CONICET | Buscador de Institutos y Recursos Humanos

Nowadays, the presence of recalcitrant organic pollutants in water has become an important environmental concern. Typically found in low concentration, different methodologies are recommended for the elimination of these compounds in waste or drinking water. Adsorption on different substrates is a widespread and well known process, particularly useful for the fast removal of pollutants in low concentration. However, the contaminant is not eliminated but concentrated at the adsorbent. Advanced oxidation technologies (AOT) have been successfully used for the removal of different families of recalcitrant compounds, although their application may find some difficulties in the presence of organic matter and high volume of water. The combination of adsorption with AOT may be an alternative allowing the fast separation of the recalcitrant pollutant from water by adsorption, followed of destruction by AOT.In this work, different examples of coupling adsorption with AOT for the removal of different recalcitrant pollutants are presented using modified bentonites as adsorbent and photo-Fenton as AOT. Bentonites are low cost minerals (abundant in Argentina) that can be suitably modified for the adsorption of hydrophilic or hydrophobic compounds. Photo-Fenton is an effective oxidation technology that can use solar light as source of energy. Three target compounds were used as model pollutants: imazalil (IMZ), a post-harvest fungicide; crystal violet (CV), a cationic dye; oxytetracycline (OTC), a veterinary antibiotic.Montmorillonite (MMT) modified with octadecyl trimethyl ammonium (OMMT) was used as adsorbent for IMZ. At pH 7 IMZ was strongly adsorbed on OMMT, but it was desorbed at pH 3. IMZ can be adsorbed from water at neutral pH, desorbed and concentrated 1:10 in a medium appropriate for the photo Fenton process. Following that procedure, 500 mg/L IMZ was completely degraded in 2 h. Mineralization (determined by Total Organic Carbon -TOC-) was 40% after 6 h.Fe(III) modified MMT (Fe-MMT) was used as adsorbent for CV. The dye was quickly removed from water, following a complex sorption kinetic that depends on the distribution of CV at MMT surface and interlayer space. Small angle X-ray scattering, wettability and surface charge measurements indicated that CV molecules accommodate in MMT interlaminar space and at the surface, allowing the sorption of 86 mg CV/g Fe-MMT. The CV/Fe-MMT system was separated from water, dispersed in an appropriate medium and submitted to the photo-Fenton treatment. TOC increased at the beginning due to desorption of oxidation byproducts but decreased with time due to mineralization.Fe-MMT was also used as sorbent for OTC. Fe-MMT strongly adsorbed OTC at pH 7, being desorption negligible at pH 3. After photo-Fenton treatment the adsorbed OTC was completely eliminated. TOC increased during the first 30 minutes, but decreased to less than 10% after 6 h. Even though the process was more efficient at pH 3, 80 % of mineralization was observed after 6 h treatment at pH 7.These results indicate that the combination of adsorption with photo-Fenton is an interesting alternative for the quick removal of organic pollutants from water, allowing their concentration and mineralization.