Hydrothermal Treatment Temperature Research Articles

Transformation Kinetics of Phosphorus and Nitrogen in Iron-Rich Sewage Sludges during Hydrothermal Treatment and Recovery of Nutrients from Process Water

Hydrothermal treatment (HT) is an emerging technique for sustainable sewage sludge management and resource recovery. Many sludges are rich in iron (Fe) due to the common addition of Fe salts in water resource recovery facilities. To develop guidance for reaction conditions targeting nutrient recovery, this study systematically investigated the influence of HT temperature, treatment time, and sludge source on the dynamic speciation evolution of phosphorus (P) and nitrogen (N) during HT of Fe-rich sewage sludge. Complementary chemical extraction and X-ray spectroscopy analyses were conducted to characterize the treatment products. For the sludge mixture (a blend of primary and waste activated sludges), P speciation did not change significantly within 4.5 h at 125 °C HT, while soluble and labile P was converted into insoluble P over time at 175 and 225 °C HT. Strengite (FePO4·2H2O) preferentially formed in the hydrochars with increasing treatment temperature and/or time, whereas 125 °C HT within 1.5 h favored the formation of vivianite (Fe3(PO4)2·8H2O). Organic P was completely decomposed into orthophosphate when the HT temperature reached up to 175 °C. Pyrrole-N was enriched in the hydrochars. Similar reaction pathways were observed during HT of anaerobically digested sludge, though some minor differences in Fe-associated P and organic P were observed. Meanwhile, HT of the two sludges released orthophosphate and ammonia into the process waters at 175 and 225 °C, which can be recovered by a sequential process involving struvite (MgNH4PO4·6H2O) precipitation and air stripping. This study provides new insights into the transformation of P and N during HT of Fe-rich sludges as well as a modular design for maximum P and N recovery from the treatment products.

Performance of functionalized monolithic silica capillary columns with different mesopore sizes using radical polymerization of octadecyl methacrylate

We report on the possibility to enhance the phase ratio and retention factor in silica monoliths. According to pioneering work done by Núñez et al. [1], this enhancement is pursued by applying a stationary phase layer via radical polymerization with octadecyl methacrylate (ODM) as an alternative to the customary octadecylsilylation (C18-derivatization). The difference in band broadening, retention factor and separation selectivity between both approaches was compared. Different hydrothermal treatment temperatures for the column preparation were applied to produce monolithic silica structures with three different mesopore sizes (resp. 10, 13, and 16 nm, as determined by argon physisorption) while maintaining similar domain size (sum of through-pore and skeleton size). It has been found that the columns with the poly(octadecyl methacrylate)-phase (ODM columns) provided a 60 to 80% higher retention factor in methanol-water mixture compared to the octadecylsilylated (ODS) columns produced by starting from similar silica backbone structures. In acetonitrile-water mixture, the enhancement is smaller (15 to 30% times higher), yet significant. By adjusting the fabrication conditions (for both the preparation of the monolithic backbones and the surface functionalization), the achieved retention factors (up k = 4.89 for pentylbenzene in 80:20% (v/v) methanol/water) are obviously higher than obtained in the pioneering study on ODM monoliths of Núñez et al. [1], and column clogging could be completely avoided. In addition, also separation efficiencies were significantly higher than shown in Ref. [1], with plate heights as low as 5.8 μm. These plate heights are however inferior to those observed on the ODS-modified sister columns. The difference can be explained by the slower intra-skeleton diffusion displayed by the ODM-modified columns, in turn caused by the larger obstruction to diffusion originating from the thicker stationary phase layer.

Preparation of Oil Palm Empty Fruit Bunch Hydrolysate

Malaysia is the second largest palm oil producer and exporter globally. When crude palm oil is produced in both plantations and oil processing mills, a large amount of oil palm empty fruit bunch (OPEFB) is simultaneously produced as a waste product. Here, we describe the preparation of hydrolysate from OPEFB. After OPEFB was hydrothermally treated at 180–200 °C, the resultant liquid phase was subjected to high-performance liquid chromatography analysis, while the solid phase was used for acidic and enzymatic hydrolysis. Hemicellulose yield from the acid-treated solid phase decreased from 153 mg/g-OPEFB to 27.5 mg/g-OPEFB by increasing the hydrothermal treatment temperature from 180 to 200 °C. Glucose yield from the enzyme-treated solid phase obtained after hydrothermal treatment at 200 °C was the highest (234 ± 1.90 mg/g-OPEFB, 61.7% production efficiency). In contrast, xylose, mannose, galactose, and arabinose yields in the hydrolysate prepared from the solid phase hydrothermally treated at 200 °C were the lowest. Thus, we concluded that the optimum temperature for hydrothermal pretreatment was 200 °C, which was caused by the low hemicellulose yield. Based on these results, we have established an effective method for preparing OPEFB hydrolysates with high glucose content.

Revealing the heating value characteristics of sludge-based hydrochar in hydrothermal process: from perspective of hydrolysate

Hydrothermal treatment (HT) is a promising method to convert sewage sludge to hydrochar biofuel. The heating value is directly correlated to the carbon content in hydrochar; however, the release of organic matter from sludge to hydrolysate and the transfer of the Maillard reaction products generated in the hydrolysate to the solid phase alter the carbon content in hydrochar. In this study, the relationship between hydrolysate and heating value of sludge-based hydrochar was presented, aiming to explain how the calorific value of hydrochar was affected by HT conditions. We adopted a direct combustion test to verify its clean combustion features. Hydrochar derived at 260 °C and residence time of 4 h (HC 260-4) exhibited the highest calorific value (HHVdaf = 26.23 MJ/kg) with an energy density of 1.43, and its fuel characteristics were similar to those of lignite. The increase in the HT temperature and residence time up to 260 °C and 4 h, respectively, was beneficial for enhancing HHVdaf. Conversely, further increase of the HT temperature to 300 °C and HT time to 6 h yielded a decrease in HHVdaf. Investigation of the underlying mechanism revealed that the protein and polysaccharide releasing from sludge to hydrolysate occurred the Maillard reaction (MR). The generated humic-like Maillard reaction product (MRP) was transferred to hydrochar, inducing an increase in the carbon content and calorific value and a decrease in the organic content of hydrolysate. As the carbohydrate content in the hydrolysate decreased, the MR was terminated, so no more MRP was transferred to hydrochar. At the same time, the protein was still continuously released at higher temperatures and longer residence times, yielding a decline in the HHVdaf. Moreover, clean energy utilization was verified from the reduced nitrogen content in hydrochar and lower CO and NOx emission of HC 260-4 in the combustion test. After the HT, increased hydrophobicity and a lower fraction of bound water improved the dewaterability, which is of great significance for applying hydrochar as biofuel. The findings of this study provided a new perspective to explain the heating value generation of hydrochar and more direct evidence to assess its clean combustion properties, with promising perspectives for practical applications.

Morphological evolution and bonding strength of a monetite coating on the Ti-6Al-4V substrate via hydrothermal treatment

ABSTRACT Monetite (CaHPO4) was coated on the Ti-6Al-4 V substrate by hydrothermal method. SEM, XRD, EDS, XPS, Raman spectroscope, and tensile test were used to characterize the morphology, phase constitutes, elemental content, elemental valence states, chemical functional groups, and bonding strength of the coating, respectively. It was revealed that the elevated temperature and prolonged duration time are favourable to the purity, densification and crystallinity of the monetite coating. The maximum bonding strength of 17.03 ± 2.79 MPa is found at the hydrothermal treatment temperature of 190 ℃ and duration time of 8 h. Both simulated mineralization experiment and the degradation experiment show that the monetite coating have good bioactivity and chemical stability, and is promising to be applied in the field of orthopaedic implant materials.

Comparative assessment of pre- and inter-stage hydrothermal treatment of municipal sludge for increased methane production.

Hydrothermal treatment (HT) is a promising technology to enhance anaerobic digestion (AD) of municipal sludge. However, the capacity of pre- and inter-stage HT (i.e., HT-AD and AD-HT-AD, respectively) to enhance the digestibility of municipal sludge has not been sufficiently explored. This study compared the efficacy of pre- and inter-stage HT performed from 90 to 185°C to enhance methane production from a mixture of primary sludge and waste activated sludge using mesophilic (35°C) biochemical methane potential tests. In both configurations, sludge solubilization increased with HT temperature. HT-AD, and to a greater extent AD-HT-AD, increased the release of ammonium nitrogen. Even though HT at 185°C dramatically increased sludge solubilization, the overall specific methane yield with HT at 185°C was lower than or comparable to that at lower HT temperatures in the HT-AD and AD-HT-AD configurations, respectively. Up to 155°C HT, the overall specific methane yield with the HT-AD configuration was higher by 4.9%-8.3% compared to the AD-HT-AD configuration. However, when the HT energy was considered, compared to the control (i.e., AD of sludge without HT), the net energy gain (ΔE) decreased as the HT temperature increased, becoming negative at an HT of 185°C. The AD-HT-AD configuration resulted in a higher overall volatile solids destruction (by 8.1 to 20.1%). In conclusion, for municipal sludge with a relatively high ultimate digestibility, as was the case in this study, HT-AD is preferable as it has a smaller footprint and is easier to operate than the AD-HT-AD configuration. However, given the significantly higher volatile solids destruction in the AD-HT-AD configuration, compared to the HT-AD configuration, AD-HT-AD may be more beneficial considering post-AD sludge handling processes. PRACTITIONER POINTS: Hydrothermal treatment (HT) increased the rate and extent of methane production from municipal sludge mixture. 155°C was the optimal temperature for either pre- or inter-stage HT to increase biogas production. Pre- and inter-stage HT resulted in comparable ultimate methane production. Pre-stage HT is preferable to inter-stage HT (smaller footprint, easier to operate). AD-HT-AD resulted in significantly higher volatile solids destruction compared to the HT-AD configuration.

The Effects of Hydrophobicity and Textural Properties on Hexamethyldisiloxane Adsorption in Reduced Graphene Oxide Aerogels.

To expand the applications of graphene-based materials to biogas purification, a series of reduced graphene oxide aerogels (rGOAs) were prepared from industrial grade graphene oxide using a simple hydrothermal method. The influences of the hydrothermal preparation temperature on the textural properties, hydrophobicity and physisorption behavior of the rGOAs were investigated using a range of physical and spectroscopic techniques. The results showed that the rGOAs had a macro-porous three-dimensional network structure. Raising the hydrothermal treatment temperature reduced the number of oxygen-containing groups, whereas the specific surface area (SBET), micropore volume (Vmicro) and water contact angle values of the rGOAs all increased. The dynamic adsorption properties of the rGOAs towards hexamethyldisiloxane (L2) increased with increasing hydrothermal treatment temperature and the breakthrough adsorption capacity showed a significant linear association with SBET, Vmicro and contact angle. There was a significant negative association between the breakthrough time and inlet concentration of L2, and the relationship could be reliably predicted with a simple empirical formula. L2 adsorption also increased with decreasing bed temperature. Saturated rGOAs were readily regenerated by a brief heat-treatment at 100 °C. This study has demonstrated the potential of novel rGOA for applications using adsorbents to remove siloxanes from biogas.

Hydrothermal synthesis and characterization of nano-particles γ-Al2O3

The study of hydrothermal treatment on the phase formation and the crystallites of gamma-alumina (γ-Al2O3) was performed. Different reaction time and temperature of hydrothermal treatment were investigated. The preparation of γ-Al2O3 includes precipitation of aluminum nitrate nonahydrate by ammonia, aging, washing, transferred the gel into the hydrothermal reactor, drying, and calcination at 600 °C. The precipitation was stopped at pH equals 7.5. The reaction times of hydrothermal treatment were 1 – 2 hours, and the temperatures were 140 – 200 °C. X-Ray Diffraction analysis was used to investigate the phase formation and the particle size. The results show all the samples represented pure nano γ-Al2O3. The examination of hydrothermal treatment of y-Al2O3 reveals as the reaction time longer, the crystallite grows bigger, as well as the higher temperature applied. The smallest γ-Al2O3 obtained based on the Scherrer equation is 4 nm and the biggest is 6.5 nm. Interestingly, the peaks of the γ-Al2O3 prepared by hydrothermal treatment at the longest time and the highest temperature have shifted into a higher diffraction angle. In the case of this sample, the peaks shifted into a higher diffraction angle. That is means there is a change in the lattice structure of γ-Al2O3 probably was affected by the lattice of hydroxyl content.

Selective Synthesis of Manganese Dioxide Polymorphs by the Hydrothermal Treatment of Aqueous KMnO4 Solutions

The hydrothermal treatment of neutral and acidified KMnO4 solutions at concentration of 0.037–0.093 mol/L and temperature of 120, 170, and 220°С for 24 h leads to selective synthesis of three different manganese dioxide modifications: α-MnO2, δ-MnO2, and β-MnO2. The temperature of hydrothermal treatment and medium acidity has been shown to affect considerably the phase composition of KMnO4 reduction products and reaction yield. The obtained samples of MnO2 have been characterized by X-ray diffraction, scanning electron microscopy, Raman spectroscopy, and diffuse reflectance spectroscopy.

Formation of Double-Helical Structures by Silica Nanotubes Templated by Mixtures of Common Nonionic Surfactants in Aqueous Solutions.

Micelles of Pluronic F108 (EO132PO50EO132)/P104 (EO27PO61EO27) surfactant mixtures swollen with toluene were found to template silica nanotubes that formed double-helical structures under appropriately selected aqueous acidic solution conditions. In particular, the double-helical nanotube structure (DHNTS) formed as a main product at 15 °C for 30-37.5 wt % of Pluronic P104 in a surfactant mixture, with 35 wt % being particularly suitable. The formation of DHNTSs appears to involve a spontaneous wrapping of micelle-templated nanotubes around one another, while a similar structure was known to form only under confinement of anodic alumina pores of appropriate diameter. In addition to DHNTSs, other helical or circular structures, such as a helical nanotube tightly wrapped around a straight nanotube, or nanotube(s) wrapped around a sphere, were observed in many cases as minor components. DHNTSs formed as a major component at a well-defined proportion of silica precursor to surfactant at 15 °C, while the relative amount of the swelling agent and the hydrochloric acid concentration could be varied considerably. The hydrothermal treatment temperature was used to adjust the pore diameter of the DHNTS. However, structures formed without the hydrothermal treatment or with the treatment at a moderate temperature appeared very soft, while the treatment at excessively high temperature resulted in a development of significant gaps in the nanotube walls. Our results establish DHNTS as a well-defined ordered mesoporous silica with ultralarge (∼35 nm) helical mesopores of some degree of diameter adjustability, accessible under aqueous conditions using common nonionic surfactants as templating agents.

Synthesis and the Cathode Properties of Na3Fe3(PO4)4 for Sodium-Ion Battery

Na-ion batteries (NiBs) are very attractive and promising for large scale electric power storage system because of the abundance for sodium source, the high cost-effectiveness and the long lifetime. Among the candidate of cathode active materials for NiBs, practical use of iron phosphate such as NaFePO4, Na2FePO4F, and Na3Fe3(PO4)4 [1] or carbonophosphate such as Na3FePO4CO3 [2] is expected from the viewpoint of cost and safety. In order to make full use of the resource and cost advantages of these materials, the raw materials used in the synthesis and the synthesis method are also important. In this presentation, we report the direct synthesis of Na3Fe3(PO4)4 by the hydrothermal method with mass productivity and the cathode properties. Synthesis was carried out using ferrous sulfate hydrate (FeSO4·nH2O), phosphoric acid, and various sodium phosphate salts as sodium sources with various the raw material composition, hydrothermal treatment temperature, and reaction time. For the purpose of controlling the reaction, synthesis was performed under the condition that an oxidizing agent or a reducing agent was added. The obtained compounds were identified by powder X-ray diffraction measurement and Rietveld analysis. Iron (Ⅱ) sulfate (FeSO4·7H2O), phosphoric acid (H3PO4), sodium dihydrogen phosphate (NaH2PO4·2H2O) and sodium persulfate (Na2S2O8) were used as raw materials, and hydrothermal synthesis was performed at 200 ° C for 16 hours. From the Rietveld analysis, the obtained compound was assigned to the layered structure Na3Fe3(PO4)4. This hydrothermal synthesis Na3Fe3(PO4)4 delivered initial discharge capacity of 160mAh g-1 between -1.2 and 1.3 V with a reference electrode of Ag/AgCl at 2 mA cm-2 in the 17 m NaClO4 aqueous solution (Figure 1). In the presentation, we will be reported the details of cathode properties of Na3Fe3(PO4)4.

Effect of hydrothermal treatment temperature on the hydroxyapatite coatings deposited by electrochemical method

Hydroxyapatite coatings on titanium alloy prepared via electrochemical method show low crystallinity and form cracks that affect implant performance. In this study, the hydrothermal treatment was applied in order to improve the properties of the hydroxyapatite coating. Ti6Al4V substrates were coated with hydroxyapatite via the electrochemical method. The samples were then hydrothermally treated under different temperatures. The effects of hydrothermal treatment temperatures on the hydroxyapatite coating composition, microstructure, crystallinity, as well as on the bonding strength between coatings and substrates, were investigated. The samples' bioactivity was measured by immersing them in a simulated body fluid. Results showed that the hydrothermal treatment healed the cracks of the hydroxyapatite coating deposited by electrochemical method. The coatings became denser with increasing hydrothermal teatment temperatures. The hydrothermal treatment temperatures had negligible effects on hydroxyapatite coating composition. At 180 °C, the hydroxyapatite coating achieved maximum crystallinity, and their bonding strength was about 23 MPa. Bioactivity experiments revealed that the hydroxyapatite coatings obtained via the electrochemical method and the hydrothermal treatment had good bioactivity.

Stability of Zeolite HZSM-5 in Liquid Phase Dehydration of Methanol to Dimethyl Ether

A high performance HZSM-5 catalyst for liquid phase dehydration of methanol to dimethyl ether (DME) was developed by optimizing Si/Al ratio and hydrothermal treatment temperature. During 6788 h long term test, DME selectivity kept above 99.96% and only slight deactivation was observed primarily due to coking and decline of HZSM-5 crystallinity.

Elucidating hydrochar morphology and oxygen functionality change with hydrothermal treatment temperature ranging from subcritical to supercritical conditions

Hydrochar, used for numerous applications including solid fuel, adsorbent medium, anode material, and soil amendment, is the major solid product or unwanted byproduct resulting when biomass undergoes for subcritical or supercritical water treatment, respectively. Regardless of the reaction temperature, hydrochar forms from biomasses at different reaction kinetics. Our hypothesis in this study is morphology and oxygen functionality of hydrochar change with reaction temperature, especially from a subcritical to supercritical region. To test this hypothesis, hydrochar was produced from microcrystalline cellulose at 220 °C–420 °C with 40 °C interval with a reaction time of 30 min. The effects of subcritical and supercritical conditions of the hydrochar characteristics were investigated using a series of analytical tools including ultimate and proximate analyses, Brunauer-Emmett-Teller (BET) surface area, scanning electron microscopy (SEM), X-Ray Diffraction (XRD) analysis, Fourier-transform infrared spectroscopy (FTIR), and Boehm Titration. Results showed that oxygen-containing acidic functional groups reached the highest (1495 ± 25 μmol/g) at 260 °C and reduced afterward with an increase of temperature, although the elemental oxygen was reduced with the increase of reaction temperature. The particle size of hydrochar increases with the increase of temperature in the subcritical region but decreases in the supercritical region.

Optimizing food waste hydrothermal parameters to reduce Maillard reaction and increase volatile fatty acid production

The occurrence of the Maillard reaction and melanoidins formation during the hydrothermal treatment of food waste can reduce the yield of volatile fatty acids (VFA); however, few studies have investigated the adverse effects of the Maillard reaction. This study identified the impact of hydrothermal treatment parameters on hydrolysis and melanoidins formation and optimized the hydrothermal treatment conditions to enhance VFA production by minimizing the impact of the Maillard reaction. A response surface methodology was employed to optimize the hydrothermal treatment parameters and VFA production was evaluated. Results showed that temperature, reaction time, and pH were significant interacting factors with respect to hydrolysis and melanoidins formation while the C/N ratio and moisture content of food waste had little impact. The optimal conditions for hydrothermal treatment (temperature of 132 °C, reaction time of 27 min, and a pH of 5.6) enhanced VFA production by 22.1%. Under optimal hydrothermal treatment conditions, a higher initial C/N ratio further increased VFA production.

Removal of AV 90 dye using ordered mesoporous carbon materials prepared via nanocasting of KIT-6: Adsorption isotherms, kinetics and thermodynamic analysis

CMK-8 type ordered mesoporous carbon (OMC) materials were prepared by hard-templating method using KIT-6 as a mesoporous silica template. The influence of synthesis parameters on the structural properties of KIT-6 and OMC samples was investigated. In the studied temperature range (60–150 °C), suitable hydrothermal treatment temperature to obtain well-ordered mesoporous KIT-6 sample was determined as 120 °C. Mesoporous carbons were prepared by using KIT-120 sample as a hard-template. NaOH solution was used to remove silica from the silica–carbon matrix and at the end of two leaching cycles, the pore volume and the surface area decreased by 1/3 with the change in NaOH concentration from 1 M to 4 M. Finally, 2 M NaOH concentration and one leaching number were determined as the best conditions to obtain mesoporous carbon (C2M1) with a high uniformity, high surface area (1020 m2/g), high pore volume (0.98 cm3/g), and relatively high wall thickness (6.25 nm). In the adsorption studies, the optimum pH value was determined as 2 for anionic Acid Violet 90 (AV 90) dye adsorption on C2M1 sorbent. The highest dye removal was achieved as 1311.5 mg/g at 298 K, pH 2 and 360 mg/L dye concentration. Langmuir, Freundlich, Temkin, and Henry adsorption isotherm models were used to examine the adsorption mechanism, and Freundlich isotherm model with a relatively higher correlation factor (R2 > 0.94) was found to be the best-fitted model to the experimental data. Pseudo second order kinetic model was determined as suitable to explain kinetic behavior of the adsorption process. Thermodynamic analysis of the experimental data revealed that the adsorption process of AV 90 dye on C2M1 sorbent was exothermic with an enthalpy change of –22.82 kJ/mol and the activation energy was found to be 45.8 kJ/mol. The N2 adsorption–desorption and FTIR analysis of the used sorbent revealed that the mesopore structure was preserved and there was no significant change in structural bonds after AV 90 adsorption. Results show that CMK-8 type mesoporous carbon material is a promising sorbent for the removal of AV 90 dye from aqueous solution.

Oxidative dehydrogenation of ethane with carbon dioxide over silica molecular sieves supported chromium oxides: Pore size effect

SBA-15 with varied pore size from 4 to 8 nm were synthesized by tuning the temperature of hydrothermal treatment, the supports were then used to load the active phase CrO x through a conventional impregnation method. The resulting catalysts were characterized by small/wide angle XRD, N 2 adsorption/desorption, FT-IR, TEM-EDX, XPS, TPR and CO 2 -TPD to study the feature of structure, surface chemical state, redox and basicity. It was found from these results that the metal species could be well dispersed on catalysts with larger pore size. Cr 6+ species could enter into the framework by substituting the Si atoms of SBA-15, and Cr 3+ mainly exist on extra framework. Pore size had profound effects on reducibility, surface composition and basicity. Cr 6+ species were necessary to activate the C-H bonds of alkanes, while the basicity played an important role in activating C-O bonds of CO 2 . The best performances were achieved over the sample Cr supported on SBA-15 with a pore diameter of 7 nm in oxidative dehydrogenation of ethane in the presence of CO 2 . • Pore size of SBA-15 was tuned by changing hydrothermal temperature. • Cr 6+ could enter the framework of SBA-15 by partially replacing Si atoms. • Cr 6+ and Cr 3+ species co-existed on extra framework of SBA-15. • Cr 6+ species were important for activating alkane. • Activation of CO 2 was related to basicity of catalysts.

Hydrothermal treatment of erythromycin fermentation residue: Harmless performance and bioresource properties

Erythromycin fermentation residue (EFR) is a byproduct of bio-fermentation process for producing erythromycin, representing both an economic and environmental burden for the pharmaceutical industry. While hydrothermal treatment (HT) can solve the pollution and toxic problems, the impacts of HT on harmless performance and the bioresource properties of the complex EFR matrix remain unclear. In this study, the abatement of residual erythromycin, its associated antibiotic resistance genes and antimicrobial activity were investigated to evaluate the harmless performance of HT for EFR, and the feasibility of recycling hydrolysates as bioenergy was also assessed. The results showed that raising HT temperature significantly improved the harmless performance. The removal rate of residual erythromycin in EFR reached over 88% and the total absolute abundance of erythromycin resistance genes decreased by more than 3 logs with HT at 160°C for 60 min, but the hydrolysates still existed specific antimicrobial activity against S. aureus.. Additionally, the HT temperature remarkably influenced the bioresource properties of EFR-hydrolyzed products. The release of the protein-like polymers into the liquid phase was enhanced, while high HT temperature worsened the nutrient substances. The elevated drying property of solid products from EFR was observed along with the higher heating value of around 20 MJ/kg, indicating a potential of recycling solid products as biofuel. Total energy production from biogas conversion and biofuel incineration treating 1.0 kg raw EFR was 1875 kJ. Hydrothermal technology was proved to realize the harmless treatment of EFR and meanwhile to be promising for recycling EFR as bioenergy.

Hydrothermal Synthesis of Aqueous Sols of Nanocrystalline HfO2

Nanocrystalline hafnium dioxide has been synthesized by hydrothermal treatment of X-ray amorphous hydrated hafnium dioxide in distilled water at 120–260°C for 1–7 days and in the presence of NaCl and NaOH as mineralizing agents. The size of HfO2 crystallites has been shown to be determined by the temperature of hydrothermal treatment and the type of mineralizing agent. The size of HfO2 crystallites obtained in alkaline medium is by 2–3 times smaller than that for HfO2 crystallites obtained in neutral medium and constitutes ~8 nm. Dispersing of nanocrystalline HfO2 obtained by hydrothermal treatment in water in the presence of dextrane and poly(vinylpyrrolidone) under exposure to ultrasound leads to preparation of stable sols of nanocrystalline HfO2.

Degradation of kanamycin from production wastewater with high-concentration organic matrices by hydrothermal treatment

It is known that many kinds of fermentative antibiotics can be removed by temperature-enhanced hydrolysis from production wastewater based on their easy-to-hydrolyze characteristics. However, a few aminoglycosides are hard to hydrolyze below 100°C because of their stability expressed by high molecular energy gap (ΔE). Herein, removal of hard-to-hydrolyze kanamycin residue from production wastewater by hydrothermal treatment at subcritical temperatures was investigated. The results showed the reaction temperature had a significant impact on kanamycin degradation. The degradation half-life (t1/2) was shortened by 87.17-fold when the hydrothermal treatment temperature was increased from 100°C to 180°C. The t1/2 of kanamycin in the N2 process was extended by 1.08-1.34-fold compared to that of the corresponding air process at reaction temperatures of 140-180°C, indicating that the reactions during hydrothermal treatment process mainly include oxidation and hydrolysis. However, the contribution of hydrolysis was calculated as 75%-98%, which showed hydrolysis played a major role during the process, providing possibilities for the removal of kanamycin from production wastewaters with high-concentration organic matrices. Five transformation products with lower antibacterial activity than kanamycin were identified using UPLC-QTOF-MS analysis. More importantly, hydrothermal treatment could remove 97.9% of antibacterial activity (kanamycin EQ, 1,109 mg/L) from actual production wastewater with CODCr around 100,000 mg/L. Furthermore, the methane production yield in anaerobic inhibition tests could be increased about 2.3 times by adopting the hydrothermal pretreatment. Therefore, it is concluded that hydrothermal treatment as a pretreatment technology is an efficient method for removing high-concentration hard-to-hydrolyze antibiotic residues from wastewater with high-concentration organic matrices.