Enhancement of ozonation of seawater-based wastewater containing pharmaceutical compounds by total residual oxidants: Salinity, ammonia, and organic matter

The ozonation process has recently been proposed as an effective treatment method for removing pharmaceutical compounds from seawater-based wastewater discharged from fish farms or hatcheries. Seawater ozonation can lead to the production of secondary stable oxidants such as bromine (HOBr/OBr⁻), which can be expressed as a total residual oxidants (TRO) owing to the high reaction rate constant with respect to ozone and bromide ion. TRO formation depends on water quality, in terms of aspects such as salinity, ammonia, and organic matter content; therefore, it is important to understand the variations in the ozone chemistry of bromide-containing water by considering the factors influencing TRO formation. In addition, the removal of pharmaceutical compounds in bromide-containing water should be evaluated owing to the different oxidation efficiency between TRO and pure aqueous ozone. This study aims to investigate the factors influencing the formation of TRO and the removal of pharmaceutical compounds during the ozonation of bromide-containing water. The results show that salinity increased the TRO formation rate by 6%, while ammonia and organic matter decreased the TRO formation rate by 51% and 39%, respectively. The removal efficiency of pharmaceutical compounds by TRO was higher compared with that by only ozone. Ammonia and organic matter inhibited the ozonation of bromide-containing water. These results indicate that TRO can be broadly used in the field of seawater ozonation; however, additional case studies on the removal of pharmaceutical compounds from seawater-based wastewater are needed to elucidate the oxidation mechanisms of various TRO.