Use of chlorine dioxide for Legionella control in hospital water systems
The safety and efficacy of chlorine dioxide (ClO2) for Legionella control were evaluated in a controlled prospective study conducted in two hospitals. The results showed that a significant reduction of Legionella positivity in the hot water was achieved by ClO2 treatment in these two hospitals. ClO2 application was safe based on the EPA MRDL for ClO2 and MCL for chlorite (ClO2-).
The impacts of pH, temperature and total organic carbon on ClO2 decay were investigated in a batch reactor to investigate the causes of the low ClO2 residual in hot water observed in the field. Temperature and TOC are both important factors governing ClO2 demand in hot water systems. The effect of pipe corrosion scale on ClO2 efficiency was investigated to predict the ClO2 loss in water distribution systems. Goethite (á-FeOOH) and magnetite (Fe3O4) were identified as the main component phases of iron corrosion scale. Cuprite (Cu2O) was the major component of copper corrosion scale. The first order reaction rate constants for ClO2 reaction with iron corrosion scales and magnetite ranged from 0.0251-0.0829 min-1. The first order reaction rate constants for ClO2 reaction with cuprite ranged from 0.0052-0.0062 min-1. Cuprite and magnetite were the main compounds in the scales that caused ClO2 loss in this study. The loss of ClO2 in the corroded iron pipe was dominated by reactions between ClO2 and these ferrous compounds in the iron pipe corrosion scales.
Possible synergy between ClO2 and free chlorine to provide more effective control of Legionella in a hospital water system was investigated in a model plumbing system. Combination of ClO2 and chlorine did not show significant synergistic effect on inactivation of Legionella in the model plumbing system. However, maintaining of 0.2 mg/L of ClO2 residual led to a significant reduction of Legionella at 40 degree Celsius in the model plumbing system.
Based on the results of this study, it can be concluded that ClO2 represents a viable alternative approach for controlling Legionella in institutional distribution systems provided that the initial demand due to the presence of corrosion scales is satisfied and that sufficient residual at distal outlets is achieved.
Advisor:Radisav Vidic; Stanley States; Robert Ries; Leonard W. Casson; Janet E. Stout
School:University of Pittsburgh
School Location:USA - Pennsylvania
Source Type:Master's Thesis
Keywords:civil and environmental engineering
Date of Publication:06/12/2007