Processos oxidativos avançados empregados na degradação de antibióticos em água residuária sintética

Abstract

Some of the substances from medicaments, personal hygiene products and cosmetics are resistant to conventional water and sewage treatments and thus reach the aquatic compartment. The proposition of analytical techniques is shown as an important step in the determination of emerging pollutants, and the analysis of specific treatments for degradation arises with the purpose of clarifying the behavior and the ecotoxicological action of these substances. The present study aimed to evaluate the degradation of sulfamethoxazole (SMX) and ciprofloxacin (CIP) antibiotics in synthetic wastewater using the advanced oxidation processes (AOPs) of direct photolysis (UV) and photo-Fenton (Fe+2/H2O2/UV), optimized conditions by means of initial planning 2² and posterior central compound rotational design (CCRD) 2² with 2 levels, 3 repetitions at the central point and 4 axial points. The by-products formed were qualitatively evaluated by means of ultra-high performance liquid chromatography with ultraviolet detection (UPLC-UV) using a C18 reversed phase column (2.6 μm) and mobile phase 0.025 mol L-1 phosphoric acid and acetonitrile in the proportion 80:20 (%v/v), with a flow rate of 0.200 mL min-1. The experiments were conducted in a laboratory scale reactor with a batch system consisting of a 125 mL vessel and a magnetic stirrer used to homogenize the solution equipped with a low pressure mercury lamp 250 W without the bulb. For the SMX drug an LD equal to 0.0099 mg L-1 and LQ of 0.0299 mg L-1 was obtained and for CIP a LD of 0.0112 mg L-1 and LQ of 0.0341 mg L-1. By means of the ferrioxalate actinometry test it was obtained that the dose to the photoreactor after 20 minutes of assay is equal to 8,53x10-3 einstein s-1. The CCDR for direct photolysis indicated better pH degradation conditions of 3.28 and [SMX] of 5.33 mg L-1, and pH equal to 0.76 and [CIP] of 9.20 mg L-1. In the case of photo-Fenton CCDR, a [Fe+2] equal to 17.26 mg L-1 and [H2O2] of 158.46 mg L-1 was observed as the best conditions for SMX, and [Fe+2] to 2.64 mg L-1 and [H2O2] of 220.50 mg L-1 for CIP, the pH used was 2.5 for both drugs. In order to study antibiotic degradation and possible by-product formation, [SMX] of 100 mg L-1 and [CIP] of 50 mg L-1 were used. Through direct photolysis, total removal of the antibiotics occurred in 40 min for SMX and 120 min for CIP. In the photo-Fenton process complete removal of SMX occurred in 30 min, and CIP in 120 min. In the Fenton process no removal was achieved for any of the drugs evaluated. Photolysis kinetics were both first order, with K1 equal to 0.077 min-1 for SMX and 0.019 min-1 for CIP. The photo-Fenton kinetics were both first order, with K1 equal to 0.088 min-1 for SMX and 0.024 min-1 for CIP. In the photolysis and photo-Fenton treatments, a degradation products was found for each drug, the identification of these was not possible due to the lack of specific analytical techniques.