Fenton oxidation using Fe2+/Fe3+/H2O2 to improve the DCO removal and to degrade the phenolic compounds in olive oil mill wastewater

The treatment of olive oil mill wastewater (OMWW) by Fenton oxidation using Fe 3+ /Fe 2+ , and hydrogen peroxide was investigated to improve the degradation of phenolic compounds and the removal of chemical oxygen demand (COD). The experimental results showed that high removal of COD (187.6 g L –1 ) and polyphenols (4 g L –1 ) required acidic conditions (pH 4), continuous presence of both Fe 2+ and Fe 3+ (at 50 g L –1 ) and hydrogen peroxide. Under these conditions, the maximum COD removal (about 98.6%) was achieved after 10 h. The obtained polyphenolic compounds abatement rate was around 81%. However, after treatment with hydrogen peroxide alone, the removal rates of COD and phenolic compounds were only 69.5% and 67.5%, respectively. HPLC analysis of the extracts showed that hydroxytyrosol was the major compound detected in OMWW (259.10 mg L –1 ). Tyrosol, para-hydroxyphenylacetic acid, para-coumaric acid, oleuropein, and quercetin were also identified at lower concentrations. After 10 h of OMWW Fenton oxidation treatment, the hydroxytyrosol and ferulic acid content decreased by 99% and 93%, respectively. However, when hydrogen peroxide was used alone, only 72% and 79.12%, respectively of hydroxytyrosol and ferulic acid were removed. These results showed that the removal of 4g L –1 of phenol and 187.6 g L –1 of COD from OMWW was rapid when high amounts of Fe 3+ , Fe 2+ and hydrogen peroxide were used.