Mémoire
| Résumé : | Micropollutants are potentially hazardous substances present in the environment at low concentra- tions (μg/L or ng/L). The extensive use of products containing micropollutants such as pharma- ceuticals, pesticides, or chemicals results in their release in water effluents. However, traditional wastewater treatments are pretty ineffective for the degradation of most of these micropollutants, so the design and implementation of advanced treatment technologies is necessary. Among these technologies, biological, and especially enzymatic treatments, are attractive because they are usu- ally cheap, efficient, and environmentally friendly. Oxydoreductase enzymes with low substrate specificity such as laccases have been demonstrated to be able to degrade various micropollutants. However, their main limitation is their non-reusability when employed as free enzymes. The use of immobilized enzymes seems therefore more appropriate, but an optimal immobilisation system has not yet been designed.This work thus aimed at characterizing the ability of laccases immobilized on membranes by a Layer-by-Layer (LbL) techique, to degrade a model micropollutant, Remazol Brillant Blue R (RBBR). To do so, a system consisting of 6 enzyme-coated membranes maintained in a batch reactor with a metallic structure has been designed. To obtain a relative quantitative evaluation, the results were compared with those obtained for RBBR degradation performed with free laccases.When the reaction was performed by free enzymes, degradation rate were consistent with the amount of introduced laccase. However, MS analyses did not strictly confirm the presence of the two commonly identified degradation products C8 and C14, suggesting that there are a vari- ety of degradation pathway involved in the RBBR degradation by laccase. Although the system containing the enzyme-coated membranes showed a high efficiency in degrading RBBR, further experiments demonstrated that the observed degradation was the result of a redox reaction by the metallic structure. The enzyme-coated membranes did not show any activity towards RBBR degradation in the studied conditions, but further tests should be performed to reach a final con- clusion on their activity. Even though the metallic structure performance for RBBR degradation sounds appealing due to its cost-effectiveness, the instability of the degradation products, along with the current limited understanding of the different chemical mechanisms involved, calls for caution. A deeper characterization of the metallic-mediated oxidation system and its degradation products should be performed to conclude on the possible benefits of this approach. |
