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Hydrothermal carbonization technology can convert fecal waste into a valuable carbonaceous product referred to as hydrochar. We investigated the potential of fecal waste-derived hydrochar as an adsorbent for virus removal in water treatment. Swine feces was hydrothermally treated under two conditions: at 180 °C for 2 h and 230 °C for 7 h. The resulting solid products (hydrochar) were evaluated as virus adsorbents in water treatment. Simultaneous removal of pathogenic rotavirus (RV) and human adenovirus (HAdV) was investigated using a sand column set-up of 10 cm bed height with and without hydrochar supplement (1.5%, w/w). The removal efficiency of both viruses in a hydrochar-amended column was >3 log (complete removal). The amount of virus released in deionized water when flushed into the virus-retaining columns indicated that the secondary energy minimum played a more important role in RV retention than that of HAdV. Zeta-potential and hydrophobicity measurements on hydrochar materials indicated that the improved virus removal performance of hydrochar-amended columns was induced by the provision of extra hydrophobic surfaces. This study provides evidence that fecal waste-derived hydrochar can be used as a competent virus adsorbent. [ABSTRACT FROM AUTHOR]

(Hydro)thermal treatments of sewage sludge is a promising option that can simultaneously target safe waste disposal, energy recovery, and nutrient recovery/recycling. The speciation of phosphorus (P) in sludge is of great relevance to P reclamation/recycling and soil application of sludge-derived products, thus it is critical to understand the effects of different treatment techniques and conditions on P speciation. This study systematically characterized P speciation (i.e. complexation and mineral forms) in chars derived from pyrolysis and hydrothermal carbonization (HTC) of municipal sewage sludges. Combined sequential extraction and P K-edge X-ray absorption near edge structure (XANES) spectroscopy analysis revealed the dependence of P transformation on treatment conditions and metal composition in the feedstocks. Pyrolysis of sludges decreased the relative abundance of phytic acid while increased the abundance of Al-associated P. HTC thoroughly homogenized and exposed P for interaction with various metals/minerals, with the final P speciation closely related to the composition/speciation of metals and their affinities to P. Results from this study revealed the mechanisms of P transformation during (hydro)thermal treatments of sewage sludges, and might be applicable to other biosolids. It also provided fundamental knowledge basis for the design and selection of waste management strategies for better P (re)cycling and reclamation. [ABSTRACT FROM AUTHOR]

In this paper, a hydrothermal carbonization (HTC) process is designed and modeled on the basis of experimental data previously obtained for two representative organic waste materials: off-specification compost and grape marc. The process accounts for all the steps and equipment necessary to convert raw moist biomass into dry and pelletized hydrochar. By means of mass and thermal balances and based on common equations specific to the various equipment, thermal energy and power consumption were calculated at variable process conditions: HTC reactor temperature T: 180, 220, 250 °C; reaction time θ: 1, 3, 8 h. When operating the HTC plant with grape marc (65% moisture content) at optimized process conditions (T = 220 °C; θ = 1 h; dry biomass to water ratio = 0.19), thermal energy and power consumption were equal to 1170 kWh and 160 kWh per ton of hydrochar produced, respectively. Correspondingly, plant efficiency was 78%. In addition, the techno-economical aspects of the HTC process were analyzed in detail, considering both investment and production costs. The production cost of pelletized hydrochar and its break-even point were determined to be 157 €/ton and 200 €/ton, respectively. Such values make the use of hydrochar as a CO2 neutral biofuel attractive.

• HTC fundamentals can be studied by high pressure differential scanning calorimetry. • The best results are obtained performing two runs on the same sample. • The validity of the assumption of equilibrium in the blank is assessed. • Thermal contribution of reactions in blank is negligible compared to HTC effect. • Secondary reactions change the system composition with negligible exothermicity. High pressure differential scanning calorimetry (DSC) is suitable to study the thermodynamics and kinetics of hydrothermal carbonization (HTC). To isolate the thermal effect of the process from the heat required to increase the DSC system temperature, a recently proposed method uses an additional run on the already reacted sample as the blank. The method assumes that the blank system is in equilibrium during the whole run; it neglects the potential for secondary reactions in the blank run, which may affect the results. This work assesses the effect of such an assumption on the final enthalpy results by performing additional re-runs on the same specimen and adopting longer isothermal segments to push the system composition closer to equilibrium. The study of HTC of cellulose at 250°C demonstrates that the thermal contribution of reactions in the second run is negligible compared to the primary HTC effects in the first run and within the experimental error. A deeper investigation of the thermal effect during re-runs shows that the biggest effect of reactions in such runs is to change the system composition rather than a direct exothermicity. Further, the exothermic activity disappears after 12 hours, suggesting that the sample has reached thermal equilibrium. [ABSTRACT FROM AUTHOR]

Highlights: [•] HMF and furfural produced during HTC are degraded on HTC 250 after 180min. [•] NIR spectroscopy can be applied for both solid and liquid products of HTC. [•] NIR accompanying with PLSR can be applied for quantitative prediction of HTC products. [Copyright &y& Elsevier]

Abstract: The general purpose of this paper is to determine the current situation of the Finnish bio-coal sector, and outline a comprehensive picture of the macro and micro-environment related to bio-coal in Finland, as well as to propose, with the help of a SWOT analysis, guidelines and hypotheses regarding how the Finnish market should improve the bio-coal business for the future. The major findings of the study are: 1) the major strength of the Finnish bio-coal sector is its secured biomass supply, higher environmental credentials, and supportive policies. The clear implication here is that the entrance requirement for the bio-coal business is relatively low, “early birds” with foresight will win out; 2) the current weakness of Finnish bio-coal development is undeniable. As an entirely new business, bio-coal does not have a clear development model, which can be attributed to the little market information available, non-viable economic structure, and distribution channels which are not yet available. We would like to advise Finnish companies to work out the cost structure, profit feasibility of the bio-coal business and construct a practicable and sustainable biomass supply system; 3) the opportunities of the Finnish bio-coal sector come along with the national sustainability development policies and construction of a bio-economy. We would suggest that they focus on decentralised local economic sales, biomass supply and energy end use; 4) the crucial threat to the bio-coal sector industry comes from competition with fossil coal and other wood-based biofuels. Improving its competitiveness requires cooperation and integration along the whole supply chain. [Copyright &y& Elsevier]

Abstract: The difference between hydrothermal carbonization and vapothermal carbonization for the densification of the energy content of biomass has been investigated systematically for the first time. Vapothermal carbonization allows for higher solid content (solid biomass mass (dry basis) per total mass of feedstock) in the reactor because the biomass is subject to saturated steam instead of liquid water. Results from the experiments show that the process efficiency can be increased due to two reasons: the carbon losses in the liquid phase are decreased and less water needs to be heated up during carbonization. It was also observed that the carbon content of the solid product is significantly lower than that of hydrothermal carbonization at the same process conditions. As it is even lower for dry torrefaction, it is concluded that liquid water facilitates the carbonization process. Calculations based on these experimental results reveal that a mechanical dewatering of wet biomass increases the process efficiency of hydrothermal processes and should be considered in practice. Due to the low efficiency of state of the art drying, torrefaction is less efficient than vapothermal carbonization. [Copyright &y& Elsevier]

Biochar is discussed as an option for climate change mitigation via C sequestration and may promote sustainable resource efficiency. Large-scale field trials and commercial business with char materials have already started. Therefore char materials have to be assessed for toxic compounds. We tested genotoxic effects of different hydrochars and biochars with the Tradescantia micronucleus test. For this purpose chromosomal aberrations in pollen cells of Tradescantia in the form of micronuclei were evaluated microscopically after defined exposition to extracts from char materials. Hydrochars from hydrothermal carbonization mostly exhibited significantly negative results. Additional germination experiments with hydrochar showed total germination inhibition at additions above five percent v/v in comparison to biochar. However, biological post-treatment of previously toxic hydrochar was successful and toxic effects were eliminated completely. Some post-treated hydrochars even showed growth stimulating effects. Our results clearly demonstrate the necessity of risk assessment with bioindicators. The chosen tests procedures can contribute to biochar and hydrochar characterization for safe application. [Copyright &y& Elsevier]

• HTC processing upgraded waste straw LHV from 17.04 to 26.17 MJ/kg. • HTC processing above 225 °C removes inorganic ash combustion activity. • WS biomass released 254.9 ± 48.8 kJ/kg of heat during HTC transient period. • The time-correction factor determination method of the HTC processing time is presented. In this study, HTC impact on the waste straw fuel properties and waste straw hydrochars combustion kinetics have been presented. HTC experiments were carried out at Parr 4650 250 ml batch reactor, at temperatures of 225, 250, and 275 °C. Each temperature was investigated at 4 residence times: 10, 20, 30, and 40 min. Denoted hydrochars yields were more influenced by temperature than residence time, with different decomposition patterns observed at 275 °C compared to 225 and 250 °C, with final solid yields of 42.0%, 66.9%, and 65.3% at 40 min residence times respectively. The study of the transient HTC period resulted in the determination of the exothermal WS activity with the heat release of the 254.9 ± 48.8 kJ/kg of biomass. LHV values of the obtained hydrochars were 18.7–20.2 MJ/kg, 19.9–22.2 MJ/kg, and 23.1–26.2 MJ/kg for HTC temperatures of 225, 250, and 275 °C respectively. TGA analysis of the hydrochar combustion highlighted significant changes in the kinetic interpretation of the combustion profiles throughout investigated temperature ranges. The influence of residence time was only significant in the case of the 275 °C HTC samples, where a major shift of the combustion reactivity towards higher-temperature char oxidation was denoted. Hydrochars combustion kinetics were modeled with the implementation of Fraser-Suzuki deconvolution, and model-fitting of nth-order Arrhenius equation, with R2 values within 0.98–0.99. [ABSTRACT FROM AUTHOR]

Anaerobic digestion (AD) with hydrothermal (HT) pretreatment (sequential HT-AD treatment) is a novel technology for sludge management. HT-AD sludge is rich in functional groups and its applications as pollutant sorbents might be a win-win strategy. This study investigated the removal of uranium (VI) from water using HT-AD sludge as affected by solution pH, temperature, and ion strength. The reusability and heavy metal risk of HT-AD sludge were also assessed. The batch sorption experiments demonstrated that even at an acidic initial pH of 3.2, the maximum adsorption of HT-AD sludge for uranium (VI) reached 117.13 mg/g, higher than that of most carbon-based materials. The inner-sphere and out-sphere complexation between uranium (VI) and the HT-AD sludge dominated the adsorption when pH was in the range of 2–6 and 6–11, respectively. The FTIR and XPS analysis indicated that the primary mechanisms of uranium (VI) adsorption by the HT-AD sludge were the surface complexation and the electric attraction between uranium (VI) and the functional groups (e.g. –COO–) on HT-AD sludge. The removal rate of uranium (VI) by HT-AD sludge only decreased by ∼7% after 3 consecutive adsorption cycles. Leaching experiment showed that less than 5% of the total heavy metal were released from HT-AD sludge. Our research proved that HT-AD sludge can be used as an efficient uranium (VI) adsorbent with good reusability and environmental safety. [Display omitted] • The maximum U(VI) adsorption capacity of HT-AD sludge was 117.13 mg/g. • The removal rate of U(VI) only decreased by ∼7% after 3 consecutive cycles. • The heavy metals in the HT-AD sludge are stable with low risk of leaching. • Oxygen-containing groups of HT-AD sludge might contribute to U(VI) adsorption. [ABSTRACT FROM AUTHOR]

A myriad of resources and efforts have been devoted to assessing the possibilities of using locally sourced biomass to produce energy, reduce CO2 emissions, and, in turn, lower dependance on petroleum. Grape pomace (GP) and walnut shells (WS) are organic waste generated in Chile. Within the last decade, the potential benefits and application of biomass have received significant attention, both in terms of producing functionalized carbon materials, and the various potential applications in the field of energy storage and environmental protection. The proposed research motivation is on the development of carbonous materials through thermal decomposition processes. Few researchers have addressed the idea of developing a multipurpose carbonaceous matrix from hydrochar, and there remains a need for an efficient method to obtain hydrochar specially from grape pomace. Hence, the general objective of this research is to study the potential of grape pomace and walnut shells treated with hydrothermal carbonization (HTC) as an alternative low-cost and efficient carbonous matrix. Proximate and elemental analysis was determined to distinguish the nature of the feedstock along with the hydrochar produced. Yield and reaction severity were also studied to study the impacts of temperature and residence time for both feedstocks. Successful results from the proposed work have broad applications for increasing the sustainability biomass applications, contributing to a positive economic impact. [ABSTRACT FROM AUTHOR]

An efficient method of synergetic dechlorination and reduction of heavy metals risk is crucial for the clean resource utilization of sewage sludge (SS) and polyvinyl chloride (PVC). In this work, SS was upgraded to hydrochar using co-hydrothermal carbonization (HTC) with PVC at different mixing ratio (30─70%) at 230 °C. Transformation behaviors of chlorine and heavy metals in hydrochars, along with fuel properties, were evaluated. The results illustrated that Mn and Zn could be effectively removed during co-HTC and low ratio addition of PVC was beneficial for reducing the toxicity of Ni and As. Meanwhile, compared with the HTC of single PVC, co-HTC with SS could further improve the dechlorination efficiency (69.49─81.35%). Particularly, the blending ratio of SS to PVC at 7:3 showed high fuel ratio and HHV (13.58 MJ/kg) with desirable combustion performance. These findings offered a potential approach to convert SS and PVC into clean solid fuel. [Display omitted] [ABSTRACT FROM AUTHOR]

Iron-based industries are one of the main contributors to greenhouse gas (GHG) emissions. Partial substitution of fossil carbon with renewable biocarbon (biomass) into the blast furnace (BF) process can be a sustainable approach to mitigating GHG emissions from the ironmaking process. However, the main barriers of using biomass for this purpose are the inherent high alkaline and phosphorous contents in ash, resulting in fouling, slagging, and scaling on the BF surface. Furthermore, the carbon content of the biomass is considerably lower than coal. To address these barriers, this research proposed an innovative approach of combining two thermochemical conversion methods, namely hydrothermal carbonization (HTC) and slow pyrolysis, for converting biomass into suitable biocarbon for the ironmaking process. Miscanthus, which is one of the most abundant herbaceous biomass sources, was first treated by HTC to obtain the lowest possible ash content mainly due to reduction in alkali matter and phosphorous contents, and then subjected to slow pyrolysis to increase the carbon content. Design expert 11 was used to plan the number of the required experiments and to find the optimal condition for HTC and pyrolysis steps. It was found that the biocarbon obtained from HTC at 199 °C for 28 min and consecutively pyrolyzed at 400 °C for 30 min showed similar properties to pulverized coal injection (PCI) which is currently used in BFs due to its low ash content (0.19%) and high carbon content (79.67%). [ABSTRACT FROM AUTHOR]

In this article, the effects of nanoparticles aggregates and concentration on linear and nonlinear optical absorption properties of ZnS and ZnS/carbon-based materials in polymethyl methacrylate (PMMA) matrix have been investigated. Carbon-based materials were synthesized via the hydrothermal carbonization method. Hazelnut shell was preferred as a feedstock of carbon material due to its high production capacity in Turkey. Thin films consisting of 10, 20, and 30 wt % nanoparticles were obtained to discover the effect of weight concentration on optical properties. The linear and nonlinear absorption properties were characterized by UV–Vis spectroscopy technique and open aperture Z-scan measurements with 4 ns pulses at 532 nm. A theoretical model containing one photon, two photon and free carrier absorption and their saturations were used for the fitting of the experimental data. The band gap decreased with the increasing of the weight concentration of nanoparticles in PMMA. Z-scan experiment results showed that the highest effective nonlinear absorption coefficient was obtained for the thin films with 30 wt% nanoparticle concentration which had also the smallest bandgap energy. The effect of nanoparticles aggregates on the band gap energy and nonlinear absorption was also observed. The transmission electron microscopy (TEM) results indicated that the addition of carbon caused the aggregation. Image 1 • Hazelnut shell is the source of waste biomass to obtain green, low-cost and renewable carbon material. • The addition of carbon causes the aggregation. • The band gap energy and the nonlinear absorption coefficient depend on the nanoparticles aggregates in the nanocomposites. • The band gap energy and nonlinear absorption coefficient can be controlled by nanoparticle weight concentration. [ABSTRACT FROM AUTHOR]

Hydrothermal carbonization (HTC) reactor systems used to convert wet organic wastes into value-added hydrochar are generally classified in the literature as liquid water-based (HTC) or vapor-based (VTC). However, the distinction between the two is often ambiguous. In this paper, we present a methodological approach to analyze process conditions for hydrothermal systems. First, we theoretically developed models for predicting reactor pressure, volume fraction of liquid water and water distribution between phases as a function of temperature. The reactor pressure model predicted the measured pressure reasonably well. We also demonstrated the importance of predicting the condition at which the reactor system enters the subcooled compression liquid region to avoid the danger of explosion. To help understand water–feedstock interactions, we defined a new solid content parameter %S(T) based on the liquid water in physical contact with feedstock, which changes with temperature due to changes in the water distribution. Using these models, we then compared the process conditions of seven different HTC/VTC cases reported in the literature. This study illustrates that a large range of conditions need to be considered before applying the label VTC or HTC. These tools can help in designing experiments to compare systems and understand results in future HTC research. [ABSTRACT FROM AUTHOR]

Hydrothermal carbonization (HTC) is a promising method to process high moisture biomass into biofuel/biomaterial. The environmental benefits of biomass depend on the processing methods and its end-use. Although life cycle assessment (LCA) of HTC of wet biomass has been conducted, co-processing of peat moss with agricultural biomass (miscanthus) is yet to be reported. This study evaluates the environmental performance of hydrothermally carbonized biomass (peat moss, miscanthus, and a blend of the two) used for energy (S 3 , S 5 , S 7) or soil amendment (S 2 , S 4 , S 6 , S 8) and compared with untreated biomass (peat moss left on-site: S 1 ; peat moss used for soil amendment: S 2) to determine the most viable pathway of biomass. Hydrochar produced from miscanthus had a lower global warming potential (GWP) compared with the hydrochar from peat moss or their blend; however, other impact categories were observed to be greater. The environmental impacts from the life cycle of biomass depend on their life cycle pathways. The highest GWP was observed in the case of peat moss used for horticulture application (S 2) followed by S 3 , S 5 , S 4 , S 6 , S 7 , S 8 and S 1. Hydrochar used in soil amendment was more environmentally benign than the energy application, but the benefits were dependent on the decomposition rate of biomass. Additionally, HTC process required a considerable amount of water even it can process high moisture biomass. Renewable energy and agricultural policy may be needed to encourage hydrochar use/production/integration into soil amendment and energy application in rural communities. Image 1 • Life cycle of hydrothermally carbonized and untreated biomass has been evaluated. • Peat moss, miscanthus, their blend are used for energy or horticulture application. • Hydrochar from miscanthus has a lower GWP than the hydrochar from peat moss. • Hydrochar horticulture application is environmentally benign than energy application. [ABSTRACT FROM AUTHOR]

In this study, the hydrothermal carbonization (HTC) technology at low temperature was applied to convert the wasted sludge into biochar, by establishing the correlation between the operation conditions and biochar characteristics. The contents of C, H, O, N and S, and the values of (O + N)/C and O/C in biochar were negatively correlated to the temperature, retention time and initial pH conditions. This implies that increasing temperature and retention time are beneficial for sludge dewatering and reduction. The maximum high heating value of biochar at 15.21 MJ/kg was achieved, which is similar to the cellulosic biochar and lignite surface known as the primary renewable fuel. The typical macromolecules such as proteins and lipids still existed on the biochar surface after low temperature HTC treatment. Decreasing the initial pH enforced the protonation effect and structural stability of the organic macromolecules in sludge, resulting in a diverse morphology with more compact microspheres on the biochar surface. Particularly, the catalytic ability to generate the carbon-centered persistent radicals was enhanced with g-factor at 2.01138–1.98428. In terms of environmental safety, the detected concentrations of heavy metals (Zn, Pb, Cu and Al) during the secondary dissolution of biochar were below 0.25 mg/L, indicating the low leaching risk for the land application. In addition, some humic acid and fulvic acid analogues were also detected in the secondary dissolution liquid, which can facilitate the redox reaction in soil microenvironment. In sum, this study confirmed that the low temperature HTC is a feasible method for sludge treatment and resource recovery. Image 1 [ABSTRACT FROM AUTHOR]

• Hydrothermal carbonization through high-pressure differential scanning calorimetry. • Kinetic parameters assessed based on calorimetric results. • nth-order reaction and autocatalytic reaction models investigated. • Very good fits obtained: R2 of 0.86 and 0.94 for digestate and sludge. Assessing kinetic parameters of hydrothermal carbonization still requires several tests and time-consuming analyses, usually relying on few data points. With a view to containing the experimental effort and testing the accuracy of models based on continuum curves, high-pressure differential scanning calorimetry was used for the first time to assess the heat release profile, the overall enthalpy change, and the kinetic parameters of a hydrothermal carbonization process in two substrates: digestate and sludge. The process-related thermal effect was established from the difference between the calorimetric curves for the unreacted samples during a first run and for the reacted samples obtained through a second run. The parameters of a kinetic model built on the Arrhenius reaction were adjusted on the basis of the calorimetric curves, adopting an nth-order and an autocatalytic reaction model. Activation energy values of 139.16 and 161.68 kJ/mol, pre-exponential factors around 2.15 × 1011 and 2.52 × 1014 s−1, reaction orders of about 2.68 and 2.46, and R 2 values of 0.86 and 0.94 were obtained for digestate and sludge, respectively. Results were consistent with the available literature. Autocatalysis was negligible for both substrates, so the process could be modeled effectively as a single Arrhenius nth-order reaction with significant loss of precision. Coupled with more traditional approaches, this newly-proposed method may pave the way to describing the set of reactions taking place during hydrothermal carbonization by means of their enthalpy values, improving our knowledge of the process's chemistry and kinetics. [ABSTRACT FROM AUTHOR]

Porous carbon materials are currently subjected to strong research efforts mainly due to their excellent performances in energy storage devices. A sustainable process to obtain them is hydrothermal carbonization (HTC), in which the decomposition of biomass precursors generates solid products called hydrochars, together with liquid and gaseous products. Hydrochars have a high C content and are rich with oxygen-containing functional groups, which is important for subsequent activation. Orange pomace and orange peels are considered wastes and then have been investigated as possible feedstocks for hydrochars production. On the contrary, orange juice was treated by HTC only to obtain carbon quantum dots. In the present study, pure orange juice was hydrothermally carbonized and the resulting hydrochar was filtered and washed, and graphitized/activated by KOH in nitrogen atmosphere at 800 °C. The resulting material was studied by transmission and scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and nitrogen sorption isotherms. We found porous microspheres with some degree of graphitization and high nitrogen content, a specific surface of 1725 m2/g, and a pore size distribution that make them good candidates for supercapacitor electrodes. [ABSTRACT FROM AUTHOR]

Hydrothermal carbonization (HTC) as a promising thermochemical process can convert organic solid wastes (e.g., biomass, plastics) into valuable products (i.e., hydrochar) at relatively low temperatures (180–250 °C) and saturated pressures (2–10 MPa). Hydrothermal conversion generally occurs via dehydration, polymerization and finally carbonization reactions. The carbon materials derived from hydrochar have high potential in various applications such as solid fuel, supercapacitor, fuel cell, and sorbent. Although the energy densification of hydrochar was increased at higher temperatures, most of the benefit was achieved at modest temperatures. Chemical structures of hydrochars include crosslinks of aromatic polymer, surface porosity, organic functional groups and ultimate components. All of these characteristics can be changed significantly by HTC, influencing the reactivity and fuel properties of hydrochars. The reaction pathways including negative and positive effects during (co)-HTC of biomass and plastic wastes are thoroughly concluded. In particular, the co-HTC of chlorinated plastic (e.g., PVC) and biomass can enhance the dechlorination and inorganics removal from hydrochar. Image 1 • Hydrothermal carbonization of biomass and plastic wastes was reviewed. • Hydrochar with high energy density can be used as a coal-alternative solid fuel. • Hydrochar can be chemically activated into porous carbons for energy storage. • HTC is mostly influenced by the feedstock types and processing conditions. • Co-HTC of plastics and biomass can improve the quality of hydrochar. [ABSTRACT FROM AUTHOR]

Recently, the use of controlled release fertilizers in agriculture has resulted in huge benefits in plant growth and cultivation. Superabsorbent polymer (SAP)‐coated fertilizers have the added advantage in retaining water in soil after irrigation and also reduce the nutrient release rate from soil in a controlled manner. This study aimed to produce a nitrogen–phosphorus–potassium (NPK) fertilizer coated with superabsorbent carbonaceous microspheres polymer (SPC) by inverse suspension polymerization method with water‐retention and controlled release properties. Two sets of experiments were conducted: (1) three different weight percentages and (2) different materials. NPK coated with SPC showed increasing water‐retention ability with respect to carbon microsphere percentages and retains >80% water at the 30th day of experiment compared with pure NPK and NPK coated with SAP. The slow release behavior of all samples was investigated by induced coupled plasma mass spectrometry spectrometry and results showed that NPK coated with SAP and SPC has a low release rate with <50% nutrient release compared with uncoated NPK at the 30th day. The release mechanism kinetics of NPK coated with SAP and SPC were studied based on the Kosmeyer–Peppas model. The mechanisms approached Fickian diffusion‐controlled release as the n value for both samples was less than 0.5. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48396. [ABSTRACT FROM AUTHOR]

Hydrothermal carbonization (HTC) is an innovative process capable of converting wet biodegradable residues into value-added materials, such as hydrochar. HTC has been studied for decades, however, a lack of detailed information on the production and composition of the process water has been highlighted by several authors. In this paper the state of the art of the knowledge on this by-product is analyzed, with attention to HTC applied to municipal and agro-industrial anaerobic digestion digestate. The chemical and physical characteristics of the process water obtained at different HTC conditions are compared along with pH, color, organic matter, nutrients, heavy metals and toxic compounds. The possibility of recovering nutrients and other valorization pathways is analyzed and technical feasibility constraints are reported. Finally, the paper describes the main companies which are investing actively in proposing HTC technology towards improving an effective process water valorization.

A reliable and reproducible procedure for the determination of the heat release rate profile and for the enthalpy change of the hydrothermal carbonization (HTC) process is applied using High Pressure Differential Scanning Calorimetry (HP-DSC). Cellulose, wood, and digestate are used as feedstocks. The temperature program is run once to let the process complete in the first run, whereas in the second the thermal effect of products is assessed. A provisional heat release profile is obtained subtracting the two curves, with a very high reproducibility (standard deviations between 1.8 and 8.0%). To consider the heat capacity difference between reactants and products, a baseline is computed and subtracted from the heat release profile. The integral of this curve gives the enthalpy change associated to HTC, which was −0.88, −0.64, and −0.25 MJ/kg for cellulose, wood and digestate respectively. This methodology can be adopted for the development of accurate thermal-based HTC kinetics. Unlabelled Image • High pressure DSC used to assess heat release rate and enthalpy change of the HTC. • High reproducibility is obtained (standard deviation between 1.8 and 8.0%). • Results consider the heat capacity difference of reactants and products. • Enthalpy change of −0.88, −0.64, and −0.25 MJ/kg for cellulose, wood, digestate. [ABSTRACT FROM AUTHOR]

In many countries, sewage sludge is directly used for energy and agricultural purposes after dewatering or digestion and dewatering. In recent years, there has been a growing interest in additional upstream hydrothermal carbonization (HTC), which could lead to higher yields in the energetic and agricultural use. Twelve energetic and agricultural valorization concepts of sewage sludge are defined and assessed for Germany to investigate whether the integration of HTC will have a positive effect on the greenhouse gas (GHG) emissions. The study shows that the higher expenses within the HTC process cannot be compensated by additional energy production and agricultural yields. However, the optimization of the HTC process chain through integrated sewage sludge digestion and process water recirculation leads to significant reductions in GHG emissions of the HTC concepts. Subsequently, nearly the same results can be achieved when compared to the direct energetic use of sewage sludge; in the agricultural valorization, the optimized HTC concept would be even the best concept if the direct use of sewage sludge will no longer be permitted in Germany from 2029/2032. Nevertheless, the agricultural valorization concepts are not generally advantageous when compared to the energetic valorization concepts, as it is shown for two concepts. [ABSTRACT FROM AUTHOR]

Olive trimmings (OT) were used as feedstock for an in-depth experimental study on the reaction kinetics controlling hydrothermal carbonization (HTC). OT were hydrothermally carbonized for a residence time τ of up to 8 h at temperatures between 180 and 250 °C to systematically investigate the chemical and energy properties changes of hydrochars during HTC. Additional experiments at 120 and 150 °C at τ = 0 h were carried out to analyze the heat-up transient phase required to reach the HTC set-point temperature. Furthermore, an original HTC reaction kinetics model was developed. The HTC reaction pathway was described through a lumped model, in which biomass is converted into solid (distinguished between primary and secondary char), liquid, and gaseous products. The kinetics model, written in MATLABTM, was used in best fitting routines with HTC experimental data obtained using OT and two other agro-wastes previously tested: grape marc and Opuntia Ficus Indica. The HTC kinetics model effectively predicts carbon distribution among HTC products versus time with the thermal transient phase included; it represents an effective tool for R&D in the HTC field. Importantly, both modeling and experimental data suggest that already during the heat-up phase, biomass greatly carbonizes, in particular at the highest temperature tested of 250 °C. [ABSTRACT FROM AUTHOR]

Hydrochar is a very interesting product from agricultural and food production residues. Unfortunately, severe conditions for complete conversion of lignocellulosic biomass is necessary, especially compared to the conversion of sugar compounds. The goal of this work is to improve the conversion of internal carbohydrates by application of a two-steps process, by acid addition and slightly higher water content. A set of experiments at different temperatures (180, 200, and 220 °C), reaction times (2 and 4 h), and moisture contents (80% and 90%) was performed to characterize the solid (high heating value (HHV), elemental) and liquid product phase. Afterwards, acid addition for a catalyzed hydrolysis reaction during hydrothermal carbonization (HTC) and a two-steps reaction (180 and 220 °C) were tested. As expected, a higher temperature leads to higher C content of the hydrochar and a higher fixed carbon (FC) content. The same effect was found with the addition of acids at lower temperatures. In the two-steps reaction, a primary hydrolysis step increases the conversion of internal carbohydrates. Higher water content has no significant effect, except for increasing the solubility of ash components. [ABSTRACT FROM AUTHOR]

Peat moss and miscanthus were hydrothermally carbonized (HTC) either individually or co-processed in a different ratio to produce hydrochar. The hydrochar and pelletized hydrochar were then characterized to determine if hydrochar can be used as an alternative to coal to produce bioenergy from existing coal-fired power plants in Ontario that have already been shut down. The properties of carbonized biomass (either hydrochar or pellets) reveal that fuel grade hydrochar can be produced from peat moss or from the blend of peat moss and miscanthus (agricultural biomass/energy crops). Hydrochar either produced from peat moss or from the blend of peat moss and miscanthus was observed to be hydrophobic and porous compared to raw peat moss or raw miscanthus. The combustion indices of carbonized biomass confirmed that it can be combusted or co-combusted to produce bioenergy and can avoid slagging, fouling, and agglomeration problems of the bioenergy industry. The results of this study revealed that HTC is a promising option for producing solid biofuel from undervalued biomass, especially from high moisture biomass. Co-processing of peat moss with rural biomass, a relatively novel idea which can be a potential solution to heat and power for the rural communities/agri-industry that are not connected with national grids and alleviate their waste management problems. In addition, the hydrochar can also be used to run some of the existing coal-fired power plants that have already been shut down in Ontario without interrupting investment and employment. [ABSTRACT FROM AUTHOR]