Volume 18, Issue 1

Pesticides are often reported in aquatic environments contamination as being a result of soil leaching and improper disposal of agricultural packages. Advanced oxidation processes have been studied as alternatives to treat such compounds in aqueous media. The aim of this study was to determine the best concentrations of H 2 O 2 and Fe 2+ that achieved the most efficient simultaneous degradation of hexazinone and diuron. The central composite design (CCD) and response surface method (RSM) were applied to evaluate and optimize the interactive effects of H 2 O 2 and Fe 2+ . The dosages of H 2 O 2 and Fe 2+ used in the photo-Fenton degradation of an aqueous solution of hexazinone and diuron ranged from 0.09 to 29.1 mmol L -1 and 0.01 to 0.92 mmol L -1 , respectively. The response surface revealed low concentrations of H 2 O 2 and Fe 2+ to the ideal degradation. These photo-Fenton conditions promoted 100% degradation of hexazinone and diuron and 76% of mineralization in only 30 minutes.

The presence of polycyclic aromatic hydrocarbons (PAHs) in sediments is a major concern of risks associated with the aquatic ecosystems through bioaccumulation in food chains. To minimize the ecological risks due to contaminated sediments, processes that can degrade the sorbed PAHs are urgently needed. The present study aims at assessing the treatment efficiency of several chemical oxidation processes using potassium permanganate (KMnO 4 ), sodium persulfate (Na 2 S 2 O 8 ), conventional Fenton, and modified Fenton. Efforts were focused on identifying the most effective liquid oxidant to obtain the maximum acceptable concentration for a total of 16 PAH compounds (1000 ng/g) and on assessing the optimal reactant doses. The concentration of PAHs in the untreated sediment was around 4226 ng/g (2-ring at 273 ng/g, 3-ring at 1285 ng/g, 4-ring at 1508 ng/g, 5-ring at 789 ng/g, and 6-ring at 369 ng/g) and 76% of degradation was required to meet the remediation goals. The removal efficiency was 5.3-72.8%, 10.7-39.1%, 0-30.9% and 31.5-68.3% by KMnO 4 , Na 2 S 2 O 8 , conventional Fenton and modified Fenton, respectively. Results demonstrated a medium reduction of a mixture of 16 PAHs in sediments; only in case of using KMnO 4 that showed the highest removal efficiency (72.8%) using a considerably large amount of oxidizer. Modified Fenton showed remarkable improvement in removal efficiency compared with the conventional Fenton method. Sodium citrate resulted in the maximum contaminant removal through H 2 O 2 activation at near neutral pH environment. Sodium pyrophosphate and sodium oxalate at higher dosages could cause negative effect on the removal efficiency. In general, the degradation of PAHs in slurry system was limited, which could be attributed to the availability and reactivity of PAHs and physical-chemical composition of the sediment.

This study investigates the advance oxidation process of common azo dye, Remazol Black B (RBB). Photocatalytic degradation of RBB was carried out using metal ion (Fe 3+ , Cu 2+ , Sn 2+ , Hg 2+ , and Co 2+ ) as photocatalyst. Fe 3+ , Cu 2+ , and Sn 2+ were used in varying all the necessary parameters in the photodegradation experiment while all five metal ions were used for the comparison of photodegradation efficiency of different metal ions in the optimal conditions that were obtained for the treatment of RBB using first three metal ions. Fe 3+ ion was widely used to demonstrate the photodegradation pattern. The degradation efficiency was observed above 90% after 90 minutes irradiation of UV light (intensity=12.83 Wm -2 ). Different kinetic models have been used to interpret the results and found that the kinetics of the degradation follow pseudo first-order model. Photodegradadation was carried out by varying the concentration of metal ion, initial concentration of RBB, the pH of the medium and light sources using each of the three metal ions (Fe 3+ , Cu 2+ , and Sn 2+ ). A tentative mechanism has been proposed to demonstrate this photocatalytic activity. More efficient degradation for all metal ions was observed at pH=1.0. Treatment performance of the investigated advanced oxidation systems was comparatively assessed in terms of bleaching and evaluated by spectrophotometric measurements.

The electronic structures of sulfonamide antibiotics (the ground state and the lowest singlet excited-state geometries) have been investigated by using density functional theory (DFT) simulations. Experimental studies on the removal of sulfamethazine, sulfathiazole and sulfamethoxazole by ozone have also been conducted by using liquid chromatography with tandem mass spectrometric detection (LC/MS/MS). The calculated ground and excited state geometries exhibited low energy of the inter-ring bonds, which suggests the weakest bonds that can be broken during the ozone oxidation process. The orbital energy calculations (HOMO-LUMO and its energy gap) demonstrate that the smaller HOMO-LUMO energy gap, the higher reactivity toward ozone oxidation. Additionally, the current study suggests potential products of the three pharmaceutical compounds based on their electronic properties, which may help better understand the unknown reaction pathways of the pharmaceutical compounds.

The degradation and detoxicity of tetracycline antibiotics were investigated in this study using enhanced sonolysis coupled with ultrasound, transition metals and oxidizing agents. The effects of oxidising agents, transition metals and their concentrations on tetracycline degradation were examined. An initial tetracycline concentration of 50 mg L -1 was used as a model solution, and the frequency and temperature of enhanced sonolysis were 20 kHz and 25°C, respectively. The addition of Fe 2+ and H 2 O 2 during sonolysis resulted in a better performance compared to the addition of other chemicals, and the better experimental concentrations were 0.2 mmol L -1 Fe 2+ and 2 mmol L -1 H 2 O 2 . Accordingly, the efficiency of tetracycline degradation after 60 min of reaction reached 91.3% followed by a mineralisation efficiency of 45.8%. The effect of initial pH on tetracycline degradation was insignificant, and the enhanced sonolysis was thus conducted at pH 6. In addition, the toxicity of the tetracycline solution was efficiently reduced by the mineralisation of tetracycline by an ultrasound/Fe 2+ /H 2 O 2 process. The degradation of tetracycline led the release of NH 3 -N, most of which occurred after 20 min of reaction.

A trickle bed electrochemical reactor was used to generate hydrogen peroxide in dilute electrolyte and then degrade an azo dye, i.e. reactive brilliant red X-3B in water by electro-Fenton process. The trickle bed reactor was composed of carbon black-polytetrafluoroethylene coated graphite chips. During the preparation of coated graphite chips, coating times and surfactant dosage were optimized to improve electro-generation of H 2 O 2 . In addition, the optimal electrolysis conditions for H 2 O 2 electro-generation were obtained as follows, cell voltage of 4.5 V, air flow rate of 0.1 m 3 /h, electrolyte flow rate of 15 mL/min, and initial pH of 3. Under the given conditions, H 2 O 2 concentration, production rate and current efficiency were 5.01 mmol/L, 134 μmol/(h·cm 2 ) and 63.7%, respectively, after 1 h of electrolysis. With addition of 0.1 mmol/L Fe 2+ , 123 mg/L X-3B was completely removed from water after 30 min of electro-Fenton treatment, whereas total organic carbon dropped slowly from 17.8 mg/L to 2.28 mg/L (87% mineralization) after 3 h. The trickle bed reactor was sufficient to treat low-strength wastewater or be used in tandem with other treatment units.

High thermally stable anatase nanopowders have a wide flexibility in high-temperature applications, and are attracting ongoing attention to increase their stability temperature. The principle feature in this study lays in the preparation of high thermally stable anatase nanowires powder by the hydrothermal reaction between Ti powder and lye. The convincing characterizations including XRD, SEM, TEM, EDX and XPS, confirmed that the TiO 2 one-dimensional (1D) nanopowder has been harvested. Due to the doping of F ions into the TiO 2 matrix, the asprepared samples show very high temperature stability up to 900 °C before being transformed into rutile structure phase, whereas the pure TiO 2 nanowires showed phase transformation at 300 °C. Hence this work is technologically and schematically interesting for the industrial preparation of highly thermally stable anatase 1D nanopowders.

In this study, photocatalytic degradation of Acid Orange 7 (AO7) by tungsten oxide nanopowder under UV irradiation was investigated with variation of pH, WO 3 dosage, initial AO7 concentration, purging gas, type of organic compounds and initial hydrogen peroxide concentration. Removal efficiency was decreased by increasing pH and initial AO7 concentration. The removal efficiency of AO7 was increased by purging of oxygen gas and by addition of hydrogen peroxide. The reaction rate constant (k obs ) was decreased from 0.0225 to 0.0006 min -1 with increasing initial AO7 concentration from 5 to 50 mg/L, respectively.

Sulfamethoxazole (SMX) is a sulfonamide broad-spectrum antibiotic drug which is frequently detected in the aquatic environment. SMX is introduced into the environment mostly via municipal wastewater effluents as conventional treatment processes do not result in complete removal. As such, there is a need to investigate new treatment methods to improve the removal of SMX. The aim of this study was to investigate SMX degradation at pH 4.8 using UV- radiation and UV- radiation combined with H 2 O 2 using a polychromatic (medium-pressure) mercury UV lamp. Primary characterization of the degradation products was performed using 1 H NMR spectroscopy and an analysis of the kinetics of degradation was performed. This study demonstrates that faster SMX degradation is achieved using a polychromatic UV light source compared to a 254 nm monochromatic light source, and that the addition of H 2 O 2 enhances UV degradation when the mg L -1 ratio of H 2 O 2 :SMX is less than 100. The calculated quantum yield was equal to 0.09 and the second-order rate constant for the degradation of SMX with hydroxyl radicals was 2.0×10 9 M -1 s -1 .

Bismuth oxybromide (BiOBr) has attracted a resurgence of interest due to the outstanding visible light driven photocatalytic performance, which has been widely reported. However, its photosensitization degradation performance of methyl orange (MO) is limited possibly caused by low negative LUMO (lowest unoccupied molecular orbitals) level of MO molecules. The work presented here deals with the improved photodegradation behavior of methyl orange molecules onto BiOBr in the presence of Rhodamine B (RhB, as photosensitizer) through a semiconductor-mediated process. It was found that MO could be photodecomposed much effectively under the assistance of RhB molecules from aqueous solution. The photosensitization process which occurred between RhB and BiOBr is of photochemical origin and responsible for the boosted photodegradation behavior towards MO, which strongly depends on the irradiation time, BiOBr dosage and concentration of model contaminant (MO) and photosensitizer (RhB).

Contamination of water by chemical and bacterial pollutants as well as ‘white pollution’ caused by carelessly discarded waste plastics are major environmental problems. In the current study, the possibility of using semiconductor photocatalysis for the removal of last traces of organic water pollutants of different types is investigated. Semiconductors ZnO and TiO 2 were characterized by standard techniques and evaluated as photocatalysts. The pollutants tested include low density polyethylene plastics (PEP), phenol, catechol and organophosphorous pesticides such as phosphamidon, monocrotophos and dichlorvos. Hydrogen peroxide (H 2 O 2 ) and peroxydisulphate (PDS) enhance the TiO 2 catalysed photomineralization rate. More than 10% of PEP could be irreversibly degraded in presence of UV-TiO 2 -PDS in 300 hr time. The degradation is pH dependent in all cases though no thumb rule can be applied. H 2 O 2 formed insitu during the degradation undergoes parallel decomposition resulting in stabilization or oscillation in its concentration depending on the equilibration or domination of the formation/ decomposition process. Anions naturally present in water such as NO 3 - , Cl - and CO 3 2- inhibit the degradation while SO 4 2- enhances the same. However, this effect depends on a number of factors and no generalized conclusions are possible. The results and the probable mechanism for the degradation of the pollutants are discussed.

Y 3+ doped TiO 2 pillared montmorillonite (denoted by Y-Ti-Na-MMT) was prepared by acid sol method using montmorillonite (Na-MMT) as the carriers. The catalysts were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), differential thermal analysis (TG), Brunauer-Emmett-Teller (BET)，X-ray photoelectron spectroscopy (XPS), and UV-vis diffuse reflectance spectra (DRS). The results showed that Y-Ti-Na-MMT had the best layer structure, the crystal type of TiO 2 nanoparticles was anatase and the introduction of Y 3+ could inhibit the growth of TiO 2 nanoparticles. The BET special surface area of Y-Ti- Na-MMT was 5.90 times of Na-MMT and 1.19 times of TiO 2 pillared montmorillonite (Ti-Na-MMT). Compared with Ti-Na-MMT, the band gaps of Y-Ti-Na-MMT calculated from cut-off wavelength decreased from 2.9 eV to 2.5 eV, exhibiting the higher light absorption. Y-Ti-Na-MMT was tested for photocatalytic degradation of methyl orange (MO) and it was more efficient in MO removal, in comparison with Ti-Na-MMT and TiO 2 . The calculated pseudo-first-order constants (Kr) were in the order of Y-Ti-Na-MMT (0.0147 min −1 ) > Ti-Na-MMT (0.0074 min −1 ) > TiO 2 (0.0027 min −1 ). The TOC removal rate increased to 39% for Y-Ti-Na- MMT. The reusing tests proved that Y-Ti-Na-MMT was stable, reusable and durable in degradation of MO.

In this study, electrochemical oxidation of Bromothymol blue (BTB) was studied in an aqueous medium (pH = 3) by electro-Fenton process (EFP). This chemical compound belongs to the family of sulfone phthalein, widely used for dyeing in the textile industry. EFP generates in a catalytic way hydroxyl radicals (•OH) which are powerful oxidant species (E 0 (•OH/H 2 O) = 2.8 V/NHE) used for the oxidation of organic pollutants. The kinetics of BTB degradation and the mineralization efficiency of its process are investigated through the effect of some operating parameters. The value of 300 mA as applied current, Fe 2+ as a catalyst with a concentration of 0.2 mM and a temperature of 40 °C are found to be the optimum operating parameters. The reaction kinetic follows a pseudo-first order with an absolute rate constant of 3.36 × 1010 M -1 s -1 . The efficiency of EFP is confirmed by the decrease of the molecule concentration during the treatment until its total disappearing. The chemical oxygen demand (COD) analyses indicate after 6 h a mineralization degree of 94% for the BTB synthetic solution, 91% for the effluent provided from a small Tunisian textile industry and 41% for the wastewater provided from a medium one. The energy consumption per unit COD mass (EC COD ) of the EFP is determined for the treatment of BTB synthetic solution and for the two real effluents. Concerning the BTB synthetic solution, the energetic cost is equal to 1.02 kWh (g COD) -1 at the beginning of the electrolysis and it has decreased to reach 0.30 kWh (g COD) -1 after 6 h. For the first effluent, the energy consumption rises from 1.20 to 0.36 kWh (g COD) -1 . An opposite phenomenon is observed for the second effluent.

A non-thermal plasma oxidation-alkali absorption NO removal system is designed by connecting sequentially an alkali aqueous solution absorption device to a gas discharge reactor. An experimental system of simulated flue gas NO removal using non-thermal plasma oxidation and Ca(OH) 2 aqueous solution absorption was established and influences of the concentrations of O 2 and H 2 O vapor on this kind of NO removal method were studied experimentally. The experimental results show that oxidation of NO in non-thermal plasma can be promoted by H 2 O vapor and the overall NO removal efficiency under this condition is higher than that of the system without H 2 O vapor added, which can be up to 7%. Due to the existence of O 2 in the present system, Ca(OH) 2 aqueous solution can play a certain role in improving the NO removal efficiency and the NO removal efficiency can increase by 10%-14% under this condition using the alkali absorption. When O 2 is added into the system and Ca(OH) 2 aqueous solution absorption device is connected sequentially to the non-thermal plasma reactor, the NO removal efficiency is enhanced after H 2 O vapor is added in the present system, which can obviously increase by 7%-17%.

The low-pressure high-frequency plasma chemical vapor deposition (CVD) system was developed with non-thermal plasma process to study the Polyethylene naphthalate (PEN) surface characteristics. Plasma surface treatment by oxygen can improve the adhesive properties. A mixture of Ar and O 2 gas was used in the plasma treatment. The oxygen gas flow rate was between 0.1 L/min and 0.5 L/min, whereas the Ar gas flow rate was set at 10 L/min. The surface was investigated by contact angle meter and X-ray photoelectron spectroscopy (XPS) to determine the differences between untreated and treated surfaces. The results indicated that the low-pressure high-frequency plasma chemical vapor deposition system could be used for surface modification.

There is growing interest in obtaining compounds with photocatalytic activity in the solar spectrum, and this has led to intense research on the topic. In our laboratory, Fe-doped TiO 2 was synthesized using the sol-gel method combined with the solvothermal technique at 200°C and calcined at temperatures between 350°C and 620°C. The samples were characterized by X-ray diffraction, Micro-Raman spectroscopy, Brunauer-Emmett-Teller specific surface area, diffuse reflectance spectroscopy, X-ray fluorescence and photocatalytic activity. All materials crystallized in the anatase phase. Additionally the 0.05% Fe-doped TiO 2 calcined at 620°C showed the presence of the rutile phase while 0.1% Fe-doped TiO 2 calcined at 620°C showed the presence of the brookite phase. Photoactivity was observed in the visible spectrum for 0.05% and 0.1% Fe-doped TiO 2 , calcined at 620°C. Visible activity was attributed to the presence of rutile and an absorption shift to the visible spectrum. Because of the temperature increment, the crystal size grew and the surface area decreased.

Argentum-loaded MCM-41 (Ag/MCM-41) was synthesized successfully by a hydrothermal method and used as a catalyst for the ozonation of p-chlorobenzoic acid (p-CBA) in aqueous solution. Ag/MCM-41 was characterized by low angle X-ray diffraction (XRD), nitrogen adsorption-desorption and transmission electron microscopy (TEM). Characterizations suggest that the prepared samples retained a highly regulated mesopores of hexagonal structure and a high BET surface area. The influences of argentum content, initial pH, reaction temperature on the catalytic ozonation were also evaluated. Ag/MCM-41/O 3 process exhibited a high catalytic activity with TOC removal at 30 min reaching 84% (only 44% by ozone alone). The presence of tert-butanol (TBA) in the process of Ag/MCM-41/O 3 inhibited the p-CBA removal, which verified the catalytic oxidation involved hydroxyl radicals. TOC removal rate only decreased 4% after being reused for four times, which indicated that Ag/MCM-41 had a good stability. Ag/MCM-41 is an effective catalyst in ozonation process.

Perfluorooctane sulfonate (PFOS) has received increasing attention due to its persistence in the environment, accumulation and global occurrence. The enhancement of the photochemical oxidative degradation of perfluorooctane sulfonate upon addition of ferric ions under 254-nm UV and 185-nm vacuum UV (VUV) light was observed for the first time. In the presence of ferric ions (100 μM) and at pH 3.0, 85.3% of the initial PFOS (20 μM) was decomposed, with the rate constant of 1.92 d -1 and the defluorination ratio reached 47.5% within 24 h under 254-nm UV irradiation. The influences of the ferric ion concentration, the solution pH and the UV wavelength on the PFOS photodecomposition were investigated. In addition, the photochemical decomposition of PFOS in the secondary effluent from a municipal wastewater plant was investigated. The coexisting organic matter in the secondary effluent greatly reduced the PFOS decomposition rate to less than 1/3 of that in pure water under 254-nm UV irradiation. However, under 185-nm VUV light the coexisting organic matter could be quickly degraded, and accordingly their adverse impacts could be largely eliminated. Moreover, the influences of initial PFOS concentration in the secondary effluent was examined under UV 254 or UV 254+185 light in the presence of ferric ions (100 μM), PFOS at a lower concentration (2 μM) decomposed much faster than that at a higher concentration (20 μM), and its decomposition intermediates, i.e., C2-C7 perfluorinated carboxylic acids, could also be decomposed and mineralized.

The electrochemical oxidation of 1,4 dihydroxybenzene, was studied by galvanostatic electrolysis using boron-doped diamond (BDD) as anode. The efficiency of the electrochemical process was found to depend mainly on the pollutant concentration present in the waste and on the applied current density. The voltammetric results showed that hydroquinone oxidation takes place in the same potential region as that of phenol where the supporting electrolyte is stable. Synthetic wastewaters containing hydroquinone have been treated in a bench-scale electrolysis plant. This plant operates in a discontinuous mode by recirculating the waste continuously through a single-chamber electrochemical flow cell. The complete mineralization of hydroquinone and the electro-generated pollutants is obtained in the electrolytic device. HPLC analyses show the formation of carboxylic acids as the main intermediates. The high efficiency of this technology can be explained in terms of the direct electro-oxidation at the BDD surface and the oxidation carried out by hydroxyl radicals and other electro-generated oxidants.

Electrical discharges generated at water-gas interface in a dielectric barrier discharge reactor have been tested for the degradation and mineralization of a model pharmaceutical compound sulfamethoxazole (SMX). Nonthermal plasma degradation of the pollutant proceeds via in-situ generation of active species like hydroxyl radical (HO•), hydrogen peroxide and ozone. It has been observed that degradation and mineralization of SMX was enhanced on addition of ZrO 2 /CeO 2 catalyst to the plasma reactor. Typical results indicated that SMX degradation followed first-order kinetics.