This study examined the oxidation of phenol by electrochemical processes using different mixed-metal oxide (MMO) anodes, namely, Ti/Pt, Ti/IrO 2 -Ta 2 O 5 , Ti/Ta 2 O 5 -SnO 2 -IrO 2 , Ti/RuO 2 and Ti/IrO 2 -RuO 2 . First, the effectiveness of different anodes by phenol oxidation was evaluated with the help of such parameters as cyclic voltammetry (CV), current efficiencies and degradation rates. The Ti/Pt anode was found to be the most effective of all types of anodes, as almost complete phenol degradation was gained with its use. Then, optimum operational conditions, applied current density and initial pH, were determined using Ti/Pt as the anode. By-products of phenol degradation (benzoquinone, hydroquinone, pyrocatechol, oxalic and maleic acid) arising gradually during the reaction were determined via high-performance liquid chromatography (HPLC) for all selected anodes. There was a considerable difference between the anodes with regard to degradation efficiency and concentrations of formed by-products. The toxicity was evaluated by measuring the natural luminescence of the bacteria, Vibrio fischeri, for all selected anodes. According to the toxicity assessment, a number of toxic by-products were formed from phenol degradation for all selected anodes. However, their toxicity decreased at the end of electrolysis on the Ti/Pt anode.

The objective of the present study is to describe a novel electro-peroxone (E-peroxone) process as a combination of two different systems for hydroxyl radical generation-ozonation and electrolysis-and to highlight its advantages for water and wastewater treatment compared to each system alone. An extensive review on the mechanism of the production of hydroxyl radical and in-situ generation of hydrogen peroxide, and the kinetics and efficiency of E-peroxone has been performed to evaluate the degradation and mineralization of different kinds of pollutants in aqueous media. The effects of experimental parameters such as ozone dose, applied current, solution of pH, anode type, and cathode selection on the efficiency of E-peroxone are discussed.

In this study, response surface methodology (RSM) was used to investigate the effects of different operating conditions on the removal of ciprofloxacin (CIP) by the electrocoagulation (EC) with pure iron electrodes. Box-Behnken design was used for the optimization of the EC process and to evaluate the effects and interactions of process variables such as applied current density, process time, initial CIP concentration and pH on the removal of CIP by the EC process. The optimum conditions for maximum CIP removal (86.6%) were found as pH = 4; Co = 5 mg.L(1-); Id = 4.325 mA.cm(2-); tprocess = 10 min. The model adequacy and the validity of the optimization step were confirmed with additional experiments which were performed under the proposed optimum conditions. The predicted CIP removal as 86.6% was achieved at each experiment by using the optimum conditions. These results specify that the RSM is a useful tool for optimizing the operational conditions for CIP removal by the EC process.

No abstract

The efficiency of TiO2 as a catalyst in the ozonation of humic acid (HA) was evaluated in a comprehensive manner. Ozonation, catalytic ozonation and adsorption experiments were conducted using both synthetic HA solution and natural water. HA degradation was evaluated in terms of DOC, VIS400 and UV254. It was shown that the addition of catalyst positively affects the mechanism of ozonation. An increase in HA degradation was observed for all these parameters. The impact of catalyst dose and initial pH value of HA on the efficacy of catalytic ozonation was investigated. The highest removal efficiencies were achieved with the dose of 1 g l(-1) of TiO2 (Degussa P-25) and in the acidic pH region. The catalytic ozonation process was efficient also on natural water component although not at the same level as it was on synthetic water. The adsorptive feature of P-25 was considered to have a clear evidence of the catalytic ozonation mechanism. The mechanism of catalysis on the surface of metal oxides was elucidated with the help of quantum-chemical calculations. In the framework of Density Function Theory (DFT), the O3 decomposition was calculated in the catalytic and non-catalytic processes. Donor-acceptor properties of the frontier (highest occupied and lowest unoccupied molecular orbitals, HOMO/LUMO) orbitals are discussed. Electron density distribution and reaction mechanism of superoxide particles formation, which participate in the process of HA ozonation are analyzed.