Oxidation of Florfenicol and Oxolinic Acid in Seawater by Ozonation

Abstract

There has been an increase in the use of antibiotics by the aquaculture industry in marine aquaculture for the prevention of diseases in fish. Antibiotics in the water discharged into the sea without treatment can cause disturbances to the marine ecosystem. Therefore, there is a need for research on how the removal of antibiotics used in aquaculture can be achieved. In this study, the removal of two types of antibiotics (florfenicol, FF, and oxolinic acid, OA) used in the aquaculture industry, by ozonation, was evaluated. Currently, there is a lack of research studies on FF and OA removal from seawater by ozonation. Seawater ozonation shows a significantly different oxidation mechanism as compared to that of freshwater. The high amount of Br− in seawater (60 mg/L) allows for a rapid reaction with ozone to produce bromine (HOBr/OBr−) at a rate of 160 M−1s−1. To predict the removal efficiency of antibiotics by ozone and bromine, the species-specific rate constants for the reaction of FF and OA with ozone and bromine were determined. The predicted removal efficiencies of FF and OA using measured rate constants were verified by the ozonation process in water containing bromide ions in similar concentrations as in seawater. The result for FF indicated less than 10% removal during 20 min, with the rate constants of FF with ozone and bromine being 3.2 M−1s−1 and 3.5 M−1s−1, respectively. However, the removal of OA using ozonation was approximately 99% or higher within 90 s. In the presence of bromide ions, approximately 60% of OA was removed by trace ozone within 15 s, and approximately 30% of OA was removed by the generated bromine after 15 s. Comparing the removability of FF and OA used in aquaculture by ozone, it was observed that FF was more difficult to remove because of its low reaction rate constant. Meanwhile, the reaction rates of OA with ozone and bromine were 2.4 × 103 M−1s−1 and 4.0 × 102 M−1s−1, respectively. At the beginning of the reaction, OA was removed by the trace ozone. Subsequently, OA was removed by the generated bromine after the ozone was decomposed.