K. C. Ho and Y. K. Wong, Environmental studies Programme, The Open University of Hong Kong

Abstract

Experiments showed that ozone was an effective agent in mitigating dinoflagellate blooms during red tide. By means of indirect diffusion of ozone (injection rate = 1 gm O₃ /m³ seawater/hr) unto red tide affected waters, all the cells of Prorocentrum triestinum, Scrippsiella trochoidea and Karenia digitata (max. concentration = 7200 cells/mL) broken within 15 minutes. The level of dissolved oxygen was found also elevated to a level acceptable to the Water Quality Objective of Hong Kong. Furthermore, the levels of ammoniacal nitrogen and total inorganic nitrogen (TIN) decreased due to rapid oxidation process. While ozone was not directly injected into the seawater for fish cultivation i.e. seawater was pumped into a separated water tank for treatment, the level of residual ozone could be maintained to an acceptable level with the cultured fishes totally unaffected after re-introduction of the treated seawater. The economic aspects of ozone injection was critical analysed. It is found that ozone injection is most suitable for land-based, tanked cultivation of aquacultural products including fish fries. The crucial factor of widespread application of this technology rests on a properly designed ozone generator that is cheap and convenient to fishermen.