Title : Electrochemical pretreatment coupled to a biological process for the treatment of a specific organic pollution – Implementation of modified electrodes for selectivity improvement
In these last years, antibiotics were considered to be an emerging environmental problem due to their continuous entry and persistence in the aquatic ecosystem. Indeed, the large accumulation of emerging pollutants in continental and marine natural waters are the consequence of the worldwide general application of intensive agricultural methods, the large-scale development of the pharmaceutical, agrochemical, and food industry, the high levels found in some specific effluents (textile, pharmaceutical, hospital waste…). Partly responsible for this pollution, low volumes containing high concentrations of persistent organic pollutants, in the range of concentrations found in some specific industrial and agricultural effluents (unused treatment solution, spray, machine, and container washing, hospital effluents…)., can result in large polluted volumes which are difficult to treat owing to their low concentrations. One solution would be to treat pollution at the source, as intended in this project.
Biological processes, the most cost-effective for wastewater treatment, which is destructive and has been extensively studied do not always appear relevant for the removal of recalcitrant compounds, owing to their toxicity and/or low biodegradability. Combining Physico-chemical and biological processes to treat biorecalcitrants compounds in wastewater has already proved its efficiency. When used as pre-treatment, Physico-chemical processes modify the structure of the pollutants leading to by-products that are expected to be more biodegradable and less toxic, allowing a subsequent biological treatment. Since total effluent mineralization is not the purpose of the Physico-chemical pre-treatment, more fine control of the system and improved energy efficiency are expected.
Electrochemical processes have been chosen as Physico-chemical pre-treatment since the electron is the major reactant avoiding the introduction of supplementary chemical reactants, which can be expensive and toxic. It is expected that the electrochemical pre-treatment will allow achieving a well-controlled degradation of the pesticides or pharmaceuticals to improve their biodegradability. Since, the presence of some functional groups in molecular structures is suspected to be linked to the biorecalcitrance of the compounds, as for instance the presence of halogens or nitro groups, the electrochemical oxidation/reduction process will specifically degrade these functional groups. The use of modified working electrodes by means of catalysts immobilized at the electrode surface or electrodeposited will help in achieving this objective. Indeed, it would allow reducing the working potential interval resulting in an improvement of energy efficiency and hence reducing cost, and to achieve a selective attack of the targeted functional groups, for fine control of the target compound degradation.
Some results are available dealing with the coupling of electrochemical processes and a biological treatment1-4, which however has not been extensively studied in the literature, especially regarding the implementation of direct reduction/oxidation of organic pollutants. It is also noteworthy that modified electrodes and catalysts are usually implemented in the field of electrochemical sensors for the former and in organic media for this latter, while the implementation of such modified electrodes, by means of catalysts immobilized at their surface, in aqueous phase 5-7 is discussed in this work.