Experimental and numerical study of methylparaben decomposition in aqueous solution using the UV/H2O2 process

The present paper aims at presenting a kinetic model that is supposed to result in the decomposition of methylparaben in completely mixed batch reactor (CMBR) using the UV/H₂O₂ process. The proposed model incorporates photochemical, chemical reactions and their constant rates to formulate the overall kinetic rate expressions which are integrated into MATLAB. Thus, the changes in pH values during the process of oxidation are taken into consideration. In addition, the effects of hydrogen peroxide (HP) dosage, as well as the concentration of hydroxyl radicals, are examined. Accordingly, the pseudo-first-order rate constant, its variation as functions of HP concentration, incident UV-light intensity and the limitations of the adopted approach are discussed. In line with that, the authors provided evidence of the validity of the kinetic model through the exposure of previous experimental studies as reported in the literature review then through the evidence of the present experimental data.     

Critical effect of hydrogen peroxide concentration in photochemical oxidative degradation of C.I. Acid Red 27 (AR27)

The photochemical decolorization of C.I. Acid Red 27 (AR27), an anionic monoazo dye, was studied in the UV/H2O2 process by using a batch reactor with a UV-C lamp emitting at 254 nm (30 W). The decolorization rate follows pseudo-first order kinetic with respect to the AR27 concentration. The results indicate that the apparent reaction rate constant in the UV/H2O2 process is a function of H2O2 concentration. In this work, a mathematical relation between the apparent reaction rate constant of the AR27 removal and used H2O2 was established. The applied amount of H2O2 was performed in two forms: (i) the light fraction absorbed by H2O2 in 254 nm, (ii) the initial concentration ratio of H2O2 to AR27. The results obtained from this mathematical model are in good agreement with experimental results.     

类Fenton反应对偶氮染料橙黄II的脱色研究

以橙黄II染料溶液为研究对象,通过正交实验确定了Fe-NTA/H2O2构成的类Fenton反应中各影响因子的最佳操作条件为:[H2O2]=20 mmol/L,[Fe-NTA]=2.5 mmol/L,pH=3。同时考察了反应时间、溶液pH值、H2O2浓度、Fe-NTA浓度对脱色效率的影响。实验表明脱色反应在30 m in内基本完成,类Fenton试剂能在较宽的pH范围内保持较好的脱色效果,而且在pH=6时,类Fenton试剂比传统Fenton试剂的脱色效率提高约75%。增加双氧水浓度可以提高橙黄II溶液脱色率,但超过20 mmol/L后效果提高不明显。在0.5~2.5 mmol/L的范围内,Fe-NTA浓度对脱色效果的影响不显著。     

Kinetic modeling on photooxidative degradation of C.I. Acid Orange 7 in a tubular continuous-flow photoreactor

The decolorization of C.I. Acid Orange 7 (AO7), an anionic monoazo dye of acid class, was investigated using UV radiation in the presence of H2O2 in a tubular continuous-flow photoreactor as a function of oxidant and dye concentrations, reactor length and volumetric flow rate. The removal efficiency of AO7 depends on the operational parameters and increases as the initial concentration of H2O2 is increased but it decreases when the flow rate and initial concentration of AO7 are increased. The decolorization rate follows pseudo-first order kinetic with respect to the dye concentration. A rate equation for decolorization of AO7 was achieved by kinetic modeling. This model allows predicting concentration of AO7 in different photoreactor lengths for different volumetric flow rates and initial concentrations of H2O2 and AO7. The calculated results obtained from kinetic model were in good agreement with experimental data.     

碳纳米管电极原位产生过氧化氢及其对亚甲基蓝脱色效果简

将碳纳米管固定化制成多孔疏水性导电薄膜构建电化学阴极还原体系,实现过氧化氢在阴极的原位产生。电极特性研究表明,电极在较宽的电压范围内均具有较好的活性。考察了阴极电位、电极成分、氧气流量和电解质浓度对过氧化氢原位产生的影响,在优化条件下经过120 min后过氧化氢达到66.17 mg/L,并探讨过氧化氢原位产生的机理。在此基础上考察原位过氧化氢氧化工艺下对亚甲基蓝的脱色效果,并分析其脱色机理。     

Fresnel lens to concentrate solar energy for the photocatalytic decoloration and mineralization of orange II in aqueous solution

The decoloration and mineralization of the azo dye orange II under conditions of artificial ultraviolet light and solar energy concentrated by a Fresnel lens in the presence of hydrogen peroxide and TiO(2)-P25 was studied. A comparative study to demonstrate the viability of this solar installation was done to establish if the concentration reached in the focus of the Fresnel lens was enough to improve the photocatalytic degradation reaction. The degradation efficiency was higher when the photolysis was carried out under concentrated solar energy irradiation as compared to UV light source in the presence of an electron acceptor such us H(2)O(2) and the catalyst TiO(2). The effect of hydrogen peroxide, pH and catalyst concentration was also determined. The increase of H(2)O(2) concentration until a critical value (14.7 mM) increased both the solar and artificial UV oxidation reaction rate by generating hydroxyl radicals and inhibiting the (e(-)/h(+)) pair recombination, but the excess of hydrogen peroxide decreases the oxidation rate acting as a radical or hole scavenger and reacting with TiO(2) to form peroxo-compounds, contributing to the inhibition of the reaction. The use of the response surface methodology allowed to fit the optimal values of the parameters pH and catalyst concentration leading to the total solar degradation of orange II. The optimal pH range was 4.5-5.5 close to the zero point charge of TiO(2) depending on surface charge of catalyst and dye ionization state. Dosage of catalyst higher than 1.1 gl(-1) decreases the degradation efficiency due to a decrease of light penetration.     

Photooxidative removal of the herbicide Acid Blue 9 in the presence of hydrogen peroxide: modeling of the reaction for evaluation of electrical energy per order (E EO)

The present work deals with photooxidative removal of the herbicide, Acid Blue 9 (AB9), in water in the presence of hydrogen peroxide (H2O2) under UV light illumination (30 W). The influence of the basic operational parameters such as amount of H2O2, irradiation time and initial concentration of AB9 on the photodegradation efficiency of the herbicide was investigated. The degradation rate of AB9 was not appreciably high when the photolysis was carried out in the absence of H2O2 and it was negligible in the absence of UV light. The photooxidative removal of the herbicide was found to follow pseudo-first-order kinetic, and hence the figure-of-merit electrical energy per order (E Eo) was considered appropriate for estimating the electrical energy efficiency. A mathematical relation between the apparent reaction rate constant and H2O2 used was applied for prediction of the electricity consumption in the photooxidative removal of AB9. The results indicated that this kinetic model, based on the initial rates of degradation, provided good prediction of the E Eo values for a variety of conditions. The results also indicated that the UV/H2O2 process was appropriate as the effective treatment method for removal of AB9 from the contaminated wastewater.     

碳纳米管电极原位产生过氧化氢及其对亚甲基蓝脱色效果

将碳纳米管固定化制成多孔疏水性导电薄膜构建电化学阴极还原体系,实现过氧化氢在阴极的原位产生。电极特性研究表明,电极在较宽的电压范围内均具有较好的活性。考察了阴极电位、电极成分、氧气流量和电解质浓度对过氧化氢原位产生的影响,在优化条件下经过120min后过氧化氢达到66．17mg／L,并探讨过氧化氢原位产生的机理。在此基础上考察原位过氧化氢氧化工艺下对亚甲基蓝的脱色效果,并分析其脱色机理。     

Copper-ligand complex for the decolorization of synthetic dyes

The reaction system containing Cu(II), hydrogen peroxide and D-arabinono-1,4-lactone was found to be effective in the decolorization and reduction of toxicity of azo, thiazine-, triphenylmethane- and anthraquinone-based synthetic dyes. More than 85% decolorization was obtained with 100ppm Acridine Orange, Azure B, Chicago Sky Blue 6B, Crystal Violet, Evans Blue, Poly B-411, Reactive Blue 2, Reactive Blue 5, and Remazol Brilliant Blue R incubated for 24h in the presence of 10mM CuSO(4), 20mM D-arabinono-1,4-lactone and 80 mM H(2)O(2). The rate of decolorization was not affected by pH in the range of 3-9. The rapid decolorization was accompanied by a fast decomposition of H(2)O(2) in the reaction mixture and by a fast production of hydroxyl radicals.     

Decolorization of structurally different synthetic dyes using cobalt(II)/ascorbic acid/hydrogen peroxide system

The cobalt(II)/ascorbic acid/hydrogen peroxide system was used for decolorization of azo, acridine, anthraquinone, thiazine and triphenylmethane dyes. More than 90% decolorization was obtained with all dyes except Remazol Brilliant Blue R (75%). With other transition metals the system was less efficient. With copper, higher concentration and prolonged incubation time was necessary to obtain the same extent of decolorization. The rate of decolorizaton was not affected by pH in the range of 3-9. The reaction is very fast, with more than 90% decolorization being attained within 15 min. The system produces hydroxyl radicals which are responsible for the decolorization.     

Photochemical degradation and mineralization of 4-chlorophenol

INTENTION, GOAL, SCOPE, BACKGROUND: Since the intermediate products of some compounds can be more toxic and/or refractory than the original compund itself, the development of innovative oxidation technologies which are capable of transforming such compounds into harmless end products, is gaining more importance every day. Advanced oxidation processes are one of these technologies. However, it is necessary to optimize the reaction conditions for these technologies in order to be cost-effective. OBJECTIVE: The main objectives of this study were to see if complete mineralization of 4-chlorophenol with AOPs was possible using low pressure mercury vapour lamps, to make a comparison of different AOPs, to observe the effect of the existence of other ions on degradation efficiency and to optimize reaction conditions. METHODS: In this study, photochemical advanced oxidation processes (AOPs) utilizing the combinations of UV, UV/H2O2 and UV/H2O2/Fe2+ (photo-Fenton process) were investigated in labscale experiments for the degradation and mineralization of 4-chlorophenol. Evaluations were based on the reduction of 4-chlorophenol and total organic carbon. The major parameters investigated were the initial 4-chlorophenol concentration, pH, hydrogen peroxide and iron doses and the effect of the presence of radical scavengers. RESULTS AND DISCUSSION: It was observed that the 4-chlorophenol degradation efficiency decreased with increasing concentration and was independent of the initial solution pH in the UV process. 4-chlorophenol oxidation efficiency for an initial concentration of 100 mgl(-1) was around 89% after 300 min of irradiation in the UV process and no mineralization was achieved. The efficiency increased to > 99% with the UV/H2O2 process in 60 min of irradiation, although mineralization efficiency was still around 75% after 300 min of reaction time. Although the H2O2/4-CP molar ratio was kept constant, increasing initial 4-chlorophenol concentration decreased the treatment efficiency. It was observed that basic pHs were favourable in the UV/H2O2 process. The results showed that the photo-Fenton process was the most effective treatment process under acidic conditions. Complete disappearance of 100 mgl(-1) of 4-chlorophenol was achieved in 2.5 min and almost complete mineralization (96%) was also possible after only 45 min of irradiation. The efficiency was negatively affected from H2O2 in the UV/H2O2 process and Fe2+ in the photo-Fenton process over a certain concentration. The highest negative effect was observed with solutions containing PO4 triple ions. Required reaction times for complete disappearance of 100 mgl(-1) 4-chlorophenol increased from 2.5 min for an ion-free solution to 30 min for solutions containing 100 mgl(-1) PO4 triple ion and from 45 min to more than 240 min for complete mineralization. The photodegradation of 4-chlorophenol was found to follow the first-order law. CONCLUSION: The results of this study showed that UV irradiation alone can degrade 4-CP, although at very slow rates, but cannot mineralize the compound. The addition of hydrogen peroxide to the system, the so-called UV/H2O2 process, significantly enhances the 4-CP degradation rate, but still requires relatively long reaction periods for complete mineralization. The photo-Fenton process, the combination of homogeneous systems of UV/H2O2/Fe2+ compounds, produces the highest photochemical elimination rate of 4-CP and complete mineralization is possible to achieve in quite shorter reaction periods when compared with the UV/H2O2 process. RECOMMENDATIONS AND OUTLOOK: It is more cost effective to use these processes for only purposes such as toxicity reduction, enhancement of biodegradability, decolorization and micropollutant removal. However the most important point is the optimization of the reaction conditions for the process of concern. In such a case, AOPs can be used in combination with a biological treatment systems as a pre- or post treatment unit providing the cheapest treatment option. The AOP applied, for instance, can be used for toxicity reduction and the biological unit for chemical oxygen demand (COD) removal.     

UV/Fenton技术处理某工厂高浓度乳化油废水

研究了UV/Fenton技术对高浓度金属清洗乳化油废水的处理效果,考察了亚铁与双氧水浓度、pH、反应时间和搅拌对COD去除效果的影响。实验结果表明,UV/Fenton技术对高浓度乳化油废水(COD平均浓度为35 000 mg/L)具有较高的去除效果,最佳工艺条件为:亚铁与双氧水浓度分别为2 400 mg/L和6 000 mg/L,pH为3,经过2 h反应,COD可降低至1 050 mg/L,去除率为97%。搅拌会降低COD的去除率。研究表明,UV/Fenton技术对高浓度乳化油废水具有很好的降解效果,且药品消耗较低,为目前此类高浓度有机废水的处理提供了技术参考。     

Photochemical degradation of 1,3-dinitrobenzene in aqueous solution in the presence of hydrogen peroxide

A study on the destruction of 1,3-dinitrobenzene (1,3-DNB) in aqueous solution was carried out under ultraviolet (UV) irradiation alone and UV irradiation in the presence of hydrogen peroxide (H2O2). The combination of UV and H2O2 is significantly effective in degrading 1,3-DNB in terms of initial reaction rate and the mineralization of organic carbons. The photodegradation process can be influenced in certain extent by increasing the content of H2O2 and the acidity of reaction matrices. It was found that a variety of phenolic intermediates and inorganic acid were formed via hydroxyl radicals attacking the parent compound. The UV/H2O2 oxidation of 1,3-DNB was characterized by pseudo-zero order reaction for the degradation of 1,3-DNB with a 20 times enhanced rate constant of 1.36 x 10(-7) Ms(-1) and the initial rate constant was dependent on the initial concentration of 1,3-DNB.     

Degradation of bisphenol A by the UV/H2O2 process: a kinetic study

A theoretical and experimental study of bisphenol A (BPA) degradation by the UV/H₂O₂ process in water is presented. The effects of the H₂O₂ concentration and the specific rate of photon emission (E_P,0) on BPA degradation were investigated. A kinetic model derived from a reaction sequence was employed to predict BPA and hydrogen peroxide concentrations over time using an annular photochemical reactor in batch recirculation mode. The local volumetric rate of photon absorption (LVRPA) inside the photoreactor was computed using a Line Source with Parallel Plane emission model (LSPP). From the proposed kinetic model and the experimental data, the second order rate constants of the reactions between hydroxyl radicals and the main reacting species (H₂O₂ and BPA) were estimated applying a nonlinear regression method. A good agreement between the kinetic model and experimental data, for a wide range of operating conditions, was obtained. For BPA, H₂O₂, and TOC concentrations, the calculated root means square errors (RMSE) were 2.3?×?10^??2, 9.8?×?10^??1, and 9.0?×?10^??2 mmol L^??1, respectively. The simplified kinetic model presented in this work can be directly applied to scaling-up and reactor design, since the estimated kinetic constants are independent of the reactor size, shape, and configuration. Further experiments were made by employing low BPA initial concentration (100 μg L^??1) in water and real wastewater. A lower degradation rate of BPA was observed in the real wastewater, although the UV/H₂O₂ process has also been able to completely degrade the target pollutant in less than 1 h.

     

Citrobacter sp. CK3对活性红KN-3B的脱色反应动力学研究

采用脱色菌Citrobacter sp. CK3,以活性红KN-3B染料为处理对象,在厌氧批式反应条件下,系统考察了pH值,温度和染料浓度对脱色反应速度的影响;通过动力学模拟及反应过程中染料的UV-Vis扫描图分析,探讨了脱色反应机理。结果表明：Citrobacter sp. CK3对活性红KN-3B的脱色反应的适宜pH为7～9;脱色反应速度在温度为32℃时达到最大。染料初浓度从57 mg/L逐渐增大到458 mg/L时脱色率逐渐降低。脱色过程中染料的偶氮键发生断裂,脱色反应符合二级反应动力学。     

Chemical absorption process for degradation of VOC gas using heterogeneous gas-liquid photocatalytic oxidation: toluene degradation by photo-Fenton reaction

A novel process for degradation of toluene in the gas-phase using heterogeneous gas-liquid photocatalytic oxidation has been developed. The degradation of toluene gas by photo-Fenton reaction in the liquid-phase has experimentally examined. The photo-Fenton reaction in the liquid-phase could improve the overall toluene absorption rate by increasing the driving force for mass transfer and as a result enhance the removal of toluene in the exhaust gas. The toluene concentrations in the inlet gas were varied in the range from 0.0968 to 8.69gm(-3) with initial hydrogen peroxide concentration of 400mgl(-1) and Fe dose of 5.0mgl(-1). It was found that toluene in the inlet gas was almost completely dissolved into water and degraded in the liquid-phase for the inlet toluene gas concentration of less than 0.42gm(-3). The dynamic process of toluene gas degradation by the photo-Fenton reaction providing information for reaction kinetics and mass transfer rate was examined. Toluene removal kinetic analysis indicated that photo-Fenton degradation was significantly affected by H(2)O(2) concentration. The experimental results were satisfactorily described by the predictions simulated using the simplified tanks-in-series model combined with toluene removal kinetic analysis. The present results showed that the proposed chemical absorption process using the photo-Fenton heterogeneous gas-liquid photocatalytic oxidation is very effective for degradation of volatile organic gases.     

Kinetics of oxidative decolorization and mineralization of Acid Orange 7 by dark and photoassisted Co2+-catalyzed peroxymonosulfate system

A kinetic model was proposed and used to interpret the experimental data for degradation of Acid Orange 7 (AO7) in aqueous solution induced by Co(2+)/peroxymonosulfate (Co/PMS) reagent in terms of both decolorization and mineralization. The pseudo first-order decolorization rate constants are related to [Co(2+)], [PMS], reciprocal of [H(+)] and [AO7](0). Activation energy of the AO7 decolorization process was determined to be 75.7 kJ mol(-1). UV and visible light can accelerate the decolorization and mineralization process due to different mechanisms. In the combined UV/Co/PMS system, UV light can decompose PMS to generate hydroxyl ((*)OH) and sulfate radicals (SO(4)(*-)), while in the Vis/Co/PMS system, excited AO7 molecules can transfer electrons to PMS or Co(3+) and thus accelerate the decomposition of PMS and catalytic cycle of Co(3+)/Co(2+).     

Decolorization of mono-azo dyes in wastewater by advanced oxidation process: A case study of acid red 1 and acid yellow 23

Advanced Oxidation Processes (AOPs) have been used as emerging wastewater treatment technologies which can effectively handle various hazardous organics in wastewater and groundwater. The photooxidation of two non-biodegradable azo dyes, acid red 1 and acid yellow 23, were studied in an UV/hydrogen peroxide photochemical reactor with a 5 kW low pressure mercury lamp. It was observed that the decomposition of both azo dyes were pseudo-first order reactions with respect to the azo dye concentrations. Simultaneously, the effects of hydrogen peroxide dosage, pH, initial concentration of the azo dyes and intensity of UV light were also studied. Moreover, the time required for the 50% removal of azo dyes and observed pseudo-first order rate constants were used as parameters to show the efficiency of azo dye treatment.     

Degradation of azo dye Procion Red MX-5B by photocatalytic oxidation

The photocatalytic oxidation (PCO) of a monoazo dye Procion Red MX-5B under various physico-chemical conditions was investigated. Degradation of the dye by PCO was enhanced by augmentation in UV intensity, titanium dioxide and hydrogen peroxide concentrations but was inhibited by increase in initial dye concentration. The PCO process was affected by pH in a peculiar way. In the presence of 100 mg/l of TiO2 and the absence of H2O2, the highest reaction rate was observed when the initial pH was 10. With 500 mg/l of TiO2 and 10 mM of H2O2, the reaction was the fastest at initial pH of 3-5. The optimal conditions for the degradation of the dye, at an UV intensity of 17 mW/cm2, were determined to be: TiO2 concentration, 500 mg/l; initial H2O2 concentration, 10 mM; initial pH, 5.0. Monitoring of TOC loss showed that the dye was mineralized by 90% within 80 min under these conditions. Nevertheless, the persistence of a low level of TOC indicated that mineralization was not complete and dead-end product(s) which was (were) resistant to PCO might have accumulated.     

Oxidation of TNT by photo-Fenton process

A series of photo-Fenton reactions have been performed for the degradation of 2,4,6-trinitrotoluene (TNT) in a 4.2-l reactor. The degradation reaction rate of TNT followed a pseudo-first-order behavior; and the rate constants for 2.4mW cm(-2)UV only, 2.4mW cm(-2)UV/H(2)O(2), Fenton, photo-Fenton (2.4mW cm(-2)) and photo-Fenton (4.7mW cm(-2)) were 0.002min(-1), 0.007min(-1), 0.014min(-1), 0.025min(-1) and 0.037min(-1), respectively. Increasing the intensity of UV light, and the concentrations of ferrous ions and hydrogen peroxide promoted the oxidation rate under the experimental conditions in this study. The weighting factor (f), the Fe(II)-promoted efficiency (r) and the promoted-UV light efficiency (p) were calculated to clarify their effects on the TNT oxidation. Moreover, the inhibition effect of hydroxyl radical was also observed in both Fenton and photo-Fenton oxidation when the concentration of Fe(II) were higher than 2.88mM. Solid phase micro-extraction was first applied to the separation of the organic byproducts from TNT oxidation. GC/MS was employed to identify the byproducts during the Fenton and photo-Fenton oxidation of TNT. These compounds were clarified as 1,3,5-trinitrobenzene, 1-methyl-2,4-dinitrobenzene 2,5-dinitrobenzoic acid and 1,3-dinitrobenzene. By these byproducts, the mechanisms of the methyl group oxidation, decarboxylation, aromatic ring breakage, and hydrolysis can be recognized and demonstrated. The pathway of TNT oxidation by photo-Fenton process was also proposed in this study.