ELECTROCHEMICAL TREATMENT OF WASTE WATERS CONTAMINATED BY ORGANIC POLLUTANTS: A LOOK ON SOME NEW APPROACHES

Abstract

Recent researches have demonstrated that electrochemical methods offer an attractive alternative to traditional routes for treating wastewaters containing toxic or/and refractory organic pollutants. These methods use a clean reagent, as the electron, very mild operative conditions (ambient temperature and pressure) and can be run with limited operative costs. Despite of the above mentioned advantages, electrochemical processes present some important disadvantages such as: • the cost of some electrodic materials such as silver (for reduction processes) and boron doped diamond (for oxidation ones). On the other hand, the cost of silver based electrodic materials can be considerably lowered by depositing silver nano particles on carbon electrodes. Furthermore, a very thin layer of BDD is usually deposited on cheaper materials and several academic and private research institutes are looking for new preparation methods in order to reduce the final costs of diamond based electrodes. • To achieve reasonable cell voltages when the medium has not an adequate conductivity, one needs adding to the system a supporting electrolyte. This is certainly a main obstacle for a wide application of electrochemical abatement. Indeed, adding chemicals to a water stream is often a problematic issue, being opposed to general administrative regulations since this may lead to the formation of secondary pollutants during electrochemical incineration of organics, and anyway increases the operative costs. • Low current efficiencies are usually achieved for direct processes when an high abatement of the organic pollutants is required, mostly due to the fact that, in this case, the rate determining step in the electrochemical conversion of the pollutant is its mass transfer rates towards electrodes whose rate is extremely reduced at low pollutant concentrations. • The economic sustainability strongly depending on energetic costs and energetic efficiency. In order to reduce these disadvantages and/or to improve the performances of the electrochemical processes, various approaches are studied worldwide such as solar assisted methods and/or microbial fuel cells. In this context, in our lab, two very different approaches are currently under investigation: 1. The utilization of microfluidic electrochemical reactors (i.e. cells with a distance between the cathode and the anode of tens or hundreds of micrometers) allowing to operate with lower cell voltages and without supporting electrolyte and on the other side to intensify the mass transport of the pollutants to the electrode surface. 2. The development of a new reverse electrodialysis process for the simultaneous generation of electrical energy and the treatment of waste waters that rules out the electrical energetic costs. The discussion of these two approaches will be the object of the contribution.