Photocatalytic degradation of oxytetracycline using TiO2 under natural and simulated solar radiation

Abstract

The main objective of the present study was to assess the photocatalytic degradation over TiO2 of an aqueous solution containing 20 mg L-1 of the antibiotic Oxytetracycline (OTC) using simulated solar radiation, seconded by a solar radiation experiment carried out in a pilot plant equipped with Compound Parabolic Collectors (CPCs) under the optimal conditions found in preliminary lab-scale experiments. These comprehended a set of 1 L aqueous experiments with TiO2 loads ranging from 0.1 to 0.5 g L-1 starting from different initial pH values. These experiments were carried out in a Solarbox equipped with a 1000 W Xe-OP lamp. OTC degradation was followed by HPLC-DAD, while its mineralization was followed by the removal of Total Organic Carbon. Results suggested that 0.5 g L-1 of TiO2 with no initial pH adjustment (pH similar to 4.4) was the best combination for the removal of both OTC (100% after 40 min of irradiation; 7.5 kJ L-1 of UV dose) and TOC (>90% after 180 min of irradiation; 38.3 kJ L-1 of UV dose). Under these conditions, the BOD5/COD ratio rose from almost 0 to nearly 0.5, showing a remarkable improvement in biodegradability, while inhibition percentage of bioluminescence of Vibrio fischeri after 15 min of exposition measured by Microtox (R) decreased significantly from 35% down to 7%. A scheme of the OTC degradation pathway is proposed, based on the results obtained from this particular experiment. The solar photocatalytic experiment done under the same conditions was carried out in a solar pilot plant equipped with CPCs. OTC and TOC removal was followed as a function of accumulated UV energy entering the reactor. Results showed a 100% OTC and almost 80% TOC removal with 1.8 kJ L-1 and 11.3 kJ L-1 of photo treatment energy, respectively.