Iron-based catalysts for photocatalytic ozonation of some emerging pollutants of wastewater

Abstract

A synthetic secondary effluent containing an aqueous mixture of emerging contaminants (ECs) has been treated by photocatalytic ozonation using Fe³⁺ or Fe₃O₄ as catalysts and black light lamps as the radiation source. For comparative purposes, ECs have also been treated by ultraviolet radiation (UVA radiation, black light) and ozonation (pH 3 and 7). With the exception of UVA radiation, O₃-based processes lead to the total removal of ECs in the mixture. The time taken to achieve complete degradation depends on the oxidation process applied. Ozonation at pH 3 is the most effective technique. The addition of iron based catalysts results in a slight inhibition of the parent compounds degradation rate. However, a positive effect is experienced when measuring the total organic carbon (TOC) and the chemical oxygen demand (COD) removals. Photocatalytic oxidation in the presence of Fe³⁺ leads to 81% and 88% of TOC and COD elimination, respectively, compared to only 23% and 29% of TOC and COD removals achieved by single ozonation. The R_CT concept has been used to predict the theoretical ECs profiles in the homogeneous photocatalytic oxidation process studied. Treated wastewater effluent was toxic to Daphnia magna when Fe³⁺ was used in photocatalytic ozonation. In this case, toxicity was likely due to the ferryoxalate formed in the process. Single ozonation significantly reduced the toxicity of the treated wastewater.

Keywords:

• Emerging contaminants
• black light
• iron-based catalysts
• photocatalytic oxidation
• R_CT concept

Funding

This work has been supported by the Spanish Ministerio de Ciencia e Innovación (MICINN) and European Feder Funds through the projects CTQ2009-13459-C05-05 and CTQ2012-35789-C02-01/PPQ. Also, Chemical Engineer A. Espejo thanks Gobierno de Extremadura for providing her a FPI grant.