Effect of Ozonation on Microbial Fish Pathogens, Ammonia, Nitrate, Nitrite, and BOD in Simulated Reuse Hatchery Water
The effectiveness of ozone as a disinfectant of makeup water and its potential for treatment of recycled water in commercial reuse hatcheries was considered in this study. Comparative survival rates in water were established for four bacterial fish pathogens (Aeromonas salmonicida, A. liquefaciens, Pseudomonas fluorescens, Yersinia ruckeri [the causative agent of enteric redmouth disease]), Bacillus polymyxa, and a bacterium–protozoan population during batch and continuous flow ozonation. A specific microbial ozone demand was exerted during batch ozonation, and > 99% mortality of the fish pathogens was observed within 60-s contact during continuous flow exposure at 1.0 and 0.1 mg O3/L. Spores of B. polymyxa were resistant to a concentration of 1.0 mg O3/L for at least 10 min. The oxidation rate for the combined bacterial–protozoan biomass closely approximated rates established in pure culture studies, with no significant difference in relative survival rates between bacteria and protozoa. Elevated carbon levels did not appear to exert a preferential ozone demand when added to suspensions of test organisms. Oxidation of carbon and nitrite by ozone was rapid at low ozone concentrations, with carbon and ammonia oxidation rates exhibiting pH-dependence. The oxidation capacity of ozone in water was greatest at elevated pH even though the measurable ozone concentration was lower. Key words: ozone, fish pathogens, BOD, nitrite, ammonia, protozoans