 °C as compared with feedstock, and also the specific surface areas were 34.8 m2/g and 27.1 m2/g with 17.4- and 13.3-fold enhancement, respectively. The migration of elements such as S, Cl, K to aqueous phase was beneficial for fuel application. The mesoporous pores were dominant in hydrochars with ample oxygenated functional groups. In addition, the wastewater involved organic acids, phenols, and nitrogen-containing compounds, etc. Evaluating the biodegradability by AD, it was found that when the initial concentration was ≤8 g COD/L, the maximum methane yields up to 275.9 mL CH 4 /g COD removal and 277.6 mL CH 4 /g COD removal were obtained. The enhanced toxicity/inhibition of representative pollutants on microorganisms was significant at higher organic loading, which could be indicated in the microbial structure and diversity. As a conclusion, the integrated production of hydrochar and methane will provide an extended route for further processing of lignocellulosic fermentative residue. [Display omitted] • Moderate temperature was beneficial for the formation of high-performance hydrochar. • The exhibited characteristics of hydrochar made HTC more suitable to treat wet biomass. • The fermentative residue was conducive to the formation of porous structure. • The biodegradability and toxicity during AD of HTCWW was further demonstrated. • The production of hydrochar and methane was integrated to maximize the energy recovery. [ABSTRACT FROM AUTHOR]

Protein, calcium carbonate, and chitin are abundant in shrimp shells. In this study, chemical treatment followed by hydrothermal carbonization was used to synthesize the nitrogen-rich hydrochar (HSHC) from shrimp shells. The untreated hydrochar exhibited a higher amount of calcium (25.37%) and less amount of nitrogen (2.68%) with alkaline pH (9.1). Interestingly chemical pre-treatment on shrimp shells boosted the nitrogen content to 6.81% and eliminated the calcium while controlling the pH to 6.4, which was beneficial for oxo-vanadate removal. The HSHC achieved vanadium(V) adsorption capacity of 21.20 mg/g at an optimal solution pH of 3.0, whereas the pristine hydrochar performed poorly (0.66 mg/g). The abundance of oxygen and nitrogen-based functional groups that developed through the chemical treatment resulted in improved adsorption coupled reduction performance of HSHC. This study proposed an inexpensive and environmentally friendly method for converting waste shrimp shells into value-added adsorbent. [Display omitted] • Nitrogen rich composite was successfully prepared by HCl washed shrimp shells • The pHzpc of the HSHC was extended to 3.84 from its original hydrochar (2.54) • The HSHC achieved a vanadium (V) adsorption capacity of 21.20 mg/g, whereas SHC performed poorly (0.66 mg/g) • Oxo-vanadate can be reduced by adsorption-coupled reduction method [ABSTRACT FROM AUTHOR]

Aiming to upgrade agro-forest wastes into value-added solid and gaseous fuels in the present investigation, hydrothermal carbonization (HTC) of spruce (SP), canola hull (CH), and canola meal (CM) was optimized in terms of operating conditions, maximizing the higher heating value of hydrochars. The optimal operating conditions were achieved at HTC temperature, reaction time, and solid-to-liquid ratio of 260 °C, 60 min, and 0.2 g mL−1, respectively. At the optimum condition, succinic acid (0.05–0.1 M) was used as HTC reaction medium to investigate the effects of acidic medium on the fuel characteristics of hydrochars. The succinic acid assisted HTC was found to eliminate ash-forming minerals e.g., K, Mg, and Ca from hydrochar backbones. The calorific values, H/C and O/C atomic ratios of hydrochars were in the range of 27.6–29.8 MJ kg−1, 0.8–1.1, and 0.1–0.2, respectively, indicating the biomass upgrading into coal-like solid fuels. Finally, hydrothermal gasification of hydrochars with their corresponding HTC aqueous phase (HTC-AP) was assessed. Gasification of CM resulted in a relatively high H 2 yield of 4.9–5.5 mol kg−1 followed by that for SP with 4.0–4.6 mol H 2 per kg of hydrochars. Results suggest that hydrochars and HTC-AP have a great potential for H 2 production via hydrothermal co-gasification, while suggesting HTC-AP reuse. [Display omitted] • Hydrothermal carbonization/gasification was used to recover energy from agro-forest wastes. • The hydrochar HHV reached 27.6–29.8 MJ kg−1 under optimal HTC operating conditions. • Succinic acid-assisted HTC decreased O/C atomic ratios of hydrochars 13.6–25.0%. • Hydrochars and HTC-aqueous phase (HTC-AP) were hydrothermally co-gasified. • Canola meal hydrochars with HTC-AP of pH 8 obtained the H 2 yield of 5.5 mol kg−1. [ABSTRACT FROM AUTHOR]

The recovery of phosphorus from sewage sludge was critical due to the depletion of phosphate ore. The present research aims to identify the phosphorus speciation and reveal the phosphorus transformation mechanism of dewatered sewage sludge during hydrothermal conversion (HTC) process, as well as to achieve the high efficiency recovery of phosphorus. Multiple analysis of SMT method, VK diagram, XANES and NMR showed that most phosphorus (>80%) was transferred to the hydrochar and presented as inorganic phosphorus (IP) after the HTC process. A dehydration trend was observed of the HTC process with the increase of sub-critical temperature. Ca-associated phosphorus increased significantly as the temperature increased. The Pyro-P gradually transformed to Ortho-P with the increase of HTC temperature and disappeared at 320 °C. The addition of HCl (6.13 and 12.3 mmol/g) in the HTC process resulted in a high percentage (>80%) of phosphorus transferred to the aqueous phase, and the bioavailability of the residual phosphorus increased significantly. The recovery rate of phosphorus could achieve 98.37% at the pH of 7.52, with the struvite purity of 90.41%. The results of this study provide new insights into the selective transfer of phosphorus in dewatered sludge by HTC process, in addition to some efficient ways for the utilisation of the HTC products. • Multiple analyses of SMT method, XANES and NMR were conducted. • Transformation mechanism of P during the HTC process were investigated. • Quantitative analysis of P speciation was conducted by LCF. • P was selectively transferred to aqueous phase by adding HCl. • HCl addition favored the further utilizations of HTC products. [ABSTRACT FROM AUTHOR]

Abstract Efforts to improve water quality have led to the development of green and sustainable water treatment approaches. Herein, nitrogen-doped magnetized hydrochar (mSBHC-N) was synthesized, characterized, and used for the removal of post-transition and transition heavy metals, viz. Pb2+ and Cd2+ from aqueous environment. mSBHC-N was found to be mesoporous (BET surface area – 62.5 m2/g) and paramagnetic (saturation magnetization – 44 emu/g). Both, FT-IR (with peaks at 577, 1065, 1609 and 3440 cm−1 corresponding to Fe – O stretching vibrations, C – N stretching, N – H in-plane deformation and stretching) and XPS analyses (with peaks at 284.4, 400, 530, 710 eV due to C 1s, N 1s, O 1s, and Fe 2p) confirmed the presence of oxygen and nitrogen containing functional groups on mSBHC-N. The adsorption of Pb2+ and Cd2+ was governed by oxygen and nitrogen functionalities through electrostatic and co-ordination forces. 75–80% of Pb2+ and Cd2+ adsorption at C o : 25 mg/L, either from deionized water or humic acid solution was accomplished within 15 min. The data was fitted to pseudo-second-order kinetic and Langmuir isotherm models, with maximum monolayer adsorption capacities being 323 and 357 mg/g for Cd2+and Pb2+ at 318 K, respectively. Maximum Cd2+ (82.6%) and Pb2+ (78.7%) were eluted with 0.01 M HCl, simultaneously allowing minimum iron leaching (2.73%) from mSBHC-N. In conclusion, the study may provide a novel, economical, and clean route to utilize agro-waste, such as sugarcane bagasse (SB), for aquatic environment remediation. Graphical abstract Image 1 Highlights • Waste sugarcane bagasse was used as precursor to produce hydrochar (SBHC). • SBHC was magnetized and functionalized to N-doped magnetized hydrochar (mSBHC-N). • mSBHC-N was characterized by XRD, FT-IR, SEM-EDX, VSM, XPS, TEM and BET analysis. • mSBHC-N showed fast and high Pb2+ (357 mg/g) and Cd2+ (323 mg/g) uptake. • Electrostatic and co-ordination forces played a foremost role in metals adsorption. [ABSTRACT FROM AUTHOR]

Abstract Hydrochars derived from hickory wood and peanut hull through hydrothermal carbonization were activated with H 3 PO 4 and KOH to improve their performance as a volatile organic compound (VOC) adsorbent. Polar acetone and nonpolar cyclohexane were used as representative VOCs. The VOC adsorptive capacities of the activated hydrochars (50.57–159.66 mg⋅g−1) were greater than that of the nonactivated hydrochars (15.98–25.36 mg⋅g−1), which was mainly caused by the enlargement of surface area. The significant linear correlation (R2 = 0.984 on acetone, and R2 = 0.869 on cyclohexane) between BET surface areas of hydrochars and their VOC adsorption capacities, together with the obvious adsorption exothermal peak of differential scanning calorimetry curve confirmed physical adsorption as the dominating mechanism. Finally, the reusability of activated hydrochar was tested on H 3 PO 4 activated hickory hydrochar (HHP), which had higher acetone and cyclohexane adsorption capacities. After five continuous adsorption desorption cycles, the adsorptive capacities of acetone and cyclohexane on HHP decreased by 6.2% and 7.8%, respectively. The slight decline in adsorption capacity confirmed the reusability of activated hydrochar as a VOC sorbent. Graphical abstract Image Highlights • Chemically activated hydrochars showed good removal of acetone and cyclohexane. • Sorption capacities of the activated hydrochars were 50.57–159.66 mg g−1 • Surface areas of hydrochars and their adsorption capacities had a strong linear correlation. • Physical adsorption was the dominant mechanism. • Activated hydrochar showed good reusability. [ABSTRACT FROM AUTHOR]

To overcome the limitations imposed by Sn–Sb electrodes, the titanium foam (PMT)-TiO 2 -NTs@NiO–C/Sn–Sb composite electrodes with cubic crystal structure are synthesized by introducing NiO@C nanosheet arrays interlayer on the TiO 2 -NTs/PMT matrix through hydrothermal and carbonization process. Then a two-step pulsed electrodeposition method is used to prepare the Sn–Sb coating. Benefiting from the advantages of stacked 2D layer-sheet structure, the obtained electrodes exhibit enhanced stability and conductivity. Synergy of inner and outer layers fabricated by different pulse times strongly influence the electrochemical catalytic properties of the PMT-TiO 2 -NTs@NiO–C/Sn–Sb (Sn–Sb) electrode. Hence, the Sn–Sb (b0.5 h + w1 h) electrode is the optimal electrode to degrade the Crystalline Violet (CV). Next, the effect of the four experimental parameters (initial CV concentration, current density, pH value and supporting electrolyte concentration) on the degradation of CV by the electrode are investigated. The degradation of the CV is more sensitive to alkaline pH, and the rapid decolorization of CV when the pH is 10. Moreover, the possible electrocatalytic degradation pathway of CV is performed using HPLC-MS. Results from the tests show that the PMT-TiO 2 -NTs/NiO@C/Sn–Sb (b0.5 h + w1 h) electrode is an interesting alternative material in industrial wastewater applications. [Display omitted] • Preparation of Ni-MOF nanosheet arrays by hydrothermal and carbonization process. • Two-step pulse method for the preparation of cubic structured electrodes. • Accelerated service life of the Sn–Sb (b0.5 h + w1 h) electrode increased by 3 times. • The rapid decolorization of CV showed up to 100% when the pH was 10. • The degradation mechanism of Crystalline Violet was proposed. [ABSTRACT FROM AUTHOR]

Capturing the abundant organic matter residing in wastewater can not only reduce the emission of CO 2 from the source, but the enriched organics can also be used for anaerobic fermentation to generate and offset energy consumption in wastewater treatment processes. The key is to find or develop low-cost materials that can capture organic matter. Herein, sewage sludge-derived cationic aggregates (SBC-g-DMC) were successfully prepared via a hydrothermal carbonization process coupled with a graft copolymerization reaction for recovering organic matter from wastewater. Based upon preliminary screening of synthesized SBC-g-DMC aggregates regarding grafting rate, cationic degree, and flocculation performance, SBC-g-DMC 2.5 aggregate prepared with 60 mg of initiator, DMC-to-SBC mass ratio of 2.5:1, 70 °C, and 2 h of reaction time was selected for further characterization and evaluation. Results showed that SBC-g-DMC 2.5 aggregate has a positively-charged surface over a wide pH range of 3–11 and a hierarchical micro-/nano-structure, endowing it with an excellent organic matter capture efficiency (97.2% of pCOD, 68.8% of cCOD, and 71.2% of tCOD). Meanwhile, SBC-g-DMC 2.5 exhibits inappreciable trapping ability for the dissolved COD, NH 3 –N, and PO 4 3−, guaranteeing the regular running of subsequent biological treatment units. Electronic neutralization, adsorption bridging, and sweep coagulation between cationic aggregates surface and organic matter were identified as the primary mechanisms for SBC-g-DMC 2.5 to capture organics. This development is expected to provide a theoretical reference for sewage sludge disposal, carbon reduction, and energy recovery during municipal wastewater treatment. [Display omitted] • Cationic aggregates (SBC-g-DMC) with high organic matter capture capability were obtained from sewage sludge. • By optimizing graft copolymerization conditions, the grafting rate of quaternary ammonium groups could reach up to 116.8%. • SBC-g-DMC exhibits an excellent capture efficiency of over 97.2% for particulate COD. • Electric neutralization are the primary mechanisms for SBC-g-DMC to capture organics. [ABSTRACT FROM AUTHOR]

This study assessed the properties and toxicity (water cress germination trials) of 38 waste-derived, novel biochar-mineral composites (BMCs) produced via slow pyrolysis and hydrothermal carbonization (hydrochars). The biochars were produced from sewage sludge and compost-like output (CLO) by varying the type of mineral additive (zeolite, wood ash and lignite fly ash), the mineral-to-feedstock ratio and the carbonization process. While pure hydrochars completely inhibited germination of water cress, this effect was ameliorated by mineral additives. Seedlings grew best in pyrolysis chars and while wood ash addition decreased plant growth in many cases, 1:10 addition to CLO doubled germination rate. The factors responsible for the phytotoxicity can be attributed to pH, salinity and organic contaminants. Importantly, while pure minerals inhibited germination, conversion of minerals into BMCs reduced their inhibitory effects due to buffered release of minerals. Overall, mineral wastes (e.g., combustion ashes) and waste biomass can be used safely as sources of nutrients and stable organic carbon (for soil carbon sequestration) when converted into specific biochar-mineral composites, exploiting synergies between the constituents to deliver superior performance. [ABSTRACT FROM AUTHOR]

Hydrothermal carbonization (HTC) thermally converts wet biomasses to carbon materials, dramatically reducing energy use for drying and improving solid product yield compared to pyrolysis process. However, researches regarding agricultural usage of hydrochar (HC) are limited. In the present study, the influence of HC amendment on CH 4 and N 2 O emissions, as well as global warming potential (GWP) and greenhouse gas intensity (GHGI) were investigated. Additionally, pyrochar (PC) treatments as well as two char-free control treatments with (CKU) or without (CK) N fertilizer were also included for comparison. Chars were produced from wheat straw (WC) and saw dust (SC) and applied at different rates (0.5% and 3%, w/w ). Both hydrochar and pyrochar decreased paddy CH 4 emissions when amended at a lower rate (0.5%) compared to CKU treatment, which was more obvious for pyrochar when applied at the rate of 3%. Contrarily, 3%-HC significantly stimulated CH 4 emissions, which were around 5 and 3 times higher than that of CKU for WC and SC, respectively. Furthermore, hydrochar showed the potential to decrease paddy N 2 O emissions (6.06–32.32%) at both application rates. However, N 2 O emissions with PC treatments varied depending on application rate (20.20–75.76%). GWP and GHGI values of 0.5%-HC and PC treatments were similar, 6.67–25.00% and 3.85–25.00% lower than those of CKU treatment, respectively. However, 3%-HC amendments led to significantly increased GWP and GHGI. This study suggested that application rate of hydrochar used in rice fields should be taken into serious consideration to fulfill its potential in GHGs mitigation and minimize environmental side effects. [ABSTRACT FROM AUTHOR]

A simple route is presented to fabricate carboxylic-functional carbon-coated polyacrylonitrile nanofibers (oPAN@C) through preoxidation and hydrothermal carbonization. PAN fibers were firstly preoxidized to form aromatic ladder structure with the resistance to hydrothermal condition, in which more carboxyl groups were introduced on the fiber surface at the present of chitosan and citric acid. The oPAN@C composites exhibit a high adsorption capacity towards methylene blue (MB) and lead ion (Pb 2+ ). The adsorption data matched the pseudo-second-order kinetic model and Langmuir model well with the maximum adsorption capacity (153.37 and 143.27 mg g −1 ) for methylene blue and Pb 2+ , respectively. Moreover, oPAN@C could be regenerated easily by hydrochloric acid, and still remained high removal efficiency after 5 cycles. Therefore, oPAN@C fibers should have potential application in sewage treatment. [ABSTRACT FROM AUTHOR]

To solve sludge disposal and management problems during dyeing wastewater treatment, the produced excess biological sludge and ferric sludge were fabricated into a magnetic biochar composite (MBC) under the optimal hydrothermal carbonization (HTC) conditions. With ferric sludge mixing, the generated MBC contained paramagnetic Fe 3 O 4 , showed a smaller diameter of approximately 200 nm, a smaller pore size, a larger specific surface area and a higher carbonization degree than BC prepared using a single biological sludge process under the same HTC conditions. Additionally, biochar and Fe 3 O 4 in the MBC were found to be tightly combined through chemical bonding, imparting MBC with its own property of magnetic recycling. The stable high Methylene Blue (MB) degradation performance in a Fenton reaction after recycling designated it as a good catalyst. The MB degradation pathway was proposed based on GC–MS results. When the MBC was used to treat actual dyeing wastewater through a Fenton process, the chemical oxygen demand (COD) and total organic carbon (TOC) removal efficiencies reached 47 ± 3.3% and 49 ± 2.7%, respectively. Therefore, MBC could be recycled as a catalyst in dyeing wastewater treatment. And a methodology is described that minimizes the produced sludge and enables sludge internal recycling in a dyeing wastewater treatment plant. [ABSTRACT FROM AUTHOR]

To investigate hydrochar as a soil amendment for the immobilization of Cd, the characteristics of hydrochars (HCs) under three temperatures and residence times, were studied, with a particular interest in soil properties, as well as the speciation, availability and plant uptake of Cd. HCs were obtained by a hydrothermal carbonization (HTC) reaction of sewage sludge (SS). Based on the study of HC properties, we found that HCs present weak acidity with relatively high ash content and low electrical conductivity (EC) values. The addition of HCs to soil decreased soil pH and EC values but increased the abundance of soil microorganism. HCs also promoted the transformation of Cd from unstable to stable speciation and can decrease the content of phyto-available Cd (optimum condition and efficiency: A13, 2 15.38%), which restrained cabbage from assimilating Cd from soil both the aboveground (optimum condition and efficiency: A35, 52.29%) and underground (optimum condition and efficiency: C15, 57.53%) parts of it. [ABSTRACT FROM AUTHOR]

Industrial wastewater typically contains both cationic and anionic heavy metals; therefore, their simultaneous removal must be considered to ensure environmental sustainability. Herein, nitrogen heteroatom (N) doped hydrochar derived from corncob was prepared via facile NH 4 Cl-aided hydrothermal carbonization and used for the simultaneous adsorption of divalent copper (Cu(II)) and hexavalent chromium (Cr(VI)) in aqueous solutions. During hydrothermal carbonization, NH 4 Cl played a vital role as the porogen and N dopant, which contributed to the efficient adsorption affinity toward coexisting Cu(II) and Cr(VI). The theoretical maximum adsorption capacities of the N-doped hydrochar were determined to be 1.223 mmol/g for Cu(II) and 1.995 mmol/g for Cr(VI), which were much better than those of the pristine hydrochar. Furthermore, in the binary-component system, the synergistic effect between Cu(II) and Cr(VI) significantly promoted the adsorption affinity of N-doped hydrochar, resulting in adsorption capacities for Cu(II) and Cr(VI) 9.48 and 1.92 times higher than those of the single-component system, respectively. A series of adsorption experiments and spectroscopic analyses demonstrated that multiple mechanisms, including electrostatic shielding, cation bridging, and redox reactions, mutually contributed to the synergistic effect in the adsorption of coexisting Cu(II) and Cr(VI). Overall, the N-doped hydrochar proved to be effective in simultaneously removing both cationic and anionic heavy metal pollutants. [Display omitted] • N-doped hydrochar was synthesized via NH 4 Cl-aided hydrothermal carbonization. • NH 4 Cl-derived NH 3 and HCl acted as N dopant and porogen, respectively. • N-doped hydrochar simultaneously removed Cu(II) and Cr(VI) from water. • Coexistence of Cu(II) and Cr(VI) provided synergistic effect on N-doped hydrochar. • Synergistic mechanism included shielding effect, cation bridge, and redox reaction. [ABSTRACT FROM AUTHOR]

Metal-free carbon-based catalysts hold great promise for the degradation of organic pollutants by peroxymonosulfate (PMS) activation because they avoid the negative effects of metal catalysts such as harmful metal ions leaching. However, these carbon-based catalysts are limited by their high cost and complex synthesis, and the mechanisms for the activation of PMS are unclear. Herein, the N-rich carbon catalysts (GCN-x) derived from glucose and g-C 3 N 4 were facilely synthesized by hydrothermal treatment and carbonization to explore the mechanism of PMS activation. The nitrogen content of catalysts could be adjusted by simply altering the ratio of glucose and g-C 3 N 4. GCN-2.4 with a ratio of glucose and g-C 3 N 4 of 2.4 displayed the highest efficiency for the degradation of pollutants represented by Levofloxacin. The electron paramagnetic resonance and quenching experiments demonstrated that the non-radical pathway was dominant in Levofloxacin degradation and singlet oxygen (1O 2) was the main active specie. Further, we found 1O 2 was generated from superoxide radical (• O 2 −) which has rarely been studied. Levofloxacin degradation rate was shown to be positively correlated with both the amount of graphitic N and pyridinic N. Graphitic N and pyridinic N were identified as the catalytic sites. The GCN-2.4/PMS system could also remove multifarious contaminants effectively. Overall, this research advances understanding of the role of N species in PMS activation and has potential practical application in wastewater treatment. [Display omitted] • The N content of GCN could be regulated by the amount of glucose. • In GCN/PMS system, nonradical pathway was dominant and singlet oxygen (1O 2) was the main active specie. • Graphitic N was the main catalytic sites to activate PMS. • GCN/PMS system had strong anti-interference ability to the pH changes and showed superior stability in multiple cycles. [ABSTRACT FROM AUTHOR]

Hydrothermal carbonization of sewage sludge converts waste into hydrochar; however, the complex organic composition of feedstock limits the product value. A novel process that combines liquid dimethyl ether extraction and hydrothermal carbonization (DE–HTC) was proposed for improving the product value by simultaneously producing biocrude/hydrochar and improving feedstock suitability for thermochemical conversion. Biocrude and hydrochar with a product yield of 2.62% and 55.83% were produced via DE–HTC, respectively. The hydrochar yield increased by 12.65%–29.90% compared to traditional single-step hydrothermal carbonization. The hydrochar energy densification was decreased by 1.16%–10.28%, while hydrochar's energy yield increased by 47%–66%, and it had a more prominent porous structure. By avoiding the decomposition of proteins during thermochemical conversion, the nitrogen content of the biocrude obtained via DE–HTC was only 0.38%. The biocrude was also further qualitatively analyzed. This study provides insights into the efficacy of a novel hydrothermal method with distinct product value advantages over direct hydrothermal carbonization. [Display omitted] • A novel process combine DME extraction & hydrothermal carbonization was proposed. • Biocrude and hydrochar with a yield of 2.62% and 55.83% were produced via DE–HTC, respectively. • The energy yield of DE-HTC was increased by 47%–66% compared to HTC directly. • Pretreatment of sewage sludge by DME extraction increased the hydrochar yield by 12.65%–29.90%. • Biocrude with was 0.38% nitrogen content was obtained in DE-HTC process. [ABSTRACT FROM AUTHOR]

Ibuprofen (IPF) is one of the most prescribed nonsteroidal anti-inflammatory drugs in recent times, but it is not readily removed in conventional wastewater treatments. Here, we investigate the adsorption characteristics of IPF onto calcined spherical hydrochar (CSH), which was synthesized through hydrothermal carbonization of sucrose followed by calcination. The adsorption experiments show that the equilibration time for IPF was 360 min, and a pseudo-second-order model was best fitted to the kinetic data. The isotherm data were best described by the Liu model with a theoretical maximum adsorption capacity of 95.6 mg/g. The thermodynamic data indicate the endothermic nature of the adsorption at 10–40 °C. The CSH was favorably regenerated and reused using methanol. In pH experiments, the IPF adsorption capacity declined gradually as pH rose from 2 to 8, dropped rapidly at pH 10, and became negligible at pH 12. The IPF adsorption to the CSH could occur through various adsorption mechanisms. Hydrogen-bond formation, π-π interactions, n -π* interactions, and electrostatic repulsion were explored and visualized with molecular modeling using CHEM3D. The Raman, FTIR, and XPS spectra suggest that π-π interactions could take place between the CSH and IPF. Considering the pK a value of IPF (4.91) and pH iep of the CSH (3.21), electrostatic repulsion between the negatively-charged CSH and anionic IPF could play a negative role in the adsorption. A pore-filling mechanism could contribute to the adsorption in view of the molecular size of IPF (9.43 Å × 7.75 Å × 6.23 Å) and the average pore diameter of the CSH (2.27 nm). In addition, hydrophobic interactions could be involved in the adsorption. Multi-factor adsorption experiments were executed with pH, temperature, CSH dosage, and initial IPF concentrations as input variables and IPF removal rate as an output variable, and an artificial neural network (ANN) model with a topology of 4:9:11:1 was developed to sufficiently describe the adsorption data (R > 0.99). Further analyses with additional experimental data confirm that the ANN model possessed good predictability for multi-factor adsorption. [Display omitted] • The CSH was synthesized via hydrothermal carbonization of sucrose followed by calcination. • Theoretical maximum IPF adsorption capacity of the CSH from the Liu model was 95.6 mg/g. • The adsorption of IPF onto the CSH exhibited the endothermic nature at 10–40 °C. • The adsorption mechanisms of IPF onto the CSH was explored by molecular modeling with CHEM3D. • Developed ANN model with a topology of 4:9:11:1 had good predictability for multi-factor IPF adsorption. [ABSTRACT FROM AUTHOR]

Biochar (e.g. pyrochar and hydrochar) is considered a promising adsorbent for Cd removal from aqueous solution. Considering the vastly different physicochemical properties between pyrochar and hydrochar, the Cd2+ sorption capacity and mechanisms of pyrochars and hydrochars should be comparatively determined to guide the production and application of biochar. In this study, the hydrochars and pyrochars were prepared from Napier grass by hydrothermal carbonization (200 and 240 °C) and pyrolysis (300 and 500 °C), respectively, and the physicochemical properties and Cd2+ sorption performances of biochars were systematically determined. The pyrochars had higher pH and ash content as well as better stability, while the hydrochars showed more oxygen-containing functional groups (OFGs) and greater energy density. The pseudo second order kinetic model best fitted the Cd2+ sorption kinetics data of biochars, and the isotherm data of pyrochar and hydrochar were well described by Langmuir and Freundlich models, respectively. In comparison with hydrochar, the pyrochar exhibited better Cd2+ sorption capacity (up to 71.47 mg/g). With increasing production temperature, the Cd2+ sorption capacity of pyrochar elevated, while the reduction was found for hydrochar. The mineral interaction, complexation with surface OFGs, and coordination with π electron were considered the main mechanisms of Cd2+ removal by biochars. The minerals interaction and the complexation with OFGs was the dominant mechanism of Cd2+ removal by pyrochars and hydrochars, respectively. Therefore, the preparation technique and temperature have significant impacts on the sorption capacity and mechanisms of biochar, and pyrochar has better potential for Cd2+ removal than the congenetic hydrochar. [Display omitted] • Cd2+ sorption capacity of biochar was affected by production technique and temperature. • Pyrochar exhibited greater Cd2+ adsorption capacity than hydrochar. • The interaction with minerals dominated the Cd2+ adsorption on pyrochars. • Complexation with OFGs was the main mechanism of Cd2+ adsorption on hydrochars. [ABSTRACT FROM AUTHOR]

Functional colloidal carbon materials find various applications, including the remediation of contaminated water and soil in so-called particle-based in-situ remediation processes. In this study, uniform and highly dispersible micro-sized carbonaceous spheres (CS) were generated by hydrothermal carbonization (HTC) of sucrose in the presence of carboxymethyl cellulose (CMC) as environmentally friendly polyelectrolyte stabilizer. In order to ensure their optimal subsurface delivery and formation of a self-contained treatment zone, a narrow size distribution and low agglomeration tendency of the particles is desired. Therefore, the obtained CS were thoroughly characterized and optimized with respect to their colloidal properties which are a crucial factor for their application as quasi-liquid sorbent. The as-prepared uniform CS are readily dispersible into single particles in water as confirmed by digital microscopy and form stable suspensions. Due to their perfectly spherical shape, particle sedimentation in aqueous suspensions is well predicted by Stokes' law. High sorption coefficients on the synthesized CS K D,CS were determined for phenanthrene (up to log (K D,CS /[L kg−1]) = 5) and other hydrophobic groundwater contaminants. This confirms the application potential of the CS, which were prepared by an economic low-temperature process using sucrose as bio-based precursor, for generating in-situ sorption barriers for groundwater and soil remediation. [Display omitted] • Carbonaceous microspheres via HTC of sucrose in presence of eco-friendly polymer. • Uniform microspheres are highly dispersible and form stable aqueous suspensions. • High sorption affinity for hydrophobic pollutants. • Potential application as in-situ sorption barriers for groundwater remediation. [ABSTRACT FROM AUTHOR]

Hydrothermal carbonization (HTC) is emerging as a promising technology for the management of sewage sludge. The fate of phytosanitary products, Polycyclic aromatic hydrocarbons (PAHs) and PCBs (Polychlorinated biphenyls) after HTC, as well as the formation of dioxins and furans, is still unclear. Moreover, only little information is available on the distribution of heavy metals and major nutrients between the hydrochars and the process water. Here, we aim to contribute to fill these gaps. HTC of sewage sludge from six different wastewater treatment plants has been carried out at 220 °C for 85 min. Feedstock, hydrochars and spent liquor have been then characterized and discussed. HTC is here proven to be a suitable technology for the immobilization of both heavy hydrocarbons and heavy metals, with the exception arsenic, which was also found in the spent liquor at a significant proportion (∼15–∼50%). DDD, DDT, DDE were detected in all sludge samples and their content was reduced by nearly one order of magnitude after the process. HTC is here proven to not be responsible at an appreciable extent of PCBs enrichment of the processed solids. Moreover, the sum of PCDDs and PCDFs in hydrochars never exceeded 20 ng kg−1 s.s. The results obtained encourage further developing of HTC, with the aim to improve the sustainability of sewage sludge management. Additional studies on the environmental impact of hydrochar when used as alternative fuel, as well as soil amendment, could lead to the overcoming of the issues which still hinder these applications. [Display omitted] • HTC is a suitable pathway for the immobilization of heavy hydrocarbons and metals. • The sum of PCDDs and PCDFs in the hydrochars did never exceed 20 ng kg−1 s.s. • HTC is here proven to not be responsible of PCBs enrichment of the processed solids. [ABSTRACT FROM AUTHOR]

Textile industry utilize a massive amount of dyes for coloring. The dye-containing effluent is released into wastewater along with heavy metals that are part of dye structure. The treatment of textile industry wastewater using conventional techniques (coagulation, membrane technique, electrolysis ion exchange, etc.) is uneconomical and less efficient (for a low concentration of pollutants). Moreover, most of these techniques produce toxic sludge, making them less environmentally friendly. Algae base industry is growing for food, cosmetics and energy needs. Algae biomass in unique compared to lignocellulosic biomass due to presence of various functional group on its surface and presence of various cations. These two characteristics are unique for biochar as a tool for environmental decontamination. Algae biomass contain functional groups and cations that can be effective for removal of organic contaminants (dyes) and heavy metals. Algae can be micro and macro and both have entirely different biomass composition which will lead to a synthesis of different biochar even under same synthesis process. This study reviews the recent progress in the development of an economically viable and eco-friendly approach for textile industry wastewater using algae biomass-derived absorbents. The strategy employed microalgal biochar to remove organic pollutants (dyes) and heavy metals from textile effluents by biosorption. This article discusses different methods for preparing algal biochar (pyrolysis, hydrothermal carbonization and torrefaction), and the adsorption capacity of biochar for dyes and heavy metals. Work on hydrothermal carbonization and torrefaction of microalgal biomass for biochar is limited. Variation in structural and functional groups changes on biochar compared to original microalgal biomass are profound in contract with lignocellulosic biomass. Existing Challenges, future goals, and the development of these technologies at the pilot level are also discussed. • Biosorption of microalgae and microalgae derived biochar are presented. • Factors effecting the biosorption of heavy metal and dyes are discussed. • Challenges, environmental concerns and way forward schemes are presented. [ABSTRACT FROM AUTHOR]

The application of hydrothermal carbonization to improve biomass-derived energy sources is crucial because of insufficient supplies of fossil fuels and concerns associated with the impact of fossil fuels on the environment. Hydrothermal carbonization technology has been developed to circumvent the energy-intensive drying step required for the thermal conversion of high-moisture organic feedstocks into fuel. In this study, the quality of livestock manure was upgraded, and its energy density was increased through hydrothermal carbonization at various temperatures. The evolution of waste biomass under hydrothermal carbonization was chemically analyzed. The increased carbon content of the resulting biochar upgraded its fuel properties, leading to energy savings in the treatment process. After hydrothermal carbonization, the H/C and O/C ratios were lower owing to chemical conversion. The optimal temperature for hydrothermal carbonization was approximately 220 °C. The inorganic content resulted in a lowered degree of agglomeration and reduced the likelihood of fouling during combustion. The thermogravimatric analysis also provided the changing combustion characteristics due to the increased fixed carbon content. Fourier transform infrared spectra revealed that hydrothermal carbonization reaction reduced the numbers of C–O and C–H functional groups and increased the number of aromatic C–H functional groups. The equilibrium moisture content decreased rapidly when hydrothermal carbonization was conducted at temperatures higher than 200 °C, and the initial moisture content was reduced by 75% after hydrothermal carbonization at 300 °C. • Livestock manure production and associated environmental regulations haves increased. • Hydrothermal carbonization was used to upgrade the livestock manure for the fuel. • The combustion performance of biochars was enhanced. • The agglomeration of biochars decreased due to reduction of inorganic matters. • The equilibrium moisture content of biochars decreased due to reduction in hydrophilic groups. [ABSTRACT FROM AUTHOR]

Hydrothermal carbonization (HTC) has become an esteemed method to convert sewage sludge into biochar. Besides dewatering and disinfection the process is suggested to reduce the micropollutant load, which would be beneficial for the use of biochar as fertilizer. This study was designed to examine reduction of micropollutants and formation of transformation products during HTC using the example of diclofenac. We investigated compounds' removal at HTC conditions in inert experiments and in real samples. Results showed that HTC temperature (>190 °C) and pressure (∼15 bar) have the potential to fully degrade diclofenac in inert experiments and spiked sewage sludge (>99%) within 1 h. However, interfering effects hinder full removal in native samples resulting in 44% remaining diclofenac. Additionally, a combination of suspected-target and non-target analysis using LC-MS/MS and LC-HRMS resulted in the determination of six transformation products. These products have been reported in biochar from HTC for the first time, although other studies described them for other processes like advanced oxidation. Based on the detected transformation products, we proposed a degradation mechanism reflecting HTC reactions such as dehydroxylation and decarboxylation. [ABSTRACT FROM AUTHOR]

sawdust was valorized using acid-assisted hydrothermal carbonization and used in the removal of endocrine disruptor bisphenol A (BPA). The effect of acid addition on the hydrothermal carbonization of sawdust and removal of BPA was studied. Two different hydrochars were prepared using deionized water (HC D) and hydrochloric acid solution (HC AH) as feed water. The prepared hydrochars were characterized using FESEM, EDS, XRD, Raman spectroscopy, FTIR, TGA, and surface area analysis to study the structural and functional changes. Then they were compared in the removal of bisphenol A. Out of the two hydrochars prepared, acid-assisted hydrothermal carbonized hydrochar (HC AH) showed better removal efficiency. Hence, HC AH was used to study the influence of different parameters like pH, adsorbent dosage, and initial bisphenol A concentration by one variable at a time approach. Further, the study of interactive effects and optimization of adsorption of bisphenol A onto HC AH was carried out using RSM-CCD. The isotherm, kinetics, and thermodynamic studies revealed that the adsorption of bisphenol A could be explained by the Freundlich isotherm, pseudo-second-order kinetics fitted well in all the initial BPA concentrations, and the adsorption of bisphenol A onto HC AH was exothermic and spontaneous. [Display omitted] • The effect of acid-assisted hydrothermal carbonization of sawdust on the removal of bisphenol A was studied. • Various analytical techniques were used to compare the structural and functional changes with and without acid addition. • Acid-assisted hydrothermal carbonized hydrochar had higher aromaticity, aliphaticity, and oxygenated functional groups. • The optimization of adsorption of BPA onto acid hydrolyzed hydrochar was carried out using OVAT and RSM-CCD. [ABSTRACT FROM AUTHOR]

Hydrothermal conversion is seen as a potential sustainable solution for the disposal and utilization of sewage sludge. One-step hydrothermal carbonization was used to prepare iron-based sludge hydrochars, and the microstructure properties of hydrochars under different hydrothermal conditions were investigated, with emphasis on the inherent interaction mechanisms between carbon and iron. The aromaticity of hydrochars increased with increasing hydrothermal temperature and time, whereas the specific surface area and pore volume as well as magnetic characteristics of hydrochars were only contingent on temperature. Once the temperature reached 160 °C, Fe 2 O 3 in sludge was completely transformed into Fe 3 O 4 in hydrochars. Simulated experiments suggest that glucose is more advantageous than protein in the iron transformation and mesopore formation. The coexistence of glucose, protein, and FeCl 3 improved the aromaticity as well as specific surface area and pore volume of hydrochars. This study provides a basis for designing high performance iron-based sludge hydrochars. [Display omitted] • Iron-based sludge hydrochar was prepared by one-step hydrothermal carbonization. • Pore structure and magnetism of hydrochars were temperature dependent. • Fe 2 O 3 was completely transformed into Fe 3 O 4 at 160 °C. • Glucose is more advantageous than protein in iron transformation of hydrochars. • Glucose, protein, and FeCl 3 together improved the performance of hydrochars. [ABSTRACT FROM AUTHOR]

Hydrothermal carbonization of wet biomasses has been known to produce added-value materials for a wide range of applications. From catalyst substrates, to biofuels and soil amendments, hydrochars have distinct advantages to offer compared to conventional materials. With respect to the agricultural application of hydrochars, both positive and negative results have been reported. The presence of N, P and K in certain hydrochars is appealing and may contribute to the reduction of chemical fertilizer application. However, regardless of biomass, hydrothermal carbonization results in the production of phytotoxic organic compounds. Additionally, hydrochars from sewage sludge often contain heavy metal concentrations which exceed the regulatory limits set for agricultural use. This review critically discusses the phytotoxic aspects of hydrochar and provides an account of the substances commonly responsible for these. Furthermore, phytotoxicity reduction approaches are proposed and compared with each other, in view of field-scale applications. [Display omitted] • The recent literature was reviewed regarding the phytotoxic effects of hydrochars. • Acute phytotoxicity is attributed to furans, polyaromatic hydrocarbons and carboxylic acids. • In the case of sewage sludge hydrochar, reduced crop growth is attributed to the presence of heavy metals. • Hydrochar washing, microbial aging and co-composting are the main phytotoxicity reduction methods. [ABSTRACT FROM AUTHOR]

Biomass-derived porous carbonaceous materials are efficient adsorbents for VOCs, but their traditional preparation method, pyrolysis combined with activation, suffers from high energy consumption, equipment corrosion, and low pore-making efficiency, which hinders their large-scale practical application. A novel method of alkali metal-catalyzed hydrothermal carbonization coupling with chemical activation for the preparation of microporous carbon is presented. Porous carbon with well-developed microporosity deriving from corn husk were prepared through the hydrothermal carbonization using potassium persulfate (K 2 S 2 O 8) as a catalyst and programmed heating activation process. And the products were applied to removal of typical oxygen-containing VOCs, ethyl acetate. The addition of K 2 S 2 O 8 in hydrothermal carbonization accelerated the biomass hydrolysis, decomposed the biopolymer, and formed functional hydrochars. Potassium salts introduced into the hydrochars, which acted as an activator in this programmed heating activation process, formed a great deal of micropores. The specific surface area of micropores increased by 81%, and the specific surface area of micropores less than 1 nm increased by 180%. The introduction of K 2 S 2 O 8 in preparation improved the adsorption performance of CH-based porous carbons 16.46% and 60.00% respectively at different preparation temperatures (600 °C and 800 °C). Basing on these results, the improvement of micropores less than 1 nm is directly related to the adsorption performance. This indicates that pores (<1 nm) respond well to the adsorption of ethyl acetate. [Display omitted] ● Introduction of K 2 S 2 O 8 in hydrothermal process form hydrochars efficiently. ● Potassium salts act as hydrothermal catalysts and activation agent respectively. ● Well-developed pore structure was built due to the introduction of potassium salts. ● The pore size less than 1 nm contributed the most to the adsorption of ethyl acetate. [ABSTRACT FROM AUTHOR]

Carbon (C)-rich, solid products from pyrolysis (pyrochars) and hydrothermal carbonization (HTC, hydrochars) are expected to reduce the bioavailability and bioaccessibility of pesticides as side effect of soil addition. To compare effects of different feedstocks (digestate, miscanthus, woodchips) and production processes (pyrolysis at 750 °C, HTC at 200 °C and 250 °C), 14 C-labeled isoproturon (IPU) was applied at 0.75 kg ha − 1 to loamy sand amended either with 0.5% or 5% pyrochars or hydrochars, which was then incubated for 50 d. Mineralization of IPU was measured as 14 C–CO 2 released from soil-char composites. Pore-water and methanol extractable 14 C-IPU was quantified as well as non-extractable 14 C-residues (NER). Furthermore, C mineralization of pyrochars, hydrochars and feedstocks was studied to assess the relationship between IPU bioaccessibility and char decomposability. In pure soil, 8.1% of applied IPU was mineralized after 50 d. This was reduced more strongly in pyrochar treatments (81 ± 6% reduction) than in hydrochar treatments (56 ± 25% reduction). Different feedstocks had no significantly different effect when 5% char was added, but their effect was significant and dependent on the production process in 0.5% amendments. Pesticide binding can occur by surface sorption as well as by diffusion and subsequent occlusion in micropores. The latter can be expected to result in high amounts of NER, as it was observed in the pyrochar treatments. Hydrochars were less stable than pyrochars and contained lower amounts of NER. Thus, in hydrochar amended soils, better accessibility of IPU to microbial degradation may be a result of full char decomposition within decades ensuring controlled pesticide degradation. [ABSTRACT FROM AUTHOR]

Hydrothermal carbonization of brewer’s spent grain resulted in a solid hydrochar and an aqueous phase rich in macromolecular dissolved organic matter. Both phases were analyzed with regard to low molecular weight organic compounds (MW < 500 Da) in lyophilized form by exhaustive solvent extraction followed by pre-chromatographic derivatization and GC/MS-analysis. Low molecular weight acids, O-functionalized phenols, cyclopentenone derivatives, and benzenediols accounted for the majority of organic analytes in both hydrothermal carbonization product streams while being absent in solvent extracts of the pristine biomass. The pattern of short chain functionalized acids in the pristine biomass and in the hydrothermally produced matrices turned out very different. Acylglycerines as the most abundant lipids in pristine brewer’s spent grain were quantitatively hydrolyzed under hydrothermal conditions. The recovery of total fatty acids present in the pristine biomass amounted to 19%. The major fraction of hydrophobic breakdown products including fatty acids, fatty alcohols, and sterols was sorbed onto the hydrochar. [ABSTRACT FROM AUTHOR]

Poly(vinyl chloride) (PVC) was subjected to hydrothermal carbonization in subcritical water at 180–260 °C. Dehydrochlorination increased with increasing reaction temperature. The release of chlorine was almost quantitative above ∼235 °C. The fraction of organic carbon (OC) recovered in the hydrochar decreased with increasing operating temperature from 93% at 180 °C to 75% at 250 °C. A wide array of polycyclic aromatic hydrocarbons (PAHs) could be detected in the aqueous phase, but their combined concentration amounted to only ∼140 μg g −1 PVC-substrate at 240 °C. A pathway for the formation of cyclic hydrocarbons and O-functionalized organics was proposed. Chlorinated hydrocarbons including chlorophenols could only be identified at trace levels (low ppb). Polychlorinated dibenzodioxins (PCDDs) and dibenzofurans (PCDFs) could not be detected. The sorption potential of the hydrochar turned out to be very low, in particular for polar organic pollutants. Our results provide strong evidence that hydrothermal carbonization of household organic wastes which can be tied to co-discarded PVC-plastic residues is environmentally sound regarding the formation of toxic organic products. Following these findings, hydrothermal treatment of PVC-waste beyond operating temperatures of ∼235 °C to allow complete release of organic chlorine should be further pursued. [ABSTRACT FROM AUTHOR]

Sewage sludge is an important vehicle for the diffusion of microplastics (MPs) into the environment, and thus, efficient removal of MPs from sludge is in urgent need. In this study, hydrothermal carbonization (HTC) is proposed and its potential for the removal of MPs from sewage sludge is assessed. Optical microscopy and micro-FTIR analysis showed that the concentrations of MPs in sewage sludge decreased significantly, exhibiting a 79% reduction with a HTC temperature of 260 °C. The potential decomposition mechanism of condensation polymers and addition polymers were investigated through HTC experiments, using polyethylene terephthalate-microplastics (PET-MPs) and polypropylene-microplastics (PP-MPs). During the HTC process, the disintegration efficiency of PET-MPs was significantly higher than PP-MPs, due to the PET ester bond being easily monomerized by hydrolysis. Furthermore, analyses of physicochemical properties of the residual PP-MPs indicated that exposure to heat cause PP to undergo pyrolysis reaction, resulting in the random rupture of polymer molecular chains. Overall, these results provide the first insight into the critical role of HTC in the removal of MPs from sewage sludge, providing a novel solution for reducing the risk posed by MPs in sewage sludge in the future. [Display omitted] • 79% of MPs in sewage sludge were removed by HTC. • MPs in HTC are mainly degraded by hydrolysis and pyrolysis. • Temperature plays a critical role in the degradation of MPs by HTC. • HTC is promising as a strong potential technology for sludge-MPs treatment. [ABSTRACT FROM AUTHOR]