Influência das espécies de ferro e matrizes aquosas na degradação do antibiótico cloranfenicol pelo processo foto-Fenton: identificação dos produtos de transformação

Abstract

In this work the degradation of a solution 2.0 μmol L-1 of the antibiotic chloramphenicol (CAP) by the photo-Fenton process in deionized water, river water and effluent from sewage treatment plant (STP) using different iron species was evaluated. The experiments were performed in tank-type reactors and the CAP degradation efficiency was based on the decay of the CAP concentration determined by high performance liquid chromatography (HPLC) as well as the H2O2 consumption and determination of the acute toxicity to the Vibrio fischeri bacteria. Degradation products (DPs) in deionized water were also identified by HPLC coupled with high resolution mass spectrometry. Initially, in deionized water and under artificial radiation, different salts and iron complexes (FeSO4.7H2O – Fe2+, Fe(NO3)3.9H2O – Fe3+, C6H11FeNO7 - FeCit and K3Fe(C2O4)3.3H2O - FeOx) and concentrations (2, 8, 16 and 32 μmol L-1) were evaluated using 44 μmol L-1 of H2O2 at initial pH 2.7. In sequence, the influence of the H2O2 concentration (22, 44 and 88 μmol L-1) was evaluated using 32 μmol L-1 of FeOx at pH 2.7. Using the best iron species – FeOx and concentrations of iron and H2O2, 32 μmol L-1 of FeOx and 44 μmol L-1 of H2O2, CAP degradation was evaluated at different pH values (2.7; 4.0, 5.0, 6.0, 7.0 and 8.0), with 100% degradation of CAP at pH 2.7. However, at initial pH 6.0 it was possible to achieve 74% CAP degradation after 60 min. It was also observed that at initial pH 6.0, multiple additions of the oxalate complexing during the experiment allow 100% CAP degradation. Then, at initial pH 6.0, experiments were performed under solar and artificial radiation, aiming to identify the DPs and to monitor the evolution of the acute toxicity to V. fischeri bacteria, as well as to compare both sources of radiation. A faster decay of CAP degradation occurred under solar radiation, which is related to the larger spectrum provided by solar radiation. It was also observed that the initial CAP solution showed no toxicity to V. fischeri, as well as the formation of low toxicity DPs using both sources of radiation. HPLC-MS-Q-TOF analyzes allowed to identify three major DPs (DP1, DP2 and DP3) of m/z 337; 166 and 335. DP1 derives from the hydroxylation of the CAP aromatic ring, the DP2 from HO• attacks on benzyl radicals and DP3 from the addition of the HO• radical to the α-carbonyl radical. Following the application of the photo-Fenton process in real matrices, the CAP degradation was evaluated in surface waters: river water and STP effluent. Initially, the influence of the FeOx concentration (16, 32, 48 e 64 μmol L-1) on the degradation of CAP in river water at initial pH 5.8 (natural river water) in the presence of 44 μmol L-1 of H2O2 was evaluated. Subsequently, the influence of H2O2 concentration (44, 60 and 88 μmol L-1) on CAP degradation was evaluated using the best concentration of FeOx - 48 μmol L-1. Better results were obtained with 48 μmol L-1 of FeOx and 44 μmol L-1 of H2O2. Under such experimental conditions, it was also observed that the replacement of the oxalate complexing during the experiment increases the efficiency of CAP degradation from 90 to 100%. The influence of the concentration of FeOx (48, 96, 144 and 192 μmol L-1) in the presence of 1500 μmol L-1 of H2O2 at initial pH 6.0 during the CAP degradation to the STP effluent matrix, was also evaluated. The concentration of CAP was below the limit of quantification of the equipment (QL < 0.42 μmol L-1) in the presence of 192 μmol L-1 of FeOx after 25 min of treatment. Then, under the best experimental conditions obtained for each matrix, experiments were performed under artificial and solar radiation, and toxicity to V. fischeri was monitored. Better results of CAP degradation in river water and STP effluent were obtained under solar radiation, with the generation of a low toxicity effluent for V. fischeri bacteria. These results show the viability of the solar photo-Fenton process as an alternative for the treatment of matrices containing this type of pollutant.