Photocatalytic degradation of antibiotics under various conditions

Abstract

Frequent detection of antibiotics in aquatic environment represents a global ecologic problem due to the fact, that these compounds are not fully biodegradable during conventional purification processes in wastewater treatment plants. The presence of antibiotics cause that the bacteria present in water and in animal or human bodies build resistance, which can be problematic for treatment of infections. However, heterogeneous photocatalysis is a promising method for the removal of harmful organic pollutants from wastewater. In this work, a reaction rate of photocatalytic degradation of sulfathiazole was determined, using TiO2 nanopowders and TiO2 EPD layers. In the next step, the effect of the additional antibiotic presence (ampicillin) and the use of greywater as a matrix on the photocatalytic reaction was evaluated. Sulfathiazole and ampicillin were photocatalytically degraded both separately and in mixture. For the photocatalytic reactions, nanoparticles of TiO2 P25 and pure anatase in two particle sizes (5 and 100 nm) were used. The photocatalysts were added into the reaction mixture both as a free powder and immobilized by electrophoretic deposition (EPD) on stainless steel plates. The degradation kinetics was determined by HPLC analysis with UV detection. The decrease in organic carbon was monitored using a TOC instrument. Theoretical degradation products were determined by DFT calculations. Firstly, the convenience of using EPD layers was evaluated. It is necessary to filtrate or centrifuge the samples after using TiO2 suspensions, which is time and money consuming. Thus, EDP layers have a more practical use for water purification purposes. The reaction rates were comparable with both suspension and EPD photocatalysts. When sulfathiazole (10-4 M) was degraded, the reaction rate was highest with P25, followed by anatase 5 nm and anatase 100 nm. The use of EPD layers instead of free powder photocatalyst had no significant effect on the reaction rate. Furthermore, the use of immobilized photocatalyst solves problems with separating the photocatalyst from the reaction mixture after the degradation is completed. The addition of ampicillin to the reaction did not have any influence on the rate of degradation of sulfathiazole when the molar concentration was kept constant. The use of greywater instead of demineralized water for the experiments had no decreasing effect on the photocatalytic degradation of both sulfathiazole and ampicillin. The mineralization of the reaction mixture determined as a decrease in total organic carbon correlated with the results of decrease in the concentration of studied analytes. When greywater was used instead of demineralized water, it had no observable effect. In this work, the photocatalytic degradation of sulfathiazole was performed using three different TiO2 forms. The photocatalytic activity of the particles in suspensions was compared with the activity of the particles deposited on the layers. Then, the photocatalytic reaction of the solution containing the mixture of two antibiotics in demineralized water and in greywater was carried out and the mineralization under the conditions mentioned above was compared.