Innovative eco-friendly easily recoverable materials for olive mill wastewater treatment

Introduction. Olive oil production, one of Europe's most flourishing agricultural industries, generates olive oil, pomace, and olive mill wastewaters (OMWW). These latter, composed of ca. 80-83 wt.% water, 2 wt.% inorganic matter, and ca. 15-18 wt.% organic compounds (i.e., polyphenols, phenols, and tannins), require proper disposal treatments. In this field, the development of efficient strategies is fundamental. Heterogeneous photocatalysis has emerged for its efficiency, sustainability, and integration potential in water purification systems. Here, innovative, sustainable and efficient photocatalysts design is the key point [1]. In this work, we present our preliminary results related to the development of eco-friendly, easily recoverable three components material (bismuth oxybromide supported onto Fe3O4-alginate spheres) for the treatment of polyphenols representatives of the OMWW fraction. Experimental/methodology. Advanced, easily recoverable materials were fabricated by co-precipitating BiOBr onto alginate spheres containing a Fe3O4 core (Fig. 1a). Targeted physico-chemical characterizations were carried out to elucidate the samples properties. Gallic acid (GA) was selected as a model polyphenol: its abatement was monitored in the dark and under solar or visible light irradiation [2]. Preliminary abatement tests of gallic acid were also carried out on BiOBr powders. Results and discussion. When BiOBr was supported onto alginate spheres with the Fe3O4 core, it was able to produce photocatalytic activity as if used in powder form. Fig. 1b depicts a SEM micrograph showing the BiOBr morphology between flower- and plate-like. Fig. 1c summarizes a results selection obtained for the GA abatement onto Fe3O4-alginate-BiOBr. In the dark region, the higher the catalyst amount, the higher was the GA abatement due to GA adsorption onto the catalyst surface, thanks to the ability of Bi centers to coordinate GA. After 180 min of irradiation, full GA photodegradation is reached for 5 g catalyst and ca. 95% for 1 g. The comparison of these results (green triangles) with those obtained only in the dark (dotted black line) confirmed that the material operates an explicit photocatalytic activity. The encouraging results as well as the great advantage of the easy recovery currently move our research efforts towards the optimization of these eco-friendly photocatalysts for olive mill wastewater treatment.