Solar photo-Fenton oxidation against the bioresistant fractions of winery wastewater

• Solar photo-Fenton was found to be efficient in polishing winery wastewater.
• The toxicity of the effluent was eliminated through solar photo-Fenton oxidation.
• Solar photo-Fenton oxidation significantly removed the color from winery wastewater.
• Mineralization was found to be lower than the COD reduction.

This work examined the solar-photo Fenton oxidation against the bioresistant fractions of winery wastewater. Winery effluents already treated by a membrane bioreactor (MBR) were subjected to further purification by solar photo-Fenton oxidation process (hv/Fe2+/H2O2). The effect of various operating variables, such as the catalyst and oxidant concentration, as well as temperature and solar irradiation on the abatement of chemical oxygen demand (COD), dissolved organic carbon (DOC), color, toxicity and phytotoxicity has been assessed. Optimum Fe2+ and H2O2 concentrations were found to be 3 mg L−1 and 250 mg L−1, respectively. Solar photo-Fenton has been demonstrated to be an effective process for the purification of winery effluents, yielding after 120 min of treatment, COD, DOC and color removal of 70 ± 3.3%, 53 ± 3.7% and 75 ± 2.2%, respectively. The residual COD and DOC values after the end of the solar treatment were 33 mg L−1 and 14.1 mg L−1, respectively. In the various operating conditions studied, the extent of mineralization (assessed by DOC) was lower than the COD decrease, implying that partial oxidation reactions of the organic content prevailed over total oxidation to CO2 and water. Moreover, the process efficiency was found to increase with temperature up to a point (∼70% at 25 °C), and then reach a plateau with a small increase by further increasing the temperature to 45 °C. Finally, the toxic and the phytotoxic compounds still present in the effluent after the biological treatment were reduced or even eliminated through solar photo-Fenton oxidation.