The electrochemical oxidation of phenol in basic media using a diamond thin-film electrode has been studied. Within the parameter ranges used (temperature: 15-60 °C, initial total carbon concentration: 360-1450 mg of C dm -3 ; current density: 15-60 mA cm -2 ), almost complete mineralization of the organic waste is obtained. The mineralization rate increases with current density and temperature. Current efficiency depends mainly on mass transfer limitations: in the absence of mass transfer limitations, instantaneous current efficiencies of 1 are obtained. The main intermediates formed are maleic, fumaric, and oxalic acids. A simple model based on mass transfer and kinetic considerations, which involves four species (phenol, maleic/fumaric acid, oxalic acid, and carbon dioxide), can be used to explain the experimental behavior of the system, regardless of the conditions applied.

The effect of the current intensity in the electrochemical oxidation of aqueous phenol wastes at an activated carbon and steel anode was investigated. Results confirm that three reaction pathways were involved in the electrochemical process:  direct degradation or electrochemical cold combustion, chemical oxidation, and polymerization. The chemical oxidation pathway was the most important for the range of current intensities studied. To interpret the experimental behavior, a simple mathematical model was proposed and tested, obtaining good agreements between experimental and simulated data.

The electrochemical oxidation of diluted cyanide aqueous wastes has been studied in a single compartment electrochemical flow cell. It has been determined that the anode material influences greatly the process's performance. Boron doped diamond and PbO 2 anodes can oxidize these wastes in the presence of both sulfate or chloride anions. On the contrary, dimensional stable anodes cannot oxidize cyanide in sulfate-containing wastewaters, and require the presence of chloride ions. The oxidation of cyanides leads to the formation of cyanate in a first step, and later to the formation of carbon dioxide and nitrogen. There is a net consumption of hydroxyl ions during the process. Energy consumptions in the range 20-70 kWh m −3 are required to decrease the initial pollutant load by 70-80%. Global current efficiencies in the range 3-8% are obtained. These low current efficiencies are justified by the low cyanide concentrations that the wastes used in this work contain.

No abstract