Hydrochar Yield Research Articles

Valorization of olive mill wastewater as a process medium in co-hydrothermal carbonization with Sicilian agro-wastes: effects of interaction on product yield and properties

This work explores the valorization of residual olive mill wastewater as a process aqueous medium for co-hydrothermal carbonization (co-HTC) of typical Sicilian agro-wastes (tangerine and orange peel wastes). Co-HTC experiments were carried out at 180 and 220 °C to assess the interaction between the feedstocks. Synergistic effects increased the yield of hydrochar and gas phases while antagonism altered the formation of aqueous products. Compared to the expected value, hydrochar yield was increased by 37 wt%, on average, while the interaction effect on gas phase was weaker (+23 wt%, on average) and increased with temperature. Both the retention of unhydrolyzed primary char and the recapture of secondary char phases from process water enhanced the hydrochar recovery in different ways according to feedstock nature and co-HTC conditions. On the basis of hydrochars characterization through elemental analysis and surface functionality, the degree of carbonization was significantly improved after co-HTC due to promoted dehydration and decarboxylation reactions. As result, co-hydrochars exhibited a moderately higher energy content and a greater thermal stability compared to samples obtained from HTC of individual substrates. Co-hydrochars also retained relatively high amounts of nutrients such as phosphorus, potassium and calcium, which could enable their use as soil improvers.

Hydrochar and Value-Added Chemical Production Through Hydrothermal Carbonisation of Woody Biomass

This study investigates the optimisation of hydrothermal carbonisation (HTC) parameters for transforming Whitewood biomass into hydrochar, focusing on bioenergy production and valuable chemical extraction as by-products. The optimal carbonisation was achieved at a process temperature of 240 -260 °C, which optimised the higher heating value of the hydrochar to 27-30 kJ/g and ensured a structural integrity similar to lignite coal. Increasing the temperature beyond 260 °C did not significantly enhance the energy content or quality of the hydrochar, establishing 260 °C as the practical upper limit for the HTC process. Residence times between 30 to 60 min were found to have minimal impact on the yield and quality of hydrochar, suggesting significant operational flexibility and the potential to double throughput without increasing energy consumption. The study also revealed that the process water by-product is rich in furan compounds, particularly furfural and hydroxymethyl furfural, with their highest concentration (125 mg/g of feedstock) occurring at 220 °C. The implementation of these findings could facilitate the development of a large-scale HTC facility, significantly reducing reliance on fossil fuels and enhancing economic viability by producing high-energy-density biofuels and high-value chemical by-products.

Hydrochar from co-hydrothermal carbonization of sewage sludge and sunflower stover: Synergistic effects and combustion characteristics

This study carried out co-hydrothermal carbonization (Co-HTC) on sewage sludge (SS) and sunflower straw (SFS) at various ratios (1:0, 3:1, 1:1, 1:3, 0:1) to prepare hydrochar. The raw samples and produced hydrochar were characterized using ultimate analysis, proximate analysis, Brunauer-Emmett-Teller (BET), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The potential synergistic impact during the reaction process were analyzed. As the SFS ratio increased, the fuel ratio of hydrothermal carbons rose from 0.29 to 0.37, while the higher heating value (HHV) improved from 7.44 (MJ/kg) to 20.86 (MJ/kg). The co-hydrothermal synergistic effect resulted in enhanced the hydrochar yield, energy yield, carbon sequestration rate and organic retention rate. Compared to raw sample, the surface of hydrochar exhibits a rougher and more fragmented structure, with an increased number of microspheres and micropores, resulted in an increased specific surface area. Thermogravimetric analysis (TGA) demonstrated that, in comparison to HTC of sludge alone, the Co-HTC of SS with SFS enhances the ignition temperature and delays the completion of combustion. Therefore, Co-HTC with SFS is an effective method for converting SS into clean solid fuel for energy applications.

Production of hydrochar from the hydrothermal carbonisation of food waste feedstock for use as an adsorbent in removal of heavy metals from water

AbstractIn this research, discarded butternut peels were converted into hydrochar products through hydrothermal carbonisation (HTC), with adjustments made to the temperature (ranging from 180 to 260℃) and residence time (spanning 45–180 min). The findings indicated that both the temperature and time of carbonisation significantly influenced the yield of hydrochar (HC), as well as its physiochemical and structural properties. Higher temperatures and prolonged residence time led to decreased yield, elevated fixed carbon content and an increased fuel ratio. Furthermore, raising the process conditions increased HHV and reduced the oxygen-containing functional groups. The HC yield dropped from 28.75 to 17.58% with increased carbonisation temperature and time. The findings of this study also suggest that modified hydrochar is a promising material for removing heavy metals from wastewater. It is a relatively low-cost and abundant material that can be produced from various biomass feedstocks, including food waste. In addition, it is a sustainable and environmentally friendly option for wastewater treatment. Hydrochar-based systems offer several advantages over traditional methods of heavy metal removal, such as chemical precipitation and ion exchange. The unique physicochemical characteristics of hydrochar, including its porous structure and oxygen-rich functional groups, offer a high surface area and more binding sites for heavy metal ions. By changing the physicochemical properties of hydrochar with chemicals like phosphoric acid, it is possible to increase its adsorption capacity. The Freundlich isotherm was the best fit for the adsorption data for all three metal ions (Pb2+, Cu2+ and Cd2+), indicating that the adsorption process is multilayer and heterogeneous.

Low-energy thermo-chemical conversion processes of municipal wet waste

Hydrothermal carbonization (HTC) is a low-energy thermochemical process that converts wet biomass into a carbon-rich solid, commonly called hydrochar, for use in a variety of areas, such as soil amendment, biofuels or to produce carbon-based materials. The purpose of this paper is to increase knowledge for the economic valorization of municipal wet waste, considered as a raw material to obtain high value-added products through an HTC process and an additional chemical activation procedure. In the first part of the work, a 4.5-liter batch reactor was designed, built, and used in the HTC experimental campaign by varying the main process parameters, namely reaction time, amount and type of organic waste (e.g. vegetables, fruits, bread, pasta), water concentration, temperature and pressure. In addition, some experiments were conducted by applying the steam explosion technique at the end of the HTC process. The HTC results showed that in biomass with high water content, increasing residence time decreases the hydrochar yield. Considering a dry heterogeneous waste with high carbon content, the yields at the end of the process are much higher. In the second part of this work, the hydrochar samples were treated with a high-temperature activation process based on the use of KOH, obtaining activated carbon. Particularly, the best results were achieved by using high KOH: hydrochar ratios, resulting in high-quality activated carbons with good porosity and a high surface area of 2890 m2/g. Finally, an energy analysis was carried out to evaluate how to make the whole process cost-effective.

Co-hydrothermal carbonization of waste biomass and phosphate rock: promoted carbon sequestration and enhanced phosphorus bioavailability

Co-hydrothermal carbonization (co-HTC) of phosphorus rock (PR) and corn straw (CS) was investigated to prepare hydrochar-based materials as soil conditioners, focusing on the morphological transformation and solid–liquid migration of carbon and phosphorus. Various analytical methods, including elemental analysis, chemical quantification, FT-IR, XRD, 3D-EEM, TG, and XANES, were used to understand the synergistic interactions of PR and CS during co-HTC and determine the properties of the resultant products. The results indicated the acidic solution and humic acid-like substances produced by HTC of CS reduced the crystallinity of the PR and served as the activating agent for PR, allowing the PR to be easily dissolved and reconstituted, producing calcium carbonate and apatite-like materials, and the formation of C–O–PO3, C–PO3, C=O, and O=C–O chemical bonds. At 220 °C, adding 5% PR significantly promoted a 10.3% rise in the yield of CS hydrochar, a 4.3% rise in carbon recovery of CS, and a 4.8% rise in carbon sequestration potential of CS. The formation of Ca–P was notably promoted and the content of AP in co-HTC hydrochar was up to 89.9%, with 39% Hydro-P and 33% CaHPO4. In the case of artificial humic acid (HAa), its content was also remarkably increased by 5.9% in the hydrochar by co-HTC. In addition, the hydrochar produced by co-HTC of CS and PR was composed of carbon with an increased aromatic degree, rich organic matter, and biologically effective mineral nutrient elements and exhibited high stability. The present study provided a promising approach for value-added utilization of waste biomass and low-grade PR towards soil application.Graphical

Synthesis of antibacterial fluorescent carbon dots and green coal-like hydrochar from tea Industry byproducts via hydrothermal carbonization

This study introduces an experimental framework employing hydrothermal carbonization (HTC) for the valorisation of factory tea waste as a solid fuel. Employing a centre composite design and response surface methodology, the investigation systematically assesses the influence of two critical process parameters, temperature (180–220 °C) and time (0–240 min), on higher heating value (HHV), hydrochar yield, and energy yield. The study identifies an optimized HTC condition (220°C, 55 min) resulting in the recorded HHV of 22.26±1.10 Mj/Kg. Combustion characteristics and kinetics of the factory tea waste-derived hydrochar (TW-hydrochar) is analysed through TGA and DTG, complemented by structural elucidation via FTIR and FE-SEM. Concurrently, the study reports the observation of carbon dots (TW-CDs) generation during TW-hydrochar production, characterized comprehensively through UV–visible spectroscopy, TEM, XRD, XPS, Zeta potential, and fluorescence methods. Further, antimicrobial properties of TW-CDs are rigorously investigated against Bacillus subtilis and Escherichia coli, manifesting pronounced antibacterial activity against B. subtilis and E. coli as evidenced by a 12 mm and 11 mm inhibition zone, respectively. This research contributes to the scientific understanding of tea waste valorization through HTC, providing insights into cleaner fuel options and the emergence of carbon dots with potential antibacterial applications.

Sustainable hydrothermal co-carbonization of residues from the vegetable oil industry and sewage sludge: Hydrochar production and liquid fraction valorisation

In this study, the hydrothermal co-carbonization (co-HTC) of residues from the vegetable oil industry (pumpkin oil cake – PC, hemp oil cake – HC) and sewage sludge (SS) was investigated for the first time. The co-HTC was performed at 250 °C and a treatment time of 5 h. The effects of the mass ratio of the feedstocks (1:1, 1:3 and 3:1) on the properties of the HTC products were investigated using various analytical methods (NMR, XRD, 3D-EEM, FTIR, etc.).The co-HTC of SS with oil cakes resulted in improved fuel properties of the hydrochar and an increase in C content from 36.9 to 53.7 wt%, and an increase in the higher heating value (HHV) from 14.8 to 23.6 MJ/kg. The combination with HC gave hydrochars with a higher HHV and higher C content than the combination with PC. The hydrochar yield varied in the range of 39.4–55.3 wt%. NMR analysis revealed a higher proportion of aliphatic (∼60 %) than aromatic compounds (∼35 %) in the hydrochars, as well as a high content of orthophosphate and unsaturated fatty acids. The liquid fractions were rich in nutrients and organic compounds, but toxic to aquatic organisms. The hydrochars and liquid fractions performed well in the germination test with plant species.

Ionic liquid-catalyzed hydrothermal carbonization of sewage sludge: Effect of residence time and liquid phase circulation on hydrochar characteristic

The ionic liquid (IL, [DMAPA]HSO4) was used to catalyze hydrothermal carbonization (HTC) of sewage sludge (SSL), the study discussed how residence time and liquid-phase circulation influence the characteristics of the hydrochar. The decarboxylation process in IL-catalyzed HTC led to lower hydrochar yield but higher higher heating value (HHV). And the secondary hydrochar formation promoted by IL favored the system for high energy feedback (EF), but iron was involved in the secondary hydrochar formation. At the optimum hydrothermal time (90 min), the EF reached 124 % and the removal efficiencies of Fe, Mg, Mn, and Zn were 66 %, 73 %, 96 %, and 90 %, respectively. Functional groups on organic acids (COO–), amides (CO), and polysaccharides (C–O–C) in the SSL were sequentially removed during the IL-catalyzed HTC process, while cross-linking and graphitization occurred, resulting in higher ignition temperatures and lower metal contents. However, multiple cycles of the liquid phase resulted in a decrease in the catalytic properties of IL, resulting in low EF hydrochar with high metal content and functional group intensity. Catalytic graphitization is the key to obtaining hydrochar with high HHV and low metal content. Therefore, future development of catalysts is needed to facilitate the dehydration, decarboxylation and graphitization process of HTC.

Hydrochar production through co-hydrothermal carbonization of water hyacinth and plastic waste

Abstract The global expansion of the economy and concerns about greenhouse gas emissions and climate change necessitate the exploration of sustainable alternatives to fossil fuels. Water hyacinth (WH) is globally recognized as one of the most problematic aquatic weeds, posing significant challenges to urban management by clogging waterways, polluting water sources, and causing harm to ecosystems. However, water hyacinth is enriched with hemicellulose, cellulose, and lignin, making it a noteworthy and superior biomass resource. Hence, this study focuses on the hydrothermal carbonization of water hyacinth into a renewable fuel source, the hydrochar. Hydrothermal treatment was implemented in this work as it can treat wet biomass, in this case, the water hyacinth, without the need of energy-extensive drying process. Plastic waste (PW), or more specifically low-density polyethylene (LDPE), was added as the co-feedstock during the HTC process with the purpose to boost the higher heating value (HHV) of the end product. The co-hydrothermal carbonization (co-HTC) process of the mixture of WH and PW at various ratios and temperatures were conducted to investigate the optimal HTC condition for high hydrochar yields. As the result, the highest hydrochar yield of 29.23 wt% was obtained with 12.5% LDPE substitution percentage, at 200 °C after a holding time of 90 min. However, in term of energy recovery efficiency (ER), the highest efficiency (27.28%) was achieved with 12.5% LDPE substitution percentage at 260 °C. The HHV value of the hydrochar produced in this work is in the range of 17.71-24.69 MJ/kg. In summary, the co-HTC of WH and LDPE could definitely be a promising alternative to bridge the gap from solid waste to renewable fuels.

The fate of Volatile Fatty Acids (VFAs) during the thermodynamic transition from hydrothermal carbonization to hydrothermal liquefaction: HtC-to-HtL

The valorization of biomass via hydrothermal treatment, a green and reliable thermochemical process, produces high-value chemicals. This study focuses on the transformation of Volatile Fatty Acids (VFAs) during the transition from Hydrothermal Carbonization (HTC) to Hydrothermal Liquefaction (HTL) and their impact on product quality. Conducted with anaerobically digested sewage sludge, the hydrothermal treatment varied temperatures from 280 °C to 340 °C. The primary objective was to investigate VFA concentrations and their link to hydrochar yield and gaseous by-product composition. A high-performance Parr 4577A hydrothermal reactor facilitated these experiments. For VFA assessment, a Shimadzu Nexis 2030 plasma GC-BID with an HP-FFAP column was utilized for the first time. The study revealed a U-shaped COD concentration curve (peaking at 10,510 mg/l at 340 °C) and an S-shaped Total Phenols profile (highest at 1314 mg/l at 325 °C). Notably, VFA concentrations dipped significantly at 295 °C and 325 °C but were higher at other temperatures, suggesting a complex underlying mechanism. This variability is partially attributed to the reduction in hydrochar mass yield with increasing temperature (46% at 280 °C to 31% at 340 °C) and a surprising spike in CO2 concentration (90% at 310 °C). These findings emphasize the critical role of carboxylation reactions in the HTC-to-HTL transition, enhancing the quality of liquid hydrothermal products.

Binary energy production from pineapple peel waste and optimized by statistical and machine learning approaches

This study uses a two-stage process to treat pineapple peel waste (PPW), including alkaline ionized water (AIW) pretreatment and microwave-assisted heating (MAH) hydrolysis. It also contains two objective functions: hydrochar yield and hydrolysis ratio. The experimental design utilizes the Taguchi method to determine optimal conditions by calculating the signal-to-noise ratio. The designed experimental results are used to predict optimal conditions through artificial neural networks (ANN). In the first step, AIW pretreatment reduces the lignin content of PPW by 17.5 % and increases the cellulose content by 14.8 %. SEM analysis reveals a roughening of its surface, while BET analysis identifies a slightly porous structure. These characteristics provide an increased efficiency for subsequent hydrolysis. In the second step, thermogravimetric analysis indicates that a substantial hemicellulose loss is observed when the hydrolysis concentration or temperature increases. This finding aligns with the ranking of factor impacts obtained from the Taguchi method. This study also demonstrates the potential of utilizing PPW for energy production. The hydrochar, hydrolyzed under optimal conditions, increases its calorific value by 10.11 % to 18.29 MJ‧kg−1, making it suitable for use as solid fuel. The hydrolysate has 52.85 g‧L-1 reducing sugar, which can be fermented to produce ethanol and is much higher than those reported in the literature. Through the Taguchi method and ANN, the optimal experimental factor combination prediction reveals the significant impact of acid hydrolysis compared to AIW pretreatment. The optimal hydrochar yield and hydrolysis ratio in the Taguchi method are 38.75 % and 63.62 %, respectively. In ANN, they are 41.51 % and 58.38 %, respectively, with relative errors of 7.08 % and 8.23 % compared to the experimental results. This research helps turn solid waste into green fuels and approach a circular bioeconomy.

Unraveling catalytic conversion of spent coffee grounds through alkaline and alkaline earth metal phosphates in hydrothermal carbonization

Hydrothermal carbonization (HTC) offers a promising pathway for sustainable energy production, with spent coffee grounds (CG) emerging as an eco-friendly feedstock for hydrochar generation. However, the potential applications of alkaline and alkaline earth metal phosphates as catalysts for novel carbonaceous materials remain largely unexplored. This study investigates the impact of alkaline types on the characteristics, morphology, and heating value of hydrochar derived from CG. Incorporating Mg3(PO4)2, K3PO4, and Na3PO4 into HTC processes resulted in significant reductions in carbon content, leading to decreased hydrochar yield, higher heating value (HHV), and energy yield (EY). Notably, HHV reduction ranged from 2 % to 15 %, depending on catalyst type and temperature. The catalysts contributed to increasing ash content in hydrochar due to their inorganic nature. The presence of catalysts minimally impacted the hydrochar surface functional groups, with a more amorphous structure observed at 200 °C across all samples. A higher abundance of microspheres was observed in hydrochar catalyzed by K3PO4 and Na3PO4 at 200 °C compared to Mg3(PO4)2. Interestingly, K3PO4 and Na3PO4 reduced nitrogen content of the hydrochar rather than Mg3(PO4)2. The proposed catalytic mechanism involved metal phosphate catalyzing hydrolysis reactions, thereby reducing hydrochar yields while augmenting volatile fatty acid (VFA) and furan contents in the process water. Alkaline and alkaline earth metal phosphates catalysts exhibited trade-offs between hydrochar properties and hydrolysis byproducts in the HTC of CG.

Innovative Solution for Invasive Species and Water Pollution: Hydrochar Synthesis from Pleco Fish Biomass

In recent years, the invasive pleco fish has emerged as a global concern due to its adverse effects on ecosystems and economic activities, particularly in various water bodies in Mexico. This study introduces an innovative solution, employing microwave-assisted hydrothermal carbonization (MHTC) to synthesize hydrochar from pleco fish biomass. The research aimed to optimize synthesis conditions to enhance hydrochar yield, calorific value, and adsorption capacities for fluoride and cadmium in water. MHTC, characterized by low energy consumption, high reaction rates, and a simple design, was employed as a thermochemical process for hydrochar production. Key findings revealed that through response surface analysis, the study identified the optimal synthesis conditions for hydrochar production, maximizing yield and adsorption capacities while minimizing energy consumption. Physicochemical characterization demonstrated that hydrochars derived from pleco fish biomass exhibited mesoporous structures with fragmented surfaces, resembling hydroxyapatite, a major component of bone. Hydrochars derived from pleco fish biomass exhibited promising adsorption capacities for fluoride and cadmium in water, with hydrochar from Exp. 1 (90 min, 160 °C) showing the highest adsorption capacity for fluoride (4.16 mg/g), while Exp. 5 (90 min, 180 °C) demonstrated superior adsorption capacity for cadmium (98.5 mg/g). Furthermore, the utilization of pleco fish biomass for hydrochar production not only offers an eco-friendly disposal method for invasive species but also addresses fluoride and cadmium contamination issues, contributing to sustainable waste management and water treatment solutions. The resulting hydrochar, rich in solid fuel content with low pollutant emissions, presents a promising approach for waste management and carbon sequestration. Moreover, the optimized synthesis conditions pave the way for sustainable applications in energy production, addressing critical environmental and public health concerns. This research provides valuable insights into the potential of microwave-assisted hydrothermal carbonization for transforming invasive species into valuable resources, thereby mitigating environmental challenges and promoting sustainable development.

Hydrothermal Pyrolysis of Sargassum Marine Macroalgae: "Synthesis and Characterization of Products"

Abstract In recent years, there has been an explosive growth and overabundance of pelagic Sargassum macroalgae in the North Atlantic Ocean, which wash up on the beaches in the United States, Mexico and the Caribbeans, causing both environmental and health issues in those coastal regions. Hydrothermal carbonization (HTC) process was investigated as a potential solution by converting this wet algae biomass into solid and liquid products, namely hydrochar and organic process water, respectively. In this study, the effects of HTC reaction temperatures on the yields and physicochemical properties of hydrochar and organic process water derived from Sargassum algae sample obtained from a coastal region in South Florida were evaluated by using various analytical techniques, including SEM, TGA, BET, FTIR and GC-MS. As a result of the increase in temperature, hydrochar yield decreased, while the yield of bio-oil increased. During the heating process, the volatile matter in hydrochar decreases, whereas the fixed carbon increases. Ash content in hydrochar increases as temperature increases. There were some interconnected pores on the surfaces of all three temperatures. It has been shown that a change in temperature has a significant effect on the chemical composition of bio-oils. In some cases, certain compounds increased as the temperature increased, but in others, it was temperature dependent. This study demonstrated that HTC technology could be a potential solution for mitigating Sargassum pollution issue by converting it into value-added bio-based products.

Enhancing hydrochar production and mitigating heavy metal risks in sewage sludge: The role of ultrasonic pretreatment in hydrothermal carbonization

Hydrothermal carbonization (HTC) is a potentially valuable technology for sewage sludge treatment and resource utilization. This study proposes a combined process of ultrasonic pretreatment and HTC to improve the yield and properties of hydrochar derived from sewage sludge (SS). SS was ultrasonically pretreated at different sound energy densities (0.6 – 1.4 W/mL) and pretreatment times (5 – 30 min), and then HTC conducted for 4 h in an autoclave. Ultrasonic pretreatment markedly enhanced the apparent structure and particle size of the feedstock, thereby improving the hydrothermal reactivity of SS. After ultrasonic pretreatment at 1.4 W/mL for 15 min, the yield of hydrochar derived from SS was 11.25% higher than that obtained after direct HTC. The hydrochar yield was also correlated with the ultrasonic pretreatment parameters. Ultrasonic pretreatment increased the specific surface area and number of oxygen-containing functional groups of the hydrochar and increased the energy density and energy yield by at most 7.63% and 9.56%, respectively. The impact of ultrasonic pretreatment on the heavy-metal pollution risk of hydrochar was evaluated in terms of the geological acumination index. Pretreatment with appropriate ultrasonic parameters decreased the pollution risks of Zn, Cu, Cr, and Pb. This study provides a valuable perspective on combined feedstock pretreatment and HTC, increasing the product value of HTC of sewage sludge.

Evaluation of the Effect of Particle Size and Biomass-to-Water Ratio on the Hydrothermal Carbonization of Sugarcane Bagasse

The generation of platform chemicals and hydrochar is of great interest because they reduce dependence on fossil resources and contribute to climate change mitigation by reducing carbon emissions. The main objective of this study was to evaluate the effect of biomass particle size and biomass-to-water ratio in a hydrothermal conversion system for the generation of value-added products obtained from sugarcane bagasse. Biomass characterization was performed using proximal, elemental, and structural analysis; hydrothermal carbonization was carried out at 220 and 260 °C for one hour; and conversion was monitored using pH, conductivity, and IR spectroscopy. Platform chemicals were quantified using HPLC-IR. Hydrochars were characterized by using scanning electron microscopy and energy dispersive spectroscopy. Optimizing biomass particle size and water ratio is crucial for maximizing the yield of platform chemicals and hydrochar. The study’s outcomes revealed that specific combinations, such as a biomass-to-water ratio of 1:50 and a particle size of 212 μm at 220 °C, resulted in a substantial 31.07% yield of platform chemicals on a dry basis. This highlights the critical role these parameters play in influencing the production efficiency of valuable chemicals. Furthermore, variations in biomass particle size and water ratio also affect the characteristics of hydrochar. For instance, utilizing a biomass-to-water ratio of 1:50 and a larger particle size of 600 μm at 260 °C led to the production of hydrochar with higher carbon content and increased porosity. These findings underscore how adjustments in these factors can impact not only chemical yields, but also the properties and quality of the resulting hydrochar.

Hydrothermal carbonization of two-phase olive mill waste (alperujo): Effect of aqueous phase recycling

Hydrothermal carbonization (HTC) is a promising technique for the conversion of lignocellulosic biomass, such as two-phase olive mill waste (TPOMW). However, the resulting generated aqueous phase (AP) rich in organic compounds is harmful if directly discharged in the environment. In this work, the use of recycled aqueous phase from the HTC process of TPOMW is evaluated as a reactive medium. The evolution of products yields, quality, morphology chemical structure, and composition with AP recycling runs are investigated by different analytical methods (Nuclear Magnetic Spectroscopy 1H and solid state 13C, Scanning Electron Microscopy, Elemental analysis, Proximate analysis, Fourier Infrared Transform spectroscopy, Total organic carbon, and total nitrogen). The results revealed significant improvement in the hydrochar yield and energy yield that increase 47.4 wt% to 53.0 wt% and 72.8%–81.3%, respectively. The increase in the number of recycling experiments promotes the lignin condensation as well as the polymerization of AP intermediates into microspheres. These phenomena lead to the increase in hydrochar yield as well as the modification of its micro-surface into a smooth porous surface through the recycling runs. Additionally, FT-IR and the solid state 13C NMR analysis demonstrated that AP recycling has no noticeable effect on the chemical structure of the produced hydrochars. Further analysis of the AP demonstrated that the total organic carbon and total nitrogen increase significantly after the first recycling run from 17.3 to 26.5 g/L and 0.4–0.6 g/L, respectively. The 1H NMR analysis revealed that AP is mainly formed by aliphatic and aromatic compounds.

The properties of Chinese Baijiu distilled spent grain-derived hydrochar: effect of in situ deep eutectic solvents formation during hydrothermal carbonization

Distilled spend grain with rice husk (DSGH), a by-product of Chinese Baijiu, can be used as a solid fuel after hydrothermal carbonization (HTC) treatment. To enhance carbonization during HTC, a new strategy based on the addition of lactic acid to DSGH and AlCl3 is proposed for the in situ formation of deep eutectic solvents (DESs). The results show that in situ DES formation significantly enhanced the recovery of organic matter, thereby increasing the yield of hydrochar. Moreover, in situ DES formation effectively hindered the reaction between NH4+ and polysaccharides. Additionally, DES disrupted the protein structure in DSGHP, thereby intensifying protein hydrolysis and deamination. Furthermore, the DES altered the HTC process of the DSGHP. In summary, the incorporation of in situ DESs significantly influenced the HTC of DSGHP, leading to notable improvements in the recovery and quality of hydrochar. This study provides valuable insights into the potential of DESs in enhancing HTC processes, particularly for biomass such as DSGHP.

Hydrothermal carbonization of organic waste using faecal sludge as a water source: Response surface methodology-Box Behnken design

In this research, organic waste was subjected to hydrothermal carbonization (HTC) using faecal sludge as the water source. HTC is a sustainable method for converting organic waste into valuable hydrochar. However, the use of portable water as a reaction medium in HTC is environmentally unsustainable and increases operational costs. The aim of this study was to optimize HTC operating parameters such as residence time, temperature, and biomass to water (BTW) ratio for maximizing both higher heating value (HHV) and hydrochar yield and also to determine the effects of these operating parameters on the hydrochar properties. This study utilized a Box Behnken design within the response surface methodology to identify optimal HTC conditions. Temperature was varied between 180 and 250 °C, residence time between 30 min and 120 min, and BTW ratio between 1 and 10. Volatile matter percentage was reduced in the hydrochar compared to that of the feedstock. A progressive rise in carbon percentage and a decline in oxygen percentage were observed with increasing temperatures. Temperature and residence time were the most significant factors affecting HHV, on the other hand, temperature and BTW ratio were the most significant factors that affected hydrochar yield. Numerical optimization of the factors revealed that a maximum HHV of 28.409 MJ/kg was obtained at 250 °C, 116 min, and a 1:9 BTW ratio, while an ideal hydrochar yield of 57.491% was obtained at 242 °C, 95 min and a BTW ratio of 1:9. This study highlights the environmental sustainability of utilizing faecal sludge as a water source in HTC, presenting a promising possibility for transforming organic waste into valuable hydrochar while addressing concerns related to water use.