ELECTROCHEMICAL TREATMENT OF WASTEWATERSDRIVEN BY REVERSE ELECTRODIALYSIS PROCESSES

Wastewater treatment technology is undergoing a transformation due to more restrictiveregulations governing the discharge and disposal of hazardous pollutants. Electrochemical basedtechnologies are very promising methods for treating wastewaters containing organic and inorganicpollutants resistant to biological processes or toxic for microorganisms. These methods presentnumerous advantages including the utilisation of a green reagent such as the electron, very highremoval of numerous recalcitrant pollutants, efficient disinfection, high flexibility and no necessity totransport or stock chemical oxidants or reducents. On the other hand, a wide utilisation of suchmethods is likely to be limited by: (i) the cost of electric energy necessary to drive electrodereactions; (ii) the cost of the supporting electrolyte for waste waters with no adequate conductibilityand (iii),for some applications, by the cost of electrodic materials. In order to overcome some ofthese drawbacks, some innovative solutions were proposed in the last years such as the utilizationof micro reactors to avoid the utilization of supporting electrolytes and to increase the currentefficiencies for electrochemical processes controlled by mass transport stages such as directoxidation processes or electro-Fenton (EF). To avoid the supply of electric energy to the systemalso the utilization of microbialfuel cells or reverse electrodialysis processes was proposed.Reverse electrodialysis is a clean, renewable energy with large global potential since the electricityis produced from supplies of water with different salt concentrations. In reverse electrodialysis(RED), cation and anion conductive membranes are placed in an alternating way in order toproduce dilute and concentrate compartments. The salt concentration difference (salt gradient)between both compartments in the cell pair creates a Nernst potential across the cell pair whichcauses an electrical current to flow through the electrical load connected to the electrodes.The electrochemical treatment of two different kinds of waste waters contaminated by Cr(VI) and amodel dye, the Acid Orange 7(AO7), respectively, driven by reverse electrodialysis processes wasstudied. It was shown that in both cases salinity gradients can be used to obtain electric energyand to successfully treat contaminated waste waters.