Nizar Bellakhal

Degradation of Acid Orange 7 by electrochemically generated •OH radicals in acidic aqueous medium using a boron-doped diamond or platinum anode: A mechanistic study

A comparative study of the degradation of Acid Orange 7 (AO 7) aqueous solutions in acidic medium of pH 3.0 by electro-Fenton process using Pt or boron-doped diamond (BDD) anode was reported. The oxidative degradation of AO 7 by electrochemically generated hydroxyl radicals follows a pseudo-first order kinetic with a similar rate constant with BDD or Pt anode. The absolute rate constant of the AO 7 hydroxylation reaction was determined as (1.10+/-0.04)x10(10)M(-1)s(-1) by using the competition kinetic method. The comparative study of TOC measurements during electro-Fenton treatment showed a higher mineralization rate with BDD than Pt anode at the first hours of electrolysis because of the higher oxidizing power of this anode. The electro-Fenton degradation of AO 7 was followed by monitoring the formation and evolution of aromatic intermediates which are oxidized to aliphatic carboxylic acids before mineralization (transformation to CO(2) and inorganic ions, i.e. sulphate, nitrate and ammonium). The follow-up of the solution toxicity evolution shows the formation of intermediates more toxic than AO 7 and the connection between toxicity and aromaticity. A mineralization reaction pathway of AO 7 by electro-Fenton degradation involving all the intermediates identified was proposed.

Electrocoagulation treatment of black liquor from paper industry.

The procedure of electrocoagulation is an effective, fast and economic technique for treatment of black liquor resulting from paper industry. The effect of electrolysis time, current density, type of electrode material and initial pH were studied in an attempt to achieve a higher removal capacity. Under the optimal experimental conditions (initial pH 7, t=50 min and J=14 mA cm(-2)), the treatment of black liquor by electrocoagulation has led to a removal capacity of 98% of COD, 92% of polyphenols and 99% of color intensity with a good repeatability (R.S.D.<3%) making it possible to highlight the industrial interest of this electrochemical process.

Indirect electroreduction as pretreatment to enhance biodegradability of metronidazole.

The removal of metronidazole, a biorecalcitrant antibiotic, by coupling an electrochemical reduction with a biological treatment was examined. Electroreduction was performed in a home-made flow cell at -1.2V/SCE on graphite felt. After only one pass through the cell, analysis of the electrolyzed solution showed a total degradation of metronidazole. The biodegradability estimated from the BOD5/COD ratio increased from 0.07 to 0.2, namely below the value usually considered as the limit of biodegradability (0.4). In order to improve these results, indirect electrolysis of metronidazole was performed with a titanium complex known to reduce selectively nitro compounds into amine. The catalytic activity of the titanium complex towards electroreduction of metronidazole was shown by cyclic voltammetry analyses. Indirect electrolysis led to an improvement of the biodegradability from 0.07 to 0.42. To confirm the interest of indirect electroreduction to improve the electrochemical pretreatment, biological treatment was then carried out on activated sludge after direct and indirect electrolyses; different parameters were followed during the culture such as pH, TOC and metronidazole concentration. Both electrochemical processes led to a more efficient biodegradation of metronidazole compared with the single biological treatment, leading to an overall mineralization yield for the coupling process of 85%.

Olive Oil Mill Wastewater Treatment by the Electro-Fenton Process

Environmental Context. The combination of the Fenton’s reagent with electrochemistry (the electro-Fenton process) represents an efficient method for wastewater treatment. This study describes the use of this process to clean olive oil mill wastewater, which is a real environmental problem in Mediterranean countries. Contrary to the conventional methods which reduce the pollution by removing the pollutants from the wastewater, the electro-Fenton process is shown to fully destroy (mineralize) olive oil mill wastes in water without previous extraction and without addition of chemical reagents. Abstract. Treatment of olive oil mill wastewater is one of the most important environmental problems for Mediterranean countries. This wastewater contains many organic compounds like polyphenols, which are very difficult to treat by classical techniques. An advanced electrochemical oxidation process, the electro-Fenton process, has been used as a way of removing chemical oxygen demand and colour intensity from olive oil mill wastewater. Vanillic acid, which has been selected as a model compound, and olive oil mill wastewater have been completely mineralized by the electro-Fenton process with a carbon felt cathode, using Fe2+ ions as the catalyst.

Application of Doehlert matrix to determine the optimal conditions of electrochemical treatment of tannery effluents.

The oxidation of organic and inorganic pollutants present in tannery effluents has been realised by electrochemical way. The influence of the electrochemical reactor parameters was carried out by the use of Doehlert matrix. The obtained results have shown that the current intensity and the electrolysis time were the main influent parameters on the removal ratio of chemical oxygen demand (COD), total organic carbon (TOC), electrochemical oxidation of trivalent chromium and sulphite ions.

Comparative mineralization of textile dye indigo by photo-Fenton process and anodic oxidation using boron-doped diamond anode

Abstract In the present study, we applied two advanced oxidation processes (AOPs); photo-Fenton and anodic oxidation (using a boron doped diamond (BDD) anode) processes, to oxidative degradation and mineralization of the textile dye Indigo in sodium dithionite aqueous media. The effect of key parameters, such as H2O2 dosage for photo-Fenton process and initial pH for anodic oxidation, on the degradation and mineralization kinetics of dye Indigo was investigated. The highest mineralization rates were observed at pH 3.0 for anodic oxidation process, and for a ratio R: [H2O2]/[Fe2+] = 40 for photo-Fenton process. Under optimal operating conditions a complete mineralization of Indigo dye was achieved after 7 h treatment by anodic oxidation whereas only 63% of TOC removal was obtained after 10 h treatment by photo-Fenton process. The carboxylic acids (glyoxylic, malonic, oxalic, acetic and formic) formed as oxidation by-products were identified and their evolution was followed by ion-exclusion chromatography. ...

Treatment of an aqueous pesticides mixture solution by direct and indirect electrochemical advanced oxidation processes.

In the present work, a comparative study on the degradation of a mixture of three pesticides (chlortoluron, carbofuran and bentazon) has been carried out by electrochemical advanced oxidation processes such as anodic oxidation and electro-Fenton using boron-doped diamond (BDD) anode. These processes are based on the in situ production of hydroxyl radical, a highly strong oxidant, which allows the degradation of organic pollutants until their mineralisation into CO2 and H2O. Obtained results showed that more than 90% of TOC removal was obtained in 4 h of treatment by both processes. The mineralisation rate was found to be higher for electro-Fenton (BDD) than that of the anodic oxidation. Also, the electro-Fenton (BDD) can mineralise the pesticide solution in 90 min while anodic oxidation requires 150 min. The released inorganic ions, such as chloride, nitrate, sulphate and ammonium, are identified and their kinetic evolution was measured by ion chromatographic analyses.

Preparation of zinc oxide films by oxygen plasma treatment of zinc foils

Exposure of zinc foils to an inductively coupled low pressure r.f. oxygen plasma leads to the formation of ZnO thin films which are spectroscopically and electrochemically characterized. The oxidation kinetics depends on the time exposure to the plasma at fixed electric power and gas pressure.

Electrochemical investigation of the oxides formed at the surface of brass (Cu–10Zn) by a humid-air plasma treatment

Abstract Linear potential sweep voltammetry was used to characterize the metal oxides formed at the surface of brass (Cu–10Zn) foils exposed to a gliding-arc-humid-air plasma. This study confirmed the formation of copper and zinc oxides (i.e. Cu2O, CuO, and ZnO). The electrochemical reduction curves in aqueous solutions of the different brass samples showed that copper and zinc oxides were characterized by their cathodic peaks. The reduction potentials of the oxides varied with the exposure time to the plasma at fixed working conditions. The analysis of the voltammetry curves showed that the initial oxide layer was formed in majority by the precursor oxide CuxO (x>4) and Cu2O. The oxidation of Cu(I) oxide (CuxO and Cu2O) lead to the formation of CuO. When the CuO layer was extensively grown, the ZnO oxide began to grow. A mechanism was proposed for the reduction of thin films containing Cu2O, CuO and ZnO oxides formed at the surface of the sample.

Heat transfer to metals in low pressure oxygen plasma: application to oxidation of the 90Cu-10Zn alloy

Abstract A low pressure inductively coupled oxygen plasma was used to oxidize the surface of α-brass (90Cu–10Zn) foils. Electrochemical and optical (i.e, UV–Vis–Nir diffuse reflectance spectroscopy and FTIR) investigation techniques show that the oxide layer initially formed on chemically cleaned samples mainly involve the copper oxides; the initial oxide layer was formed in majority by copper oxides Cu 2 O and CuO. When the CuO layer is extensively grown, a ZnO layer begins growing together with CuO. The thickness and composition of the oxide films formed at the surface are governed by matter and energy transfers between the plasma and brass surface. The influence of the reactor working parameters is also considered.