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Advanced oxidation processes applied to the sulfaquinoxaline degradation : degradation products and toxicity

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Author(s):
Vanessa Ribeiro Urbano
Total Authors: 1
Document type: Doctoral Thesis
Institution: Universidade Estadual de Campinas, Faculdade de Engenharia Civil, Arquitetura e Urbanismo
Defense date:
Advisor: José Roberto Guimarâes
Abstract

Sulfaquinoxaline (SQX), which belongs to the sulfonamides¿ class, is a synthetic antimicrobial and bacteriostatic agent used in animals for prevention of coccidiosis and bacterial infections. Due to its low adsorption on soil, it is usually found in water matrices. Since the conventional wastewater treatment plants do not degrade it efficiently, this compound has been detected on the environment. The advanced oxidation processes (AOP), generates hydroxyl radicals (HO¿), and are efficient on sulfonamide¿s degradation. This work evaluated the sulfaquinoxaline degradation (initial concentration: 500 µg L-1) by peroxidation (H2O2), photolysis (UV), peroxidation assisted by ultraviolet radiation (UV/H2O2), ozonation in basic medium (O3/HO-), photocatalysis (UV/TiO2, UV/TiO2/H2O2), Fenton¿s reagent (Fe2+/H2O2) and photo-Fenton (UV/Fe2+/H2O2). SQX quantification was performed using high performance liquid chromatography-diode array detection (HPLC-DAD) and the degradation products were evaluated by high performance liquid chromatography and tandem mass spectrometry (HPLC-MS/MS). The solutions submitted to the degradation processes were evaluated according to the antimicrobial activity using Escherichia coli and Staphylococcus aureus bacteria, and toxicity using Vibrio fischeri bacterium. The peroxidation process degraded less than 5% SQX. The photolysis process degraded 58% SQX after 14 min of reaction and the solutions submitted to this process inhibited approximately 8% of Vibrio fischeri luminescence. The AOPs were efficient on SQX degradation: 99% of its initial concentration was degraded at least in one of the experimental conditions tested. At the processes UV/TiO2 (TiO2: 20 to 100 mg L-1) and UV/TiO2/H2O2 (TiO2: 5 and 100 mg L-1 / H2O2: 0.8 mmol L-1) more than 99% SQX was degraded after 11 min of reaction. At the process UV/H2O2 (H2O2: 9 mmol L-1) 99.6% of SQX was degraded after 11.4 min of reaction. For all the pH values evaluated on the ozonation process (3, 7, and 11), more than 99% SQX was degraded; and the ozone demand was low at pH 3 value, and the solutions treated did not present residual toxicity. The toxicity of the solutions submitted to the processes UV/TiO2, UV/TiO2/H2O2, UV/H2O2 and O3/HO- increased, reaching 94% of luminescence inhibition of Vibrio fischeri bacterium at the process UV/TiO2 (TiO2: 5 mg L-1). The degradation products of SQX were classified as toxic and persistent, and their chemical structures were proposed. The processes Fenton¿s reagent and photo-Fenton were evaluated in two reactors, laboratory bench (2 L) and pilot scale (15 L). The efficiency of SQX degradation (initial concentration: 25 mg L-1) was very similar between the reactors, 92% at laboratory bench and 95% at pilot scale. No inhibition of bacteria growth was after submitting the solutions to Fenton¿s reagent and photo-Fenton processes. At laboratory bench, the presence or absence of radiation was more significant to mineralization, and the interaction of this variable with the variable H2O2 concentration, was more significant to the degradation of SQX. The concentration of H2O2 was the most significant variable to mineralization and degradation of SQX at pilot scale (AU)

FAPESP's process: 13/04656-8 - Degradation of pharmaceuticals by peroxidation combined with ultraviolet radiation and ozonation: antimicrobial activity and toxicity
Grantee:José Roberto Guimarães
Support type: Regular Research Grants