| Biofilm disinfection in new and repaired water mains is conventionally achieved by using chlorine. Considering the practical limitations of chlorine for biofilm disinfection, ozone was investigated as an alternate disinfectant. A number of laboratory experiments were carried out for biofilm disinfection with ozone and free chlorine at "field conditions" (i.e. different concentration-time or Ct products). The results were compared with those of suspended bacteria in terms of log inactivation of heterotrophic plate count bacteria.; The results show that biofilm inactivation was limited to 1 log for an ozone Ct value of up to 56 mg x min/L in comparison to over 3 log inactivation of suspended bacteria at Ct value of up to 62 mg x min/L. The bacterial inactivation was greater than the measurement limit for both biofilm and suspended bacteria at free chlorine Ct of over 40,000 mg x min/L. At these "field conditions", ozone was considerably less effective than free chlorine, particularly for bioflm. |
