Reductions in Bacterial Microorganisms by Filtration and Ozonation of the Surface Water Supply at the U.S. Fish and Wildlife Service Northeast Fishery Center

A water filtration and ozonation system was recently installed to treat creek water used to culture species of concern at the U.S. Fish and Wildlife Ser- vice's Northeast Fishery Center, Lamar National Fish Hatchery (NFH). Past experi- ence with fish culture indicates that the following bacterial pathogens are endemic to the creek water supply: Aeromonas salmonicida, Yersinia ruckeri, Flavobacterium columnaris, and Flavobacterium psychrophilia. Water samples were collected from sites located before and after filtration and ozonation and examined for culturable bacteria. Variable operation of the filtration/ozonation system was used to exam - ine (�) the effect of microscreen filtration (i.e., using drum filters containing 37-µm sieve panels) on ozone inactivation of bacterial microorganisms, (2) the effect of dissolved ozone contact times on inactivation of bacterial microorganisms, and (3) the effect of water quality fluctuations on the dissolved ozone demand measured during the course of these tests. Inactivation exceeded 98% for all bacteria when ozone C*t values were about �.0 and reached �00% at 2�.3, regardless of water qual- ity parameters or implementation of microscreen filtration. These results indicate that the use of ozonation to treat surface water supplies used for fish culture facili - ties will effectively inactivate the majority of bacteria entering the system and will likely serve to prevent introduction of bacteria that can be pathogenic to fish.and Erie, which facilitated recovery of the burbot populations there. Although sea lam- preys have been controlled in Lake Ontario, alewives are probably still too abundant to permit burbot recovery.