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Query: UMLS:C1835664 (TOC)
 2,763 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Degradation of 20 different dyes in aqueous solutions by the Fenton process was performed. These dyes include 6 types: acidic, reactive, direct, cationic, disperse and vat dyes. The former four types of dyes were decolorized and their TOC values were decreased greatly, while the color and TOC removals of the latter two types were lower. The catalytic activities of four metal ions on the degradation efficiencies of Vat Blue BO, which was chosen as a model dye because of its lowest color and TOC removals, were compared in the dark and under the ultraviolet light irradiation. The catalytic ability of different metals was Fe2+>Cu2+>Mn2+>Ag+ in the dark, and the same sequence was obtained under irradiation condition with greater degradation efficiency. Furthermore, the efficiencies of three oxidation processes, including H2O2/UV, Fe2+/H2O2 and Fe2+/H2O2/UV were compared. The results showed that the oxidation by Fe2+/H2O2/UV was the strongest, and even greater than the arithmetic sum of the other two processes, which suggests the synergistic effect of ultraviolet and ferrous ions on the degradation reaction.
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PMID:Degradation of dyes in aqueous solutions by the Fenton process. 1548 21

The photocatalytic removal kinetics of fenitrothion at a concentration of 0.5mgl(-1) in pure and natural waters were investigated in Fe(III)/H2O2/UV-Vis, Fe(III)/UV-Vis and H2O2/UV-Vis oxidation systems, with respect to decreases in fenitrothion concentrations with irradiation time using a solar simulator. Fenitrothion concentrations were determined by HPLC analysis. Furthermore, total mineralization of fenitrothion in these systems was evaluated by monitoring the decreases in DOC concentrations with solar simulator irradiation time by TOC analysis. It was shown that the degradation rate of fenitrothion was much faster in the Fe(III)/H2O2/UV-Vis system than the Fe(III)/UV-Vis and H2O2/UV-Vis systems in both pure and river waters. Consequently, the mineralization rate of fenitrothion was much faster in the Fe(III)/H2O2/UV-Vis system than in the other two systems. The high *OH generation rate measured in the Fe(III)/H2O2/UV-Vis system was the key to faster degradation of fenitrothion. Increases in the concentrations of H2O2 and Fe led to better final degradation of fenitrothion. These results suggest that the photo-Fenton reaction (Fe(III)/H2O2/UV-Vis) system is likely to be an effective method for removing fenitrothion from contaminated natural waters.
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PMID:Photocatalytic removal of fenitrothion in pure and natural waters by photo-Fenton reaction. 1548 26

The removal of pollutants in saline medium by the Fenton's reagent needs a more detailed investigation, since the presence of chloride may inhibit or retard degradation. Phenol was used as a model pollutant and the influence of some important process variables for the removal of total organic carbon and phenol were investigated, such as FeSO4 and H2O2 concentrations, pH and salinity. The reactivity of iron cations and alternative procedures of applying UV radiation (photo-Fenton) were evaluated. Phenol was fast and completely removed by the Fenton's process even in a high saline medium (50,000mg NaCll(-1)). However, TOC was only moderately or poorly removed in saline media, depending on the salt concentration. When the photo-Fenton process was used, mineralization was improved and high TOC removals were observed in moderately saline media (NaCl concentration < or =10,000mgl(-1)). For the highest NaCl concentration tested (50,000mgl(-1)) only a moderate TOC removal was observed (50%).
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PMID:Phenol removal from high salinity effluents using Fenton's reagent and photo-Fenton reactions. 1548 34

With the aim to evaluate the effect of temperature, 4-chloro-3-methyl phenol (CMP) degradation by Fenton's reagent was investigated at 25 and 70 degrees C under the following initial conditions: [CMP]0 = 10 mM, [Fe2+]0 = 0.5 mM; ([H2O2]0/[CMP]0) = 80, pH0 = 3. The results indicated that CMP degradation was strongly influenced by temperature. In fact, the maximum TOC removal, achieved after ca. 24h, was by far greater at 70 degrees C (85%) than at 25 degrees C (36%). The same happened for organic chlorine (TOX) conversion into inorganic chloride, i.e. 100%, after 3 h at 70 degrees C, and 87%, after 27 h at 25 degrees C. As the recorded trends of CMP removal and chloride formation were basically the same, hydroxy substitution (ipso-substitution) was hypothesised as one likely mechanism of CMP degradation. The higher level of mineralization recorded at 70 degrees C was ascribed to: (i) a greater *OH concentration; (ii) a consequently greater extent of CMP oxidation to organic acids; (iii) a higher decarboxylation rate of such acids. An interesting consequence of such extended organic acids decarboxylation was a pH increase up to 8 that, in turn, caused, in the treated mixture, the decomposition of excess H2O2 as well as the precipitation of iron ions. These two latter outcomes are technologically important considering that usually, before discharging Fenton treated wastewater, specific polishing steps are required just to remove iron ions, decompose excess hydrogen peroxide and neutralise the pH.
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PMID:Temperature activated degradation (mineralization) of 4-chloro-3-methyl phenol by Fenton's reagent. 1576 92

The viability of the degradation of aqueous solutions of aniline, nitrobenzene, and 4-chlorophenol by the so-called Photoelectro-Fenton process in a pilot reactor is reported. The Electro-Fenton process stage, based on the flow of oxygen through a gas diffusion cathode to produce H2O2, allows mineralization of about a half of the TOC content in ca. 1 h, because anodic oxidation is coupled with Fenton reaction in the presence of Fe2+ catalyst. An intensity of 20 A was applied in a flow cell comprising a Ti/Pt anode and a carbon-PTFE cathode. After electrolysis, samples of the effluent were exposed to sunlight, and almost complete mineralization was reached after ca. 50 min. Effect of parameters such as electrolysis time, pH, initial concentration, and solar or UVA irradiation on the process efficiencies and the running costs are studied. The Photoelectro-Fenton process using sunlight effectively diminishes these costs. The analogous behavior of the three aromatics suggests similar degradation pathways, regardless of the different groups attached to the ring.
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PMID:Mineralization of aromatics in water by sunlight-assisted electro-fenton technology in a pilot reactor. 1581 45

In this paper we evaluated the H2O2/UV and the Fenton's oxidation processes for the treatment of tannery wastewater under different experimental conditions. Efficiencies were judged by the amounts of organic substances degraded or eliminated under these treatment techniques. Daphnia magna and Vibrio fischeri were used to monitor toxicity. Organic compounds contained in the untreated and treated tannery wastewater were determined and identified using substance specific techniques. Gas chromatography-mass spectrometry (GC-MS) in positive electron impact (EI(+)) mode was applied to determine volatile organics. Atmospheric pressure ionization (API) mass (MS) and tandem mass spectrometry (MS-MS) coupled with flow injection analysis (FIA) or liquid chromatography (LC) were used to detect or identify polar organic pollutants. The experimental results indicated that both oxidation processes--H2O2/UV at pH 3 and Fenton at pH 3.5--are able to reduce TOC content by mineralisation of the organic compounds.
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PMID:Applicability of Fenton and H2O2/UV reactions in the treatment of tannery wastewaters. 1596 3

This paper reports an investigation on the performance of the H2O2 electrogeneration process on a rotating RVC cylinder cathode, and the optimization of the O2 reduction rate relative to cell potential. A study for the simultaneous oxidation of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) by the in situ electrogenerated H2O2 is also reported. Experiments were performed in 0.3 M of K2SO4, pH of 10 and 3.5. Oxygen concentration in solution was kept in 25 mg L(-1). Maximum hydrogen peroxide generation rate was reached at -1.6 V versus SCE for both, acidic and alkaline solutions. Then, 100 mg L(-1) of 2,4-D was added to the solution. First order apparent rate constants for 2,4-D degradation ranged from 0.9 to 6.3x10(-5) m s(-1), depending on the catalyst used (UV or UV+Fe(II)). TOC reduction was favored in acidic medium where a decreasing of 69% of the initial concentration was observed in the process catalyzed by UV+Fe(II). This figure was an indication that some of the intermediates derived from 2,4-D decomposition remained in solution, mainly as lighter aliphatic compounds.
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PMID:Oxidation of pesticides by in situ electrogenerated hydrogen peroxide: study for the degradation of 2,4-dichlorophenoxyacetic acid. 1670 13

The presence of disinfection byproducts (DBPs) such as trihalomethanes (THMs) and haloacetic acids (HAAs) in drinking water is of great concern due to their adverse effects on human health. Emerging regulation limiting the concentration of DBPs in drinking water has increased demands for technologies and processes which reduce the formation of DBPs in drinking water. In this study, UV-H2O2 based advance oxidation process (AOP) was used to treat raw surface water. Experiments were conducted using low pressure mercury vapor UV lamps in collimated beam and flow-through annular photoreactors. The effect of UV fluence (0-3500 mJ cm(-2)) and hydrogen peroxide concentration (0-23 mg l(-1)) in reducing the concentration of THMs and HAAs was examined. The UV-H2O2 AOP was then coupled with a downstream biological activated carbon (BAC) treatment to assess the synergetic benefits of combining the two treatments. It was observed that UV-H2O2 AOP was only effective at reducing DBPs at UV fluences of more than 1000 mJ cm(-2) and initial H2O2 concentrations of about or greater than 23 mg l(-1). However, the combined AOP-BAC treatment showed significant reductions of 43%, 52%, and 59% relative to untreated raw water for DBPs, TOC, and UV254, respectively.
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PMID:UV-H2O2 based AOP and its integration with biological activated carbon treatment for DBP reduction in drinking water. 1709 44

Nitrobenzene (NB) was selected as the model pollutant in water and the efficiency and mechanism of degradation of NB in aqueous solution by O3/H2O2 were investigated. The effects of pH, H2O2 dose and the inhibitor or accelerant of .OH on the removal rate of NB were studied. H2O2 could obviously improve the ozonation decay rate of NB when the pH value of the solution was below 7. The removal rate of NB was enhanced remarkably while H2O2 dose was increased from 1.0 m g/L. to 4.0 mg/L. However, as H2O2 dose increased from 4.0 mg/L to 20 mg/L, the removal efficiency of NB decreased. Different quantities of H2O2 were yielded in different reaction phases of single ozonation system. Both systems of single ozonation and H2O2-catalysed ozonation could not reduce TOC observably. During the NB degradation process, organonitrogen was almost completely converted to nitrate and the pH value of the solution reduced significantly. Results of LC-MS and GC-MS analysis showed that the main intermediate products were phenolic compounds and carbonyl compounds. A possible reaction pathway of the catalytic ozonation of NB was also proposed. It was found that the catalytic ozonation of NB could be divided into two steps. First, hydroxyl radical attacked phenyl ring to form phenolic compounds, then the ring was opened, forming into various aliphatic compounds or being mineralized to inorganic compounds.
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PMID:[Effect and mechanism of degradation of nitrobenzene in aqueous solution by O3/H2O2]. 1711 34

This study reports an investigation into the degradation of 2,4-dichlorophenoxyacetic acid in bubble contactor column by O3/H2O2 process, which is widely used as a principal advanced oxidation process. The degradation of 2,4-dichlorophenoxyacetic acid was studied under different H2O2/03 molar ratio and pH value. Meanwhile, TOC removal was investigated both in distilled water and tap water. The influences of ozone transfer and consumed hydrogen peroxide were also discussed. The degradation products and oxidation intermediates were identified by GC-MS and LC-MS. A possible reaction mechanism was thus proposed.
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PMID:Degradation of 2,4-dichlorophenoxyacetic acid in water by ozone-hydrogen peroxide process. 1729 39


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