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In this study, modeling and optimization of Hydrothermal Carbonization (HTC) of Poultry litter were conducted to convert it into high-value materials. The aim was to understand the process and predict the effect of the influencing parameters on the product properties. The recovery of Inorganic Phosphorous (IP) and Carbon (C) was regarded as the model's response, although temperature and reaction time were thought to be important variables. Response Surface Methodology (RSM) was used along with temperature and time data sets ranging from 150 to 300C and 30-480 min, respectively, to identify the parameters influencing the response, three-dimensional networks, and optimization. Next, Multilayer Perceptron (MLP) and Radial Basis Function (RBF) were used to compare the results and improve the model fit. For these two neural networks, 7 neurons in two layers and 14 neurons in one layer were the ideal numbers. With fewer neurons and better accuracy and efficiency, the MLP model beat RBF with lower Mean Squared Error (MSE) values for both C (0.0015812 vs. 0.0037103) and IP (0.0014376 vs. 0.00623011) recovery and a higher R 2 value (R 2 C recovery  = 0.99742, R 2 IP recovery  = 0.99816). These results demonstrate that MLP is a viable technique for maximizing resource recovery through HTC condition optimization, with potential uses in nutrient recycling and sustainable waste management. By examining the three-dimensional grids and obtained contours, it was found that temperature had a greater effect on the response, and the impact of time was more pronounced at lower temperatures. With increasing temperature and reaction time, C recovery decreased, while IP recovery increased. Furthermore, the optimal values for temperature and time were suggested to be 182.329 C and 427.746 min, respectively. The optimal product values under these conditions for C and IP recovery were obtained as 59.611 % and 29.114 mg/g, respectively., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.Nomenclature AbbreviationstTimeTTemperature (C)CCarbonPPhosphorousR2Correlation coefficientANNArtificial Neural NetworkRBFRadial Basis FunctionsMLPMultilayer PerceptronMSEMean Square ErrorHTCHydrothermal CarbonizationHCHydrocharIPInorganic PhosphorousPLPoultry litterMSEMean Squared ErrorSubscriptxEquation inputyEquation outputwWeightbBiasσBasis widthiExperiment set ijExperiment set jkExperiment set k, (© 2024 The Authors.)

Dairy manure, a significant source of phosphorus (P), can potentially cause environmental risk due to P runoff when dairy manure is directly applied to cropland. Thus, there is an increasing interest in mitigating P loss from manure prior to land applications. This study aimed to investigate the potential of hydrochar produced by hydrothermal carbonization (HTC) for P recycling from dairy manure with and without the addition of CaO, focusing on the plant bioavailability, stabilization, and transformation of P in the resultant hydrochar. Hydrochar was prepared under different temperatures (180-240°C). The effect of CaO addition (0-10% of raw manure on dry wt. basis) was also evaluated at 220°C. Results showed that water-soluble P (WSP), a key indicator of P runoff loss, was significantly reduced in hydrochar, particularly with CaO addition. In addition, the plant available P in hydrochar increased with HTC temperature increase till 220°C, which accounted for ∼90% of total P content, then decreased with temperatures higher than 220°C. The addition of CaO slightly reduced plant bioavailability when compared to hydrochar produced at 220°C without additive. The P fractionation and speciation analyses indicated the transformation of P into Ca-associated apatite P. Hydrochar produced at 220°C with 10% CaO addition resulted in a high P recovery (∼85%) and a reduced runoff risk by 97%. The results demonstrate the efficacy of P recycling through hydrochar produced from dairy manure through HTC, which offers a sustainable approach to managing dairy waste while mitigating the potential environmental risks of P runoff.

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., (Copyright © 2021. Published by Elsevier Ltd.)

Herein, mesoporous activated carbon (AC) was prepared through potassium hydroxide (KOH) activation of hydrochar derived from the hydrothermal carbonization (HTC) of chickpea stem (CS), and successfully applied to remove methylene blue (MB) dye from aqueous solutions in a batch system. The HTC-CSAC was prepared depending on different impregnation ratios (hydrochar:KOH, 50-150%), impregnation times (12-48 h), activation temperatures (400-600 ° C ) and activation times (30-60 min). To define HTC-CSAC, various analytical techniques such as iodine adsorption number (IAN), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) were used. In the removal process of MB by the best HTC-CSAC with a high IAN of 887 mg g -1 obtained under conditions including impregnation ratio of 70%, activation time of 45 min, activation temperature of 600 ° C and impregnation time of 24 h, the effects of adsorption parameters such as pH factor (2-10), adsorbent dosage (50-100 mg), initial MB concentration (40-80 mg/L) and contact time (90-180 min) were studied. Besides, a detailed evaluation of the adsorption mechanism for the removal of MB by HTC-CSAC was performed. The Langmuir model indicated the best isotherm data correlation, with a maximum monolayer adsorption capacity ( Q max ) of 96.15 mg g -1 . The adsorption isotherm findings demonstrated that the MB removal process is feasible, and that this process takes place through the physical interaction mechanism. Additionally, the HTC-CSAC adsorbent exhibited a high regeneration and reuse performance in MB removal. After five consecutive adsorption-desorption cycles, HTC-CSAC maintained the reuse efficiency of 77.86%. As a result, the prepared HTC-CSAC with a high BET surface area of 455 m 2 g -1 and an average pore diameter of 105 Å could be recommended as a promising and reusable adsorbent in the treatment of synthetic dyes in wastewaters.

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.

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 m 2 /g, and a pore size distribution that make them good candidates for supercapacitor electrodes., Competing Interests: The authors declare no conflict of interest.

The mesophilic anaerobic co-digestion of the liquid fraction from hydrothermal carbonization (LFHTC) of dewatered waste activated sludge with primary sewage sludge (PSS) has been studied. Mixtures of different composition (25, 50 and 75% of LFHTC on a chemical oxygen demand (COD) basis), as well as the individual substrates, have been tested using two inocula (flocculent (FS) and granular (GS) sludges). Methane production decreased as the LFHTC/PSS ratio increased, which can be related to the presence of recalcitrant compounds in the LFHTC, such as alkenes, phenolics, and other oxygen- and nitrogen-bearing aromatics hard-to-degrade through anaerobic digestion. Methane yield reached 248 ± 11 mL CH 4 STP/g COD added with the GS inoculum and 25% LFHTC. A 74 and a 30% increase of methane production was achieved in the 25% LFHTC runs respect to the obtained in the similar experiments with 100% LFHTC, using the FS and GS inocula, respectively. In those late runs, the COD was reduced more than 86%, with a negligible concentration of total volatile fatty acids. With both inocula, total Kjeldahl nitrogen hydrolysis increased as the LFHTC to PSS mixture ratio decreased, reaching values higher than 79% at the end of the experiments. Methane yield values fitted well the first-order, Cone and Weibull kinetic models for both inocula. Significant differences in the kinetic constant values, ranging from 0.100 to 0.168 d -1 and 0.059-0.068 d -1 , were found with the FS and GS inocula, respectively. The results obtained support the potential integration of HTC of dewatered waste activated sludge in wastewater treatment plants., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

To optimize the energy yield (EY) of food waste (FW) via hydrothermal carbonization (HTC), a response surface method was applied. Hydrochars and spent liquor were further conducted to evaluate their characterization and anaerobic digestion potential. Results found that optimal parameters for HTC of FW were suggested as temperature of 260 °C, reaction time of 4 h and moisture of 80%, with higher EY of 66.1%. Higher heating value, good combustion quality, lower H/C and O/C ratios indicated that hydrochar could be utilized as a safe solid fuel. Biochemical methane potential (BMP) experiment showed that spent liquor and hydrochars could be used as feedstocks for anaerobic digestion. Interestingly, hydrochars added in the spent liquor could promote the specific methane yield, which was 2.53 times higher than no addition of hydrochars. The finding of this study could provide useful information for HTC of FW and the utilization of hydrochars and spent liquor., (Copyright © 2018. Published by Elsevier Ltd.)

This research deals with the effect of the temperature on the physical, thermal, electrochemical, and adsorption properties of the carbon micro-spheres using hydrothermal carbonization (HTC). Until recently, limited research has been conducted regarding the effects of delignification during the HTC process of biomass residues especially Dimocarpus longan . In this regard, lignin was first extracted from the lingo-cellulosic waste of Longan fruit peel ( Dimocarpus longan ). The holocellulose (HC) separated from lignin and raw biomass substrates (Longan fruit exocarp/peel powder, LFP) were carbonized at different temperatures using water as the green catalyst. Hydrothermal carbonization (HTC) was performed for both of the samples (LFP and HC) at 200 °C, 250 °C, and 300 °C for 24 h each. The surface morphological structures, the porosity, and the Brunauer-Emmett-Teller (BET) surface area of the prepared micro-spherical carbon were determined. The BET surface areas obtained for HC-based carbon samples were lower than that of the raw LFP based carbon samples. The carbon obtained was characterized using ultimate and proximate analyses. The surface morphological features and phase transformation of the synthesized micro-spherical carbon was characterized by a field-emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) analysis. The results demonstrated that the extraction of lignin could significantly alter the end properties of the synthesized carbon sample. The carbon spheres derived from LFP showed a higher carbon content than the HC-based carbon. The absence of lignin in the holo-cellulose (HC) made it easy to disintegrate in comparison to the raw, LFP-based carbon samples during the HTC process. The carbonaceous samples (LFP-300 and HC-300) prepared at 300 °C were selected and their adsorption performance for Pb (II) cations was observed using Langmuir, Freundlich, and Temkin linear isotherm models. At 30 °C, the equilibrium data followed the Langmuir isotherm model more than the Freundlich and Temkin model for both the LFP-300 sample and the HC-300 sample. The potential of the synthesized carbon microspheres were further analyzed by thermodynamic characterizations of the adsorption equilibrium system.

In the present study, the influence of substrate pre-treatment (grinding and sieving) on batch anaerobic digestion of the organic fraction of municipal solid waste (OFMSW) was first assessed, then followed by co-digestion experiments with the liquid fraction from hydrothermal carbonization (LFHTC) of dewatered sewage sludge (DSS). The methane yield of batch anaerobic digestion after grinding and sieving (20 mm diameter) the OFMSW was considerably higher (453 mL CH 4 STP g -1 VS added ) than that of untreated OFMSW (285 mL CH 4 STP g -1 VS added ). The modified Gompertz model adequately predicted process performance. The maximum methane production rate, R m , for ground and sieved OFMSW was 2.4 times higher than that of untreated OFMSW. The anaerobic co-digestion of different mixtures of OFMSW and LFHTC of DSS did not increase the methane yield above that of the anaerobic digestion of OFMSW alone, and no synergistic effects were observed. However, the co-digestion of both wastes at a ratio of 75% OFMSW-25% LFHTC provides a practical waste management option. The experimental results were adequately fitted to a first-order kinetic model showing a kinetic constant virtually independent of the percentage of LFHTC (0.52-0.56 d -1 ) and decreasing slightly for 100% LFHTC (0.44 d -1 )., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

(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., (Copyright © 2016 Elsevier Ltd. All rights reserved.)