The Role of Bismuth in Developing Bio-Based Materials for Efficient Polyphenol Adsorption and Solar Photodegradation

Olive oil production is one of Europe's best-performing agricultural sectors. It produces olive oil and undesirable by-products (wastes), such as olive mill wastewater (OMWW) and organic waste. OMWW contains large amounts of organic compounds (primarily polyphenols, phenols, and tannins). Polyphenols have dual effects: beneficial for nature and humans but harmful in high concentrations in wastewater. If not adequately treated in wastewater, polyphenols can threaten biodiversity, ecological balance, and water quality and pose a risk to human health. Effective management of these compounds in industrial waste is an urgent task for scientists. However, in a circular economy vision, the possibility of recovering polyphenols in large quantities represents an important challenge. Based on these premises, the purpose of the present work is developing and optimizing different bismuth-modified, easily recoverable materials composed of alginate spheres modified with a magnetic core and bismuth oxyhalides or Bi3+ ions as an active phase to recover and/or photodegrade polyphenols under solar light irradiation. Here, we present our first results obtained using synthetic wastewater containing gallic acid (GA), 3,4,5-Trimethoxybenzoic acid (345TMBA), and 4-Hydroxybenzoic acid (4HBA) as model polyphenols. After adequately optimizing the conditions, 98% of polyphenols were collected, and the remaining part was effectively and quickly photodegraded.