Effect of Ozonation on Microbial Fish Pathogens, Ammonia, Nitrate, Nitrite, and BOD in Simulated Reuse Hatchery Water

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Abstract
The effectiveness of O3 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 4 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 O3 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 C levels did not appear to exert a preferential O3 demand when added to suspensions of test organisms. Oxidation of C and nitrite by O3 was rapid at low O3 concentrations, with C and NH3 oxidation rates exhibiting pH-dependence. The oxidation capacity of O3 in water was greatest at elevated pH even though measurable O3 concentration was lower.

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