Integration of ozone and solar TiO2-photocatalytic oxidation for the degradation of selected pharmaceutical compounds in water and wastewater

• Ozonation and solar TiO2 photocatalysis allow complete removal of ECs and phenolic intermediates.
• Mineralization level and reaction products depend on the ozone dose and/or solar radiation dose.
• Treated effluents from single or combined treatments are biodegradable.
• The degree of mineralization achieved by TiO2 photocatalysis is influenced by the water matrix.
• Pre-ozonation slightly improves the mineralization rate achieved by solar TiO2 photocatalysis.

The degradation of a mixture of four pharmaceutical compounds (atenolol, hydrochlorothiazide, ofloxacin and trimethoprim) in distilled water and in a synthetic solution simulating a typical secondary effluent from a municipal wastewater treatment plant by ozonation, solar TiO2-photocatalytic oxidation and a sequence of both methods has been investigated. Degradation by ozone led to the complete removal of the selected emerging compounds (EC) but an accumulation of ozonation by-products (e.g., phenolic intermediates and carboxylic acids) in solution was observed. The presence of ozone-consuming substances in the synthetic effluent had not a negative impact on the removal of the pharmaceuticals but on their mineralization (TOC removal <8%). By photocatalytic oxidation, the pharmaceutical compounds were completely removed with UVA radiation doses lower than 0.3 kJ per mg EC while about 70% TOC conversion was achieved with a UVA radiation dose of 1 kJ per mg EC. The presence of organic and inorganic matter in the secondary effluent had a negative impact on the mineralization of pharmaceuticals. Thus, initial TOC removal rate was five times lower when treating the pharmaceuticals in the synthetic effluent compared to distilled water. The application of a sequential ozone – TiO2 solar photocatalytic oxidation treatment allowed complete removal of pharmaceuticals by ozonation and further mineralization of ozonation by-products by the photocatalytic treatment.

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