A large variety of organic and inorganic compounds may be found in wastewater. Among these compounds, aromatics are characterized by their high toxicity and very low degradability by conventional treatments.

This paper presents the results of an investigation about the oxidation of two substituted benzenes in a semi-batch reactor: phenol, substituted with an electron-donating group (-OH), and benzoic acid substituted with an electron- withdrawing group (-COOH). The advanced oxidation processes studied were UV, ozone, hydrogen peroxide and its combinations. The pH dependence and the influence of the initial concentration of hydrogen peroxide were studied to find the optimal conditions for a complete and fast oxidation of both compounds.

Experimental results indicated that both phenol and benzoic acid are destroyed more rapidly by ozone at higher pH (9–12), while ozonation combined with hydrogen peroxide or/and UV is considerably faster at low pH (3–7).