Estudo de degradação da tetraciclina em água e esgoto empregando fotólise direta

Abstract

Emerging pollutants are chemical compounds from a variety of commercial products that can be found in environmental and biological matrices. They are generally not monitored because they have no legal regulations regarding their disposal and presence in the environment, have a potential risk to human health and ecosystems. In this category of micropollutants, it is worth mentioning the pharmaceutical substances. As residual antibiotics have their main effect on bacterial resistance, as they have been reported in studies on water, sewage and sediments, it is necessary to investigate degradation mechanisms such as solar radiation and the use of artificial photolysis as an alternative to advanced treatment. In this research, the degradation of tetracycline was studied using an artificial source of irradiation by direct photolysis. Degradation tests were performed using a 100 mL capacity bench reactor equipped with an artificial radiation source composed of a high pressure mercury vapor lamp (254 nm). Aqueous solutions were prepared in distilled water and treated sewage. The variables pH and initial concentration established in the tests were previously optimized using experimental design. The analytical determinations were performed in a UV-VIS spectrophotometer. The experimental data were adjusted to kinetic models to obtain the reaction rates and the half-life in the studied conditions. The optimization indicated the concentration of 5 mg L-1 and pH 10 as more suitable, being used in all subsequent stages. Further degradation was observed in complex matrices such as sewage and surface waters, indicating that the persistence also depends on dissolved species capable of being part of the degradation mechanisms. The kinetics that apparently describes the phototransformation of the compounds under the studied conditions was that of pseudo-first order. The results indicate the application of direct photolysis as promising for the degradation of tetracycline in contaminated aqueous solutions. However, current literature has indicated the predominance of substitution mechanisms in the original compound in detriment of complete cleavage or mineralization, which does not ensure inactivation of microcontaminants, since the compounds formed may still have an ecotoxicological effect.