Abstract
In this study, a combination of an ozone gas producer and an ultrafine-bubble compressor was used to degrade tetracycline, which is a well-known antibiotic and medicine commonly used in human and animal care, and effects of varying the reaction parameters were studied. Experiments indicate that each gram of introducing ozone can degrade 2.72 g of tetracycline at pH 3 and 1.48 g at pH 11. However, basic conditions contribute to increased mineralization of tetracycline because of the ·OH radical oxidation mechanism. Higher reaction temperatures and higher ozone dosages enhance the reactivity between the ozone molecules, ·OH radicals, and tetracycline, resulting in a decline in the toxicity of the tetracycline solution as measured by cell viability. The mineralization of organic compounds is the key to decreasing the toxicity of the solution. Ultrafine-bubble ozonation can provide homogeneity of gas bubbles in solution hence it not only reduces the requirement of ozone and thus the operational cost of the reaction, but also extends the efficacy of the method to the treatment of solutions with high tetracycline concentrations.
Highlights
More than 4000 pharmaceutical medicines are currently in use around the world, and the annual total global antibiotic consumption is estimated to be 100,000–200,000 tons
At low pH, the degradation of tetracycline occurred within a reaction time of 20 min (0.026 g O3 ), which indicates that lower pH assists tetracycline degradation, due to a cationic tetracycline species observed in aqueous solution, and the oxidization potentials of ·OH radicals are higher in acidic medium than in basic medium [26,27,28,29]
The performance of tetracycline degradation and detoxification by an ultrafine-bubble compressor equipped with an ozone gas producer was found to be effective, where each gram of ozone could degrade as high as 5.68 g tetracycline if the initial tetracycline concentration was 500 mg/L
Summary
More than 4000 pharmaceutical medicines are currently in use around the world, and the annual total global antibiotic consumption is estimated to be 100,000–200,000 tons. Because of excessive consumption and the disposal of unused or expired antibiotics, these compounds are released into the environment in large quantities. 15,000 tons of antibiotics are discharged into the environment every year [1,2]. In Taiwan, more than 1600 tons of antibiotics are used each year, of which 70% are used in animal husbandry feed additives. In China, annual antibiotic consumption per person was about. The abuse of antibiotics all over the world has significantly increased the resistance of bacteria to current antibiotics and led to more than 25,000 deaths due to drug-resistant bacteria in Europe each year [4,5]
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