Decolorization and Modeling of Synthetic Wastewater Using O3 and H2O2/O3 Processes

This research deals with the decolorization of synthetic wastewater, prepared with the acid 1:2 metal-complex textile dye C.I. Acid Blue 193, using the ozonation (O₃) and H₂O₂/O₃ processes. To minimize the number of experiments, they were performed using the 2^k factorial design. Five influential parameters were examined: initial dye concentration, ozone flow rate, initial pH value, decolorization time and H₂O₂ addition. The decolorization efficiency was 95% in 20 minutes (pH = 7; O₃ flow rate of 2 g/L.h) and a higher increase in the toxicity after the ozonation process (39%) indicates the formation of carcinogenic by-products. According to the variance test analysis, the initial dye concentration, the ozone flow rate, the initial pH value and the decolorization time and their first- and second-order interactions are significant, while the H₂O₂ addition was not important with respect to the discussed range. With the help of these significant factors a regression model was constructed and the adequacy of the model was checked. The obtained regression polynomial was used to model the relation between the absorbance and the influential parameters by fitting the response surface. This response surface may be used to predict the absorbance result from a set of influential parameters, or it can be rearranged in such a way as to predict the set of process decolorization parameters necessary to reduce the absorbance of wastewater with the given initial dye concentration, below the prescribed limit. It is also shown that the 2^k factorial design can be suitable for predicting the operating expenses of the ozonation.     

Reduction of Biocide-Polluted Wastewater Using O3 and H2O2/O3 Oxidation Processes

The objective of the presented study was to test various oxidation processes with the aim being to reduce the concentration and toxicity of biocide wastewater from a Slovenian phytopharmaceutical factory. Laboratory-scale experiments employing two AOP processes – ozonation (O₃) and peroxone (H₂O₂/O₃) – were applied to reduce the concentration of the active components involved, i.e., methylisothiazolone (MI), chloromethylisothiazolone (CMI) and dichloromethylisothiazolone (DCMI). The reduction of the biocide wastewater load for the performed oxidation processes was evaluated using ecological parameters. The H₂O₂/O₃ oxidation procedure using an O₃ flow rate of 1g/L h, at a pH value of 10 and with the addition of 5 ml of H₂O₂ (0.3 M) proved to be the most effective treatment. The toxicity of the biocide-load wastewater with an initial EC₅₀ = 0.38%, decreased to EC₅₀ (24h) >100% and EC₅₀ (48h) = 76%.     

Horizontal Flow Filtration Bed: Impact on Removal of Natural Organic Matter and Iron Co-Existing in Water Source

Removal of natural organic matter and iron co-existing in water source is a challenge and a major problem in the developing world where the most commonly applied process in water treatment is pre-chlorination which results in early formation chlorinated by-products. Results from this study proved that horizontal roughing filter system with natural pumice is a promising option for pre-treatment of such waters. The filter recorded average reductions of total and ferrous iron of 39% and 89%, respectively, and trihalomethanes formation potential of 35% after 1 hour and 29% after 6 hours along the filter. Further reductions of 49% and 61% were achieved when the pretreated water was subjected to coagulation.     

The Synergistic Effect of Adsorption-Photocatalysis for Removal of Organic Pollutants on Mesoporous Cu2V2O7/Cu3V2O8/g-C3N4 Heterojunction

Cu₂V₂O₇/Cu₃V₂O₈/g-C₃N₄ heterojunctions (CVCs) were prepared successfully by the reheating synthesis method. The thermal etching process increased the specific surface area. The formation of heterojunctions enhanced the visible light absorption and improved the separation efficiency of photoinduced charge carriers. Therefore, CVCs exhibited superior adsorption capacity and photocatalytic performance in comparison with pristine g-C₃N₄ (CN). CVC-2 (containing 2 wt% of Cu₂V₂O₇/Cu₃V₂O₈) possessed the best synergistic removal efficiency for removal of dyes and antibiotics, in which 96.2% of methylene blue (MB), 97.3% of rhodamine B (RhB), 83.0% of ciprofloxacin (CIP), 86.0% of tetracycline (TC) and 80.5% of oxytetracycline (OTC) were eliminated by the adsorption and photocatalysis synergistic effect under visible light irradiation. The pseudo first order rate constants of MB and RhB photocatalytic degradation on CVC-2 were 3 times and 10 times that of pristine CN. For photocatalytic degradation of CIP, TC and OTC, it was 3.6, 1.8 and 6.1 times that of CN. DRS, XPS VB and ESR results suggested that CVCs had the characteristics of a Z-scheme photocatalytic system. This study provides a reliable reference for the treatment of real wastewater by the adsorption and photocatalysis synergistic process.     

Decomposition and oxidation of CH3 13CH2OH on A12O3, Pd/Al2O3, and PdO/Al2O3 catalysts

Temperature-programmed desorption (TPD) and oxidation (TPO) were used to investigate the decomposition and oxidation of ethanol on Al₂O₃, Pd/Al₂O₃, and PdO/Al₂O₃. Ethyl--¹³C alcohol (CH₃ ¹³CH₂OH) was adsorbed on the catalysts so that reaction pathways of the two carbons could be distinguished. Alumina was mainly a dehydration catalyst, but dehydrogenation was also observed and some carbon remained on the surface. In the presence of O₂, A1₂O₃ oxidized the decomposition products and the-carbon was oxidized faster. Ethanol, which was adsorbed on A1₂O₃, decomposed much faster on Pd/A1₂O₃ by diffusing to Pd and undergoing CO elimination to form CH₄,¹³CO, H₂, and surface carbon. On PdO/A1₂O₃, the decomposition was slower than on Pd/A1₂O₃ until lattice oxygen was extracted above 450 K; the decomposition products were oxidized by lattice oxygen. In the presence of gas phase O₂, Pd/Al₂O₃ was an active oxidation catalyst at low temperature, but lattice oxygen had to be extracted from PdO/A1₂O₃ before it had significant oxidation activity.     

Reduction of lean NOx by ethanol over Ag/Al2O3 catalysts in the presence of H2O and SO2

The reduction of lean NOx using ethanol in simulated diesel engine exhaust was carried out over Ag/Al₂O₃ catalysts in the presence of H₂O and SO₂. The Ag/Al₂O₃ catalysts are highly active for the reduction of lean NOx by ethanol but the reaction is accompanied by side reactions to form CH₃CHO, CO along with small amounts of hydrocarbons (C₃H₆, C₂H₄, C₂H₂ and CH₄) and nitrogen compounds such as NH₃ and N₂O. The presence of H₂O enhances the NOx reduction while SO₂ suppresses the reduction. The presence of SO₂ along with H₂O suppresses the formation of acetaldehyde and NH₃. By infrared spectroscopy, it was revealed that the reactivity of NCO species formed in the course of the reaction was greatly enhanced in the presence of H₂O. The NCO species readily reacts with NO in the presence of O₂ and H₂O at room temperature, being converted to N₂ and CO₂ (CO). Addition of SO₂ suppresses the formation of NCO species and lowers the reactivity of the NCO species. However, the reduction of NOx is still kept at high conversion levels in the presence of H₂O and SO₂ over the present catalysts. About 80% of NOx in the simulated diesel engine exhaust was removed at 743 K. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis and photocatalytic properties of H2La2Ti3O10/TiO2 intercalated nanomaterial

H₂La₂Ti₃O₁₀/ TiO₂ intercalated nanomaterial was fabricated by successive intercalation reactions of H₂La₂Ti₃O₁₀ with n-C₆H₁₃NH₂/C₂H₅OH mixed solution and acid TiO₂ sol, followed by irradiating with a high-pressure mercury lamp. The intercalated materials possess a gallery height of 0.46 nm and a specific surface area of 31.58 m²·g⁻¹, which indicate the formation of a porous material. H₂La₂Ti₃O₁₀/TiO₂ shows photocatalytic activity for the decomposition of organic dye under irradiation with visible light and the activity of TiO₂ intercalated material was superior to the unsupported one.     

Fe(III)/H2O2-Like System for Removal of Azo Dye from Aqueous Solution

Fe(III)/H₂O₂ system is an effective method for separating the organic compounds from aqueous solution, whereas it is often investigated under lower pH conditions. In order to improve performance of the system, a Fe(III)/H₂O₂-like system that was composed of iron-based coagulant and H₂O₂ was developed, which has the combined effect of flocculation and oxidation. The system when used for decolorization of an organic azo dye solution, Procion Red MX-5B, under wider pH range, indicated higher decolorization efficiency. Parameters affecting the decolorization such as coagulant dosage, H₂O₂ concentration, initial solution pH, temperature, and initial dye concentration were examined in this study. The results indicated that with appropriate coagulant dosage, H₂O₂ concentration, and pH, it was more effective for the decolorization, especially in a weak alkaline environment (pH = 7-8); the pseudo-first-order kinetics could express the azo dye concentration as a function of the reaction time. This study further illustrated that the azo dye solution was degraded to a degree with 53.22% TOC removal at an initial total TOC concentration of 14.92 mg/L. Overall, the established system in this study was favorable to the decolorization of soluble azo dye.     

Effects of space velocity on methanol synthesis from Co2/Co/H2 over Cu/ZnO/Al2O3 catalyst

The space velocity had profound and complicated effects on methanol synthesis from CO₂/CO/H₂ over Cu/ZnO/Al₂O₃ at 523 K and 3.0MPa. At high space velocities, methanol yields as well as the rate of methanol production increased continuously with increasing CO₂ concentration in the feed. Below a certain space velocity, methanol yields and reaction rates showed a maximum at CO₂ concentration of 5–10%. Different coverages of surface reaction intermediates on copper appeared to be responsible for this phenomenon. The space velocity that gave the maximal rate of methanol production also depended on the feed composition. Higher space velocity yielded higher rates for CO₂/ H₂ and the opposite effect was observed for the CO/H₂ feed. For CO₂/CO/H₂ feed, an optimal space velocity existed for obtaining the maximal rate.     

Ozone-Based Technologies for Parabens Removal from Water: Toxicity Assessment

Ozone was tested for the detoxification of a mixture of five parabens. A combined O₃/H₂O₂ process was optimized leading to up to 50% of COD removal in 15 min, while less than 50 min were needed to achieve total degradation. The toxic effect of the raw mixture and after 15 min of treatment by O₃/H₂O₂ was evaluated using V. fischeri and C. fluminea and it was observed a strong detoxification after 15 min of oxidation. Moreover, while the raw effluent promoted the formation of reactive oxygen species in Wistar rat brain slices, no changes were observed after the O₃/H₂O₂ treatment.     

Trapping of CH3O formed from CO + H2

Methoxy formed on Al₂O₃ from¹³CO and H₂ coadsorption on Ni/Al₂O₃ was trapped by C₂H₅OH adsorption and temperature-programmed reaction (TPR). The presence of excess C₂H₅OH significantly increases the rate of¹³CH₃OH and (¹³CH₃)₂O formation. The¹³CH₃OH forms by the reaction of C₂H₅OH with¹³CH₃O on Al₂O₃. In the absence of C₂H₅OH,TPR following¹³CO and H₂ coadsorption did not produce significant amounts of¹³CH₃OHor(¹³CH₃)₂O.     

UV/H2O2 Treatment: A Practical Solution for Organic Contaminant Control and Primary Disinfection

PWN's water treatment plant Andijk was commissioned almost 40 years ago. It services water from the IJssel Lake by conventional surface water treatment. In view of taste and odor problems the plant was retrofitted with GAC filtration 25 years ago. The finished water quality still complies with all E.C. and Dutch drinking water standards. Nevertheless an upgrade is desired to avoid the use of chlorine and to extend the barriers against pathogenic micro-organisms and a broad range of organic micropollutants such as pesticides, rocket fuel by-products (NDMA), fuel oxygenates (MTBE), solvents (dioxane), endocrine disruptors, algae toxins, pharmaceuticals, etc. UV/H₂O₂ treatment was selected for both primary disinfection and organic contaminant control. The disinfection requirements were based on a 10^?4 health risk. The required 3 log inactivation for Giardia and Cryptosporidium was achieved by an UV dose lower than 20 mJ/cm². The highest UV dose, 105 mJ/cm², was needed for the inactivation of spores of Sulphite Reducing Clostridia. Reactivation of protozoa was established for UV doses up to 25 mJ/cm², for doses higher than 45 mJ/cm² no reactivation was observed. In view of the raw water concentrations the required organic contaminant degradation was set at 80%. Collimated beam and pilot-plant work showed that the required degradation can be achieved by the proper combination of electric energy and H₂O₂. In a UV reactor optimized for organic contaminant control, UV dose of 540 mJ/cm² (about 0.5 kWh/m³) and 6 mg/L H₂O₂ were needed. Under those conditions pesticides (atrazine), NDMA, MTBE, dioxane, endocrine disruptors (bisphenol A), microcystine and pharmaceuticals (diclofenac, ibuprofen) could be removed up to the required 80%. Bromate formation was absent while formation of primary metabolites was insignificant. The UV dose for organic contaminant control is about five times higher than the dose needed for disinfection. The UV/H₂O₂ process was implemented into the existing treatment train between the sand and GAC filters. In the GAC filters excess H₂O₂ is degraded, nitrite is converted into nitrate and biodegradable reaction products are consumed by bacteria. The full-scale installation with 3 streets of 4 Trojan Swift 16L30 reactors has been in operation since October 2004. Disinfection and organic contaminant control are as expected.     

Effective Coke Removal in Methane to Benzene (MTB) Reaction on Mo/HZSM-5 Catalyst by H2 and H2O Co-addition to Methane

The catalytic dehydro-aromatization reaction over Mo/HZSM-5 catalyst was drastically stabilized by the co-addition of 5.4% H₂ and 1.8% H₂O to methane feed at 750 °C, 0.3 MPa and methane space velocity of 3000 mL g⁻¹ h⁻¹, suppressing the coke formation effectively, compared with single hydrogen or steam addition.     

31-P NMR study study of acidic sites on Al2O3 and Al2O3-SnO2 after reaction with CCl2F2/H2

The surface acidic properties of two series of samples,-Al₂O₃ and-Al₂O₃-SnO₂ after reaction with CCl₂F₂/H₂ (CFC12/H₂), have been investigated by solid state high resolution CP/MAS 31-PNMR, using trimethylphosphine (TMP) as a probe molecule. It was found after reaction, that Brønsted acid sites were formed on the-Al₂O₃ surface. The longer the reaction time, the more rigidly TMP bonded to the acid sites. For the-Al₂O₃-SnO₂ system, Brønsted acid sites were also found on both the Al₂O₃ and SnO₂ surfaces after reaction of the-Al₂O₃-SnO₂ system with CFC12/H₂. The signal intensity relevant to these sites, indicates that the SnO₂ component is attached to, and therefore covers Brønsted sites of-Al₂O₃. Two types of Lewis acid site initially present on SnO₂ were not observed after reaction with CFC12/H₂.     

Isotope effect of H2/D2 and H2O/D2O for the PROX reaction of CO on the FeOx/Pt/TiO2 catalyst

The oxidation reaction of CO with O₂ on the FeOx/Pt/TiO₂ catalyst is markedly enhanced by H₂ and/or H₂O, but no such enhancement occurs on the Pt/TiO₂ catalyst. Isotope effects were studied by H₂/D₂ and H₂O/D₂O on the FeOx/Pt/TiO₂ catalyst, and almost the same magnitude of isotope effect of ca. 1.4 was observed for the enhancement of the CO conversion by H₂/D₂ as well as by H₂O/D₂O at 60 °C. This result suggests that the oxidation of CO with O₂ via such intermediates as formate or bicarbonate in the presence of H₂O, in which H₂O or D₂O acts as a molecular catalyst to promote the oxidation of CO as described below.      

On the development of metallic particles and their initial catalytic properties in the CO + H2 reaction over Co/Al2O3 catalyst

Formation of Co^o phases with different surface structure over 10 wt% Co/Al₂O₃ and their catalytic properties were induced by pretreatments in H₂ at 570 K for 1 h or 20 h. Electronic behaviour of the Co^o phase, which consists of small (after 1 h reduction) or large bulk-like particles (after 20 h reduction), did not change during the CO hydrogenation after 5 h on stream as was determined by XPS. On the basis of the measured C₂₊ hydrocarbon selectivities the CO molecules are suggested to dissociate on small Co particles to a larger extent than on large cobalt particles. The slight decrease in the catalytic activity with increasing time on stream obtained for the long-term reduced sample is explained by the change in the surface Co^o content detected by XPS. The increase in the catalytic activity along with the change in olefin selectivity, measured for the sample reduced for 1 h, is interpreted by the change of a reaction path involving the Co^o-support interface during the initial period of the reaction.     

ZnO/Cr2O3 catalyst for reverse-water-gas-shift reaction of CAMERE process

The stability and the activity of Fe₂O₃/Cr₂O₃ and ZnO/Cr₂O₃ catalysts were examined for a reverse-watergas-shift reaction (RWReaction). The initial activities of those catalysts were quite high so that the conversion reached close to equilibrium. The activity of Fe₂O₃/Cr₂O₃ catalyst decreased from 33.5 to 29.8% during the RWReaction for 75 h at 873 K with GHSV (ml/gcat · h) of 100,000. Moreover, the coke formation on the Fe₂O₃/Cr₂O₃ catalyst caused clogging in the RWReactor of the CAMERE process. On the other hand, the ZnO/Cr₂O₃ catalyst showed no coke formation and no deactivation for the RWReaction at 873 K with GHSV (ml/gcat · h) of 150,000. The ZnO/Cr₂O₃ was a good catalyst for the RWReaction of the CAMERE process.     

Activity and stability of Cu/ZnO/Al2O3 catalyst promoted with B2O3 for methanol synthesis

The addition of B₂O₃ to a Cu/ZnO/Al₂O₃ catalyst increased the activity of the catalyst for methanol synthesis after an induction period during the reaction. The stability of the B₂O₃-containing Cu/ZnO/Al₂O₃ catalyst was greatly improved by the addition of a small amount of colloidal silica to the catalyst. This revised version was published online in July 2006 with corrections to the Cover Date.     

Changes in Ba Phases in BaO/Al2O3 upon Thermal Aging and H2O Treatment

The effects of thermal aging and H₂O treatment on the physicochemical properties of BaO/Al₂O₃ (the NO_x storage component in the lean NO_x trap systems) were investigated by means of X-ray diffraction (XRD), BET, TEM/EDX and NO₂ TPD. Thermal aging at 1000 °C for 10 h converted dispersed BaO/BaCO₃ on Al₂O₃ into low surface area crystalline BaAl₂O₄. TEM/EDX and XRD analysis showed that H₂O treatment at room temperature facilitated a dissolution/reprecipitation process, resulting in the formation of a highly crystalline BaCO₃ phase segregated from the Al₂O₃ support. Crystalline BaCO₃ was formed from conversion of both BaAl₂O₄ and a dispersed BaO/BaCO₃ phase, initially present on the Al₂O₃ support material after calcinations at 1000 and 500 °C, respectively. Such a phase change proceeded rapidly for dispersed BaO/BaCO₃/Al₂O₃ samples calcined at relatively low temperatures with large BaCO₃ crystallites observed in XRD within 10 min after contacting the sample with water. Significantly, we also find that the change in barium phase occurs even at room temperature in an ambient atmosphere by contact of the sample with moisture in the air, although the rate is relatively slow. These phenomena imply that special care to prevent the water contact must be taken during catalyst synthesis/storage, and during realistic operation of Pt/BaO/Al₂O₃ NO_x trap catalysts since both processes involve potential exposure of the material to CO₂ and liquid and/or vapor H₂O. Based on the results, a model that describes the behavior of Ba-containing species upon thermal aging and H₂O treatment is proposed.     

In situ synthesis,mechanical and cyclic oxidation properties of Ti3AlC2/Al2O3 composites

ABSTRACT

Ti₃AlC₂/Al₂O₃ composite materials were successfully fabricated from TiO₂/TiC/Ti/Al powders by the in situ reactive hot pressed technique. The microstructure, mechanical and oxidation properties of the composites were investigated in the paper. Vickers hardness increased with the Al₂O₃ content. The relative density of Ti₃AlC₂/Al₂O₃ composites exhibits a declining tendency with Al₂O₃ content especially exceeds 10 vol.?%. The Ti₃AlC₂/Al₂O₃ composites show excellent electrical conductivity. The flexural strength and fracture toughness of Ti₃AlC₂/10 vol. % Al₂O₃ are 461 ± 20?MPa and 6.2?±?0.2?MPa m^1/2, respectively. The cyclic oxidation behaviour of resistance of Ti₃AlC₂/10 vol. % Al₂O₃ composites at 800–1000°C generally obeys a parabolic law. The oxide scale of sample consists of a mass of α-Al₂O₃ and TiO₂, forming a dense and adhesive protect layer. The result indicates that the Al₂O₃ can greatly improve the oxidation resistance of Ti₃AlC₂.