Electrocatalytic treatment of wastewaters

The electrocoagulation tests were carried out considering both relatively high metal contents (in the range of ppm) and very low metal concentrations (in the range of ppb). The experiments with very low metal concentrations were carried out in the framework of a collaboration project with the metropolitan water agency of Turin (SMAT). The scope of the work was to investigate the performance of the electrocoagulation process, in order to produce drinking water, using aluminum electrodes to remove nickel and chromium from two different water-well samples. Different experimental parameters, such as stirring, distance between the electrodes and current density, were examined. The test campaign carried out on these two water samples has shown that the removal process of nickel is faster than that of chromium. In the case of water poisoned by nickel, a final concentration of 5 ppb was achieved, starting from 41 ppb, while the chromium case showed a final concentration of 10 ppb compared to the initial one of 20 ppb. As far as the second part of the thesis is concerned, several experiments were carried out in order to obtain a complete understanding of the organic electooxidation process. To this end, a preliminary approach, based on a voltammetric analysis in a solution containing phenol in laboratory cells with Pt electrodes, was carried out. In this preliminary investigation, phenol was used as a model organic contaminant, since this compound has been widely investigated and reported on in the literature. As a result of the study on the model compound, general knowledge of the voltammetric technique was obtained and the best conditions for cleaning and reactivating the Pt electrodes in the presence of phenol were assessed. The investigation was then devoted to the abatement of urea by means of electroxidation. Cyclic voltammetry tests with laboratory cells were carried out, and these were followed by a series of tests in a pilot plant cell. In this investigation, it was possible to determine the conditions for urea oxidation by using different kinds of electrodes which, according to what has been reported in the literature, can be classified as active or non-active. The best conditions for the abatement of urea were through the use of boron diamond doped (BDD) electrodes and Pt electrodes. Finally, purposely fabricated SnO2-Sb2O5/ Ti electrodes were tested, due to their highly promising behaviour with respect to the increase in the oxygen evolution overpotential and service life. Different thicknesses of the Sn-Sb oxide layers were considered and a complete physico-chemical and electrochemical characterization of the electrodes was obtained.