A review of industrial catalytic wet air oxidation processes

Methods of Thermal Treatment of Radioactive Waste

Throughout the world, and especially in the European Union, numerous technologies for the thermal treatment of radioactive waste are available or being developed. These technologies can be applied to a large range of different radioactive waste streams, including non-standard types of waste that present specific waste management challenges. Thermal treatment can result in a significant reduction in volume and hazard, which are beneficial for safe storage and disposal. Thermal treatment also removes organic material that can form complexing agents and increase the mobility of radionuclides in the landfill. In the paper, basic thermal techniques are presented, and some examples of the installations are shown. Common knowledge of these methods may result in an increased public acceptance of nuclear energy in a country just introducing it, as Poland is.

Bibliometric analysis of advanced oxidation processes (AOPs) in wastewater treatment: global and Ibero-American research trends

Advanced oxidation processes (AOPs) constitute a developing area of particular interest for researchers in different fields due to their broad range of applications. However, there are few studies dedicated to the bibliometric analysis of AOPs. Hence, a systematic literature review of research publications (research articles, review articles, and book chapters) from 1980 to 2018 was carried out to visualize and evaluate research trends on AOPs around the world and, especially in Ibero-America (IA), on the field of wastewater treatment. Using the most extensive databases in literature search, Scopus and Web of Science (WoS), which encompass 95% of the publications in the world, a total of 18,751 records were retrieved by limiting the search results to words associated with AOPs in the titles, keyword, and abstracts. Raw data were manually organized and filtered, standardizing authors and institution names, publication titles, and keywords for the purpose of eliminating double-counted entries. Similarly, homonymous authors and institutions were identified for all records retrieved. The bibliometric dataset was processed using the VantagePoint software. The research trends visualized about AOPs were as follows: number of publications per triennium, publications by country, participation by continent, most important journals and authors, most referenced institutions, global network of co-authors, and keywords network visualization, highlighting the Ibero-American contribution to global research.

A New Route for Low Pressure and Temperature CWAO: A PtRu/MoS2_Hyper-Crosslinked Nanocomposite

PtRu/MoS₂ nanoparticles (NPs) (PtRu alloy partially coated by one-layer MoS₂ nanosheets) were prepared through a ‘wet chemistry’ approach. The obtained NPs were directly embedded, at 5 parts per hundred resin/rubber (phr) loading, in a poly (divinylbenzene-co-vinyl benzyl chloride) hyper-crosslinked (HCL) resin, synthesized via bulk polymerization of the resin precursors, followed by conventional FeCl₃ post-crosslinking. The obtained HCL nanocomposites were characterized to evaluate the effect of the NPs. It shows a high degree of crosslinking, a good dispersion of NPs and a surface area up to 1870 ± 20 m²/g. The catalytic activity of the HCL nanocomposite on phenol wet air oxidation was tested at low air pressure (P_air = 0.3 MPa) and temperature (T = 95 °C), and at different phenol concentrations. At the lower phenol concentration, the nanocomposite gives a total organic carbon (TOC) conversion of 97.1%, with a mineralization degree of 96.8%. At higher phenol concentrations, a phenol removal of 99.9%, after 420 min, was achieved, indicating a quasi-complete depletion of phenol, with a TOC conversion of 86.5%, corresponding to a mineralization degree of 84.2%. Catalyst fouling was evaluated, showing good reusability of the obtained nanocomposite.

Catalytic wet oxidation of high concentration pharmaceutical wastewater with Fe3+ as catalyst

Catalytic wet oxidation of high concentration pharmaceutical wastewater with Fe³⁺ as catalyst was carried out in a batch reactor. Results showed that the degradation of pharmaceutical wastewater was enhanced significantly by Fe³⁺. The effects of reaction parameters, such as the catalyst dose, reaction temperature, time, and initial oxygen pressure, were discussed. The chemical oxygen demand (COD) removal increased with the increases of catalyst dose, temperature, time and oxygen supply. With the initial COD 34,000-35,000 mg/L, approximately 70% COD removal can be achieved under the conditions of catalyst 1.0 g and oxygen pressure 1.0 MPa at 250 °C after 60 min. The results of kinetic studies showed that two reaction steps existed in this oxidation process, which followed an apparent first-order rate law. This process provides an effective approach for the pretreatment of high concentration pharmaceutical wastewater.

Synthesis and application of pillared clay heterogeneous catalysts for wastewater treatment: a review

The use of pillared interlayered clays (PILCs) as heterogenous catalysts in wastewater treatment technologies, particularly advanced oxidation processes (AOPs), is gaining popularity for the treatment of refractory wastewater effluents. The recent literature involving these solid materials is reviewed, with more focus on studies that aim at reducing the synthesis costs and escalating the synthesis process to industrial scale. Their role as active solid materials in the AOPs such as photocatalysis, catalytic wet peroxide oxidation (CWPO), the Fenton process and catalytic wet air oxidation (CWAO) of refractory organic compounds in polluted aqueous streams is also reviewed. These processes are evaluated to evidence their main direction for future research, particularly with reference to possible industrial use of these technologies to treat refractory organic wastewater using pillared clay-based catalysts. The pillared clay catalysts demonstrate good application prospects for the removal of refractory wastewater effluents using AOP technology. The reviewed studies suggest that the photocatalytic process is useful in low concentrations of these compounds, while CWPO, the Fenton process and CWAO are recommended for higher concentrations. However, catalyst development to reduce the severity of oxidation reaction conditions, with focus on the low cost, catalyst stability, reusability and environmental friendliness are the key aspects to be addressed by future research work.

Highly efficient degradation of high-loaded phenol over Ru–Cu/Al2O3 catalyst at mild conditions

Ru–Cu/Al₂O₃ catalysts were prepared via co-impregnation method and used for catalytic wet oxidation of highly concentrated phenol under mild conditions.

δ-MnO2 with an ultrahigh Mn4+ fraction is highly active and stable for catalytic wet air oxidation of phenol under mild conditions

The self-reactivated δ-MnO₂ catalyst was developed, and showed high activity and stability for the CWAO of phenol at a very low temperature.

Catalytic wet air oxidation of high-concentration organic pollutants by upflow packed-bed reactor using a Ru–Ce catalyst derived from a Ru3(CO)12 precursor

The low loading Ru–Ce catalyst have high activity in CWAO due to a strong interaction with the support.

Wet oxidation of sewage sludge: full-scale experience and process modeling

Nowadays, sewage sludge management represents one of the most important issues in wastewater treatment. Within the European project "ROUTES," wet oxidation (WO) was proposed for sludge minimization. Four different types of sludge were treated in an industrial WO plant: (1) municipal primary sludge (chemical oxygen demand COD: 73.0 g/L; volatile suspended solid VSS: 44.1 g/L); (2) secondary sludge from an industrial wastewater treatment plant (WWTP) without primary sedimentation (COD: 71.8 g/L; VSS: 34.2 g/L); (3) secondary sludge from a mixed municipal and industrial WWTP without primary sedimentation (COD: 61.9 g/L; VSS: 38.7 g/L); and (4) mixed primary (70%) and secondary (30%) municipal sludge (COD: 81.2 g/L; VSS: 40.6 g/L). The effect of process parameters (temperature, reaction time, oxygen dosage) on WO performance was investigated. Depending on operating conditions, VSS and COD removal efficiency varied in the range 80-97% and 43-71%, respectively. A correlation between process efficiency and the initial VSS/TSS (total suspended solids) ratio was highlighted. Furthermore, a mathematical model of WO process for simulating VSS and COD profiles was developed.

Catalytic wet oxidation of aqueous methylamine: comparative study on the catalytic performance of platinum-ruthenium, platinum, and ruthenium catalysts supported on titania

Promotion of the dispersion of Ru species supported on TiO2 was achieved by introduction of Pt component and the role of Pt in enhancing the catalytic performances of Pt-Ru was investigated with catalytic wet air oxidation of methylamine used as a probing reaction. It was found that Pt-Ru/TiO2 displayed a much better catalytic performance compared with Pt/TiO2 and Ru/TiO2 catalysts due to having the highest dispersion of active species. Both high total organic carbon conversion and nitrogen selectivity (∼100%) over Pt-Ru/TiO2 catalyst were achieved at low temperature (200 °C). X-ray photoelectron spectroscopy characterization indicated that there were strong interactions between metal particles and the support, which may increase the catalytic performance of catalysts.

Treatment of municipal landfill leachate by catalytic wet air oxidation: Assessment of the role of operating parameters by factorial design

The wet air oxidation (WAO) of municipal landfill leachate catalyzed by cupric ions and promoted by hydrogen peroxide was investigated. The effect of operating conditions such as WAO treatment time (15-30min), temperature (160-200°C), Cu(2+) concentration (250-750mgL(-1)) and H(2)O(2) concentration (0-1500mgL(-1)) on chemical oxygen demand (COD) removal was investigated by factorial design considering a two-stage, sequential process comprising the heating-up of the reactor and the actual WAO. The leachate, at an initial COD of 4920mgL(-1), was acidified to pH 3 leading to 31% COD decrease presumably due to the coagulation/precipitation of colloidal and other organic matter. During the 45min long heating-up period of the WAO reactor under an inert atmosphere, COD removal values up to 35% (based on the initial COD value) were recorded as a result of the catalytic decomposition of H(2)O(2) to reactive hydroxyl radicals. WAO at 2.5MPa oxygen partial pressure advanced treatment further; for example, 22min of oxidation at 200°C, 250mgL(-1) Cu(2+) and 0-1500mgL(-1) H(2)O(2) resulted in an overall (i.e. including acidification and heating-up) COD reduction of 78%. Amongst the operating variables in question, temperature had the strongest influence on both the heating-up and WAO stages, while H(2)O(2) concentration strongly affected the former and reaction time the latter. Nonetheless, the effects of temperature and H(2)O(2) concentration were found to depend on the concentration levels of catalyst as suggested by the significance of their 3rd order interaction term.

Heterogeneous catalytic wet air oxidation of refractory organic pollutants in industrial wastewaters: a review

Catalytic wet air oxidation (CWAO) is one of the most economical and environmental-friendly advanced oxidation process. It makes a promising technology for the treatment of refractory organic pollutants in industrial wastewaters. Various heterogeneous catalysts including noble metals and metal oxides have been extensively studied to enhance the efficiency of CWAO. The present review is concerned about the literatures published in this regard. Phenolics, carboxylic acids, and nitrogen-containing compounds were taken as model pollutants in most cases, and noble metals such as Ru, Rh, Pd, Ir, and Pt as well as oxides of Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, and Ce were applied as heterogeneous catalysts. Reports on their characterization and catalytic performances for the CWAO of aqueous pollutants are reviewed. Discussions are also made on the reaction mechanisms and kinetics proposed for heterogeneous CWAO and also on the typical catalyst deactivations in heterogeneous CWAO, i.e. carbonaceous deposits and metal leaching.

Wet air oxidation of epoxy acrylate monomer industrial wastewater

Epoxy acrylate monomer industrial wastewater contained highly concentrated and toxic organic compounds. The wet air oxidation (WAO) and catalytic wet air oxidation (CWAO) were used to eliminate pollutants in order to examine the feasibility of the WAO/CWAO as a pre-treatment method for the industrial wastewater. The results showed that in the WAO 63% chemical oxygen demand (COD) and 41% total organic carbon (TOC) removals were achieved and biological oxygen demand (BOD(5))/COD ratio increased from 0.13 to 0.72 after 3h reaction at 250 degrees C, 3.5MPa and the initial concentration of 100g(COD)/L. Among homogenous catalysts (Cu(2+), Fe(2+), Fe(3+) and Mn(2+) salts), Cu(2+) salt exhibited better performance. CuO catalyst was used in the CWAO of the wastewater, COD and TOC conversion were 77 and 54%, and good biodegradability was achieved. The results proved that the CWAO was an effective pre-treatment method for the epoxy acrylate monomer industrial wastewater.

P-chlorophenol wastewater treatment by microwave-enhanced catalytic wet peroxide oxidation

A microwave-enhanced catalytic wet peroxide oxidation (MW-CWPO) technology was investigated to treat a high concentration of p-chlorophenol wastewater under a mild condition. The MW-CWPO experiments were carried out in a microwave autoclave using copper(II) oxide (CuO)-loaded active carbon as a catalyst. The p-chlorophenol was directly ring-opened within 5 minutes at 343 K and 0.3 MPa and then mineralized to carbon dioxide and water. More than 90% of the total organic carbon was removed within 15 minutes. The reaction activation energy (Ea) of hydrogen peroxide (H2O2) decomposition was decreased from 47.7 to 43.1 kJ/mol under microwave irradiation. The H2O2 catalytic decomposition was fitted to a second-order reaction under microwave irradiation, while it followed a first-order reaction without microwave irradiation. The experimental results indicate that the MW-CWPO method has significant potential applications for a high concentration of p-chlorophenol wastewater.

Concurrent destruction strategy: NaNO2-catalyzed, trichlorophenol-coupled degradation of p-nitrophenol using molecular oxygen

Oxidative degradation of p-nitrophenol (PNP) was investigated with NaNO(2) as the catalyst and dioxygen as the oxidizing agent in the presence of trichlorophenol (TCP). Although degradation of PNP alone was proved to be inefficient toward the NaNO(2)-mediated oxidative degradation system, when PNP in combination with TCP was used as the substrate, NaNO(2) showed relatively high catalytic activity for eradicating both PNP and TCP with molecular oxygen. Reaction conditions to the degradation system, e.g., temperatures, reaction time, pH, NaNO(2) and TCP concentrations were optimized. PNP could be highly efficiently degraded in the NaNO(2)/TCP/O(2) system (more than 99% removal for PNP) and the TOC removal of the mixture of PNP and TCP could reach 71% at 150 degrees C, 0.5 MPa oxygen pressure. Degradation products were determined, and 93% carbon atom was clarified. A plausible overall mechanism for the formation of active species is described, in which peroxylnitrite was believed to be a dominating active intermediate being responsible for destroying the substrates, PNP and TCP. The novel NaNO(2)-based concurrent oxidation system for PNP and TCP provides a potential application in treatment of multi-component industrial effluents.

Technologies for the removal of phenol from fluid streams: a short review of recent developments

The available technologies for the abatement of phenol from water and gaseous streams are briefly reviewed, and the recent advancements summarized. Separation technologies such as distillation, liquid-liquid extraction with different solvents, adsorption over activated carbons and polymeric and inorganic adsorbents, membrane pervaporation and membrane-solvent extraction, have been discussed. Destruction technologies such as non-catalytic, supercritical and catalytic wet air oxidation, ozonation, non-catalytic, catalytic and enzymatic peroxide wet oxidation, electrochemical and photocatalytic oxidation, supercritical wet gasification, destruction with electron discharges as well as biochemical treatments have been considered. As for the abatement of phenol from gases, condensation, absorption in liquids, adsorption on solids, membrane separation, thermal, catalytic, photocatalytic and biological oxidation have also been considered. The experimental conditions and the performances of the different techniques have been compared.

Investigation of the catalytic wet peroxide oxidation of phenol over different types of Cu/ZSM-5 catalyst

In this work oxidation of phenol with hydrogen peroxide on Cu/ZSM-5 catalysts was studied. The catalysts samples were prepared by two different methods: by ionic exchange from the protonic form of commercial ZSM-5 zeolite, and by direct hydrothermal synthesis. Characterization of the catalysts extends to X-ray diffraction (XRD), while the adsorption techniques were used for the measurement of the specific surface area. The catalytic tests were carried out in a stainless steel Parr reactor in batch operation mode at the atmospheric pressure and the temperature range from 50 to 80 degrees C. The mass ratio of the active metal component on the zeolite was in the range of 1.62-3.24 wt.%. for catalyst prepared by direct hydrothermal synthesis and 2.23-3.52 wt.% for catalyst prepared by ion exchange method. The initial concentration of phenol and hydrogen peroxide was 0.01 and 0.1 mol dm(-3), respectively. The influence of different methods of Cu/ZSM-5 preparation on their catalytic performance was monitored in terms of phenol conversion and degree of metal leached into aqueous solution.

Microwave assisted catalytic wet air oxidation of H-acid in aqueous solution under the atmospheric pressure using activated carbon as catalyst

Catalytic wet air oxidation (CWAO) is a promising method for the treatment of heavily contaminated wastewater. However, its application is restricted due to severe operation conditions (high pressure and high temperature). A microwave (MW) assisted oxidation method was investigated aiming to treat heavily contaminated wastewater under milder conditions. H-acid (1-amino-8-naphthol-3, 6-disulfonic acid) was selected as target compound to evaluate the performance of this novel process. The removal of H-acid and TOC (total organic carbon) for H-acid solution of 3000 mg/L reached as high as 92.6% in 20 min and 84.2% in 60 min, respectively under optimal conditions. The existence of activated carbon and oxygen proved to be critical for effective treatment. The activated carbon acted not only as a catalyst for H-acid decomposition, but also as a special material for the absorption of MW energy. Air was supplied to the reactor as an oxygen source at constant flows. The amino group in H-acid was converted ultimately into nitrate, and sulfonic group into sulfate. This observation gave an evidence of H-acid mineralization although other organic intermediates were unable to be determined. The value of BOD(5)/COD (ratio of 5d biochemical oxygen demand to chemical oxygen demand) increased from 0.008 to 0.467 indicating a significant improvement of biodegradability for the solution, which is beneficial for the further biological treatment of the wastewater.