Abdellatif Gadri

Treatment of aqueous wastes contaminated with Congo Red dye by electrochemical oxidation and ozonation processes.

Synthetic aqueous wastes polluted with Congo Red (CR) have been treated by two advanced oxidation processes: electrochemical oxidation on boron doped diamond anodes (BDD-EO) and ozonation under alkaline conditions. For same concentrations, galvanostatic electrolyses have led to total COD and TOC removals but ozonation process can reach only 85% and 81% of COD and TOC removals, respectively. UV-vis qualitative analyses have shown different behaviors of CR molecules towards ozonation and electrochemical oxidation. Rapid discoloration has been observed during ozonation, whereas color persistence till the end of galvanostatic electrolyses has been seen during BDD-EO process. It seems that the oxidation mechanisms involved in the two processes are different: simultaneous destruction of azoic groups is suggested during ozonation process but consecutive destruction of these groups is proposed during BDD-EO. However, energetic study has evidenced that BDD-EO appears more efficient and more economic than ozonation in terms of TOC removals. These results have been explained by the fact that during BDD-EO, other strong oxidants electrogenerated from the electrolyte oxidation such as persulfates and direct-oxidation of CR and its byproducts on BDD anodes complement the hydroxyl radicals mediated oxidation to accomplish the total mineralization of organics.

Electrochemical mineralization of the antibiotic levofloxacin by electro-Fenton-pyrite process.

Levofloxacin is a large spectrum antibiotic from fluoroquinolones family, widely used and detected in natural waters. Here, this drug was degraded by a novel heterogeneous electro-Fenton (EF) process, so-called EF-pyrite, in which pyrite powder in suspension regulates the solution pH to 3.0 and supplies 0.2mM Fe(2+) as catalyst to the solution. Trials were performed with a stirred boron-doped diamond (BDD)/carbon-felt cell under O2 bubbling for cathodic H2O2 generation. Hydroxyl radicals formed from water oxidation at the BDD anode and in the bulk from Fentons reaction between Fe(2+) and H2O2 were the main oxidizing agents. The effect of applied current and antibiotic concentration over the mineralization rate and degree, mineralization current efficiency and specific energy consumption was studied. An almost total mineralization was achieved for a 0.23mM drug solution operating at 300mA for 8h. The kinetic decay of the drug was followed by reversed-phase HPLC and obeyed a pseudo-first-order reaction. Ion-exclusion HPLC analysis of treated solutions revealed that oxalic and oxamic acids, the most persistent final products, were the predominant pollutants remaining in solution at long electrolysis time. Ion chromatography analysis confirmed the release of F(-), NO3(-) and NH4(+) ions during levofloxacin mineralization.

Electrochemical treatment of concentrate from reverse osmosis of sanitary landfill leachate.

Conventional sanitary landfill leachate treatment has recently been complemented and, in some cases, completely replaced by reverse osmosis technology. Despite the good quality of treated water, the efficiency of the process is low and a large volume of reverse osmosis concentrate has to be either discharged or further treated. In this study, the use of anodic oxidation combined with electro-Fenton processes to treat the concentrate obtained in the reverse osmosis of sanitary landfill leachate was evaluated. The anodic oxidation pretreatment was performed in a pilot plant using an electrochemical cell with boron-doped diamond electrodes. In the electro-Fenton experiments, a boron-doped diamond anode and carbon-felt cathode were used, and the influence of the initial pH and iron concentration were studied. For the experimental conditions, the electro-Fenton assays performed at an initial pH of 3 had higher organic load removal levels, whereas the best nitrogen removal was attained when the electrochemical process was performed at the natural pH of 8.8. The increase in the iron concentration had an adverse impact on treatment under natural pH conditions, but it enhanced the nitrogen removal in the electro-Fenton assays performed at an initial pH of 3. The combined anodic oxidation and electro-Fenton process is useful for treating the reverse osmosis concentrate because it is effective at removing the organic load and nitrogen-containing species. Additionally, this process potentiates the increase in the biodegradability index of the treated effluent.

Enhanced degradation of the antibiotic tetracycline by heterogeneous electro-Fenton with pyrite catalysis

There is actually increasing concern about the accumulation of antibiotics, such as tetracycline, in soil and water bodies. There is therefore a need for efficient methods to degrade antibiotics and thus clean waters. Here we tested the degradation of tetracycline using the heterogeneous electro-Fenton-pyrite method and compared the results with the conventional electro-Fenton method. The reaction was performed with a boron-doped diamond or Pt anode and carbon-felt cathode allowing electrogeneration of H2O2 from O2 reduction. Results show an increasing tetracycline mineralization using the following methods: anodic oxidation with electrogenerated H2O2, electro-Fenton and then electro-Fenton-pyrite using boron-doped diamond. Ion-exclusion HPLC revealed the complete removal of malic malonic, succinic, acetic, oxalic and oxamic acids. Nitrogen present in tetracycline was mainly mineralized in NH4+. The higher efficiency of electro-Fenton-pyrite is explained by self-regulation of soluble Fe2+ and pH to 3.0 from pyrite catalyst favoring larger ·OH generation from Fenton’s reaction.

Anodic Oxidation of Aqueous Wastes Containing Hydroquinone on BDD Electrode

Abstract 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.

Electrochemical treatment of aqueous solutions of organic pollutants by electro-Fenton with natural heterogeneous catalysts under pressure using Ti/IrO2-Ta2O5 or BDD anodes

The treatment of toxic organic pollutants by electro-Fenton (EF) presents some drawbacks such as the necessity to work at low pH and the low solubility of oxygen in water contacted with air or oxygen at room pressure that results often in slow and relatively low abatements. Here, the coupled adoption of natural heterogeneous catalysts and of relatively high pressure was proposed in order to improve the performances of EF for the treatment of organic pollutants. Caffeic acid (CA) and 3-chlorophenol were used as model resistant organic pollutants. EF process was performed using both conventional homogeneous FeSO4 and natural heterogeneous catalysts (pyrite, chalcopyrite, Fe2O3 and Fe3O4) as iron catalysts and oxygen at various pressures in the absence or in the presence of BDD anode. The effect of the nature of the catalyst, the oxygen pressure, the current density and the catalyst load was widely investigated in order to optimize the process. It was shown that the coupled utilization of a natural heterogeneous catalyst such as chalcopyrite and a relatively high pressure allows to obtain the total removal of CA and a high removal of the TOC (about 75%) in short times (2 h) with relatively high current efficiencies using an Iridium based anode. In the case of 3-chlorophenol, the utilization of a BDD anode was necessary to achieve a high removal of the pollutant and the TOC. It was shown that the removal of 3-chlorophenol can be effectively performed in different water bodies and with different initial concentrations of 3-chlorophenol.

Towards sustainable removal of methylthioninium chloride by using adsorption-electroradical regeneration

The current need for effective regeneration processes to be used in valorization of spent adsorbent demands the research of novel alternative techniques such as application of Advances Oxidation Processes. In this sense, the recent application of electroradical (ER) processes turned out to be very promising in terms of the drugs degradation from different environments. Thus, in this study, harnessing of a low cost natural adsorbent, Tunisian bentonite (BE), was evaluated for the removal of a model drug such as methylthioninium chloride (MC), and then its regeneration by ER processes was demonstrated. Initially, the BE was characterized and the adsorption of the MC was studied. This process followed a pseudo-first order kinetic and Langmuir isotherm fitted well to data reaching uptake values around 145-155 mg g-1. After that, BE regeneration by an ER process such as electro-Fenton process was ascertained. Due to the high buffering capacity of the BE, the addition of citric acid (1 mM) was necessary in order to assure the acidic medium to favor the oxidation reaction. By operating under optimized experimental conditions (current intensity 300 mA, pH 3, Fe2+ (1 mM) and citric acid (1 mM)) near complete adsorbent regeneration was achieved after 300 min of treatment and the pseudo-first-order model fitted well the degradation data. Furthermore, the adsorbent was efficiently used in successive cycles of adsorption-regeneration without operational problems that proved the efficiency of this technology. From the obtained results, a side-by-side configuration was designed and simulated, confirming the viability of the design at large scale.