Evaluation of solar photo-Fenton and ozone based processes as citrus wastewater pre-treatments

• Ozonation and solar photo-Fenton were evaluated for the pre-treatment of CWW.
• The ozone-based processes are only effective to remove color and turbidity.
• The solar photo-Fenton is the most adequate process to remove organic matter.
• An economic study on the best pre-treatment alternative is presented.

In the present study, different ozone based processes (O3, O3/OH−, O3/UV, O3/H2O2 and O3/UV/H2O2) and solar photo-Fenton treatment were evaluated for the pre-treatment of synthetic samples of citrus wastewater. The highest removal of organic matter in ozone based processes was achieved at high pH values, using H2O2 and UV radiation at 254 nm. After the application of ozone for 150 min at 1.9 gO3/L, 1017 mg/L of H2O2, UV radiation and pH ∼ 7, the removal efficiency of chemical oxygen demand and dissolved organic carbon was 15.7% and 10.9%, respectively. Apparent color, real color and turbidity were reduced significantly, mainly at the initial stages of the reaction. The solar photo-Fenton treatment (pH of citrus wastewater, [H2O2] = 15,937 mg/L, 510 mg/L of Fe3+ and reaction time of 30 min) produced a removal of 77% of chemical oxygen demand and 53% of dissolved organic carbon. This photocatalytic process is the most appropriate technique for the pretreatment of citrus effluent. An estimation of the total production costs of the photo-Fenton process shows that when solar light is used the cost of the treatment is 13.8 €/m3.

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