Survival of two bacterial fish pathogens (Aeromonas salmonicida and the Enteric Redmouth Bacterium) in ozonated, chlorinated, and untreated waters

Ozone and chlorine inactivation curves were determined in three water types at 20 °C for the destruction of the fish pathogens Aeromonas salmonicida, the etiologic agent of furunculosis, and the enteric redmouth bacterium (ERM). In phosphate-buffered distilled water, 0.01 mg/ℓ ozone inactivated 10³ cells/ml of ERM and A. salmonicida in 1/2 and 10 min, respectively. Chlorine at this concentration had little effect on either pathogen and a residual of at least 0.05 mg/ℓ was needed to achieve a complete kill within a 10-min contact time. In soft lake water (30 mg/ℓ as CaCO₃) a chlorine residual of 0.1 mg/ℓ rapidly  inactivated A. salmonicida and ERM but in hard water (120 mg/ℓ) A. salmonicida was more resistant and 0.2 mg/ℓ chlorine was required. Ozonation of the two lake waters at 90 mg O₃∙h⁻¹∙ℓ⁻¹ (equivalent to a 0.01 mg/ℓ residual in ozone demand-free water) was required to destroy both pathogens within 10 min.In untreated soft lake water 10³ cells/ml of A. salmonicida survived only 2 days, while the ERM bacterium (10³ cells/ml) survived even after 20 day s in soft and hard untreated lake waters.