This work presents a novel approach of wastewater treatment technology that consists of a combined electrodialysis/electro-oxidation process, specially designed to allow increasing the efficiency in the oxidation of ionic organic pollutants contained in diluted waste. Respect to conventional electrolysis, the pollutant is simultaneously concentrated and oxidized, enhancing the performance of the cell due to the higher concentration achieved in the nearness of the anode. A proof of concept is tested with the ionic pesticide 2,4-D (2,4-dichlorophenoxyacetic acid) and results show that the efficiency of this new technology overcomes that electrolysis by more than double, regardless the supporting electrolyte used (either NaCl or NaSO). Moreover, the removal rate of 2,4-D when using NaCl was found to be more efficient, due to the best performance of the electrode material selected (DSA) towards the formation of oxidants in chloride supporting electrolyte. These results open the way for overcoming the efficiency limitations of electrochemical treatment processes for the treatment of solutions with low concentrated ionic pollutants.

Electrocoagulation is usually applied to remove pollutants from the liquid phase, but in this work it is investigated to concentrate pollutants, with the final aim to get a later much more efficient treatment by electrolysis. Results obtained during the treatment of wastes polluted with commercial oxyfluorfen (Fluoxil®) show that electrocoagulation exhibits a good efficiency in removing this model non-ionic halogenated pesticide. It was observed that the chemicals contained in Fluoxil® with higher solubility than oxyfluorfen are less efficiently removed, explaining the lower removal of TOC as compared to that of oxyfluorfen. An improvement in the design of the electrocoagulation was faced by increasing the amount of particles in the reactor, allowing to deplete the pesticide concentration down to levels 2-log below the inlet concentration. The herbicide is concentrated in a solid phase, from where it can be released to a concentrated waste just by changing the pH.

The improvement in the treatment efficiency of diluted effluents is one of the great challenges faced by electrochemical technology nowadays. In the present work, it is aimed to develop an electrochemical cell for the simultaneous concentration and degradation of ionic organic pollutants. This combined cell (so called EDEO device) integrates the concentration of the organic by electrodialysis (ED) with its electrooxidation (EO). For the particular case of the 2,4-dichlorophenoxyacetic acid (2,4-D), the performance of the cell has been tested with two anode materials (boron-doped diamond, BDD and mixed mineral oxides, MMO) and with two supporting electrolytes in order to explore four combinations that are expected to cover a wide range of possible actual scenarios. Results demonstrate that the combined EDEO process exhibits a degradation rate and a mineralization current efficiency markedly higher than the equivalent EO device when working with MMO anodes, either with NaCl or with Na2SO4. It was checked that the use of a BDD anode clearly increases the efficiency and the rate of the treatment due to the formation of strong oxidants. In this case, the effect of working with the combined EDEO in the rate of 2,4-D degradation is negligible because the 2,4-D transport rate becomes comparable to the degradation rate, being the combined process unable to generate a concentration greater than that accounted in the single EO device.

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