Catalytic Wet Oxidation Research Articles

Mitigating Microfiber Pollution in Laundry Wastewater: Insights from a Filtration System Case Study in Galle, Sri Lanka

Synthetic fibers are widely used in daily life due to their durability, elasticity, low cost, and ease of use. The textile industry is the primary source of synthetic microfibers, as these materials are mostly used in production processes. Globally, plastic pollution has been identified as a major environmental threat in this era, since plastics are not degradable but break down into smaller particles such as mesoplastics, microplastics, and microfibers. Synthetic microfiber pollution is a significant issue in aquatic ecosystems, including oceans and rivers, with laundry wastewater being a major source. This problem is particularly pressing in cities like Galle, Sri Lanka, where numerous tourist hotels are located. Despite the urgency, there has been a lack of scientific and systematic analysis to fully understand the extent of the issue. This study addresses this gap by analyzing the generation of microfibers from laundry activities at a selected hotel and evaluating the efficiency of a laundry wastewater filtration system. This study focused on a fully automatic front-loading washing machine (23 kg capacity) with a load of 12 kg of polyester–cotton blend serviettes (black and red). Samples (1 L each) were taken from both treated and untreated wastewater during four wash cycles, with a total of 100 L of water used for the process. The samples were filtered through a 100 μm sieve and catalytic wet oxidation along with density separation were employed to extract the microfibers, which were then collected on a membrane filter paper (0.45 μm). Microfibers were observed and analyzed for shapes, colors and sizes under a stereo microscope. Results revealed that untreated laundry wastewater contained 10,028.7 ± 1420.8 microfibers per liter (n = 4), while treated wastewater samples recorded 191.5 ± 109.4 microfibers per liter (n = 4). Most of the microfibers observed were black and white/transparent colors. Further analysis revealed that 1 kg of polyester–cotton blend fabric can generate 336,833 microfibers per wash, which was reduced to 6367 microfibers after treatment. The filtration unit recorded an impressive efficiency of 98.09%, indicating a remarkably high capacity for removing microfibers from wastewater. These findings highlight the potential of such filtration techniques to significantly reduce microfiber emissions from laundry wastewater, presenting a promising approach to mitigating environmental pollution from microfibers.

Performance of catalytic wet oxidation on thermochemical aqueous effluents assessed by FT-ICR MS

Aqueous phase (AP) is frequently observed in bio-oil from biomass thermochemical conversion or as an upgrading coproduct. However, AP contains high organic content that can be toxic and that must be reduced or removed to be then treated in existing wastewater plants. A promising method to upgrade these APs is the catalytic wet peroxide oxidation (CWPO) that was applied here on APs of both hydrothermal liquefaction and pyrolysis bio-oils from softwood and hardwood. Efficiency of the CWPO was assessed by investigating the molecular composition of raw and treated APs by ultra-high-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) with electrospray ionization (ESI) in negative- and positive-ion modes. Combination of FT-ICR MS and multivariate statistical analyses evidenced efficiency of the process with new compounds resulting from the oxidative depolymerization, characterized by lower unsaturation degree and molecular weight, and higher oxygen atom count. Refractory compounds were also observed, which are notably characterized by high unsaturation degrees. Interestingly, both detection modes were shown to be complementary for the understanding of the CWPO process. ESI (-) allowed to assess the completion of the oxidation process in detecting carboxylic acid conversion products and to specifically evidence refractory products. ESI (+) was informative on the CWPO process, especially on the conversion of the basic compounds, with the decrease of the detected species. Eventually, softwood AP was shown to be more reluctant to CWPO than the hardwood one.

The Treatment of Antibiotic Excess Sludge via Catalytic Wet Oxidation with Cu-Ce/γ-Al2O3 and the Production of a Carbon Source

In the present study, the effectiveness of catalytic wet oxidation triggered by using Cu-Ce/γ-Al2O3 to degrade antibiotic excess sludge was investigated, during which some small molecule carboxylic acids were produced, which are valuable in biological wastewater treatment as an organic carbon source. The influence of reaction parameters on the degradation efficiency was explored through single-factor and orthogonal experiments, including catalyst amount, reaction temperature and time, and oxygen supply amount. The results illustrated that the treatment system can achieve 81.2% COD and 93.8% VSS removal rates under optimized reaction conditions. Carboxylic acids produced after the sludge degradation mainly included acetic acid, propanoic acid, etc. The results of wastewater biological treatment experiments exhibited that the degraded solution after catalytic wet oxidation has potential to be used as a carbon source to meet the demand of biological treatment, which helps the removal of COD and TN. This work confirms the effectiveness of catalyst for enhancing antibiotic excess sludge treatment, which provided a new idea for the rational disposal of antibiotic excess sludge.

Catalytic wet oxidation degradation of malachite green with Cu-coated sediment as catalyst: parameter optimization using response surface methodology

Catalytic wet oxidation degradation of malachite green with Cu-coated sediment as catalyst: parameter optimization using response surface methodology

The Catalytic Wet Oxidation of Excess Activated Sludge from a Coal Chemical Wastewater Treatment Process

An improved catalytic wet oxidation method for the disposal of excess activated sludge from a coal chemical wastewater treatment process by using the prepared Cu-Ce/γ-Al2O3 catalyst was reported. The effects of catalyst dosage, reaction temperature and time, and initial oxygen pressure on the degradation of the sludge were investigated. The maximum removal rate of volatile suspended solids, 93.2%, was achieved at 260 °C for 60 min with the catalyst 7.0 g·L−1 and initial oxygen pressure 1.0 MPa. The removal rate of chemical oxygen demand was 78.3% under the same conditions. The production of volatile fatty acids, including mainly acetic acid, propanoic acid, and isobutyric acid, increased with the increasing temperature. These acids have the potential to be carbon sources for the biological treatment of wastewater. Scanning electron microscopy images showed that the sludge became a loose porous structure, which is beneficial for dewatering performance. The results of an energy dispersive spectroscopy analysis illustrated that the carbon element in the sludge substantially migrated from solid to liquid phases. Therefore, these results demonstrated that the proposed catalytic wet oxidation method offers a promising pathway for the disposal and utilization of excess activated sludge from the coal chemical wastewater treatment process.

High-Performance Catalytic Wet Oxidation of Excess Activated Sludge Derived from Pharmaceutical Wastewater Treatment Process over a Cu/γ-Al2O3 Catalyst

The performance of catalytic wet oxidation of excess activated sludge derived from pharmaceutical wastewater treatment over a Cu/γ-Al2O3 catalyst was investigated. The experiments were performed with a stainless steel autoclave reactor by using the prepared Cu/γ-Al2O3 catalyst. The effects of reaction conditions were examined, including additional catalyst amount, reaction temperature, time, and initial oxygen pressure. Results demonstrated that the catalyst, fabricated via co-precipitating method, has excellent catalytic performance. Through the study on condition optimization, the highest removal rates of volatile suspended solids (VSS, 93.6%) and total chemical oxygen demand (TCOD, 76.5%) were acquired with the reaction temperature 260 °C, time 60 min, initial oxygen pressure 1.0 MPa, and the prepared catalyst 5.0 g/L. The volatile fatty acids (VFAs) produced from the wet oxidation of sludge included acetic (mainly), propanoic, isobutyric, and isovaleric acids, which have great potential for the utilization as organic carbon sources in biological wastewater treatment plant. These results demonstrated that the proposed method, catalytic wet oxidation over Cu/γ-Al2O3 catalyst, is effective for treating excess activated sludge and resource utilization of organic carbon in the sludge.

Synergistic catalytic wet oxidation of ammonia over carbon-supported low-loading Ru/Cu bimetallic catalyst

The manner of ammonia-containing wastewater in industrial production has always been an urgent issue that needs to be solved. Accordingly, a carbon-supported low-loading Ru/Cu bimetallic catalyst with high activity and hydrothermal stability was produced through facile disposal for catalytic wet air oxidation (CWAO). In the preparation process, Ru and Cu ions were loaded onto micro mesoporous carbon prepared through the calcination of potassium citrate by impregnation. Various characteristic techniques were utilized to characterize their structures and morphology, and results show that the calcination temperature with micro-mesopores’ characteristics could regulate the morphology of carbon. The results of catalytic experiments demonstrated that the obtained catalyst showed excellent catalytic performance in the process of CWAO. The Ru/Cu@C-700 catalyst achieved 99.6 % conversion of ammonia water at 800 ppm and 99.1 % selectivity to nitrogen at 200 °C and 2 MPa O2 in 4 h. The ammonia nitrogen content in the treated water was less than 15 ppm, meeting the standard for direct discharge. Moreover, no apparent deactivation phenomenon was observed after five cycles, indicating that the prepared catalyst can effectively prevent the leaching of ruthenium and copper nanoparticles. The low loading (less than 1 %) of the Ru/Cu bimetallic catalyst can significantly reduce costs and can synergistically enhance conversion and selectivity, providing an effective strategy for studying the CWAO of ammonia.

Treatment of Dyes Wastewater by the Catalytic Wet Persulfate Oxidation Process in Reactors Using Red Mud Combined with Biochar as Catalyst

Treatment of Dyes Wastewater by the Catalytic Wet Persulfate Oxidation Process in Reactors Using Red Mud Combined with Biochar as Catalyst

Removal efficiency and reaction kinetics of phenolic compounds in refinery wastewater by nano catalytic wet oxidation

A novel nano-catalyst based on iron oxide (MnO2/Fe2O3) was developed to promote wet oxidation of phenol. MnO2 was doped in Fe2O3 matrix to prepare composite nano-catalyst with different doping percentage (0, 2 and 5%). The catalytic phenol oxidation was conducted under different reaction temperatures and residence times. To evaluate the optimal kinetic parameters aiming to maximize phenol removal under the optimal conditions for the catalytic wet phenol oxidation process, modeling was applied on the batch reactor using the novel synthesis nano-catalyst (MnO2/Fe2O3) and the model developed was fed with the experimental data. gPROMS package was used to model the process of phenol oxidation and to optimize the experimental data. The error predicted between the simulated and experimental data was less than 5%. The optimal operating conditions were 294 min residence time, 70oC reaction temperature, and 764 ppm initial concentration of phenol over the prepared 5% MnO2/Fe2O3. Running of wet oxidation of phenol under the optimal operating conditions resulted in 98% removal of phenol from refinery wastewater.

Promoted wet peroxide oxidation of chlorinated volatile organic compounds catalyzed by FeOCl supported on macro-microporous biomass-derived activated carbon

Chlorinated volatile organic compounds (CVOCs) are a recalcitrant class of air pollutants, and the strongly oxidizing reactive oxygen species (ROS) generated in advanced oxidation processes (AOPs) are promising to degrade them. In this study, a FeOCl-loaded biomass-derived activated carbon (BAC) has been used as an adsorbent for accumulating CVOCs and catalyst for activating H2O2 to construct a wet scrubber for the removal of airborne CVOCs. In addition to well-developed micropores, the BAC has macropores mimicking those of biostructures, which allows CVOCs to diffuse easily to its adsorption sites and catalytic sites. Probe experiments have revealed HO• to be the dominant ROS in the FeOCl/BAC + H2O2 system. The wet scrubber performs well at pH 3 and H2O2 concentrations as low as a few mM. It is capable of removing over 90% of dichloroethane, trichloroethylene, dichloromethane and chlorobenzene from air. By applying pulsed dosing or continuous dosing to replenish H2O2 to maintain its appropriate concentration, the system achieves good long-term efficiency. A dichloroethane degradation pathway is proposed based on the analysis of intermediates. This work may provide inspiration for the design of catalyst exploiting the inherent structure of biomass for catalytic wet oxidation of CVOCs or other contaminants.

Conversion rules of sulfur compounds in iron chelate desulfurization system

ABSTRACT Iron chelate desulfurization is a popular method in the coking industry due to its low generation of secondary salts. The conversion of sulfur compounds in the system plays a crucial role in this process. In this paper, the favorable conditions for the formation of polysulfide ions (Sx 2-) were investigated by ultraviolet-visible spectrophotometry (UV-Vis) in the reaction system of EDTA-Fe and Na2S. The reaction solution was analyzed by high-performance liquid chromatography (HPLC), aiming to obtain the main forms of the presence of Sx 2- after the reaction. HS− was first converted to Sx 2-, and then to elemental sulfur (S8). In the experimental range, the concentration of Sx 2- increased with increasing the concentration ratio of reactants (c(Na2S)/c(EDTA-Fe)) and decreasing the temperature, was maximal at pH 9.84. At c(Na2S)/c(EDTA-Fe) of 120, the forms of Sx 2- reached a maximum, which was S3 2--S10 2-. When the concentration ratio reached 130, S8 was generated, as the concentration ratio increased on this basis, the time for S8 to appear was shortened from 21 min to 12 min. Therefore, the study of the conversion rules of sulfur compounds in the iron chelate desulfurization system provides both the ideas to suppress the generation of by-salts in this system and new evidence to reveal the common problem of sulfur compounds conversion in the wet catalytic oxidation desulfurization process.

Wet Catalytic Oxidation of a FeMnCe-Activated Semi-Coke Catalyst for Treating Piperazine Wastewater.

A FeMnCe-activated semi-coke catalyst (FeMnCe/ASC) was prepared by the co-precipitation method using semi-coke as the raw material. The structure and morphology were characterized by X-ray diffraction, Brunauer-Emmett-Teller, scanning electron microscopy, and transmission electron microscopy analyses. The catalytic activity and stability of the FeMnCe/ASC catalyst were investigated with piperazine as the target degradation pollutant and ammonia nitrogen and chemical oxygen demand (COD) as the evaluation indexes. The results showed that the average pore size of FeMnCe/ASC mesopores was 6.68 nm, and the active components were uniformly dispersed on the carrier surface. Under the optimum conditions of piperazine solution including a mass concentration of 100 mg/L, a catalyst mass concentration of 4.0 g/L, a reaction temperature of 240 °C, an oxygen partial pressure of 1.2 MPa, a stirring speed of 500 rpm, and a reaction time of 120 min, the degradation rates of both ammonia nitrogen and COD reached 100%. After the catalyst was recycled five times, the degradation rates of ammonia nitrogen and COD still reached more than 90%. The elemental valence changes before and after the reaction were analyzed by X-ray photoelectron spectroscopy, and the intermediate products generated from piperazine degradation were analyzed by gas chromatography-mass spectroscopy to evaluate the mechanism of piperazine degradation and speculate about the degradation pathway of piperazine.

Wet oxidation and catalytic wet oxidation of pharmaceutical sludge

In this work, wet oxidation and catalytic wet oxidation of pharmaceutical sludge using homogeneous and heterogeneous catalysts were investigated. The results indicate that wet oxidation is a promising method for the highly efficient degradation of pharmaceutical sludge. Under optimal conditions, the highest removal efficiencies of volatile suspended solids (VSS) 86.8% and chemical oxygen demand (COD) 62.5% were achieved at 260 °C for 60 min with an initial oxygen pressure of 1.0 MPa. NaOH exhibited excellent acceleration performance on the VSS removal. The highest VSS removal efficiency of 95.2% was obtained at 260 °C for 60 min with an initial oxygen pressure of 1.0 MPa and 10 g·L−1 of NaOH. By using a Cu–Ce/γ-Al2O3 catalyst, the highest removal rates of VSS 87.3% and COD 72.6% were achieved at 260 °C for 60 min with an initial oxygen pressure of 1.0 MPa and 10 g·L−1 of catalyst. The wet oxidation reaction can be maintained itself owing to the exothermic heat. The produced low-molecular-weight carboxylic acids have potential commercial utilization as organic carbon sources in the biological wastewater treatment processes. The inorganic residues can be utilized for the building materials production. These results implied that the catalytic wet oxidation is a promising method for the volume reduction and resource utilization of pharmaceutical sludge.

Study on the catalytic degradation of sodium lignosulfonate to aromatic aldehydes over nano-CuO: Process optimization and reaction kinetics

As one of the few renewable aromatic resources, the research of depolymerization of lignin into high-value chemicals has attracted extensive attention in recent years. Catalytic wet aerobic oxidation (CWAO) is an effective technology to convert lignin like sodium lignosulfonate (SL), a lignin derivative, into aromatic aldehydes such as vanillin and syringaldehyde. However, how to improve the yield of aromatic aldehyde and conversion efficiency is still a challenge, and many operating conditions that significantly affect the yield of these aromatic compounds have rarely been investigated systematically. In this work, we adopted the stirred tank reactor (STR) for the CWAO process with nano-CuO as catalyst to achieve the conversion of SL into vanillin and syringaldehyde. The effect of operating conditions including reaction time, oxygen partial pressure, reaction temperature, SL concentration, rotational speed, catalyst amount, and NaOH concentration on the yield of single phenolic compound was systematically investigated. The results revealed that all these operating conditions exhibit a significant effect on the aromatic aldehyde yield. Therefore, they should be regulated in an optimal value to obtain high yield of these aldehydes. More importantly, the reaction kinetics of the lignin oxidation was explored. This work could provide basic data for the optimization and design of industrial operation of lignin oxidation.

Non-catalytic and catalytic wet oxidation of landfill leachate over CuO and MoO3

Non-catalytic and catalytic wet oxidation of landfill leachate over CuO and MoO3

Development of a Sustainable Tungsten and Iron Bimetal-Immobilized SBA-15 Composite for Enhanced Wet Catalytic Oxidation of Dye Capacity.

In this study, wet catalytic decomposition of Orange (II) dye was carried out with tungsten and iron bimetal-incorporated mesoporous SBA-15 (W-Fe@SBA-15) under visible light. The synthesized hybrid composite material was characterized by physicochemical methods, powder X-ray diffraction (PXRD) spectroscopy, scanning electron microscopy combined with energy-dispersive X-ray (SEM-EDX) spectroscopy studies, Fourier transform infrared (FT-IR) spectroscopy, transmission electron microscopy (TEM), atomic force microscopy (AFM), thermogravimetric analysis (TGA), and surface property studies to understand the nature of the dye degradation process and for catalytic studies. The maximum degradation of Orange (II) dye measured by a UV-visible spectrophotometer was 99% at a contaminant volume of 2.7 × 10-4 mol/L and a catalyst quantity of 2 g/L in 140 min reaction time. Using gas chromatography-mass spectrometry (GC-MS), the final products were chemically identified. The mechanistic steps of the process were carried out through a series of experiments. The recyclability of the catalyst added a novel feature for such a heterogeneous catalysis that can reduce secondary pollutants in water with no leaching effect observed.

Catalytic Wet Oxidation of Glucose over Oxidized Transition Metal and Alloy Catalysts

AbstractThe catalytic wet oxidation process was used to study the degradation of carbohydrates in wastewater with glucose as a model compound. The transition metals Co and Mo were transformed into their insoluble metal oxide forms, Co3O4 and MoO3. A novel catalyst was prepared by using a CuNiIn alloy, which was oxidized at 700 °C to generate an insoluble CuNiIn mixed oxide. Wet oxidation reactions were performed at 150–210 °C for 60 min at 20 bar O2 pressure. The catalytic performance of the CuNiIn oxide powder reached a reduction in chemical oxygen demand of > 80 %. Molybdenum and cobalt were highly leached into the reaction media, confirming CuNiIn oxide as the best catalyst used in terms of its performance and acetic acid production.

Fracking wastewater treatment: Catalytic performance and life cycle environmental impacts of cerium-based mixed oxide catalysts for catalytic wet oxidation of organic compounds

Water scarcity and the consequent increase of freshwater prices are a cause for concern in regions where shale gas is being extracted via hydraulic fracturing. Wastewater treatment methods aimed at reuse/recycle of fracking wastewater can help reduce water stress of the fracking process. Accordingly, this study assessed the catalytic performance and life cycle environmental impacts of cerium-based mixed oxide catalysts for catalytic wet oxidation (CWO) of organic contaminants, in order to investigate their potential as catalysts for fracking wastewater treatment. For these purposes, MnCeOx and CuCeOx were tested for phenol removal in the presence of concentrated NaCl (200 g L−1), which represented a synthetic fracking wastewater. Removal of phenol in pure (“phenolic”) water without NaCl was also considered for comparison. Complete (100 %) phenol and a 94 % total organic carbon (TOC) removal were achieved in both the phenolic and fracking wastewaters by utilising MnCeOx (5 g L−1) and insignificant metal leaching was observed. However, a much lower activity was observed when the same amount of CuCeOx was utilised: 23.3 % and 20.5 % for phenol and TOC removals, respectively, in the phenolic, and 69.1 % and 63 % in the fracking wastewater. Furthermore, severe copper leaching from CuCeOx was observed during stability tests conducted in the fracking wastewater. A life cycle assessment (LCA) study carried out as part of this work showed that the production of MnCeOx had 12–98 % lower impacts than CuCeOx due to the higher impacts of copper than manganese precursors. Furthermore, the environmental impacts of CWO were found to be 94–99 % lower than those of ozonation due to lower energy and material requirements. Overall, the results of this study suggest that the adoption of catalytic treatment would improve both the efficiency and the environmental sustainability of both the fracking wastewater treatment and the fracking process as a whole.

Reusable Plasma‐Sprayed Transition Metal Oxide Catalyst for Catalytic Wet Oxidation of Organic Waste

AbstractCatalytic wet oxidation (CWO) is an efficient and environmentally friendly method for decomposing organic wastes. This work uses transition metal oxide powders of FeO, MnO2, NiO and the novel mixed oxide Co1.5Mn1.5O4, for plasma‐spraying on stainless‐steel substrates to prepare catalyst plates. These catalysts were used to treat d‐glucose as a model compound for organic waste, using CWO process reactions at temperatures from 150 °C to 170 °C and in the presence of oxygen (20 bar and 40 bar). The catalysts were pre‐oxidised to their suitable phases for better catalytic activity. The plasma‐sprayed Fe2O3 catalysts showed the highest chemical oxygen demand (COD) reduction of 72 %. At high reaction severity the catalyst performances were similar improving the overall performance compared to non‐catalytic wet oxidation reactions. Plasma‐sprayed Fe2O3 was found to be the best catalyst for future CWO trials due to its ability to withstand the reaction severity and acetic acid production.

Removal of Malachite Green Dye from Aqueous Solution by Catalytic Wet Oxidation Technique Using Ni/Kaolin as Catalyst.

In this study, natural Algerian kaolin was used as a support and impregnated with nickel at different loading amounts (2 wt.%, 5 wt.%, and 7 wt.%) in order to prepare a supported catalyst. The wet impregnation technique was used in this preparation; nickel oxide (NiO) was the active phase precursor of the catalyst, and the catalysts were designated as follows: 2%, 5%, and 7% Ni/kaolin. These catalysts were put to the test in catalytic wet peroxide oxidation (CWPO) for degrading the organic contaminant malachite green dye (MG). Analytical techniques such as FTIR spectroscopy, X-ray diffraction, BET, and X-fluorescence were used to examine the structure, morphology, and chemical composition of the support and the produced catalysts. Several parameters, including temperature, catalytic dose, metal loading, hydrogen peroxide volume, and kinetic model were systematically investigated. The combination of improved parameters resulted in a significant increase in the catalytic activity, achieving a high removal rate of MG dye of 98.87%.