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Humic acids were used to simulate natural organic compounds in water for the investigation of DMP oxidation by three different AOPs (advanced oxidation processes) of UV-H2O2, O3 and UV-O3. The results showed that pseudo-first-order reaction equation could describe the oxidation of DMP by UV-H2O2 perfectly, which was strongly affected humic acids in water. The relationship between pseudo-first-order reaction rate and TOC value could be expressed as K = 0. 162 0 [TOC]-0.8171. It was also found that humic acids in the water exhibited obvious influence on the oxidation of DMP by UV-O3. However, effect of humic acids on the oxidation of DMP by ozone was not obvious. It was also analyzed that oxidation of DMP was dominated by ozone oxidation both in ozonation process and UV-O3 process; the importance of "OH in the oxidation of DMP was enhanced as the concentration of DMP decreased in UV-O3 process. The degree of impact form humic acids towards different AOPs could be ranked in a decreasing order as UV-H2O3, UV-O3, 03.
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PMID:[Effects of organic pollutants in drinking water on the removal of dimethyl phthalate by advanced oxidation processes]. 1730 47

Nitrobenzene, glycolic acid and acetic acid were selected to be degraded by O3/UV. During the degradation of nitrobenzene by O3/ UV, addition of MnO2, an effective catalyst to decompose H2O2 in water, decreased the degradation efficiency obviously, and the degradation efficiency of O3 /UV was even lower than that of ozonation alone, for example, the TOC removal rates of nitrobenzene by O3 /UV, O3 and O3/UV + MnO2 were 44% , 41% and 39% in 40 minutes, respectively. These results demonstrate that intermediate H2O2 plays an important role in enhancement of degradation efficiency of O3/UV. Furthermore, the characteristic of organic, which acts as promoter or inhibitor in the process of ozonation, also affects the degradation efficiency of O3/UV directly, when glycolic acid, a promoter in ozonation, was degraded, the combination UV radiation with ozonation could remove it efficiency, the removal rate of glycolic acid reached 76% in 30 minutes; however, when acetic acid, an inhibitor in ozonation, was degraded by O3/UV, the removal rate of acetic acid was very low, which was similar with that of ozonation alone.
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PMID:[Study on the mechanism of ozonation of organic combination with UV radiation]. 1748 94

Simple measurements of H2O2 concentration or CO2 evolution were used to evaluate the effectiveness of the use of Fenton's reagent to mineralize organic compounds in water and soil contaminated by crude petroleum. This methodology is suitable for application in small treatment and remediation facilities. Reagent concentrations of H2O2 and Fe(2+) were found to influence the reaction time and temperature, as well as the degree of mineralization and biodegradability of the sample contaminants. Some H2O2/Fe(2+) combinations (H2O2 greater than 10% and Fe(2+) greater than 50mM) resulted in a strong exothermic reaction, which causes peroxide degradation and violent gas liberation. Up to 75% TOC removal efficiency was attained in water and 70% in soil when high H2O2 (20%) and low Fe(2+) (1mM) concentrations were used. Besides increasing the degree of mineralization, the Fenton's reaction enhances the biodegradability of petroleum compounds (BOD5/COD ratios) by a factor of up to 3.8 for contaminated samples of both water and soil. Our experiments showed that low reagent concentrations (1% H2O2 and 1mM Fe(2+)) were sufficient to start the degradation process, which could be continued using microorganisms. This leads to a decrease in reagent costs in the treatment of petroleum-contaminated water and soil samples. The simple measurements of H2O2 concentration or CO2 evolution were effective to evaluate the Fenton's reaction efficiency.
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PMID:A simple methodology to evaluate influence of H2O2 and Fe(2+) concentrations on the mineralization and biodegradability of organic compounds in water and soil contaminated with crude petroleum. 1749 49

The aim of the present work is to study a coupled system to treat biorecalcitrant wastewaters. The combination consists of an advanced oxidation process (AOP) named photo-Fenton (Ph-F), which is a photochemical treatment and a sequencing batch biofilter reactor (SBBR). The synthetic wastewater used to optimise this process is a solution of 200 ppm of 4-chlorophenol (4-CP). The first part of the work is the study of the biodegradability enhancement achieved by the photochemical process, measured as the ratio between the biochemical oxygen demand (BOD5) and the chemical oxygen demand (COD). The second step is the start-up and optimisation of the biological process. The results showed that it is necessary to severely treat the toxic solution (with 500 ppm of [H2O2]0) in order to achieve more than 90% of TOC removal in the whole process. The photochemical and biological treatments lasted 50 minutes and 24 hours, respectively.
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PMID:Coupled photochemical-biological system to treat biorecalcitrant wastewater. 1767 33

Two advanced oxidation processes (AOPs), ozonation and photo-Fenton, combined with a pilot aerobic biological reactor at field scale were employed for the treatment of industrial non-biodegradable saline wastewater (TOC around 200 mgL(-1)) containing a biorecalcitrant compound, alpha-methylphenylglycine (MPG), at a concentration of 500 mgL(-1). Ozonation experiments were performed in a 50-L reactor with constant inlet ozone of 21.9 g m(-3). Solar photo-Fenton tests were carried out in a 75-L pilot plant made up of four compound parabolic collector (CPC) units. The catalyst concentration employed in this system was 20 mgL(-1) of Fe2+ and the H2O2 concentration was kept in the range of 200-500mgL(-1). Complete degradation of MPG was attained after 1,020 min of ozone treatment, while only 195 min were required for photo-Fenton. Samples from different stages of both AOPs were taken for Zahn-Wellens biocompatibility tests. Biodegradability enhancement of the industrial saline wastewater was confirmed (>70% biodegradability). Biodegradable compounds generated during the preliminary oxidative processes were biologically mineralised in a 170-L aerobic immobilised biomass reactor (IBR). The global efficiency of both AOP/biological combined systems was 90% removal of an initial TOC of over 500 mgL(-1).
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PMID:Advanced oxidation process-biological system for wastewater containing a recalcitrant pollutant. 1767 53

A comparative study of O3 alone and O3/H2O2 was made to evaluate their respective effectiveness for removal of persistent organic pollutants (POPs) from water with 4, 4'-dibro minated biphenyl (4, 4'-DBB) as the model pollutant, and UV254 was used as the surrogate parameter for TOC and DOC. It was found that both processes enhanced the removal rate. Especially, it has been made a further enhancement of the removal of 4, 4'-DBB as H2O2 was added under the alkaline-condition. The final removal rate of 4 mg/L 4, 4'-DBB solution reached 78.0% after reacting for 270 min, while the UV254 value varies with the removal rate and reached 76.9%-77.8% ultimately. It means that the total organic carbon has been removed obviously. Two kinds of solution of different concentration with the same amount of oxidant reacting for the same time have been compared with each other and the results showed that the higher the initial concentration was, the smaller the removal rate was, however, the more the absolute amount could be removed. It was also found that 4, 4'-DBB's removal followed pseudo-first order reaction and the promoted factor f for 4, 4'-DBB removal rate constant was about 1.54.
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PMID:[Treatment of 4, 4'-dBB in aqueous solution using O3/H2O2 system and its synergetic kinetics]. 1799 May 46

Tannic acid, being polyhydroxyl, is a macromolecule natural organic matter. The efficiency and mechanism of degradation of tannic acid by O3 and O3/H2O2 was studied. The results showed that the addition of H2O2 had no obvious improvement on the ozonation efficiency of tannin. It was observed that the addition of H2O2 decreased the removal efficiency of TOC by 10%. The relative intensity of .OH generated in the O3-H2O2 system was detected by electronic spin resonance (ESR) and it was found that tannin consumed the .OH radicals, which may be associated with the polyhydroxyl structure of tannin. Derived with PFBBr and analysed by GC-ECD, the by-products of tannin ozonation were found to be aldehydes such as acetaldehyde, glyoxal and methyl glyoxal. Analysis with an ion chromatogram showed that the final products of tannin were oxalic acid, ketomalonic acid and oxalic acid, which consisted of 35% of TOC in both systems.
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PMID:Degradation of macromolecular tannic acid by O3/H2O2. 1858 96

The oxidation of 10 nonionic surfactants (6 alcohol ethoxylates and 4 alkylphenol ethoxylates) by Fenton and H2O2/UV processes was investigated in synthetic (deionized water) and real aqueous matrices, i.e. secondary effluent from municipal wastewater treatment plant and groundwater. Batch tests were carried out to assess the optimal dosages of reagents leading to the total removal of surfactants. Regardless to the specific surfactant, both Fenton and H2O2/UV treatments of synthetic solutions containing one single surfactant (C0=14 mg l(-1)) always caused its rapid and quantitative removal (96-99%) with a corresponding very low (0-18%) TOC decrease. Only for the Fenton treatment, linear relationships were found between the amounts of H2O2 and Fe2+ necessary for surfactant removal and the ethoxy chain length of each surfactant. Conversely, in the case of H2O2/UV treatment the H2O2 dosage causing the quantitative oxidation of the treated surfactant depended on the length of both chains: the ethoxy and the hydrophobic one. Mixtures of the 10 surfactants (1.4 mg l(-1) each) were treated in both synthetic and real matrices. These latter were different in the case of Fenton (i.e. municipal secondary effluent) or H2O2/UV (i.e. real groundwater) treatments. Fenton treatment of municipal secondary effluent containing the surfactants mixture led to its total removal when a molar ratio [Total surfactants]/[H2O2]/[Fe2+] equal to 1/17/12 was used. As for H2O2/UV treatment of real groundwater samples, quantitative removal of surfactants mixture was achieved with a molar ratio [Total surfactants]/[H2O2] equal to 1/7.4. Surfactants mixture removals, if compared in deionized water and in real matrices, showed the same matrix effect during both treatments, i.e. less amounts of reagents were always required in synthetic solutions.
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PMID:Oxidation of nonionic surfactants by Fenton and H2O2/UV processes. 1861 47

The simulative wastewater containing Acid Orange 7 (AO7) of 300 mg/L was electrolytically treated by a three-phase three-dimensional electrode reactor. Particular attention was paid on the comparison of treatment efficiency of different cathodes in the system. Intermediate products and concentration of *OH and H2O2 were further investigated using HPLC, UV-Vis scan and GC-MS, with the purpose of investigating the electrolysis behavior of AO7 with different cathodes. Results showed that activated carbon fiber (ACF) cathode was more effective than graphite or stainless steel cathode. Despite all of the three investigated cathodes showed high efficiency in the decolorization of AO7 (more than 96% after 60 min of electrolysis under 20 V), the TOC removal ratio of ACF system (57.4%) was much higher than those of the other two. Although the generation of *OH and H2O2 were both found in the three systems, the concentration in the system with ACF as the cathode was much higher than those in the other two, which resulted in the better mineralization ability. Moreover, the same degradation route of AO7 was found in the three systems, which involved the generation of ketone and naphthol compounds.
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PMID:[Effect of cathode material on electrolytic treatment of Acid Orange 7 by a three-phase three-dimensional electrode reactor]. 1863 43

A comparative study between two advanced oxidation technologies for pollutant degradation has been made. With the use of dichloroacetic acid (DCA) as the model pollutant, the reactions with hydrogen peroxide and UV radiation (H2O2/UV, 253.7 nm) and photocatalysis with titanium dioxide (TiO2/UV, 300-400 nm) are analyzed. Three criteria have been selected to compare the performances of both processes: (i) the percentage conversion of DCA and TOC (total organic carbon) at a fixed reaction time; (ii) the quantum efficiency, employing the true radiation absorption rates for both activated species (H2O2 and TiO2); (iii) the specific energy consumption to degrade 50% of the initial TOC. The optimal molar concentration ratio of H2O2/DCA and the optimal catalyst concentration have been employed in the experiments. The results indicate that, under the optimal operating conditions, the H2O2/UV process exhibits, by a large difference, the best performance taking into account the above-mentioned criteria. Nevertheless, both systems show similar values of specific energy consumption when a thinner reactor is employed. These results cannot be safely extrapolated to other contexts if (i) other compounds of different structure are degraded and (ii) a different catalyst is used. Moreover, they were obtained under optimized conditions, and typical, real-life situations may render quite different results due to the robustness of the titanium dioxide operation. They should serve as an indication that, under the studied conditions, a much-improved catalyst performance must be achieved to parallel, with a heterogeneous process, a yield similar to the one obtained with the homogeneous system.
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PMID:Comparison of H2O2/UV and heterogeneous photocatalytic processes for the degradation of dichloroacetic acid in water. 1876 87


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