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

Advanced oxidation processes (AOPs) using UV, UV/H2O2, Fenton and photo-Fenton treatment were investigated at laboratory scale for aqueous solutions of 2,4-dichlorophenol (DCP). The effects on degradation of different reactant concentrations, irradiation time, temperature and pH were assessed. DCP removal, TOC mineralization, dechlorination and change in oxidation state were monitored. UV photolysis was less efficient for total DCP degradation than other AOPs. In contrast, photo-Fenton reaction in acidic conditions led to a higher DCP degradation in a short time. Sixty minutes of treatment were sufficient for 100% DCP removal with 75 mg l(-1) H2O2 and 10 mg l(-1) Fe(II) initial concentrations. In these conditions, a first-order degradation constant for DCP of 0.057 min(-1) was obtained.
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PMID:A comparative study of the advanced oxidation of 2,4-dichlorophenol. 1507 20

In this work, a real wastewater (deriving from the chemical-pharmaceutical field) was treated by means of H2O2/UV process under different conditions in a pilot-scale plant. Several methods were used in order to assess the oxidation efficiency and to understand the main reaction features. It was shown that non-conventional COD measurement (with a 75 degrees C digestion of the sample) is helpful for understanding reaction mechanisms, when integrated with TOC and COD analyses and GC-MS determinations. For the biodegradability study, beside BOD (5 and 20 days) measurements, OUR and AUR tests provide additional information especially when wastewater is tested by taking the activated sludge from the treatment plant which should really be fed with it. Finally, dehydrogenase activity measurements can show the presence of complex organic matter, which may be degraded only by an acclimated biomass.
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PMID:How to assess chemical oxidation efficiency. 1507 39

The effect of combining the photocatalytic processes using TiO2 and the photo-Fenton reaction with Fe3+ or ferrioxalate as a source of Fe2+ was investigated in the degradation of 4-chlorophenol (4CP) and dichloroacetic acid (DCA) using solar irradiation. Multivariate analysis was used to evaluate the role of three variables: iron, H2O2 and TiO2 concentrations. The results show that TiO2 plays a minor role when compared to iron and H2O2 in the solar degradation of 4CP and DCA in the studied conditions. However, its presence can improve TOC removal when H2O2 is totally consumed. Iron and peroxide play major roles, especially when Fe(NO3)3 is used in the degradation of 4CP. No significant synergistic effect was observed by the addition of TiO2 in this process. On the other hand, synergistic effects were observed between FeOx and TiO2 and between H2O2 and TiO2 in the degradation of DCA.
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PMID:Evaluation of the combined solar TiO2/photo-Fenton process using multivariate analysis. 1507 71

Because of its potential use as fertilizer, urine ("yellow water") is a resource originating from sanitation. Its separate collection in no-mix toilets is a beneficial aspect of ecological (source control) sanitation. In order to avoid dilution of the fertilizing nutrients with toilet flush water, the utilization of yellow water as toilet flush liquid seems to be advantageous. To be accepted for this purpose, urine has to be decolorized (and also deodorized). In this study activated carbon adsorption, irradiation with UV light of different wavelengths, the advanced oxidation processes ultrasound, UV/H2O2, and photocatalytic oxidation have failed to decolorize urine. Biological treatment caused brown colour of the treated urine. Only ozonation was successful in colour removal, although it did not affect TOC. In spite of darkening of yellow water during biological treatment (generation of humic substances), smaller ozone doses were required for decolorizing the biologically pre-treated urine than for original urine. Photocatalytic oxidation of biologically treated urine also removed brown colour, but the original yellow colour remained. In ozonated urine, yellow colour was reconstituted unless hydrogen peroxide was added. In addition to colour removal, ozone contributed to deodorization as a consequence of ammonia stripping and probably of phenol oxidation.
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PMID:Screening of chemical oxidation processes and other methods for decolorization of urine for its re-use as toilet-flush liquid in ecological sanitation systems. 1507 78

The effect of the photo-Fenton process on biodegradability enhancement of 100 mg x L(-1) aqueous 2,4-dichlorophenol (2,4-DCP) solution has been investigated. An initial concentration of 65 mg x L(-1) H2O2 and 10 mg x L(-1) Fe (II) during 35 minutes of irradiation time was sufficient for total 2,4-DCP removal. At these working conditions, biodegradability, measured as BODS/COD ratio, was increased from 0 for the original solution up to 0.15. Biological oxidation of photo-Fenton pre-treated solutions was performed in a sequencing batch reactor (SBR). After 32 days of start-up, the reactor was fed with different pre-treated solutions and cycle duration was reduced progressively. TOC removal efficiencies in the SBR went from 30 up to 70%.
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PMID:Combining photo-Fenton process with biological sequencing batch reactor for 2,4-dichlorophenol degradation. 1507 86

In this study ozone and the H2O2/O3 oxidation system are used to decolorize aqueous solutions of Orange II (Or-II) and Acid Red 27 (AR-27). Investigations are carried out in a semi-batch bubble column reactor. A system of series-parallel reactions is proposed to describe the mechanism of dye oxidation. The stoichiometric ratio for the first reaction is found to be 1 mol dye per mol O3, while the overall ozone demand for both reactions one and two is found to be 5 and 6 moles for Or-II and AR-27 respectively. Molecular and radical kinetics are compared: a radical scavenger, t-butanol, can be added to ensure only the molecular reaction of ozone, or hydrogen peroxide can be supplied through a peristaltic pump, to initiate radical reactivity. Results reveal that colour removal is ensured by direct ozone attack. For both dyes, TOC removal efficiencies of 50 - 60 % are obtained by the action of the hydroxyl free radical. However, this is not improved by addition of H2O2, thus demonstrating that organic species alone ensure HO degrees radical production during ozonation. Both the mass transfer and the ozone reactivity with the dyes are considered to evaluate the kinetic parameters for the molecular pathway.
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PMID:Oxidation pathways for ozonation of azo dyes in a semi-batch reactor: a kinetic parameters approach. 1517 46

2.5GHz of microwave irradiation can cause a considerable improvement of oxidative decomposition of aqueous phenol in a UV/H2O2 system. The experimental results showed that the microwave irradiation can raise both the phenol conversion and the TOC removal efficiency up to or above 50%. Also, the microwave irradiation could considerably enhance the oxidative degradation of phenol in the UV/H2O2 system even under a suppression of thermal effect. Addition of hydrogen peroxide by more than a stoichiometric amount was critical to mineralize aqueous phenol to create a short reaction time. Also, microwave irradiation can accelerate the degradation rate of intermediates, hydroquinone and catechol, produced in the course of phenol oxidative decomposition. From the kinetic study, the disappearance rate of phenol can be expressed as dX/dt = kPH[M]0(alpha - X)(1 - X), where alpha equivalent [H2O2]0/[M]0 + kOH[OH*]/kPH[M]0, shows a good correlation with the experimental data. The kinetic analysis showed that an indirect reaction of phenol with OH radical might be dominant in the absence of microwave irradiation, meanwhile a direct reaction of phenol with hydrogen peroxide might be dominant in the presence of microwave irradiation except for low concentrations of hydrogen peroxide.
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PMID:Improvement of oxidative decomposition of aqueous phenol by microwave irradiation in UV/H2O2 process and kinetic study. 1520 9

A variety of advanced oxidation processes (AOPs; O3/OH-, H2O2/UV, Fe2+/H2O2, Fe3+/H2O2, Fe2+/H2O2/UV and Fe3+/H2O2/UV) have been applied for the oxidative pre-treatment of real penicillin formulation effluent (average COD0 = 1395 mg/L; TOC0 = 920 mg/L; BOD(5,0) approximately 0 mg/L). For the ozonation process the primary involvement of free radical species such as OH* in the oxidative reaction could be demonstrated via inspection of ozone absorption rates. Alkaline ozonation and the photo-Fenton's reagents both appeared to be the most promising AOPs in terms of COD (49-66%) and TOC (42-52%) abatement rates, whereas the BOD5 of the originally non-biodegradable effluent could only be improved to a value of 100 mg/L with O3/pH = 3] treatment (BOD5/COD, f = 0.08). Evaluation on COD and TOC removal rates per applied active oxidant (AOx) and oxidant (Ox) on a molar basis revealed that alkaline ozonation and particularly the UV-light assisted Fenton processes enabling good oxidation yields (1-2 mol COD and TOC removal per AOx and Ox) by far outweighed the other studied AOPs. Separate experimental studies conducted with the penicillin active substance amoxicillin trihydrate indicated that the aqueous antibiotic substance can be completely eliminated after 40 min advanced oxidation applying photo-Fenton's reagent (pH = 3; Fe(2+):H2O2 molar ratio = 1:20) and alkaline ozonation (at pH = 11.5), respectively.
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PMID:Pre-treatment of penicillin formulation effluent by advanced oxidation processes. 1522 36

This study investigates the effect of mixing intensity and reagents addition strategy on Fenton's reagent degrading a common reactive diazo type dyestuff, Reactive Black 5. Within the experimental conditions used in the study, the effect of mixing intensity on TOC removal was observed to be both significant and complex. Using factorial analysis, it was found that if the reagents are added near to each other, higher mixing intensity will enhance the effectiveness of the degradation process. However, a very, high mixing level may cause reduction in performance. It was also observed that the mixing intensity effect interacts with Fe2+ or/and H2O2 dosage. The benefit of increasing mixing intensity appears to be higher for lower reagents dosage. The effect of reagents addition strategy was found to be inter-dependent with mixing intensity level. It was also deduced that proper chemical addition strategy could be used to reduce the mixing intensity requirement of the process.
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PMID:Fenton oxidation of Reactive Black 5: effect of mixing intensity and reagent addition strategy. 1524 35

Organic pollutants can be sonodegraded by two pathways: pyrolysis, oxidation by free radicals, or the combination of both. The sonolytic degradation mechanisms and byproducts formation of aqueous trihalomethanes (THMs) were investigated at acoustic frequency of 20 kHz. The main sonodegradation mechanism of the chloroform, dichlorobromomethane, dibromochloromethane, and bromoform was found to be pyrolysis. The sonolysis degradation pathway of iodoform is free radicals oxidation. Hydrogen peroxide, nitrate, chloride, bromide, iodide, and iodate ions were detected and quantified as the inorganic products of the THMs sonication. A total of 48% TOC removal was achieved after a 180-min sonication of the THMs mixture.
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PMID:Mechanisms and inorganic byproducts of trihalomethane compounds sonodegradation. 1548 96


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