Discoloration and mineralization of Orange II by using a bentonite clay-based Fe nanocomposite film as a heterogeneous photo-Fenton catalyst

Discoloration and mineralization of an azo dye Orange II was conducted by using a bentonite clay-based Fe nanocomposite (Fe-B) film as a heterogeneous photo-Fenton catalyst in the presence of UVC light and H(2)O(2). Under optimal conditions (pH=3.0, 10 mM H(2)O(2), and 1 x 8W UVC), 100% discoloration and 50-60% TOC removal of 0.2 mM Orange II can be achieved in 90 and 120 min, respectively. The mineralization kinetics of 0.2 mM Orange II is much slower than the corresponding discoloration kinetics. Under the same conditions, the Fe leaching from the Fe-B-coated catalyst film is very low. The Fe-B-coated catalyst film could be used in the pre-treatment of wastewater for an integrated system consisting of a photochemical reactor and a biological reactor. Multi-run experimental results reveal that the Fe-B-coated catalyst film could have a long-term stability for the discoloration and mineralization of Orange II. A comparison between the performance of the Fe-B-coated catalyst film and a suspended Fe-B catalyst in the discoloration and mineralization of Orange II was also discussed.     

Factorial experimental design of winery wastewaters treatment by heterogeneous photo-Fenton process

Winery wastewaters are difficult to treat by conventional biological processes because they are seasonal and experience a substantial flow variations. Photocatalytic advanced oxidation is a promising technology for wastewaters containing high amounts of organic matter. In this work, the photo-Fenton process in heterogeneous phase is presented as an alternative methodology for the treatment of winery wastewaters. As a consequence of the great number of existing variables, an experimental design methodology has been used in order to study the influence and interaction of various variables and to obtain a reduced empirical model which describes the organic matter degradation process. Applying photo-Fenton treatment in heterogeneous phase under energetic conditions for synthetic samples simulating winery wastewaters results in purification levels of up to 50% (measured as total organic carbon). Different reduced models are obtained and their utilization depends mainly on the degree of degradation of organic matter required.     

Phenol degradation in water through a heterogeneous photo-Fenton process catalyzed by Fe-treated laponite

New photo-Fenton catalysts have been prepared from synthetic layered clay laponite (laponite RD). Two series of Fe-laponite catalysts were synthesised, with or without thermal treatment of the mixture Fe polycations-laponite in the intercalation procedure. In each series, the intercalated solids underwent calcination at four temperatures, 250, 350, 450, and 550 °C. The catalysts were used for photo-assisted Fenton conversion of phenol, analyzing the influence of five operating factors: the wavelength of the light source (254 nm UV-C and 360 UV-A radiation), the amount of the catalyst (between 0 and 2 g/L), the initial phenol concentration (between 0.5 and 1.5 mmol/L), the initial concentration of hydrogen peroxide (between 20 and 100 mmol/L), and the initial pH of the solution (between 2.5 and 3.5). In all experiments, the temperature was kept constant at 30 °C. The results have shown that the almost complete conversion of phenol was possible, after only 5 min, under the following operating conditions: UV-C radiation; a pH of the aqueous solution of 3; a dose of 1 g_catalyst/L, and a hydrogen peroxide concentration of 50 mmol/L for a solution containing 1 mmol/L of phenol. The catalyst prepared under thermal treatment and calcined at 350 °C showed the best catalytic performance. A kinetic model was proposed for the process, testing its validity and estimating the rate constants.     

UV light assisted decolorization of dark brown colored coffee effluent by photo-Fenton reaction

The photochemical decolorization of coffee effluent has been examined by photo-Fenton (UV/Fe²⁺/H₂O₂) process. Effects of UV light intensity, initial coffee concentration, iron dose and H₂O₂ dose on the color removal of model coffee effluent have been investigated. The rate of decolorization increased with decreasing initial coffee effluent concentration. It was found that the Fe ion dose and UV light intensity enhanced the decolorization rate. The decolorization process of coffee effluent could be divided into three established phases. At the beginning of the photo-Fenton process, the instantaneous and significant increase in color of the solution was found (Phase-I). In the subsequent phase (Phase-II), the decolorization rate was initially fast and subsequently decreased. In Phase-III, the rate was accelerated and then the complete decolorization of model coffee effluent was achieved. In order to elucidate the mechanisms of coffee effluent color removal process, the concentration changes in Fe³⁺ and Fe²⁺ besides H₂O₂ were measured during the course of the photo-Fenton process. The rate-determining step in Phase-II was the photo-Fenton reaction or photoreduction of Fe³⁺. On the other hand, the decolorization process in Phase-III was highly affected by Fenton reaction or decomposition of H₂O₂ with Fe²⁺. About 93% mineralization of 250 mg L⁻¹ model coffee effluent was achieved after 250 min. A comparative study for TiO₂, ZnO and photo-Fenton oxidation processes has been also carried out and the photo-Fenton process was found to be the most effective for color removal of coffee effluent.     

Oxidation of explosives by Fenton and photo-Fenton processes

In this study, the Fenton process was used to explore the possibility of treating explosives, namely 2,4,6-trinitrophenol (PA), ammonium picronitrate (AP), 2,4-dinitrotoluene (DNT), methyl-2,4,6-trinitrophenylnitramine (Tetryl) and 2,4,6-Trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX). The photo-Fenton process was also conducted to compare its oxidation efficiency with the Fenton process. The inhibition of hydroxyl radical and theory of crystal field stabilization energy were introduced in this study. Results show that oxidation efficiencies in Fenton system are in the following sequence: DNT > PA > AP > TNT > Tetryl > RDX > HMX. The degradation of the explosives obeys a pseudo-first-order behavior, and possible decomposing mechanisms are also discussed. For all explosives, the oxidation rates significantly increased with increasing the concentration of Fe(II), as well as illumination with UV light.     

Photocatalytic degradation of Reactive Red 22 in aqueous solution by UV-LED radiation

Photocatalytic processes using TiO(2) as a catalyst have attracted extensive attention for decomposition of organic contaminants. The determination of optimum reactor design and operational conditions are the major concerns for the development and potential application of the photocatalytic process. Various photoreactor types, photocatalyst arrangements, light sources, and operation conditions were reported. This study was focused on the application of the ultraviolet light emitting diode (UV-LED) as the UV light source for the photocatalytic decomposition of Reactive Red 22 (RR 22). The temporal behavior of the photocatalytic decomposition of RR 22 in aqueous solution by the UV-LED/TiO(2) with a rectangular planar fixed-film reactor operated in a recirculation mode was studied under various conditions including initial dye concentration, periodic illumination, light intensity, and arrangements of TiO(2) coating. The decomposition of RR 22 in aqueous solution by TiO(2) photocatalytic processes with the UV-LED was found to be technically feasible with a high TiO(2) coated weight (1.135g) and low pH value (pH 2). A Langmuir-Hinshelwood-type kinetic equation was adequate for modeling the photocatalytic decomposition of RR 22 by the UV-LED/TiO(2) photocatalytic processes. The experimental results indicated that the photonic efficiency with periodic illumination was much higher than those with continuous illumination. The photonic efficiencies with the quartz-liquid-catalyst (QLC) arrangement were higher than those with the quartz-catalyst-liquid (QCL) arrangement for experiments conducted at lower applied light intensity; however, the photonic efficiencies for these two arrangements were nearly identical for experiments conducted at higher light intensities.     

Reactive Red 120 dye removal from aqueous solution by adsorption on nano-alumina

The adsorption of Reactive Red 120 dye from aqueous solutions by using nano-alumina has been investigated. The batch adsorption studies were carried out to determine the impact of pH, contact time, concentration of dye, and the adsorbent dose on adsorption process. The maximum adsorption efficiency was observed at pH 3. However with an increase of the adsorbent dose, the dye removal efficiency increased, while the amount of dye adsorbed per unit mass (mg/g) decreased. A pseudo-second-order model best described the adsorption kinetics of the specified dye onto nano-alumina. In this case the Langmuir isotherm model appeared to be most suitable. Findings of the present study reveal that nano-alumina can be an effective adsorbent for the removal of Reactive Red 120 from aqueous solutions.     

Decolorization of dark brown colored coffee effluent by solar photo-Fenton reaction: effect of solar light dose on decolorization kinetics

The decolorization of dark brown colored coffee effluent by solar photo-Fenton process has been studied. Effects of accumulated solar light energy and dosage of Fenton reagents (iron and hydrogen peroxide) on the color removal have been examined. With increasing Fe dosage the rate of the decolorization increased but the enhancement was not pronounced beyond 10 mg L⁻¹. Although addition of H₂O₂ increased the decolorization rate up to around 1000 mg L⁻¹ of H₂O₂, further addition of H₂O₂ could not enhance the color removal. At excess dosages of Fenton reagents, the color removal was not improved due to their scavenging of hydroxyl radicals. It was found that the pseudo-first order decolorization kinetic constant based on the accumulated solar energy is a sole parameter unifying solar photo-Fenton decolorization processes under the different weather conditions. The kinetic constant can be readily used to calculate the amount of solar energy required to achieve a certain degree of color removal. The mineralization was rather slower as compared with the decolorization. The decolorization capability with solar irradiation was found to be comparable to UV light irradiation. The present results suggest that abundant solar energy driving decolorization of coffee effluent by photo-Fenton reaction is highly efficient.     

Degradation of estrone in aqueous solution by photo-Fenton system

Photodegradation of estrone (E1) in aqueous solutions by UV-VIS/Fe(III)/H2O2 system (photo-Fenton system) was preliminarily investigated under a 250-W metal halide lamp (lambda > or = 313 nm). The influences such as initial pH value, initial concentration of Fe(III), H2O2 and E1 on degradation efficiency of E1 were discussed in detail. The results indicated that E1 could be decomposed efficiently in UV-VIS/Fe(III)/H2O2 system. After 160-min irradiation, the photodegradation efficiency of 18.5 micromol L(-1) E1 reached 98.4% in the solution containing 20.8 micromol L(-1) Fe(III), and 1664 micromol L(-1) H2O2 at initial pH value 3.0. The degradation efficiencies of E1 were dependent on initial pH value, Fe (III) concentration and H2O2 concentration. The degradation of four estrogens estrone (E1), estradiol (E2), 17alpha-ethynylestradiol (EE2) and diethylstibestrol (DES) in UV-VIS/Fe(III)/H2O2 system were also conducted. Under the conditions of pH 3.0, the E1 apparent kinetics equation -dC(E1)/dt=0.00093[H2O2]0.47[Fe(III)]0.63[E1]0.24 (r=0.9935, n=11) was obtained. The E1 mineralization efficiency was lower than degradation efficiency under the same conditions, which implied the mineralization occurred probably only at aromatic ring. There are several intermediate products produced during the course of E1 degradation. The comparison of the degradation efficiencies of E1, E2, EE2 and DES degradation in UV-VIS/Fe(III)/H2O2 system were also conducted, and the relative degradability among different estrogens were followed the sequence: DES>E2>EE2>E1.     

Effect of initial solution pH on the degradation of Orange II using clay-based Fe nanocomposites as heterogeneous photo-Fenton catalyst

Effect of initial solution pH on the discoloration and mineralization of 0.2 mM Orange II by using two clay-based Fe nanocomposites (Fe-B (Fe supported on bentonite clay) and Fe-Lap-RD (Fe supported on laponite clay)) as catalysts was studied in detail. It was found that the initial solution pH not only influences the photo-catalytic activity of Fe-B and Fe-Lap-RD but also the Fe leaching from the two catalysts. Both catalysts show the best photo-catalytic activity at an initial solution pH of 3.0, and the activity of the catalysts decreases as the initial solution pH increases. At optimal conditions, 100% discoloration and mineralization of 0.2 mM Orange II are achieved in 60 and 120 min reaction in the presence of 10 mM H2O2, 1.0 g/L Fe-B, and 1 x 8 W UVC at initial solution pH of 3.0. 100% discoloration and 90% mineralization of 0.2 mM Orange II are achieved when Fe-Lap-RD is used as catalyst under the same conditions. Both catalysts also display a reasonable good photo-catalytic activity and negligible Fe leaching at an initial solution pH of 6.6 that is very close to neutral pH. This characteristic makes it possible for the Fe-B and Fe-Lap-RD to have a long-term stability. It also becomes feasible for the photo-Fenton process to treat the original wastewater without the need to pre-adjust the solution pH.     

Degradation of the antibiotic amoxicillin by photo-Fenton process--chemical and toxicological assessment

The influence of iron species on amoxicillin (AMX) degradation, intermediate products generated and toxicity during the photo-Fenton process using a solar simulator were evaluated in this work. The AMX degradation was favored in the presence of the potassium ferrioxalate complex (FeOx) when compared to FeSO₄. Total oxidation of AMX in the presence of FeOx was obtained after 5 min, while 15 min were necessary using FeSO₄. The results obtained with Daphnia magna biossays showed that the toxicity decreased from 65 to 5% after 90 min of irradiation in the presence of FeSO₄. However, it increased again to a maximum of 100% after 150 min, what indicates the generation of more toxic intermediates than AMX, reaching 45% after 240 min. However, using FeOx, the inhibition of mobility varied between 100 and 70% during treatment, probably due to the presence of oxalate, which is toxic to the neonates. After 240 min, between 73 and 81% TOC removal was observed. Different pathways of AMX degradation were suggested including the opening of the four-membered β-lactamic ring and further oxidations of the methyl group to aldehyde and/or hydroxylation of the benzoic ring, generating other intermediates after bound cleavage between different atoms and further oxidation to carboxylates such acetate, oxalate and propionate, besides the generation of nitrate and ammonium.     

Degradation of a four-pesticide mixture by combined photo-Fenton and biological oxidation

Complete degradation of a pesticide mixture by a combination of a photo-Fenton pretreatment and an activated-sludge batch reactor is demonstrated. Four commercial pesticides, Laition, Metasystox, Sevnol and Ultracid were chosen for this experiment. The active ingredients are, respectively, dimethoate, oxydemeton-methyl, carbaryl and methidathion. The original pesticide concentration was 200 mg L⁻¹. Biotreatment began after 31% photocatalytic mineralization, which after 5 h in a 6-L stirred batch-mode tank reactor with non-acclimated activated sludge, leaves the photo-Fenton effluent completely degraded. This biotreatment time is shorter than commonly found in municipal wastewater treatment plants (∼8-10 h). Therefore, the combined process is effective for rapid pesticide degradation in wastewater with complete removal of parent compounds and the associated DOC concentration. Nonetheless, assessment of this technology should take into account higher pesticide concentrations and how this factor affects both the photocatalytic and the biological oxidation.     

Degradation of the emerging contaminant ibuprofen in water by photo-Fenton

In this study the degradation of the worldwide Non-Steroidal Anti-Inflammatory Drug (NSAID) ibuprofen (IBP) by photo-Fenton reaction by use of solar artificial irradiation was carried out. Non-photocatalytic experiments (complex formation, photolysis and UV/Vis-H₂O₂ oxidation) were executed to evaluate the isolated effects and additional differentiated degradation pathways of IBP. The solar photolysis cleavage of H₂O₂ generates hydroxylated-IBP byproducts without mineralization. Fenton reaction, however promotes hydroxylation with a 10% contamination in form of a mineralization. In contrast photo-Fenton in addition promotes the decarboxylation of IBP and its total depletion is observed. In absence of H₂O₂ a decrease of IBP was observed in the Fe(II)/UV-Vis process due to the complex formation between iron and the IBP-carboxylic moiety. The degradation pathway can be described as an interconnected and successive principal decarboxylation and hydroxylation steps. TOC depletion of 40% was observed in photo-Fenton degradation. The iron-IBP binding was the key-point of the decarboxylation pathway. Both decarboxylation and hydroxylation mechanisms, as individual or parallel process are responsible for IBP removal in Fenton and photo-Fenton systems. An increase in the biodegradability of the final effluent after photo-Fenton treatment was observed. Final BOD₅ of 25 mg L⁻¹ was reached in contrast to the initial BOD₅ shown by the untreated IBP solution (BOD₅ < 1 mg L⁻¹). The increase in the biodegradability of the photo-Fenton degradation byproducts opens the possibility for a complete remediation with a final post-biological treatment.     

Optimizing the treatment of landfill leachate by conventional Fenton and photo-Fenton processes

Landfill, a matured and economically appealing technology, is the ultimate approach for the management of municipal solid wastes. However, the inevitable generation of leachate from landfill requires further treatment. Among the various leachate treatment technologies available, advanced oxidation processes (AOPs) are among powerful methods to deal with the refractory organic constituents, and the Fenton reagent has evolved as one promising AOPs for the treatment of leachates. Particularly, the combination of UV-radiation with Fenton's reagent has been reported to be a method that allows both the photo-regeneration of Fe²⁺ and photo-decarboxylation of ferric carboxylates. In this study, Fenton and photo-Fenton processes were fine tuned for the treatment of leachates from the Colmenar Viejo (Madrid, Spain) Landfill. Results showed that it is possible to define a set of conditions under which the same COD and TOC removals (≈ 70%) could be achieved with both the conventional and photo-Fenton processes. But Fenton process generated an important quantity of iron sludge, which will require further disposal, when performed under optimal COD removal conditions. Furthermore conventional Fenton process was able to achieve slightly over an 80% COD removal from a “young” leachate, while for “old” and ”mixed” leachates was close to a 70%. The main advantage showed by the photo-assisted Fenton treatment of landfill leachate was that it consumed 32 times less iron and produced 25 times less sludge volume yielding the same COD removal results than a conventional Fenton treatment.     

Decontamination industrial pharmaceutical wastewater by combining solar photo-Fenton and biological treatment

Characterization and treatment of a real pharmaceutical wastewater containing 775 mg dissolved organic carbon per liter by a solar photo-Fenton/biotreatment were studied. There were also many inorganic compounds present in the matrix. The most important chemical in this wastewater was nalidixic acid (45 mg/L), an antibiotic pertaining to the quinolone group. A Zahn-Wellens test demonstrated that the real bulk organic content of the wastewater was biodegradable, but only after long biomass adaptation; however, the nalidixic acid concentration remained constant, showing that it cannot be biodegraded. An alternative is chemical oxidation (photo-Fenton process) first to enhance biodegradability, followed by a biological treatment (Immobilized Biomass Reactor - IBR). In this case, two studies of photo-Fenton treatment of the real wastewater were performed, one with an excess of H₂O₂ (kinetic study) and another with controlled H₂O₂ dosing (biodegradability and toxicity studies). In the kinetic study, nalidixic acid completely disappeared after 190 min. In the other experiment with controlled H₂O₂, nalidixic acid degradation was complete at 66 mM of H₂O₂ consumed. Biodegradability and toxicity bioassays showed that photo-Fenton should be performed until total degradation of nalidixic acid before coupling a biological treatment. Analysis of the average oxidation state (AOS) demonstrated the formation of more oxidized intermediates. With this information, the photo-Fenton treatment time (190 min) and H₂O₂ dose (66 mM) necessary for adequate biodegradability of the wastewater could be determined. An IBR operated in batch mode was able to reduce the remaining DOC to less than 35 mg/L. Ammonium consumption and NO₃⁻ generation demonstrated that nitrification was also attained in the IBR. Overall DOC degradation efficiency of the combined photo-Fenton and biological treatment was over 95%, of which 33% correspond to the solar photochemical process and 62% to the biological treatment.     

Fenton and photo-Fenton oxidation of textile effluents

The simultaneous use of Fenton reagent and irradiation for the treatment of textile wastewaters generated during a hydrogen peroxide bleaching process is investigated. The experimental conditions tested during this study provide the simultaneous occurrence of Fenton, Fenton-like and photo-Fenton reactions. The batch experimental results are assessed in terms of total organic carbon reduction. Identification of some of the chemical constituents of the effluent was performed by means of GC-MS. Other pollution related features of the initial effluent-like COD and color were also measured. The main parameters that govern the complex reactive system, i.e., light intensity, temperature, pH, Fe(II) and H2O2 initial concentrations have been studied. Concentrations of Fe(II) between 0 and 400 ppm, and H2O2 between 0 and 10,000 ppm were used. Temperatures above 25 degrees C and up to 70 degrees C show a beneficial effect on organic load reduction. A set of experiments was conducted under different light sources with the aim to ensure the efficiency of using solar light irradiation. The combination of Fenton, Fenton-like and photon-Fenton reactions has been proved to be highly effective for the treatment of such a type of wastewaters, and several advantages for the technique application arise from the study.     

Enhancing biodegradability of priority substances (pesticides) by solar photo-Fenton

In this paper, we present the photo-Fenton treatment in a solar pilot-plant scale of several EU priority hazardous substances (Alachlor, Atrazine, Chlorfenvinphos, Diuron and Isoproturon) dissolved in water. The results have been evaluated not only from the point of view of contaminant disappearance and mineralisation, but also of toxicity reduction and enhancement of biodegradability. Degradation was monitored by total organic carbon, pesticide concentration by HPLC-UV, inorganics released by ion chromatography, and biodegradability by the Zahn-Wellens (Z-W) test. The total volume of the solar photoreactor, composed of compound parabolic collectors with a total area of 4.16m2, was between 70 and 82 L. The treatment was shown to be effective, mineralising all of the pesticides tested, both alone and in mixtures. In order to find out the conditions for biocompatibility using the photo-Fenton reaction as a pre-treatment step, wastewater inoculated with unacclimated municipal sludge containing pesticides after certain degradation time was evaluated by the Z-W test. Biodegradability was enhanced (70% considered biodegradable) by the photo-Fenton treatment after 12-25min. It may be concluded that the photo-Fenton treatment consistently enhances biodegradability of wastewater containing pesticides.     

Degradation of sulfamethoxazole in water by solar photo-Fenton. Chemical and toxicological evaluation

In this work, the photocatalytic degradation of the antibiotic sulfamethoxazole (SMX) by solar photo-Fenton at pilot plant scale was evaluated in distilled water (DW) and in seawater (SW). Degradation and mineralization of SMX were strongly hindered in SW compared to DW. The influence of H₂O₂ and iron concentration on the efficiency of the photocatalytic process was evaluated. An increase in iron concentration from 2.6 to 10.4 mg L⁻¹ showed only a slight improvement in SMX degradation and mineralization. However, an increase in H₂O₂ concentration up to 120 mg L⁻¹ during photo-Fenton in DW decreased SMX solution toxicity from 85% to 20%, according to results of Daphnia magna bioassays. The same behaviour was not observed after photo-Fenton treatment in SW. Despite 45% mineralization in SW, toxicity increased from 16% to 86% as shown by Vibrio fischeri bioassays, which suggests that the intermediates generated in SW are different from those in DW. A SMX degradation pathway during the photo-Fenton treatment in DW is proposed.     

微波诱导催化氧化降解活性艳红的研究

文中采用微波诱导氧化工艺对活性艳红水溶液的降解进行了初步研究.实验分别考察了活性艳红水溶液不同初始浓度、催化剂投加量、H2O2投加量、微波辐照时间和pH等因素对活性艳红降解效果的影响.结果表明:取100mL浓度为300 mg/L活性艳红水溶液加入12 g改性氧化铝催化剂,辐照时间1.5 min,H2O2用量为4 mL,pH为6.0的条件下,活性艳红水溶液的褪色率达98.2%,CODσ去除率达84.5%.微波降解活性艳红具有降解速率快、成本低、没有中间产物生成和不会造成二次污染等优点,适合于大规模治理染料废水.     

Characterization of the degradation performance of the sulfamethazine antibiotic by photo-Fenton process

The present study provides results describing the degradation performance of the Sulfamethazine (SMT) antibiotic via photo-Fenton treatment. Experiments were carried out using 1 L solution samples of SMT (50 mg L⁻¹) under different conditions. HPLC results reveal that both Fenton and photo-Fenton reactions were able to completely remove SMT antibiotic from the studied samples in less than 2 min treatment. Half-life times and kinetic parameters (assuming a pseudo-first-order kinetics at reaction initial stage, far from the equilibrium) for SMT degradation were determined and discussed. Hence, appropriate Fenton reagent loads are given to attain different targets proposed. TOC and HPLC data also revealed the presence of reaction intermediates; thus toxicity assays were performed regarding bacterial growth rate. The toxicity of an SMT solution was shown to increase during its degradation by means of photo-Fenton reactions.