Iron oxide nanoparticles as heterogeneous electro-Fenton catalysts for the removal of AR18 azo dye.

Heterogeneous electro-Fenton mineralization of Acid Red 18 (AR18) in aqueous solution was studied with magnetite Fe3O4 (MNPs) and haematite Fe2O3 (HNPs) nanoparticles as catalysts. High mineralization yields of AR18 were obtained with magnetite, 81% TOC removal after 180 min of electrolysis in 40 mg L-1 Fe3O4, pH 3.0, at 50 mA of current intensity and in 50 mM Na2SO4. In order to explain the obtained mineralization yield achieved with MNPs, the quantification of hydrogen peroxide (H2O2), hydroxyl radical (•OH) and iron leaching were performed at 50 and 100 mA. From the high iron concentration found in the bulk solution and the slight impact of the catalyst mass concentration on TOC removal, the formation of hydroxyl radicals occurs mainly through homogeneous process. In the presence of hydroxyl radical scavenger, degradation remained total after 15 min showing the involvement of a direct electrochemical oxidation of the dye at the electrode surface. The hydroxyl radical oxidation is responsible for at least 50% of mineralization.

Electrochemical advanced oxidation processes using novel electrode materials for mineralization and biodegradability enhancement of nanofiltration concentrate of landfill leachates.

The objective of this study was to implement electrochemical advanced oxidation processes (EAOPs) for mineralization and biodegradability enhancement of nanofiltration (NF) concentrate from landfill leachate initially pre-treated in a membrane bioreactor (MBR). Raw carbon felt (CF) or FeIIFeIII layered double hydroxides-modified CF were used for comparing the efficiency of homogeneous and heterogeneous electro-Fenton (EF), respectively. The highest mineralization rate was obtained by heterogeneous EF: 96% removal of dissolved organic carbon (DOC) was achieved after 8 h of electrolysis at circumneutral initial pH (pH0 = 7.9) and at 8.3 mA cm-2. However, the most efficient treatment strategy appeared to be heterogeneous EF at 4.2 mA cm-2 combined with anodic oxidation using Ti4O7 anode (energy consumption = 0.11 kWh g-1 of DOC removed). Respirometric analyses under similar conditions than in the real MBR emphasized the possibility to recirculate the NF retentate towards the MBR after partial mineralization by EAOPs in order to remove the residual biodegradable by-products and improve the global cost effectiveness of the process. Further analyses were also performed in order to better understand the fate of organic and inorganic species during the treatment, including acute toxicity tests (Microtox®), characterization of dissolved organic matter by three-dimensional fluorescence spectroscopy, evolution of inorganic ions (ClO3-, NH4+ and NO3-) and identification/quantification of degradation by-products such as carboxylic acids. The obtained results emphasized the interdependence between the MBR process and EAOPs in a combined treatment strategy. Improving the retention in the MBR of colloidal proteins would improve the effectiveness of EAOPs because such compounds were identified as the most refractory. Enhanced nitrification would be also required in the MBR because of the release of NH4+ from mineralization of refractory organic nitrogen during EAOPs.

Sulfamethazine removal by means of a combined process coupling an oxidation pretreatment and activated sludge culture - preliminary results.

A coupled electrochemical process and biological treatment was used to remove a biorecalcitrant antibiotic: sulfamethazine (SMT). The pretreatment was performed in a home-made flow cell involving graphite felt as a working electrode at potentials of 1 and 1.6 V/saturated calomel electrode (SCE); it was followed by a biological process involving activated sludge purchased from a local wastewater treatment plant. Activated sludge cultures of pretreated and non-pretreated SMT solution were carried out for 3 weeks, and different parameters were monitored, especially total organic carbon (TOC) and SMT concentrations. high-performance liquid chromatography results revealed that the target molecule was not assimilated by activated sludge. However, and confirming the improvement previously observed for the biological oxygen demand/chemical oxygen demand (BOD5/COD) ratio, from 0.08 before electrolysis to 0.58 after electrolysis, a pretreatment step in oxidation at 1.6 V/SCE led to a fast decrease of TOC during the subsequent biological treatment, since the mineralization yields increased from 10% for a non-pretreated SMT solution to 76.6% after electrolysis in oxidation (1.6 V/SCE), confirming the efficiency of coupling the electro-oxidation process with a biological treatment for the mineralization of SMT. Moreover, when the electrolysis was performed at 1 V/SCE, no biodegradation was observed, underlining the importance of the electrochemical pretreatment.

Degradation of enoxacin antibiotic by the electro-Fenton process: Optimization, biodegradability improvement and degradation mechanism.

This study aims to investigate the effectiveness of the electro-Fenton process on the removal of a second generation of fluoroquinolone, enoxacin. The electrochemical reactor involved a carbon-felt cathode and a platinum anode. The influence of some experimental parameters, namely the initial enoxacin concentration, the applied current intensity and the Fe(II) amount, was examined. The degradation of the target molecule was accompanied by an increase of the biodegradability, assessed from the BOD5 on COD ratio, which increased from 0 before treatment until 0.5 after 180 min of electrolysis at 50 mg L(-1) initial enoxacin concentration, 0.2 mmol L(-1) Fe(II) concentration and 300 mA applied current intensity. TOC and COD time-courses were also evaluated during electrolysis and reached maximum residual yields of 54% and 43% after 120 min of treatment, respectively. Moreover, a simultaneous generation of inorganic ions (fluorides, ammonium and nitrates) were observed and 3 short chain carboxylic acids (formic, acetic and oxalic acids) were identified and monitored during 180 min of electrolysis. By-products were identified according to UPLC-MS/MS results and a degradation pathway was proposed.

Trace lead analysis based on carbon-screen-printed-electrodes modified via 4-carboxy-phenyl diazonium salt electroreduction.

This paper describes the use of 4-carboxyphenyl-grafted screen-printed carbon electrodes (4-CP-SPEs) for trace lead analysis. These novel and simple use of electrodes were easily prepared by the electrochemical reduction of the corresponding diazonium salt. Pb detection was then performed by a three-steps method in order to avoid oxygen interference: (i) immersion of the grafted screen-printed electrode (SPE) in the sample and adsorption of Pb(II), (ii) reduction of adsorbed Pb(II) by chronoamperometry (CA), and (iii) oxidation of Pb by Anodic Square Wave Voltammetry (SWV). The reoxidation response was exploited for lead detection and quantification. In order to optimize the analytical responses, the influence of the adsorption medium pH and the adsorption time were investigated. Moreover, an interference study was carried out with Cu(II), Hg(II), Al(III), Mn(II), Zn(II), Cd(II) and no major interference can be expected to quantify Pb(II). The described method provided a limit of detection and a limit of quantification of 1.2 × 10(-9)M and 4.1 × 10(-9)M, respectively. These performances indicate that the 4-CP-SPE could be considered as an efficient tool for environmental analysis.

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.

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.

Treatment of electroplating wastewater containing Cu2+, Zn2+ and Cr(VI) by electrocoagulation.

The performance of electrocoagulation, with aluminium sacrificial anode, in the treatment of metal ions (Cu2+, Zn2+ and Cr(VI)) containing wastewater, has been investigated. Several working parameters, such as pH, current density and metal ion concentrations were studied in an attempt to achieve a higher removal capacity. Results obtained with synthetic wastewater revealed that the most effective removal capacities of studied metals could be achieved when the pH was kept between 4 and 8. In addition, the increase of current density, in the range 0.8-4.8 A dm(-2), enhanced the treatment rate without affecting the charge loading, required to reduce metal ion concentrations under the admissible legal levels. The removal rates of copper and zinc were found to be five times quicker than chromium because of a difference in the removal mechanisms. The process was successfully applied to the treatment of an electroplating wastewater where an effective reduction of (Cu2+, Zn2+ and Cr(VI)) concentrations under legal limits was obtained, just after 20 min. The electrode and electricity consumptions were found to be 1 g l(-1) and 32 A h l(-1), respectively. The method was found to be highly efficient and relatively fast compared to conventional existing techniques.