Techniques integration for degrading emerging pollutants and on the horizon

Resumo

Ionic liquids (ILs) are an alternative to conventional organic solvents and they have great potential to improve and develop new processes in Green Chemistry. This paradigmatic characteristic has contributed to the fact that ILs have overcome the laboratory scale and they are postulated as candidates for their production and use on a large scale. Thus, the first family of ILs based on imidazolium cation is already applied at the industrial level, and consequently it has been registered in the REACH regulation of chemical substances. One of the differentiating aspects of these compounds is their high thermochemical stability, which in turn can pose a high environmental risk due to their persistence and toxicity after their release into aquatic and edaphic ecosystems. Based on these considerations, the search for effective remediation methods according to the family to be treated is a priority research line within the framework of the current Community Water Directive (2000/60/EC) and, in particular, ILs have been classified as “pollutants on the horizon”. Therefore, it is necessary to advance in the development of technically and economically viable technologies that allow to degrade these liquid salts in an adequate time, with the minimum environmental and social impact. However, the lack of in-depth studies on this subject makes it necessary to present this Thesis focused on the treatment of these pollutants on the horizon. To begin with, the degradation capacity of hydroxyl or sulfate radicals will be evaluated, followed by the optimization of the chosen process. The complex nature of these pollutants makes their complete remediation by conventional technologies difficult and costly. That is why in recent years, as an alternative to reduce the overall costs of the process and to improve the overall effectiveness of the treatment, the use of electrochemical biological sequential treatments is being proposed. Thus, those ILs that are not biodegradable by conventional biological processes could be biodegraded after a short electrochemical treatment, which would be sufficient to reduce the toxicity of the source contaminants. In this context, one of the objectives of this research will be the design of hybrid strategies that combine electrochemical and biological systems for the degradation of ILs in water. However, ionic liquids are not found alone in the aqueous medium, other contaminants such as pharmaceutical compounds may appear. Therefore, its degradation will also be evaluated in this Thesis. Further, in this Thesis it is planned to develop a new tool to optimize in situ the reaction that occurs in the electrochemical process that is being carried out. In this way, differential pulse voltammetry is applied to obtain a better understanding of the reactions and processes that take place in the reaction medium, to develop a more efficient treatment for the degradation of these pollutants. This will allow solving the presence of new pollutants on the horizon of anthropogenic origin, so the benefits of this Thesis reach not only the chemical industry, but society in general, by reducing the environmental impact that could be the growing application of these solvents.