Case study: Ozonation and distribution system biostability

Biodegradable organic matter that is not removed during water treatment can lead to the proliferation of bacteria within the distribution system. This, in turn, can deteriorate water quality, accelerate corrosion rates of pipes, and potentially increase the incidence of bacteriological diseases. The main objective of this project was to collect and analyze full-scale system data on short-term and long-term responses to the implementation of ozonation with respect to its impact on bacterial regrowth potential as quantified by assimilable organic carbon (AOC) and biodegradable dissolved organic carbon (BDOC). A major observation made during the sampling period was that ozonation caused a significant increase in the AOC concentration of the distribution system (more than 200% in the short term and more than 100% in the long term). Use of ozone also caused a significant increase in the bacterial counts within the distribution system for both the long and short terms. In contrast, ozonation affected BDOC and dissolved organic carbon (DOC) concentrations only slightly compared with its impact on AOC concentrations. However, this may be because of the source water, which had low DOC and BDOC concentrations (1.2 and 0.11 mg/L, respectively).