Previous studies of the Group evidenced that the kinetics of the removal of pollutants from industrial wastewater by electrolysis is a function of the anode material and of the applied electrochemical parameters. These factors govern the type of electrode reactions, including an eventual direct discharge of pollutants and the relative contribution of direct and mediated electro-oxidation. On the basis of the experimental results two anode materials: Ti/Pt-Ir and Ti/PdO-Co₃O₄ can be indicated as appropriate for electrochemical treatment of those wastewaters, in which removal of pollutants is to be achieved by an indirect, Cl₂ mediated oxidation. These two materials proved to be excellent catalysts for the chlorine evolution reaction. Under certain conditions, participation of other mediators, apart of active chlorine, as e.g. hydrogen peroxide or hydroxyl radicals, was also proved possible. Generally, the depletion of pollutants was well described by a pseudo-first order kinetics. For example the kinetic rate constant equal to 0.75 min^-1 was achieved for N-NH₃ removal from tannery wastewater using the Ti/PdO-Co₃O₄ anode. In case the organic load is efficiently removed by a conventional biological process, electrochemical oxidation can be applied as a post-treatment step to remove residual N-NH₃ with low energy consumption (0.4 kWh/m³), offering a valid alternative to biological nitrification/denitrification. Experimental results proved also the feasibility of application of electro-oxidation for the destruction of the pollutants present in dyeing baths containing partially soluble disperse dyes. Electrochemical oxidation, which leaded to substantial decolorisation, is a promising tod for treatment of this kind of wastewater. The efficiency of the treatment depended on the nature of the supporting electrolyte and the bulk pH in the reactor and, to a lesser degree, on the type of the anode material. The best results were obtained in a chloride-rich medium under acidic pH using the Ti/Pt-Ir anode. Since a cyclic voltammetry study showed no direct discharge of pollutants at the Ti/Pt-Ir anode, it was concluded that the process was mediated by chlorine-hypochlorite species obtained via electro-oxidation of chlorides at the anode and (·OH) radicals generated during water discharge. The apparent pseudo-first order rate constant for the removal of colour was equal to 2.54 x10^-4 s^-1 under conditions of free pH evolution. The control of pH at the acidic level at the value of 4.5 resulted in an over 30-fold increase of the reaction rate. Less encouraging results obtained during the comparative chemical oxidation of pollutants by hypochlorite ions indicate that electrochemical oxidation is preferred to the commonly applied chemical treatment. Interesting results were also obtained for direct anodic oxidation of cyanides, a reaction which proceeded simultaneously with the formation of the catalytic film of Cu oxides on the electrode. This was possible for low agitation rates, as otherwise film was sheared from the electrode surface. A shearing rate y and shearing stress t acting on the anode surface were quantified by a polarographic method consisting in measuring the limiting diffusional current IL of the reduction of ferricyanide ions on the cathode. This method gives generally results which agree accurately with the laser Doppler measures. The experiments performed using a solution containing a mixture of 2 x 10^-3 M potassium ferricyanide, 5x 10^-2 M potassium ferrocyanide and 0.5 M sodium hydroxide as supporting electrolyte served to define the average limiting current IL, that can be related to the average surface shear rate by appropriate equations, which are reported in the Poster. An alternative biological treatment for azo dyes was also tested. When the azo dyes are subjected to anaerobic treatment they can undergo, by contrary to what is observed under aerobic conditions, a reductive clearage with a rupture of the -N=N- bond and formation of aromatic amines. A study undertaken to elucidate the influence of the ratio between the concentration of the dye and that of additional carbon, on the performance of anaerobic reactor treating synthetic textile wastewater containing the Procion Brilliant Red H-EGXL dye, was performed using a fed-batch reactor, operated under isothermal conditions at 30 °C, with different feed. Removal of colour from the synthetic textile wastewater has been shown to be feasible in the reactor operating under anaerobic/anoxic conditions, provided the dye concentration in the feed being lower than 2.2 g/L. However, the obtained effluent contained still the organic load and nitrogen and it was necessary to apply a post treatment using electrochemical oxidation.

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