Objective: In order to evaluate the potential of Legionella growth in water distribution system, we constructed a pilot-scale water re-circulation system that allowed simulation of real-world conditions and compared the efficiency of different disinfection treatments applicable to Legionella control.
Methods: A pilot-scale system consists of four PPR re-circulation loops and dead legs. During the study, each of three loops received continuous application of one of the following disinfection treatments: copper-sliver ionization (0.4/0.04mg/L), chlorine dioxide (0.5 mg/L) and thermal eradication (maintained over
Results: Before treatments, the system was highly contaminated with L. pneumophila in water (3.4×103/ml) and biofilm (2.4×104/cm2). In the water and the biofilm of the loops, Chlorine dioxide and thermal eradication were very effective in reducing the microbial flora, including L. pneumophila. Heterotrophic bacteria were still detectable after copper–silver ionization application, the contamination remained significantly higher. Copper–silver did not remove the biofilm. Only chlorine dioxide led to detectable effects in the dead leg. After interrupting the treatments, L. pneumophila quickly recovered their initial levels in all cases.
Conclusions: Chlorine dioxide, applied as a continuous treatment, was identified in this study as the most efficient for controlling L. pneumophila in pilot-scale water re-circulation system. Once a system is colonized by L. pneumophila, eradication of the agent from the environment become very difficulty or is practically impossible.