Survival of bacteria after ozonation

The change of the bacterial population after each water treatment process was examined in a full-scale water treatment plant that uses ozone as a primary disinfectant. The fluctuation of heterotrophic bacterial number along the water treatment processes was determined. After ozonation, the bacterial number decreased to 13 CFU/mL. The surviving bacteria after each water treatment process were identified to genus or species level. The significant finding was the predominance of double-layered gram-positives (75%) among the surviving bacteria after ozonation. It included Mycobacterium spp., Bacillus spp., Corynebacterium spp., and Micrococcus spp. On the other hand, the dominance of gram-negatives was observed in most other water samples but each treatment process exerted different selection on dominant bacterial groups. The proportion of opportunistic pathogens was the lowest in the ozonated water.