Pyrylium salt-photosensitized degradation of phenolic contaminants present in olive oil wastewater with solar light: Part III. Tyrosol and p-hydroxyphenylacetic acid

Photodegradation of tyrosol and p-hydroxyphenylacetic acid, present in olive oil wastewater, can be achieved using 2,4,6-triphenylpyrylium salt as solar photocatalyst. Fluorescence quenching measurements support the involvement of electron transfer as the key step in this process, with formation of substrate-derived radical cations. Important degradation yields are achieved. Other advanced oxidation methods (ozone and/or UV-radiation) have been tested as well; as expected, tyrosol and p-hydroxyphenylacetic acid abatement is faster, but ozone and UV are dangerous and expensive for industrial uses. However, ozone and UV do not show an important synergistic effect in tyrosol and p-hydroxyphenylacetic acid oxidation. p-Hydroxymandelic acid and p-hydroxybenzaldehyde have been detected and identified by HPLC as intermediates; on the basis of these data, a reaction mechanism involving oxidation at the benzylic position is proposed.