NaNO(2)/FeCl(3) catalyzed wet oxidation of the azo dye Acid Orange 7

A combination of ferric chloride and sodium nitrite significantly improved the wet oxidation of the azo dye Acid Orange 7 (AO7) in acid aqueous media (pH 2.6) under moderate conditions (T=150 degrees C; oxygen pressure=0.5 MPa). To evaluate the catalytic system, wet oxidation of AO7 was carried out at temperatures between 90 and 150 degrees C and oxygen pressures ranging from 0.1 to 0.5 MPa. The effect of initial solution pH from 2.6 to 11.4 and the amount of catalyst on the degradation of AO7 were also investigated. AO7 initial concentration was kept 200 mg L(-1). The degradation process was monitored by UV-visible spectroscopy, HPLC, IC (ion chromatography), GC-MS and TOC analysis. At 150 degrees C and 0.5 MPa oxygen pressure, 56% TOC was removed after 4h of treatment, while no obvious TOC removal were achieved without catalyst at the same experimental condition. The main degradation products were some small organic acids: formic acid, acetic acid, pyruvic acid, oxalic acid, succinic acid (identified and quantified by IC) and phthalic acid (identified by GC-MS).     

Simultaneous oxidation of EDTA and reduction of metal ions in mixed Cu(II)/Fe(III)-EDTA system by TiO2 photocatalysis

Both the photooxidation of EDTA and the photoreduction of metal ions in metal-EDTA systems were investigated. EDTA oxidation by TiO(2) photocatalysis occurred sequentially as Cu(II)-EDTA>Cu(II)/Fe(III)-EDTA>Fe(III)-EDTA. For Cu(II)-EDTA, EDTA was completely decomposed after only 60min of irradiation. The rate of EDTA decomposition was directly correlated with the initial Cu(II) concentration in the case of a mixed Cu(II)/Fe(III)-EDTA system. The metal ions in a single metal-EDTA complex were removed following significant decomposition of EDTA. For a mixed Cu(II)/Fe(III)-EDTA system, however, no copper was removed whereas almost all of the iron was removed. The iron and copper species deposited on the TiO(2) surface were identified via EPR and XPS as mixed FeO/Fe(3)O(4) and Cu(0)/Cu(2)O, respectively.     

Hydroxyl radical concentration profile in photo-Fenton oxidation process: generation and consumption of hydroxyl radicals during the discoloration of azo-dye Orange II

Dynamic behaviors of hydroxyl (OH) radical generation and consumption in photo-Fenton oxidation process were investigated by measuring OH radical concentration during the discoloration of azo-dye Orange II. The effects of operating parameters for photo-Fenton discoloration, i.e. dosages of H₂O₂ and Fe, initial dye concentration, solution pH and UV irradiation, on the generation and consumption of OH radicals playing the main role in advanced oxidation processes were extensively studied. The scavenger probe or trapping technique in which coumarin is scavenger of OH radical was applied to estimate OH radical concentration in the photoreactor during the photo-Fenton discoloration process. The OH radical generation was enhanced with increasing the dosages of Fenton regents, H₂O₂ and Fe. At the initial stage of photo-Fenton discoloration of Orange II, the OH radical concentration rapidly increased (Phase-I) and the OH radical concentration decreased after reaching of OH radical concentration at maximum value (Phase-II). The decrease in OH radical concentration started when the complete discoloration of Orange II was nearly achieved and the H₂O₂ concentration became rather low. The dynamic behavior of OH radical concentration during the discoloration of Orange II was found to be strongly linked with the change in H₂O₂ concentration. The generation of OH radical was maximum at solution pH of 3.0 and decreased with an increase of solution pH. The OH radical generation rate in the Fenton Process was rather slower than that in the photo-Fenton process.     

Evaluation and comparison of advanced oxidation processes for the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D): a review

Environmental Science and Pollution Research - Organochlorine pesticides have generated public concern worldwide because of their toxicity to human health and the environment, even at low...     

Cu(II)-Glyphosate system: A study by anodic stripping voltammetry and the influence on Cu adsorption by montmorillonite

The influence of the pesticide glyphosate (GPS) on the adsorption of Cu (II) on montmorillonite has been examined. The complexation of Cu(II) with GPS was studied using anodic stripping voltammetry in differential pulse mode (DPASV). It has been concluded that the complexes present a labile behaviour and GPS shows a low but noticeable degree of heterogeneity, probably due to complexation of Cu bv more than one GPS species. Cu(II) adsorption on montmorillonite is drastically decreased in the presence of GPS, due to several reasons: decrease in free Cu concentration due to formation of Cu-GPS complexes; surface loading of GPS on montmorillonite, obstructing interlamellar Cu²⁺ adsorption and competitive effect between protons and Cu²⁺ for interlamellar positions.     

Electrochemical advanced oxidation and biological processes for wastewater treatment: a review of the combined approaches

As pollution becomes one of the biggest environmental challenges of the twenty-first century, pollution of water threatens the very existence of humanity, making immediate action a priority. The most persistent and hazardous pollutants come from industrial and agricultural activities; therefore, effective treatment of this wastewater prior to discharge into the natural environment is the solution. Advanced oxidation processes (AOPs) have caused increased interest due to their ability to degrade hazardous substances in contrast to other methods, which mainly only transfer pollution from wastewater to sludge, a membrane filter, or an adsorbent. Among a great variety of different AOPs, a group of electrochemical advanced oxidation processes (EAOPs), including electro-Fenton, is emerging as an environmental-friendly and effective treatment process for the destruction of persistent hazardous contaminants. The only concern that slows down a large-scale implementation is energy consumption and related investment and operational costs. A combination of EAOPs with biological treatment is an interesting solution. In such a synergetic way, removal efficiency is maximized, while minimizing operational costs. The goal of this review is to present cutting-edge research for treatment of three common and problematic pollutants and effluents: dyes and textile wastewater, olive processing wastewater, and pharmaceuticals and hospital wastewater. Each of these types is regarded in terms of recent scientific research on individual electrochemical, individual biological and a combined synergetic treatment.     

Application of zeolite-activated carbon macrocomposite for the adsorption of Acid Orange 7: isotherm, kinetic and thermodynamic studies

In this study, the adsorption behavior of azo dye Acid Orange 7 (AO7) from aqueous solution onto macrocomposite (MC) was investigated under various experimental conditions. The adsorbent, MC, which consists of a mixture of zeolite and activated carbon, was found to be effective in removing AO7. The MC were characterized by scanning electron microscopy (SEM), energy dispersive X-ray, point of zero charge, and Brunauer–Emmett–Teller surface area analysis. A series of experiments were performed via batch adsorption technique to examine the effect of the process variables, namely, contact time, initial dye concentration, and solution pH. The dye equilibrium adsorption was investigated, and the equilibrium data were fitted to Langmuir, Freundlich, and Tempkin isotherm models. The Langmuir isotherm model fits the equilibrium data better than the Freundlich isotherm model. For the kinetic study, pseudo-first-order, pseudo-second-order, and intraparticle diffusion model were used to fit the experimental data. The adsorption kinetic was found to be well described by the pseudo-second-order model. Thermodynamic analysis indicated that the adsorption process is a spontaneous and endothermic process. The SEM, Fourier transform infrared spectroscopy, ultraviolet–visible spectral and high performance liquid chromatography analysis were carried out before and after the adsorption process. For the phytotoxicity test, treated AO7 was found to be less toxic. Thus, the study indicated that MC has good potential use as an adsorbent for the removal of azo dye from aqueous solution.     

Photogeneration of hydroxyl radical in Fe(III)-citrate-oxalate system for the degradation of fluconazole: mechanism and products

Environmental Science and Pollution Research - The photochemical role of Fe(III)-citrate complex is significant in natural waters due to its ubiquitous existence and excellent photoreactivity at...     

Peroxymonosulfate-Co(II) oxidation system for the removal of the non-ionic surfactant Brij 35 from aqueous solution

The non-ionic surfactant Brij 35 was effectively removed from concentrated aqueous solution by the peroxymonosulfate/Co(II) system, using oxone (2KHSO₅·KHSO₄·K₂SO₄) as a source of peroxymonosulfate. At pH = 2.3 and initial Brij 35 concentration in the range 680-2410 mg L⁻¹, 86-94% removal was achieved after 24 h, using Co(II) = 15 μM and oxone = 5.9 mM. The effectiveness of removal did not change when initial pH was in the range 2.3-8.2. After five subsequent additions of Co(II) and oxone to the solution, COD and TOC removals increased up to 64% and 33%, respectively. Radical quenching tests confirmed that sulfate radical was the dominant radical species in the system. The main identified by-products from surfactant degradation were: (a) low molecular weight organic acids; (b) aldehydes and formates with shorter ethoxy chain than Brij 35; (c) alcohol ethoxylates carrying hydroxyl groups bonded to ethoxy chain. By-products identification allowed to hypothesize the pathways of Brij 35 degradation.     

Biogeochemical processes at the fringe of a landfill leachate pollution plume: potential for dissolved organic carbon, Fe(II), Mn(II), NH4, and CH4 oxidation

Various redox reactions may occur at the fringe of a landfill leachate plume, involving oxidation of dissolved organic carbon (DOC), CH4, Fe(II), Mn(II), and NH4 from leachate and reduction of O2, NO3 and SO4 from pristine groundwater. Knowledge on the relevance of these processes is essential for the simulation and evaluation of natural attenuation (NA) of pollution plumes. The occurrence of such biogeochemical processes was investigated at the top fringe of a landfill leachate plume (Banisveld, the Netherlands). Hydrochemical depth profiles of the top fringe were captured via installation of a series of multi-level samplers at 18, 39 and 58 m downstream from the landfill. Ten-centimeter vertical resolution was necessary to study NA within a fringe as thin as 0.5 m. Bromide appeared an equally well-conservative tracer as chloride to calculate dilution of landfill leachate, and its ratio to chloride was high compared to other possible sources of salt in groundwater. The plume fringe rose steadily from a depth of around 5 m towards the surface with a few meters in the period 1998-2003. The plume uplift may be caused by enhanced exfiltration to a brook downstream from the landfill, due to increased precipitation over this period and an artificial lowering of the water level of the brook. This rise invoked cation exchange including proton buffering, and triggered degassing of methane. The hydrochemical depth profile was simulated in a 1D vertical reactive transport model using PHREEQC-2. Optimization using the nonlinear optimization program PEST brought forward that solid organic carbon and not clay minerals controlled retardation of cations. Cation exchange resulted in spatial separation of Fe(II), Mn(II) and NH4 fronts from the fringe, and thereby prevented possible oxidation of these secondary redox species. Degradation of DOC may happen in the fringe zone. Re-dissolution of methane escaped from the plume and subsequent oxidation is an explanation for absence of previously present nitrate and anaerobic conditions in pristine groundwater above the plume. Stable carbon isotope (delta13C) values of methane confirm anaerobic methane oxidation immediately below the fringe zone, presumably coupled to reduction of sulfate, desorbed from iron oxide. Methane must be the principle reductant consuming soluble electron-acceptors in pristine groundwater, thereby limiting NA for other solutes including organic micro-pollutants at the fringe of this landfill leachate plume.     

A combined photolytic-electrolytic system for the simultaneous recovery of copper and degradation of phenol or 4-chlorophenol in mixed solutions

The effects of the presence of copper on the photooxidation of phenol and 4-chlorophenol and of the presence of the phenols on the recovery of copper by electrodeposition are studied in three systems: a photolytic cell in the presence and absence of TiO2 as a catalyst or H2O2 as an oxidant; an electrolytic cell and a combined photolytic-electrolytic system. The optimum system for the simultaneous removal of copper and destruction of the phenols which overcomes the effects of copper-phenol reactions is a combined system with concentrator electrode technology incorporated into the electrolytic cell. This combined system achieves >99% removal of copper and destruction of phenol or 4-chlorophenol in an 8 h period.     

A comparative study of the effects of chloride, sulfate and nitrate ions on the rates of decomposition of H2O2 and organic compounds by Fe(II)/H2O2 and Fe(III)/H2O2

The effects of chloride, nitrate, perchlorate and sulfate ions on the rates of the decomposition of hydrogen peroxide and the oxidation of organic compounds by the Fenton's process have been investigated. Experiments were conducted in a batch reactor, in the dark at pH < or = 3.0 and at 25 degrees C. Data obtained from Fe(II)/H2O2 experiments with [Fe(II)]0/[H2O2]0 > or = 2 mol mol(-1), showed that the rates of reaction between Fe(II) and H2O2 followed the order SO4(2-) > ClO4(-) = NO3- = Cl-. For the Fe(III)/H2O2 process, identical rates were obtained in the presence of nitrate and perchlorate, whereas the presence of sulfate or chloride markedly decreased the rates of decomposition of H2O2 by Fe(III) and the rates of oxidation of atrazine ([atrazine]0 = 0.83 microM), 4-nitrophenol ([4-NP]0 = 1 mM) and acetic acid ([acetic acid]0 = 2 mM). These inhibitory effects have been attributed to a decrease of the rate of generation of hydroxyl radicals resulting from the formation of Fe(III) complexes and the formation of less reactive (SO4(*-)) or much less reactive (Cl2(*-)) inorganic radicals.     

Methane fluxes from differentially managed grassland study plots: the important role of CH4 oxidation in grassland with a high potential for CH4 production.

Methane oxidation fluxes were monitored with the closed chamber method in eight treatment plots on a semi-wet grassland site near Giessen, Germany. The management regimes differed in the amount of nitrogen (NH4NO3) fertilizer applied and in the height of the in-ground water table. No inhibition of CH4 oxidation occurred, regardless of the amount of annual N fertilizer applied. Instead, the mean CH4 consumption rates were correlated with the mean soil moisture of the plots. However, the correlation between daily soil water content and corresponding CH4 oxidation rate was always weak. During drought period (late summer) water stress was observed to restrict CH4 oxidation rates. The findings led to the question whether methane production with soil depth might modify the CH4 fluxes measured at the surface. Therefore, two new methods were applied: (1) soil air sampling with silicone probes; and (2) anaerobic incubations of soil cores to test for the methane production potential of the grassland soil. The probe measurements revealed that the CH4 sink capacity of a specific site was related to the vertical length of its CH4 oxidizing column, i.e. the depth of the CH4 producing horizon. Anaerobically incubated soil cores produced large amounts of CH4 comparable with tropical rice paddy soil. Under field conditions, heavy autumnal rain in 1998 led to a dramatic increase of soil CH4 concentrations upto 51 microliters l-1 at a depth of 5 cm. Nevertheless, no CH4 was released when soil surface CH4 fluxes were measured simultaneously. The results thus demonstrate the high CH4 oxidation potential of the thin aerobic topsoil horizon in a non-aquatic ecosystem.     

Electroassisted methods for waste destruction: silver(II) and peroxydisulfate reagents in the electrochemically mediated oxidation of polyaromatic sulfonates

The electrochemical oxidation is a promising process for organic pollutants which are recalcitrant to biological degradation. The anodic oxidation of 1,5-naphthalenedisulfonic acid, hereafter NDS, was evaluated at a Pt anode using in situ generated Ag(II) cation or peroxydisulfate [S2O(8)(2-)] anion as mediators. Kinetics of the direct chemical oxidation of NDS in the presence of Na2S2O8, and the identification of some oxidation intermediates are also reported. An analysis of the results shows that Ag(II) is characterized by a high-reaction rates, while [S2O(8)(2-)] performs the oxidation of NDS in a complete way.     

Application of an integrated Weather Research and Forecasting (WRF)/CALPUFF modeling tool for source apportionment of atmospheric pollutants for air quality management: A case study in the urban area of Benxi,China

In this study, the authors endeavored to develop an effective framework for improving local urban air quality on meso-micro scales in cities in China that are experiencing rapid urbanization. Within this framework, the integrated Weather Research and Forecasting (WRF)/CALPUFF modeling system was applied to simulate the concentration distributions of typical pollutants (particulate matter with an aerodynamic diameter <10 μm [PM₁₀], sulfur dioxide [SO₂], and nitrogen oxides [NO_x]) in the urban area of Benxi. Statistical analyses were performed to verify the credibility of this simulation, including the meteorological fields and concentration fields. The sources were then categorized using two different classification methods (the district-based and type-based methods), and the contributions to the pollutant concentrations from each source category were computed to provide a basis for appropriate control measures. The statistical indexes showed that CALMET had sufficient ability to predict the meteorological conditions, such as the wind fields and temperatures, which provided meteorological data for the subsequent CALPUFF run. The simulated concentrations from CALPUFF showed considerable agreement with the observed values but were generally underestimated. The spatial-temporal concentration pattern revealed that the maximum concentrations tended to appear in the urban centers and during the winter. In terms of their contributions to pollutant concentrations, the districts of Xihu, Pingshan, and Mingshan all affected the urban air quality to different degrees. According to the type-based classification, which categorized the pollution sources as belonging to the Bengang Group, large point sources, small point sources, and area sources, the source apportionment showed that the Bengang Group, the large point sources, and the area sources had considerable impacts on urban air quality. Finally, combined with the industrial characteristics, detailed control measures were proposed with which local policy makers could improve the urban air quality in Benxi. In summary, the results of this study showed that this framework has credibility for effectively improving urban air quality, based on the source apportionment of atmospheric pollutants.

Implications: The authors endeavored to build up an effective framework based on the integrated WRF/CALPUFF to improve the air quality in many cities on meso-micro scales in China. Via this framework, the integrated modeling tool is accurately used to study the characteristics of meteorological fields, concentration fields, and source apportionments of pollutants in target area. The impacts of classified sources on air quality together with the industrial characteristics can provide more effective control measures for improving air quality.

Through the case study, the technical framework developed in this study, particularly the source apportionment, could provide important data and technical support for policy makers to assess air pollution on the scale of a city in China or even the world.