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

Modeling hydrothermal carbonization (HTC) and pyrolysis carbonization (PLC) for the conversion of biomass into high-quality biochar for various applications shows promise. Unlike the extensive modeling studies on lignocellulosic biomass, research on aquatic biomass (AB) had not been reported until now. In this study, we compiled 586 data points from existing literature and trained five tree-based models to predict the yields of hydrochar and pyrochar and their properties, including nitrogen recovery degree, energy density, energy recovery degree, and residual sulfur degree, based on 10 feedstock and process parameters. The random forest regression (RFR) model demonstrated the highest predictive accuracy among these models. It achieved R2 values ranging from 0.89 to 0.98 for hydrochar yield, nitrogen recovery degree of hydrochar, energy recovery degree of hydrochar, and residual sulfur degree of hydrochar. The extreme gradient boosting (XGB) model also showed exemplary performance, with R2 values between 0.84 and 0.94 for energy density of hydrochar, pyrochar yield, and nitrogen recovery degree of pyrochar. Results on feature importance highlighted that, beyond the well-documented impact of process parameters, the properties of biochar were significantly influenced by the elemental compositions, such as nitrogen and sulfur contents of the feedstock. The relationship between these factors was further elucidated using partial dependence plots. Finally, we used RFR model for hydrochar yield and XGB model for pyrochar yield as examples, to test generalization ability of developed models with new data, further explaining their application methods. Overall, this study provided valuable insights into predicting and understanding the HTC and PLC processes of AB to produce high-quality biochar for various applications using low resources and time costs. Besides, we presented an iterative learning application method where the developed models demonstrated exceptionally high performance with new data. This method is highly versatile and can be adopted across various directions in the field of machine learning. Highlights: • A machine-learning framework for producing biochar from aquatic biomass was developed. • XGB and RFR models showed the excellent performance for biochar yield and properties. • The developed models had high generalization ability (R2 = 0.97–0.98) through appropriate iterative operation. [ABSTRACT FROM AUTHOR]

This study presents the preparation of magnetic carbon nanocomposites (MCNCs) through a two-step procedure: (i) in situ co-precipitation of magnetite (Fe3O4) nanoparticles into four different carbonaceous matrixes and (ii) post-pyrolysis treatment to coat the magnetic core. Four post-pyrolysis MCNCs were obtained: MACP (post-pyrolyzed magnetic activated carbon), MCCP (post-pyrolyzed magnetic charcoal), MHCPOR (post-pyrolyzed magnetic hydrochar from orange residue), and MBCPSFH (post-pyrolyzed magnetic biochar from sunflower husk). These four samples were compared with the starting MCNCs prepared without post-pyrolysis treatment: MAC, MCC, MHCOR, and MBCSFH, respectively. After post-pyrolysis treatment, a thin carbon layer surrounding some of the magnetite nanoparticles was identified by transmission electron microscopy. Post-pyrolysis modified the porous structure and chemical composition of MCNCs. Furthermore, a leaching test with acid sulfuric solution at 90 °C was carried out. The results suggested that the MHCPOR and MBCPSFH were more stable in an acidic medium than MACP and MCCP, indicating that the coat generated during post-pyrolysis of hydrochar and biochar could partially protect the magnetic core by reducing Fe leaching into the aqueous solution. Biochar and the hydrochar-based MCNCs before and after post-pyrolysis treatment exhibit superparamagnetic properties; however, their saturation magnetization (Ms) decreased considerably. These results open the potential application fields of MCNCs obtained by post-pyrolysis of biochar and hydrochar-based materials in acidic mediums. [ABSTRACT FROM AUTHOR]

The usage of orange peel wastes for solid biofuel production can provide a sustainable solution for solid waste management while also reducing the negative effects of fossil fuels. The aim of this study is to compare the combustion properties of orange peel wastes and solid biofuels obtained from them. In this context, the combustion behaviour of orange peel wastes and hydrochar and biochar samples obtained as a result of their hydrothermal carbonization and pyrolysis were investigated by the thermogravimetric method in this study. In addition, the combustion kinetics of these fuels were determined using the Kissinger-Akahira-Sunosa (KAS) and Flynn–Wall–Ozawa (FWO) methods. As a result of the thermogravimetric analysis, it is seen that the combustion behavior of raw biomass and hydrochar are quite similar, but the combustion of biochar is different from them. The combustion of raw waste and its hydrochar took place in multiple steps, the combustion of biochar took place in a single step. While the average combustion activation energy values of orange peel, hydrochar and biochar were calculated by KAS method as 159.876, 208.561 and 77.656 kJ/mol, respectively; they were calculated by the FWO method as 161.717, 208.600 and 85.209 kJ/mol, respectively. According to these results, the production of biochar from orange peel wastes by pyrolysis and the use of the obtained biochars in combustion systems are more suitable in terms of energy efficiency. Future research of the combustion of solid biofuels from orange peel will be very important to determine their potential for use in combustion systems, either directly or as an additive, and to increase energy efficiency. [ABSTRACT FROM AUTHOR]

Pyrochar (Biochar) produced from the thermochemical conversion of biomass has been widely used as a soil amendment to improve agricultural soil quality. Since polycyclic aromatic hydrocarbons (PAHs) can be produced in such processes, the occurrence of PAHs in pyrochars has been extensively studied, and standards such as the European Biochar Certificate (EBC) and International Biochar Initiative (IBI) contain limit values for biochars applied to soils. However, studies on PAH levels in hydrochars from hydrothermal processes, which can be an alternative to wet biomass are scarce. This study focuses on comparing the occurrence of 16 PAHs regulated by the US EPA in 22 char samples (including pyrochars from pyrolysis, hydrochars from hydrothermal carbonization, and, for the first time, hydrothermal humification) using an ultrasonic extraction method. Results showed that the sum of the 16 EPA PAHs in all samples was well below the requirements of the two standards, except for pyrochar produced at the farm scale. They ranged from 131 to 9358 µg·kg−1 in the seven pyrochars and from not detected to 333 µg·kg−1 for the fourteen hydrochars. Our findings indicate that hydrochar produced via hydrothermal methods exhibits much lower concentrations and is a safe option for soil amendment and environmental applications. [ABSTRACT FROM AUTHOR]

Poultry litter was converted to biochar by torrefaction and to hydrochar by hydrothermal carbonisation. Many parameters were measured for the resulting chars, to investigate the effects of the production method and production temperature. SEM showed the presence of large quantities of crystalline material on the surface of the biochars. The elemental composition of some crystals was determined as 35% K and 31% Cl. This was confirmed as sylvite (KCl) crystals, which explains the high levels of water-extractable potassium in the biochar and may also be important in germination inhibition. Biochars almost totally inhibited germination, whilst hydrochars decreased germination. Although germination occurred on hydrochar, root growth was severely inhibited. Consequently, the germination index may be better to determine total phytotoxicity as it measures both effects and could be used as a bioassay for chars used as soil amendments. Washing removed germination inhibition in a low-temperature char (350 °C), possibly by removing KCl; however, root toxicity remained. There were very low levels of heavy metals, suggesting they are not the source of toxicity. In biochars, pore mean size decreased with temperature from 350 °C to 600 °C, due to changes in pore size distribution. The mean pore size was measured directly using SEM. The merits of this method are discussed. Low-temperature biochars seem best suited for fuel as they have a high calorific value, high hydrophobicity, a low ash content and a high yield. Higher temperatures are better for soil amendment and sequestration applications with a smaller mean pore size, higher surface area, and higher pH. [ABSTRACT FROM AUTHOR]

Poultry litter was converted to biochar by torrefaction and to hydrochar by hydrothermal carbonisation. Many parameters were measured for the resulting chars, to investigate the effects of the production method and production temperature. SEM showed the presence of large quantities of crystalline material on the surface of the biochars. The elemental composition of some crystals was determined as 35% K and 31% Cl. This was confirmed as sylvite (KCl) crystals, which explains the high levels of water-extractable potassium in the biochar and may also be important in germination inhibition. Biochars almost totally inhibited germination, whilst hydrochars decreased germination. Although germination occurred on hydrochar, root growth was severely inhibited. Consequently, the germination index may be better to determine total phytotoxicity as it measures both effects and could be used as a bioassay for chars used as soil amendments. Washing removed germination inhibition in a low-temperature char (350 °C), possibly by removing KCl; however, root toxicity remained. There were very low levels of heavy metals, suggesting they are not the source of toxicity. In biochars, pore mean size decreased with temperature from 350 °C to 600 °C, due to changes in pore size distribution. The mean pore size was measured directly using SEM. The merits of this method are discussed. Low-temperature biochars seem best suited for fuel as they have a high calorific value, high hydrophobicity, a low ash content and a high yield. Higher temperatures are better for soil amendment and sequestration applications with a smaller mean pore size, higher surface area, and higher pH.

The planting-breeding integration system is an important pathway to achieve the sustainable development of both animal husbandry and crop yield. Currently, the large-scale farming leads to highly concentrated animal waste, which is difficult to manage and process in a short period. Moreover, the manure contains environmental risks such as organics, heavy metals, antibiotics and antibiotic-resistant genes, which affect the existing ecological cycle system. Hydrothermal technology can convert animal waste into bio-oil, hydrochar, aqueous products, and gas products, with potentials in fuel, soil improvement, phytopathogen control, and greenhouse gas fertilization applications, respectively. According to over a decade of researches, an ecological cycling agricultural model called "planting-breeding integration system based on hydrothermal resource utilization" is proposed. This article systematically reviews the role and application potential of hydrothermal conversion products from animal waste: discusse the current research status of hydrothermal conversion of animal waste into bio crude oil as fuel for agricultural internal combustion engines; elucidates the role of aqueous products as potential agricultural fungicides in crop disease prevention and control; summarizes the research progress of hydrochar from animal waste in physicochemical characteristics, and field application; and analyzes the components of gas-phase products and their potential for greenhouse planting. Through calculation based on previous studies, hydrothermal conversion technology has significant energy and ecological benefits in constructing a new type of integrated farming model. Taking fresh swine manure with a water content of 80% as an example, after hydrothermal conversion, the produced bio-oil can generate approximately 2 000 MJ of energy as fuel; the aqueous product contains high contents of nitrogen and phosphorus elements, presenting significant potential as fertilizer and exhibits important anti-pathogen efficacy. Additionally, the produced 0.1-0.12 t of hydrochar via hydothermal conversion holds important carbon sequestration ability. Furthermore, through hydrothermal treatment, heavy metals in manure are efficiently immobilized, and pathogens and antibiotics are also rendered harmless, facilitating safe subsequent application of manure. Under this model, it will help increase the land's capacity to assimilate animal manure, construct an ecologically sustainable green circular agriculture, and achieve efficient management of animal manure and agriculture residuces. However, this model is still in a conceptual stage, and conducting large-scale application still faces significant challenges. On this basis, this article summarizes the main challenges and shortcomings of this model, and looks forward to the research direction of recycling application of animal waste and hydrothermal conversion products. Evaluating the ecological and environmental safety of aqueous products and hydrochar in field applications is an urgent task: Establishing standard procedures for hydrothermal conversion to obtain stale products, and systematically analyzing the ecological safety, environmental migration pathways, and toxic effects of conversion products are important prerequisites for promoting the development of this plantingbreeding integration system. Demonstrating the technical and economic feasibility and production safety this system is another issue that needs to be addressed. Constructing factories to achieve on-site treatment of animal waste, and coupling with various economic and renewable energy sources to support the hydrothermal conversion process are important means to improve the economic feasibility. This article will provide a reference for the high-value utilization of animal manure via hydrothermal conversion and the research of a highly-efficient planting-breeding integration system. [ABSTRACT FROM AUTHOR]

Biochar (BC) and hydrochar (HC) have attracted considerable attention owing to their versatile characteristics and proven effectiveness in diverse technical fields. Solid BC is generated as a result of the dry carbonisation process of pyrolysis, in contrast to the slurry HC, which is produced during the hydrothermal carbonisation process. In this study, we evaluated the adsorption potential of two hydrochar samples (HCs) and three biochar samples (BCs) produced from sugar cane bagasse. The adsorption capacity of these samples was tested for ammonium, nitrate, and phosphate ions under various conditions. The BCs and HCs were subjected to characterisation using a CHNS/O analyser, the zeta potential, and Fourier transform infrared (FTIR). Elevating the pyrolysis temperature of the biochar resulted in changes in the fixed carbon and ash contents, while the volatile matter and H/C and O/C atomic ratios decreased. As the residence time increased, the H/C ratio and volatile matter content of the hydrochars (HCs) decreased. However, the fixed carbon content, ash content, and O/C and C/N ratios exhibited an increase. Thermodynamics, adsorption isotherms, and pH were also taken into consideration. The FTIR spectra analysis indicated that the carboxyl and ester functional groups present in both the BCs and HCs displayed reduced peak intensities subsequent to the adsorption of the three ions. While the adsorption was exothermic, we noticed that the adsorption capacity increased with temperature. The results indicate that sorption was homogenous across all binding sites, as evidenced by the optimal fit to the Langmuir isotherm. The research findings indicate that the adsorption capacity of various BC and HC adsorbents is significantly influenced by the surface area of the adsorbents in the case of nitrate and phosphate, but in the case of ammonia, adsorption is dictated by the functional polar groups present on the adsorbent surface. [ABSTRACT FROM AUTHOR]

Microalgal biomass has been considered the third-generation biofuel production feedstock, but microalgae-derived biochar still needs to be thoroughly understood. This study aims to evaluate the production and physicochemical properties of microalgae-derived hydrochar produced by hydrothermal carbonization (HTC) process by comparison with pyrochar produced by dry thermal carbonization (DTC) process for environmental applications. Microalgal biochar was produced with commercially available Chlorella vulgaris microalgae using HTC and DTC processes under various temperature conditions. Pyrochar presented higher pH, ash contents, porosity, and surface area than hydrochar. Hydrochar gave more oxygen-containing functional groups on the surface and higher lead adsorption than pyrochar, making the microalgal hydrochar applicable in soil amendment and various environmental remediations. HTC could be an economically feasible thermochemical process for microalgal biochar production. It can produce hydrochar with high production yield from wet microalgae at low temperatures without a drying process. [ABSTRACT FROM AUTHOR]

Biochar could be a brilliant additive supporting the anaerobic fermentation process. However, it should be taken into account that in some cases it could also be harmful to microorganisms responsible for biogas production. The negative impact of carbon materials could be a result of an overdose of biochar, high biochar pH, increased arsenic mobility in the methane fermentation solution caused by the carbon material, and low porosity of some carbon materials for microorganisms. Moreover, when biochar is affected by an anaerobic digest solution, it could reduce the biodiversity of microorganisms. The purpose of the article is not to reject the idea of biochar additives to increase the efficiency of biogas production, but to draw attention to the properties and ways of adding these materials that could reduce biogas production. These findings have practical relevance for organizations seeking to implement such systems in industrial or local-scale biogas plants and provide valuable insights for future research. Needless to say, this study will also support the implementation of biogas technologies and waste management in implementing the idea of a circular economy, further emphasizing the significance of the research. [ABSTRACT FROM AUTHOR]

In this study, energetic properties of cellulose (CL) and lignin (LN) were enhanced through torrefaction (TF) and hydrothermal carbonization (HTC) processes. TF was conducted at 200 to 300 °C for 30 min under 100 mL/min CO2. HTC was conducted at 180 to 220 °C for 30 min using liquid fraction (LF) recirculation. The derived biochar and hydrochar were investigated in the parameters of mass yield, proximate and ultimate analysis, energetic properties, thermal decomposition properties, surface chemical functional groups, and surface morphology. TF affected CL and LN properties rather than HTC. Energetic properties of CL and LN were greatly enhanced using TF. On the other hand, HTC affected the energetic properties of CL and LN marginally, and the effect of LF recirculation on hydrochar energetic properties could have been negligible. CL and LN chars with maximum HHV improvement (0.73 and 0.13) and energy yield (161.61 and 96.37%) could be derived through TF. The O/C and H/C ratios of the biochar were decreased and found to be similar to those of lignite and sub-bituminous coal. In addition, HHV of CL hydrochar was much lower than that of CL biochar, while HHV of LN hydrochar could be comparative with LN biochar. These results suggested that TF constitutes an outstanding technology for producing char fuel from lignocellulosic biomass. LF recirculation during the HTC process could enhance its economic feasibility and environmental friendliness. Biomass with high LN content could serve as a promising material for producing solid fuel. [ABSTRACT FROM AUTHOR]

This study investigates the suitability of different lignocellulosic sources, namely eucalyptus, apple bagasse, and out-of-use wood, for injection into blast furnaces (BFs). While wastes possess carbon potential, their high moisture renders them unsuitable for direct energy utilization. Additionally, the P and K impurities, particularly in apple bagasse, can pose operational and product quality challenges in BF. Thus, different thermochemical processes were performed to convert raw biomass into a more suitable carbon fuel. Low-temperature carbonization was selected for eucalyptus, yielding a biochar with properties closer to the low-rank coal. Hydrothermal carbonization was chosen for apple bagasse and out-of-use wood, resulting in hydrochars with enhanced fuel characteristics and fewer adverse inorganic species but still limiting the amount in binary PCI blends. Thermogravimetry evaluated the cause–effect relationships between coal and coal- and bio-based chars during co-pyrolysis, co-combustion and CO2-gasification. No synergistic effects for char formation were observed, while biochars benefited ignition and reactivity during combustion at the programmed temperature. From heat-flow data in combustion, the high calorific values of the chars were well predicted. The CO2-gasification profiles of in situ chars revealed that lignin-rich hydrochars exhibited higher reactivity and conversion than those with a higher carbohydrate content, making them more suitable for gasification applications. [ABSTRACT FROM AUTHOR]

Agri-food residues or by-products have increased their contribution to the global tally of unsustainably generated waste. These residues, characterized by their inherent physicochemical properties and rich in lignocellulosic composition, are progressively being recognized as valuable products that align with the principles of zero waste and circular economy advocated for by different government entities. Consequently, they are utilized as raw materials in other industrial sectors, such as the notable case of environmental remediation. This review highlights the substantial potential of thermochemical valorized agri-food residues, transformed into biochar and hydrochar, as versatile adsorbents in wastewater treatment and as promising alternatives in various environmental and energy-related applications. These materials, with their enhanced properties achieved through tailored engineering techniques, offer competent solutions with cost-effective and satisfactory results in applications in various environmental contexts such as removing pollutants from wastewater or green energy generation. This sustainable approach not only addresses environmental concerns but also paves the way for a more eco-friendly and resource-efficient future, making it an exciting prospect for diverse applications. [ABSTRACT FROM AUTHOR]

In this study, the chars were derived through dry and wet torrefaction (DT and WT) of oil palm leaf (OPL), and techno-economic feasibility for char production was evaluated. DT was performed at 200 to 300 °C for 30 min under CO2 atmosphere. WT was performed at 180 to 220 °C for 30 min over process water (PW) reuse. Fuel properties of the DT-char and WT-char products, including mass yield, physiochemical characteristics, fuel properties, thermal stability, surface chemical functional groups, and surface structure were investigated. The study results indicated that DT affected OPL characteristics rather than WT, where the char with outstanding fuel properties was derived through DT. WT affected the fuel properties of OPL marginally. OPL chars with the highest HHV (28.67 MJ/kg), HHV improvement (0.48) and energy yield (131.78 %) could be derived via the DT. The O/C and H/C ratios of the DT-char were reduced and similar to those of lignite coal. PW reuse in WT slightly affected the char fuel properties, thus it is the outstanding method of PW utilization. Techno-economic feasibility analysis results determined that DT is the profitable process for converting OPL to char fuel, and its simple payback period is 14.13 years. These results recommended that DT constitutes a dominant technology for producing char fuel from OPL.

[Display omitted] • A cigarette-butts-derived activated carbon micro-spheres were synthesized. • The activated carbon with large BET specific surface area has a high NH 3 adsorption capacity. • The "waste-treat-waste" concept is expected to be achieved. Waste cigarette filters mainly contain hardly degradable cellulose acetate, toxic nicotine, and traces of heavy metals, and therefore cause environmental pollution hazards when discarded. In order to convert cigarette butt waste into a valuable product, this article investigates the preparation of activated carbon from cigarette butts via a two-step process of hydrothermal reaction and a subsequent chemical activation with phosphoric acid as an activator. During hydrothermal reaction, it was found that a process of decarboxylation and dehydration cleavage of acetate occurs, leading to micron fragments and subsequent agglomeration into carbonaceous micro-spheres. The cigarette-butts-derived activated carbon micro-spheres have a high BET surface area of ∼ 1406 m2/g and NH 3 adsorption capacity of ∼ 35.9 mg/g. It was revealed that the ammonia adsorption capacity tends to be positively and linearly correlated with the acidic functional group content of the activated carbon surface while negatively with BET surface area. [ABSTRACT FROM AUTHOR]

Straw biochar prepared by three methods (i.e., pyrochar, HNO3-modified pyrochar, and hydrochar) was added to the anaerobic digestion system with acetic acid and ethanol as substrates to explore the effects of biochar on methane production, substrate degradation, and microbial community structure. The biogas yields of the biochar-supplemented groups all increased, and the maximum methane yield was found in the hydrochar group, which was 45.4% higher than the control. In the ethanol-fed reactor, the maximum partial pressure of hydrogen in the headspace of the hydrochar reactor was reduced from 3.5% (blank reactor) to 1.9%. Overall, methane production is directly proportional to the electron exchange capacity (EEC) value of biochar. Furthermore, the bio-aging process increased the EEC of each kind of biochar to 5.5–8.1%, which was favorable for the sustainable promotion of methanogenesis. The increased methane yield from the bio-aged biochar could either be attributable to the changes in surface oxygen-containing functional groups or the selectively enriched microbial community on the biochar, such as Geobacter, which could participate in direct interspecies electron transfer. [ABSTRACT FROM AUTHOR]

Biochar (BC) and hydrochar (HC) have attracted considerable attention owing to their versatile characteristics and proven effectiveness in diverse technical fields. Solid BC is generated as a result of the dry carbonisation process of pyrolysis, in contrast to the slurry HC, which is produced during the hydrothermal carbonisation process. In this study, we evaluated the adsorption potential of two hydrochar samples (HCs) and three biochar samples (BCs) produced from sugar cane bagasse. The adsorption capacity of these samples was tested for ammonium, nitrate, and phosphate ions under various conditions. The BCs and HCs were subjected to characterisation using a CHNS/O analyser, the zeta potential, and Fourier transform infrared (FTIR). Elevating the pyrolysis temperature of the biochar resulted in changes in the fixed carbon and ash contents, while the volatile matter and H/C and O/C atomic ratios decreased. As the residence time increased, the H/C ratio and volatile matter content of the hydrochars (HCs) decreased. However, the fixed carbon content, ash content, and O/C and C/N ratios exhibited an increase. Thermodynamics, adsorption isotherms, and pH were also taken into consideration. The FTIR spectra analysis indicated that the carboxyl and ester functional groups present in both the BCs and HCs displayed reduced peak intensities subsequent to the adsorption of the three ions. While the adsorption was exothermic, we noticed that the adsorption capacity increased with temperature. The results indicate that sorption was homogenous across all binding sites, as evidenced by the optimal fit to the Langmuir isotherm. The research findings indicate that the adsorption capacity of various BC and HC adsorbents is significantly influenced by the surface area of the adsorbents in the case of nitrate and phosphate, but in the case of ammonia, adsorption is dictated by the functional polar groups present on the adsorbent surface.

The amount of cattle manure generated accounts for over 40% of the livestock manure in South Korea. Most livestock manure is utilized as a fertilizer and a soil amendment. However, the soil nutrients have exceeded saturation in South Korea. Accordingly, cattle manure, including lignocellulosic biomass, was applied for solid fuel production in this study. The three different types of carbonization process, namely, hydrothermal carbonization, torrefaction, and carbonization (slow pyrolysis), were estimated for a comparison of the hydrochar, torrefied char, and biochar characteristics derived from cattle manure. The processes were performed at temperatures ranging from 190 to 450 °C. The evaluation of the hydrochar, torrefied char, and biochar produced by three processes was conducted by the proximate, ultimate, calorific value, fuel ratio, and energy yield, which were used for the analysis of fuel quality. Additionally, the ash properties, including silicon dioxide, chlorine, and base-to-acid ratio (B/A) on hydrochar, torrefied char, and biochar were investigated to predict ash deposition during combustion. These analyses are essential to stabilize the operation of the combustion chamber. The thermogravimetric analysis represented the upgraded quality of hydrochar, torrefied char, and biochar by three different carbonization processes. [ABSTRACT FROM AUTHOR]

• Machine learning techniques predicts the properties of digestate-derived biochar. • eXtreme Gradient Boosting predicts hydrochar properties from compositions and HTC parameters. • Ash content, C content, and HTC temperature (T) dominate multi-task predictions. • Chain regression technique enhances predictability of yielded model. Hydrothermal carbonization (HTC) is a promising solution for digestate valorization, and machine learning (ML) is a helpful tool for modeling hydrochar properties. This study utilized two ensemble tree-based ML algorithms, the random forest (RF) and the eXtreme Gradient Boosting (XGB), for predicting digestate-derived hydrochar yield, properties (Cc, Hc Nc, Oc, Sc , Ashc, HHVc), and HTC process index including energy yield (EY), energy densification (ED), and carbon recovery (CR). In most cases, XGB showed better predictive performance, including yield, Cc, Hc, Nc, Ashc, HHVc, EY, and ED prediction, while RF revealed better performance in Oc, Sc , and CR prediction. XGB and RF showed satisfactory performance in predicting Cc, Hc, Oc, Sc , Ashc, and HHVc, with test R2 of 0.856–0.942 and 0.864–0.947, respectively. The multi-task model for predicting yield and hydrochar properties (Cc, Hc, Nc, Oc, Sc , Ashc, HHVc) was also developed. XGB reveals better performance than RF, with the average test R2 of XGB could achieve 0.895, which is comparable to the current published work. The SHapley Additive exPlanations (SHAP) analysis reveals that digestate ash content, C content, and HTC temperature (T) dominate multi-task predictions. The chain regressor technique enhanced the model performance toward multi-task prediction, including EY, ED, and CR: in RF, the test R2 of ED and CR were increased by 38 % and 26 %, respectively, while in XGB, the test R2 of ED was improved by 48 %. The developed ML model in this work could satisfactorily predict hydrochar properties, forming a basis for optimizing HTC process parameters and determining suitable applications for digestate valorization. ML effectively maps the correlation between input features and output responses, making ML a time-efficient and practicable tool for prediction tasks and identifying essential features, especially for multi-output prediction with high-dimension. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Chitin and chitosan hydrochars were prepared by hydrothermal and microwave treatments. • Adsorption capacities of hydrochars toward pharmaceuticals were compared. • The mechanism of pharmaceutical adsorption depended on the HT treatment temperature. • Alkaline activation of CS and CT biochars increases adsorption capacities by 5–40 %. Hydrothermal treatment of fishery waste-derived chitin (CT) and chitosan (CS) was performed to prepare hydrochar adsorbents for the removal of pharmaceuticals of environmental concern. By systematically studying the effect of treatment conditions on the biochar structure, the correlation between hydrochar properties and the adsorption capacities was clarified to optimize the adsorption performance. CS hydrochars obtained by lower-temperature treatment showed high adsorption capacities for the pharmaceuticals having carboxyl groups attributed to the electrostatic binding. A decrease in the density of available amines in CS hydrochars prepared at higher temperatures resulted in lower adsorption capacities and the manifestation of different adsorption mechanisms based on hydrophobic and π-π interactions. CT hydrochars showed lower adsorption capacities than CS hydrochars due to inefficient carbonization and lack of adsorption sites. The hydrochar adsorbents prepared in this study address simultaneously the problems of marine waste bioresource utilization and environmental cleaning from the emergent pollutants. [ABSTRACT FROM AUTHOR]

[Display omitted] • Adding biomass and hydrothermal treatment (HTT) increased hydrochar heating value. • HTT of sludge alone had the lowest capital and operational expenditures. • HTT of sludge–cane bagasse led to the highest hydrochar energy recovery. • HTT of sludge–softwood sawdust led to the highest hydrochar revenue. • Saved sludge disposal cost was the most significant factor affecting the economics. Digested sludge is a waste stream from anaerobic digestion (AD) in wastewater treatment plants. Hydrothermal treatment (HTT) of sludge mixed with lignocellulosic biomass is an attractive approach to improve sludge dewaterability and generate value-added products. However, process economics has not been well understood. In this study, firstly, the effect of biomass type on the energy properties of hydrochars was studied. Secondly, two scenarios were simulated to evaluate the effects of biomass type on the economics (processing 50,000 tonnes of sludge per year) of HTT of digested sludge for solid fuel and soil amendment applications. The two HTT scenarios included sludge alone and sludge-biomass mixtures (four cases for four biomass feedstocks) at 180 °C for 60 min. In both scenarios, HTT liquids were returned to existing AD facilities for biomethane production to offset the energy cost of the HTT process. The results showed that the higher heating value significantly increased from 16.0–17.0 MJ kg−1 in the sludge alone case to 18.0–23.0 MJ kg−1 in sludge–biomass mixtures (except for rice husk). With the use of saved transport cost as a revenue source, HTT of sludge–biomass led to a net present value (NPV) range of AU$ 9.9–20.3 million (20 years) and an internal rate of return (IRR) range of 25.0 %–45.2 % for solid fuel application of resulting hydrochar compared to an NPV of AU$ 18.4 million and an IRR of 55.0 % from HTT of sludge alone scenario. HTT of sludge-biomass led to a NPV range of AU$ 4.5–14.5 million and an IRR range of 17.2 %–35.7 % for soil amendment application while the hydrochar from HTT of sludge alone was not recommended for soil application due to the high contents of heavy metals. This study provides useful and critical information for process scale-up and commercialization for integration into wastewater treatment plants. [ABSTRACT FROM AUTHOR]

Accumulation of chicken manure with litter (sawdust or fragmented straw) that is produced in large quantities at poultry farms (in producing 1 kg of poultry, 1–3 kg of manure with litter is obtained) poses a serious problem for the environment. Poultry farms are among the largest consumers of electricity, which can be generated by combusting manure with litter, also jointly with coal, in bubbling or circulating fluidized bed furnaces. For making the combustion more efficient and environmentally friendly (reducing carbon oxide emissions) the manure wetness and the content of volatiles in it should be decreased, and its heating value should be increased. To this end, manure with litter can be subjected, prior to its combustion, to pretreatment using the hydrothermal carbonization or torrefaction method. The article presents a comparison of the results obtained from studies of methods for processing a mixture of chicken manure and sawdust into biofuel in superheated steam. Chicken manure and its mixture with sawdust in the ratios 1 : 1, 1 : 2, and 2 : 1 were subjected to thermochemical treatment. Hydrothermal carbonization was carried out in a batch laboratory autoclave at a temperature of 220°С for 1 and 4 h. Biomass torrefaction was carried out in a fluidized bed reactor with the bed formed by biochar particles that were preliminarily obtained in superheated steam at temperatures of 300 and 350°С. It has been found that by applying the hydrothermal carbonization method, the carbon content in manure with litter can be increased from 42 to 63%, and the higher heating value from 16.7 to 17.8 MJ/kg. In turn, by applying the method of fluidized bed torrefaction in superheated steam, these indicators can be increased to 75% and 18.8 MJ/kg, respectively. The hydrothermal carbonization and torrefaction processes require significant energy expenditures. For making both processes more economically efficient, the possibility of extracting, from the spent water (or condensate), 5-hydroxymethylfurfural, which is regarded as a key reagent, a so-called platform chemical, for producing various practically important substances, including polymers, pharmaceutical drugs, solvents, and fuels, is being researched. It has been determined that the content of 5-hydroxymethylfurfural in these aqueous media makes 0.02–0.80 g/dm3 and depends on the biomass thermochemical treatment method and temperature at which the process was performed. [ABSTRACT FROM AUTHOR]

The conversion of lignocellulosic waste ascends as a promising path to generate new materials with wide industrial and environmental uses. Pyrolytic biochar (PBc), hydrochar (Hc), and activated hydrochar (AcHc) produced from the waste of Picea Abies bark were considered bio-based sorbents for lead uptake from aqueous effluents. PBc was obtained through slow pyrolysis (550 °C), while Hc resulted under hydrothermal conversion (280 °C). In order to enhance the specific surface, Hc was subjected to a physical activation, resulting AcHc. All three carbonaceous materials were prepared through relatively simple processes from a readily locally available resource. The carbonaceous materials were characterized using infrared spectroscopy and scanning electron microscopy. The Pb (II) removal has been tested in batch mode on a synthetic monocomponent wastewater matrix, as well as on a real mine drainage effluent. A significant effect of pH was observed, while the equilibrium was achieved in a short time, about 60 min for PBc and Hc and 120 min for AcHc. Langmuir model predicted a maximum adsorption capacity of 15.94 mg/g for PBc, 9.99 mg/g for Hc, and 37.46 mg/g for AcHc. All materials studied had good uptake capacities for lead with no drastic effect of typical coexisting species. [ABSTRACT FROM AUTHOR]

Agri-food residues or by-products have increased their contribution to the global tally of unsustainably generated waste. These residues, characterized by their inherent physicochemical properties and rich in lignocellulosic composition, are progressively being recognized as valuable products that align with the principles of zero waste and circular economy advocated for by different government entities. Consequently, they are utilized as raw materials in other industrial sectors, such as the notable case of environmental remediation. This review highlights the substantial potential of thermochemical valorized agri-food residues, transformed into biochar and hydrochar, as versatile adsorbents in wastewater treatment and as promising alternatives in various environmental and energy-related applications. These materials, with their enhanced properties achieved through tailored engineering techniques, offer competent solutions with cost-effective and satisfactory results in applications in various environmental contexts such as removing pollutants from wastewater or green energy generation. This sustainable approach not only addresses environmental concerns but also paves the way for a more eco-friendly and resource-efficient future, making it an exciting prospect for diverse applications.

In this study, hydrochars and biochars were prepared from rice husk (RH) and Zizania latifolia straw (ZL) at various pyrolysis temperatures as absorbents, for removing toxic ions from single and competitive solutions of cadmium (Cd) and/or lead (Pb). The adsorption efficiencies of Cd and Pb in both hydrochars and biochars were lower in the competitive solution than in the single solution, and the absorbents had a stronger affinity for Pb than for Cd. Compared to hydrochars, biochars showed more favorable Cd and Pb adsorption capacities in the single or competitive solutions, and the ZL biochars had the maximum adsorption capacity among them. The SEM and FTIR analyses suggest that the predominant adsorption mechanisms of biochars and hydrochars are surfaces monolayer adsorption, precipitation, complexation, and coordination with π electrons. However, hydrochars derived from ZL exhibited an optimal additional Pb adsorption capacity in the high-level (5 ~ 10 mg L−1 Cd and Pb) competitive solution. This extra Pb adsorption of hydrochars was likely attributed to the Si–O–Si groups and more bumpy structure. Zizania latifolia straw biochar had a huge potential removal of Cd or/and Pb, and applying hydrochars as absorbents was beneficial to the removal of Cd and Pb in polluted solutions. [ABSTRACT FROM AUTHOR]

A study was conducted as split plot layout with three replications at the research greenhouse of Bu-Ali Sina University, Hamedan in 2017 in order to investigate the consequences of using biochar and hydrochar, produced from potato plant residue on bean plant growth indices, chlorophyll content, and root mycorrhizal symbiosis in drought stress. The main plot and subplots in this study have been two drought levels and four amendment treatments, respectively. The study shows that the drought stress and the application amendments in various forms have had significant effects on plant growth indices, chlorophyll content, and root mycorrhizal colonization. Drought stress reduces root and shoot dry weights up to 39.8, 46.1%, leaf chlorophyll a (Chl a) content up to 52.6%, chlorophyll b (Chl b) content up to 58%, and total chlorophyll up to 54.52%. Although the number of rhizobium nodule on the root of plant decreases in drought stress, the rate of root mycorrhiza rises by 19.2% in drought stress. The use of biochar increased the mycorrhizal symbiotic indices significantly. It increases root colonization 11.34% and Glomeromycota spore number 50.5% in soil. The application of raw residue in soil has had the most positive effects on the plant growth indices and the leaf chlorophyll contents, leading to increased shoot dry weights (49.8%) and chlorophyll a, b and total contents (3.54%, 36.8%, and 14.5% respectively). The findings of this study show that among the treatments, the best plant growth index has been obtained in the use of potato biochar, which reduces the harmful effects of drought stress on the bean plant. [ABSTRACT FROM AUTHOR]

Straw biochar prepared by three methods (i.e., pyrochar, HNO3-modified pyrochar, and hydrochar) was added to the anaerobic digestion system with acetic acid and ethanol as substrates to explore the effects of biochar on methane production, substrate degradation, and microbial community structure. The biogas yields of the biochar-supplemented groups all increased, and the maximum methane yield was found in the hydrochar group, which was 45.4% higher than the control. In the ethanol-fed reactor, the maximum partial pressure of hydrogen in the headspace of the hydrochar reactor was reduced from 3.5% (blank reactor) to 1.9%. Overall, methane production is directly proportional to the electron exchange capacity (EEC) value of biochar. Furthermore, the bio-aging process increased the EEC of each kind of biochar to 5.5–8.1%, which was favorable for the sustainable promotion of methanogenesis. The increased methane yield from the bio-aged biochar could either be attributable to the changes in surface oxygen-containing functional groups or the selectively enriched microbial community on the biochar, such as Geobacter, which could participate in direct interspecies electron transfer.

Water pollution is one of the major environmental challenges in contemporary times. Biochar from hydrothermal processes (known as hydrochars) has been explored as adsorbents for the removal of pollutants from wastewater. Hydrochars are a special class of biochar that is obtained from hydrothermal processes such as hydrothermal carbonisation (HTC) and hydrothermal liquefaction (HTL). Because of its good pore volume, surface area, high efficiency, and regeneration ability, hydrochar is an appealing choice for the remediation of a wide range of contaminants. This review aimed to focus the uniqueness of hydrochar properties and evaluate their performance on the adsorption of different pollutants from wastewater. It was observed that hydrochars can be effectively applied to a wide variety of pollutants including heavy metals, dyes, Pharmaceutically Active Compounds (PhACs), Endocrine Disruption Chemicals (EDCs), nitrates, phosphates and sulphate. The utilisation of hydrochar in water treatment solves constraints such as lack of regeneration, environmental friendliness, commercial feasibility, and disposal, handling or management concerns. [Display omitted] • Hydrochars are a special class of biochar obtained from hydrothermal processes. • The adsorption of various pollutants from wastewater by hydrochar is reviewed. • The use of hydrochar will contribute to the reduction of solid wastes and promote the circular economy. [ABSTRACT FROM AUTHOR]