Oxidation of organic pollutants in photo-Fenton process in presence of humic substances

Influence of Humic Acids (HA) in concentration of 10-50 mg/l on efficiency of phenol removal in photo-Fenton process was evaluated in this work. Natural zeolite, surface modified with Fe(II) ions, was used as a catalyst of oxidation reaction. The results of the study show that the efficiency of phenol removal decreases along with the increase of concentration of HA. Humic acids form stable complexes with ions of iron (III), which decreases the concentration of Fe (III) available for the photo Fenton reaction. It was also found that the presence of HA affects the selectivity of the catalyst of Fenton reaction. In that case the preferred oxidation product is hydroquinone, whereas for oxidation of phenol without HA, during first stage of reaction, catechol is the dominant intermediate product of the oxidation. The results also indicate a significant impact of solution pH on the efficiency of phenol degradation and type of intermediate products.