Cleaning of olive mill wastewaters by visible light activated carbon doped titanium dioxide

Carbon doped titanium dioxide (CDT) was tested as catalyst for photodegradation of phenolic compounds of olive mill wastewater (OMW). The activation of the catalyst was triggered by exposure to visible light radiation. The cleaning effectiveness of this catalyst towards the polluted wastewater from olive oil industry was demonstrated by means of HPLC and UV-visible spectroscopy combined with phenol compound determination. The photodegradation activity was tested on systems having different initial concentration of phenols and in the presence of different amounts of CDT. By introducing a suitable parameter, namely the ratio between the amount of catalyst and the amount of total phenols Ti/TPh, it was demonstrated that the proposed degradation method could be scaled up without losing its effectiveness. The OMW decolorization occurring in the presence of CDT particles under visible light radiation is marked enough to be directly appreciated with the naked eye. The decolorization is strongly associated with the removal of phenols. In fact, while bleaching the solutions, CDT successfully removed 70% of the phenols in 24 hours. HPLC analysis demonstrates that CDT was effective in degrading the higher part of the phenols of OMW. An exception is represented by hydroxytyrosol that seemed to have high resistance in the first 24 hours of treatment.