Catalytic Wet Air Oxidation Research Articles

The catalytic wet air oxidation of pharmaceutical wastewater with alkali-activated Mn and Cu composites: preparation of precursors by calcination of kaolin with Mn and Cu

In recent decades, the concentration of pharmaceutical residues and narcotics has increased in municipal wastewater. Decomposing these toxic organic chemicals is challenging and requires new techniques and advanced catalytic materials. Precursors of metal composites were prepared by calcining an aqueous suspension of natural clay–based kaolin with Mn and Cu, binding chemically the active metals to the aluminosilicate frame structure of the precursor. The specific surface area of Mn and Cu composite was 67 m2/g and 81 m2/g, respectively. The mechanical durability was determined in terms of compressive strength, and 3.3 MPa and 3.6 MPa were obtained, respectively. In the CWAO of pharmaceutical wastewater, Mn composite gave the highest conversions of 54% and 46% of the chemical oxygen demand (COD) and total organic carbon (TOC), respectively. Metal composites were mechanically and chemically highly durable, inducing only 1.2 wt.% and 1.4 wt.% mass loss. In CWAO, Mn and Cu composite increased the biodegradation of organic species in the wastewater by 65% and 75%, respectively.

Impact of H2 Reduction on the Performance and Stability of Phenol Catalytic Wet Air Oxidation (CWAO) Over Cu−Ce/AC Catalysts

AbstractIn this study, we utilized the carbon precursor derived from walnut shells to synthesize a series of Ce‐modified Cu‐based carbon catalysts (Cu−Ce/AC) via the impregnation method. We investigated the performance and stability of Cu−Ce/AC catalysts for CWAO phenol after H2 reduction at various temperatures. The Cu−Ce/AC‐250 catalyst exhibited its highest performance at 250 °C, achieving complete phenol conversion. Characterization results from techniques including XRD, BET, FTIR, ICP‐OES, SEM‐EDS, XPS, and H2‐TPR indicated that the active components of the H2‐reduced catalysts were more evenly distributed across the catalyst surface, thereby enhancing the availability of reactive sites for phenol oxidation. Simultaneously, under the appropriate temperature, the H2 atmosphere can reduce a portion of the Cu2+ on the catalyst surface to Cu+, thereby mitigating the loss of Cu components.

Enhanced prednisone removal by catalytic wet air oxidation using sewage sludge derived catalyst

Sewage sludge-based catalysts have been used for the first time for the catalytic wet air oxidation (CWAO) of prednisone, a glucocorticoid pharmaceutical pollutant present in various aquatic environmental matrices. This research focuses on transforming dry sludge into carbonaceous catalysts through pyrolysis and post-treatment. Various parameters have been considered for the synthesis, finding that pyrolysis temperature and acid washing are determinant for specific surface area development. The sewage sludge derived catalysts exhibit high catalytic activity in the CWAO of prednisone (Dcat= 0.3 g·L−1, T= 100 °C, P= 15 bar). The development of porosity enhances their catalytic properties, the C-750-N catalysts demonstrated the highest activity for prednisone with 66 % TOC reduction, initial reaction rate 0.0092 mg·s−1 and 66 % CO2 selectivity. The study provides valuable insights into the synthesis, characterization, and application of sewage sludge-derived catalysts, offering a sustainable solution for wastewater treatment and pharmaceutical pollutant removal. Our present study indicates that catalysts with unique reforming properties may be potentially applicable for prednisone treatment and industrial applications.

Crystal phase-driven performance of MnO2 in aqueous phase low-temperature thermal catalysis: Synergistic interactions between Mn3+ and surface lattice oxygen

Catalytic oxidation at mild conditions is crucial for mitigating the high pressure and high temperature challenges associated with current catalytic wet air oxidation (CWAO) technologies in wastewater treatment. Among potential materials for catalytic oxidation reactions, polycrystalline MnO2 existed in natural minerals holds considerable promise. However, the relationships between different crystal phases of MnO2 and their catalytic activity sources in aqueous phase remain uncertain and subject to debate. In this research, we synthesized various MnO2 crystal phases, comprising α-, β-, δ-, γ-, ε-, and λ-MnO2, and assessed their catalytic oxidation efficiency during low-temperature heating for treatment of organic pollutants. Our findings demonstrate that λ-MnO2 exhibits the highest catalytic activity, followed by δ-MnO2, γ-MnO2, α-MnO2, ε-MnO2, and β-MnO2. The variations in catalytic activity among different MnO2 are attributed to variances in their oxygen vacancy abundance and redox activity. Furthermore, we identified the primary active species, which include Mn3+ and superoxide radicals (•O2–) generated by surface lattice oxygen of MnO2. This research highlights the critical role of crystal phases in influencing oxygen vacancy content, redox activity, and overall catalytic performance, providing valuable insights for the rational design of MnO2 catalysts tailored for effective organic pollutant degradation in CWAO applications.

The Influence of Au Loading and TiO2 Support on the Catalytic Wet Air Oxidation of Glyphosate over TiO2+Au Catalysts

This study aimed to explore the impact of varying amounts of added Au (0.5 to 2 wt.%) and the structural characteristics of anatase TiO2 supports (nanoparticles (TP, SBET = 88 m2/g) and nanorods (TR, SBET = 105 m2/g)) on the catalytic efficiency of TiO2+Au catalysts in eliminating the herbicide glyphosate from aqueous solutions via the catalytic wet air oxidation (CWAO) process. The investigation was conducted using a continuous-flow trickle-bed reactor. Regardless of the TiO2 support and the amount of Au added, the addition of Au has a positive effect on the glyphosate degradation rate. Regarding the amount of Au added, the highest catalytic activity was observed with the TP + 1% Au catalyst, which had a higher Schottky barrier (SB) than the TP + 2% Au catalyst, which helped the charge carriers in the TiO2 conduction band to increase their reduction potential by preventing them from returning to the Au. The role of glyphosate degradation product adsorption on the catalyst surface is crucial for sustaining the long-term catalytic activity of the investigated TiO2+Au materials. This was particularly evident in the case of the TR + 1% Au catalyst, which had the highest glyphosate degradation rate at the beginning of the CWAO experiment, but its catalytic activity then decreased over time due to the adsorption of glyphosate degradation products, which was favoured by the presence of strong acidic sites. In addition, the TR + 1% Au solid had the smallest average Au particle size of all analyzed materials, which were more easily deactivated by the adsorption of glyphosate degradation products. The analysis of the degradation products of glyphosate shows that the oxidation of glyphosate in the liquid phase involves the rupture of C–P and C–N bonds, as amino-methyl-phosphonic acid (AMPA), glyoxylic acid and sarcosine were detected.

Removal and complete combustion of 1,4-dioxane in water by a two-step reaction combining adsorption and catalytic combustion

Catalytic wet air oxidation is not so effective to decompose 1,4-dioxane in water, while there have been several studies on this reaction. As an alternative, we propose a two-step purification system for removal and complete combustion of 1,4-dioxane, where the first step is removing 1,4-dioxane from water by adsorption, and in the second step, the adsorbent is heated to release 1,4-dioxane, and the released 1,4-dioxane is completely combusted by gas-phase catalytic reaction. We had searched for adsorbents and combustion catalysts suitable for the system and found a high-silica MFI zeolite and Pt/SiO2, respectively. The high-silica MFI zeolite adsorbed up to 121 mg g−1 of 1,4-dioxane, and 1.1 mmol L−1 of 1,4-dioxane in water was almost completely removed by 10 g L−1 dose. The zeolite was reusable for adsorption-desorption cycles at least five times without any loss of the performance. Pt/SiO2 was highly active for the complete combustion of 1,4-dioxane even at 200 °C. By using the high-silica MFI zeolite and Pt/SiO2, we conducted the release of 1,4-dioxane from the zeolite by heating and the gas-phase catalytic combustion of 1,4-dioxane using two reactors connected in series, which were filled with the zeolite and Pt/SiO2, respectively, and demonstrated that all 1,4-dioxane was released by 300 °C and was completely combusted in the upstream and downstream reactors, respectively.

Effective decolorization of sulfur black dye and assessment of anti-microbial activity using core/shell nanoparticles based on chitosan

Sulfur dyes, a type of dye produced in large quantities is known for its depth of color. But huge quantities of sulfides, electrolytes, and inorganic salts present in effluents containing sulfur dyes cause serious problems to environment, human, and aquatic life. Hence, in this research, chitosan – sodium tripolyphosphate@TiO2 [chitosan – TPP@TiO2] polymeric core/shell nanoparticles were synthesized by Ionic Gelation Method and their decolorization of sulfur black dye was examined. Structural confirmation was established through XRD and HR-TEM measurements. Surface morphological studies with elemental analysis were investigated using HR-SEM and EDS. Core/shell formation was confirmed through XPS measurements and their optical and thermal properties were explored. Sulfur black dye decolorization studies showed 88.3% decolorization within 6 min under dark conditions at ambient conditions due to the combined effects of adsorption and catalytic wet air oxidation (CWAO). The anti-bacterial and anti-fungal activities of chitosan – TPP@TiO2 core/shell nanoparticles were analyzed.

Synthesis of PbOx to graphite felt anodes to improve the electro-assisted catalytic wet air oxidation of oxygen species for efficient dye degradation

Electro-assisted catalytic wet air oxidation (ECWAO) is an environmentally-friendly pollutant removal process with energy-saving and mild reaction properties. However, it requires an electrode with high catalytic capacity and stability, and the catalytic mechanism behind the process still needs to be further clarified. Herein, we report a graphite felt (GF)-supported PbOx catalyst which can chemically adsorb oxygen and activate it into free radicals by an anodic electric field to promote wet air oxidation. XRD, SEM, EDS, XPS, BET and TG measurements indicated that PbO and PbO2 were successfully doped and loaded onto the GF, increasing the specific surface area and number of active sites. The best RhB degradation efficiencies achieved were 91.26 % over 15 min and 96.68 % over 90 min. The PbOx@C/GF maintained good catalytic performance over eight cycles in the pH range of 3–11 with negligible metal leaching. The RhB degradation pathway of RhB was analyzed through GC–MS results. A free radical quenching experiment, a contrast experiment, and an electrochemical test revealed the process of oxygen being adsorbed by Pb(II) and activated to degrade organic matter was revealed. Five kinds of dyes were degraded by the electrode via the ECWAO process, and the degradation rate reached over 93.7 % within 90 min. The degradation specific energy consumption (SEC) of probe pollutant RhB is 48.70 kW·h/kg-COD. The industrial practical dye wastewater COD removal rate was close to 100 %, and the SEC was 24.44 kW·h/kg-COD. Therefore, it can be concluded that a graphite felt (GF)-supported PbOx catalyst can act as an anode for ECWAO to chemically adsorb oxygen and activate it into free radicals using an anodic electric field to promote wet air oxidation.

Improved phenol degradation by catalytic wet air oxidation on the Co3O4 spinel catalysts supported on SBA-15 modified with TiO2

The removal of phenol from aqueous industrial effluents by catalytic wet-air oxidation (CWAO) is a challenging process that requires novel catalysts resistant to leaching of the active phases during residence time in a batch reactor. In this sense, this work demonstrated that this can be archived with the catalyst having the spinel phase Co3O4 supported on mesoporous silica SBA-15 doped with an optimized amount of TiO2 (3 wt%). In the phenol CWAO reaction carried out at 160 °C and 10 bar O2, this best Co3O4/TiO2/SBA-15 catalyst showed an increase of phenol conversion from 49.0 % to 68.3 % and of CO2 selectivity from 87 % to 98 %. The extensive catalyst characterization and overall activity results indicated that this was related to the strength and nature of the acid sites and the oxidation states of the cobalt oxide phases. Combined factors influenced the final behaviour of the catalyst, such as its intrinsic activity, dispersion of the active phase, inhibition of CoSiO4 phase formation, high Lewis acidity and the large amount of active Co3O4 spinel phase. The presence of TiO2 nanoparticles (NPs) decorating the support surface improved the stability of the catalyst by inhibiting the leaching of cobalt species during the reaction. After three reaction cycles, the most efficient Co/3Ti/S15 catalyst showed high CO2 selectivity (∼92.7 %) and low selectivity towards carboxylic acid (∼5.3 %) and polyphenolic compounds (∼2%). It is proposed that surface oxidation is the rate-determining step in the CWAO reaction over TiO2/SBA-15-supported Co3O4 spinel catalysts.

Efficient removal of piperazine by catalytic wet air oxidation using RuNiCe/γ-Al2O3-activated carbon

The RuNiCe/AAC catalyst represents an efficacious solution for the treatment of industrial wastewater, particularly in instances where the concentration of chemical oxygen demand (COD) and ammonia nitrogen (NH3-N) is elevated.

Study on the dispose of landfill leachates over tombarthite catalyst by catalytic wet air oxidation

Study on the dispose of landfill leachates over tombarthite catalyst by catalytic wet air oxidation

In situ growth of an ultrathin Cu/g-C3N4 coating over SBA-15 for catalytic wet air oxidation of pollutants under extremely mild conditions

Catalytic wet air oxidation (CWAO) is a very promising technology for the elimination of various refractory pollutants, but to activate dioxygen under mild conditions is a great challenge.

Advanced Oxidation Processes and Their Application in the Treatment of Different Types of Wastewater Samples

Over the years, urbanization has caused the quality of the water to decline gradually. The production of wastewater has been steadily rising alongside the growth of numerous businesses, including medicines, textiles, processed foods, and many more. Organic molecules from a variety of sources make up the majority of contaminants in wastewater. Some of these chemical molecules are not biodegradable, and it is challenging for anaerobic bacteria to break them down entirely. Because of the molecular structure of them, they can be quite persistent. Several advanced oxidation processes (AOPs) have been studied to remediate wastewater that contains trace organic chemicals (TrOCs). These include ozonation, Fenton oxidation, catalytic wet air oxidation, and photocatalytic oxidation. AOPs have excellent efficiencies, quick oxidation rates, and no secondary pollutants. Each AOP adheres to a particular mechanism in specific circumstances. In this article, we have comprehensively reviewed the underlying mechanism, and factors affecting oxidative pollutant degradation efficiency.

Preparation of porous metakaolin-based alkali-activated materials by microwave curing as supports for non-noble metal catalysts

Generally, alkali activated materials (AAMs) are prepared by curing an alkaline paste via conventional methods such as at room temperature for weeks, even months, or in oven for days to achieve the required properties. In this paper, fast electromagnetic radiation (microwaves) was investigated in detail as an alternative to conventional methods to produce environmentally friendly porous metakaolin-based AAMs as supports for catalysts (MK-AAMs). Hydrogen peroxide was used as a foaming agent to achieve porosity of the porous MK-AAMs. The non-porous MK-AAMs without a foaming agent were used as reference for the porous MK-AAMs. Curing of the MK-AAMs were conducted at room temperature (CU1), in an oven (CU2), and by microwaves (CU3). The specific surface area (SSA) of porous and non-porous MK-AAMs cured via CU1–3 was 36, 49, 90 m2/g and 9.0, 23, 24 m2/g, respectively. The average compressive strength (MPa) was 3.8, 2.7, 2.1 and 8.9, 6.4, 5.2, respectively. The catalytical performance of porous and non- porous MK-AAMs with Cu-catalyst (i.e., Cu-composites) were tested with an aqueous solution of bisphenol A (BPA) in catalytic wet air oxidation (CWAO). After 5 h of oxidation, the highest BPA conversion of 97 % was achieved with the porous Cu-composites. A slight mass loss of 1.5 wt % was observed in the Cu composites due to erosion caused by strong fluid flow in the CWAO experiments. Based on the various analyzes performed, no significant structural or chemical changes were observed in porous and non-porous MK-AAMs regardless of the curing method of CU1–3, which also confirmed that MK-AAMs can be produced by microwaves without losing the desired properties of the materials, such as porosity and mechanical durability.

Optimization of catalytic wet air oxidation process in microchannel reactor for TBBS wastewater treatment

ABSTRACT Catalytic wet air oxidation (CWAO) process is employed for the treatment of N-tert-butyl-2-benzothiazolesulfenamide (TBBS) wastewater in a microchannel reactor that enables continuous operation of the reaction and allows for thorough mixing of oxygen and pollutants. To achieve the optimal process performance, four key parameters of pressure, temperature, time, and the mass ratio of input oxygen to wastewater COD are optimized using both response surface methodology (RSM) and backpropagation artificial neural network (BP-ANN). According to the correlation coefficients of model results and experimental data, BP-ANN performs better than RSM in simulation and prediction. The analysis of variance in RSM shows that all parameters are significant for the obtained quadratic model, but their interactions with each other are not significant. Connection weights algorithm is used to determine the relative importance of these parameters for the process efficiency, and it is demonstrated that temperature is the most influential parameter with a relative importance of 35.61%, followed by pressure (29.74%), time (19.53%) and ROC (15.12%).

Chemically activated hydrochars as catalysts for the treatment of HTC liquor by catalytic wet air oxidation

Hydrothermal carbonization (HTC) is a highly efficient and valuable technology for treating wet solid wastes and producing solid carbon-based materials named hydrochar. In this work, a hydrochar coming from the HTC of an anaerobic digestion sludge of wastewater treatment plant was used to assess the influence of several activation agents, a base (KOH) and different chloride salts (FeCl3, ZnCl2, and CuCl2) with the exact molar quantities, to develop materials with enhanced surface area and potential inclusion of metal active species for application in wet air oxidation processes. The KOH as an activating agent increased the surface area of hydrochar up to ca. 1000 m2/g of BET surface area. The employment of CuCl2 and FeCl3 as activating agents allows Cu- and Fe-rich doped materials of remarkable surface areas with 49.1 and 42.5 wt% of each metal, respectively. Likewise, the catalytic behavior of the different synthesized carbon-based materials as metal-free and metal-doped catalysts was evaluated for the Catalytic Wet Air Oxidation (CWAO) of a HTC aqueous liquor from a HTC process of animal manure to produce a valuable stream of higher biochemical methane potential in anaerobic digestion. CWAO effluents increased the proportion of carboxylic acids as final by-products due to the oxidation of more complex organic compounds of the initial effluent (ketones, phenols, aromatics and olefins). The CWAO treatments improve the anaerobic digestion rate in biochemical methane potential tests, although the methane production was limited by the lower TOC concentration of the treated streams after CWAO. This research contributes to developing sustainable and efficient strategies for the HTC-liquor treatment, using its solid hydrochar as catalysts, closing the loop of a Circular Economy.

Catalytic wet air oxidation of phenol over nano mesoporous lanthanum oxide synthesized by chitosan template method

The study investigates the effectiveness of nano mesoporous lanthanum oxide (La2O3), synthesized by the chitosan template method, as a catalyst for the wet air oxidation of phenol (WAO). To relate the performance of the synthesized La2O3 to its chemical and textural characteristics, it was subjected to a thorough characterization using various analytical techniques, including TG-DTG, XRD, FTIR, BET, TEM, TPD-CO2, TPD-NH3, and H2-TPR. Nanomesoporous La2O3 displayed remarkable efficiency in removing phenol and total organic carbon (TOC) while exhibiting a greater preference towards non-organic compounds. Significant improvement in removal efficiency and selectivity when compared to non-catalytic wet air oxidation is observed for the catalyst. The study investigated the impact of temperature, catalyst dosage, airflow, and phenol pumping rate on the catalytic wet air oxidation (CWAO) of phenol. Even after 6 h of continuous reaction, La2O3 exhibited exceptional catalytic stability. The mesoporous nature and presence of Lewis basic sites in nano-La2O3 may be crucial in facilitating the degradation of phenol and enhancing the efficiency of TOC removal. The study concludes that the chitosan template method is an effective approach for synthesizing nano mesoporous lanthanum oxide, which could be used as a promising catalyst for the treatment of phenol-containing wastewater.

Catalytic wet air oxidation of sulfamethoxazole and tetracycline using platinum-based catalysts at eco-operating conditions

Conventional wastewater treatment plants (WWTP) are unsuitable for emerging contaminants' elimination. Most of these pollutants persist after the treatment and threaten the receiving environment. Catalytic wet air oxidation (CWAO) is one of the promising solutions to treat these concentrated active molecules. This study reports the catalytic degradation tests on sulfamethoxazole (SM) and tetracycline (TET) using platinum (Pt) supported on cerium oxide (Ce) and mixed cerium and zirconium oxides (CeZr). Pt/CeZr catalyst showed 98 % TET elimination at 50 °C under atmospheric pressure (Patm). Furthermore, the test at room conditions reached 92 % removal. Pt/Ce test enabled 77 % SM elimination and reached 45 % SM mineralization. Toxicity assessment confirmed the environmental legibility of the treated solution using CWAO. The outcomes of this study showed an eco-energetic, eco-friendly, and efficient way to treat wastewater loaded with pharmaceutical pollutants.

Interpretable artificial intelligence for advanced oxidation systems: Principle, operations and performance

Advanced oxidation processes have been widely studied and employed due to their potent mineralization capacity for pollutants. However, the intricate reaction mechanisms of these processes pose limitations for fitting and predicting performance. In this study, we comprehensively derived and assessed neural networks for three advanced oxidation methods: catalytic oxidation, catalytic wet air oxidation, and electrochemical oxidation. Our analysis encompassed multilayer perceptron principles, forward and back propagation process, strategies for handling overfitting, and performance evaluation matrices. Additionally, we utilized Bayesian optimization to probe the impact of network architecture on outcomes. Two conventional methods, multiple linear regression and response surface methodology, are employed for comparison. Our results demonstrate that neural networks exhibit more robust performance in fitting and predicting advanced oxidation processes as indicated by statistical indicators. Importantly, we tackle the "black box" issue of neural networks by incorporating the shapley additive explanations interpretable model of game theory to elucidate the impact of advanced oxidation features on outcomes. The superior performance of explainable artificial intelligence techniques implies their vast potential for broad applications in environmental science and technology.

Treatment of Highly Alkaline Industrial Organic Raffinate Containing Pyridine and Its Derivatives by Coupling of Catalytic Wet Air Oxidation and Biological Processes

Treatment of Highly Alkaline Industrial Organic Raffinate Containing Pyridine and Its Derivatives by Coupling of Catalytic Wet Air Oxidation and Biological Processes