Influence of the operating conditions on highly oxidative radicals generation in Fenton's systems (original) (raw)
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Oxidação em processos Fenton e Foto-Fenton em efluentes de curtumes
Acta Scientiarum-technology, 2003
Fenton and Photo-Fenton processes are attractive alternatives in effluent treatment, especially when applied to recalcitrant compounds. The aim of this work was to evaluate the efficiency of Fenton and Photo-Fenton processes for the treatment of wastewater from leather industry, investigating the reduction of COD, ammoniac nitrogen concentration and toxicity in treated wastewaters. The results showed that the kinetic of degradation by Fenton and Photo-Fenton reactions can be divided in two stages: an initial fast process, where approximately 70% of the COD reduction takes place, followed, by a slow process, where a reaction takes up to 4 hours, resulting in about 90% of COD reduction. Different mass ratios of Fe 2+ /H 2 O 2 were tested and the results showed that the efficiency of the Fenton and photo-Fenton reactions increases from 65 to 90% as the concentration of hydroxyl radicals (• OH) increases. No significant difference in the ammoniac nitrogen amount reduction for the Fenton and Photo-Fenton processes was observed, either before or after coagulation. The ammonia removal was ascribed to the oxidation of nitrogen organic compounds, possibly forming N 2 and nitrate ions. The toxicity biossays using Artemia salina decreased as the wastewater was degraded and increased if the hydrogen peroxide residue at the end of the reaction was high.
Humic acid modified Fenton reagent for enhancement of the working pH range
Applied Catalysis B: Environmental, 2007
The suitability of the Fenton process for the remediation of soil and groundwater is limited by the necessity to acidify the reaction medium. This study examines the applicability of humic acid (HA) as an iron chelator in a modified Fenton system with the aim of extending the optimum pH range for this process towards neutral conditions. Addition of HA at a concentration of 50-100 mg L À1 greatly enhances the rate of oxidation of organic compounds in a catalytic Fenton system in the range of pH 5-7. Similar rates at pH 5 in the presence of HA can be achieved as at pH 3 for a typical Fenton process in the absence of HA (k 0 = 9 Â 10 À3 min À1 for benzene degradation at c H 2 O 2 ¼ 0:13 M). A comparison of the relative reactivities of various model compounds supported the hypothesis that OH radicals are the main reactive species in the HA-modified Fenton system. In contrast, however, another type of chelated Fe-catalyst (Fe-TAML) proved to be more selective than expected for OH radicals. A longterm study revealed that the HA itself is oxidized and thereby loses its ability to enhance the degradation of the pollutant molecules. Therefore, the HA-modified Fenton system is effective for degrading pollutants which are at least as reactive towards OH radicals as the HA itself, such as BTEX, phenols or PAHs. The results obtained indicate that the HA-modified Fenton system is also applicable for compounds with a high sorption tendency towards HA.
A review of classic Fenton's peroxidation as an advanced oxidation technique
Hydrogen peroxide (H 2 O 2) is a strong oxidant and its application in the treatment of various inorganic and organic pollutants is well established. Still H 2 O 2 alone is not effective for high concentrations of certain refractory contaminants because of low rates of reaction at reasonable H 2 O 2 concentrations. Improvements can be achieved by using transition metal salts (e.g. iron salts) or ozone and UV-light can activate H 2 O 2 to form hydroxyl radicals, which are strong oxidants. Oxidation processes utilising activation of H 2 O 2 by iron salts, classically referred to as Fenton's reagent is known to be very effective in the destruction of many hazardous organic pollutants in water. The first part of our paper presents a literature review of the various Fenton reagent reactions which constitute the overall kinetic scheme with all possible side reactions. It also sum-marises previous publications on the relationships between the dominant parameters (e.g. [H 2 O 2 ], [Fe 2+ ],. . .). The second part of our review discusses the possibility of improving sludge dewater-ability using Fenton's reagent.
Abstract In these years, due to the increasing presence of molecules in industrial waste water from factories and petroleum refineries, the conventional biological methods cannot be used for complete treatment of the effluent therefore the need to newer technologies to degrade these refractory molecules into smaller molecules became very imperative. Advanced oxidation processes (AOPs) constitute a promising technology for the treatment of wastewaters. Fenton’s oxidation was one of the best known metal catalyzed oxidation reactions of water-miscible organic compounds. The mixture of FeSO4 or any other ferrous complex and H2O2 (Fenton’s reagent) at low enough pH, results in Fe2+ catalytic decomposition of H2O2 and proceeds via a free radical chain process that produces hydroxyl radicals which have extremely high oxidizing ability and could oxidize hard to decompose organic compounds in a short time. This work aims at highlighting Fenton’s oxidation processes operating at ambient conditions viz. photo-catalytic oxidation, Fenton’s chemistry and use of hydrogen peroxide. The pre-oxidation of an extremely polluted pharmaceutical wastewater, Direct Blue 71 (DB71) oil recovery industry wastewater, the fish canning industrial wastewater, Active pharmaceutical intermediates (API) in waste waters by Fenton’s oxidation process to degrade organic pollutants. The work highlights the basics of these individual processes including the reactor design aspects, the optimum parameters such as dosage of ferrous sulfate and hydrogen peroxide, pH and initial concentration of pollutants and a complete overview of the various applications to wastewater treatment by Fenton’s oxidation processes in the recent years. This study presents a general review on the effectiveness of Fenton’s technique for the treatment of semi-aerobic landfill leachate (Treatment with Fenton’s reagent appears to be an appropriate method for oxidizing recalcitrant
Degradation Characteristics of Humic Acid during Photo-Fenton Processes
Environmental Science & Technology, 2001
Changes in the molecular and structural characteristics of humic acid (HA) during photo-Fenton processes were studied. When aqueous solutions at pH 5.0, which contained HA, Fe(III), and H 2 O 2 , were irradiated (λ > 370 nm), the concentrations of total organic carbon (TOC) decreased with increasing irradiation time, indicating that a portion of the HA was mineralized to CO 2 during this process. To investigate the changes in molecular and structural characteristics, the HA was reisolated from the reaction mixtures after each period of irradiation. The increased elution volumes required for isolation by gel permeation chromatography indicated that the molecular size of HA decreased as a result of the irradiation. In the FTIR spectra, ether and epoxide functional groups were identified, after irradiation. These products could be formed via radical coupling and/ or via peroxy radical addition reactions to the unsaturated groups in the HA, such as vinyl and aromatic groups. Moreover, an analysis of structural fragments in HA by pyrolysis-GC/ MS showed that the cinnamic acid moieties (CA) disappeared, as a result of irradiation. In the molecular weight fractionated HA, the majority of the iron species were complexed with the high molecular weight HA fraction, and the CA levels of the high molecular weight fraction were larger than those in the low molecular weight fraction. These results are consistent with residues, as the reactive sites in the photo-Fenton systems. Therefore, the degradation of these sites in the high molecular weight fraction may serve as a factor in decreasing the molecular size of HA.
Removal of Natural Organic Matter in Water for Human Consumption by Homogeneous Fenton Process
2018
The presence of natural organic matter (NOM) in natural waters impairs the performance of water treatment plants, the effectiveness of the disinfection process and biological stability. Consequently, loss of drinking water quality may occur due to the formation of disinfection by-products; increased color, odor and taste; and biological growth in the reservation and distribution systems. Thus, there is a need to study technological alternatives to obtain potable water for public supply, meeting drinking standards. Among the promising technological alternatives are the advanced oxidative processes, which involve the formation of highly reactive hydroxyl radicals (●OH), which degrade the organic molecules present in contaminated waters. The aim of this research was to study the application of the homogeneous Fenton process in the removal of humic acid. Several assays were performed by adding pre-determined amounts of ferrous sulfate and hydrogen peroxide in a solution of 30 mg/L of hu...
Water Science and Technology, 2004
This study aims to investigate the effects of selected organic substances on the degradation of hydrogen peroxide during the Fenton reaction. Since the presence of organic substances can strongly affect the mechanism of the Fenton reaction, the information on effects of organic substances on the reaction would be a vital guide to the success of its application to the destruction of organics in wastewater. Several organic compounds having different structures were selected as model pollutants: 4-chlorophenol, 1,4-dioxane, chloroform, a dye (reactive black-5), and EDTA. Oxidation of 4-chlorophenol and reactive black-5 resulted in enormously fast degradation of hydrogen peroxide, while others such as 1,4-dioxane and chloroform showed much slower degradation. These experimental data were compared to simulation results from a computational model based on a simple áOH-driven oxidation model. Modelling results for chloroform and 1,4-dioxane were in relatively good agreement with the experi...
Environmental Science & Technology, 2000
Orange II, the 4-(2-hydroxy-1-naphthylazo)benzenesulfonic acid Na-salt, was taken as a model for the oxidation of organic compounds in photoassisted Fenton process in the presence of Cl-anion in solution. The HO • radicals seem to originate due to the photolysis of Fe(OH) 2+ complexes in solution, whereas the Cl 2-• radical was a product of the photolysis of the FeCl 2+ complexes. The rate constants for the reaction of HO • and Cl 2-• radicals with Or II were determined by laser kinetic spectroscopy: k OH • +OrII) 6.0 × 10 9 (M s)-1 and k Cl2 • +OrII) 3.7 × 10 7 (M s)-1. A significant decrease in the rate of decoloration was observed for Orange II upon addition of Cl-(10 mM), but further addition of Clonly marginally affected the latter reaction rate. Chlorinated hydrocarbons are observed as the products of Orange II oxidation in photoassisted and dark Fenton processes in the presence of Clanions. Light irradiation was observed to decrease the amount of chlorinated organic products (AOX) in solution as compared to dark Fenton processes. The results obtained are shown to be in agreement with the radical reaction theory for the particular case of the Fenton reaction. Kinetic modeling of the Orange II decoloration was carried out taking into consideration the rate constants found for the reaction k HO • +OrII and k Cl2 • +OrII .
Fenton chemistry encompasses reactions of hydrogen peroxide in the presence of iron to generate highly reactive species such as the hydroxyl radical and possibly others. In this review, the complex mechanisms of Fenton and Fenton-like reactions and the important factors influencing these reactions, from both a fundamental and practical perspective, in applications to water and soil treatment, are discussed. The review covers modified versions including the photoassisted Fenton reaction, use of chelated iron, electro-Fenton reactions, and Fenton reactions using heterogeneous catalysts. Sections are devoted to nonclassical pathways, by-products, kinetics and process modeling, experimental design methodology, soil and aquifer treatment, use of Fenton in combination with other advanced oxidation processes or biodegradation, economic comparison with other advanced oxidation processes, and case studies.
Journal of Hazardous Materials, 2009
In this study, we investigated the feasibility of using Fenton oxidation to remove sorbed polycyclic aromatic hydrocarbons (PAHs) in aged soil samples with creosote oil from a wood preserving site. The optimal dosage of reagents was determined by a statistical method, the central composite rotatable experimental design. The maximum PAH removal was 80% with a molar ratio of oxidant/catalyst equal to 90:1. In general low molecular weight PAHs (3 rings) were degraded more efficiently than higher molecular weight PAHs (4 and 5 rings). The hydrogen peroxide decomposition kinetic was studied in the presence of KH 2 PO 4 as stabilizer. The kinetic data were fitted to a simple model, the pseudo-first-order which describes the hydrogen peroxide decomposition. The PAH kinetic degradation was also studied, and demonstrated that non-stabilized hydrogen peroxide was consumed in less than 30 min, whilst PAH removal continued for up to 24 h. In a second part of the work, a combined chemical and biological treatment of the soil was carried out and shown to be dependent on the pre-oxidation step. Different reagent doses (H 2 O 2 :Fe) were used (10, 20, 40, 60:1) in the pre-treatment step. An excess of hydrogen peroxide resulted in a poor biological removal, thus the optimal molar ratio of H 2 O 2 :Fe for the combined process was 20:1. The combined treatment resulted in a maximum total PAH removal of 75% with a 30% increase in removal due to the biodegradation step. The sample with highest PAH removal in the pre-oxidation step led to no further increase in removal by biological treatment. This suggests that the more aggressive chemical preoxidation does not favour biological treatment. The physico-chemical properties of the pollutants were an important factor in the PAH removal as they influenced chemical, biological and combined treatments.