Towards the simultaneous generation of electric energy and the abatement of organic pollutants by reverse electrodialysis processes

Abstract

In reverse electrodialysis (RED) processes, electrical energy is directly extracted from chemical potential gradients arising from salinity differences, especially from sea and river water [1]. In RED there are at least four complementary elements: (1) electrodes, where electron transfer reactions occur to allow the transformation of the charge carrier from ion to electron; (2) ion selective exchange membranes, which allow the selective transport of ions; (3) solvents, which make a continuum for ion transport; (4) electrolytes, i.e. the current carriers between cathode and anode. The redox process is usually chosen in order to limit the energetic losses, the cost of redox specie and electrodes, the passage of specie from the electrode compartments to the side ones. Here, we want to propose for the first time, in a RED system, the utilization of an electrochemical process aimed to the treatment of waste waters with the purpose of developing a process for the simultaneous generation of electric energy and the abatement of organic pollutants driven by salinity gradients. Acid Orange 7 (AO7) was chosen as model pollutant to test the proposed approach. The electrochemical abatement of AZO 7 was achieved by anodic oxidation in the absence and in the presence of NaCl at DSA electrodes, by electroFenton method and a coupled process. Experiments were carried out in undivided and divided electrochemical cells and in stack equipped with 30-50 cell pairs.