O papel do excesso otimizado de H2O2 na rápida mineralização dos fármacos Ácido Acetil Salicílico e Hidroclorotiazida utilizando diferentes reatores fotoquímicos

Abstract

Studies of drugs as emerging pollutants have been gaining importance in the scientific community. Unfortunately, the mineralization of drugs through various Advanced Oxidative Processes (POAs) takes several hours to reach rates above 60%. In an attempt to overcome this mark, this work devotes to optimize and understand the kinetic conditions to mineralize drugs via radiation-assisted oxidation (UVA and UVC), with an emphasis on the Foto-Fenton process and using both a tubular and a simple mixture photochemical reactor. Two drugs were selected. AcetylSalicylic Acid (ASA) was selected because traces of ASA were found in the treated effluent from the sewage station in Natal-RN. ASA was treated as a generalist model of an emerging pharmaceutical micropollutant. Besides Hydrochlorothiazide (HCT) was chosen as a model of a persistent micropollutant. The optimization employed a statistical factor-planning tool to study how the concentrations of the micropollutant, Fe2+, and H2O2 affect both mineralization and degradation. The factorial design indicates that the initial concentration of H2O2 is a crucial variable to achieve a rapid rate of mineralization of both AAS and HCT. Using optimized content of H2O2 and Fe2+ in the photo-Fenton process (H2O2 / Fe+/UVA), a mineralization of more than 90% for AAS and 100% for HCT were achieved in about 10 minutes and 30 minutes, respectively. The underlying reason for such remarkable performance is attributed to the optimized excess of [H2O2], which proved to lay between 4 to 9 for AAS and between 6 to 11 for HCT. Measurements of the remaining concentration of H2O2, for oxidation of both AAS and HCT via photo-Fenton, strongly indicate that the excess of [H2O2] optimizes the instantaneous concentration/production of radical •OH, being 33 to 35% of the total radicals •OH effectively consumed by the mineralization of AAS and HCT. Considering other POAs studied, the photo-H2O2 oxidation (H2O2/UVC) notoriously benefits from the optimization of the excess of H2O2, being capable of degrading almost 100% of both AAS and HCT in a few minutes; however, the degree of mineralization proves to be refractory and never exceeds the maximum limit of 35%. Oxidation of AAS and HCT via photo-Fenton under optimized excess of H2O2 signals to be the most effective, if not the unique, alternative for attaining the absolute degree of mineralization among POAs, which is vital considering the toxicology of HCT. The LC50 for the HCT was 37.25 mg.L-1, and it was obtained with a group of Mysidaceas, a typical crustacean of the aquatic fauna of RN State. Further toxicology tests used the population of Mysidaceas cultivated in the effluent from the post-treatment of this work. Mortality above 50% of the Mysidaceas population was observed except for the photoFenton effluent (H2O2/Fe2+/UVA) for which absolute HCT mineralization was obtained. As one central thesis, this work defends the excess of [H2O2] as a vital parameter to optimizethe mineralization in almost absolute degree (100%) within the shortest time of treatment ever, which in turn, reduces the energy consumed by both the lamp and the recirculation pump.