Influence of inorganic ions on MTBE degradation by Fenton's reagent

The effect of selected inorganic anions on the effectiveness of the Fenton advanced oxidative treatment of waters contaminated with methyl t-butyl ether (MTBE) was examined. With respect to the chloride or phosphate ions used, inhibition of oxidation was clearly in evidence, whereas addition of sulfates or perchlorates influenced these rates to a much smaller extent. Anions suppress MTBE decomposition in the following sequence: ClO4- 相似文献   

Optimization of the azo dye Procion Red H-EXL degradation by Fenton's reagent using experimental design

Chemical oxidation by Fenton's reagent of a reactive azo dye (Procion Deep Red H-EXL gran) solution has been optimized making use of the experimental design methodology. The variables considered for the oxidative process optimization were the temperature and the initial concentrations of hydrogen peroxide and ferrous ion, for a dye concentration of 100mg/L at pH 3.5, the latter being fixed after some preliminary runs. Experiments were carried out according to a central composite design approach. The methodology employed allowed to evaluate and identify the effects and interactions of the considered variables with statistical meaning in the process response, i.e., in the total organic carbon (TOC) reduction after 120 min of reaction. A quadratic model with good adherence to the experimental data in the domain analysed was developed, which was used to plot the response surface curves and to perform process optimization. It was concluded that temperature and ferrous ion concentration are the only variables that affect TOC removal, and due to the cross-interactions, the effect of each variable depends on the value of the other one, thus affecting positively or negatively the process response.     

Degradation of carbon tetrachloride by modified Fenton's reagent

The degradation of tetrachloromethane (carbon tetrachloride-CT) by modified Fenton's reagent (catalyzed hydrogen peroxide) was investigated using a range of hydrogen peroxide concentrations and 1 mM iron(III) catalyst. The documented reactive species in modified Fenton's reactions, hydroxyl radical (OH*), is not reactive with CT, yet CT degradation was observed in the Fenton's reactions and was confirmed by chloride generation. Because CT is not reactive with OH*, a reductive mechanism which may involve superoxide radical anion is proposed for CT degradation in modified Fenton's systems. Scavenging of reductants by excess chloroform prevented CT degradation, confirming a reductive mechanism. Similar to CT, three other oxidized aliphatic compounds, hexachloroethane, bromotrichloromethane, and tetranitromethane, were also degraded by modified Fenton's reagent. The results show that modified Fenton's reactions act through a reductive mechanism to degrade compounds that are not reactive with OH*, which broadens the scope of this process for hazardous waste treatment and remediation.     

Pre-oxidation of an extremely polluted industrial wastewater by the Fenton's reagent

The pre-oxidation of an extremely polluted pharmaceutical wastewater (chemical oxygen demand (COD) value of 362,000mg/l) using the Fenton's reagent has been systematically studied using an experimental design technique. The parameters influencing the COD removal of the wastewater, namely temperature, ferrous ion and hydrogen peroxide concentrations have been optimized to achieve a COD global reduction of 56.4%.The total range of the proposed experimental design, however, could not be tested because under some conditions (hydrogen peroxide concentration over 5M) the Fenton's reaction became violent and could not be controlled, probably due to the high exothermic effect associated with COD oxidation. For the tested conditions, the optimal values of hydrogen peroxide and ferrous ion concentration were 3 and 0.3M, respectively, whereas temperature only showed a mild positive effect on COD removal. In addition, during the first 10min of Fenton's reaction, more than 90% of the total COD removal can be achieved.Fenton's reaction has proved to be a feasible technique for the pre-oxidation of the wastewater under study, and can be considered a suitable pre-treatment for this type of wastewaters.     

Removal of Acid Orange 7 from water by electrochemically generated Fenton's reagent

The removal of azo dye Acid Orange 7 (AO7) from water was investigated by the electro-Fenton technology using electrogenerated hydroxyl radicals (OH) which leads to the oxidative degradation of AO7 up to its complete mineralization. H(2)O(2) and Fe (II) ions are electrogenerated in a catalytic way at the carbon-felt cathode. AO7 decay kinetics and evolution of its oxidation intermediates were monitored by high-performance liquid chromatography. The absolute rate constant of AO7 hydroxylation reaction has been determined as (1.20+/-0.17)x10(10)M(-1)s(-1). The optimal current value for the degradation of AO7 was found as 300 mA. AO7 degradation rate was found to decrease by increase in Fe(3+) concentration beyond 0.1mM. Mineralization of AO7 aqueous solutions was followed by total organic carbon (TOC) measurements and found to be 92%. Based on TOC evolution and identification of aromatic intermediates, short-chain carboxylic acids and inorganic ions released during treatment, a plausible mineralization pathway was proposed.     

Gallic acid degradation in aqueous solutions by UV/H2O2 treatment, Fenton's reagent and the photo-Fenton system

Gallic acid (3,4,5-trihydroxybenzoic acid) is a major pollutant present in the wastewater generated in the boiling cork process, as well as in other wastewaters from food manufacturing industries. Its decay in aqueous solutions has been studied by the action of several oxidation systems: monochromatic UV radiation alone and combined with hydrogen peroxide, Fenton's reagent and the combination Fenton's reagent with UV radiation (photo-Fenton system). The influence of the pH is discussed and the quantum yields are determined in the UV radiation system. Also, the influence of operating variables (initial concentrations of H2O2 and Fe(II), and pH) is established in the Fenton's reaction. The apparent pseudo-first-order rate constants are evaluated in all the experiments conducted in order to compare the efficiency of each one of the processes. Increases in the degradation levels of gallic acid are obtained in the combined processes in relation to the single UV radiation system, due to reactions of the very reactive OH*. These improvements are determined in every process by calculating the partial contribution to the overall decomposition rate of the radical pathways. For the oxidant concentrations applied, the most effective process in removing gallic acid was found to be the photo-Fenton system. The rate constant for the reaction of gallic acid with OH was also determined by means of a competition kinetics model, being its value 11.0+/-0.1 x 10(9)l mol(-1)s(-1).     

A comparative study of ultrasonic cavitation and Fenton's reagent for bisphenol A degradation in deionised and natural waters

Bisphenol A (BPA), a xenobiotic that exhibits endocrine disrupting action can be found in surface water. Its complete elimination can be obtained by advanced oxidation processes, notably upon the application of ultrasonic waves. In order to evaluate the feature of ultrasound relevance and the involvement of the hydroxyl radical in the BPA sonochemical degradation, ultrasound action was compared to Fenton's reaction in the cases of deionised acidic water (pH 3) and natural water (pH 7.6, main ions concentration: Ca(2+)=486mgL(-1), Na(+)=9.1mgL(-1), Cl(-)=10mg L(-1), SO(4)(2-)=1187mgL(-1), HCO(3)(-)=402mgL(-1)). Ultrasound was performed at 300kHz and 80W. Fenton's process was operated using ferrous sulphate (100micromolL(-1)) and continuous H(2)O(2) addition at the rate as it is produced when sonication is applied in water in absence of substrate. Experiments carried out in deionised water show that both processes exhibit identical BPA elimination rate and identical primary intermediates. Main chemical pathways involve reactions with OH radical. Chemical oxygen demand (COD) and total organic carbon (TOC) analyses show that the Fenton's process is slightly more efficient than ultrasonic treatment for the removal of BPA by-products in the case of deionised water. Experiments conducted in natural water evidenced the inhibition of the Fenton process while the ultrasound action was not hampered.     

Treatment of landfill leachate by Fenton's reagent in a continuous stirred tank reactor

The treatment of landfill leachate by Fenton process was carried out in a continuous stirred tank reactor (CSTR). The effect of operating conditions such as reaction time, hydraulic retention time, pH, H(2)O(2) to Fe(II) molar ratio, Fenton's reagent dosage, initial COD strength, and temperature on the efficacy of Fenton process was investigated. It is demonstrated that Fenton's reagent can effectively degrade leachate organics. Fenton process reached the steady state after three times of hydraulic retention. The oxidation of organic materials in the leachate was pH dependent and the optimal pH was 2.5. The favorable H(2)O(2) to Fe(II) molar ratio was 3, and organic removal increased as dosage increased at the favorable H(2)O(2) to Fe(II) molar ratio. Temperature gave a positive effect on organic removal.     

Phenanthrene and pyrene oxidation in contaminated soils using Fenton's reagent

Fenton's reagent has shown its applicability to oxidizing these biorefractory organic contaminants. The purpose of this contribution was to investigate the influence of operating parameters on the process efficiency for soil highly contaminated by PAHs. Five variables were selected: pH, reaction time, UV irradiation, hydrogen peroxide concentration and Fe (II) amendment. Their effects on the oxidation of (i) phenanthrene and on (ii) phenanthrene and pyrene present in freshly contaminated soil samples were studied through batch reactor experiments following factorial designs. For phenanthrene oxidation run with a soil contaminated at 700 mg kg(-1), one set of variables enabled us to reach a residual concentration lower than 40 mg kg(-1) (Dutch legislation threshold). The most important factor was the reaction time, followed at a certain distance by UV irradiation, Fe (II), H(2)O(2) concentration and pH, this last variable being the least significant. The possibility of operating without pH adjustment is of importance in the treatment at the field scale. This shows the feasibility of photo-Fenton-like oxidation for the treatment of soil highly contaminated with PAH and the relative importance of the process variables.     

Optimisation of Fenton's reagent usage as a pre-treatment for fermentation brines

Pre-treatment of fermentation brines from green olives has been carried out by the Fe(II)/Fe(III)/H(2)O(2) system. Reagent concentration exerted a positive influence on chemical oxygen demand (COD) removal. Hydrogen peroxide uptake showed values in the range 0.3-1.6mol of COD eliminated per mol of H(2)O(2) consumed depending on operating conditions. The optimum working pH was found to be in the interval 2.0-3.5. Reaction temperature increased the COD degradation rate, although similar COD conversion values were obtained after 5h of treatment regardless of the value of this parameter. An analysis of the biodegradability of this type of effluent demonstrated the beneficial effect of the chemical pre-oxidation. According to the experimental results, it is suggested that there is an inhibitory effect of the wastewater due to its COD content and nature rather than attributable to the presence of high amounts of sodium chloride. Biodegradation efficiency increased as temperature was raised up to 30 degrees C. A further increase of this parameter up to 40 degrees C resulted in the death of the microorganisms.     

Petroleum oxidation using Fenton's reagent over beach sand following a spill

Removal and oxidation of petroleum adhered onto the beach sand after a spill over Guanabara Bay in Rio de Janeiro (Brazil) have been studied using Fenton's reagent (Fe2+ + H2O2). Jar tests were done on 5 and 20 g sand suspended in 200 ml aqueous solution containing iron(II) salt and hydrogen peroxide under constant stirring. The H2O2(g):Fe(g)2+ ratio varied from 0.5:1 to 50:1, pH was 2.0 and 6.0 and reaction time 1 and 3 h. Initially, the contaminated sand content of oil and grease (O&G) was 32 g/kg sand. The statistical analysis showed time and iron-sand and H2O2-iron-sand interactions to be the most significant variables, with an average O&G removal from the contaminated sand being just 30% after 3 h reaction. However, oil was removed from the sand (by up to 97%) and passed to the aqueous phase, making waste final disposal easier. The post-reaction analysis showed the supernatant to be biodegradable. Chromatographic analysis results were that the Fenton's reaction favored both the change and reduction of oil saturated and aromatic fractions.     

Model applications and mechanism study on the degradation of atrazine by Fenton's system

Atrazine (ATZ), 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine, was effectively degraded by hydroxyl radicals that were generated by FeII/H2O2 in the Fenton's process. Up to 98% ATZ removal can be achieved in the process if the doses of FeII and H2O2 are selected appropriately. Oxidation capacity of the process was successfully predicted through a kinetic approach with three simple and measurable parameters (i.e., two rate constants and a break point time), which makes the model useful in predicting, controlling and optimizing the degradation of ATZ. In addition, the transformation pathways of ATZ decay was successfully investigated by using a novel technology, liquid chromatography electrospray tandem mass spectrometry (LC/ESI-MS/MS). Ten intermediates were identified in the process. The alkylic-oxidation followed by dealkylation and/or dechlorination-hydroxylation were found to be the major pathways of the decay of ATZ in Fenton's process. All the detected intermediates were found to be dealkylated in different levels or positions. The dealkylated species may be further dechlorinated but generally at a lower fraction (<10%) due to the depletion of oxidants.     

Determination of total mercury in water and urine by a gold film sensor following Fenton's reagent digestion

Fenton's reagent (Fe(II) + H2O2) is utilized for the digestion of environmental water samples and urine. Following the digestion, which converts organic forms of Hg to inorganic Hg(II), Hg(0) is liberated by borohydride reduction and measured by a conductometric gold film sensor. Quantitative recovery of Hg from samples spiked with mercuric chloride, methylmercury(II) chloride, and phenylmercury(II) acetate was attainable in the presence of naturally occurring suspended matter and humic and fulvic acids as well as 3% NaCl. The digestion is performed at moderate pH (3-4) and temperature (less than or equal to 50 degrees C) and does not use large amounts of any reagent. Excellent agreement is shown for reference water, wastewater, and urine standards. The limit of detection, facilitated by the low blank value, is 500 pg of Hg or 10 ng/L for a 50-mL sample.     

The mechanism and applicability of in situ oxidation of trichloroethylene with Fenton's reagent

Fenton's reagent is the result of reaction between hydrogen peroxide (H(2)O(2)) and ferrous iron (Fe(2+)), producing the hydroxyl radical (-*OH). The hydroxyl radical is a strong oxidant capable of oxidizing various organic compounds. The mechanism of oxidizing trichloroethylene (TCE) in groundwater and soil slurries with Fenton's reagent and the feasibility of injecting Fenton's reagent into a sandy aquifer were examined with bench-scale soil column and batch experiment studies. Under batch experimental conditions and low pH values ( approximately 3), Fenton's reagent was able to oxidize 93-100% (by weight) of dissolved TCE in groundwater and 98-102% (by weight) of TCE in soil slurries. Hydrogen peroxide decomposed rapidly in the test soil medium in both batch and column experiments. Due to competition between H(2)O(2) and TCE for hydroxyl radicals in the aqueous solutions and soil slurries, the presence of TCE significantly decreased the degradation rate of H(2)O(2) and was preferentially degraded by hydroxyl radicals. In the batch experiments, Fenton's reagent was able to completely dechlorinate the aqueous-phase TCE with and without the presence of soil and no VOC intermediates or by-products were found in the oxidation process. In the soil column experiments, it was found that application of high concentrations of H(2)O(2) with addition of no Fe(2+) generated large quantities of gas in a short period of time, sparging about 70% of the dissolved TCE into the gaseous phase with little or no detectable oxidation taking place. Fenton's reagent completely oxidized the dissolved phase TCE in the soil column experiment when TCE and Fenton's regent were simultaneously fed into the column. The results of this study showed that the feasibility of injecting Fenton's reagent or H(2)O(2) as a Fenton-type oxidant into the subsurface is highly dependent on the soil oxidant demand (SOD), presence of sufficient quantities of ferrous iron in the application area, and the proximity of the injection area to the zone of high aqueous concentration of the target contaminant. Also, it was found that in situ application of H(2)O(2) could have a gas-sparging effect on the dissolved VOC in groundwater, requiring careful attention to the remedial system design.     

Degradation of EDTA and novel complexing agents in pulp and paper mill process and waste waters by Fenton's reagent

Fenton's process was used in oxidative degradation of ethylediaminetetraacetic acid (EDTA) and novel complexing agents, namely BCA5 and BCA6, in distilled water and spiked samples of integrated pulp and paper mill waste water and ECF-pulp bleaching effluent. In waste water, over 90% of EDTA was degraded within 3 min when temperature was 60 degrees C, pH 4, and molecular ratio of H2O2:Fe2+:EDTA was 70:2:1 (0.26 mM EDTA) or higher. In spiked ECF bleaching effluent up to 42% of EDTA was degraded in similar reaction conditions, still higher than published results indicate biological waste water treatment of pulp and paper mill waste water being capable of. In pH 3, EDTA proved readily degradable by Fenton's process in otherwise similar conditions. According to these results, Fenton's process could be used as a pre-treatment method for EDTA-containing bleaching effluents prior to the biological waste water treatment. In addition, BCA5 and BCA6 proved their superiority in terms of degradability also by Fenton's process in both pH 3 and 4.     

A combined treatment approach using Fenton's reagent and zero valent iron for the removal of arsenic from drinking water

Studies on the development of an arsenic remediation approach using Fenton's reagent (H2O2 and Fe(II)) followed by passage through zero valent iron is reported. The efficiency of the process was investigated under various operating conditions. Potable municipal water and ground water samples spiked with arsenic(III) and (V) were used in the investigations. The arsenic content was determined by ICP-QMS. A HPLC-ICPMS procedure was used for the speciation and determination of both As(III) and (V) in the processed samples, to study the effectiveness of the oxidation step and the subsequent removal of the arsenic.The optimisation studies indicate that addition of 100 microl of H2O2 and 100 mg of Fe(II) (as ferrous ammonium sulphate) per litre of water for initial treatment followed by passing through zero valent iron, after a reaction time of 10 min, is capable of removing arsenic to lower than the US Environmental Protection Agency (EPA) guideline value of 10 microg/l, from a starting concentration of 2 mg/l of As(III). Using these suggested amounts, several experiments were carried out at different concentrations of As(III). Residual hydrogen peroxide in the processed samples can be eliminated by subsequent chlorination, making the water, thus, processed, suitable for drinking purposes. This approach is simple and cost effective for use at community levels.     

流态化预氧化PAN基纤维性能的研究

采用流态化预氧化技术对PAN基纤维进行预氧化实验,并对不同工艺方案下制得的预氧丝进行了氧含量、体密度、XRD、红外光谱等测试与分析。纤维经45min流态化预氧化后氧含量达到10.1%,体密度达到1.38g/cm3,XRD、红外光谱结果显示纤维发生了环化、脱氢的化学反应和组织结构变化,最终转变为耐热的梯形结构。实验结果说明,通过进一步优化工艺,流态化预氧化技术可以在保证预氧化质量的同时,大幅缩短预氧化时间,降低生产成本。     

Enhanced TiO2 photocatalytic degradation of bisphenol E by beta-cyclodextrin in suspended solutions

Enhancement of beta-cyclodextrin (beta-CD) on TiO(2) photocatalytic degradation of bisphenol E (BPE, bis(4-hydroxyphenyl)ethane) was investigated under a 250 W metal halide lamp (lambda> or =365 nm) in this work. In the system of photocatalytic degradation of BPE, the photodegradation rate of BPE in aqueous solutions containing beta-CD and TiO(2) was obviously faster than that in aqueous solutions containing only TiO(2). After 40 min of irradiation, beta-CD could increase the photodegradation efficiency by about 26% for 10 mg l(-1) BPE in the UV-vis/TiO(2) system and the photodegradation of 2.5-20.0 mg l(-1) BPE in aqueous solutions was found to follow pseudo-first-order law and the adsorption constant and the reaction rate constant of BPE in the system containing beta-CD and TiO(2) are obviously higher than those in the system containing only TiO(2), the influence factors on photodegradation of BPE were studied and described in details, such as beta-CD concentration, pH, BPE initial concentration and gas medium. The formation of CO(2) as a result of mineralization of BPE was observed during the photodegradation process. After 120 min of irradiation, the mineralization efficiency of BPE reached 61% in the presence of beta-CD, whereas mineralization efficiency was only 23% in the absence of beta-CD. The enhancement of photodegradation of BPE could be dependent on the enhancement of adsorption of BPE on TiO(2) surface and moderate inclusion-depth of BPE in the beta-CD cavity.     

Effect of sequestration on PAH degradability with Fenton's reagent: roles of total organic carbon,humin, and soil porosity

The phenomenon of contaminant sequestration—and the physicochemical soil parameters which drive this process—has recently been studied by several authors with regard to microbial contaminant degradation. Very little work has been done to determine the effects of contaminant sequestration on the chemical treatability (oxidizability) of soil contaminants; the current study was conducted to address this data gap. A suite of six model soils, ranging in organic matter content from 2.32 to 24.28%, were extensively characterized. Measured parameters included: (1) levels of total organic carbon (TOC); (2) contents of humic acid (HA); fulvic acid (FA) and humin; and (3) total porosity and surface area. Each soil was then spiked with coal tar and, after varying periods of aging/sequestration, subjected to slurry-phase Fenton’s reagent oxidation. Percent recoveries of 12 PAHs, ranging from 3 to 6 aromatic rings, were determined. Results indicated that the susceptibility of each PAH to chemical oxidation was a function of TOC in four of the soils (those with TOC greater than approximately 5%), but was strongly dependent on soil porosity for low-TOC soils. The importance of these two parameters changed with increasing sequestration time, with the relative contribution of porosity-mediated sequestration becoming more important over time. Porosity-mediated effects were more rapid and significant with lower-molecular-weight PAHs (e.g. those with three or four aromatic rings) than with higher-molecular-weight, more hydrophobic compounds. These observations are discussed in light of current physicochemical models of the contaminant sequestration process.