Combined treatment of olive mill wastewater by Fenton's reagent and anaerobic biological process

Abstract

This work presents the application of Fenton's reagent process combined with anaerobic digestion to treat an olive mill wastewater (OMW). Firstly, OMW was pre-treated by chemical oxidation in a batch reactor with Fenton's reagent, using a fixed H₂O₂/COD ratio of 0.20, pH = 3.5 and a H₂O₂/Fe²⁺ molar ratio of 15:1. This advanced oxidation treatment allowed reaching reductions of 17.6 and 82.5% of chemical oxygen demand (COD) and total polyphenols (TP), respectively. Secondly, OMW treatment by anaerobic digestion was performed using previously adapted microorganisms immobilized in Sepiolite. These biological tests were carried out varying the substrate concentration supplied to the reactor and COD conversions from 52 to 74% were obtained. Afterwards, Fenton's reagent followed by anaerobic digestion was applied to OMW treatment. This combined process presented a significant improvement on organic load removal, reaching COD degradations from 64 to 88%. Beyond the pollutant load removal, it was also monitored the yield of methane generated throughout anaerobic experiments. The methane produced ranged from 281 cm³ to 322 cm³ of CH₄/g COD removed. Additionally, a methane generation kinetic study was performed using the Monod Model. The application of this model allowed observing a kinetic constant increase of the combined process (k_FN = 0.036 h⁻¹) when compared to the single anaerobic process (k_F = 0.017 h⁻¹).

Keywords:

• Anaerobic biological treatment
• chemical oxidation
• combined treatment
• Fenton's reagent
• Monod model kinetic study
• olive mill wastewater

Funding

Authors are grateful for the financial support provided by FCT - Fundação para a Ciência e a Tecnologia (Portugal) to the Centro de Química de Vila Real through the Project PEst‑C/QUI/UI0616/2014 and Project INNOFOOD - INNOvation in the FOOD sector through the valorisation of food and agro-food by-products - NORTE-07-0124-FEDER-0000029.