EVALUATION OF OZONE BIOLOGICAL TREATMENT FOR DISINFECTION BY-PRODUCTS CONTROL AND BIOLOGICALLY STABLE WATER

Impacts of ozonation followed by biological filtration on the formation of disinfection byproducts and the production of biologically stable water were studied on pilot plant and full-scale at two U.S. locations (Oakland, CA and Tampa, FL). Also evaluated is a method to estimate bacterial regrowth potential by comparing it to assimilable organic carbon (AOC) measurements. At both locations, settled plant water is diverted to the pilot plant where it is split into two parallel trains. One train is ozonated, then filtered through anthracite/sand dual media followed by GAC or through a GAC/sand dual media filter. The other train (control) is identical except that the water is not ozonated. The full scale plants have sedimentation, ozonation, then GAC/sand filtration. Results indicate that ozonation reduces THM formation potential, as does biological filtration. AOC levels are increased during ozonation, then are decreased by all types of filtration media tested; however even GAC filtration did not reduce AOC levels to their pre-ozone values. Water temperature affected biofiltration -- below 13-degrees-C, dual media filtration did not reduce AOC levels to any significant extent. THMs, formaldehyde, chloroacetic acids, and chloroacetonitriles were disinfection byproducts followed during this study. Aldehyde levels were highest after ozonation, but were reduced significantly during filtration. Measurable levels of formaldehyde were found in chlorinated control water. The other DBPs were found in relative proportions to THMs. Evaluation of the bacterial regrowth potential procedure indicated that it correlates well with P17-AOC data, but not with NOX-AOC data. This observation was not surprising because the biological filtration did not reduce NOX-AOC levels well. Thus, it is likely that NOX-type organisms are not indigenous to the natural waters tested.