Application of sono & photo-chemical technologies for antibiotics removal

Abstract

ABSTRACT: Currently, there is a special concern about the presence and potential hazardous effects of antibiotics in the aquatic environment. These are part of the so-called emerging contaminants (EC), whose presence in aquatic ecosystems, even at low concentrations, represents a significant risk to environmental and human health. Cephalexin (CPX) and doxycycline (DOX) are two of the most used antibiotics to treat bacterial infections in human medicine, veterinary practices, animal husbandry, agriculture, aquaculture among others. Nevertheless, due to their excessive consumption and incomplete absorption during their metabolization, they have been detected in different environmental matrices and the effluents of wastewater treatment plants, which reflects that conventional methods are not enough to eliminate this type of compounds. In this sense, the need to develop new treatment alternatives that allow its total removal and minimize the eventual adverse effects has been evidenced. UV/H2O2 and ultrasound (US) are advanced oxidation technologies (AOT), which have demonstrated to be suitable alternatives for the degradation of antibiotics residues in contaminated water. These technologies are based on pollutants removal by generating radical species, especially the hydroxyl radical (HO•), which has the potential to oxidize different organic molecules. This research presents the main results about the removal of the antibiotics CPX and DOX using simulated sunlight radiation/H2O2 and low frequency US. The effects of operational parameters such as the solution initial pH, the concentration of H2O2 and the applied US power were assessed considering the response surface methodology and a face centered, central composite experimental design. In addition, in order to clarify the mechanisms of reaction, some control experiments, including photolysis, hydrolysis and the presence of a scavenger agent, were conducted. The effect of pollutants initial concentration, the total organic carbon variation and toxicity of the treated samples were also evaluated. The results indicated that evaluated operational factors affect significantly each treatment performance and that this kind of technologies are able to remove completely the studied antibiotics. In addition, in terms of mineralization, experimental results showed a reduction of the organic carbon present in the solutions and a significant increase of ions (nitrates and sulfates) concentration, suggesting that part of the organic matter was transformed into CO2, H2O and inorganic species. Likewise, toxicity assays demonstrated that both US and UV/H2O2 technologies are efficient not only to reduce pollutants presence but also, to inhibit samples toxicity, reducing the potential risk of hazardous effects on ecosystems and living beings. Finally, it could be concluded that the HO• free radicals seem to be the main responsible specie to CPX and DOX removal using UV/H2O2 and US technologies under the evaluated experimental conditions.