Wet Peroxide Oxidation Process Research Articles

Synergistic catalytic degradation of Methotrexate using Ce-based high-entropy metal oxides: Insights from DFT calculations and CWPO performance

Methotrexate (MTX), a widely used anticancer drug, is a refractory organic pollutant posing serious threats to ecosystems and human health. This study focuses on the development of a novel catalyst composed of Ce-based high-entropy metal oxides (NHEMO) supported on nepheline for the catalytic wet peroxide oxidation (CWPO) process, targeting MTX degradation in simulated wastewater. The NHEMO catalyst exhibited a unique high-entropy structure that enhances catalytic performance by facilitating diverse electronic interactions, which was confirmed through X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses showing a well-defined crystal structure and uniform dispersion of metal oxides. Additionally, X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDS) revealed a stable metal composition and high oxidation states of active metal sites. At a reaction temperature of 160 °C, with a residence time of 150 s and an oxidation coefficient of 5, the catalyst achieved a MTX removal rate of 93.49 % and a chemical oxygen demand (COD) removal of 99.95 %. Density Functional Theory (DFT) calculations further demonstrated that H2O2 decomposes into both adsorbed (surface-bound) and free (solution-phase) hydroxyl radicals (·OH). These radicals synergistically degrade MTX through both radical and non-radical pathways, ensuring comprehensive pollutant breakdown. The catalyst also showed excellent stability and a very low metal dissolution rate during the reaction, maintaining high catalytic activity after repeated recycling. This catalyst offers high cost-effectiveness, activity, and stability, providing a promising solution for treating refractory organic pollutants in pharmaceutical wastewater.

Efficient degradation of phenol wastewater using CuFe2O4 as highly active catalyst in the microwave-assisted catalytic wet peroxide oxidation process

Six kinds of CuFe2O4, including capsule-shaped CuFe2O4-C, plate-shaped CuFe2O4-P, polyhedral-shaped CuFe2O4-O, and irregular shaped catalysts prepared by co-precipitation (CuFe2O4-CO), by microwave heating (CuFe2O4-MW), and by hydrothermal synthesis (CuFe2O4-S), were used in the microwave-assisted catalytic wet peroxide oxidation (MW-CWPO) process to remove phenol from wastewater. The physicochemical properties of the catalysts were dependent on preparation methods. The catalytic activities were in the order of CuFe2O4-CO (95.3 %) >> CuFe2O4-P (78.8 %) > CuFe2O4-C (72.7 %) > CuFe2O4-MW (67.1 %) > CuFe2O4-S (63.3 %) > CuFe2O4-O (60.0 %). Effects of CuFe2O4-CO dosage, H2O2, pH, phenol initial concentration, anions, and MW in the MW-CWPO process were then systematically studied. Under optimal conditions of pH = 3, H2O2 = 1 mL/L, and CuFe2O4-CO = 0.5 g/L, MW energy of 99 kJ (550 W, 3 min) and 132 kJ (550 W, 4 min) were found essential to achieve 99.6 % removal rate of phenol and 95.3 % removal rate of chemical oxygen demand (COD). Possible degradation pathways were suggested: phenol was firstly oxidized into hydroquinone and catechol, which further degraded into p-benzoquinone, 1,2-benzoquinone, respectively. Finally, these compounds transformed into oxalic acid, CO2, and H2O within 4 min. The proposed mechanism suggested that the catalyst CuFe2O4-CO generates more “hot spots” due to its irregular shape, which enhances MW scattering and absorbing abilities. Consequently, the chemical composition and crystal structure of the catalyst significantly promote the decomposition of H2O2 to generate free radicals. The CuFe2O4-CO has an opportunity of potential engineering application due to its high efficiency and stability.

Microplastic pollution and ecological risk assessment of a pond ecosystem.

Microplastic (MP) pollution has been observed in various ecosystems as a result of the rapid increase in plastic production over the past half-century. Nevertheless, the extent of MP pollution in different ecosystems, particularly in freshwater ecosystems, has not been well-studied, and there are limited investigations on this particular topic, specifically in Türkiye. Here, we quantify the occurrence and distribution of MPs in surface water samples collected from Topçu Pond (Türkiye) for the first time. Water samples were collected at five stations and filtered (30 L for each station) through stacked stainless steel sieves (5mm, 328µm, and 61µm mesh size) with a diameter of 30cm. The abundance, size, color, shape, and type of collected debris samples were analyzed after the wet peroxide oxidation process. MP particles were observed in all samples at an average abundance of 2.4 MPs/L. The most abundant MP size class and type were 0-999µm and fiber respectively. On the other hand, prevalent colors were black and colorless in general. According to the Raman analysis results, the identified MP derivatives were polypropylene (40%), polyamide (30%), ethylene acrylic acid (20%), and polyvinylchloride (10%). Moreover, the pollution load index (PLI) index was used to determine the pollution status. PLI values were determined as 1.91 at station S1, 1.73 at station S2, 1.31 at station S3, 1 at station S4 and 1.24 at station S5. The PLI value determined for the overall pond was 1.4. The results of this research show that MP pollution is present in Topçu Pond and contributes to the expanding literature on MP pollution in pond ecosystems.

Microplastic contamination in rivers: a survey from the Nan River, Thailand

BackgroundSince the 1970s, microplastic contamination has been discovered in various environments. These emerging pollutants threaten water quality and freshwater ecosystems. We aimed to assess microplastic contamination in the Nan River by quantifying their presence, characterising their morphology, and identifying their polymer composition. MethodsThe survey was conducted along the Nan River in northern Thailand, which is divided into three distinct zones based on land use (ie, community areas, agricultural areas, and natural areas). A wide array of samples, including surface water, sediment, and specimens from five aquatic species—Barbonymus altus, Laides hexanema, Kryptopterus cryptopterus, Pomacea canaliculata, and Pseudodon cambodjensis cambodjensis—were collected. The presence of microplastics was analysed via the wet peroxide oxidation process for sample digestion, morphological characteristics were assessed through microscopic examination, and Fourier transform infrared spectrophotometry was used to identify the polymer composition of the microplastics. FindingsNatural areas had the highest mean concentration of microplastics in surface water (23·67 pcs/L, SD 14·22), whereas community areas had the highest mean concentration in soil sediment (24·67 pcs/g, 15·04). No statistically significant differences in the amounts of microplastics were observed among the various land-use zones. Microplastics were predominantly found in the gastrointestinal tracts of fish specimens, with varying quantities observed among different aquatic species; B altus had the highest concentration (11·80 pcs/g, 8·98). The primary microplastic shapes identified were filaments (53·99%), fragments (35·58%), and cylindrical forms (10·43%). We identified ten different polymer types, with polypropylene, nylons, and polymethyl methacrylate being the most prevalent among them. InterpretationAnalysing microplastic pollution in this area brings attention to the issues affecting the rivers of Thailand and emphasises ecological risks, particularly microplastic presence in aquatic species. Because of the Nan River's ecological importance, we call for increased research and collaboration to address the increasing threat of microplastic pollution. FundingNaresuan University.

Formation of secondary microplastics during degradation of plastics originating from the MV X-Press Pearl maritime disaster

AbstractThe MV X-Press Pearl maritime incident had a profound impact on the marine and coastal ecosystems along the west coast of Sri Lanka. Considerable quantities of plastic pellets, specifically nurdles or pellets measuring less than 5 mm and estimated at 1680 tonnes, were released into the Indian Ocean. A notable portion of these plastic pellets/primary microplastics (MPs), has the potential to degrade into secondary MPs. The objective of this study was to investigate and understand the degradation process of plastic pellets into secondary MPs under the extreme conditions of fire and exposure to chemicals during the MV X-Press Pearl maritime disaster. Beach sand samples were collected from 40 locations along the affected west coast of Sri Lanka, at both mean sea level and the berm. An additional 20 samples were collected for a background study covering the entire coastline of Sri Lanka. The Wet Peroxide Oxidation (WPO) process was employed to separate microplastics, and observations of secondary MP quantities were recorded. Fourier Transform Infra-Red Spectroscopic (FTIR) analysis was carried out to identify functional groups of MPs. The variance in average values of secondary MPs at mean sea level (large MPs (i.e. size > 0. 5 mm) = 33 ± 56 items per 1 mm2 and total MPs (i.e. observed through microscope under 40× magnification) = 61 ± 66 items per 1 mm2) and the berm (large = 61 ± 154 items per 1 mm2 and total MPs = 106 ± 165 items per 1 mm2) suggested significant dispersal of large quantities of MPs to other areas in the Indian Ocean with oceanic currents. The baseline average value of secondary total MPs in other coastal areas of the country was approximately 53 ± 66 items per 1 mm2. The positive correlation between large and total secondary MPs and plastic pellets pollution index indicates that a considerable amount of plastic pellets were degraded into secondary MPs within 6 to 8 days after the accident, under the influence of nitric acid and heat/fire. These secondary MPs are mainly composed of low-density polyethylene (LDPE) and linear low-density polyethylene (LLDPE), as identified by FTIR observations. Consequently, these lightweight polymers have the potential to spread across a wider region, posing a severe environmental threat on a global scale as a transoceanic marine pollutant.

Wet peroxide oxidation process catalyzed by Cu/Al2O3: phenol degradation and Cu2+ dissolution behavior.

Catalytic wet peroxide oxidation (CWPO) has become an important deep oxidation technology for organics removal in wastewater treatments. Supported Cu-based catalysts belong to an important type of CWPO catalyst. In this paper, two Cu catalysts, namely, Cu/Al2O3-air and Cu/Al2O3-H2 were prepared and evaluated through catalytic degradation of phenol. It was found that Cu/Al2O3-H2 had an excellent catalytic performance (TOC removal rate reaching 96%) and less metal dissolution than the Cu/Al2O3-air case. Moreover, when the organic removal rate was promoted at a higher temperature, the metal dissolution amounts was decreased. Combined with hydroxyl radical quenching experiments, a catalytic oxidation mechanism was proposed to explain the above-mentioned interesting behaviors of the Cu/Al2O3-H2 catalyst for CWPO. The catalytic test results as well as the proposed mechanism can provide better guide for design and synthesis of good CWPO catalysts.

Improvement of the activity of a new nano magnetic titanium catalyst by using alkaline for refinery wastewater oxidation treatment in a batch baffled reactor

In order to reach pure water, it is essential to develop new technology for eliminating phenol from the wastewater. In this work, a nano-composite catalyst (5 % Fe2O3 + 10 % alkaline/TiO2) has been prepared and its performance to enhance the activity of catalytic wet peroxide oxidation (CWPO) process for removal of phenol has been examined. The new nano-composite catalyst is tested by Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), thermal gravimetric analysis (TGA), Energy dispersive X-ray (EDX) and scanning-electron-microscopy (SEM). A baffled batch reactor is used to evaluate the activity of new nano-composite catalyst at various temperatures (30–80 °C) and reaction times (30–90 min), utilizing hydrogen peroxide (H2O2) as oxidizing agent. The new design of digital baffled batch reactor prevents the fuel swirling, thus improving agitation. The experimental data of the CWPO technology prove that the best phenol removal (95.931 %) was carried out at 80 °C, the reaction time of 90 min, and in the presence of nano-composite catalyst ((5 % Fe2O3 + 10 % alkaline)/TiO2). Modeling investigation for the CWPO is examined in order to estimate the better process kinetic. The simulation technique explains dramatic agreement in comparing with the experimental data (error < 5 %). The optimal CWPO conditions in order to achieve pure water (phenol removal >99 %) are at reaction time of 198 min, process temperature of 85 °C, and initial phenol concentration of 1000 ppm.

Enhancing H2O2 utilization efficiency for catalytic wet peroxide oxidation through the doping of La in the Fe-ZSM-5 Catalyst.

Iron-loaded zeolite (Fe-zeolite) has shown great potential as an efficient catalyst for degrading organic pollutants with high concentrations in the catalytic wet peroxide oxidation (CWPO) process under mild conditions. Here, 0.4 wt% Lanthanum (La) was added in the 1.0 wt% Fe-ZSM-5 by two-step impregnation method for an enhanced H2O2 utilization efficiency. For a systematical comparison, the CWPO process at 55 °C, where m-cresol with a high concentration of 1000 mg/L as a substrate, was studied over Fe-ZSM-5 and Fe-La-ZSM-5 catalysts. Compared with Fe-ZSM-5, Fe-La-ZSM-5 showed 15% higher H2O2 utilization efficiency with comparable total organic carbon (TOC) removal at around 40%, meanwhile with a 15% reduced metal leaching. Transmission electron microscopy (TEM) with elemental mapping (EDS), surface acidity analysis by Fourier transform infrared (FT-IR) and NH3-temperature programmed desorption (NH3-TPD), redox property analysis by Raman spectroscopy and H2-temperature-programmed reduction (H2-TPR) of both catalysts revealed, that the La doped Fe-ZSM-5 can provide an altered surface acidity, a more uniform and evenly dispersed surface Fe species with a promoted reducibility, which effectively promoted the accurate decomposition of H2O2 into the reactive •OH radicals, enhanced the H2O2 utilization efficiency, and increased the catalyst stability. Also, more than 90% conversion was maintained during the continuous experiment for more than 10 consecutive test days under 55 °C without pH adjustment, showing a promising possibility of the Fe-La-ZSM-5 for a practical wastewater treatment process.

Highly active Mn-Cu bimetallic oxide catalyst assembled as 3D-printed monolithic agitating paddles for advanced oxidation process

Catalytically agitating paddles are essential to perform liquid-solid heterogeneous catalytic reactions on an industrial scale due to the improved mass transfer and easy catalyst recovery. Herein, bimetallic oxides were formed after the calcination of nanomaterials derived from metal-organic frameworks (MOFs). Particularly, Mn(M)-BTC nanomaterials were synthesized by self-assembly of Mn2+ ions (mixed with various dopants such as Cu2+, Ce3+, or Fe2+) and H3BTC ligands in a mixed solvent of ethanol and water. It was found that in the powdery form, the Mn-Cu oxide derivate exhibited the highest degradation rate in the catalytic wet peroxide oxidation process (CWPO process), which was significantly higher than that of single metal oxide as well as Mn-Fe and Mn-Ce oxide derivates. The reason was caused by the synergistic effect between Mn-Cu promoted the formation of Mn3+ and Cu+ species to boost the CWPO reaction. Furthermore, the obtained Mn-Cu powdery catalysts were 3D-printed to obtain monolithic agitating paddles with different geometries, which were then mounted on a central shaft in the stirred reactor. An advanced oxidation process was used to investigate the effect of 3D patterns on the degradation efficiency of various organic dyes. It was discovered that the 3D-printed grid with higher cell density (484 cpsi) had better liquid mixing efficiency and thus better catalytic performance, which could be repeatedly used more than seven times. Additionally, the numerical simulation analysis (computational fluid dynamics) revealed a good mixing efficiency and improved mass transfer in the entire reactor equipped with the designed monolithic agitating impellers.

Spatial and seasonal distribution of microplastic in surface water of Bueng Boraphet Wetland-a Ramsar wetland in Thailand.

This study sought to assess microplastic contamination in the surface water of the inland freshwater wetland, Bueng Boraphet Wetland, Thailand, which is a lentic system with various land-use patterns, including community areas, agricultural areas, and natural resource conservation areas. In 2019, water samples were collected during the wet and dry periods from the three land-use zones at depths of 0-30cm using a plankton net with 333µm in mesh size. The water samples were digested via a wet peroxide oxidation process prior to the identification of microplastic morphology using a stereomicroscope. The polymer types of microplastic were analyzed using Fourier transform infrared spectrophotometry. Microplastic was found to range from 0.00 to 4.61 particles/m2 (0.34 ± 0.81 particles/m2) or 0.0 to 19.57 particles/m3 (1.44 ± 3.4 particles/m3). Furthermore, significantly high amounts of microplastics were found in samples from the community area. No microplastic was detected in the sample from the natural resource conservation area. The quantity of microplastic did not significantly differ between the sampling periods. Polymer types, including polyester, polypropylene, and polyethylene terephthalate, were identified in this study. The microplastics were predominantly small and were colored black or red. Microplastic with a fiber shape (93.8%) was observed. Besides the specific gravity of the microplastic and hydrological characteristics, the high concentration of microplastics found in samples from the community area (0.62 ± 0.79 particles/m2 or 2.63 ± 3.36 particles/m3) is likely related to the high human pressure. As microplastic contamination can impact aquatic animals and wetland ecosystems, appropriate control measures for human activities and plastic waste management are required.

Developing Fe/zeolite catalysts for efficient catalytic wet peroxidation of three isomeric cresols.

Five Fe/zeolite (i.e., Fe/ZSM-5-1, Fe/ZSM-5-2, Fe/ZSM-5-3, Fe/MCM-22, and Fe/MOR) were prepared and tested as catalysts in the catalytic wet peroxide oxidation process (CWPO). Their adsorption and catalytic effects on the removal of three isomeric cresols were systematically explored. Sufficient characterizations were carried out to illuminate the iron species dispersed on the catalysts' surface porous channels. Other properties of the catalysts such as the Si/Al ratio, crystalline structures, and morphologies were systematically studied. After loaded with iron, the catalysts maintained zeolite's framework, which possessed specific porous structures and surface areas. Interestingly, the Si/Al ratio seemed to be an important issue influencing the adsorption and catalytic degradation of cresols due to n-π interaction and the acceleration of HO• generation, respectively. The amount of framework-Fe and Fe3+Al-Si in Fe/ZSM-5-3 was the most, which was crucial for its better catalytic ability than the other Fe/ZSM-5 catalysts (71.19% for m-cresol conversion). In conclusion, the catalytic activities of all the Fe/zeolites followed the sequence: Fe/ZSM-5-3> Fe/ZSM-5-2> Fe/ZSM-5-1> Fe/MCM-22>Fe/MOR. For three cresols, m-cresol was more susceptible to the attack of HO• than p- and o-cresol because more positions of m-cresol could be easy to be approached by the oxidizing agent. Considering the mild reaction condition in this study, such as 30 °C, pH=4.0, and catalyst dosage=1.0 g/L, the Fe/ZSM-5-3 was a promising zeolite catalyst for the degradation of refractory contaminants in practical wastewater.

Graphite as catalyst for UV-A LED assisted catalytic wet peroxide oxidation of ibuprofen and diclofenac

Ibuprofen (IBU) and Diclofenac (DCF) are two of the most common non-steroidal anti-inflammatory drugs used worldwide. Their occurrence in natural streams, as contaminants of emerging concern, evidences the inefficiency of conventional wastewater treatment plants for their removal. The photocatalytic methods developed so far usually demand either highly energetic light sources working in the UV-C range, or exclusive tailor-made catalysts, which compromise the economy of the process. In this work, IBU and DCF degradation are addressed in a UV-A LED (395 nm) assisted Catalytic Wet Peroxide Oxidation process using graphite as catalyst. Total IBU and DCF removal is achieved in t < 60 min working at [IBU or DCF]0: 20 µM, [H2O2]0: 800 µM, [Graphite]: 1 g · L−1 and pH0:3.0, with a 53% TOC removal and ECTOC: 31.0 kWh gTOC−1. Results show a high influence of the interaction between the graphite's surface and H2O2, which enables pollutant adsorption as first step in the oxidation reaction. Further redox reactions on the graphite surface lead to the cleavage of the reaction intermediates, making active sites available again. Nonetheless, in absence of an external energy source this process is very slow. UV-A radiation promotes these reactions as well as H2O2 decomposition into hydroxyl and hydroperoxyl radicals, enhancing the contaminant removal rate. The UV-A assisted CWPO process is also effective in surface water and WWTP effluent. Furthermore, graphite shows a great stability in IBU removal from WWTP effluent upon five consecutive cycles.

New insights on the removal of diclofenac and ibuprofen by CWPO using a magnetite-based catalyst in an up-flow fixed-bed reactor

This research has been focused on the removal of two anti-inflammatory drugs, diclofenac (DCF) and ibuprofen (IBU), by a continuous catalytic wet peroxide oxidation (CWPO) process using a lab-synthesized nanomagnetic catalyst (Fe3O4/MWCNTs). The central composite rotatable design (CCRD) method was used to study the effect of DCF and IBU concentration (expressed as theoretical oxygen demand (ThOD) between 0 and 52.5 mg L−1) and of the feed stream pH (from 3 to 7) on the removal of total organic carbon (TOC) and the concentration of aromatic compounds (Arm) and total phenolic compounds (TP) by CWPO. It could be observed that DCF was preferably removed from the DCF-IBU aqueous mixture at pH values ranging from 3 to 5. In addition, feed stream pH had a significant effect on the pollutants removal, as well as on TOC, TP and aromatic compounds removal, observing an increasing in the pollutants degradation when feed stream pH decreased from 7 to 3. Quadratic models predicted for response variable, such as TOC, TP and aromatic compounds removal, and their maximum model-predicted removal values were of 90.0, 80.2 and 90.0%, respectively. Finally, as a proof of concept, three environmentally-relevant aqueous matrices, spiked with DCF-IBU mixture, were treated. In this case, relatively high TOC degradation values were found after 20 h reaction time (ca. 57.7, 73.9 and 54.5% in surface water, WWTP effluent and hospital wastewater, respectively). This work deals the first study about DCF-IBU removal in aqueous solution by CWPO, as well as a continuous study using real wastewater that allow to extend the experimental results to a real scenario.

Degradation of MO and H2O2 on Cu/γ‐Al2O3 pellets in a fixed bed reactor: Kinetics and transport characteristics

AbstractPelletized Cu catalysts (Cu/γ‐Al2O3) with different diameters (dp = 1.1–4.2 mm) were prepared and examined kinetically for methyl orange (MO) degradation using a fixed bed reactor. A Cu/γ‐Al2O3 catalyst (dp = 2.3 mm) exhibited high degradation activity (Conv.MO &gt; 95%) and superior leaching resistance (Cu leaching &lt;0.6 mg/L in 200 hr). Apparent kinetics showed that both MO degradation and H2O2 decomposition were mainly controlled by internal mass transfer. A plug‐flow reactor model with mass‐transfer coefficients was developed, and a modified empirical correlation for external mass transfer (Sh = 1.5Re'1.10Sc0.42) was proposed to accurately describe the species transport from/to the catalyst pellets in the low Reynolds number regime. The model was verified against conversions of pollutants degradation and H2O2 decomposition separately in a fixed bed with relative errors &lt;5% compared with experimental data; thus, it could be used as an effective tool for further design and optimization of reactor configuration and reaction conditions for the continuous catalytic wet peroxide oxidation process.

Removal of Cr(VI) and methyl orange by activated carbon fiber supported nanoscale zero-valent iron in a continuous fixed bed column.

The application of activated carbon fiber supported nanoscale zero-valent iron (ACF-nZVI) in the continuous removal of Cr(VI) and methyl orange (MO) from aqueous solution was studied in depth. The breakthrough curves of Cr(VI) in a fixed bed with ACF-nZVI were measured, and compared with those in the fixed bed with ACF. The catalytic wet peroxide oxidation (CWPO) process for MO was also carried out using ACF-nZVI after reacting with Cr(VI) in the same fixed bed. The results showed that the breakthrough time of ACF-nZVI was significantly longer than that of ACF. Higher pH values were unfavorable for the Cr(VI) removal. The breakthrough time increased with decreasing inlet Cr(VI) concentration or increasing bed height. The Yoon-Nelson and bed depth service time (BDST) models were found to show good agreement with the experimental data. The Cr(VI) removal capacity when using ACF-nZVI was two times higher than that when using ACF. Under the optimal empty bed contact time of 1.256 min, the fixed bed displayed high MO conversion (99.2%) and chemical oxygen demand removal ratio (55.7%) with low Fe leaching concentration (<5 mg/L) after continuous running for 240 min. After three cycles, the conversion of MO remained largely unchanged.

UV-assisted Catalytic Wet Peroxide Oxidation and adsorption as efficient process for arsenic removal in groundwater

Arsenic is a toxic and carcinogenic element present in groundwater as arsenite, As(III) and/or arsenate, As(V), due to natural lixiviation or because of anthropogenic activities. The World Health Organization threshold in drinking water is 10 μg/L, well below the concentration found in the water resources of numerous populations, as in the Duero basin (Spain). As(V) can be easily removed by adsorption onto iron-based adsorbents, whereas As(III) is harder to remove. Therefore, in this work we propose the use of ilmenite (FeTiO3), a low-cost catalyst, as both photocatalyst and adsorbent in the UV-A assisted Catalytic Wet Peroxide Oxidation process. The main aim of this technology is to oxidize arsenite into arsenate, for its subsequent adsorption onto the Fe sites of the catalyst. This technology has proven to be effective for the oxidation and removal of 10 mg/L As(III) working at 1000 mg/L ilmenite, 60 mg/L H2O2, 0, pH0: 7 and room temperature (25 °C), in both ultrapure water and groundwater collected from Lastras de Cuéllar (Segovia, Spain). Furthermore, we propose a complete kinetic model which comprises the H2O2 decomposition, As(III) oxidation and As(V) adsorption, which is in agreement with the experimental data.

The influence of the catalyst on the CO formation during catalytic wet peroxide oxidation process

Herein, the formation of carbon monoxide as a harmful product upon the Catalytic Wet Peroxide Oxidation process is studied in presence of different solid catalysts: an iron supported activated carbon catalyst, a metal-free catalyst based on Graphene Nanoplatelets, and 1.6 wt.% Fe containing Cr2AlC MAX phase catalyst. The CWPO performance and the evolution of the gas effluent have been compared to that obtained in a conventional Fenton process.Carbon monoxide yield released was significantly lower in Catalytic Wet Peroxide Oxidation process in relation to that obtained in the Fenton process, where CO concentration reaches a maximum of 6651 mg/Nm3. By contrast, in presence of activated carbon-Fe catalyst and, notably, Graphene Nanoplatelets and Cr2AlC MAX phase catalysts, a more progressive phenol and aromatics intermediates oxidation resulted in a much lower CO maximum concentration in the gas phase at the exit of the reactor of 2454 mg/Nm3, 170 mg/Nm3 and 187 mg/Nm3, respectively.Hence, when compared to the homogeneous Fenton oxidation, Catalytic Wet Peroxide Oxidation process results be a more sustainable treatment for high-loaded phenolic wastewaters by decreasing the hazardous CO gaseous emissions avoiding this way a secondary pollution during the oxidation process.

Editorial Catalysts: Special Issue on Trends in Catalytic Wet Peroxide Oxidation Processes

The catalytic wet peroxide oxidation (CWPO) process is an advanced oxidation technology that has shown great potential for the decontamination of wastewater [...]

Condensation By-Products in Wet Peroxide Oxidation: Fouling or Catalytic Promotion? Part I. Evidences of an Autocatalytic Process

The present work is aimed at the understanding of the condensation by-products role in wet peroxide oxidation processes. This study has been carried out in absence of catalyst to isolate the (positive or negative) effect of the condensation by-products on the kinetics of the process, and in presence of oxygen, to enhance the oxidation performance. This process was denoted as oxygen-assisted wet peroxide oxidation (WPO-O2) and was applied to the treatment of phenol. First, the influence of the reaction operating conditions (i.e., temperature, pH0, initial phenol concentration, H2O2 dose and O2 pressure) was evaluated. The initial phenol concentration and, overall, the H2O2 dose, were identified as the most critical variables for the formation of condensation by-products and thus, for the oxidation performance. Afterwards, a flow reactor packed with inert quartz beads was used to facilitate the deposition of such species and thus, to evaluate their impact on the kinetics of the process. It was found that as the quartz beads were covered by condensation by-products along reaction, the disappearance rates of phenol, total organic carbon (TOC) and H2O2 were increased. Consequently, an autocatalytic kinetic model, accounting for the catalytic role of the condensation by products, provides a well description of wet peroxide oxidation performance.

Condensation By-Products in Wet Peroxide Oxidation: Fouling or Catalytic Promotion? Part II: Activity, Nature and Stability

The deposition of condensation by-products onto the catalyst surface upon wet peroxide and wet air oxidation processes has usually been associated with catalyst deactivation. However, in Part I of this paper, it was demonstrated that these carbonaceous deposits actually act as catalytic promoters in the oxygen-assisted wet peroxide oxidation (WPO-O2) of phenol. Herein, the intrinsic activity, nature and stability of these species have been investigated. To achieve this goal, an up-flow fixed bed reactor packed with porous Al2O3 spheres was used to facilitate the deposition of the condensation by-products formed in the liquid phase. It was demonstrated that the condensation by-products catalyzed the decomposition of H2O2 and a higher amount of these species leads to a higher degree of oxidation degree The reaction rates, conversion values and intermediates’ distribution were analyzed. The characterization of the carbonaceous deposits on the Al2O3 spheres showed a significant amount of condensation by-products (~6 wt.%) after 650 h of time on stream. They are of aromatic nature and present oxygen functional groups consisting of quinones, phenols, aldehydes, carboxylics and ketones. The initial phenol concentration and H2O2 dose were found to be crucial variables for the generation and consumption of such species, respectively.