Photo-Fenton Treatment of Actual Agro-Industrial Wastewaters

In this work, the treatment of actual agro-industrial wastewaters by photo-Fenton process was investigated. The actual agro-industrial wastewaters (AIW) were received from physicochemical treatment plants of wastewaters coming from the olive oil milling industry. These brown colored aqueous wastes have been characterized by high organic content with chemical oxygen demand (COD) in the range 2000-7000 mg O-2 L-1, which makes difficult the degradation of these wastewaters by traditional biological methods. The photo-Fenton process was successfully used to totally decolorize these effluents and to satisfactory remove aromaticity and COD contained in these wastes. The influence of some experimental parameters such as H2O2 and Fe2+ doses, initial COD content, initial pH, and temperature on color, aromaticity, and COD removals has been studied to find out the optimum conditions leading to maximum efficiency of the photo-Fenton process. The best results of photo-Fenton process treatment of AIW (2000 mg O-2 L) have been obtained using 3 g L-1 H2O2 and 30 mg L-1 Fe2+ at pH 3 and T = 26 degrees C and after 3 h UV irradiation. The comparison among photo-Fenton, Fenton, and UV/H2O2 processes has shown that the photo-Fenton process is more efficient and cost-effective than the two other processes. During the photo-Fenton process, photodecomposition and catalytic by Fe2+ ions decomposition of H2O2 leads to the production of higher amounts of hydroxyl radicals, proving that the efficiency of an advanced process is generally related to the amount of hydroxyl radicals produced during the treatment. The degradation of organics contained in the actual agro-industrial wastes during photo-Fenton treatment involves many successive oxidation/reduction reactions, including a rapid release of chromophores leading to the total decolorization, then an oxidative opening of benzene rings into aliphatic intermediates without carbon dioxide formation, and finally a slower oxidation of the aliphatic intermediates by hydroxyl radicals to achieve high COD removal.