Granular Activated Carbon from Grape Seeds Hydrothermal Char

Hydrochar and hydrochar co-compost from OFMSW digestate for soil application: 3. Toxicological evaluation

Modern societies produce ever-increasing amounts of waste, e.g. organic fraction of municipal solid waste (OFMSW). According to the best available techniques, OFMSW should be treated through anaerobic digestion to recover biogas and subsequently composted. An innovative scheme is under investigation, where anaerobic digestion is combined with hydrothermal carbonization (HTC) and composting. The final product, referred to as hydrochar co-compost (HCO), is under study to be used as an unconventional soil improver/fertilizer. Recent studies showed that HCO is not phytotoxic. However, nothing is known about the toxicity of HCO on cells as part and organisms as a whole. This study aims to investigate in vitro genotoxicity and cytotoxicity of the HCO and its precursors in the production process. In particular, we tested water and methanolic extracts of HCO (WEHCO and MEHCO) from one side and methanolic extracts of hydrochar (MEH) and OFMSW digestate (MED) as well as liquor produced downstream HTC (HTCL) from the other side. Genotoxicity was investigated using cytokinesis-block micronucleus assay in Chinese Hamster Ovarian K1 (CHO-K1) cells. Cytotoxicity was tested in vitro against a panel of human cells line. Zebrafish embryo toxicity upon MEH treatment was also investigated. Results show that incubation of CHO-K1 cells with all the tested samples at different concentrations did not cause any induction of micronucleus formation compared to the vehicle-treated control. Treatment of cells with MEH, MED, HTCL and MEHCO, but not WEHCO, induced some degree of cytotoxicity and MEH showed to be more cytotoxic against tested cells compared to the MEHCO. Toxicity effect at the highest tested concentrations of MEH on zebrafish embryos resulted in coagulation, induction of pericardial edema and death. In conclusion, the hydrochar co-compost cytotoxicity is similar to standard compost cytotoxicity. Hence composting the hydrochar from OFMSW digestate is a good step to eliminate the cytotoxicity of hydrochar.

Nano-Structured Carbon: Its Synthesis from Renewable Agricultural Sources and Important Applications

Carbon materials are versatile in nature due to their unique and modifiable surface and ease of production. Nanostructured carbon materials are gaining importance due to their high surface area for application in the energy, biotechnology, biomedical, and environmental fields. According to their structures, carbon allotropes are classified as carbon nanodots, carbon nanoparticles, graphene, oxide, carbon nanotubes, and fullerenes. They are synthesized via several methods, including pyrolysis, microwave method, hydrothermal synthesis, and chemical vapor deposition, and the use of renewable and cheaper agricultural feedstocks and reactants is increasing for reducing cost and simplifying production. This review explores the nanostructured carbon detailed investigation of sources and their relevant reports. Many of the renewable sources are covered as focused here, such as sugar cane waste, pineapple, its solid biomass, rise husk, date palm, nicotine tabacum stems, lapsi seed stone, rubber-seed shell, coconut shell, and orange peels. The main focus of this work is on the various methods used to synthesize these carbon materials from agricultural waste materials, and their important applications for energy storage devices, optoelectronics, biosensors, and polymer coatings.

Valorization of cow manure via hydrothermal carbonization for phosphorus recovery and adsorbents for water treatment

The increased quantities of manure being generated by livestock and their extensive agronomic use have raised concerns around run-off impacting soil and groundwater quality. Manure contains valuable nutrients (especially phosphorus) that are critical to agriculture, but when directly land-applied the run-off of such nutrients contributes to eutrophication of waterways. This study investigates the hydrothermal carbonization of cow manure at two industrially feasible process extremes: 190 °C, 1 h and 230 °C, 3 h, to concentrate and then recover phosphorus from the solid hydrochar via acid leaching and precipitation. Up to 98 wt% of phosphorus initially present in the hydrochar (88% in the raw manure) can be recovered, with the dominant crystalline species being hydroxyapatite. Acid leached hydrochars were subsequently pyrolyzed at 600 °C for 30 min, and then evaluated as adsorbent materials for water remediation by using methylene blue as a model adsorbate. Although pyrolyzed hydrochars have surface areas an order of magnitude higher (160-236 m²/g) than the non-pyrolyzed acid leached hydrochars (11-23 m²/g), their adsorption capacity is three times lower. Furthermore, while the higher carbonization temperature leads to greater recovery of phosphorus, it likewise leads to higher heavy metal concentrations in the precipitate (ranging from 0.1 to 100 mg_metal/g_ppt). As such, lower temperature carbonization followed by acid-extraction - without further solid processing - is a potential pathway to recover phosphorus and adsorbent materials.

Thermal Analysis and Kinetic Modeling of Pyrolysis and Oxidation of Hydrochars

This study examines the kinetics of pyrolysis and oxidation of hydrochars through thermal analysis. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) techniques were used to investigate the decomposition profiles and develop two distributed activation energy models (DAEM) of hydrochars derived from the hydrothermal carbonization of grape seeds produced at different temperatures (180, 220, and 250 °C). Data were collected at 1, 3, and 10 °C/min between 30 and 700 °C. TGA data highlighted a decomposition profile similar to that of the raw biomass for hydrochars obtained at 180 and 220 °C (with a clear distinction between oil, cellulosic, hemicellulosic, and lignin-like compounds), while presenting a more stable profile for the 250 °C hydrochar. DSC showed a certain exothermic behavior during pyrolysis of hydrochars, an aspect also investigated through thermodynamic simulations in Aspen Plus. Regarding the DAEM, according to a Gaussian model, the severity of the treatment slightly affects kinetic parameters, with average activation energies between 193 and 220 kJ/mol. Meanwhile, the Miura–Maki model highlights the distributions of the activation energy and the pre-exponential factor during the decomposition.

Feasibility of Coupling Anaerobic Digestion and Hydrothermal Carbonization: Analyzing Thermal Demand

Anaerobic digestion is a biological process with wide application for the treatment of high organic-containing streams. The production of biogas and the lack of oxygen requirements are the main energetic advantages of this process. However, the digested stream may not readily find a final disposal outlet under certain circumstances. The present manuscript analyzed the feasibility of valorizing digestate by the hydrothermal carbonization (HTC) process. A hypothetical plant treating cattle manure and cheese whey as co-substrate (25% v/w, wet weight) was studied. The global performance was evaluated using available data reported in the literature. The best configuration was digestion as a first stage with the subsequent treatment of digestate in an HTC unit. The treatment of manure as sole substrate reported a value of 752 m3/d of biogas which could be increased to 1076 m3/d (43% increase) when coupling an HTC unit for digestate post-treatment and the introduction of the co-substrate. However, the high energy demand of the combined configurations indicated, as the best alternative, the valorization of just a fraction (15%) of digestate to provide the benefits of enhancing biogas production. This configuration presented a much better energy performance than the thermal hydrolysis pre-treatment of manure. The increase in biogas production does not compensate for the high energy demand of the pre-treatment unit. However, several technical factors still need further research to make this alternative a reality, as it is the handling and pumping of high solid slurries that significantly affects the energy demand of the thermal treatment units and the possible toxicity of hydrochar when used in a biological process.

Study of the Potential Uses of Hydrochar from Grape Pomace and Walnut Shells Generated from Hydrothermal Carbonization as an Alternative for the Revalorization of Agri-Waste in Chile

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.

Novel biochar and hydrochar for the adsorption of 2-nitrophenol from aqueous solutions: An approach using the PVSDM model

Two new adsorbents, namely avocado-based hydrochar and LDH/bone-based biochar, were developed, characterized, and applied for adsorbing 2-nitrophenol. The pore volume and surface diffusion model (PVSDM) was numerically solved for different geometries and applied to interpret the adsorption decay curves. Both adsorbents presented interesting textural and physicochemical characteristics, which achieved maximum adsorption capacities of 761 mg/g for biochar and 562 mg/g for hydrochar. The adsorption equilibrium data were well fitted by Henry isotherm. Besides, thermodynamic investigation revealed endothermic adsorption with the occurrence of electrostatic interactions. PVSDM predicted the adsorption decay curves for different adsorbent geometries at different initial concentrations of 2-nitrophenol. The surface diffusion was the main intraparticle mass transport mechanism. Furthermore, the external mass transfer and surface diffusion coefficients increased with the increase of 2-nitrophenol concentration.

Cationic Dye Adsorption on Hydrochars of Winery and Citrus Juice Industries Residues: Performance, Mechanism, and Thermodynamics

With the increasing needs of clean water supplies, the use of biomass wastes and residues for environmental remediation is essential for environmental sustainability. In this study, the residues from winery and citrus juice industries, namely grape skin and orange peel, respectively, were first converted to hydrochars by hydrothermal carbonization (HTC) and then a cationic dye (methylene blue) adsorption was studied on hydrochars. Hydrochars from both feedstocks were produced at three different temperatures (180, 220, and 250 °C) and a fixed residence time (1 h) to evaluate the hydrochar’s performance on the dye adsorption. The hydrochars were characterized in terms of their pH, pH at point of zero charge (pHPZC), surface functionalities, and surface area. A batch adsorption study of the dye was carried out with variable adsorbate concentration, pH, and temperature. Two adsorption isotherms namely Langmuir and Freundlich models were fitted at 4, 20, and 36 °C. The thermodynamic properties of adsorption (Gibbs free energy (ΔG), enthalpy (ΔH) and entropy (ΔS)) were evaluated from the isotherms fittings. Results showed that the dye adsorption on both hydrochars was significant and followed Langmuir isotherm. The maximum adsorption capacity on citrus waste hydrochar was higher than the winery waste hydrochar at any corresponding HTC temperature. Although hydrochars showed the lowest surface area (46.16 ± 0.11 and 34.08 ± 1.23 m2/g for citrus and winery wastes, respectively) at 180 °C, their adsorption was the highest, owing to their maximum density of total oxygen functional groups (23.24 ± 0.22 and 32.69 ± 1.39 µmol/m2 for citrus and winery wastes, respectively), which decreased with the increase in HTC temperature. This research shows a sustainable route for the production of highly effective adsorbent materials at lower HTC temperatures from citrus and winery wastes.

Characterization of Chemically and Physically Activated Carbons from Lignocellulosic Ethanol Lignin-Rich Stream via Hydrothermal Carbonization and Slow Pyrolysis Pretreatment

The aim of the present work is to investigate the possibility of producing activated carbons from the residual lignin stream of lignocellulosic ethanol biorefineries, as this represents an optimal opportunity to exploit a residual and renewable material in the perspective of sustainable bioeconomy, increasing biorefinery incomes by producing value-added bioproducts in conjunction with biofuels. Activated carbons (ACs) were produced via chemical (KOH) and physical (CO2) activation. Char samples were obtained by slow pyrolysis (SP) and hydrothermal carbonization (HTC). Several HTC experiments were carried out by varying residence time (0.5–3 h) and reaction temperature (200–270 °C), in order to evaluate their influence on the product yield and on the morphological characteristics of the hydrochar (specific surface area, total pore volume and pore size distribution). ACs from hydrochars were compared with those obtained from pyrochar (via physical activation) and from the raw lignin-rich stream (via chemical activation). In both cases, by increasing the HTC temperature, the specific surface of the resulting activated carbons decreased from 630 to 77 m2 g−1 for physical activation and from 675 to 81 m2 g−1 for chemical activation, indicating that an increase in the severity of the hydrothermal pretreatment is deleterious for the activated carbons quality. In addition, the HTC aqueous samples were analyzed, with GC-MS and GC-FID. The results suggest that at low temperatures the reaction mechanisms are dominated by hydrolysis, instead when the temperature is increased to 270 °C, a more complex network of reactions takes place among which decarboxylation.

Sewage Sludge Hydrochar: An Option for Removal of Methylene Blue from Wastewater

Municipal sewage sludge was subjected to a hydrothermal carbonization (HTC) process for developing a hydrochar with high adsorption capacity for water remediation in terms of dye removal. Three hydrochars were produced from municipal sewage sludge by performing HTC at 190, 220 and 250 °C, with a 3 h reaction time. Moreover, a portion of each hydrochar was subjected to a post-treatment with KOH in order to increase the adsorption capacity. Physicochemical properties of sludge samples, raw hydrochars and KOH-modified hydrochars were measured and batch adsorption studies were performed using methylene blue (MB) as a reference dye. Data revealed that both raw and modified hydrochars reached good MB removal efficiency for solutions with low MB concentrations; on the contrary, MB in high concentration solutions was efficiently removed only by modified hydrochars. Interestingly, the KOH treatment greatly improved the MB adsorption rate; the modified hydrochars were capable of capturing above 95% of the initial MB amount in less than 15 min. The physicochemical characterization indicates that alkali modification caused a change in the hydrochar surface making it more chemically homogeneous, which is particularly evident for the 250 °C hydrochar. Thus, the adsorption process can be regarded as a complex result of various phenomena, including physi- and chemi-sorption, acid–base and redox equilibria.

Activated Carbon Produced by Pyrolysis of Waste Wood and Straw for Potential Wastewater Adsorption

Pyrolysis of straw pellets and wood strips was performed in a fixed bed reactor. The chars, solid products of thermal degradation, were used as potential materials for activated carbon production. Chemical and physical activation processes were used to compare properties of the products. The chemical activation agent KOH was chosen and the physical activation was conducted with steam and carbon dioxide as oxidising gases. The effect of the activation process on the surface area, pore volume, structure and composition of the biochar was examined. The samples with the highest surface area (1349.6 and 1194.4 m²/g for straw and wood activated carbons, respectively) were obtained when the chemical activation with KOH solution was applied. The sample with the highest surface area was used as an adsorbent for model wastewater contamination removal.

Hydrothermal carbonization of various lignocellulosics: Fuel characteristics of hydrochars and surface characteristics of activated hydrochars

In the present study, various lignocellulosic biowastes (wood sawdust, olive pomace, walnut shell, apricot seed, tea stalk, hazelnut husk) were hydrothermally carbonized at 220 °C for 90 min. Since the hydrochars have several end-uses, this study particularly investigates their end-use as solid fuels and precursors of activated carbon after chemical activation. Activated hydrochars were obtained from the hydrochars of wood sawdust, olive pomace, walnut shell, apricot seed, tea stalk, hazelnut husk by chemical activation with KOH at 600 °C. As fuels, all hydrochars had higher fixed carbon content, lower volatile matter content and higher ignition temperatures compared to their original biomass samples. Olive pomace hydrochar, which has high heating value (25.56 MJ/kg) and low ash content (5.5%), has the best fuel properties among hydrochars investigated. Activated hydrochars demonstrated BET surface areas of 308.9-666.7 m²/g (activated hydrochar of wood sawdust and tea stalk), and total pore volumes of 0.25-0.73 cm³/g (activated hydrochar of olive pomace and wood sawdust). The average pore size distribution of the activated hydrochars ranged between 1.05 nm (olive pomace)- 4.74 nm (wood sawdust). All agricultural-based activated hydrochars had similar average pore size distribution of 1.05-1.25 nm, which fell in the range of super-microporous structure. With the average pore size of 4.74 nm, activated hydrochar of wood sawdust could be classified under mesoporous structure. This study clearly points out that biomass type definitely affected fuel properties of hydrochars and the porous structure of the activated hydrochars.

Low-Cost Activated Grape Seed-Derived Hydrochar through Hydrothermal Carbonization and Chemical Activation for Sulfamethoxazole Adsorption

Activated carbons were prepared by chemical activation with KOH, FeCl3 and H3PO4 of the chars obtained via hydrothermal carbonization of grape seeds. The hydrochars prepared at temperatures higher than 200 °C yielded quite similar proximate and ultimate analyses. However, heating value (24.5–31.4 MJ·kg−1) and energy density (1.04–1.33) significantly increased with carbonization temperatures between 180 and 300 °C. All the hydrochars showed negligible BET surface areas, while values between 100 and 845 m2·g−1 were measured by CO2 adsorption at 273 K. Activation of the hydrochars with KOH (activating agent to hydrochar ratio of 3:1 and 750 °C) led to highly porous carbons with around 2200 m2·g−1 BET surface area. Significantly lower values were obtained with FeCl3 (321–417 m2·g−1) and H3PO4 (590–654 m2·g−1), showing these last activated carbons important contributors to mesopores. The resulting materials were tested in the adsorption of sulfamethoxazole from aqueous solution. The adsorption capacity was determined by the porous texture rather than by the surface composition, and analyzed by FTIR and TPD. The adsorption equilibrium data (20 °C) fitted the Langmuir equation well. The KOH-activated carbons yielded fairly high saturation capacity reaching up to 650 mg·g−1.

Biochar as a Multifunctional Component of the Environment—A Review

The growing demand for electricity, caused by dynamic economic growth, leads to a decrease in the available non-renewable energy resources constituting the foundation of global power generation. A search for alternative sources of energy that can support conventional energy technologies utilizing fossil fuels is not only of key significance for the power industry but is also important from the point of view of environmental conservation and sustainable development. Plant biomass, with its specific chemical structure and high calorific value, is a promising renewable source of energy which can be utilized in numerous conversion processes, enabling the production of solid, liquid, and gaseous fuels. Methods of thermal biomass conversion include pyrolysis, i.e., a process allowing one to obtain a multifunctional product known as biochar. The article presents a review of information related to the broad uses of carbonization products. It also discusses the legal aspects and quality standards applicable to these materials. The paper draws attention to the lack of uniform legal and quality conditions, which would allow for a much better use of biochar. The review also aims to highlight the high potential for a use of biochar in different environments. The presented text attempts to emphasize the importance of biochar as an alternative to classic products used for energy, environmental and agricultural purposes.

Lithium recovery from spent Li-ion batteries using coconut shell activated carbon

Lithium is one of scarce natural resources in the world that need to be preserve. One of the way in preserving the resource is by recovery the rich source of the lithium such as in the spent batteries. It is necessary to develop a recovery method which is efficient and low-cost to be able to recover the lithium in an economic scale. In this study, low-cost activated carbon (AC) from coconut shell charcoal was prepared by chemical and physical activation methods and tested for Li removal from Co, Mn, and Ni ions in semi-continuous columns adsorption experiments. The maximum surface area is 365 m²/g with the total pore volume is 0.148 cm³/g that can be produced by physical activation at 800 °C. In the same activation temperature, activation using KOH has larger ratio of micropore volume than physical activation. Then, the adsorption capacity and selectivity of metal ions were investigated. A very low adsorption capacity of AC for Li ions in batch adsorption mode provides an advantage in column applications for separating Li from other metal ions. The AC sample with chemical activation provided better separation than the samples with physical activation in the column adsorption method. During a certain period of early adsorption (lag time), solution collected from the column outlet was found to be rich in Li due to the fast travel time of this light element, while the other heavier metal ions were mostly retained in the AC bed. The maximum lag time is 97.3 min with AC by KOH activation at 750 °C.