Ultrasound enhanced catalytic ozonation of tetracycline in a rectangular air-lift reactor

The antibiotics tetracycline (TC) was degraded by ultrasound (US) enhanced catalytic ozonation using goethite catalyst (US/goethite/O3) in a rectangular air-lift reactor. The effect of important operational parameters, including gaseous ozone concentration, gas flow rate, free radical scavenger, pH, and power density, on the removal of TC was investigated. The results showed that the TC removal followed pseudo-first-order kinetics and the removal rate increased with increasing gaseous ozone concentration, pH, gas flow rate and power density. The presence of free radical scavenger inhibited the removal rate to some extent. The catalyst stability was evaluated by measuring TC removal rate and iron leaching for three successive cycles. Almost no changes in the particle size and the surface area of the catalyst were observed before and after the reaction. The main intermediates were identified and the degradation pathway of TC was proposed. Toxicity test with Daphnia magna showed that the acute toxicity increased during the first stage of the reaction, and then gradually decreased with the progress of the oxidation.